Joint crystallization of KCuAl[PO4]2 and K(Al,Zn)2[(P,Si)O4]2: crystal chemistry and mechanism of formation of phosphate-silicate epitaxial heterostructure

Yakubovich, O.; Kiriukhina, G.; Shvanskaya, L.; Volkov, A.; Dimitrova, O.

doi:10.1107/S2052520620005715

research papers

STRUCTURAL SCIENCE
CRYSTAL ENGINEERING
MATERIALS

ISSN: 2052-5206

Volume 76| Part 3| June 2020| Pages 483-491

https://doi.org/10.1107/S2052520620005715

Joint crystallization of KCuAl[PO₄]₂ and K(Al,Zn)₂[(P,Si)O₄]₂: crystal chemistry and mechanism of formation of phosphate-silicate epitaxial heterostructure

Olga Yakubovich,^a ^* Galina Kiriukhina,^a,^b Larisa Shvanskaya,^a Anatoliy Volkov ^a,^b and Olga Dimitrova ^a

^aM.V. Lomonosov Moscow State University, Leninskye Gory 1, Moscow, 119991, Russian Federation, and ^bThe Institute of Experimental Mineralogy RAS, Akademika Osip`yana st 4, Chernogolovka, Moscow region 142432, Russian Federation
^*Correspondence e-mail: yakubol@geol.msu.ru

Edited by J. Hadermann, University of Antwerp, Belgium (Received 18 March 2020; accepted 25 April 2020; online 22 May 2020)

Two novel phases, potassium copper aluminium bis(phosphate), KCuAl[PO₄]₂ (I), and potassium zinc aluminium bis(phosphate-silicate), K(Al,Zn)₂[(P,Si)O₄]₂ (II), were obtained in one hydrothermal synthesis experiment at 553 K. Their crystal structures have been studied using single-crystal X-ray diffraction. (I) is a new member of the A⁺M²⁺M³⁺[PO₄]₂ family. Its open 3D framework built by AlO₅ and PO₄ polyhedra includes small channels populated by columns of CuO₆ octahedra sharing edges, and large channels where K⁺ ions are deposited. It is assumed that the stability of this structure type is due to the pair substitution of Cu/Al with Ni/Fe, Co/Fe or Mg/Fe in different representatives of the series. From the KCuAl[PO₄]₂ structural features, one may suppose it is a potentially electrochemically active material and/or possible low-temperature antiferromagnet. In accordance with results obtained from X-ray diffraction data, using scanning electron microscopy, microprobe analysis and detailed crystal chemical observation, (II) is considered as a product of epitaxial intergrowth of phosphate KAlZn[PO₄]₂ and silicate KAlSi[SiO₄]₂ components having closely similar crystal structures. The assembly of `coherent intergrowth' is described in the framework of a single diffraction pattern.

Keywords: X-ray diffraction; potassium copper aluminophosphate; phosphate-silicate heterostructure; coherent scattering; epitaxial oscillatory zoning; crystal chemistry; functional materials.

CCDC references: 1999127; 1999128

1. Introduction

The extensive present-day interest of the scientific community in the study of first-row transition metal phosphates is due to their physicochemical properties, the most important of which are magnetism and electrochemical activity. The promise of fluoro-phosphates and vanadates as magnetically and electrochemically active materials has been shown in recent research [see, for example, Keates et al. (2013 )]. Novel materials based on phosphates with 2D and 1D subsystems of the magnetic structure, formed by first-row transition metals, show highly functional characteristics, inherent to frustration of the exchange interaction of magnetically active ions (Shvanskaya et al., 2015 ; Yakubovich, Kiriukhina et al., 2013 ; Yakubovich, Yakovleva et al., 2013 ). Research into the physical properties of such objects lies in the field of quantum cooperative phenomena and contributes to the development of theoretical ideas about the structure of matter (Lin & Ding, 2013 ).

The operation of modern electric energy storage batteries is based on the ability of alkali metal ions to migrate inside the cathode material, viz. to penetrate the crystalline structure during a battery discharge and to be extracted during charging. Commercial usage of synthetic triphylite, LiFePO₄, as a cathode material with increased working voltage stimulated a new interest in mineral-like phosphates of alkali and transition metals. Particular attention is currently being paid to compounds with Na and K atoms due to their greater availability and lower cost, in comparison with Li (Kubota et al., 2018 ; Pramudita et al., 2017 ).

Recently, we have analysed the crystal chemical diversity of isoformula phosphates AMM′[PO₄]₂ (A⁺ = Na, K, Rb, NH₄, M²⁺ = Cu, Ni, Co, Fe, Zn, M′³⁺ = Fe, Al, Ga), including 18 representatives (Yakubovich et al., 2019 ). It has been shown that the rich crystal chemistry of the discussed morphotropic series (seven structure types) is due to the possibility of different coordination of M and M′ atoms in the oxygen environment, from tetrahedral to octahedral, including five vertices, as well as to the size of alkali metal ions. It should be emphasized that some members of this family have a number of significant physical properties. Thus, KCuFe[PO₄]₂ is an antiferromagnet, also demonstrating the electrochemical properties of conductivity based on the migration of potassium ions through open channels of the crystal structure (Badri et al., 2011 ).

Within a programme to explore the synthesis and crystal structures of compounds, potentially interesting as possible battery electrodes and/or magnetic materials, the phosphate crystallization system was complicated by the addition of the SiO₂ component in order to expand the chemical diversity of growing phases and to investigate crystal chemical regularities governing the formation of a particular structure. This article is aimed at providing the results of structural research of two new K/Al-bearing members of the AMM′[TO₄]₂ family, obtained in middle-temperature hydrothermal conditions.

2. Experimental: synthesis and crystallization

The title compounds were obtained in one trial of soft hydrothermal synthesis carried out in a 5 ml stainless steel bomb protected by a fluoroplastic coating. A starting mixture of Al(OH)₃, K₄P₂O₇, Zn(NO₃)₂, CuCl₂ and SiO₂ in a 3:3:3:1:1 weight ratio with distilled water filled 80% of the autoclave. The duration of the experiment at T = 553 K and P = 70 MPa was 14 days. The pH value of the crystallization medium measured after the experiment and cooling the autoclave was equal to 6. The obtained products were separated by filtration, washed with water, dried and analysed with a scanning electron microscope (Jeol JSM-6480LV Oxford X-Max^N) equipped with an energy-dispersive diffraction spectrometer (performed at the Laboratory of Local Methods for Studying Materials, Department of Petrology, Faculty of Geology, M. V. Lomonosov Moscow State University). Most of the trial (∼80%) was represented by intergrowths of very small (up to 0.05 mm) flattened prismatic crystals of blue colour of various intensities. Crystals of the second phase, in much smaller quantities, are also very small light-green isometric individuals, as shown in Fig. 1.

Figure 1
Photos of crystals of the title compounds: KCuAl[PO₄]₂ (a) and K(Al,Zn)₂[(P,Si)O₄]₂ (b).

According to the results of preliminary qualitative microprobe analysis, Cu, K, P, Al, O were present in the composition of the light-green crystals [hereafter (I)], while Zn, K, P, Al, Si, O were identified in the blue crystals [hereafter (II)]. To obtain quantitative data on the chemical composition the crystals were pressed into epoxy resin and the obtained polished carbon-coated samples were examined on the same microscope for composition using microprobe analysis at an accelerating voltage of 20 kV and a current of 10 nA. The electron beam flux was limited to 10 lumen to minimize sample destruction; spectrum accumulation time was 100 s. The following standards were used: anorthite, CaAl₂Si₂O₈, for determining Al and Si, synthetic KTiPO₅ for P, potassium feldspar, KAlSi₃O₈, for K, ZnS for Zn, and copper metal for Cu.

3. Results and discussion

Crystal data, data collection and structure refinement details are summarized in Table 1. All calculations were performed with SHELX programs (Sheldrick, 2015a ,b ) in the framework of the WinGX software package (Farrugia, 2012 ). The formulae KCuAl[PO₄]₂ (I) and K(Al,Zn)₂[(P,Si)O₄]₂ (II) correspond to established crystal structures and coincide well with chemical data. From the information obtained, it can be seen that the atoms of the d elements (Cu and Zn) were distributed between the phases during crystallization, and that the Si atoms became part of the blue crystals, exclusively. Presumably, there was a separation of the solution into regions of increased concentrations of Cu on the one hand and Zn and Si on the other. Two chemical reactions describing (I) and (II) formation may be supposed within the suggested paradigm:

Table 1
Experimental details

	(I)	(II)
Crystal data
Chemical formula	AlCuKO₈P₂	Al₃K₂O₁₆P₃SiZn
M_r	319.56	601.51
Crystal system, space group	Monoclinic, P2₁/c	Monoclinic, C2/c
Temperature (K)	293	293
a, b, c (Å)	5.0270 (8), 14.047 (2), 9.263 (1)	13.234 (1), 13.121 (1), 8.6581 (8)
β (°)	102.29 (1)	100.14 (1)
V (Å³)	639.11 (15)	1479.9 (2)
Z	4	4
Radiation type	Mo Kα	Mo Kα
μ (mm⁻¹)	4.72	2.89
Crystal size (mm)	0.07 × 0.06 × 0.06	0.06 × 0.06 × 0.05

Data collection
Diffractometer	Xcalibur, Sapphire3	Xcalibur, Sapphire3
Absorption correction	Multi-scan (CrysAlis PRO). Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	Gaussian (CrysAlis PRO). Numerical absorption correction based on Gaussian integration over a multifaceted crystal model.
T_min, T_max	0.957, 1.000	0.800, 0.856
No. of measured, independent and observed [I > 2σ(I)] reflections	9355, 1469, 1360	8821, 1303, 1176
R_int	0.057	0.060
(sin θ/λ)_max (Å⁻¹)	0.650	0.594

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.049, 0.093, 1.23	0.059, 0.096, 1.29
No. of reflections	1469	1303
No. of parameters	122	118
Weighting scheme	w = 1/[σ²(F_o²) + (0.014P)² + 5.5P] where P = (F_o² + 2F_c²)/3	w = 1/[σ²(F_o²) + (0.014P)² + 13.2P] where P = (F_o² + 2F_c²)/3
Δρ_max, Δρ_min (e Å⁻³)	0.63, −1.02	0.42, −0.42
Computer programs: CrysAlis PRO (version 1.171.37.35, release 13-08-2014 CrysAlis171.NET, compiled Aug. 13 2014,18:06:01) (Agilent, 2014 ), SHELXT (Sheldrick, 2015a,b), SHELXL2016/6 (Sheldrick, 2015a,b), DIAMOND (Brandenburg, 2006 ).

Al(OH)₃ + CuCl₂ + K₄P₂O₇ → KCuAl[PO₄]₂ + 2KCl + KOH + H₂O;

6Al(OH)₃ + 2Zn(NO₃)₂ + 3K₄P₂O₇ + 2SiO₂ → 2K₂Al₃ZnP₃SiO₁₆ + 4KNO₃ + 4KOH + 7H₂O.

