(IUCr) Crystallography Journals Online

Abstract top

A new germanium(II) phosphate, sodium tetragermanium tris(phosphate), Na[Ge₄(PO₄)₃], has been synthesized by a solid-state reaction. The compound is isotypic with A[Sn₄(PO₄)₃] (A = Na, K, NH₄). It features a [Ge₄(PO₄)₃]^- framework made up of GeO₃ pyramids and PO₄ tetrahedra, which are linked by shared corners, yielding a three-dimensional structure. The crystal studied showed partial inversion twinning.

Comment top

Open-framework metal phosphates exhibit interesting structural types and physical properties that have been the subject of intensive research due to their potential applications in the areas of catalysis, ion–exchange and phase separation (Cheetham et al., 1999). Among these compounds, germanium phosphates are rare compared to other phosphate compounds. Most of reported germanophosphate contain germanium (IV) with octahedral coordination environment to oxygen atoms. To the best of our knowledge, germanophosphate with Ge(II) are very rare. Our group has demonstrated that A₂HPO₄ and metal can serve as reducing and oxidizing reagents to synthesize metal phosphates. In an attempt to synthesize compounds in the system using A₂HPO₄ as the precursor, we obtained a new quaternary compound Na[Ge₄(PO₄)₃]. As confirmed by measurements on single crystals, the synthesis of Na[Ge₄(PO₄)₃] is presented as follows:

4Na₂HPO₄+17Ge+15GeO₂+10P₂O₅→8Na[Ge₄(PO₄)₃]+2H₂

The structure of Na[Ge₄(PO₄)₃] is shown in Figure 1. The asymmetric unit contains two germanium, one phosphorus, four oxygen and one sodium atom (Figure 2). The Ge atoms occupy two different crystallographic sites and each site being coordinated by three O atoms to form distorted pyramids with Ge—O distances ranging from 1.87 (1) to 1.92 (1) Å, which agrees well with bond valence sum calculations (Brown & Altermatt, 1985). Similar Ge—O distances are reported in GeCl(H₂PO₂) (Weakley & Watt, 1979). The coordination environment of the Ge²⁺ atoms is similar to Sn²⁺ in A[Sn₄(PO₄)₃] (A=Na, K, NH₄) (Ayyappan et al., 2000, Bontchev & Moore, 2004, Deng et al., 2004, Mao et al., 2004).. The phosphorus atoms is tetrahedrally coordinated with P—O distances in a range 1.53 (1) to 1.54 (1) Å, which agrees with literature values. The structure of the title compound contains [PO₄]^3- layers stacked along the c–axis with a repeat sequence of six layers. The [PO₄]^3- units on the ab plane form 6 membered–ring with corner–shared [PO₄] and Ge(2)O₃ units, which are connected by Ge(1)O₃ pyramids to construct the two–dimensional framework. The two-dimensional layers are additionally connected to each other by out of planeGe(1)O₃ groups to form a three–dimensional framework. Each sodium atom is coordinated by nine oxygen atoms with Na—O distances ranging between 2.46 (1) and 2.71 (1) Å in a basket–like cage.

sodium tetragermanium tris(phosphate) top

Crystal data top

Na[Ge₄(PO₄)₃]	Z = 6
M_r = 598.26	F₀₀₀ = 1680
Trigonal, R3c	D_x = 3.334 Mg m⁻³
Hall symbol: R 3 -2" c	Mo Kα radiation λ = 0.71073 Å
a = 9.377 (8) Å	Cell parameters from 2164 reflections
b = 9.377 (8) Å	θ = 3.1–28.3º
c = 23.48 (3) Å	µ = 10.49 mm⁻¹
α = 90º	T = 298 (2) K
β = 90º	Rod, colourless
γ = 120º	0.2 × 0.13 × 0.1 mm
V = 1788 (3) Å³

Data collection top

Bruker SMART CCD area-detector diffractometer	567 reflections with I > 2σ(I)
Monochromator: graphite	R_int = 0.068
T = 298(2) K	θ_max = 28.3º
φ and ω scans	θ_min = 3.1º
Absorption correction: multi-scan (SADABS; Bruker, 2000)	h = −11→6
T_min = 0.488, T_max = 1	k = −12→10
2164 measured reflections	l = −14→31
639 independent reflections

