CsAlZr₂(PO₄)₄: an anhydrous aluminium zirconium phosphate with a novel three-dimensional framework

Caesium aluminium dizirconium tetra­kis­[phosphate(V)], CsAlZr₂(PO₄)₄, has been synthesized by high-temperature reaction and studied by single-crystal X-ray diffraction at room temperature. This represents the first detailed structural analysis of an anhydrous phosphate containing both zirconium and aluminium. The structure features a complicated three-dimensional framework of [AlZr₂(PO₄)₄] constructed by PO₄, AlO₄ and ZrO₆ polyhedra inter­connected via corner-sharing O atoms, and one-dimensional Cs chains which are located in the infinite tunnels within the [AlZr₂(PO₄)₄] framework, which run along the c axis. The Cs, Al, one P and two O atoms lie on a mirror plane, while a second P atom lies on a twofold axis.

S1. Comment

Anhydrous inorganic metal phosphates prepared by high-temperature solid-state reactions have been part [the focus?] of intensive research activities and their number has grown steadily (Kanatzidis et al., 2007; Ettis et al., 2003;Zaripov et al., 2009; Zatovsky et al., 2007; Xiong et al., 2007; Ranmohotti et al., 2006; Parreu et al., 2006). The crystal chemistry of these compounds with partial structures mainly built from PO₄ tetrahedral building units reveals a large structural variety, which is usually accompanied by intriguing magnetism, electric, optical and thermal expansion properties. Furthermore, chemical and thermal stability ensures their wide application in many fields. Introduction of M^IV (M = Ti, Zr, Ge, Sn) cations into the phosphates can form [result in?] many different three-dimensional frameworks with the basic unit of MO₆ octahedra and PO₄ tetrahedra, such as KTiPO₅ (Tordjman et al., 1974) and NaZr₂(PO₄)₃ (Hagman et al., 1968). As for Zr^IV metal, the reported phosphates include KZr₂(PO₄)₃ (Sljukic et al., 1969), K₄CeZr(PO₄)₄ (Ogorodnyk, et al., 2006), Na₃AZr(PO₄)₃ (A = Mg, Ni; Chakir et al., 2006), A₂Mg_0.5Zr_1.5(PO₄)₃ (A = K, Rb, Cs; Orlova et al., 2005) and NaNbZr(PO₄)₃ (Bennouna et al., 1995) etc. We expected that introduction of AlO₄ groups which may serve as bridges between ZrO₆ and PO₄ building units would result in new zirconium phosphate compounds with novel architectures. Our research efforts in this regard have led to a novel caesium aluminium zirconium phosphate compound, namely, CsAlZr₂(PO₄)₄. To the best of our knowledge, it represents the first compound in the quinary Cs/Al/Zr/P/O system.

The title compound, CsAlZr₂(PO₄)₄, crystallizes in the orthorhombic space group Pbcm, with 15 crystallographically independent atoms, viz. one Cs, one Al, one Zr, three P and nine O atoms. Fig. 1 illustrates a selected unit of the compound, which highlights that the Zr atom is six-coordinated by O atoms in an octahedral geometry. The Zr—O bond distances are in the range 2.038 (3)–2.095 (3) Å, with a mean value of 2.067 (3) Å, which is in good agreement with those found in other zirconium(IV) compounds, such as BaZr(PO₄)₂ (Bregiroux et al., 2009), Zr₂(MoO₄)(PO₄)₂ (Cetinkol et al., 2009) and Rb₂Zr(IO₃)₆ (Shehee et al., 2005). The P and Al atoms all have the four-coordinated geometry with O atoms. The P—O distances fall in the range 1.510 (3)–1.540 (3) Å, and the O—P—O angles range from 105.7 (2) to 112.40 (17)°, which is comparable to those reported in other metal phosphates (Ettis et al., 2003; Zhao et al., 2010). The Al—O bond distances fall in the range 1.720 (4)–1.729 (4) Å, and the O—Al—O bond angles range from 102.9 (2) to 115.13 (13)°, which is similar to those reported in other aluminium(III) compounds, such as Ca₁₂Al₁₄O₃₂Cl₂ (Iwata et al., 2008) and Sr(Al₂Si₂O₈) (Nedic et al., 2008).

