The γ-polymorph of AgZnPO₄ with an ABW zeolite-type framework topology

The γ-polymorph of the title compound, silver zinc orthophos­phate, was synthesized under hydro­thermal conditions. The structure consists of ZnO₄, PO₄ and AgO₄ units. The coord­ination spheres of Zn^II and P^V are tetra­hedral, whereas the Ag^I atom is considerably distorted from a tetra­hedral coordination. Each O atom is linked to each of the three cations. An elliptic eight-membered ring system is formed by corner-sharing of alternating PO₄ and ZnO₄ tetra­hedra, leading to a framework with an ABW-type zeolite structure. The framework encloses channels running parallel to [100] in which the Ag cations are located, with Ag⋯Ag contacts of 3.099 (3) Å. This short distance results from d¹⁰⋯d¹⁰ inter­actions, which play a substantial role in the crystal packing. The structure of γ-AgZnPO₄ is distinct from the two other polymorphs α-AgZnPO₄ and β-AgZnPO₄, but is isotypic with NaZnPO₄-ABW, NaCoPO₄-ABW and NH₄CoPO₄-ABW.

Related literature

For general background to A^IB^IIPO₄ phosphates, see: Elouadi & Elammari (1990); Bu et al. (1996); Moring & Kostiner (1986). For the α- and β- polymorphs of AgZnPO₄, see: Hammond et al. (1998); Elammari et al. (1987, 1988). For bond-valence analysis, see: Brown & Altermatt (1985). For d¹⁰⋯d¹⁰ inter­actions, see: Jansen (1987). For compounds with isotypic structures, see: Chippindale et al. (1999); Feng et al. (1997); Ng & Harrison (1998). For nomenclature of zeolites, see: Baerlocher et al. (2007).

Experimental

Crystal data

• AgZn(PO₄)

• M_r = 268.21

• Monoclinic, P 2₁ /n

• a = 5.1664 (2) Å

• b = 10.4183 (3) Å

• c = 7.3263 (2) Å

• β = 90.304 (2)°

• V = 394.33 (2) ų

• Z = 4

• Mo Kα radiation

• μ = 11.32 mm⁻¹

• T = 296 K

• 0.25 × 0.08 × 0.05 mm

Data collection

• Bruker X8 APEXII diffractometer

• Absorption correction: multi-scan (SADABS; Bruker, 2005) T_min = 0.351, T_max = 0.568

• 9307 measured reflections

• 1745 independent reflections

• 1621 reflections with I > 2σ(I)

• R_int = 0.033

Refinement

• R[F² > 2σ(F²)] = 0.019

• wR(F²) = 0.044

• S = 1.08

• 1745 reflections

• 65 parameters

• Δρ_max = 1.18 e Å⁻³

• Δρ_min = −1.30 e Å⁻³

Table 1
Selected bond lengths (Å)

Ag1—O2^i	2.2992 (13)
Ag1—O1	2.3506 (13)
Ag1—O4^ii	2.3982 (13)
Ag1—O3^iii	2.4975 (14)
Zn1—O1	1.9372 (13)
Zn1—O2^iv	1.9439 (13)
Zn1—O3^ii	1.9440 (13)
Zn1—O4^v	1.9516 (13)
P1—O3	1.5283 (14)
P1—O1	1.5366 (13)
P1—O2	1.5401 (13)
P1—O4	1.5415 (13)
Symmetry codes: (i) -x+1, -y+2, -z; (ii) x-1, y, z; (iii) ; (iv) -x+1, -y+2, -z+1; (v) .

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: WinGX (Farrugia, 1999).

Supporting information

S1. Comment

A crystal-chemical classification of A^IB^IIPO₄ compounds was carried out by Elouadi and Elammari (1990) who used the combination of the coordination number and the correlative cationic radii r(A) and r(B) as basic parameters to predict the structural evolution versus the nature of both A and B elements. In fact, the appearance of a structural variety does not depend only on the size and the nature of both cations A and B, but could also be favored by specific parameters such as the Jahn-Teller effect, which mainly characterizes compounds containing Cu(II). In addition, the structural stability is also expected to be both temperature- and pressure-dependent. Therefore, the thermodynamic conditions for the preparation of all phases considered are of prime importance. This is also corroborated by the fact that most of the compounds A^IB^IIPO₄ undergo at least one phase transition (Elammari et al., 1988). For instance, it has been found that the thermal treatment (quenching, sintering, etc.) is a key parameter to foresee the structural variety to be stabilized at room temperature (Moring & Kostiner 1986; Bu et al., 1996). In addition to α-AgZnPO₄ and β-AgZnPO₄ characterized by Hammond et al.(1998), we report here on the crystal structure of a new form of silver zinc phosphate (γ-AgZnPO₄) that was hydrothermally synthesized.

