Nonapotassium trialuminium hexa­phosphate

Zuoliang Liu; Guochun Zhang; Jianxiu Zhang; Peizhen Fu; Yicheng Wu

doi:10.1107/S160053681001305X

. 2010 Apr 17;66(Pt 5):i37–i38. doi: 10.1107/S160053681001305X

Nonapotassium trialuminium hexaphosphate

Zuoliang Liu ^a,^‡, Guochun Zhang ^a,^*, Jianxiu Zhang ^a, Peizhen Fu ^a, Yicheng Wu ^a

PMCID: PMC2979140 PMID: 21578985

Abstract

In the title compound, K₉Al₃(PO₄)₆, the anionic substructure is built of interlinked [PO₄] and [AlO₄] tetrahedra. Each O atom of the [AlO₄] tetrahedron is common to a positionally different [PO₄] tetrahedron; thus, each [AlO₄] tetrahedron is surrounded by four positionally different [PO₄] tetrahedra. On the other hand, each [PO₄] tetrahedron shares its two O atoms with two positionally different [AlO₄] tetrahedra; the other two phosphate O atoms are terminal ones coordinated by K atoms. The terminal O atoms are usually closer to the K atoms than the bridging O atoms between the [AlO₄] and [PO₄] tetrahedra. There are nine symmetry-independent K atoms in the structure. The coordination numbers of the K atoms are 6 or 7 or 8 up to a distance of 3.31 Å. There are channels in the anionic substructure oriented along the [10 Inline graphic ] direction that are filled by K atoms.

Related literature

For applications of metal phosphates, see: Barone & Nancollas (1978 ▶); Dickinson et al. (1996 ▶). For non-centrosymmetric phosphates with non-linear optical properties, see: Noor & Dam (1986 ▶); Aguilo & Wuensdregt (1985 ▶); Masse & Grenier (1971 ▶). For the non-centrosymmetric structures of A ₃Al₂(PO₄)₃ (A = K, Rb and Tl), which have three-dimensional [Al₂P₃O₁₂]³⁻ frameworks, see: Nandini Devi & Vidyasagar (2000 ▶). For the structure of KAlP₂O₇, see: Ng & Calvo (1973 ▶);

Experimental

Crystal data

K₉Al₃(PO₄)₆
M _r = 1002.66
Monoclinic,
a = 20.289 (4) Å
b = 9.835 (2) Å
c = 13.521 (3) Å
β = 100.56 (3)°
V = 2652.2 (9) Å³
Z = 4
Mo Kα radiation
μ = 2.02 mm⁻¹
T = 113 K
0.26 × 0.20 × 0.18 mm

Data collection

Bruker SMART 1000 diffractometer
Absorption correction: numerical (CrystalClear; Rigaku/MSC, 2005 ▶) T _min = 0.622, T _max = 0.713
35263 measured reflections
11751 independent reflections
10169 reflections with I > 2σ(I)
R _int = 0.028

Refinement

R[F ² > 2σ(F ²)] = 0.023
wR(F ²) = 0.059
S = 1.10
11751 reflections
380 parameters
Δρ_max = 0.54 e Å⁻³
Δρ_min = −0.52 e Å⁻³

Data collection: CrystalClear (Rigaku/MSC, 2005 ▶); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: Mercury (Macrae et al., 2006 ▶); software used to prepare material for publication: CrystalStructure (Rigaku/MSC, 2005 ▶).

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S160053681001305X/fb2181sup1.cif

e-66-00i37-sup1.cif^{(130.9KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S160053681001305X/fb2181Isup2.hkl

e-66-00i37-Isup2.hkl^{(574.5KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Characterization of K—O coordination spheres; coordination number as well as minimal and maximal distances (Å) within the coordination spheres for each K atom are given.

Atom K	Coordination number	K—O distances
K1	8	2.6202 (10)–3.2026 (12)
K2	7	2.5994 (9)–2.9721 (10)
K3	6	2.6337 (11)–2.9790 (11)
K4	6	2.7005 (10)–3.0451 (10)
K5	8	2.6787 (9)–3.3087 (12)
K6	7	2.6690 (10)–3.0404 (9)
K7	7	2.6369 (9)–3.0973 (10)
K8	7	2.5736 (9)–3.0747 (10)
K9	7	2.6965 (9)–3.3094 (11)

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Table 2. Characterization of K—O coordination spheres; the minimal and maximal K—O distances (Å) for the terminal and bridging O atoms (there is only one bridging oxygen in the coordination spheres of K2, K3, and K8).

