Crystal structure of langbeinite-related Rb0.743K0.845Co0.293Ti1.707(PO4)3

Strutynska, N.Y.; Bondarenko, M.A.; Ogorodnyk, I.V.; Baumer, V.N.; Slobodyanik, N.S.

doi:10.1107/S2056989015001826

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Volume 71| Part 3| March 2015| Pages 251-253

doi:10.1107/S2056989015001826

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Crystal structure of langbeinite-related Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃

Nataliia Yu. Strutynska,^a ^* Marina A. Bondarenko,^a Ivan V. Ogorodnyk,^a Vyacheslav N. Baumer ^b,^c and Nikolay S. Slobodyanik ^a

^aDepartment of Inorganic Chemistry, Taras Shevchenko National University of Kyiv, 64/13, Volodymyrska Str., 01601 Kyiv, Ukraine, ^bSTC "Institute for Single Crystals", NAS of Ukraine, 60 Lenin Ave., 61001 Kharkiv, Ukraine, and ^cV. N. Karazin National University, 4, Svobody Square, 61001 Kharkiv, Ukraine
^*Correspondence e-mail: Strutynska_N@bigmir.net

Edited by I. D. Brown, McMaster University, Canada (Received 23 January 2015; accepted 27 January 2015; online 7 February 2015)

Potassium rubidium cobalt(II)/titanium(IV) tris(orthophosphate), Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃, has been obtained using a high-temperature crystallization method. The obtained compound has a langbeinite-type structure. The three-dimensional framework is built up from mixed-occupied (Co/Ti^IV)O₆ octahedra (point group symmetry .3.) and PO₄ tetrahedra. The K⁺ and Rb⁺ cations are statistically distributed over two distinct sites (both with site symmetry .3.) in the large cavities of the framework. They are surrounded by 12 O atoms.

Keywords: crystal structure; high-temperature crystallization; langbeinite-type structure; three-dimensional framework.

CCDC reference: 1045876

1. Chemical context

Nowadays, there are a number of reports on the synthesis and investigation of langbeinite-related complex phosphates, which exhibit interesting properties such as magnetic (Ogorodnyk et al., 2006 ), luminescence (Zhang et al., 2013 ; Chawla et al., 2013 ) and phase transitions (Hikita et al., 1977 ). It should be noted that compounds with a langbeinite-type structure are prospects for use as a matrix for the storage of nuclear waste (Orlova et al., 2011 ). Zaripov et al. (2009 ) and Ogorodnyk et al. (2007a ) proved that caesium can be introduced into the cavity of a langbeinite framework that can be used for the immobilization of ¹³⁷Cs in an inert matrix for safe disposal.

A large number of compounds with a langbeinite framework based on a variety of different valence elements are known. Three major types of substitutions of the elements are known as well as their combinations. They are: metal substitution in octahedra, element substitution in anion tetrahedra, and substitution of ions in cavities. Among these compounds, potassium-containing langbeinites are the most studied (Ogorodnyk et al., 2006, 2007b ,c ; Norberg, 2002 ; Orlova et al., 2003 ). However, several reports concerning phosphate langbeinites with Rb⁺ in the cavities of the framework are known: Rb₂FeZr(PO₄)₃ (Trubach et al., 2004 ), Rb₂YbTi(PO₄)₃ (Gustafsson et al., 2005 ) and Rb₂TiY(PO₄)₃ (Gustafsson et al., 2006 ).

Herein, the structure of Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃, potassium rubidium cobalt(II)/titanium(IV) tris(orthophosphate) is reported.

2. Structural commentary

The asymmetric unit of Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃ consists of two mixed-occupied (Co/Ti^IV), two (Rb/K), one P and four oxygen positions (Fig. 1). The structure of the title compound is built up from mixed (Co/Ti^IV)O₆ octahedra and PO₄ tetrahedra, which are connected via common O-atom vertices. Each octahedron is linked to six adjacent tetrahedra and reciprocally, each tetrahedron is connected to four neighboring octahedra into a three-dimensional rigid framework (Fig. 2).

Figure 1
The asymmetric unit of Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃, showing displacement ellipsoids at the 50% probability level.

Figure 2
Two-dimensional net and three-dimensional framework for Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃.