The structure of this monophosphate consists of zinc and phosphorus atoms tetrahedrally coordinated to oxygen atoms, whereas the silver atom is surrounded by four O atoms in a considerably distorted coordination, with Ag–O bond lengths between 2.2992 (13) and 2.4975 (14) Å. As shown in Fig. 1, the PO₄ and ZnO₄ tetrahedra share a vertex and are almost regular with P–O and Zn–O distances in the range 1.5283 (14)–1.5415 (13) Å and 1.9372 (13)–1.9516 (13) Å, respectively (Table 1). The expected +I, +II and +V oxidation states of the Ag, Zn and P atoms were confirmed by bond valence sum calculations (Brown & Altermatt, 1985) with 0.94, 2.09 and 4.93 valence units, respectively.

A three-dimensional polyhedral view of the crystal structure is represented in Fig. 2. It shows PO₄ tetrahedra linked to ZnO₄ tetrahedra by sharing corners in the way to build an eight-membered ring system surrounding the silver atoms. This arrangements give rise to eight-membered elliptical channels running parallel to [100] where the Ag^I atoms are located with short Ag···Ag contacts of 3.099 (3) Å. This short distance is due to d¹⁰···d¹⁰ interactions (Jansen, 1987) that play an important role in the crystal structure.

It is particularly interesting to compare the crystal structures of the three different polymorphs of AgZnPO₄: The high-temperature β-AgZnPO₄ polymorph adopts a monoclinic beryllonite-type structure similar to that of NaZnPO₄ (Elammari et al., 1987) whereas the low-temperature α-AgZnPO₄ polymorph crystallizes with a hexagonal structure like that of high-p/low-T KZnPO₄. In both α- and β- polymorphs, corner-sharing PO₄ and ZnO₄ tetrahedra form a fully ordered framework containing six-membered rings with distinct topologies around the Ag^I atoms (Hammond et al., 1998). As noted above, in the case of γ-AgZnPO₄ they build up an elliptical eight-membered ring system of alternating PO₄ and ZnO₄ tetrahedra around the Ag^I atoms with an ABW zeolite topology UUUUDDDD, where U and D represent tetrahedra pointing up and down, respectively (Baerlocher et al., 2007).

Compounds isotypic with γ-AgZnPO₄ are relatively rare, however, there are three phases which adopt the same stucture, viz. NaZnPO₄-ABW (Ng & Harrison, 1998), NaCoPO₄-ABW (Chippindale et al., 1999) and NH₄CoPO₄-ABW (Feng et al., 1997).

Related literature

For general background to A^IB^IIPO₄ phosphates, see: Elouadi & Elammari (1990); Bu et al. (1996); Moring & Kostiner (1986). For the α- and β- polymorphs of AgZnPO₄, see: Hammond et al. (1998); Elammari et al. (1987, 1988). For bond-valence analysis, see: Brown & Altermatt (1985). For d¹⁰···d¹⁰ interactions, see: Jansen (1987). For compounds with isotypic structures, see: Chippindale et al. (1999); Feng et al. (1997); Ng & Harrison (1998). For nomenclature of zeolites, see: Baerlocher et al. (2007).

S2. Experimental

The hydrothermal exploration of the Ag₂O–ZnO–P₂O₅ system, in order to search for new phases, in particular with alluaudite-like structure, has allowed to isolate a new form of silver zinc orthophosphate. The reaction mixture contained silver nitrate (AgNO₃; 0.1699 g), zinc oxide (ZnO; 0.1221 g), 85 %_wt phosphoric acid (H₃PO₄; 0,10 ml) and water (12 ml) and was hydrothermally treated in a 23 ml Teflon-lined autoclave under autogeneous pressure at 468 K for two days. After being filtered off, washed with deionized water and air dried, the reaction product consists of a white powder and some colorless parallelepipedic crystals corresponding to the title compound.

S3. Refinement

The highest peak and the deepest hole in the final Fourier map are 0.53 Å and 0.52 Å, respectively, from Ag1.

Computing details

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. Plot of parts of the crystal structure of the title compound showing the most important interatomic bonds. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) -x + 1, -y + 2, -z; (ii) x - 1, y, z; (iii) x - 1/2, -y + 3/2, z - 1/2; (iv) -x, -y + 2, -z; (v) -x + 1, -y + 2, -z + 1; (vi) x - 1/2, -y + 3/2, z + 1/2.]
	Fig. 2. A three-dimensional polyhedral view of the crystal structure of the monophosphate γ-AgZnPO4. PO4 tetrahedra are pink, ZnO4 tetrahedra are light-blue and silver atoms are grey.

silver zinc orthophosphate

Crystal data

AgZn(PO4)	F(000) = 496
Mr = 268.21	Dx = 4.518 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 1745 reflections
a = 5.1664 (2) Å	θ = 3.4–35.0°
b = 10.4183 (3) Å	µ = 11.32 mm^−1
c = 7.3263 (2) Å	T = 296 K
β = 90.304 (2)°	Plate, colourless
V = 394.33 (2) Å^3	0.25 × 0.08 × 0.05 mm
Z = 4

