Bis(tetraphenylphosphonium) tris(oxalato-O,O′)germanate(IV)

The synthesis and structure of the title compound, (C₂₄H₂₀P)₂[Ge(C₂O₄)₃], are reported. The PPh₄⁺ cations in the structure form infinite zigzag chains in which the P...P distances alternate between 6.229 (1) and 7.118 (1) Å, and the P...P...P angle is 131.4 (1) Å. The shorter P...P distance is associated with a sixfold phenyl embrace. However, the longer P...P distance is associated with both phenyl–phenyl interactions and interactions between the cations and a twofold symmetric [Ge(C₂O₄)₃]²⁻ anion. In the cation–anion interactions, the P...O distance is 4.444 (2) Å, the O...P—C_distal angle is 175.0 (1)° and the shortest H...O distances are 2.74 and 3.09 Å.

S1. Comment

As part of a study of the packing of salts of phenylphosphonium cations (Dance & Scudder, 1995, 1996, 1998; Hasselgren et al., 1997), we have characterized the new salt (PPh₄)₂[Ge(C₂O₄)₃], (I). The structure consists of recognizable PPh₄⁺ cations and [Ge(C₂O₄)₃]^2- anions, the latter having crystallographic twofold symmetry (Fig. 1). The structure is almost isostructural with that of (AsPh₄)₂[Tc(C₂O₄)₃] (Colmanet et al., 1987). \sch

The bond distances and angles within the anion (Fig. 1 and Table 1) can be compared with those found in K₂[Ge(C₂O₄)₃]·H₂O, (II) (Jorgensen & Weakley, 1980). The s.u.s found for (I) are smaller than those found for (II). In no case do the bond distances or ligand bite angles observed for the anion in (I) differ significantly from those observed in (II). In addition, the C—O_terminal distances of (I) do not differ significantly from each other, even though atom O1Ox1 appears to be involved in an Anion···Cation interaction, as discussed below.

The cations in (I) are linked into pairs, closest approach 6.229 (1) Å, by a sixfold phenyl embrace, or 6PE, which is an attractive interaction (Dance & Scudder, 1995, 1996, 1998). In addition, each cation is linked to a further cation at a distance of 7.118 (1) Å by a fourfold phenyl embrace, or 4PE (Dance & Scudder, 1998). This 4PE is unusual in that it is made up of two offset face-to-face interactions, with a twofold axis bisecting the P···P vector, instead of the more commonly found centre of inversion at its midpoint. The P···P···P angle is 131.4 (1)°. In this way, infinite zigzag chains of alternating 6- and 4PEs are formed. However, the longer P···P distance is associated not only with the 4PE, but also with cation-anion interactions.

The single shortest P···O interaction at each P atom is 4.444 (2) Å. While this is longer than the sum of the van der Waals radii (3.35 Å; Bondi, 1964), the near-linearity of O1Ox1, P and the distal carbon [O···P—C_distal 175.0 (1)°] is reminiscent of the near-linearity of P···P—C_distal that characterizes the 6PE (Dance & Scudder, 1995, 1996). As in the 6PE, the linearity is presumably indicative of an attractive interaction. A study of [MePh₃P]₂[Cr₂O₇] shows that such attraction occurs via C—H···O hydrogen bonding (Lorenzo et al., 1999). In the present case, the shortest H···O distances are 2.74 and 3.09 Å, compared with values of 2.39–3.15 Å in [MePh₃P]₂[Cr₂O₇]. The twofold axis referred to above leads to two identical P···O interactions emanating from a single anion spanning each 4PE (Fig. 2). Similarly modified zigzag chains occur in (AsPh₄)₂[Tc(C₂O₄)₃], where the As···As distances are 6.27 and 7.23 Å, the As···O distance is 4.35 Å and the O···As—C angle is 174.3°. Related chains also occur in (AsPh₄)₂[Zn(S₂C₂O₂)₂] (Golic et al., 1986). In this Zn salt there are two chains, one with As···As distances of 6.48 and 7.26 Å, the other with distances of 6.06 and 8.06 Å. Each chain is associated with one end of the anion to form two different O···As contacts, at 4.49 and 5.16 Å, the corresponding O···As—C_distal angles being 163.6 and 167.5°.

