The reaction of tetrakis(μ-acetato)dimolybdenum(II) in aqueous suspension with various dicarboxylic acids yields compounds of the general formula, Mo 2(dicarboxylate) 2· nH 2O. Phthalic acid also gives tri- and tetra-phthalates, and 1,8-naphthalene dicarboxylic acid yields only the tris complex. For malonic and acetylenedicarboxylic acids, only partial substitution occurs. Tetrakis(μ-acetato)dimolybdenum(II) in aqueous suspension also reacts with monocarboxylic acids, and with benzoic acid, Mo 2(benzoate) 4 is obtained. A polymeric structure is suggested for these compounds in the light of their spectral properties.