The structure of CsAlZr₂(PO₄)₄ features a complicated three-dimensional framework of [AlZr₂(PO₄)₄] constructed by interconnected PO₄, AlO₄ and ZrO₆ polyhedra. Fig. 2 shows the polyhedral connectivity of them. All PO₄ tetrahedra are isolated from each other, and they are linked to adjacent polyhedra only by corner-sharing O atoms. The P1O₄ tetrahedron is coordinated by two Al1O₄ and two Zr1O₆ polyhedra; the P2O₄ tetrahedron is coordinated by four Zr1O₆ octahedra; P3O₄ is coordinated by one Al1O₄ tetrahedron and three Zr1O₆ octahedra. As for the connection of ZrO₆ polyhedra, the Zr1O₆ polyhedron is coordinated by six PO₄ tetrahedra, that is, three P3O₄, two P2O₄ and one P1O₄ polyhedra. On the other hand, AlO₄ tetrahedra are also isolated from each other: four corners are shared with two P1O₄ and two P3O₄ polyhedra. It is notable that all nine asymmetric O atoms are all in bicoordinate bridging mode. As in all the above-mentioned groups, AlO₄, ZrO₆ and PO₄ are interconnected via corner-sharing O atoms to form the three-dimensional framework of [AlZr₂(PO₄)₄].

Furthermore, the framework [AlZr₂(PO₄)₄] delimits infinite tunnels along the c axis in which the Cs atoms are located through coulombic action of Cs⁺ cations and O^2- anions to form the final structure of CsAlZr₂(PO₄)₄. It is interesting to note that the Cs atoms are in linear array with the adjacent Cs···Cs distance 8.9897 (6) Å. Considering the coordination of Cs atoms, they have an 11-fold coordination of O atoms, which come from six two AlO₄, four ZrO₆ and six PO₄ groups, as shown in Fig. 3. The Cs—O bond distances range from 3.131 (4) to 3.658 (3) Å. Compounds containing 11-coordinated-geometry Cs atoms have been reported in the literature, for example CsPr(PO₃)₄ (Horchani-Naifer & Férid, 2007), CsGd(PO₃)₄ (Naïli & Mhiri, 2005) and Cs₂GeP₄O₁₃ (Zhao et al., 2009).

Finally, the structure can be checked by bond-valence-sum (BVS) analysis (Brese & O'Keeffe, 1991). The calculated total BVS for Cs1, Al1, Zr1, P1, P2 and P3 are 1.005, 3.260, 4.236, 5.038, 4.886 and 5.001, respectively, which show the oxidation states of Cs, Al, Zr and P are +1, +3, +4 and +5, respectively.

Related literature

For related literature, see: Bennouna et al. (1995); Bregiroux et al. (2009); Cetinkol et al. (2009); Chakir et al. (2006); Ettis et al. (2003); Hagman & Kierkegaard (1968); Herbstein (2000); Horchani-Naifer & Férid (2007); Iwata et al. (2008); Kanatzidis & Poeppelmeier (2007); Naïli & Mhiri (2005); Nedic et al. (2008); Ogorodnyk et al. (2006); Orlova et al. (2005); Parreu et al. (2006); Ranmohotti et al. (2006); Shehee et al. (2005); Sljukic et al. (1969); Tordjman et al. (1974); Xiong et al. (2007); Zaripov et al. (2009); Zatovsky et al. (2007); Zhao & Li (2010); Zhao et al. (2009).

