The determination of the crystal structure of diammonium vanadyl oxalate dihydrate

The development of the structural chemistry of oxalates and vanadyl complexes is reviewed. The structure of diammonlum vanadyl oxalate dihydrate has been determined by x-ray analysis, using photographic and counter methods of data collection. The counter method gave an R factor of 0.039 and produced atomic coordinates with a satisfactory degree of accuracy. Contrary to predictions based on spectroscopic evidence, the vanadium atom is six coordinate, the anion [V0 (C(_2)O(_4))(_2)H(_2)0](^2-) containing a distorted octahedral arrangement of oxygens about the metal atom. The two chelated oxalate groups have a cis arrangement with respect to one another and a water molecule occupies an apical position trans to the vanadyl group. A comparison of vanadium to oxygen bond lengths with corresponding vanadium to ligand distances in other octahedralvanadyl complexes, shows that there is a general agreement. The bond lengths in the oxalate groups also agree with those in similar structures. The effect of the V = 0 group on C - 0 bond lengths in the trans chelated oxalate group has been observed and this accords with results reported by other workers. The water molecules and ammonium ions generate a network of hydrogen bonds in which all the oxygen atoms are involved.