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

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.

Related literature

Open–framework series of isotypic tin(II) phosphates with general formula A[Sn₄(PO₄)₃] (A = Na, K, NH₄) were synthesized by hydro­thermal methods (Ayyappan et al., 2000; Bontchev & Moore, 2004; Deng et al., 2004; Mao et al., 2004). For related literature, see: Brown & Altermatt (1985); Cheetham et al. (1999); Weakley & Watt (1979).

Experimental

Crystal data

• Na[Ge₄(PO₄)₃]

• M_r = 598.26

• Trigonal, R 3c

• a = 9.377 (8) Å

• c = 23.48 (3) Å

• V = 1788 (3) ų

• Z = 6

• Mo Kα radiation

• μ = 10.49 mm⁻¹

• T = 298 (2) K

• 0.2 × 0.13 × 0.1 mm

Data collection

• Bruker SMART CCD area-detector diffractometer

• Absorption correction: multi-scan (SADABS; Bruker, 2000) T_min = 0.488, T_max = 1 (expected range = 0.171–0.350)

• 2164 measured reflections

• 639 independent reflections

• 567 reflections with I > 2σ(I)

• R_int = 0.068

Refinement

• R[F² > 2σ(F²)] = 0.058

• wR(F²) = 0.133

• S = 1.09

• 639 reflections

• 62 parameters

• 1 restraint

• Δρ_max = 1.71 e Å⁻³

• Δρ_min = −1.06 e Å⁻³

• Absolute structure: Flack (1983), 146 Friedel pairs

• Flack parameter: 0.23 (8)

Data collection: SMART (Bruker, 2000); cell refinement: SAINT (Bruker, 2000); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ATOMS (Dowty, 2005); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Supporting information

S1. Comment

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.

Related literature

Open–framework series of isotypic tin(II) phosphates with general formula A[Sn₄(PO₄)₃] (A=Na, K, NH₄) were synthesized by hydrothermal methods (Ayyappan et al., 2000, Bontchev & Moore, 2004, Deng et al., 2004, Mao et al., 2004).

For related literature, see: Brown & Altermatt (1985); Cheetham et al. (1999); Weakley & Watt (1979).

S2. Experimental

Na[Ge₄(PO₄)₃] were synthesized from mixtures of Na₂HPO₄ (99%, Riedel-de Haën), Ge (99.999%, Alfa), GeO₂ (99.999%, Cerac), and P₂O₅ (99.999%, J.T.Baker) in stoichiometric proportions according to the solid state method. Initially, all reagents were mixed in an Ar-filled glove box (total weight≈0.5 g), placed in a silica tube, sealed under vacuum (P≈10^-4 torr), and heated slowly to 600 °C over 48 h, followed by furnace cooling to room temperature on simply terminating the power. The length of the reaction tube was kept about 7~8 cm to avoid the prospective explosion due to the formation of gaseous hydrogen. The product contains hydrogen gas and brittle, colorless, transparent rod-shape crystals. The crystalline product was confirmed to be pure Na[Ge₄(PO₄)₃] by powder X-ray diffraction. Attempts to synthesize the analogue K[Ge₄(PO₄)₃] with the precursor K₂HPO₄ failed.

S3. Refinement

The structures were solved by direct methods and refined by full matrix least–squares techniques with the SHELXTL software package. Analysis of single-crystal X–ray diffraction data revealed four unique sites for Na, Ge and P and four unique sites for O atoms. The structural analysis yielded a charge–balanced formula Na[Ge₄(PO₄)₃]. All atomic positions were refined with anisotropic displacement parameters. The highest peak in the difference map is 1.67 e/ų and 0.96 Å from Ge1, while the minimum peak is -1.08 e/ų and 1.51 Å from O3.