In summary, the structure of (I) has allowed the recognition of an unusual chain structure of the cations occurring here and in some other EPh₄⁺ salts of oxygen-bearing anions.

S2. Experimental

A solution of K₂[Ge(C₂O₄)₃]·H₂O (0.440 g, 1.02 mmol) in warm water (ca 15 ml) and a solution of Ph₄PBr (0.853 g, 2.03 mmol) in methanol (ca 15 ml) were mixed, producing a white precipitate. The solid white product was separated by filtration, washed with water:methanol (1:1 v/v), dried and dissolved in boiling methanol. X-ray quality crystals of (I) were obtained as part of the second batch of crystals formed when the methanolic solution was allowed to cool to room temperature.

S3. Refinement

The asymmetric unit of (I) consists of one cation and half of one anion. The A single ring was used to model all four phenyl rings, with their location and orientation as variables. H atoms were included in calculated positions and were not refined. The thermal motion of each phenyl ring was described by a 12 parameter TL model (where T is the translation tensor and L is the libration tensor).

Computing details

Data collection: CAD-4 Operations Manual (Enraf-Nonius, 1977); cell refinement: CAD-4 Operations Manual; data reduction: local programs; program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: RAELS (Rae, 1989); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: local programs.

Figures

	Fig. 1. A view of the [Ge(C2O4)3]^2- anion in (I) showing the labelling of the atoms. Displacement ellipsoids are shown at the 10% probability level and H atoms have been omitted for clarity.
	Fig. 2. A view of the chain structure adopted by the cations and anions in (I). One anion, with the twofold axis running through it, spans each fourfold phenyl embrace.

Bis(tetraphenylphosphonium) (trioxalato-O,O')germanate(IV)

Crystal data

2C24H20P^+·C6O12Ge^2^−	F(000) = 2088.0
Mr = 1015.4	Dx = 1.42 Mg m^−3
Monoclinic, C2/c	Cu Kα radiation, λ = 1.5418 Å
a = 22.759 (5) Å	Cell parameters from 10 reflections
b = 13.618 (2) Å	θ = 25–27°
c = 15.813 (3) Å	µ = 2.04 mm^−1
β = 104.34 (1)°	T = 294 K
V = 4748 (2) Å^3	Plate, colourless
Z = 4	0.15 × 0.13 × 0.06 mm

Data collection

Nonius CAD-4 diffractometer	Rint = 0.017
ω/2θ scans	θmax = 70°
Absorption correction: analytical (de Meulenaer & Tompa, 1965)	h = −27→27
Tmin = 0.64, Tmax = 0.90	k = −16→0
4616 measured reflections	l = 0→19
4439 independent reflections	1 standard reflections every 30min min
3646 reflections with I > 3σ(I)	intensity decay: none

Refinement

Refinement on F	H-atom parameters not refined
R[F^2 > 2σ(F^2)] = 0.034	w = 1/[σ^2(F) + 0.0016F^2]
wR(F^2) = 0.050	(Δ/σ)max = 0.013
S = 1.78	Δρmax = 0.38 e Å^−3
3646 reflections	Δρmin = −0.40 e Å^−3
174 parameters