The oxygen environment of the metal atoms in the (Co/Ti^IV)1O₆ octahedra is slightly distorted, with M—O bonds of 1.940 (2) and 1.966 (2) Å. These distances are close to the corresponding bond lengths in K₂Ti₂(PO₄)₃ [d(Ti—O) = 1.877 (10)–1.965 (10) Å; Masse et al., 1972 ], which could be explained by the small occupancy of cobalt in the mixed (Co/Ti^IV)1 [occupancy = 0.1307 (9)] and (Co/Ti^IV)2 [occupancy = 0.162 (3)] sites. It should be noted that (Co/Ti^IV)2—O distances [1.949 (2) and 1.969 (2) Å] are slightly shorter than those in K₂Co_0.5Ti_1.5(PO₄)₃ (Ogorodnyk et al., 2006).

The orthophosphate tetrahedra are also slightly distorted with P—O bond lengths ranging from 1.525 (2) to 1.531 (2) Å. These distances are almost identical to the corresponding ones in K₂Co_0.5Ti_1.5(PO₄)₃ [d(P—O) =1.525 (2)–1.529 (9) Å; Ogorodnyk et al., 2006). A comparison of the corresponding interatomic distances for the octahedra and tetrahedra in Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃ and K₂Co_0.5Ti_1.5(PO₄)₃ shows that partial substitution of K⁺ by Rb⁺ and decreasing the amount of cobalt slightly influences the distances in the polyhedra for Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃.

The K⁺ and Rb⁺ cations are located in large cavities of the three-dimensional framework in Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃. They are statistically distributed over two distinct sites in which they have partial occupancies of 0.540 (9) and 0.330 (18) for Rb1 and K1, respectively, and 0.203 (8) and 0.514 (17) for Rb2 and K2, respectively. For the determination of the (Rb/K)1 and (Rb/K)2 coordination numbers (CN), Voronoi–Dirichlet polyhedra (VDP) were built using the DIRICHLET program included in the TOPOS package (Blatov et al., 1995 ). Analysis of the solid-angle (Ω) distribution revealed twelve (Rb/K)—O contacts for both the (Rb/K)1 and (Rb/K)2 sites (cut-off distance of 4.0 Å, neglecting those corresponding to Ω < 1.5%; Blatov et al., 1998 ). The results of the construction of the Voronoi–Dirichlet polyhedra (Blatov et al., 1995) indicated that the coordination scheme for (Rb/K)1 is described as [9 + 3] [nine meaning `ion–covalent' bonds are in the range 2.896 (2)–3.095 (2) Å which have Ω > 5.0% and three (Rb/K)1—O distances equal to 3.438 (8) Å with Ω = 2.42%]. The (Rb/K)—O distances in the [(Rb/K)2O₁₂]-polyhedra are in the range 2.870 (2)–3.219 (2) Å (4.91% < Ω < 9.5%).

The corresponding K1—O contacts in K₂Co_0.5Ti_1.5(PO₄)₃ (Ogorodnyk et al., 2006) are in the range 2.872 (2)–3.231 (3) Å while the K2—O distances in the K2O₁₂ polyhedra are in the range 2.855 (2)–3.473 (3) Å, slightly longer than those in Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃. These results indicate that the substitution of K⁺ cations by Rb⁺ cations in Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃ caused a decrease of the (Rb/K)—O bond length. This fact confirms the rigidity of the framework and the suitability of the cavity dimensions to accommodate different sized ions whose size and nature insignificantly influence the framework.

3. Synthesis and crystallization

The title compound was prepared during crystallization of a self-flux in the Rb₂O–K₂O–P₂O₅–TiO₂–CoO system. The starting components RbH₂PO₄ (4.0 g), KPO₃ (2.4 g), TiO₂ (0.532 g) and CoO (0.50 g) were ground in an agate mortar, placed in a platinum crucible and H₃PO₄ (85%, 0.42 g) was added. The mixture was heated up to 1273 K. The melt was kept at this temperature for one h. After that, the temperature was decreased to 873 K at a rate of 10 K h⁻¹. The crystals of Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃ were separated from the rest flux by washing in hot water. The chemical composition of a single crystal was verified using EDX analysis. Analysis found: K 6.72, Rb 13.85, Co 3.74, Ti 16.86, P 19.96 and O 38.87 at%, while Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃ requires K 6.86, Rb 13.15, Co 3.60, Ti 17.06, P 19.36 and O 39.97 at%.

4. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. The O-atom sites were determined from difference Fourier maps. It was assumed that both types of alkaline ions occupy cavity sites while the transition metals occupy framework sites. The occupancies were refined using linear combinations of free variables taking into account the total charge of the cell.

