Steric, Activation Method and Solvent Effects on the Structure of Paddlewheel Diruthenium Complexes

Conventional heating and solvothermal synthetic methods (with or without microwave activation) have been used to study the reaction of o-, m- and p-methoxybenzoic acid with [Ru2Cl(μ-O2CMe)4]. The tetrasubstituted series [Ru2Cl(µ-O2CC6H4-R)4], with R = o-OMe, m-OMe and p-OMe, has been prepared by the three procedures. Depending on the synthetic method and the experimental conditions, three compounds have been isolated (1a, 1b, 1c) with the o-methoxybenzoate ligand. However, with the m- and p-methoxybenzoate ligands, only the complexes 2 and 3 have been obtained, respectively. Compound 1a, with stoichiometry [Ru2Cl(µ-O2CC6H4-o-OMe)4]n, shows a polymeric structure with the chloride ions bridging the diruthenium units to form linear chains. Compounds 2 and 3, with the same stoichiometry, predictably form zig-zag chains in accordance with their insolubility and their magnetic measurements. Compound 1b, [Ru2Cl(µ-O2CC6H4-o-OMe)4(EtOH)], is a discrete molecular species with a chloride ion and one ethanol molecule occupying the axial positions of the dimetallic unit. Compound 1c is a cation-anion complex, [Ru2(µ-O2CC6H4-o-OMe)4(MeOH)2][Ru2Cl2(µ-O2CC6H4-o-OMe)4]. The cationic complex has two solvent molecules at the axial positions whereas the anionic complex has two chloride ligands at these positions. Complexes have been characterized by elemental analyses, mass spectrometry and IR and UV-vis-NIR spectroscopies. A magnetic study of complexes 1a, 1b, 2 and 3 have also been carried out. The crystal structure of compounds 1b and 1c have been solved by single X-ray crystal methods.