3.1. Crystal structure of KCuAl[PO₄]₂ (I)

The average result of a quantitative microprobe analysis of phase (I) at two points is K₂O 14.86, CuO 24.42, Al₂O₃ 15.8, P₂O₅ 44.42, total 99.5 wt%. The formula of the compound calculated on the basis of four cations (Cu²⁺ + Al³⁺ + 2P⁵⁺) is K_1.01Cu_0.99Al_1.00P_2.01O_8.02 and matches the formula KCuAl[PO₄]₂ established as a result of the X-ray diffraction study.

A symmetrically independent fragment of the structure of (I) includes a Cu-centred octahedron, an AlO₅ five-vertex polyhedron, two PO₄ tetrahedra and two K atoms (Fig. 2). Oxygen octahedra around Cu are characterized by four close Cu—O distances in the range 1.942 (4)–2.014 (4) Å, and two longer distances of 2.317 (4) and 2.431 (4) Å (Table 2). Such a distortion of the CuO₆ octahedra is typical of the Cu²⁺ ion of the d⁹ configuration and is associated with the static Jahn–Teller effect. The Al—O bond lengths in AlO₅ trigonal bipyramids are split into two groups of close values. These are three distances in the interval 1.794 (4)–1.802 (4) Å, and two distances in trans positions equal to 1.885 (4) and 1.909 (4) Å. The P—O bond lengths in the P-centred tetrahedra range from 1.512 (4) to 1.558 (2) Å, with the same average value of 1.532 (4) Å. The distortion pattern of the Cu-, Al- and P-centred polyhedra is consistent with the bond valence data (Brown & Altermatt, 1985 ) (Table 3). Large K atoms split between two positions statistically populated 80% (K1) and 20% (K2) are surrounded by nine O atoms at distances in the interval 2.858 (7)–3.244 (9) Å, or by 11 O atoms, with K—O distances ranging from 2.75 (2) to 3.39 (2) Å.

Table 2
Selected bond lengths (Å) for (I)

K1 and K2 represent an 80:20 split of the K site.

Cu1—O2ⁱ	1.942 (4)	K2—O6^v	3.03 (2)
Cu1—O1	1.981 (4)	K2—O8^iv	3.07 (2)
Cu1—O8ⁱⁱ	2.010 (4)	K2—O3^v	3.11 (2)
Cu1—O1ⁱⁱⁱ	2.014 (4)	K2—O5^vii	3.24 (3)
Cu1—O8^iv	2.317 (4)	K2—O6^vi	3.27 (3)
Cu1—O7ⁱⁱ	2.431 (4)	K2—O2ⁱ	3.29 (3)
K1—O4	2.858 (8)	K2—O7^vii	3.39 (2)
K1—O6^v	2.873 (7)	P1—O6	1.519 (4)
K1—O2^vi	2.887 (6)	P1—O2	1.527 (4)
K1—O5^vii	2.893 (14)	P1—O4	1.530 (4)
K1—O3^v	2.894 (9)	P1—O1	1.558 (4)
K1—O1	2.935 (7)	P2—O5	1.512 (4)
K1—O5^iv	3.110 (7)	P2—O8	1.525 (4)
K1—O4^v	3.189 (14)	P2—O3	1.529 (4)
K1—O7^vii	3.219 (8)	P2—O7	1.543 (4)
K1—O8^iv	3.244 (9)	Al1—O7	1.794 (4)
K2—O4	2.75 (2)	Al1—O4	1.800 (4)
K2—O1	2.85 (2)	Al1—O3^viii	1.802 (4)
K2—O2^vi	2.886 (19)	Al1—O6^v	1.884 (4)
K2—O5^iv	3.02 (2)	Al1—O5^ix	1.908 (4)
Symmetry codes: (i) x + 1, y, z; (ii) x, −y + $[3\over 2]$ , z − ½; (iii) −x + 1, −y + 2, −z + 1; (iv) −x + 2, y + ½, −z + $[3\over 2]$ ; (v) x, −y + $[3\over 2]$ , z + ½; (vi) x + 1, −y + $[3\over 2]$ , z + ½; (vii) −x + 1, y + ½, −z + $[3\over 2]$ ; (viii) x − 1, y, z; (ix) −x + 1, −y + 1, −z + 1.

Table 3
Bond valence data for KCuAl[PO₄]₂

The calculation is made without considering the splitting of the K position.

Atom	K	Cu	Al	P1	P2	Σ
O1	0.114	0.442		1.173		2.13
		0.404
O2	0.130	0.491		1.275		1.90
O3	0.127		0.665		1.268	2.06
O4	0.141		0.668	1.265		2.13
	0.057
O5	0.128		0.498		1.328	2.03
	0.071
O6	0.135		0.531	1.303		1.97
O7	0.053	0.131	0.679		1.221	2.08
O8	0.050	0.409			1.282	1.92
		0.178
Σ	1.00	2.05	3.04	5.02	5.10

Figure 2
A view of KCuAl[PO₄]₂, showing the basic structural units with the atom-labelling scheme. Displacement ellipsoids are presented at the 90% probability level. Symmetry codes: (*) 1 + x, $[3\over 2]$ − y, ½ + z; (**) 2 − x, ½ + y, $[3\over 2]$ − z; (′) x, $[3\over 2]$ − y, −½ + z; (′′) 1 + x, y, z; (′′′) 1 − x, 2 − y, 1 − z; (*′) x, $[3\over 2]$ − y, ½ + z; (*′′) 1 + x, y, 1 + z.

Centrosymmetric four-membered rings built by AlO₅ and P2O₄ polyhedra sharing vertices form chains parallel to the [100] direction. Each of these chains at the vertices and centre of the unit cell is associated with four neighbouring chains through corner-bridging linkage provided by P1O₄ tetrahedra (Fig. 3) to assemble a 3D [Al(PO₄)₂]³⁻_∞ anionic para-framework. All oxygen vertices of the AlO₅ bipyramids are shared with P-centred tetrahedra, while two vertices of the P1O₄ and one vertex of the P2O₄ tetrahedra remain `pendant', e.g. not shared with other polyhedra of the aluminophosphate framework. Columns of the CuO₆ octahedra sharing edges are included in an open space between `pendant' vertices of the PO₄ tetrahedra. Owing to the distortion of phosphate tetrahedra, as well as to the valence contributions of K and Cu atoms, a local bond balance at the corresponding oxygen atoms is achieved (Table 3). The large K atoms are placed in open framework channels restricted by six-membered windows.

Figure 3
The KCuAl[PO₄]₂ crystal structure displayed along the a axis.

KCuAl[PO₄]₂ crystallizes in a structure type established for phosphates of the AM²⁺M³⁺[PO₄]₂ (A = K, Rb; M²⁺ = Ni, Mg, Co, Cu; M³⁺ = Fe, Al) family (Yakubovich et al., 2019 and references therein), obtained by the flux method and in hydrothermal conditions. The new compound is the second in this row, along with RbCuAl(PO₄)₂, containing Cu as the divalent metal and Al as the trivalent metal. A feature of their crystal structures, in comparison with the structures of Ni, Co or Mg ferriphosphates, is the CuO₆ octahedra distortion with four close Cu—O distances in the Cu-centred squares and two substantially removed apical O atoms in the trans position. As a second dissimilarity, we note significantly smaller sizes of AlO₅ bipyramids with an average Al—O distance of 1.838 (4) Å compared with the sizes of FeO₅ polyhedra, for which the average Fe—O distances are 1.93–1.94 Å. Such differences in geometry allow us to conclude that this structure type is quite stable, since it is realized upon the occupancy of M³⁺O₅ polyhedra by either Al³⁺ cations or significantly larger Fe³⁺ cations. Moreover, simultaneous replacement of the relatively regular M²⁺O₆ (M²⁺ = Ni, Mg, Co) octahedra by strongly distorted CuO₆ polyhedra, in accordance with the Jahn–Teller effect, also occurs in the framework of the same 3D configuration. It is very likely that the stability of this structure type is due just to the pair substitution of Cu/Al with Ni/Fe, Co/Fe or Mg/Fe. It is also important to emphasize that isotype phases with alkali metal atoms of both K and Rb may be realized for copper aluminium phosphates, i.e. the ACuAl[PO₄]₂ crystal structure is stable with changing alkali metal atom in the channels of the heteropolyhedral framework. In addition, the displacement of K atoms from the centre of the channels and their occupation of two structural positions at unacceptably short distances suggest the possibility of migration of the alkaline cations through the crystal structure and allow prediction of the associated ion-exchange, ion-conducting and/or electrochemical properties of the mineralogically probable aluminophosphate.

A study of the magnetic behaviour of the Rb analogue, RbCuAl(PO₄)₂, showed that at T_N = 10.5 K the compound orders antiferromagnetically and exhibits spontaneous magnetization (Yakubovich et al., 2016 ). Similar magnetic properties can be expected for the K species.

3.2. Crystal structure of K(Al,Zn)₂[(P,Si)O₄]₂ (II)

The main structural units that form the K(Al,Zn)₂[(P,Si)O₄]₂ crystal structure present two pairs of symmetrically independent tetrahedra and large K atoms. Refined close amounts of atoms in two independent positions jointly populated by Al³⁺ and Zn²⁺ ions [G_Al1 = 0.749 (5) and G_Al2 = 0.738 (5)] were fixed at the values of 0.75 for the final refinement. Thus, two (Al,Zn)O₄ tetrahedra are mainly occupied by Al, and two (P,Si)O₄ tetrahedra by P atoms (Fig. 4). The tetrahedra of the first type centred by Al and Zn, statistically distributed in a ratio of ∼3:1, are similar in size and distortion; the Al/Zn—O distances lie in the range 1.754 (4)–1.796 (4) Å, and the average Al/Zn—O distances in the tetrahedra are 1.778 (4) and 1.771 (4) Å and practically equal (with an accuracy of the standard deviation) (Table 4). These values are obviously larger than the average Al—O distance, 1.747 Å, for the AlO₄ tetrahedra in the ordered structure of anorthite, CaAl₂Si₂O₈ (Wainwright & Starkey, 1971 ), and significantly smaller than the average Zn—O distance, 1.940 Å, for the Zn atom in tetrahedral coordination (Yakubovich & Melnikov, 1989 ), which is consistent with a significant prevalence of Al in these polyhedra.

Table 4
Selected bond lengths (Å) for (II)

Al1—O2	1.760 (5)	P2—O7	1.543 (5)
Al1—O1ⁱ	1.769 (5)	P2—O2ⁱⁱⁱ	1.545 (5)
Al1—O5ⁱⁱ	1.785 (4)	P2—O6^vi	1.549 (4)
Al1—O6	1.796 (4)	K1—O7ⁱⁱ	2.749 (4)
Al2—O3ⁱⁱⁱ	1.753 (5)	K1—O5ⁱⁱ	2.880 (5)
Al2—O4^iv	1.771 (5)	K1—O6^vii	2.974 (4)
Al2—O8	1.774 (5)	K1—O4ⁱⁱ	2.983 (5)
Al2—O7	1.785 (5)	K1—O3	3.000 (5)
P1—O3^v	1.539 (5)	K1—O5ⁱⁱⁱ	3.017 (5)
P1—O5	1.546 (4)	K1—O1ⁱⁱ	3.104 (5)
P1—O8^v	1.550 (5)	K1—O2	3.114 (5)
P1—O4	1.555 (5)	K1—O8ⁱⁱ	3.194 (5)
P2—O1	1.541 (5)	K1—O7^v	3.366 (5)
Symmetry codes: (i) x, y + 1, z; (ii) −x + ½, y + ½, −z + ½; (iii) x, −y + 1, z − ½; (iv) −x + 1, y, −z + ½; (v) x, −y + 1, z + ½; (vi) −x + 1, −y + 1, −z; (vii) −x + ½, −y + $[3\over 2]$ , −z.