Table 1
Experimental details

Crystal data
Chemical formula	Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃
M_r	480.40
Crystal system, space group	Cubic, P2₁3
Temperature (K)	293
a (Å)	9.8527 (1)
V (Å³)	956.46 (2)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	6.63
Crystal size (mm)	0.10 × 0.07 × 0.05

Data collection
Diffractometer	Oxford Diffraction Xcalibur-3
Absorption correction	Multi-scan (Blessing, 1995 )
T_min, T_max	0.559, 0.734
No. of measured, independent and observed [I > 2σ(I)] reflections	1414, 1414, 1312
R_int	0.025
(sin θ/λ)_max (Å⁻¹)	0.804

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.026, 0.051, 1.05
No. of reflections	1414
No. of parameters	67
No. of restraints	3
Δρ_max, Δρ_min (e Å⁻³)	0.37, −0.36
Absolute structure	Flack (1983 ), 612 Friedel pairs
Absolute structure parameter	0.024 (10)
Computer programs: CrysAlis CCD and CrysAlis RED (Oxford Diffraction, 2006 $[Oxford Diffraction (2006). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Abingdon, England.]$ ), SHELXS97 and SHELXL97 (Sheldrick, 2008 ), DIAMOND (Brandenburg, 1999 ), WinGX (Farrugia, 2012 ) and enCIFer (Allen et al., 2004 ).

Supporting information

CCDC reference: 1045876

Crystal structure: contains datablocks global, I. DOI: 10.1107/S2056989015001826/br2246sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S2056989015001826/br2246Isup2.hkl

checkCIF report

Chemical context top

Nowadays, there are a number of reports on the synthesis and investigation of langbeinite-related complex phosphates, which exhibit interesting properties such as magnetic (Ogorodnyk et al., 2006), luminescence (Zhang et al., 2013; Chawla et al., 2013) and phase transitions (Hikita et al., 1977). It should be noted that compounds with a langbeinite-like structure are prospects for use as a matrix for the storage of nuclear waste (Orlova et al., 2011). Zaripov et al. (2009) and Ogorodnyk et al. (2007a) proved that caesium can be introduced into the cavity of a langbeinite framework that can be used for the immobilization of ¹³⁷Cs in an inert matrix for safe disposal.

A large number of compounds with a langbeinite framework based on a variety of different valence element are known. Three major types of substitutions of the elements are known as well as their combinations. They are: metal substitution in octahedra, element substitution in anion tetrahedra, and substitution of ions in cavities. Among these compounds, potassium-containing langbeinites are the most studied (Ogorodnyk et al., 2006, 2007b,c; Norberg, 2002; Orlova et al., 2003). However, several reports concerning phosphate langbeinites with Rb in the cavities of the framework are known: Rb₂FeZr(PO₄)₃ (Trubach et al., 2004), Rb₂YbTi(PO₄)₃ (Gustafsson et al., 2005) and Rb₂TiY(PO₄)₃ (Gustafsson et al., 2006).

Herein, the structure of Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃, potassium rubidium cobalt(II)/titanium(IV) tris(orthophosphate) is reported.

Structural commentary top

The unit of Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃ consists of two mixed-occupied (Co/Ti^IV), two (Rb/K), one P and four oxygen positions (Fig. 1). The structure of Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃ is built up from mixed (Co/Ti^IV)O₆ octahedra and PO₄ tetrahedra, which are connected via common O-atom vertices. Each octahedron is linked to six adjacent tetrahedra and reciprocally, each tetrahedron is connected to four neighboring octahedra into three-dimensional rigid framework (Fig. 2).

The oxygen environment of the metal atoms in the (Co/Ti^IV)1O₆ octahedra shows slightly distorted geometry, with M—O bonds of 1.940 (2) and 1.966 (2) Å. These distances are close to the corresponding bond lengths in K₂Ti₂(PO₄)₃ [d(Ti—O) = 1.877 (10)–1.965 (10) Å; Masse et al., 1972], which could be explained by the small occupancy of cobalt in the mixed (Co/Ti^IV)1 [occupancy = 0.1307 (9)] and (Co/Ti^IV)2 [occupancy = 0.162 (3)] sites. It should be noted that (Co/Ti^IV)2—O distances [1.949 (2) and 1.969 (2) Å] are slightly shorter than those in K₂Co_0.5Ti_1.5(PO₄)₃ (Ogorodnyk et al., 2006).

The orthophosphate tetrahedra are also slightly distorted with P—O bond lengths ranging from 1.525 (2) to 1.531 (2) Å. These distances are almost identical to corresponding in K₂Co_0.5Ti_1.5(PO₄)₃ [d(P—O) =1.525 (2)–1.529 (9) Å; Ogorodnyk et al., 2006). A comparison of the corresponding interatomic distances for the octahedra and tetrahedra in Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃ and K₂Co_0.5Ti_1.5(PO₄)₃ shows that partial substitution of K by Rb and decreasing the amount of cobalt slightly influences the distances in the polyhedra for Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃.