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.08P)²] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.058	(Δ/σ)_max = 0.017
wR(F²) = 0.133	Δρ_max = 1.71 e Å⁻³
S = 1.09	Δρ_min = −1.06 e Å⁻³
639 reflections	Extinction correction: none
62 parameters	Absolute structure: Flack (1983), 146 Friedel pairs
1 restraint	Flack parameter: 0.23 (8)
Primary atom site location: structure-invariant direct methods

Crystal data top

Na[Ge₄(PO₄)₃]	γ = 120º
M_r = 598.26	V = 1788 (3) Å³
Trigonal, R3c	Z = 6
a = 9.377 (8) Å	Mo Kα
b = 9.377 (8) Å	µ = 10.49 mm⁻¹
c = 23.48 (3) Å	T = 298 (2) K
α = 90º	0.2 × 0.13 × 0.1 mm
β = 90º

Data collection top

Bruker SMART CCD area-detector diffractometer	639 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2000)	567 reflections with I > 2σ(I)
T_min = 0.488, T_max = 1	R_int = 0.068
2164 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.058	1 restraint
wR(F²) = 0.133	Δρ_max = 1.71 e Å⁻³
S = 1.09	Δρ_min = −1.06 e Å⁻³
639 reflections	Absolute structure: Flack (1983), 146 Friedel pairs
62 parameters	Flack parameter: 0.23 (8)

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.

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
Ge1	1.0000	1.0000	0.07489 (10)	0.0243 (6)
Ge2	1.41201 (19)	1.47337 (17)	0.10322 (6)	0.0214 (4)
P1	1.3317 (4)	1.1233 (4)	0.14139 (17)	0.0190 (7)
Na1	0.6667	0.3333	0.0506 (4)	0.025 (2)
O1	1.4071 (13)	1.2667 (13)	0.0985 (4)	0.024 (2)
O2	1.1603 (13)	0.9917 (13)	0.1226 (5)	0.032 (2)
O3	1.6040 (13)	1.5600 (13)	0.1466 (4)	0.027 (2)
O4	1.5371 (12)	1.5216 (13)	0.0335 (4)	0.026 (2)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ge1	0.0271 (9)	0.0271 (9)	0.0187 (11)	0.0136 (4)	0.000	0.000
Ge2	0.0170 (8)	0.0212 (8)	0.0242 (6)	0.0083 (6)	−0.0022 (5)	−0.0022 (6)
P1	0.0169 (17)	0.0186 (17)	0.0205 (14)	0.0082 (14)	0.0026 (12)	0.0008 (12)
Na1	0.025 (3)	0.025 (3)	0.026 (5)	0.0125 (16)	0.000	0.000
O1	0.025 (5)	0.027 (6)	0.019 (4)	0.012 (5)	−0.005 (4)	0.000 (4)
O2	0.019 (5)	0.031 (6)	0.050 (6)	0.016 (5)	0.002 (4)	0.010 (5)
O3	0.027 (6)	0.028 (5)	0.020 (4)	0.009 (5)	0.000 (4)	−0.004 (4)
O4	0.018 (5)	0.024 (6)	0.019 (4)	−0.001 (4)	0.002 (4)	0.008 (4)

Geometric parameters (Å, °) top

Ge1—O2	1.908 (10)	Na1—O1^viii	2.462 (11)
Ge1—O2ⁱ	1.908 (10)	Na1—O4^vii	2.627 (11)
Ge1—O2ⁱⁱ	1.908 (10)	Na1—O4ⁱⁱ	2.627 (11)
Ge1—Na1ⁱⁱⁱ	3.343 (11)	Na1—O4^viii	2.627 (11)
Ge2—O3	1.864 (10)	Na1—O2^ix	2.705 (13)
Ge2—O1	1.918 (11)	Na1—O2^x	2.705 (13)
Ge2—O4	1.931 (10)	Na1—O2^xi	2.705 (13)
Ge2—Na1^iv	3.477 (5)	Na1—P1^ix	3.254 (7)
P1—O2	1.522 (12)	Na1—P1^x	3.254 (7)
P1—O3^v	1.534 (11)	Na1—P1^xi	3.254 (7)
P1—O1	1.540 (11)	O1—Na1^iv	2.462 (11)
P1—O4^vi	1.540 (9)	O2—Na1ⁱⁱⁱ	2.705 (13)
P1—Na1ⁱⁱⁱ	3.254 (7)	O3—P1^xii	1.534 (11)
Na1—O1^vii	2.462 (11)	O4—P1^xiii	1.540 (9)
Na1—O1ⁱⁱ	2.462 (11)	O4—Na1^iv	2.627 (11)