Figure 4
Basic structural units for K(Al,Zn)₂[(P,Si)O₄]₂ with the atom-labelling scheme. Displacement ellipsoids are presented at the 70% probability level. Symmetry codes: (*) x, y, −1 + z; (**) x, 1 − y, −½ + z; (′) ½ − x, −½ + y, −½ − z; (′′) ½ − x, ½ + y, −½ − z; (*′) 1− x, y, ½ − z; (′*) 1 − x, 1 − y, −z.

An amount of P and Si in both independent positions (∼3:1) was set based on a requirement of the electroneutrality of the chemical formula, because the P:Si ratio cannot be refined using X-ray diffraction data due to the similar scattering power of these atoms. The bond lengths in both symmetrically independent (P,Si)O₄ tetrahedra vary in close limits with the average (P,Si)—O distances equal to 1.547 (4) and 1.544 (4) Å, which confirms the similar distribution of phosphorus and silicon atoms over two structural positions. These values show a major amount of P atoms in polyhedra, since usual average P—O distances for orthophosphates are equal to 1.530 Å (Yakubovich & Urusov, 1997 ), whereas the average Si—O distances are 1.614 Å (Wainwright & Starkey, 1971). The K atoms are at the centre of nine-vertex polyhedra with K—O distances ranging from 2.746 (4) to 3.196 (4) Å; the tenth O atom is located 3.367 (5) Å away from the K site.

The crystal structure of K(Al_1.5Zn_0.5)[(P_1.5Si_0.5)O₈] is a 3D network of two types of tetrahedra, statistically populated by two different atoms. In the first case, these are Al and Zn metal atoms, in the second P atoms (non-metal, typical acid-forming agent) and Si (metalloid). A mixed-type anionic framework built from alternating (Al,Zn)O₄ and (P,Si)O₄ tetrahedra sharing vertices is stabilized by large K⁺ ions in the cavities [Fig. 5(a)]. The minerals celsian, BaAl₂Si₂O₈ (Griffen & Ribbe, 1976 ), and filatovite, K(Al,Zn)₂[(As,Si)O₄]₂ (Filatov et al., 2004 ), crystallize in the same structure type, as do a large group of phosphates with first-row transition metals and Al (Yakubovich et al., 2019). The structural feature of the isotypic natural and synthetic compounds of this family is the close topology of their cationic substructures to that of feldspars with the characteristic design of a `crosslinked Jacob's ladder' (Taylor, 1933 ) (Fig. 6).

Figure 5
The crystal structures of K(Al,Zn)₂[(P,Si)O₄]₂ (a) and K(Al,Si)₂[SiO₄]₂ (b) viewed along an axis of about 8.6 Å. The eight-membered rings built by [(Al,Si)O₄] and [SiO₄] tetrahedra sharing vertices in K(Al,Si)₂[SiO₄]₂, of the same topology as in the K(Al,Zn)₂[(P,Si)O₄]₂ structure, are shown in dark blue (c).

Figure 6
The cationic arrangements formed by `Jacob's ladder' chains of atom-centred tetrahedra in the celsian (a) and orthoclase (feldspar) (b) structures.

3.3. Composite K(Al,Zn)₂[(P,Si)O₄]₂ crystals as a product of epitaxial intergrowth of KAlSi[SiO₄]₂ and KAlZn[PO₄]₂

The above data show the coincidence of the chemical compositions of the K(Al,Zn)₂[(P,Si)O₄]₂ phase, obtained by microprobe analysis and as a result of the crystal structure refinement. At the same time, it is known that crystal structures with isomorphic occupancy of positions in oxygen tetrahedra by P and Si atoms are quite rare, among synthetic compounds and minerals. Most often, if these elements together are part of the mineral composition, they are distributed at different positions, for example, in the crystal structures of phosinaite (Krutik et al., 1980 ; McDonald et al., 1996 ), harrisonite (Grice & Roberts, 1993 ) or lomonosovite (Belov et al., 1977 ). Bearing this in mind, an additional study of phase (II) was undertaken using a scanning electron microscope. An obvious separation of the crystals into two zones with sharply defined regions differing in colour was observed (Fig. 7).

Figure 7
Polished zoned crystals (II) of epitaxial intergrowth of silicate (dark) and phosphate (light) components. Scanning electron microscopy image, backscattered-electron mode.

To obtain quantitative data on the chemical composition of both stuck fragments, a microprobe analysis of polished crystals of K(Al,Zn)₂[(P,Si)O₄]₂, at two points of the light and two points of the dark sectors, was undertaken. It revealed a clear correlation between the colour of the studied areas and their chemical composition. Thus, P and Zn atoms on one hand and Si atoms on the other hand occur distributed between sectors with different colours. The average chemical composition of the light part of the sample was found to be `phosphate': K₂O 14.91, ZnO 24.22, Al₂O₃ 17.04, P₂O₅ 45.20, total 101.37 wt%, while the average chemical composition of the dark part is essentially `silicate': K₂O 11.33, ZnO 1.14, Al₂O₃ 13.82, P₂O₅ 3.81, SiO₂ 68.18, total 98.28 wt%. The empirical formulae corresponding to these two compositions, calculated for four cations that form the framework of the crystal structure, are as follows: K_0.99Zn_0.95Al_1.05P_2.00O_8.02 and K_0.65Zn_0.04Al_0.74P_0.15Si_3.08O_7.99. The idealized formulae are KZnAlP₂O₈ and KAlSi₃O₈.

When dealing with microbeam analysis it is difficult to avoid capturing a neighbouring region in a double-phase crystal, with diverse composition of its components. A comparison of the sizes of the light and dark areas of the studied samples has allowed us to assume partial `capture' of neighbouring light fragments of phosphate composition, when the electronic probe is exposed to narrow areas of dark coloration (see Fig. 7). Despite the measures taken (limiting the diameter of the electron beam), such an effect may happen. It is shown by small amounts of P and Zn atoms in the results of chemical analysis of the silicate section.

The observed configuration (Fig. 7), with a high probability, represents the epitaxial intergrowth of two phases of different composition: zincaluminophosphate, K(Zn,Al)₂[PO₄]₂, and aluminosilicate, KAlSi₃O₈. The photograph clearly shows a large zone of the light areas of the phosphate composition within the crystals, in comparison with the smaller size of the dark areas of silicate. This observation correlates with the initial amounts of the corresponding reagents used in the crystal synthesis. A significantly larger volume of the phosphate component in the solution apparently caused the primary nucleation and growth of the phosphate crystal. Gradually, as P and Zn were scooped up by the growing crystal and depleted locally, when a threshold concentration of Si was reached on the surface of the phosphate crystal, the formation of silicate followed. During the development, a silicate crystal (the dark zone in Fig. 7) shielded the surface of the growth of the phosphate phase from the nutrient medium, until the Si concentration in it decreased to critical values at which point phosphate began to grow again, as shown by the light outer rim. Such zoning (rhythmic formations) during the growth of mineral aggregates is widespread in nature (Parsons et al., 2015 ). Epitaxial oscillatory zoning, as a special case, is due to structural control. For instance, two sets of oscillatory zones developed during epitaxial growth of the mineral erythrite, (Co,Zn,Ni,Fe)₃(AsO₄)₂·8H₂O, with inhomogeneous distributions of metal atoms in the octahedra, have been shown recently (Antao & Dhaliwal, 2017 ). Under the condition of geometric proportionality of crystallizing fragments, which is usually associated with the closeness of their crystal structures and is the basis for a continuous transition at the interface, the assemblies of `coherent intergrowth' are realized, which can be described in the framework of a single diffraction pattern. Diffraction arises here as a single phenomenon because of the consistency of the phases of the scattered waves.

As noted above, a large group of first-row transition metal and/or aluminium phosphates with the general formula AMM′[PO₄]₂ crystallizes in the celsian, BaAl₂Si₂O₈, structure type. The isotypic celsian and filatovite, K(Al,Zn)₂(As,Si)₂O₈, are structurally similar to feldspar KAlSi₃O₈ (Prince et al., 1973 ; Smith & Brown, 1988 and references therein) (Fig. 5), one of the most widespread minerals in the earth's crust. The crystal structure of the recently studied phosphate, K(Zn,Al)₂[PO₄]₂ (Wang et al., 2020 ), with chemical composition being about 75% of the composition of the title epitaxial crystals K(Al,Zn)₂[(P,Si)O₄]₂ (Fig. 5), is also described by the celsian structure type. Crystal characteristics and cation–oxygen bond lengths in tetrahedra-forming structures of orthoclase, K(Al_0.5Si_0.5)₂[SiO₄]₂, epitaxial intergrowth K(Al_0.75Zn_0.25)₂[(P_0.75Si_0.25)O₄]₂ and the phosphate phase K(Al_0.5Zn_0.5)₂[PO₄]₂, are summarized in Table 5. From the presented data, a correlation is observed between the number of cations in the tetrahedra, the values of their ionic radii, and the sizes of unit cells of the compounds.

Table 5
Crystal data for the group of K(M,M′)₂[TO₄]₂ compounds with mixed anionic frameworks built from tetrahedra

Ionic radii of cations in tetrahedral surrounding of the O atoms: R_Al³⁺ = 0.51, R_Zn²⁺ = 0.74, R_Si⁴⁺ = 0.37, R_P⁵⁺ = 0.35 Å.

Compound, structure type	Unit-cell parameters and volume [a, b, c (Å), β (°), V (Å³)]	Space group, Z, ρ_c (g cm⁻³)	Distance limits M—O and T—O (Å)	Reference
K^M(Al_0.75Zn_0.25)₂^T[(P_0.75Si_0.25)O₄]₂ Celsian structure type: BaAl₂[SiO₄]₂	13.2340 (10), 13.1210 (10), 8.6581 (8),100.140 (10), 1479.9 (2)	C2/c, 8, 2.700	1.754 (4)–1.796 (4), 1.537 (4)–1.555 (4)	This work
Orthoclase, K^M(Al_0.5Si_0.5)₂^T[SiO₄]₂	8.5632 (11), 12.963 (14), 7.2099 (11), 116.073 (9), 718.9 (2)→ a′ = d1 = 13.395, b = 12.963, c′ = d2 = 8.427, β′ = 100.89, V′ = 1436.9	C2/m, 4, 2.570	1.661 (5)–1.673 (5), 1.609 (5)–1.629 (5)	Prince et al. (1973)
K^M(Al_0.5Zn_0.5)₂^T[PO₄]₂, Celsian structure type: BaAl₂[SiO₄]₂	13.2906 (7),13.1956 (8), 8.6660 (5), 99.920 (2), 1497.10 (5)	C2/c, 8, 2.852	1.814 (2)–1.852 (2), 1.514 (2)–1.531 (2)	Wang et al. (2020)

The crystal structures of the above minerals and synthetic phosphates are based on the topologically identical 2D networks with four- and eight-membered rings formed by two types of tetrahedra (Fig. 5). Such grid layers are combined into a framework by vertex-bridging of tetrahedra adjacent along the third crystallographic axis. Large K atoms are placed in the framework channels. The mentioned analogy is characteristic not only for layers, but also in the rotation of tetrahedra relative to the net planes. 3D constructions of tetrahedra in both cases can be interpreted as assembled from eight-membered rings of two types: UUUUDDDD and UDDUDUUD, where the symbols U and D denote the directions of the apical vertices of the tetrahedra (up and down) relative to the plane of the layer.