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Ge	0.50000 (1)	0.67883 (3)	0.25000 (1)	0.0390 (1)
O1Ox1	0.3675 (1)	0.5235 (2)	0.2879 (2)	0.0875 (7)
O2Ox1	0.4597 (1)	0.5879 (1)	0.3033 (1)	0.0542 (4)
O3Ox1	0.3365 (1)	0.6153 (2)	0.1224 (2)	0.0941 (8)
O4Ox1	0.4307 (1)	0.6750 (1)	0.1569 (1)	0.0532 (4)
C1Ox1	0.4027 (1)	0.5720 (2)	0.2605 (2)	0.0553 (6)
C2Ox1	0.3860 (1)	0.6225 (2)	0.1720 (2)	0.0570 (6)
O1Ox2	0.5217 (1)	0.9419 (2)	0.1738 (2)	0.108 (1)
O2Ox2	0.5293 (1)	0.7799 (1)	0.1906 (1)	0.0531 (4)
COx2	0.5141 (1)	0.8670 (2)	0.2114 (2)	0.0637 (8)
P	0.3387 (1)	0.2199 (1)	0.1827 (1)	0.0404 (2)
C1	0.3836 (1)	0.2781 (1)	0.1193 (1)	0.0427 (5)
C2	0.4276 (1)	0.3466 (1)	0.1573 (1)	0.0545 (5)
C3	0.4579 (1)	0.3989 (1)	0.1059 (1)	0.0652 (6)
C4	0.4444 (1)	0.3831 (2)	0.0169 (1)	0.0656 (7)
C5	0.4008 (1)	0.3153 (2)	−0.0213 (1)	0.0687 (8)
C6	0.3703 (1)	0.2626 (1)	0.0296 (1)	0.0566 (6)
C7	0.3201 (1)	0.0988 (1)	0.1382 (1)	0.0471 (6)
C8	0.3665 (1)	0.0384 (1)	0.1254 (1)	0.0600 (6)
C9	0.3531 (1)	−0.0545 (1)	0.0900 (1)	0.0774 (9)
C10	0.2939 (1)	−0.0872 (1)	0.0674 (1)	0.0817 (9)
C11	0.2476 (1)	−0.0277 (2)	0.0799 (1)	0.0775 (7)
C12	0.2605 (1)	0.0653 (1)	0.1153 (1)	0.0604 (6)
C13	0.3794 (1)	0.2167 (1)	0.2950 (1)	0.0426 (6)
C14	0.4232 (1)	0.1451 (1)	0.3256 (1)	0.0566 (6)
C15	0.4550 (1)	0.1448 (1)	0.4126 (1)	0.0644 (8)
C16	0.4434 (1)	0.2155 (1)	0.4689 (1)	0.0611 (8)
C17	0.4001 (1)	0.2867 (2)	0.4390 (1)	0.0712 (9)
C18	0.3680 (1)	0.2876 (1)	0.3522 (1)	0.0607 (7)
C19	0.2722 (1)	0.2923 (1)	0.1770 (1)	0.0453 (5)
C20	0.2292 (1)	0.2618 (1)	0.2203 (1)	0.0547 (4)
C21	0.1792 (1)	0.3203 (2)	0.2194 (1)	0.0675 (5)
C22	0.1721 (1)	0.4088 (1)	0.1756 (1)	0.0711 (6)
C23	0.2146 (1)	0.4396 (1)	0.1324 (1)	0.0675 (7)
C24	0.2647 (1)	0.3816 (1)	0.1329 (1)	0.0547 (5)
HC2	0.4374	0.3581	0.2218	0.069
HC3	0.4895	0.4481	0.1332	0.087
HC4	0.4663	0.4210	−0.0200	0.079
HC5	0.3913	0.3042	−0.0858	0.093
HC6	0.3387	0.2135	0.0018	0.072
HC8	0.4094	0.0620	0.1418	0.069
HC9	0.3864	−0.0979	0.0808	0.100
HC10	0.2844	−0.1542	0.0419	0.102
HC11	0.2048	−0.0518	0.0634	0.100
HC12	0.2270	0.1083	0.1243	0.070
HC14	0.4317	0.0939	0.2849	0.079
HC15	0.4865	0.0934	0.4345	0.090
HC16	0.4664	0.2150	0.5315	0.072
HC17	0.3918	0.3377	0.4801	0.104
HC18	0.3366	0.3393	0.3307	0.084
HC20	0.2343	0.1977	0.2522	0.061
HC21	0.1483	0.2984	0.2506	0.083
HC22	0.1360	0.4508	0.1751	0.086
HC23	0.2092	0.5038	0.1007	0.083
HC24	0.2955	0.4040	0.1015	0.061