S2. Experimental

Single crystals of CsAlZr₂(PO₄)₄ have been prepared by high-temperature reaction in air. A powder mixture of Cs₂CO₃ (0.8854 g), Al₂O₃ (0.1662 g), ZrO₂ (0.4018 g) and NH₄H₂PO₄ (3.000 g) in a Cs:Al:Zr:P molar ratio of 1.66:1:1:8 was first ground in an agate mortar and then transferred to a platinum crucible. The sample was gradually heated in air at 1173 K for 20 h. At this stage, the reagents were partially melted. After that, the intermediate product was cooled slowly to 773 K at a rate of 5 K h^-1, kept at this temperature for 10 h and then quenched to room temperature. After boiling in NH₃ (5%) solution, a transparent prismatic-shaped white crystal with dimensions of 0.16 × 0.10 × 0.10 mm was selected carefully from the mixture for X-ray diffraction analysis.

S3. Refinement

The orthorhombic unit-cell parameters determined by the diffractometer were a = ????Å, b = ????Å and c = ????Å [authors to supply their original cell parameters and s.u.s]. Given that the standard uncertainties (s.u. values) of unit-cell parameters calculated by the cell determination software on area-detector diffractometers are usually significantly smaller than the reproducibility of the parameters (Herbstein, 2000), the unit-cell s.u. values used in the final refinement and reported here have been set to values estimated to reflect more realistically the precision of the unit-cell parameters. The highest peak in the difference electron-density map is 0.06 Å from the Zr1 site and the deepest hole is 0.56 Å from the Cs1 site.

Computing details

Data collection: CrystalClear (Rigaku, 2004); cell refinement: CrystalClear (Rigaku, 2004); data reduction: CrystalClear (Rigaku, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXL97 (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures

	Fig. 1. The asymmetric unit of CsAlZr2(PO4)4, expanded to show the coordination environments of the Zr1, Al1, P1, P2 and P3 atoms. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) x, y, z; (ii) 1-x, 1/2 + y, 1.5 - z; (iii)1 + x, y, z; (iv) x, y, 1.5 - z; (v) -x, 1/2 + y, z; (vi) -x, 1 - y, 2 - z; (vii) x, 1.5 - y, 2 - z; (viii) 1 - x, 1 - y, 2 - z; (ix) 1 - x, -1/2 + y, z.]
	Fig. 2. A view of the three-dimensional crystal structure of CsAlZr2(PO4)4. Cs1—O bonds have been omitted for clarity.
	Fig. 3. A view of the coordination of the Cs1 atom.

Caesium aluminium dizirconium tetrakis[phosphate(V)]

Crystal data

CsAlZr2(PO4)4	F(000) = 1344
Mr = 722.21	Dx = 3.246 Mg m^−3
Orthorhombic, Pbcm	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2c 2b	Cell parameters from 3559 reflections
a = 8.742 (2) Å	θ = 2.2–27.5°
b = 9.403 (3) Å	µ = 4.41 mm^−1
c = 17.979 (3) Å	T = 293 K
V = 1477.9 (6) Å^3	Prism, white
Z = 4	0.16 × 0.10 × 0.10 mm

Data collection

Rigaku Mercury70 CCD diffractometer	1751 independent reflections
Radiation source: fine-focus sealed tube	1696 reflections with I > 2σ(I)
Graphite Monochromator monochromator	Rint = 0.027
Detector resolution: 14.6306 pixels mm^-1	θmax = 27.5°, θmin = 2.3°
ω scans	h = −10→11
Absorption correction: multi-scan (ABSCOR; Higashi, 1995)	k = −9→12
Tmin = 0.539, Tmax = 0.667	l = −23→22
10513 measured reflections

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F^2 > 2σ(F^2)] = 0.028	Secondary atom site location: difference Fourier map
wR(F^2) = 0.068	w = 1/[σ^2(Fo^2) + (0.0309P)^2 + 5.7964P] where P = (Fo^2 + 2Fc^2)/3
S = 1.15	(Δ/σ)max = 0.001
1751 reflections	Δρmax = 0.49 e Å^−3
117 parameters	Δρmin = −1.79 e Å^−3