The K⁺ and Rb⁺ cations are located in large cavities of the three-dimensional framework in Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃. They are statistically distributed over two distinct sites in which they have partial occupancies of 0.540 (9) and 0.330 (18) for Rb1 and K1, respectively and 0.203 (8) and 0.514 (17) for Rb2 and K2, respectively. For the determination of the (Rb/K)1 and (Rb/K)2 coordination numbers (CN), Voronoi–Dirichlet polyhedra (VDP) were built using the DIRICHLET program included in the TOPOS package (Blatov et al., 1995). Analysis of the solid-angle (Ω) distribution revealed twelve (Rb/K)—O contacts for both the (Rb/K)1 and (Rb/K)2 sites (cut-off distance of 4.0 Å, neglecting those corresponding to Ω < 1.5%; Blatov et al., 1998). The results of the construction of the Voronoi–Dirichlet polyhedra (Blatov et al., 1995) indicated that the coordination scheme for (Rb/K)1 is described as [9 + 3] [nine meaning `ion–covalent' bonds are in the range 2.896 (2)–3.095 (2) Å which have Ω > 5.0% and three (Rb/K)1—O distances equal to 3.438 (8) Å with Ω = 2.42%]. The (Rb/K)—O distances in the [(Rb/K)2O₁₂]-polyhedra are in the range 2.870 (2)–3.219 (2) Å (4.91% < Ω < 9.5%).

The corresponding K1—O contacts in the K₂Co_0.5Ti_1.5(PO₄)₃ (Ogorodnyk et al., 2006) are in the range 2.872 (2)–3.231 (3) Å while the K2—O distances in the K2O₁₂ polyhedra are in the range 2.855 (2)–3.473 (3) Å, slightly longer than those in Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃. These results indicate that the substitution of K atoms by Rb atoms in Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃ caused a decrease of the (Rb/K)—O bond length. This fact confirms the rigidity of the framework and the suitability of the cavity dimensions to accommodate different sized ions whose size and nature insignificantly influence the framework.

Synthesis and crystallization top

The title compound was prepared during crystallization of the self-flux of the Rb₂O–K₂O–P₂O₅–TiO₂–CoO system. The starting components RbH₂PO₄ (4.0 g), KPO₃ (2.4 g), TiO₂ (0.532 g) and CoO (0.50 g) were ground in an agate mortar, placed in a platinum crucible and H₃PO₄ (0.42 g) was added. The mixture was heated up to 1273 K. The melt was kept at this temperature for one hour. After that, the temperature was decreased to 873 K at a rate of 10 K h^-1. The crystals of Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃ were separated from the rest flux by washing in hot water. The chemical composition of a single crystal was verified using EDX analysis. Analysis found: K 6.72, Rb 13.85, Co 3.74, Ti 16.86, P 19.96 and O 38.87 at%, while Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃ requires K 6.86, Rb 13.15, Co 3.60, Ti 17.06, P 19.36 and O 39.97 at%.

Refinement top

Crystal data, data collection and structure refinement details are summarized in Table 1. The structure was solved by direct method. The O-atom sites were determined from difference Fourier maps. It was assumed that both types of alkaline metals occupy cavity sites while the transition metals occupy framework sites. The occupancies were refined using linear combinations of free variables taking into account the total charge of the cell.

Related literature top

For related structure, see: Ogorodnyk et al. (2006); Ogorodnyk et al. (2007b); Ogorodnyk etal. (2007c); Gustafsson et al. (2006). For application of langbeinite-related phosphates, see: Zhang et al. (2013); Chawla et al. (2013); Orlova et al. (2011). For crystal-space analysis using Voronoi–Dirichlet polyhedra, see Blatov et al. (1995); Blatov et al. (1998).

Computing details top

Data collection: CrysAlis CCD (Oxford Diffraction, 2006); cell refinement: CrysAlis CCD (Oxford Diffraction, 2006); data reduction: CrysAlis RED (Oxford Diffraction, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: WinGX (Farrugia, 2012) and enCIFer (Allen et al., 2004).

Figures top

	Fig. 1. A connected set of numbered atoms in Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃, showing displacement ellipsoids at the 50% probability level.
	Fig. 2. Two-dimensional net and three-dimensional framework for Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃.