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ge	0.0409 (2)	0.0421 (2)	0.0328 (2)	0.0000 (1)	0.0066 (1)	0.0000 (1)
O1Ox1	0.089 (2)	0.086 (2)	0.098 (2)	−0.030 (1)	0.042 (1)	0.007 (1)
O2Ox1	0.058 (1)	0.054 (1)	0.053 (1)	0.0044 (8)	0.0178 (8)	0.0165 (8)
O3Ox1	0.057 (1)	0.128 (2)	0.084 (2)	−0.034 (1)	−0.007 (1)	0.004 (2)
O4Ox1	0.0479 (9)	0.066 (1)	0.0402 (9)	−0.0165 (8)	0.0001 (7)	0.0046 (8)
C1Ox1	0.060 (1)	0.047 (1)	0.064 (2)	−0.008 (1)	0.025 (1)	−0.003 (1)
C2Ox1	0.052 (1)	0.062 (2)	0.055 (2)	−0.011 (1)	0.008 (1)	−0.006 (1)
O1Ox2	0.089 (2)	0.061 (1)	0.169 (3)	−0.014 (1)	0.021 (2)	0.043 (2)
O2Ox2	0.0494 (9)	0.054 (1)	0.054 (1)	−0.0112 (7)	0.0105 (8)	0.0070 (8)
COx2	0.041 (1)	0.051 (1)	0.089 (2)	−0.009 (1)	−0.004 (1)	0.011 (2)
P	0.0379 (3)	0.0484 (3)	0.0340 (3)	−0.0029 (2)	0.0075 (2)	−0.0019 (2)
C1	0.0387 (7)	0.0481 (8)	0.0398 (7)	−0.0036 (7)	0.0066 (6)	−0.0047 (6)
C2	0.0534 (8)	0.0621 (9)	0.0496 (6)	−0.0189 (7)	0.0157 (6)	−0.0129 (6)
C3	0.070 (1)	0.069 (1)	0.0622 (9)	−0.0274 (8)	0.0274 (9)	−0.0146 (8)
C4	0.069 (1)	0.074 (1)	0.0580 (8)	−0.020 (1)	0.0243 (8)	−0.0022 (8)
C5	0.068 (1)	0.094 (1)	0.0453 (6)	−0.0253 (9)	0.0157 (7)	−0.0018 (7)
C6	0.0534 (9)	0.076 (1)	0.0397 (7)	−0.0178 (7)	0.0098 (6)	−0.0061 (6)
C7	0.0509 (9)	0.0527 (7)	0.038 (1)	−0.0080 (5)	0.0106 (7)	−0.0027 (6)
C8	0.0677 (8)	0.0581 (7)	0.054 (1)	0.0024 (7)	0.0152 (8)	−0.0085 (7)
C9	0.105 (1)	0.0590 (7)	0.067 (1)	0.0035 (8)	0.018 (1)	−0.0137 (7)
C10	0.120 (2)	0.0580 (7)	0.062 (1)	−0.0186 (7)	0.013 (1)	−0.0125 (8)
C11	0.091 (1)	0.0695 (9)	0.067 (1)	−0.0329 (9)	0.010 (1)	−0.0126 (9)
C12	0.0587 (8)	0.0653 (8)	0.055 (1)	−0.0212 (6)	0.0105 (8)	−0.0080 (7)
C13	0.0453 (8)	0.0458 (8)	0.0376 (6)	−0.0002 (7)	0.0119 (5)	0.0003 (5)
C14	0.0637 (9)	0.0540 (8)	0.0457 (6)	0.0108 (7)	0.0016 (6)	−0.0007 (5)
C15	0.073 (1)	0.062 (1)	0.0480 (7)	0.0072 (8)	−0.0035 (7)	0.0030 (6)
C16	0.068 (1)	0.071 (1)	0.0400 (6)	−0.0042 (9)	0.0046 (6)	0.0020 (5)
C17	0.080 (1)	0.088 (1)	0.0410 (6)	0.0148 (9)	0.0058 (6)	−0.0127 (6)
C18	0.067 (1)	0.071 (1)	0.0410 (6)	0.0155 (7)	0.0079 (6)	−0.0108 (6)
C19	0.0412 (6)	0.0538 (8)	0.040 (1)	−0.0040 (5)	0.0082 (6)	−0.0030 (7)
C20	0.0439 (6)	0.0672 (8)	0.056 (1)	−0.0051 (6)	0.0175 (7)	−0.0052 (6)
C21	0.0466 (6)	0.085 (1)	0.074 (1)	0.0009 (7)	0.0199 (7)	−0.0130 (9)
C22	0.0521 (7)	0.082 (1)	0.075 (2)	0.0123 (8)	0.0083 (8)	−0.015 (1)
C23	0.0626 (9)	0.0677 (8)	0.067 (1)	0.0141 (8)	0.0066 (8)	−0.0013 (7)
C24	0.0545 (7)	0.0566 (8)	0.051 (1)	0.0037 (6)	0.0089 (6)	0.0025 (7)