From the information available (Wang et al., 2020), the activation energies for electrical transport were found to be equal to 0.49 eV for K(Zn,Al)₂(PO₄)₂. It means that potassium ions are ready to migrate through structure channels at increasing temperature under an external electric field. Similar behaviour of the K ions can be expected in the case of epitaxial phosphate-silicate crystals.

The difference in the sizes of unit cells of the two discussed structure types, as can be seen in Fig. 5, is associated with the different population of polyhedra in the eight-membered rings (Brown & Parsons, 1989 ). Thus, in the orthoclase, K(Al_0.5Si_0.5)₂[SiO₄]₂, structure there are alternating pairs of one type of tetrahedron within the rings (Si-Si-Al/Si-Al/Si-Si-Si-Al/Si-Al/Si…), while in the K(Al_0.5Zn_0.5)₂[PO₄]₂ (and celsian) structure different tetrahedra alternate through one (P-Al/Zn-P-Al/Zn-P-Al/Zn-P-Al/Zn…) ring. This situation leads to an almost twofold increase in one of the unit-cell parameters of the phosphate phase in comparison with the size of the same period in the isoformula silicate analogue, and to nearly a doubling in the unit-cell volume of the latter (Table 5). Likewise, an alternative distribution of cations in the tetrahedra of eight-membered rings correlates with a change of the symmetry group from C2/m, characterizing the K(Al_0.5Si_0.5)₂[SiO₄]₂ crystal structure, to C2/c in the structure of K(Al_0.5Zn_0.5)₂[PO₄]₂. It is noteworthy that these two monoclinic space groups are coupled by the group–subgroup relation.

The similarity of the silicate and phosphate structures is also revealed in the xz projection (Fig. 8). The close unit-cell parameters along the monoclinic axes (∼13 Å) and the comparable sizes of the other two parameters (a and c) of K(Al_0.5Zn_0.5)₂[PO₄]₂ with the sizes of the diagonals of the xz plane of K(Al_0.5Si_0.5)₂[SiO₄]₂ (Table 5) emphasize their structural similarity and topological correspondence.

Figure 8
The crystal structures of K(Al_0.5Zn_0.5)₂[PO₄]₂ (celsian structure type) (a) and orthoclase K(Al_0.5Si_0.5)₂[SiO₄]₂ (b) projected along the monoclinic axis. The diagonals of the orthoclase ac plane (Table 5

) are shown in red.

In accordance with the condition of geometric proportionality of crystallizing fragments, which is associated with the proximity of the structures of the two phases and is the basis for a continuous transition at the interface, a `coherent intergrowth' structure is formed, which can be described in the framework of a single diffraction pattern (Fig. 9). Indeed, coherent intergrowth along grain boundaries of two components different in chemical composition but close in crystal structure ensures the diffraction pattern of a single-phase sample. Since in the X-ray diffraction experiment we collect information on the averaged crystal structure and make calculations based on the intensities of reflections obtained from such a mixed crystal, the resulting crystal chemical formula K(Al_0.75Zn_0.25)₂[(P_0.75Si_0.25)O₄]₂ corresponds to the quantitative ratios of the two phases in the composition of the sample with an `epitaxial heterostructure', for which an X-ray diffraction study was performed.

Figure 9
Diffuse reflections, marking small incoherency on the phase boundary of the phosphate and silicate components, on the h0l and 0kl layers of the reciprocal lattice of the epitaxial phosphate-silicate heterocrystal.

In a recent paper (Shchipalkina et al., 2020 ) a continuous solid–solution between potassium feldspar KAlSi₃O₈ and filatovite K(Al,Zn)₂(As,Si)₂O₈ from Tolbachik fumaroles was discussed. The authors pointed out that a slow transition from K feldspar to filatovite, due to increasing the As₂O₅ content from the central part to the peripheral zones of a crystal, can be occasionally observed within one sample. Based on numerous microprobe analyses, they concluded that the substitution scheme Al³⁺ + As⁵⁺ → 2Si⁴⁺, which controls the conversion of K feldspar to filatovite, should be expanded with a more complex equation, e.g. M²⁺ + As⁵⁺ → Al³⁺ + Si⁴⁺, where M²⁺ corresponds to Zn and Cu. This assumption allowed proposition of the formula of a Si-free end-member of filatovite, KAlZnAs₂O₈. Curiously, this hypothetical arsenate with celsian structure type exactly corresponds to the phosphate component KAlZnP₂O₈ of our epitaxial composite.

4. Conclusion

Two novel phases KCuAl(PO₄)₂ (I) and K(Al,Zn)₂[(P,Si)O₄]₂ (II) were obtained in one hydrothermal synthesis experiment. We assume that the phase formation process started from the separation of Cu and Zn atoms between two phases, and Si atoms entering into only one of them. (I) and (II) were investigated using scanning electron microscopy, microprobe analysis and X-ray diffraction. (I) crystallizes in the KNiFe[PO₄]₂ structure type inherent for the first subgroup of the AM²⁺M³⁺(PO₄)₂ family (A = K, Rb; M²⁺ = Ni, Mg, Co, Cu; M³⁺ = Fe, Al). We have supposed that the stability of this structure type is due to the pair substitution of Cu/Al with Ni/Fe, Co/Fe or Mg/Fe. Based on crystal chemical features of (I) we consider the compound as a potential candidate for an electrochemically active material and/or a possible low-temperature antiferromagnet.

In accordance with obtained experimental data and detailed crystal chemical analysis of (II) we came to the conclusion that composite K(Al,Zn)₂[(P,Si)O₄]₂ crystals present the product of an epitaxial intergrowth of the silicate KAlSi[SiO₄]₂ and phosphate KAlZn[PO₄]₂ phases with identical topology of their cationic substructures and similar crystal structures (that of the minerals orthoclase and celsian, accordingly). Our assumption was based on the results of a morphological study of the samples with a clear division into two zones with sharply defined boundaries and strongly different colours. A microprobe analysis of light and dark sectors revealed their differing compositions, e.g. phosphate and silicate. In our opinion, the two-phase crystal studied using X-ray diffraction was the assembly of phosphate and silicate `coherent intergrowth' with epitaxial `heterostructure', which could be described in the framework of a single diffraction pattern due to phase matching of scattered waves. The proposed scenario is supported by rare cases of isomorphic distribution of P and Si atoms in oxygen tetrahedra in crystal structures of mineral and synthetic solids. Most often, if these elements together are part of one crystal, they occupy different structural positions.

Supporting information

CCDC references: 1999127; 1999128

Crystal structure: contains datablocks I, II. DOI: https://doi.org/10.1107/S2052520620005715/je5028sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2052520620005715/je5028Isup2.hkl

Structure factors: contains datablock II. DOI: https://doi.org/10.1107/S2052520620005715/je5028IIsup3.hkl

Computing details top

For both structures, data collection: CrysAlis PRO, Agilent Technologies, Version 1.171.37.35 (release 13-08-2014 CrysAlis171 .NET) (compiled Aug 13 2014,18:06:01); cell refinement: CrysAlis PRO, Agilent Technologies, Version 1.171.37.35 (release 13-08-2014 CrysAlis171 .NET) (compiled Aug 13 2014,18:06:01); data reduction: CrysAlis PRO, Agilent Technologies, Version 1.171.37.35 (release 13-08-2014 CrysAlis171 .NET) (compiled Aug 13 2014,18:06:01); program(s) used to solve structure: SHELXT (Sheldrick, 2015); program(s) used to refine structure: SHELXL2016/6 (Sheldrick, 2016); molecular graphics: DIAMOND (Brandenburg, 2006).

potassium copper aluminium bis(phosphate) (I) top

Crystal data top

AlCuKO₈P₂	F(000) = 620
M_r = 319.56	D_x = 3.321 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 5.0270 (8) Å	Cell parameters from 3068 reflections
b = 14.047 (2) Å	θ = 3.7–30.1°
c = 9.263 (1) Å	µ = 4.72 mm⁻¹
β = 102.29 (1)°	T = 293 K
V = 639.11 (15) Å³	Isometric, light green
Z = 4	0.07 × 0.06 × 0.06 mm

Data collection top

Xcalibur, Sapphire3 diffractometer	1469 independent reflections
Radiation source: Enhance(Mo)X-ray Source	1360 reflections with I > 2σ(I)
Detector resolution: 16.0630 pixels mm^-1	R_int = 0.057
ω scans	θ_max = 27.5°, θ_min = 2.7°
Absorption correction: multi-scan CrysAlisPro, Agilent Technologies, Version 1.171.37.35 (release 13-08-2014 CrysAlis171 .NET) (compiled Aug 13 2014,18:06:01) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	h = −6→6
T_min = 0.957, T_max = 1.000	k = −18→18
9355 measured reflections	l = −12→12

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F² > 2σ(F²)] = 0.049	Secondary atom site location: difference Fourier map
wR(F²) = 0.093	w = 1/[σ²(F_o²) + (0.014P)² + 5.5P] where P = (F_o² + 2F_c²)/3
S = 1.23	(Δ/σ)_max < 0.001
1469 reflections	Δρ_max = 0.63 e Å⁻³
122 parameters	Δρ_min = −1.02 e Å⁻³