O2—Ge1—O2ⁱ	89.0 (5)	O2^ix—Na1—O2^x	59.2 (4)
O2—Ge1—O2ⁱⁱ	89.0 (5)	O1^vii—Na1—O2^xi	135.5 (4)
O2ⁱ—Ge1—O2ⁱⁱ	89.0 (5)	O1ⁱⁱ—Na1—O2^xi	122.3 (4)
O2—Ge1—Na1ⁱⁱⁱ	54.0 (3)	O1^viii—Na1—O2^xi	83.0 (3)
O2ⁱ—Ge1—Na1ⁱⁱⁱ	54.0 (3)	O4^vii—Na1—O2^xi	77.9 (4)
O2ⁱⁱ—Ge1—Na1ⁱⁱⁱ	54.0 (3)	O4ⁱⁱ—Na1—O2^xi	113.5 (4)
O3—Ge2—O1	90.1 (5)	O4^viii—Na1—O2^xi	55.5 (3)
O3—Ge2—O4	91.2 (4)	O2^ix—Na1—O2^xi	59.2 (4)
O1—Ge2—O4	83.8 (4)	O2^x—Na1—O2^xi	59.2 (4)
O3—Ge2—Na1^iv	70.3 (3)	O1^vii—Na1—P1^ix	69.3 (2)
O1—Ge2—Na1^iv	43.3 (3)	O1ⁱⁱ—Na1—P1^ix	158.4 (3)
O4—Ge2—Na1^iv	48.4 (3)	O1^viii—Na1—P1^ix	100.0 (3)
O2—P1—O3^v	108.5 (6)	O4^vii—Na1—P1^ix	27.8 (2)
O2—P1—O1	110.8 (6)	O4ⁱⁱ—Na1—P1^ix	97.9 (3)
O3^v—P1—O1	110.5 (6)	O4^viii—Na1—P1^ix	119.8 (3)
O2—P1—O4^vi	108.4 (6)	O2^ix—Na1—P1^ix	27.7 (2)
O3^v—P1—O4^vi	109.1 (6)	O2^x—Na1—P1^ix	86.4 (3)
O1—P1—O4^vi	109.5 (6)	O2^xi—Na1—P1^ix	66.4 (3)
O2—P1—Na1ⁱⁱⁱ	55.7 (4)	O1^vii—Na1—P1^x	100.0 (3)
O3^v—P1—Na1ⁱⁱⁱ	122.1 (4)	O1ⁱⁱ—Na1—P1^x	69.3 (2)
O1—P1—Na1ⁱⁱⁱ	127.4 (4)	O1^viii—Na1—P1^x	158.4 (3)
O4^vi—P1—Na1ⁱⁱⁱ	52.8 (4)	O4^vii—Na1—P1^x	119.8 (3)
O1^vii—Na1—O1ⁱⁱ	100.8 (4)	O4ⁱⁱ—Na1—P1^x	27.8 (2)
O1^vii—Na1—O1^viii	100.8 (4)	O4^viii—Na1—P1^x	97.9 (3)
O1ⁱⁱ—Na1—O1^viii	100.8 (4)	O2^ix—Na1—P1^x	66.4 (3)
O1^vii—Na1—O4^vii	60.6 (3)	O2^x—Na1—P1^x	27.7 (2)
O1ⁱⁱ—Na1—O4^vii	159.5 (5)	O2^xi—Na1—P1^x	86.4 (3)
O1^viii—Na1—O4^vii	76.3 (3)	P1^ix—Na1—P1^x	92.9 (2)
O1^vii—Na1—O4ⁱⁱ	76.3 (3)	O1^vii—Na1—P1^xi	158.4 (3)
O1ⁱⁱ—Na1—O4ⁱⁱ	60.6 (3)	O1ⁱⁱ—Na1—P1^xi	100.0 (3)
O1^viii—Na1—O4ⁱⁱ	159.5 (5)	O1^viii—Na1—P1^xi	69.3 (2)
O4^vii—Na1—O4ⁱⁱ	117.71 (15)	O4^vii—Na1—P1^xi	97.9 (3)
O1^vii—Na1—O4^viii	159.5 (5)	O4ⁱⁱ—Na1—P1^xi	119.8 (3)
O1ⁱⁱ—Na1—O4^viii	76.3 (3)	O4^viii—Na1—P1^xi	27.8 (2)
O1^viii—Na1—O4^viii	60.6 (3)	O2^ix—Na1—P1^xi	86.4 (3)
O4^vii—Na1—O4^viii	117.71 (15)	O2^x—Na1—P1^xi	66.4 (3)
O4ⁱⁱ—Na1—O4^viii	117.71 (15)	O2^xi—Na1—P1^xi	27.7 (2)
O1^vii—Na1—O2^ix	83.0 (3)	P1^ix—Na1—P1^xi	92.9 (2)
O1ⁱⁱ—Na1—O2^ix	135.5 (4)	P1^x—Na1—P1^xi	92.9 (2)
O1^viii—Na1—O2^ix	122.3 (4)	P1—O1—Ge2	127.8 (6)
O4^vii—Na1—O2^ix	55.5 (3)	P1—O1—Na1^iv	118.9 (6)
O4ⁱⁱ—Na1—O2^ix	77.9 (4)	Ge2—O1—Na1^iv	104.4 (5)
O4^viii—Na1—O2^ix	113.5 (4)	P1—O2—Ge1	132.2 (6)
O1^vii—Na1—O2^x	122.3 (4)	P1—O2—Na1ⁱⁱⁱ	96.7 (5)
O1ⁱⁱ—Na1—O2^x	83.0 (3)	Ge1—O2—Na1ⁱⁱⁱ	91.2 (4)
O1^viii—Na1—O2^x	135.5 (4)	P1^xii—O3—Ge2	141.5 (7)
O4^vii—Na1—O2^x	113.5 (4)	P1^xiii—O4—Ge2	123.5 (6)
O4ⁱⁱ—Na1—O2^x	55.5 (3)	P1^xiii—O4—Na1^iv	99.4 (6)
O4^viii—Na1—O2^x	77.9 (4)	Ge2—O4—Na1^iv	98.3 (4)