Atom K	K—O_terminal / K—O_bridge distances
K1	2.6202 (12)–3.2027 (18) / 3.0287 (14)–3.1684 (16)
K2	2.5994 (12)–2.9722 (14) / 2.8588 (14)
K3	2.6337 (13)–2.9790 (14) / 2.8348 (13)
K4	2.7006 (13)–2.7762 (15) / 2.9576 (15)–3.0451 (13)
K5	2.6787 (11)–3.3088 (19) / 3.1012 (15)–3.2476 (15)
K6	2.6690 (14)–2.9869 (16) / 2.8236 (13)–3.0405 (13)
K7	2.6368 (12)–2.9005 (15) / 2.7891 (14)–3.0974 (13)
K8	2.5737 (12)–3.0747 (13) / 2.9491 (13)
K9	2.6965 (2)–2.8865 (13) / 2.9783 (12)–3.3095 (16)

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Acknowledgments

This work was supported financially by the National Natural Science Foundation of China under grant No. 50672104.

supplementary crystallographic information

Comment

Various metal phosphates have been widely used due to their good optical and chemical properties. For example, Ca₅(PO₄)₃F has been used in dentistry (Barone & Nancollas, 1978) and Sr₅(PO₄)₃F (Dickinson et al., 1996) has been used as a laser crystal in laser technology. Especially, some non-centrosymmetric phosphates have been used as important crystals with nonlinear optical properties, such as KH₂PO₄ (KDP) (Noor & Dam, 1986), NH₄H₂PO₄ (ADP) (Aguilo & Wuensdregt, 1985) and KTiOPO₄ (KTP) (Masse & Grenier, 1971). Aluminophosphates have attracted much attention because of their diverse structures.

Aluminophosphates contain 1D, 2D or 3D infinite frameworks with varying chemical composition. Nandini Devi & Vidyasagar (2000) reported non-centrosymmetric structures of A₃Al₂(PO₄)₃ (A=K, Rb and Tl). These compounds have 3D [Al₂P₃O₁₂]^3- frameworks. The latter study has inspired us to investigate the A₂O—Al₂O₃—P₂O₅ (A=K, Rb, Cs) system in order to search for new functional materials. As a result of our study a new aluminophosphate, the title structure K₉Al₃(PO₄)₆, has been discovered.

In K₉Al₃(PO₄)₆, all the aluminium and phosphorus atoms adopt the tetrahedral coordination. Each [AlO₄] tetrahedron shares each of its O atoms with a positionally different neighbour [PO₄] tetrahedron, while each [PO₄] tetrahedron shares its two O atoms with two different neighbour [AlO₄] tetrahedral. There are two pairs of chemically different O atoms around the P atoms: The terminal and the bridging oxygens that are involved in P-O-Al connections (Fig. 1). The P-O distance to the bridging oxygens vary in the interval 1.5645 (10) - 1.5881 (8) Å, while the P-O distances to the terminal oxygens are in the interval 1.4993 (10) - 1.5087 (9) Å.

There are channels in the anionic substructure along [1 0 1] (Fig. 2). These channels are filled by K atoms (Fig. 3). The coordination numbers of K atoms are 6 or 7 or 8 up to the distance 3.31 Å (Tab. 1). The terminal phosphate oxygens tend to be closer to K atoms than the bridging ones (Tab. 2).

Experimental

Single crystals of K₉Al₃(PO₄)₆ have been obtained by the high temperature solution method in a electric resistance furnace. Starting materials of the analytical grade KH₂PO₄ (136.15 g) and K₂CO₃ (69.03 g), high purity Al₂O₃ (51.08 g) and KF (58.33 g), in the respective molar ratio 2:1:1:2, were mixed and melt in a platinum crucible with a diameter of 60 mm and a height of 60 mm at 1273 K. The solution was stirred with a platinum plate for 24 hours. After the solution had been cooled to 1123 K at a rate of 10 Kh^-1, a platinum wire attached to an alumina shaft was slowly dipped into the solution, which was then followed by a slow cooling at the rate of 0.5 Kh^-1. Thus, a few colourless, transparent plate K₉Al₃(PO₄)₆ crystals with typical size of 3 × 3 × 0.5 mm crystallized on the platinum wire. After one week, the crystals were drawn out from the solution at 1050 K and cooled down to room temperature at the rate of 10 Kh^-1.