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Cu1	0.74086 (14)	0.95540 (5)	0.45632 (8)	0.01199 (19)
K1	0.6843 (18)	0.8279 (4)	0.8045 (11)	0.0185 (12)	0.80 (5)
K2	0.726 (5)	0.8224 (14)	0.777 (3)	0.0185 (12)	0.20 (5)
P1	0.2358 (3)	0.82680 (9)	0.45459 (15)	0.0072 (3)
P2	0.7890 (3)	0.50961 (10)	0.66871 (15)	0.0076 (3)
Al1	0.2585 (3)	0.62940 (10)	0.61265 (17)	0.0049 (3)
O1	0.4104 (7)	0.9137 (3)	0.5232 (4)	0.0088 (7)
O2	−0.0620 (8)	0.8359 (3)	0.4655 (4)	0.0120 (8)
O3	0.9125 (8)	0.5881 (3)	0.5893 (4)	0.0118 (8)
O4	0.3612 (8)	0.7412 (3)	0.5468 (4)	0.0107 (8)
O5	0.7449 (8)	0.4182 (3)	0.5807 (4)	0.0147 (8)
O6	0.2641 (8)	0.8119 (3)	0.2962 (4)	0.0129 (8)
O7	0.5145 (8)	0.5458 (3)	0.6968 (5)	0.0152 (8)
O8	0.9667 (8)	0.4907 (3)	0.8211 (4)	0.0131 (8)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cu1	0.0122 (3)	0.0097 (3)	0.0158 (4)	0.0007 (3)	0.0068 (3)	0.0005 (3)
K1	0.0204 (18)	0.0185 (9)	0.015 (2)	0.0001 (10)	0.0014 (15)	−0.0011 (11)
K2	0.0204 (18)	0.0185 (9)	0.015 (2)	0.0001 (10)	0.0014 (15)	−0.0011 (11)
P1	0.0093 (6)	0.0049 (6)	0.0080 (7)	−0.0008 (5)	0.0032 (5)	0.0003 (5)
P2	0.0092 (7)	0.0064 (6)	0.0082 (6)	−0.0004 (5)	0.0039 (5)	−0.0017 (5)
Al1	0.0067 (7)	0.0030 (7)	0.0050 (7)	−0.0003 (6)	0.0017 (6)	−0.0009 (6)
O1	0.0096 (18)	0.0045 (17)	0.0128 (19)	−0.0019 (14)	0.0037 (14)	−0.0010 (15)
O2	0.0092 (18)	0.0080 (18)	0.019 (2)	−0.0011 (14)	0.0035 (15)	−0.0008 (15)
O3	0.0108 (19)	0.0111 (19)	0.014 (2)	−0.0021 (15)	0.0042 (15)	0.0016 (15)
O4	0.017 (2)	0.0055 (17)	0.0098 (19)	−0.0003 (15)	0.0028 (15)	0.0032 (14)
O5	0.025 (2)	0.0081 (18)	0.014 (2)	−0.0031 (16)	0.0102 (17)	−0.0028 (16)
O6	0.019 (2)	0.0101 (19)	0.010 (2)	−0.0003 (16)	0.0039 (16)	−0.0004 (15)
O7	0.0120 (19)	0.017 (2)	0.019 (2)	0.0055 (16)	0.0092 (16)	0.0044 (17)
O8	0.0117 (19)	0.016 (2)	0.0114 (19)	0.0018 (16)	0.0034 (15)	0.0025 (16)

Geometric parameters (Å, º) top

Cu1—O2ⁱ	1.942 (4)	K2—O1	2.85 (2)
Cu1—O1	1.981 (4)	K2—O2^vii	2.886 (19)
Cu1—O8ⁱⁱ	2.010 (4)	K2—O5^iv	3.02 (2)
Cu1—O1ⁱⁱⁱ	2.014 (4)	K2—O6^vi	3.03 (2)
Cu1—O8^iv	2.317 (4)	K2—O8^iv	3.07 (2)
Cu1—O7ⁱⁱ	2.431 (4)	K2—O3^vi	3.11 (2)
Cu1—P2ⁱⁱ	2.7698 (15)	K2—O5^viii	3.24 (3)
Cu1—Cu1^v	2.8488 (14)	K2—O6^vii	3.27 (3)
Cu1—Cu1ⁱⁱⁱ	2.9872 (14)	K2—O2ⁱ	3.29 (3)
Cu1—K2	3.53 (2)	K2—O7^viii	3.39 (2)
Cu1—K1	3.752 (10)	K2—P1^vii	3.44 (2)
K1—O4	2.858 (8)	P1—O6	1.519 (4)
K1—O6^vi	2.873 (7)	P1—O2	1.527 (4)
K1—O2^vii	2.887 (6)	P1—O4	1.530 (4)
K1—O5^viii	2.893 (14)	P1—O1	1.558 (4)
K1—O3^vi	2.894 (9)	P2—O5	1.512 (4)
K1—O1	2.935 (7)	P2—O8	1.525 (4)
K1—O5^iv	3.110 (7)	P2—O3	1.529 (4)
K1—O4^vi	3.189 (14)	P2—O7	1.543 (4)
K1—O7^viii	3.219 (8)	Al1—O7	1.794 (4)
K1—O8^iv	3.244 (9)	Al1—O4	1.800 (4)
K1—P1	3.532 (6)	Al1—O3^ix	1.802 (4)
K1—P2^viii	3.534 (11)	Al1—O6^vi	1.884 (4)
K2—O4	2.75 (2)	Al1—O5^x	1.908 (4)