Potassium rubidium cobalt(II)/titanium(IV) tris(orthophosphate) top

Crystal data top

Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃	D_x = 3.336 Mg m⁻³
M_r = 480.40	Mo Kα radiation, λ = 0.71073 Å
Cubic, P2₁3	Cell parameters from 1414 reflections
Hall symbol: P 2ac 2ab 3	θ = 2.9–34.9°
a = 9.8527 (1) Å	µ = 6.63 mm⁻¹
V = 956.46 (2) Å³	T = 293 K
Z = 4	Tetrahedron, dark red
F(000) = 920	0.1 × 0.07 × 0.05 mm

Data collection top

Oxford Diffraction Xcalibur-3 diffractometer	1414 independent reflections
Radiation source: fine focus sealed tube	1312 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.025
ϕ and ω scans	θ_max = 34.9°, θ_min = 2.9°
Absorption correction: multi-scan (Blessing, 1995)	h = −10→10
T_min = 0.559, T_max = 0.734	k = 0→11
1414 measured reflections	l = 1→15

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.0183P)²] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.026	(Δ/σ)_max = 0.051
wR(F²) = 0.051	Δρ_max = 0.37 e Å⁻³
S = 1.05	Δρ_min = −0.36 e Å⁻³
1414 reflections	Extinction correction: SHELXL97 (Sheldrick, 2008)
67 parameters	Extinction coefficient: 0.0026 (6)
3 restraints	Absolute structure: Flack (1983), 612 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.024 (10)

Crystal data top

Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃	Z = 4
M_r = 480.40	Mo Kα radiation
Cubic, P2₁3	µ = 6.63 mm⁻¹
a = 9.8527 (1) Å	T = 293 K
V = 956.46 (2) Å³	0.1 × 0.07 × 0.05 mm

Data collection top

Oxford Diffraction Xcalibur-3 diffractometer	1414 independent reflections
Absorption correction: multi-scan (Blessing, 1995)	1312 reflections with I > 2σ(I)
T_min = 0.559, T_max = 0.734	R_int = 0.025
1414 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.026	3 restraints
wR(F²) = 0.051	Δρ_max = 0.37 e Å⁻³
S = 1.05	Δρ_min = −0.36 e Å⁻³
1414 reflections	Absolute structure: Flack (1983), 612 Friedel pairs
67 parameters	Absolute structure parameter: 0.024 (10)

Special details top

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

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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

	x	y	z	U_iso*/U_eq	Occ. (<1)
Rb1	0.71155 (4)	0.71155 (4)	0.71155 (4)	0.02169 (18)	0.540 (9)
K1	0.71155 (4)	0.71155 (4)	0.71155 (4)	0.02169 (18)	0.330 (18)
Rb2	0.93045 (5)	0.93045 (5)	0.93045 (5)	0.0199 (3)	0.203 (8)
K2	0.93045 (5)	0.93045 (5)	0.93045 (5)	0.0199 (3)	0.514 (17)
Ti1	0.14135 (4)	0.14135 (4)	0.14135 (4)	0.00760 (12)	0.8693 (9)
Co1	0.14135 (4)	0.14135 (4)	0.14135 (4)	0.00760 (12)	0.1307 (9)
Ti2	0.41386 (3)	0.41386 (3)	0.41386 (3)	0.00709 (12)	0.838 (3)
Co2	0.41386 (3)	0.41386 (3)	0.41386 (3)	0.00709 (12)	0.162 (3)
P1	0.45604 (5)	0.22826 (5)	0.12582 (5)	0.00682 (10)
O1	0.30739 (16)	0.23395 (16)	0.08086 (17)	0.0141 (3)
O2	0.54329 (18)	0.29756 (17)	0.01814 (17)	0.0179 (3)
O3	0.50157 (16)	0.08190 (16)	0.14744 (18)	0.0168 (3)
O4	0.47835 (17)	0.30686 (19)	0.25786 (18)	0.0190 (4)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Rb1	0.02169 (18)	0.02169 (18)	0.02169 (18)	0.00120 (13)	0.00120 (13)	0.00120 (13)
K1	0.02169 (18)	0.02169 (18)	0.02169 (18)	0.00120 (13)	0.00120 (13)	0.00120 (13)
Rb2	0.0199 (3)	0.0199 (3)	0.0199 (3)	−0.00172 (19)	−0.00172 (19)	−0.00172 (19)
K2	0.0199 (3)	0.0199 (3)	0.0199 (3)	−0.00172 (19)	−0.00172 (19)	−0.00172 (19)
Ti1	0.00760 (12)	0.00760 (12)	0.00760 (12)	0.00051 (11)	0.00051 (11)	0.00051 (11)
Co1	0.00760 (12)	0.00760 (12)	0.00760 (12)	0.00051 (11)	0.00051 (11)	0.00051 (11)
Ti2	0.00709 (12)	0.00709 (12)	0.00709 (12)	−0.00033 (11)	−0.00033 (11)	−0.00033 (11)
Co2	0.00709 (12)	0.00709 (12)	0.00709 (12)	−0.00033 (11)	−0.00033 (11)	−0.00033 (11)
P1	0.0059 (2)	0.0076 (2)	0.0070 (2)	−0.00019 (16)	0.00100 (16)	−0.00054 (17)
O1	0.0088 (7)	0.0167 (8)	0.0169 (8)	0.0001 (5)	−0.0032 (6)	0.0021 (6)
O2	0.0183 (9)	0.0185 (8)	0.0170 (8)	0.0001 (7)	0.0075 (6)	0.0049 (6)
O3	0.0160 (8)	0.0130 (8)	0.0214 (8)	0.0064 (6)	0.0022 (6)	0.0034 (6)
O4	0.0196 (9)	0.0229 (10)	0.0146 (8)	−0.0027 (7)	0.0001 (7)	−0.0099 (6)