Data collection

Bruker X8 APEXII diffractometer	1745 independent reflections
Radiation source: fine-focus sealed tube	1621 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.033
φ and ω scans	θmax = 35.0°, θmin = 3.4°
Absorption correction: multi-scan (SADABS; Bruker, 2005)	h = −7→8
Tmin = 0.351, Tmax = 0.568	k = −16→16
9307 measured reflections	l = −11→11

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.019	w = 1/[σ^2(Fo^2) + (0.0138P)^2 + 0.5475P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.044	(Δ/σ)max = 0.001
S = 1.08	Δρmax = 1.18 e Å^−3
1745 reflections	Δρmin = −1.30 e Å^−3
65 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.0685 (12)

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
Ag1	0.20254 (3)	0.891281 (15)	0.021499 (19)	0.01931 (6)
Zn1	0.19054 (4)	0.840764 (19)	0.52546 (3)	0.01037 (6)
P1	0.69041 (8)	0.89550 (4)	0.29147 (6)	0.00877 (8)
O1	0.3966 (2)	0.87815 (14)	0.31182 (18)	0.0159 (2)
O2	0.7616 (3)	1.03856 (12)	0.27484 (18)	0.0161 (2)
O3	0.8268 (3)	0.83575 (14)	0.45641 (19)	0.0166 (2)
O4	0.7730 (3)	0.83197 (12)	0.11089 (18)	0.0155 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ag1	0.02148 (8)	0.02283 (8)	0.01363 (8)	0.00195 (5)	0.00071 (5)	0.00377 (5)
Zn1	0.01202 (9)	0.00970 (9)	0.00939 (9)	−0.00034 (6)	−0.00004 (6)	0.00058 (6)
P1	0.00988 (16)	0.00839 (16)	0.00805 (16)	−0.00085 (12)	0.00051 (12)	0.00001 (12)
O1	0.0099 (5)	0.0272 (7)	0.0107 (5)	−0.0013 (5)	0.0007 (4)	0.0032 (5)
O2	0.0289 (7)	0.0083 (5)	0.0110 (5)	−0.0043 (5)	0.0007 (5)	−0.0006 (4)
O3	0.0139 (5)	0.0184 (6)	0.0176 (6)	−0.0014 (4)	−0.0044 (4)	0.0069 (5)
O4	0.0189 (6)	0.0130 (5)	0.0147 (6)	−0.0045 (4)	0.0059 (5)	−0.0055 (4)

Geometric parameters (Å, º)

Ag1—O2^i	2.2992 (13)	P1—O1	1.5366 (13)
Ag1—O1	2.3506 (13)	P1—O2	1.5401 (13)
Ag1—O4^ii	2.3982 (13)	P1—O4	1.5415 (13)
Ag1—O3^iii	2.4975 (14)	O2—Zn1^v	1.9438 (13)
Ag1—Ag1^iv	3.0990 (3)	O2—Ag1^i	2.2992 (13)
Zn1—O1	1.9372 (13)	O3—Zn1^vii	1.9440 (13)
Zn1—O2^v	1.9439 (13)	O3—Ag1^viii	2.4975 (14)
Zn1—O3^ii	1.9440 (13)	O4—Zn1^ix	1.9516 (13)
Zn1—O4^vi	1.9516 (13)	O4—Ag1^vii	2.3982 (13)
P1—O3	1.5283 (14)
O2^i—Ag1—O1	146.80 (5)	O3—P1—O2	110.33 (8)
O2^i—Ag1—O4^ii	114.78 (5)	O1—P1—O2	110.97 (8)
O1—Ag1—O4^ii	97.40 (5)	O3—P1—O4	112.03 (8)
O2^i—Ag1—O3^iii	95.66 (5)	O1—P1—O4	108.10 (8)
O1—Ag1—O3^iii	90.50 (5)	O2—P1—O4	106.28 (7)
O4^ii—Ag1—O3^iii	92.72 (5)	P1—O1—Zn1	130.50 (8)
O2^i—Ag1—Ag1^iv	74.30 (4)	P1—O1—Ag1	108.80 (7)
O1—Ag1—Ag1^iv	114.78 (4)	Zn1—O1—Ag1	120.61 (6)
O4^ii—Ag1—Ag1^iv	65.84 (3)	P1—O2—Zn1^v	126.57 (8)
O3^iii—Ag1—Ag1^iv	147.90 (3)	P1—O2—Ag1^i	113.75 (7)
O1—Zn1—O2^v	114.19 (6)	Zn1^v—O2—Ag1^i	119.64 (6)
O1—Zn1—O3^ii	109.25 (6)	P1—O3—Zn1^vii	129.49 (8)
O2^v—Zn1—O3^ii	109.40 (7)	P1—O3—Ag1^viii	114.76 (7)
O1—Zn1—O4^vi	108.94 (6)	Zn1^vii—O3—Ag1^viii	103.00 (6)
O2^v—Zn1—O4^vi	109.17 (6)	P1—O4—Zn1^ix	127.61 (8)
O3^ii—Zn1—O4^vi	105.52 (6)	P1—O4—Ag1^vii	112.61 (7)
O3—P1—O1	109.09 (8)	Zn1^ix—O4—Ag1^vii	110.53 (6)

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