O2ⁱ—Cu1—O1	100.66 (15)	O6—P1—K2	129.7 (6)
O2ⁱ—Cu1—O8ⁱⁱ	90.13 (16)	O2—P1—K2	118.3 (5)
O1—Cu1—O8ⁱⁱ	158.29 (16)	O4—P1—K2	50.8 (3)
O2ⁱ—Cu1—O1ⁱⁱⁱ	169.84 (16)	O1—P1—K2	54.8 (3)
O1—Cu1—O1ⁱⁱⁱ	83.22 (15)	K2^xi—P1—K2	136.4 (5)
O8ⁱⁱ—Cu1—O1ⁱⁱⁱ	89.38 (15)	O6—P1—K1	135.6 (3)
O2ⁱ—Cu1—O8^iv	85.67 (15)	O2—P1—K1	112.5 (3)
O1—Cu1—O8^iv	101.56 (15)	O4—P1—K1	52.04 (17)
O8ⁱⁱ—Cu1—O8^iv	97.97 (14)	O1—P1—K1	55.12 (16)
O1ⁱⁱⁱ—Cu1—O8^iv	84.35 (15)	K2^xi—P1—K1	134.8 (5)
O2ⁱ—Cu1—O7ⁱⁱ	99.48 (15)	K2—P1—K1	5.9 (3)
O1—Cu1—O7ⁱⁱ	93.44 (14)	O6—P1—K1^xi	76.3 (3)
O8ⁱⁱ—Cu1—O7ⁱⁱ	66.03 (14)	O2—P1—K1^xi	52.0 (2)
O1ⁱⁱⁱ—Cu1—O7ⁱⁱ	89.58 (15)	O4—P1—K1^xi	86.14 (18)
O8^iv—Cu1—O7ⁱⁱ	163.00 (14)	O1—P1—K1^xi	163.92 (19)
O2ⁱ—Cu1—P2ⁱⁱ	92.71 (12)	K2^xi—P1—K1^xi	5.7 (3)
O1—Cu1—P2ⁱⁱ	127.15 (12)	K2—P1—K1^xi	132.9 (5)
O8ⁱⁱ—Cu1—P2ⁱⁱ	32.53 (11)	K1—P1—K1^xi	130.7 (3)
O1ⁱⁱⁱ—Cu1—P2ⁱⁱ	92.33 (11)	O6—P1—K1ⁱⁱ	49.5 (2)
O8^iv—Cu1—P2ⁱⁱ	130.49 (10)	O2—P1—K1ⁱⁱ	140.92 (19)
O7ⁱⁱ—Cu1—P2ⁱⁱ	33.73 (9)	O4—P1—K1ⁱⁱ	61.7 (2)
O2ⁱ—Cu1—Cu1^v	86.57 (12)	O1—P1—K1ⁱⁱ	106.53 (19)
O1—Cu1—Cu1^v	144.92 (12)	K2^xi—P1—K1ⁱⁱ	85.0 (4)
O8ⁱⁱ—Cu1—Cu1^v	53.65 (11)	K2—P1—K1ⁱⁱ	86.2 (4)
O1ⁱⁱⁱ—Cu1—Cu1^v	84.97 (11)	K1—P1—K1ⁱⁱ	91.55 (18)
O8^iv—Cu1—Cu1^v	44.32 (10)	K1^xi—P1—K1ⁱⁱ	88.88 (11)
O7ⁱⁱ—Cu1—Cu1^v	119.41 (10)	O6—P1—K2ⁱⁱ	46.7 (4)
P2ⁱⁱ—Cu1—Cu1^v	86.18 (4)	O2—P1—K2ⁱⁱ	142.9 (4)
O2ⁱ—Cu1—Cu1ⁱⁱⁱ	141.85 (12)	O4—P1—K2ⁱⁱ	65.6 (4)
O1—Cu1—Cu1ⁱⁱⁱ	42.03 (10)	O1—P1—K2ⁱⁱ	104.1 (4)
O8ⁱⁱ—Cu1—Cu1ⁱⁱⁱ	127.51 (12)	K2^xi—P1—K2ⁱⁱ	86.8 (4)
O1ⁱⁱⁱ—Cu1—Cu1ⁱⁱⁱ	41.19 (10)	K2—P1—K2ⁱⁱ	87.5 (5)
O8^iv—Cu1—Cu1ⁱⁱⁱ	93.81 (10)	K1—P1—K2ⁱⁱ	93.0 (3)
O7ⁱⁱ—Cu1—Cu1ⁱⁱⁱ	92.00 (10)	K1^xi—P1—K2ⁱⁱ	91.0 (3)
P2ⁱⁱ—Cu1—Cu1ⁱⁱⁱ	115.34 (5)	K1ⁱⁱ—P1—K2ⁱⁱ	4.3 (3)
Cu1^v—Cu1—Cu1ⁱⁱⁱ	118.92 (5)	O5—P2—O8	109.9 (2)
O2ⁱ—Cu1—K2	66.9 (5)	O5—P2—O3	112.4 (2)
O1—Cu1—K2	53.8 (4)	O8—P2—O3	110.7 (2)
O8ⁱⁱ—Cu1—K2	147.3 (4)	O5—P2—O7	109.7 (2)
O1ⁱⁱⁱ—Cu1—K2	109.2 (5)	O8—P2—O7	105.7 (2)
O8^iv—Cu1—K2	59.1 (3)	O3—P2—O7	108.2 (2)
O7ⁱⁱ—Cu1—K2	137.8 (3)	O5—P2—Cu1^vi	129.53 (16)
P2ⁱⁱ—Cu1—K2	158.0 (4)	O8—P2—Cu1^vi	45.14 (15)
Cu1^v—Cu1—K2	100.1 (3)	O3—P2—Cu1^vi	117.54 (16)
Cu1ⁱⁱⁱ—Cu1—K2	80.2 (5)	O7—P2—Cu1^vi	60.99 (16)
O2ⁱ—Cu1—K1	71.4 (2)	O5—P2—K1^xii	53.2 (2)
O1—Cu1—K1	50.82 (17)	O8—P2—K1^xii	94.56 (19)
O8ⁱⁱ—Cu1—K1	150.69 (18)	O3—P2—K1^xii	154.6 (2)
O1ⁱⁱⁱ—Cu1—K1	104.8 (2)	O7—P2—K1^xii	65.6 (2)
O8^iv—Cu1—K1	59.13 (11)	Cu1^vi—P2—K1^xii	82.11 (18)
O7ⁱⁱ—Cu1—K1	137.87 (11)	O5—P2—K2^xiii	57.6 (4)
P2ⁱⁱ—Cu1—K1	161.71 (15)	O8—P2—K2^xiii	59.4 (4)
Cu1^v—Cu1—K1	101.41 (8)	O3—P2—K2^xiii	105.4 (5)
Cu1ⁱⁱⁱ—Cu1—K1	75.72 (18)	O7—P2—K2^xiii	146.3 (5)
K2—Cu1—K1	4.6 (3)	Cu1^vi—P2—K2^xiii	101.2 (4)
O4—K1—O6^vi	53.32 (13)	K1^xii—P2—K2^xiii	84.7 (4)
O4—K1—O2^vii	101.7 (2)	O5—P2—K1^xiii	57.55 (18)
O6^vi—K1—O2^vii	73.19 (15)	O8—P2—K1^xiii	62.7 (2)
O4—K1—O5^viii	99.1 (3)	O3—P2—K1^xiii	100.0 (3)
O6^vi—K1—O5^viii	73.0 (3)	O7—P2—K1^xiii	151.7 (3)
O2^vii—K1—O5^viii	116.2 (4)	Cu1^vi—P2—K1^xiii	105.63 (18)
O4—K1—O3^vi	168.3 (5)	K1^xii—P2—K1^xiii	88.83 (12)
O6^vi—K1—O3^vi	116.7 (4)	K2^xiii—P2—K1^xiii	5.7 (3)
O2^vii—K1—O3^vi	78.94 (18)	O5—P2—K2^xii	57.1 (4)
O5^viii—K1—O3^vi	70.6 (3)	O8—P2—K2^xii	92.2 (4)
O4—K1—O1	50.01 (15)	O3—P2—K2^xii	157.1 (4)
O6^vi—K1—O1	93.06 (16)	O7—P2—K2^xii	63.0 (4)
O2^vii—K1—O1	149.1 (4)	Cu1^vi—P2—K2^xii	78.2 (4)
O5^viii—K1—O1	84.3 (2)	K1^xii—P2—K2^xii	4.0 (3)
O3^vi—K1—O1	131.4 (2)	K2^xiii—P2—K2^xii	86.3 (4)
O4—K1—O5^iv	141.1 (5)	K1^xiii—P2—K2^xii	90.7 (3)
O6^vi—K1—O5^iv	155.2 (2)	O7—Al1—O4	119.21 (19)
O2^vii—K1—O5^iv	82.78 (17)	O7—Al1—O3^ix	115.24 (19)
O5^viii—K1—O5^iv	113.7 (3)	O4—Al1—O3^ix	125.37 (19)
O3^vi—K1—O5^iv	50.54 (12)	O7—Al1—O6^vi	91.33 (19)
O1—K1—O5^iv	111.1 (3)	O4—Al1—O6^vi	88.48 (18)
O4—K1—O4^vi	100.0 (2)	O3^ix—Al1—O6^vi	94.46 (19)
O6^vi—K1—O4^vi	47.9 (2)	O7—Al1—O5^x	92.34 (19)
O2^vii—K1—O4^vi	68.2 (2)	O4—Al1—O5^x	86.18 (18)
O5^viii—K1—O4^vi	49.0 (2)	O3^ix—Al1—O5^x	87.65 (18)
O3^vi—K1—O4^vi	69.2 (3)	O6^vi—Al1—O5^x	174.52 (18)
O1—K1—O4^vi	122.5 (3)	O7—Al1—K1^xi	145.29 (17)
O5^iv—K1—O4^vi	117.0 (3)	O4—Al1—K1^xi	80.1 (2)
O4—K1—O7^viii	106.32 (16)	O3^ix—Al1—K1^xi	51.4 (3)
O6^vi—K1—O7^viii	115.1 (4)	O6^vi—Al1—K1^xi	119.4 (2)
O2^vii—K1—O7^viii	149.6 (4)	O5^x—Al1—K1^xi	58.4 (2)
O5^viii—K1—O7^viii	47.88 (18)	O7—Al1—K2	88.1 (4)
O3^vi—K1—O7^viii	71.2 (2)	O4—Al1—K2	45.4 (4)
O1—K1—O7^viii	61.28 (13)	O3^ix—Al1—K2	142.9 (5)
O5^iv—K1—O7^viii	82.92 (14)	O6^vi—Al1—K2	54.6 (5)
O4^vi—K1—O7^viii	95.0 (4)	O5^x—Al1—K2	121.5 (5)
O4—K1—O8^iv	104.8 (3)	K1^xi—Al1—K2	122.0 (4)
O6^vi—K1—O8^iv	157.3 (3)	O7—Al1—K2^xi	143.9 (3)
O2^vii—K1—O8^iv	122.3 (3)	O4—Al1—K2^xi	76.4 (4)
O5^viii—K1—O8^iv	109.0 (2)	O3^ix—Al1—K2^xi	56.7 (5)
O3^vi—K1—O8^iv	84.26 (14)	O6^vi—Al1—K2^xi	123.0 (4)
O1—K1—O8^iv	65.14 (19)	O5^x—Al1—K2^xi	54.3 (4)
O5^iv—K1—O8^iv	46.00 (15)	K1^xi—Al1—K2^xi	5.7 (3)
O4^vi—K1—O8^iv	149.6 (4)	K2—Al1—K2^xi	119.6 (3)
O7^viii—K1—O8^iv	61.30 (12)	O7—Al1—K1	89.81 (17)
O4—K1—P1	24.97 (9)	O4—Al1—K1	48.08 (18)
O6^vi—K1—P1	69.53 (12)	O3^ix—Al1—K1	137.7 (3)
O2^vii—K1—P1	126.6 (2)	O6^vi—Al1—K1	49.1 (3)
O5^viii—K1—P1	87.64 (18)	O5^x—Al1—K1	126.8 (3)
O3^vi—K1—P1	152.8 (3)	K1^xi—Al1—K1	121.87 (8)
O1—K1—P1	25.82 (9)	K2—Al1—K1	5.7 (3)
O5^iv—K1—P1	132.7 (4)	K2^xi—Al1—K1	120.1 (4)
O4^vi—K1—P1	108.9 (2)	O7—Al1—K1ⁱⁱ	87.98 (14)
O7^viii—K1—P1	82.16 (12)	O4—Al1—K1ⁱⁱ	52.10 (14)
O8^iv—K1—P1	87.8 (2)	O3^ix—Al1—K1ⁱⁱ	128.16 (15)
O4—K1—P2^viii	95.44 (18)	O6^vi—Al1—K1ⁱⁱ	132.63 (15)
O6^vi—K1—P2^viii	89.6 (3)	O5^x—Al1—K1ⁱⁱ	43.53 (14)
O2^vii—K1—P2^viii	140.3 (5)	K1^xi—Al1—K1ⁱⁱ	82.5 (2)
O5^viii—K1—P2^viii	24.73 (11)	K2—Al1—K1ⁱⁱ	78.0 (5)
O3^vi—K1—P2^viii	77.5 (3)	K2^xi—Al1—K1ⁱⁱ	76.9 (5)
O1—K1—P2^viii	64.53 (15)	K1—Al1—K1ⁱⁱ	83.5 (2)
O5^iv—K1—P2^viii	105.51 (19)	P1—O1—Cu1	122.8 (2)
O4^vi—K1—P2^viii	73.7 (3)	P1—O1—Cu1ⁱⁱⁱ	124.2 (2)
O7^viii—K1—P2^viii	25.89 (11)	Cu1—O1—Cu1ⁱⁱⁱ	96.78 (15)
O8^iv—K1—P2^viii	86.54 (13)	P1—O1—K2	98.7 (4)
P1—K1—P2^viii	76.10 (11)	Cu1—O1—K2	92.0 (6)
O4—K2—O1	51.9 (4)	Cu1ⁱⁱⁱ—O1—K2	119.2 (5)
O4—K2—O2^vii	104.4 (6)	P1—O1—K1	99.06 (18)
O1—K2—O2^vii	156.2 (8)	Cu1—O1—K1	97.6 (3)
O4—K2—O5^iv	154.5 (12)	Cu1ⁱⁱⁱ—O1—K1	114.0 (3)
O1—K2—O5^iv	116.3 (7)	K2—O1—K1	7.1 (4)
O2^vii—K2—O5^iv	84.4 (5)	P1—O2—Cu1^ix	124.6 (2)
O4—K2—O6^vi	52.6 (4)	P1—O2—K2^xi	97.8 (6)
O1—K2—O6^vi	91.7 (6)	Cu1^ix—O2—K2^xi	121.3 (4)
O2^vii—K2—O6^vi	71.0 (5)	P1—O2—K1^xi	103.3 (3)
O5^iv—K2—O6^vi	150.2 (9)	Cu1^ix—O2—K1^xi	120.06 (19)
O4—K2—O8^iv	112.6 (8)	K2^xi—O2—K1^xi	7.3 (4)
O1—K2—O8^iv	68.6 (5)	P1—O2—K2^ix	124.0 (4)
O2^vii—K2—O8^iv	129.0 (8)	Cu1^ix—O2—K2^ix	80.3 (4)
O5^iv—K2—O8^iv	48.2 (3)	K2^xi—O2—K2^ix	109.8 (6)
O6^vi—K2—O8^iv	159.9 (7)	K1^xi—O2—K2^ix	102.6 (4)
O4—K2—O3^vi	155.4 (11)	P2—O3—Al1ⁱ	130.9 (3)
O1—K2—O3^vi	126.2 (8)	P2—O3—K1ⁱⁱ	127.6 (3)
O2^vii—K2—O3^vi	75.5 (5)	Al1ⁱ—O3—K1ⁱⁱ	99.4 (3)
O5^iv—K2—O3^vi	49.6 (3)	P2—O3—K2ⁱⁱ	131.8 (5)
O6^vi—K2—O3^vi	106.4 (9)	Al1ⁱ—O3—K2ⁱⁱ	94.2 (5)
O8^iv—K2—O3^vi	83.9 (5)	K1ⁱⁱ—O3—K2ⁱⁱ	5.7 (4)
O4—K2—O5^viii	93.6 (7)	P1—O4—Al1	139.5 (3)
O1—K2—O5^viii	79.7 (6)	P1—O4—K2	103.6 (4)
O2^vii—K2—O5^viii	106.4 (9)	Al1—O4—K2	106.9 (5)
O5^iv—K2—O5^viii	106.9 (7)	P1—O4—K1	103.0 (2)
O6^vi—K2—O5^viii	66.3 (6)	Al1—O4—K1	104.0 (2)
O8^iv—K2—O5^viii	105.0 (6)	K2—O4—K1	7.2 (4)
O3^vi—K2—O5^viii	63.6 (6)	P1—O4—K1ⁱⁱ	93.3 (2)
O4—K2—O6^vii	102.1 (8)	Al1—O4—K1ⁱⁱ	101.5 (2)
O1—K2—O6^vii	127.8 (10)	K2—O4—K1ⁱⁱ	108.5 (7)
O2^vii—K2—O6^vii	47.8 (4)	K1—O4—K1ⁱⁱ	115.7 (4)
O5^iv—K2—O6^vii	65.9 (5)	P2—O5—Al1^x	140.8 (3)
O6^vi—K2—O6^vii	105.9 (6)	P2—O5—K1^xii	102.1 (2)
O8^iv—K2—O6^vii	89.8 (7)	Al1^x—O5—K1^xii	109.4 (2)
O3^vi—K2—O6^vii	95.8 (5)	P2—O5—K2^xiii	97.4 (4)
O5^viii—K2—O6^vii	152.4 (8)	Al1^x—O5—K2^xiii	94.8 (5)
O4—K2—O2ⁱ	68.2 (6)	K1^xii—O5—K2^xiii	107.5 (6)
O1—K2—O2ⁱ	58.4 (5)	P2—O5—K1^xiii	98.2 (2)
O2^vii—K2—O2ⁱ	115.3 (9)	Al1^x—O5—K1^xiii	90.1 (2)
O5^iv—K2—O2ⁱ	86.4 (7)	K1^xii—O5—K1^xiii	113.7 (3)
O6^vi—K2—O2ⁱ	118.9 (7)	K2^xiii—O5—K1^xiii	6.7 (4)
O8^iv—K2—O2ⁱ	54.3 (5)	P2—O5—K2^xii	99.8 (4)
O3^vi—K2—O2ⁱ	134.7 (7)	Al1^x—O5—K2^xii	112.0 (4)
O5^viii—K2—O2ⁱ	137.3 (6)	K1^xii—O5—K2^xii	2.5 (4)
O6^vii—K2—O2ⁱ	70.2 (6)	K2^xiii—O5—K2^xii	106.9 (7)
O4—K2—O7^viii	104.5 (6)	K1^xiii—O5—K2^xii	113.1 (4)
O1—K2—O7^viii	59.8 (4)	P1—O6—Al1ⁱⁱ	145.6 (3)
O2^vii—K2—O7^viii	139.6 (10)	P1—O6—K1ⁱⁱ	106.7 (3)
O5^iv—K2—O7^viii	81.4 (5)	Al1ⁱⁱ—O6—K1ⁱⁱ	101.1 (3)
O6^vi—K2—O7^viii	106.4 (8)	P1—O6—K2ⁱⁱ	111.9 (5)
O8^iv—K2—O7^viii	61.1 (4)	Al1ⁱⁱ—O6—K2ⁱⁱ	94.9 (6)
O3^vi—K2—O7^viii	66.5 (5)	K1ⁱⁱ—O6—K2ⁱⁱ	6.5 (4)
O5^viii—K2—O7^viii	44.2 (4)	P1—O6—K2^xi	83.4 (5)
O6^vii—K2—O7^viii	146.4 (7)	Al1ⁱⁱ—O6—K2^xi	110.5 (5)
O2ⁱ—K2—O7^viii	101.3 (5)	K1ⁱⁱ—O6—K2^xi	101.7 (3)
O4—K2—P1^vii	115.1 (7)	K2ⁱⁱ—O6—K2^xi	105.9 (6)
O1—K2—P1^vii	153.5 (11)	P2—O7—Al1	136.6 (3)
O2^vii—K2—P1^vii	26.1 (2)	P2—O7—Cu1^vi	85.27 (18)
O5^iv—K2—P1^vii	64.3 (4)	Al1—O7—Cu1^vi	125.2 (2)
O6^vi—K2—P1^vii	95.5 (5)	P2—O7—K1^xii	88.5 (3)
O8^iv—K2—P1^vii	103.9 (7)	Al1—O7—K1^xii	115.3 (2)
O3^vi—K2—P1^vii	75.9 (4)	Cu1^vi—O7—K1^xii	94.41 (19)
O5^viii—K2—P1^vii	126.4 (8)	P2—O7—K2^xii	93.0 (5)
O6^vii—K2—P1^vii	25.98 (18)	Al1—O7—K2^xii	113.8 (4)
O2ⁱ—K2—P1^vii	96.1 (7)	Cu1^vi—O7—K2^xii	91.3 (4)
O7^viii—K2—P1^vii	140.4 (7)	K1^xii—O7—K2^xii	5.7 (3)
O6—P1—O2	111.7 (2)	P2—O8—Cu1^vi	102.3 (2)
O6—P1—O4	108.6 (2)	P2—O8—Cu1^xiii	175.6 (2)
O2—P1—O4	108.8 (2)	Cu1^vi—O8—Cu1^xiii	82.03 (14)
O6—P1—O1	110.0 (2)	P2—O8—K2^xiii	95.3 (4)
O2—P1—O1	112.5 (2)	Cu1^vi—O8—K2^xiii	149.7 (6)
O4—P1—O1	105.0 (2)	Cu1^xiii—O8—K2^xiii	80.5 (4)
O6—P1—K2^xi	70.6 (5)	P2—O8—K1^xiii	92.7 (2)
O2—P1—K2^xi	56.1 (5)	Cu1^vi—O8—K1^xiii	155.4 (3)
O4—P1—K2^xi	88.0 (4)	Cu1^xiii—O8—K1^xiii	83.07 (16)
O1—P1—K2^xi	165.6 (4)	K2^xiii—O8—K1^xiii	5.9 (4)