Geometric parameters (Å, º) top

Rb1—O1ⁱ	2.8956 (17)	Rb2—O4^ix	3.219 (2)
Rb1—O1ⁱⁱ	2.8956 (17)	Rb2—O4^viii	3.219 (2)
Rb1—O1ⁱⁱⁱ	2.8956 (17)	Ti1—O2^x	1.9404 (17)
Rb1—O2^iv	3.0780 (19)	Ti1—O2^xi	1.9404 (17)
Rb1—O2^v	3.0780 (19)	Ti1—O2^xii	1.9404 (17)
Rb1—O2^vi	3.0780 (19)	Ti1—O1^xiii	1.9657 (16)
Rb1—O4^iv	3.0945 (18)	Ti1—O1	1.9657 (16)
Rb1—O4^vi	3.0945 (18)	Ti1—O1^xiv	1.9657 (16)
Rb1—O4^v	3.0945 (18)	Ti2—O3ⁱⁱ	1.9494 (16)
Rb2—O3^iv	2.8703 (18)	Ti2—O3ⁱⁱⁱ	1.9494 (16)
Rb2—O3^vi	2.8703 (18)	Ti2—O3ⁱ	1.9494 (16)
Rb2—O3^v	2.8703 (18)	Ti2—O4^xiii	1.9691 (17)
Rb2—O2^vii	2.9452 (19)	Ti2—O4	1.9691 (17)
Rb2—O2^viii	2.9452 (19)	Ti2—O4^xiv	1.9691 (17)
Rb2—O2^ix	2.9452 (19)	P1—O3	1.5252 (17)
Rb2—O4^iv	3.028 (2)	P1—O2	1.5266 (17)
Rb2—O4^vi	3.028 (2)	P1—O4	1.5299 (17)
Rb2—O4^v	3.028 (2)	P1—O1	1.5312 (16)
Rb2—O4^vii	3.219 (2)