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
Cs1	0.34872 (5)	0.75153 (4)	0.7500	0.02454 (12)
Zr1	0.24879 (4)	0.46864 (3)	0.928485 (18)	0.00506 (10)
P1	0.09892 (14)	0.42270 (13)	0.7500	0.0066 (2)
Al1	0.79989 (17)	0.60136 (15)	0.7500	0.0063 (3)
O1	0.1042 (5)	0.2611 (4)	0.7500	0.0169 (8)
P2	0.03635 (13)	0.7500	1.0000	0.0053 (2)
O2	−0.0711 (4)	0.4619 (4)	0.7500	0.0171 (8)
P3	0.60769 (10)	0.62612 (9)	0.89837 (5)	0.00688 (18)
O3	0.1770 (3)	0.4834 (3)	0.81800 (15)	0.0164 (6)
O4	0.0641 (3)	0.3407 (3)	0.94850 (16)	0.0159 (6)
O5	0.1357 (3)	0.6526 (3)	0.95246 (16)	0.0147 (6)
O6	0.4391 (3)	0.5871 (3)	0.89610 (15)	0.0132 (5)
O7	0.6852 (3)	0.5524 (3)	0.96277 (15)	0.0163 (6)
O8	0.6245 (3)	0.7866 (3)	0.90189 (17)	0.0177 (6)
O9	0.6802 (3)	0.5740 (3)	0.82518 (15)	0.0170 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cs1	0.0319 (2)	0.01503 (19)	0.0267 (2)	0.00488 (14)	0.000	0.000
Zr1	0.00625 (17)	0.00477 (17)	0.00416 (17)	−0.00025 (10)	−0.00008 (11)	0.00026 (11)
P1	0.0068 (6)	0.0074 (6)	0.0054 (6)	0.0013 (4)	0.000	0.000
Al1	0.0066 (7)	0.0066 (7)	0.0057 (7)	0.0002 (5)	0.000	0.000
O1	0.020 (2)	0.0068 (17)	0.024 (2)	0.0052 (15)	0.000	0.000
P2	0.0055 (5)	0.0032 (5)	0.0071 (6)	0.000	0.000	−0.0009 (4)
O2	0.0092 (18)	0.0111 (18)	0.031 (2)	0.0026 (14)	0.000	0.000
P3	0.0088 (4)	0.0074 (4)	0.0044 (4)	−0.0022 (3)	0.0001 (3)	0.0003 (3)
O3	0.0211 (14)	0.0217 (15)	0.0064 (12)	−0.0059 (11)	−0.0046 (11)	0.0001 (11)
O4	0.0128 (13)	0.0167 (13)	0.0181 (14)	−0.0080 (10)	0.0013 (11)	0.0017 (11)
O5	0.0172 (14)	0.0106 (13)	0.0163 (13)	0.0055 (10)	−0.0004 (11)	−0.0030 (10)
O6	0.0101 (12)	0.0138 (13)	0.0158 (13)	−0.0042 (10)	0.0007 (10)	0.0016 (10)
O7	0.0179 (14)	0.0214 (14)	0.0097 (13)	0.0009 (11)	−0.0044 (11)	0.0024 (11)
O8	0.0168 (14)	0.0101 (13)	0.0261 (16)	−0.0058 (10)	−0.0033 (12)	−0.0006 (11)
O9	0.0225 (14)	0.0201 (14)	0.0085 (12)	−0.0031 (11)	0.0073 (11)	−0.0043 (11)

Geometric parameters (Å, º)