Symmetry codes: (i) x+1, y, z; (ii) x, −y+3/2, z−1/2; (iii) −x+1, −y+2, −z+1; (iv) −x+2, y+1/2, −z+3/2; (v) −x+2, −y+2, −z+1; (vi) x, −y+3/2, z+1/2; (vii) x+1, −y+3/2, z+1/2; (viii) −x+1, y+1/2, −z+3/2; (ix) x−1, y, z; (x) −x+1, −y+1, −z+1; (xi) x−1, −y+3/2, z−1/2; (xii) −x+1, y−1/2, −z+3/2; (xiii) −x+2, y−1/2, −z+3/2.

potassium zinc aluminium bis(phosphate-silicate) (II) top

Crystal data top

Al₃K₂O₁₆P₃SiZn	F(000) = 1176
M_r = 601.51	D_x = 2.700 Mg m⁻³
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 13.234 (1) Å	Cell parameters from 2260 reflections
b = 13.121 (1) Å	θ = 3.0–29.9°
c = 8.6581 (8) Å	µ = 2.89 mm⁻¹
β = 100.14 (1)°	T = 293 K
V = 1479.9 (2) Å³	Plate, blue
Z = 4	0.06 × 0.06 × 0.05 mm

Data collection top

Xcalibur, Sapphire3 diffractometer	1303 independent reflections
Radiation source: Enhance (Mo) X-ray Source	1176 reflections with I > 2σ(I)
Detector resolution: 16.0630 pixels mm^-1	R_int = 0.060
/w scans	θ_max = 25.0°, θ_min = 3.0°
Absorption correction: gaussian CrysAlisPro, Agilent Technologies, Version 1.171.37.35 (release 13-08-2014 CrysAlis171 .NET) (compiled Aug 13 2014,18:06:01) Numerical absorption correction based on gaussian integration over a multifaceted crystal model	h = −15→15
T_min = 0.800, T_max = 0.856	k = −15→15
8821 measured reflections	l = −10→10

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F² > 2σ(F²)] = 0.059	Secondary atom site location: difference Fourier map
wR(F²) = 0.096	w = 1/[σ²(F_o²) + (0.014P)² + 13.2P] where P = (F_o² + 2F_c²)/3
S = 1.29	(Δ/σ)_max < 0.001
1303 reflections	Δρ_max = 0.42 e Å⁻³
118 parameters	Δρ_min = −0.42 e Å⁻³

Special details top

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Al1	0.36768 (9)	0.93751 (10)	0.11136 (13)	0.0135 (3)	0.75
Al2	0.42151 (9)	0.37427 (9)	−0.04604 (14)	0.0142 (3)	0.75
P1	0.35517 (11)	0.43393 (12)	0.59287 (17)	0.0160 (4)	0.75
P2	0.42386 (12)	0.13702 (11)	−0.03024 (18)	0.0151 (4)	0.75
Si1	0.35517 (11)	0.43393 (12)	0.59287 (17)	0.0160 (4)	0.25
Si2	0.42386 (12)	0.13702 (11)	−0.03024 (18)	0.0151 (4)	0.25
Zn1	0.36768 (9)	0.93751 (10)	0.11136 (13)	0.0135 (3)	0.25
Zn2	0.42151 (9)	0.37427 (9)	−0.04604 (14)	0.0142 (3)	0.25
K1	0.18167 (11)	0.75169 (14)	0.21957 (17)	0.0348 (4)
O1	0.3901 (3)	0.0698 (4)	0.0976 (5)	0.0293 (11)
O2	0.3689 (3)	0.8973 (4)	0.3057 (5)	0.0363 (12)
O3	0.3577 (4)	0.6042 (4)	0.2615 (5)	0.0397 (13)
O4	0.4432 (3)	0.3850 (4)	0.5205 (5)	0.0320 (11)
O5	0.2534 (3)	0.3957 (3)	0.4942 (5)	0.0273 (10)
O6	0.4582 (3)	0.8675 (3)	0.0208 (5)	0.0252 (11)
O7	0.3917 (3)	0.2469 (4)	0.0026 (5)	0.0326 (11)
O8	0.3662 (3)	0.4486 (3)	0.0887 (5)	0.0278 (11)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Al1	0.0109 (6)	0.0153 (7)	0.0140 (6)	−0.0009 (5)	0.0014 (5)	0.0033 (5)
Al2	0.0145 (7)	0.0124 (7)	0.0160 (6)	0.0005 (5)	0.0033 (5)	0.0022 (5)
P1	0.0156 (8)	0.0156 (9)	0.0162 (8)	−0.0023 (7)	0.0012 (6)	0.0025 (6)
P2	0.0163 (8)	0.0136 (9)	0.0161 (8)	0.0005 (6)	0.0044 (6)	−0.0007 (6)
Si1	0.0156 (8)	0.0156 (9)	0.0162 (8)	−0.0023 (7)	0.0012 (6)	0.0025 (6)
Si2	0.0163 (8)	0.0136 (9)	0.0161 (8)	0.0005 (6)	0.0044 (6)	−0.0007 (6)
Zn1	0.0109 (6)	0.0153 (7)	0.0140 (6)	−0.0009 (5)	0.0014 (5)	0.0033 (5)
Zn2	0.0145 (7)	0.0124 (7)	0.0160 (6)	0.0005 (5)	0.0033 (5)	0.0022 (5)
K1	0.0360 (9)	0.0432 (9)	0.0283 (8)	0.0008 (8)	0.0139 (6)	0.0059 (8)
O1	0.036 (3)	0.030 (3)	0.024 (2)	−0.002 (2)	0.010 (2)	0.005 (2)
O2	0.029 (3)	0.052 (3)	0.026 (3)	0.006 (2)	0.001 (2)	0.002 (2)
O3	0.047 (3)	0.048 (3)	0.025 (3)	0.000 (3)	0.009 (2)	−0.012 (2)
O4	0.025 (2)	0.033 (3)	0.040 (3)	0.002 (2)	0.012 (2)	−0.004 (2)
O5	0.021 (2)	0.026 (2)	0.033 (2)	−0.003 (2)	−0.0004 (18)	−0.004 (2)
O6	0.017 (2)	0.025 (3)	0.034 (3)	−0.0005 (18)	0.005 (2)	−0.002 (2)
O7	0.038 (3)	0.024 (2)	0.042 (3)	0.010 (2)	0.026 (2)	0.003 (2)
O8	0.032 (3)	0.016 (2)	0.035 (3)	0.0001 (19)	0.003 (2)	0.002 (2)

Geometric parameters (Å, º) top

Al1—O2	1.760 (5)	P1—K1^vii	3.646 (2)
Al1—O1ⁱ	1.769 (5)	P2—O1	1.541 (5)
Al1—O5ⁱⁱ	1.785 (4)	P2—O7	1.543 (5)
Al1—O6	1.796 (4)	P2—O2^iv	1.545 (5)
Al1—K1	3.701 (2)	P2—O6^viii	1.549 (4)
Al1—K1ⁱⁱⁱ	3.760 (2)	P2—K1^vi	3.574 (2)
Al2—O3^iv	1.753 (5)	P2—K1^iv	3.828 (2)
Al2—O4^v	1.771 (5)	K1—O7ⁱⁱ	2.749 (4)
Al2—O8	1.774 (5)	K1—O5ⁱⁱ	2.880 (5)
Al2—O7	1.785 (5)	K1—O6ⁱⁱⁱ	2.974 (4)
Al2—K1^vi	3.7149 (19)	K1—O4ⁱⁱ	2.983 (5)
Al2—K1^iv	3.828 (2)	K1—O3	3.000 (5)
P1—O3^vii	1.539 (5)	K1—O5^iv	3.017 (5)
P1—O5	1.546 (4)	K1—O1ⁱⁱ	3.104 (5)
P1—O8^vii	1.550 (5)	K1—O2	3.114 (5)
P1—O4	1.555 (5)	K1—O8ⁱⁱ	3.194 (5)
P1—K1^vi	3.579 (2)	K1—O7^vii	3.366 (5)