Symmetry codes: (i) −y+2, x−y+1, z; (ii) −x+y+1, −x+2, z; (iii) −y+4/3, −x+5/3, z+1/6; (iv) x+1, y+1, z; (v) −y+3, x−y+1, z; (vi) −x+y+4/3, y−1/3, z+1/6; (vii) −y+2, x−y, z; (viii) x−1, y−1, z; (ix) −y+5/3, −x+4/3, z−1/6; (x) x−1/3, x−y+1/3, z−1/6; (xi) −x+y+2/3, y−2/3, z−1/6; (xii) −x+y+2, −x+3, z; (xiii) −x+y+5/3, y+1/3, z−1/6.

supplementary materials

A quaternary germanium(II) phosphate, Na[Ge₄(PO₄)₃]

C.-S. Lee and S.-F. Weng

	Fig. 1. The framework of Na[Ge₄(PO₄)₃] [Symmetry codes: (i)-y,x-y,z (ii)-x + y, -x, z (ix)-y + 2/3, -x + 1/3, z + 5/6 (x)-x + y+2/3, y + 1/3, z + 5/6. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. The alternating full/empty sequence of channels running parallel to the a– and b–axes.

supplementary materials

A quaternary germanium(II) phosphate, Na[Ge4(PO4)3]

C.-S. Lee and S.-F. Weng

A quaternary germanium(II) phosphate, Na[Ge₄(PO₄)₃]