Cs1—O2^i	3.131 (4)	P1—O2	1.531 (4)
Cs1—O6	3.149 (3)	Al1—O1^iii	1.720 (4)
Cs1—O6^ii	3.149 (3)	Al1—O9^ii	1.729 (3)
Cs1—O3^ii	3.178 (3)	Al1—O9	1.729 (3)
Cs1—O3	3.178 (3)	Al1—O2^vii	1.729 (4)
Cs1—O9^iii	3.330 (3)	O1—Al1^vi	1.720 (4)
Cs1—O9^iv	3.330 (3)	P2—O5^viii	1.525 (3)
Cs1—O9	3.607 (3)	P2—O5	1.525 (3)
Cs1—O9^ii	3.607 (3)	P2—O4^i	1.535 (3)
Cs1—O8^ii	3.657 (3)	P2—O4^ix	1.535 (3)
Cs1—O8	3.658 (3)	O2—Al1^x	1.729 (4)
Zr1—O5	2.038 (3)	O2—Cs1^xi	3.131 (4)
Zr1—O4	2.045 (3)	P3—O7	1.510 (3)
Zr1—O7^v	2.048 (3)	P3—O8	1.517 (3)
Zr1—O6	2.085 (3)	P3—O6	1.519 (3)
Zr1—O3	2.088 (3)	P3—O9	1.540 (3)
Zr1—O8^vi	2.095 (3)	O4—P2^ix	1.535 (3)
P1—O3	1.512 (3)	O7—Zr1^v	2.048 (3)
P1—O3^ii	1.512 (3)	O8—Zr1^iii	2.095 (3)
P1—O1	1.520 (4)	O9—Cs1^vi	3.330 (3)
O2^i—Cs1—O6	120.31 (5)	O7^v—Zr1—O6	95.35 (11)
O2^i—Cs1—O6^ii	120.31 (5)	O5—Zr1—O3	89.94 (11)
O6—Cs1—O6^ii	113.07 (10)	O4—Zr1—O3	88.25 (11)
O2^i—Cs1—O3^ii	97.77 (9)	O7^v—Zr1—O3	177.97 (11)
O6—Cs1—O3^ii	92.87 (7)	O6—Zr1—O3	86.47 (11)
O6^ii—Cs1—O3^ii	53.71 (7)	O5—Zr1—O8^vi	176.76 (11)
O2^i—Cs1—O3	97.77 (9)	O4—Zr1—O8^vi	88.67 (11)
O6—Cs1—O3	53.72 (7)	O7^v—Zr1—O8^vi	89.43 (12)
O6^ii—Cs1—O3	92.86 (7)	O6—Zr1—O8^vi	87.19 (11)
O3^ii—Cs1—O3	45.24 (10)	O3—Zr1—O8^vi	89.78 (12)
O2^i—Cs1—O9^iii	50.63 (8)	O3—P1—O3^ii	107.9 (2)
O6—Cs1—O9^iii	97.33 (7)	O3—P1—O1	111.33 (14)
O6^ii—Cs1—O9^iii	143.60 (7)	O3^ii—P1—O1	111.33 (14)
O3^ii—Cs1—O9^iii	147.42 (7)	O3—P1—O2	110.32 (14)
O3—Cs1—O9^iii	122.03 (7)	O3^ii—P1—O2	110.32 (14)
O2^i—Cs1—O9^iv	50.63 (8)	O1—P1—O2	105.7 (2)
O6—Cs1—O9^iv	143.60 (7)	O1^iii—Al1—O9^ii	115.13 (13)
O6^ii—Cs1—O9^iv	97.33 (7)	O1^iii—Al1—O9	115.13 (13)
O3^ii—Cs1—O9^iv	122.03 (7)	O9^ii—Al1—O9	102.9 (2)
O3—Cs1—O9^iv	147.42 (7)	O1^iii—Al1—O2^vii	110.1 (2)
O9^iii—Cs1—O9^iv	47.90 (10)	O9^ii—Al1—O2^vii	106.39 (13)
O2^i—Cs1—O9	156.22 (5)	O9—Al1—O2^vii	106.39 (13)