O2—Al1—O1ⁱ	112.7 (2)	O4ⁱⁱ—K1—O1ⁱⁱ	128.64 (13)
O2—Al1—O5ⁱⁱ	104.7 (2)	O3—K1—O1ⁱⁱ	75.12 (13)
O1ⁱ—Al1—O5ⁱⁱ	114.4 (2)	O5^iv—K1—O1ⁱⁱ	89.79 (13)
O2—Al1—O6	111.7 (2)	O7ⁱⁱ—K1—O2	101.15 (14)
O1ⁱ—Al1—O6	109.9 (2)	O5ⁱⁱ—K1—O2	55.69 (12)
O5ⁱⁱ—Al1—O6	103.1 (2)	O6ⁱⁱⁱ—K1—O2	149.44 (13)
O2—Al1—K1	57.00 (16)	O4ⁱⁱ—K1—O2	97.29 (13)
O1ⁱ—Al1—K1	142.25 (16)	O3—K1—O2	78.38 (13)
O5ⁱⁱ—Al1—K1	49.48 (15)	O5^iv—K1—O2	102.75 (13)
O6—Al1—K1	107.34 (15)	O1ⁱⁱ—K1—O2	130.67 (12)
O2—Al1—K1ⁱⁱⁱ	120.10 (18)	O7ⁱⁱ—K1—O8ⁱⁱ	55.30 (13)
O1ⁱ—Al1—K1ⁱⁱⁱ	127.24 (15)	O5ⁱⁱ—K1—O8ⁱⁱ	84.97 (13)
O5ⁱⁱ—Al1—K1ⁱⁱⁱ	52.22 (15)	O6ⁱⁱⁱ—K1—O8ⁱⁱ	129.26 (12)
O6—Al1—K1ⁱⁱⁱ	50.90 (13)	O4ⁱⁱ—K1—O8ⁱⁱ	75.61 (13)
K1—Al1—K1ⁱⁱⁱ	73.97 (4)	O3—K1—O8ⁱⁱ	132.80 (12)
O3^iv—Al2—O4^v	114.4 (2)	O5^iv—K1—O8ⁱⁱ	165.60 (13)
O3^iv—Al2—O8	110.6 (2)	O1ⁱⁱ—K1—O8ⁱⁱ	104.48 (12)
O4^v—Al2—O8	113.5 (2)	O2—K1—O8ⁱⁱ	66.53 (12)
O3^iv—Al2—O7	106.6 (2)	O7ⁱⁱ—K1—O7^vii	74.72 (13)
O4^v—Al2—O7	107.8 (2)	O5ⁱⁱ—K1—O7^vii	99.35 (12)
O8—Al2—O7	103.0 (2)	O6ⁱⁱⁱ—K1—O7^vii	147.65 (13)
O3^iv—Al2—K1^vi	127.77 (17)	O4ⁱⁱ—K1—O7^vii	142.08 (14)
O4^v—Al2—K1^vi	116.00 (16)	O3—K1—O7^vii	52.53 (12)
O8—Al2—K1^vi	59.21 (15)	O5^iv—K1—O7^vii	99.26 (12)
O7—Al2—K1^vi	44.68 (14)	O1ⁱⁱ—K1—O7^vii	85.44 (12)
O3^iv—Al2—K1^iv	49.45 (17)	O2—K1—O7^vii	45.73 (12)
O4^v—Al2—K1^iv	145.73 (17)	O8ⁱⁱ—K1—O7^vii	80.28 (12)
O8—Al2—K1^iv	100.74 (14)	O7ⁱⁱ—K1—P2ⁱⁱ	24.02 (10)
O7—Al2—K1^iv	61.54 (16)	O5ⁱⁱ—K1—P2ⁱⁱ	163.79 (11)
K1^vi—Al2—K1^iv	80.50 (4)	O6ⁱⁱⁱ—K1—P2ⁱⁱ	91.60 (10)
O3^vii—P1—O5	106.9 (3)	O4ⁱⁱ—K1—P2ⁱⁱ	121.95 (10)
O3^vii—P1—O8^vii	111.1 (3)	O3—K1—P2ⁱⁱ	92.02 (11)
O5—P1—O8^vii	112.7 (2)	O5^iv—K1—P2ⁱⁱ	115.21 (10)
O3^vii—P1—O4	110.8 (3)	O1ⁱⁱ—K1—P2ⁱⁱ	25.46 (8)
O5—P1—O4	106.6 (3)	O2—K1—P2ⁱⁱ	118.56 (10)
O8^vii—P1—O4	108.7 (3)	O8ⁱⁱ—K1—P2ⁱⁱ	79.03 (9)
O3^vii—P1—K1^vi	118.5 (2)	O7^vii—K1—P2ⁱⁱ	80.59 (8)
O5—P1—K1^vi	51.42 (18)	O7ⁱⁱ—K1—P1ⁱⁱ	130.91 (12)
O8^vii—P1—K1^vi	130.39 (18)	O5ⁱⁱ—K1—P1ⁱⁱ	24.81 (9)
O4—P1—K1^vi	55.37 (17)	O6ⁱⁱⁱ—K1—P1ⁱⁱ	80.62 (9)
O3^vii—P1—K1^vii	53.6 (2)	O4ⁱⁱ—K1—P1ⁱⁱ	25.40 (9)
O5—P1—K1^vii	54.28 (18)	O3—K1—P1ⁱⁱ	121.46 (10)
O8^vii—P1—K1^vii	137.62 (19)	O5^iv—K1—P1ⁱⁱ	87.48 (9)
O4—P1—K1^vii	113.68 (19)	O1ⁱⁱ—K1—P1ⁱⁱ	152.39 (10)
K1^vi—P1—K1^vii	76.81 (5)	O2—K1—P1ⁱⁱ	76.57 (9)
O1—P2—O7	106.1 (2)	O8ⁱⁱ—K1—P1ⁱⁱ	80.76 (9)
O1—P2—O2^iv	110.1 (3)	O7^vii—K1—P1ⁱⁱ	122.11 (9)
O7—P2—O2^iv	109.9 (3)	P2ⁱⁱ—K1—P1ⁱⁱ	146.19 (6)
O1—P2—O6^viii	110.9 (2)	P2—O1—Al1^ix	133.1 (3)
O7—P2—O6^viii	109.5 (3)	P2—O1—K1^vi	94.6 (2)
O2^iv—P2—O6^viii	110.1 (3)	Al1^ix—O1—K1^vi	130.5 (2)
O1—P2—K1^vi	59.95 (18)	P2^vii—O2—Al1	152.9 (3)
O7—P2—K1^vi	46.46 (17)	P2^vii—O2—K1	105.5 (2)
O2^iv—P2—K1^vi	129.19 (19)	Al1—O2—K1	94.70 (18)
O6^viii—P2—K1^vi	119.99 (18)	P1^iv—O3—Al2^vii	151.7 (3)
O1—P2—K1^iv	107.74 (18)	P1^iv—O3—K1	102.0 (2)
O7—P2—K1^iv	61.13 (19)	Al2^vii—O3—K1	104.2 (2)
O2^iv—P2—K1^iv	51.62 (19)	P1—O4—Al2^v	142.7 (3)
O6^viii—P2—K1^iv	141.21 (18)	P1—O4—K1^vi	99.2 (2)
K1^vi—P2—K1^iv	82.30 (5)	Al2^v—O4—K1^vi	117.7 (2)
O7ⁱⁱ—K1—O5ⁱⁱ	140.25 (15)	P1—O5—Al1^vi	143.1 (3)
O7ⁱⁱ—K1—O6ⁱⁱⁱ	109.16 (14)	P1—O5—K1^vi	103.8 (2)
O5ⁱⁱ—K1—O6ⁱⁱⁱ	96.58 (13)	Al1^vi—O5—K1^vi	102.41 (18)
O7ⁱⁱ—K1—O4ⁱⁱ	112.68 (14)	P1—O5—K1^vii	101.1 (2)
O5ⁱⁱ—K1—O4ⁱⁱ	50.13 (12)	Al1^vi—O5—K1^vii	99.89 (19)
O6ⁱⁱⁱ—K1—O4ⁱⁱ	67.70 (12)	K1^vi—O5—K1^vii	99.10 (13)
O7ⁱⁱ—K1—O3	105.38 (14)	P2^viii—O6—Al1	137.7 (3)
O5ⁱⁱ—K1—O3	100.83 (14)	P2^viii—O6—K1ⁱⁱⁱ	120.9 (2)
O6ⁱⁱⁱ—K1—O3	96.89 (13)	Al1—O6—K1ⁱⁱⁱ	101.16 (17)
O4ⁱⁱ—K1—O3	141.76 (13)	P2—O7—Al2	138.7 (3)
O7ⁱⁱ—K1—O5^iv	138.67 (14)	P2—O7—K1^vi	109.5 (2)
O5ⁱⁱ—K1—O5^iv	80.89 (13)	Al2—O7—K1^vi	108.2 (2)
O6ⁱⁱⁱ—K1—O5^iv	55.82 (12)	P2—O7—K1^iv	95.2 (2)
O4ⁱⁱ—K1—O5^iv	97.13 (13)	Al2—O7—K1^iv	90.67 (18)
O3—K1—O5^iv	48.62 (12)	K1^vi—O7—K1^iv	105.28 (13)
O7ⁱⁱ—K1—O1ⁱⁱ	49.37 (13)	P1^iv—O8—Al2	127.8 (3)
O5ⁱⁱ—K1—O1ⁱⁱ	170.08 (13)	P1^iv—O8—K1^vi	139.9 (2)
O6ⁱⁱⁱ—K1—O1ⁱⁱ	75.18 (12)	Al2—O8—K1^vi	92.30 (17)

Symmetry codes: (i) x, y+1, z; (ii) −x+1/2, y+1/2, −z+1/2; (iii) −x+1/2, −y+3/2, −z; (iv) x, −y+1, z−1/2; (v) −x+1, y, −z+1/2; (vi) −x+1/2, y−1/2, −z+1/2; (vii) x, −y+1, z+1/2; (viii) −x+1, −y+1, −z; (ix) x, y−1, z.

Acknowledgements

We are much obliged to N. G. Zinovieva and I. V. Pekov for a fruitful discussion and valuable comments. We thank N. N. Koshlyakova for the microprobe analysis of the crystals. We are also grateful to N. V. Zubkova for her help with the X-ray experiments.

Funding information

The following funding is acknowledged: Russian Foundation for Basic Research (grant No. 18-29-12076 to Olga Yakubovich); Russian Science Foundation (grant No. 19-77-00081 to Galina Kiriukhina).

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Volume 76| Part 3| June 2020| Pages 483-491

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