CRYSTALLIZATION BEHAVIOR OF MESO-LAMBDA(DELTA-LAMBDA)-[CO(TRANS-(R,S) (MEEN)2)(C2O4)][PB2CL5]CENTER-DOT-2H2O, LAMBDA(LAMBDA-LAMBDA)-[([CO(TRANS-(R,R) (MEEN)2)(C2O4)]BR)2]CENTER-DOT-3H2O AND MESO-DELTA(DELTA-LAMBDA)-[CO(CIS-(R,S) (MEEN)2)(C2O4)]I (MEEN = N-METHYLETHYLENEDIAMINE)

Proton NMR spectroscopy of a D2O solution of the solid obtained by evaporating to dryness a reaction solution containing HCl, [Co(O2CMe)2].4H2O, PbO2, H2C2O4 and meen (meen = N-methylethylene-diamine in water revealed the presence of two different isomers of the cation [Co(meen)2(C2O4)]+. Three isomers [Co(meen)2(C2O4)][Pb2Cl5].2H2O 1, [{[Co(meen)2(C2O4)]Br}2] 2 and [Co(meen)2-(C2O4)]I 3 were isolated eventually by the selective use of appropriate counter anions and their crystal structures determined. The H-1 NMR spectra of D2O solutions of pure crystalline material from the same batch as that from which the structural crystals were derived showed the presence of single species of each of the three isolated compounds. Given their structures it is evident that the isomer with both methyls in the equatorial plane (trans to the oxalato oxygens) was either not formed or it rearranged soon after being formed. Complexes 1 and 2 are conformational isomers differing only in the relative position of one of the two axial methyl groups; 1 is stable in solution for at least 1 week at 21-degrees-C, as demonstrated by its H-1 NMR spectrum and rearrangement of cation 2 to 1 and 3 takes several days. Compound 3 contains the expected axial-equatorial isomer.