O1ⁱ—Rb1—O1ⁱⁱ	90.95 (5)	O2^ix—Rb2—O4^v	94.29 (5)
O1ⁱ—Rb1—O1ⁱⁱⁱ	90.95 (5)	O4^iv—Rb2—O4^v	87.83 (5)
O1ⁱⁱ—Rb1—O1ⁱⁱⁱ	90.95 (5)	O4^vi—Rb2—O4^v	87.83 (5)
O1ⁱ—Rb1—O2^iv	145.70 (5)	O3^iv—Rb2—O4^vii	86.01 (4)
O1ⁱⁱ—Rb1—O2^iv	82.60 (4)	O3^vi—Rb2—O4^vii	55.94 (4)
O1ⁱⁱⁱ—Rb1—O2^iv	55.72 (4)	O3^v—Rb2—O4^vii	157.18 (5)
O1ⁱ—Rb1—O2^v	55.72 (4)	O2^vii—Rb2—O4^vii	46.55 (5)
O1ⁱⁱ—Rb1—O2^v	145.70 (5)	O2^viii—Rb2—O4^vii	86.90 (5)
O1ⁱⁱⁱ—Rb1—O2^v	82.60 (4)	O2^ix—Rb2—O4^vii	101.29 (5)
O2^iv—Rb1—O2^v	119.386 (9)	O4^iv—Rb2—O4^vii	53.03 (6)
O1ⁱ—Rb1—O2^vi	82.60 (4)	O4^vi—Rb2—O4^vii	104.695 (9)
O1ⁱⁱ—Rb1—O2^vi	55.72 (4)	O4^v—Rb2—O4^vii	137.38 (4)
O1ⁱⁱⁱ—Rb1—O2^vi	145.70 (5)	O3^iv—Rb2—O4^ix	55.94 (4)
O2^iv—Rb1—O2^vi	119.386 (9)	O3^vi—Rb2—O4^ix	157.18 (5)
O2^v—Rb1—O2^vi	119.386 (9)	O3^v—Rb2—O4^ix	86.01 (4)
O1ⁱ—Rb1—O4^iv	165.33 (5)	O2^vii—Rb2—O4^ix	86.90 (5)
O1ⁱⁱ—Rb1—O4^iv	82.87 (5)	O2^viii—Rb2—O4^ix	101.29 (5)
O1ⁱⁱⁱ—Rb1—O4^iv	102.41 (5)	O2^ix—Rb2—O4^ix	46.55 (5)
O2^iv—Rb1—O4^iv	46.75 (5)	O4^iv—Rb2—O4^ix	104.695 (9)
O2^v—Rb1—O4^iv	131.42 (5)	O4^vi—Rb2—O4^ix	137.38 (4)
O2^vi—Rb1—O4^iv	82.92 (5)	O4^v—Rb2—O4^ix	53.03 (6)
O1ⁱ—Rb1—O4^vi	82.87 (5)	O4^vii—Rb2—O4^ix	115.47 (2)
O1ⁱⁱ—Rb1—O4^vi	102.41 (5)	O3^iv—Rb2—O4^viii	157.18 (5)
O1ⁱⁱⁱ—Rb1—O4^vi	165.33 (5)	O3^vi—Rb2—O4^viii	86.01 (4)
O2^iv—Rb1—O4^vi	131.42 (5)	O3^v—Rb2—O4^viii	55.94 (4)
O2^v—Rb1—O4^vi	82.92 (5)	O2^vii—Rb2—O4^viii	101.29 (5)
O2^vi—Rb1—O4^vi	46.75 (5)	O2^viii—Rb2—O4^viii	46.55 (5)
O4^iv—Rb1—O4^vi	85.47 (6)	O2^ix—Rb2—O4^viii	86.90 (5)
O1ⁱ—Rb1—O4^v	102.41 (5)	O4^iv—Rb2—O4^viii	137.38 (4)
O1ⁱⁱ—Rb1—O4^v	165.33 (5)	O4^vi—Rb2—O4^viii	53.03 (6)
O1ⁱⁱⁱ—Rb1—O4^v	82.87 (5)	O4^v—Rb2—O4^viii	104.695 (9)
O2^iv—Rb1—O4^v	82.92 (5)	O4^vii—Rb2—O4^viii	115.47 (2)
O2^v—Rb1—O4^v	46.75 (5)	O4^ix—Rb2—O4^viii	115.47 (2)
O2^vi—Rb1—O4^v	131.42 (5)	O2^x—Ti1—O2^xi	90.14 (7)
O4^iv—Rb1—O4^v	85.47 (6)	O2^x—Ti1—O2^xii	90.14 (7)
O4^vi—Rb1—O4^v	85.47 (6)	O2^xi—Ti1—O2^xii	90.14 (7)
O3^iv—Rb2—O3^vi	101.27 (5)	O2^x—Ti1—O1^xiii	91.43 (7)
O3^iv—Rb2—O3^v	101.27 (5)	O2^xi—Ti1—O1^xiii	88.09 (7)
O3^vi—Rb2—O3^v	101.27 (5)	O2^xii—Ti1—O1^xiii	177.64 (7)
O3^iv—Rb2—O2^vii	99.30 (5)	O2^x—Ti1—O1	88.09 (7)
O3^vi—Rb2—O2^vii	96.75 (5)	O2^xi—Ti1—O1	177.64 (7)
O3^v—Rb2—O2^vii	149.30 (5)	O2^xii—Ti1—O1	91.43 (7)
O3^iv—Rb2—O2^viii	149.30 (5)	O1^xiii—Ti1—O1	90.39 (7)
O3^vi—Rb2—O2^viii	99.30 (5)	O2^x—Ti1—O1^xiv	177.64 (7)
O3^v—Rb2—O2^viii	96.75 (5)	O2^xi—Ti1—O1^xiv	91.43 (7)
O2^vii—Rb2—O2^viii	55.61 (6)	O2^xii—Ti1—O1^xiv	88.09 (7)
O3^iv—Rb2—O2^ix	96.75 (5)	O1^xiii—Ti1—O1^xiv	90.39 (7)
O3^vi—Rb2—O2^ix	149.30 (5)	O1—Ti1—O1^xiv	90.39 (7)
O3^v—Rb2—O2^ix	99.30 (5)	O3ⁱⁱ—Ti2—O3ⁱⁱⁱ	91.87 (7)
O2^vii—Rb2—O2^ix	55.61 (6)	O3ⁱⁱ—Ti2—O3ⁱ	91.87 (7)
O2^viii—Rb2—O2^ix	55.61 (6)	O3ⁱⁱⁱ—Ti2—O3ⁱ	91.87 (7)
O3^iv—Rb2—O4^iv	49.64 (5)	O3ⁱⁱ—Ti2—O4^xiii	94.30 (7)
O3^vi—Rb2—O4^iv	52.65 (5)	O3ⁱⁱⁱ—Ti2—O4^xiii	172.63 (8)
O3^v—Rb2—O4^iv	116.41 (6)	O3ⁱ—Ti2—O4^xiii	83.90 (7)
O2^vii—Rb2—O4^iv	94.29 (5)	O3ⁱⁱ—Ti2—O4	83.90 (7)
O2^viii—Rb2—O4^iv	138.73 (5)	O3ⁱⁱⁱ—Ti2—O4	94.30 (7)
O2^ix—Rb2—O4^iv	133.42 (5)	O3ⁱ—Ti2—O4	172.63 (8)
O3^iv—Rb2—O4^vi	116.41 (6)	O4^xiii—Ti2—O4	90.39 (7)
O3^vi—Rb2—O4^vi	49.64 (5)	O3ⁱⁱ—Ti2—O4^xiv	172.63 (8)
O3^v—Rb2—O4^vi	52.65 (5)	O3ⁱⁱⁱ—Ti2—O4^xiv	83.90 (7)
O2^vii—Rb2—O4^vi	133.42 (5)	O3ⁱ—Ti2—O4^xiv	94.30 (7)
O2^viii—Rb2—O4^vi	94.29 (5)	O4^xiii—Ti2—O4^xiv	90.39 (7)
O2^ix—Rb2—O4^vi	138.73 (5)	O4—Ti2—O4^xiv	90.39 (7)
O4^iv—Rb2—O4^vi	87.83 (5)	O3—P1—O2	110.75 (9)
O3^iv—Rb2—O4^v	52.65 (5)	O3—P1—O4	108.52 (11)
O3^vi—Rb2—O4^v	116.41 (6)	O2—P1—O4	106.48 (10)
O3^v—Rb2—O4^v	49.64 (5)	O3—P1—O1	110.87 (9)
O2^vii—Rb2—O4^v	138.73 (5)	O2—P1—O1	108.74 (10)
O2^viii—Rb2—O4^v	133.42 (5)	O4—P1—O1	111.40 (10)

