Department of Chemistry, Jadavpur University, Calcutta 700032 Manuscript received 25 January 1974; revised 17 October 1974; accepted 13 January 1975 Two dioxornolybdenum (VI) chelates having the compositions MoO2(en)CI2 and MoO2(Sal2en. H2OCI2[Sal2en H2 = N, N'-disalicyl ethylenediimine] are isolated by reacting MoO2CI2H2O with the appropriate ligands in suitable solvents and they have been characterised by i.r., TGA and magnetic susceptibility studies. The former undergoes 'base solvolysis' and the latter 'acid solvolysis' ia methanol as followed by their conductance measurement in the said solvent. Such conductance study reveals that the complexes MoO2CI2L2 (L = pyridine, 4.nitropyridine and quinoline N-oxides; triphenyl phosphide oxide; hexamethyl phosphoramide and dimethyl sul­phoxide) also undergo 'base solvolysis' in methanol but at a very high dilution (˷10-4 M) the triphenyl phosphine oxide, quinoline N-oxide and dimethyl sulphoxide complexes probably undergo further decomposition (a maxima in \(\sqrt{C}{M}\) vs. ∆M plots) when the organic ligand nuke­cales leave the inner sphere of coordination and the solvated organic ligands associate with the protons to a marked extent. This observation suggests that the standard free energy change accompanying the transfer of H [∆G\(_o^t\) (H+)] from methanol to the methanolated ligand species in these three cases are negative. A probable qualitative theoretical model in the case of the DMSO complexes has also been incorporated.