Computing details

Data collection: SMART (Bruker, 2000); cell refinement: SMART (Bruker, 2000); data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ATOMS (Dowty, 2005); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

	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.

sodium tetragermanium tris(phosphate)

Crystal data

Na[Ge4(PO4)3]	Dx = 3.334 Mg m^−3
Mr = 598.26	Mo Kα radiation, λ = 0.71073 Å
Trigonal, R3c	Cell parameters from 2164 reflections
Hall symbol: R 3 -2" c	θ = 3.1–28.3°
a = 9.377 (8) Å	µ = 10.49 mm^−1
c = 23.48 (3) Å	T = 298 K
V = 1788 (3) Å^3	Rod, colourless
Z = 6	0.2 × 0.13 × 0.1 mm
F(000) = 1680

Data collection

Bruker SMART CCD area-detector diffractometer	639 independent reflections
Radiation source: fine-focus sealed tube	567 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.068
ϕ and ω scans	θmax = 28.3°, θmin = 3.1°
Absorption correction: multi-scan (SADABS; Bruker, 2000)	h = −11→6
Tmin = 0.488, Tmax = 1	k = −12→10
2164 measured reflections	l = −14→31

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)] = 0.058	w = 1/[σ^2(Fo^2) + (0.08P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.133	(Δ/σ)max = 0.017
S = 1.09	Δρmax = 1.71 e Å^−3
639 reflections	Δρmin = −1.06 e Å^−3
62 parameters	Absolute structure: Flack (1983), 146 Friedel pairs
1 restraint	Absolute structure parameter: 0.23 (8)

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
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 (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
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, º)

Ge1—O2	1.908 (10)	Na1—O1^viii	2.462 (11)
Ge1—O2^i	1.908 (10)	Na1—O4^vii	2.627 (11)
Ge1—O2^ii	1.908 (10)	Na1—O4^ii	2.627 (11)
Ge1—Na1^iii	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—Na1^iii	2.705 (13)
P1—Na1^iii	3.254 (7)	O3—P1^xii	1.534 (11)
Na1—O1^vii	2.462 (11)	O4—P1^xiii	1.540 (9)
Na1—O1^ii	2.462 (11)	O4—Na1^iv	2.627 (11)
O2—Ge1—O2^i	89.0 (5)	O2^ix—Na1—O2^x	59.2 (4)
O2—Ge1—O2^ii	89.0 (5)	O1^vii—Na1—O2^xi	135.5 (4)
O2^i—Ge1—O2^ii	89.0 (5)	O1^ii—Na1—O2^xi	122.3 (4)
O2—Ge1—Na1^iii	54.0 (3)	O1^viii—Na1—O2^xi	83.0 (3)
O2^i—Ge1—Na1^iii	54.0 (3)	O4^vii—Na1—O2^xi	77.9 (4)
O2^ii—Ge1—Na1^iii	54.0 (3)	O4^ii—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)	O1^ii—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)	O4^ii—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—Na1^iii	55.7 (4)	O1^vii—Na1—P1^x	100.0 (3)
O3^v—P1—Na1^iii	122.1 (4)	O1^ii—Na1—P1^x	69.3 (2)
O1—P1—Na1^iii	127.4 (4)	O1^viii—Na1—P1^x	158.4 (3)
O4^vi—P1—Na1^iii	52.8 (4)	O4^vii—Na1—P1^x	119.8 (3)
O1^vii—Na1—O1^ii	100.8 (4)	O4^ii—Na1—P1^x	27.8 (2)
O1^vii—Na1—O1^viii	100.8 (4)	O4^viii—Na1—P1^x	97.9 (3)
O1^ii—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)
O1^ii—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—O4^ii	76.3 (3)	O1^vii—Na1—P1^xi	158.4 (3)
O1^ii—Na1—O4^ii	60.6 (3)	O1^ii—Na1—P1^xi	100.0 (3)
O1^viii—Na1—O4^ii	159.5 (5)	O1^viii—Na1—P1^xi	69.3 (2)
O4^vii—Na1—O4^ii	117.71 (15)	O4^vii—Na1—P1^xi	97.9 (3)
O1^vii—Na1—O4^viii	159.5 (5)	O4^ii—Na1—P1^xi	119.8 (3)
O1^ii—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)
O4^ii—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)
O1^ii—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)
O4^ii—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—Na1^iii	96.7 (5)
O1^ii—Na1—O2^x	83.0 (3)	Ge1—O2—Na1^iii	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)
O4^ii—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.