Tin-119 Mössbauer and X-ray crystallographic evidence for differences in the co-ordination of tin in oxalatostannates( II ) and malonatostannates( II )

The Mössbauer parameters for the series of oxalatostannates(II) M2Sn(C2O4)2·xH2O are rationalised in terms of distorted square-pyramidal tin environments. The crystal structure of the malonato-complex K2Sn2[CH2(CO2)2]3·H2O is reported: monoclinic, space group P21/n, with a= 11.233(2), b= 18.776(2), c= 8.171 (1)Å, β= 90.15(1)°, and Z= 4; R= 0.0277 for 5 805 reflections. Unlike the oxalate groups in the oxalato-complexes, the malonate moieties are bridging rather than chelating and the tin atoms are in trigonal rather than distorted four-pyramidal environments. Mössbauer data are reported for the malonate series of compounds M2Sn2[CH2(CO2)2]3·xH2O (M = NH4, K, Na, Rb, or Cs; x= 0, 1, or 3) and the data for the potassium salt are shown to be consistent with the crystal structure.