Variable Magnetic Interactions between S = 1/2 Cation Radical Salts of Functionalizable Electron-Rich Dithiolene and Diselenolene Cp₂Mo Complexes

A series of Cp₂Mo­(dithiolene) and Cp₂Mo­(diselenolene) complexes containing N-alkyl-1,3-thiazoline-2-thione-4,5-dithiolate ligand (R-thiazdt, R = Me, Et, CH₂CH₂OH) and N-alkyl-1,3-thiazoline-2-thione-4,5-diselenolate ligand (R-thiazds, R = Me, Et) have been synthesized. These heteroleptic molybdenum complexes have been characterized by electrochemistry, spectroelectrochemistry, and single crystal X-ray diffraction. They act as very good electron donor complexes with a first oxidation potential 200 mV lower than in the prototypical Cp₂Mo­(dmit) complex and exhibit almost planar MoS₂C₂ (or MoSe₂C₂) metallacycles. All five complexes formed charge transfer salts with a weak (TCNQ) and a strong acceptor (TCNQF₄), affording ten different charge-transfer salts, all with 1:1 stoichiometry. Crystal structure determinations show that the S/Se substitution in the metallacycle systematically affords isostructural salts, while the Cp₂Mo­(R-thiazdt) complexes with R equals ethyl or CH₂CH₂OH can adopt different structures, depending on the involvement of the hydroxyl group into intra- or intermolecular hydrogen bonding interactions. Magnetic susceptibility data of the salts are correlated with their structural organization, demonstrating that a face-to-face organization of the Me-thiazdt (or Me-thiazds) ligand favors a strong antiferromagnetic interaction, while the bulkier R = Et or R = CH₂CH₂OH substituents can completely suppress such intermolecular interactions, with the added contribution of hydrogen bonding to the solid state organization