O6—Cs1—O9	42.14 (6)	P1—O1—Al1^vi	152.6 (3)
O6^ii—Cs1—O9	83.33 (7)	O5^viii—P2—O5	110.5 (2)
O3^ii—Cs1—O9	99.01 (7)	O5^viii—P2—O4^i	109.30 (15)
O3—Cs1—O9	82.43 (7)	O5—P2—O4^i	108.76 (15)
O9^iii—Cs1—O9	109.28 (6)	O5^viii—P2—O4^ix	108.76 (15)
O9^iv—Cs1—O9	129.38 (6)	O5—P2—O4^ix	109.30 (15)
O2^i—Cs1—O9^ii	156.22 (5)	O4^i—P2—O4^ix	110.2 (2)
O6—Cs1—O9^ii	83.33 (7)	P1—O2—Al1^x	144.6 (3)
O6^ii—Cs1—O9^ii	42.14 (6)	P1—O2—Cs1^xi	126.88 (19)
O3^ii—Cs1—O9^ii	82.43 (7)	Al1^x—O2—Cs1^xi	88.48 (15)
O3—Cs1—O9^ii	99.01 (7)	O7—P3—O8	112.40 (17)
O9^iii—Cs1—O9^ii	129.38 (6)	O7—P3—O6	110.18 (16)
O9^iv—Cs1—O9^ii	109.28 (6)	O8—P3—O6	109.57 (16)
O9—Cs1—O9^ii	44.02 (8)	O7—P3—O9	108.93 (16)
O2^i—Cs1—O8^ii	117.00 (6)	O8—P3—O9	108.18 (17)
O6—Cs1—O8^ii	120.11 (7)	O6—P3—O9	107.42 (16)
O6^ii—Cs1—O8^ii	41.92 (6)	O7—P3—Cs1	167.35 (12)
O3^ii—Cs1—O8^ii	95.48 (7)	O8—P3—Cs1	76.81 (11)
O3—Cs1—O8^ii	132.06 (7)	O6—P3—Cs1	57.51 (10)
O9^iii—Cs1—O8^ii	105.73 (7)	O9—P3—Cs1	74.73 (12)
O9^iv—Cs1—O8^ii	70.42 (6)	P1—O3—Zr1	151.60 (18)
O9—Cs1—O8^ii	77.99 (6)	P1—O3—Cs1	101.64 (13)
O9^ii—Cs1—O8^ii	39.86 (6)	Zr1—O3—Cs1	106.08 (10)
O2^i—Cs1—O8	117.00 (6)	P2^ix—O4—Zr1	152.20 (18)
O6—Cs1—O8	41.92 (6)	P2—O5—Zr1	154.79 (18)
O6^ii—Cs1—O8	120.11 (7)	P3—O6—Zr1	153.56 (17)
O3^ii—Cs1—O8	132.06 (7)	P3—O6—Cs1	98.47 (12)
O3—Cs1—O8	95.48 (7)	Zr1—O6—Cs1	107.16 (10)
O9^iii—Cs1—O8	70.42 (6)	P3—O7—Zr1^v	154.52 (19)
O9^iv—Cs1—O8	105.73 (7)	P3—O8—Zr1^iii	150.87 (18)
O9—Cs1—O8	39.86 (6)	P3—O8—Cs1	79.37 (11)
O9^ii—Cs1—O8	77.99 (6)	Zr1^iii—O8—Cs1	126.35 (11)
O8^ii—Cs1—O8	96.60 (9)	P3—O9—Al1	150.4 (2)
O5—Zr1—O4	94.54 (11)	P3—O9—Cs1^vi	127.23 (14)
O5—Zr1—O7^v	90.96 (11)	Al1—O9—Cs1^vi	82.17 (11)
O4—Zr1—O7^v	89.87 (11)	P3—O9—Cs1	80.94 (12)
O5—Zr1—O6	89.58 (11)	Al1—O9—Cs1	97.16 (12)
O4—Zr1—O6	173.30 (11)	Cs1^vi—O9—Cs1	102.02 (7)

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