Tetraphenylphosphonium hydrogen oxalate

In the title compound, C24H20P+·C2HO4 −, two symmetry-independent ion pairs are present. The cations aggregate into puckered sheets via zigzag infinite chains of sixfold phenyl embraces and parallel fourfold phenyl embraces, while the anions form hydrogen-bonded chains between the sheets of cations. In the two independent oxalate anions, the angles between the normals to the two least-squares carboxylate COO planes are unusually large, viz. 72.5 (1) and 82.1 (1)°.

In the title compound, C 24 H 20 P + ÁC 2 HO 4 À , two symmetryindependent ion pairs are present. The cations aggregate into puckered sheets via zigzag infinite chains of sixfold phenyl embraces and parallel fourfold phenyl embraces, while the anions form hydrogen-bonded chains between the sheets of cations. In the two independent oxalate anions, the angles between the normals to the two least-squares carboxylate COO planes are unusually large, viz. 72.5 (1) and 82.1 (1) .

Related literature
For a related investigation of the packing of Ph 4 P + ions in the presence of differently shaped and/or charged anions, see: Dean et al. (2004). For a discussion of phenyl braces, see: Scudder & Dance (1998).
Between the sheets of PPh 4 + cations, hydrogen-bonded chains of alternating crystallographically independent HC 2 O 4 − anions, C and D, run parallel to the b axis ( Figure 2). The distances between the O atoms involved in the hydrogen bonds are 2.505 (2) and 2.500 (2) Å for O4C···O1D and O4D····O1C, respectively (Table 1). For the two independent molecules, the angle between the normals to the least squares planes defined by the two carboxylate COO groups are 72.5 (1) and  et al., 1999)].

Experimental
Ph 4 P + HC 2 O 4 − was the only crystalline product isolated from an attempt to synthesize (Ph 4 P + ) 2 C 2 O 4 2− in crystalline form.
Thus, Ph 4 P + Br − (0.859 g, 2.05 mmol) and Ag 2 C 2 O 4 (0.380 g, 1.25 mmol) were stirred together at ambient laboratory temperature in ca 15 ml of Me 2 CO in a foil-wrapped vial. After 2 days, the precipitate was allowed to settle and the mother liquor was separated by decantation. Slow evaporation of the mother liquor for 6 days at ambient laboratory temperature, led to a small number of colourless plate-like crystals. The data crystal was selected from these. No further formation of X-ray quality crystals occurred on further evaporation of the mother liquor. The carbon atoms of the cations were refined anisotropcally with 12-parameter TL rigid-body thermal parameters with their centres of libration at the appropriate P atom used for each phenyl ring. The remainimg non-hydrogen atoms were refined with single atom anisotropic thermal parameters. Hydrogen atoms were included in positions calculated each cycle (C-H = 1.00 Å), and their thermal motions were either included in the appropriate rigid group or assigned equal to U eq of their bonded atom.