Geometric parameters (Å, º)

Ge—O2Ox1	1.862 (2)	P—C1	1.784 (2)
Ge—O4Ox1	1.873 (2)	P—C7	1.802 (2)
Ge—O2Ox2	1.879 (2)	P—C13	1.789 (2)
O1Ox1—C1Ox1	1.200 (3)	P—C19	1.789 (2)
O2Ox1—C1Ox1	1.323 (3)	C1—C2	1.392 (1)
O3Ox1—C2Ox1	1.207 (3)	C1—C6	1.392 (1)
O4Ox1—C2Ox1	1.312 (3)	C2—C3	1.386 (1)
C1Ox1—C2Ox1	1.520 (4)	C3—C4	1.380 (1)
O1Ox2—COx2	1.214 (3)	C4—C5	1.380 (1)
O2Ox2—COx2	1.300 (3)	C5—C6	1.386 (1)
COx2—COx2^i	1.514 (6)
O2Ox1—Ge—O4Ox1	85.6 (1)	O2Ox2—COx2—COx2^i	113.3 (2)
O2Ox1—Ge—O2Ox2	171.3 (1)	C1—P—C7	107.4 (1)
O2Ox1—Ge—O2Ox1^i	96.7 (1)	C1—P—C13	109.9 (1)
O2Ox1—Ge—O4Ox1^i	92.3 (1)	C1—P—C19	108.8 (1)
O2Ox1—Ge—O2Ox2^i	89.2 (1)	C7—P—C13	112.3 (1)
O4Ox1—Ge—O2Ox2	87.8 (1)	C7—P—C19	111.7 (1)
O4Ox1—Ge—O2Ox1^i	92.3 (1)	C13—P—C19	106.7 (1)
O4Ox1—Ge—O4Ox1^i	176.8 (1)	P—C1—C2	120.4 (1)
O4Ox1—Ge—O2Ox2^i	94.5 (1)	P—C1—C6	119.7 (1)
O2Ox2—Ge—O2Ox2^i	85.8 (1)	C2—C1—C6	119.6 (1)
Ge—O2Ox1—C1Ox1	114.1 (2)	C1—C2—C3	120.0 (1)
Ge—O4Ox1—C2Ox1	114.3 (2)	C2—C3—C4	120.1 (1)
O1Ox1—C1Ox1—O2Ox1	124.2 (3)	C3—C4—C5	120.3 (1)
O1Ox1—C1Ox1—C2Ox1	123.0 (3)	C4—C5—C6	120.1 (1)
O2Ox1—C1Ox1—C2Ox1	112.8 (2)	C1—C6—C5	120.0 (1)
O3Ox1—C2Ox1—O4Ox1	124.6 (3)	P—C7—C8	119.0 (1)
O3Ox1—C2Ox1—C1Ox1	122.8 (3)	P—C7—C12	121.5 (1)
O4Ox1—C2Ox1—C1Ox1	112.7 (2)	P—C13—C14	120.8 (1)
Ge—O2Ox2—COx2	113.2 (2)	P—C13—C18	119.6 (1)
O1Ox2—COx2—O2Ox2	124.3 (3)	P—C19—C20	120.1 (1)
O1Ox2—COx2—COx2^i	122.4 (2)	P—C19—C24	120.3 (1)

Symmetry code: (i) −x+1, y, −z+1/2.