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

Experimental details

Crystal data
Chemical formula	Rb_0.743K_0.845Co_0.293Ti_1.707(PO₄)₃
M_r	480.40
Crystal system, space group	Cubic, P2₁3
Temperature (K)	293
a (Å)	9.8527 (1)
V (Å³)	956.46 (2)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	6.63
Crystal size (mm)	0.1 × 0.07 × 0.05

Data collection
Diffractometer	Oxford Diffraction Xcalibur-3 diffractometer
Absorption correction	Multi-scan (Blessing, 1995)
T_min, T_max	0.559, 0.734
No. of measured, independent and observed [I > 2σ(I)] reflections	1414, 1414, 1312
R_int	0.025
(sin θ/λ)_max (Å⁻¹)	0.804

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.026, 0.051, 1.05
No. of reflections	1414
No. of parameters	67
No. of restraints	3
Δρ_max, Δρ_min (e Å⁻³)	0.37, −0.36
Absolute structure	Flack (1983), 612 Friedel pairs
Absolute structure parameter	0.024 (10)

Computer programs: CrysAlis CCD (Oxford Diffraction, 2006), CrysAlis RED (Oxford Diffraction, 2006), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 1999), WinGX (Farrugia, 2012) and enCIFer (Allen et al., 2004).

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Volume 71| Part 3| March 2015| Pages 251-253

doi:10.1107/S2056989015001826

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