Chloranilate bridged dinuclear copper(II) complexes: Syn-anti geometry tuned by steric factor and supramolecular interactions
Four dinuclear Cu(II) coordination compounds, [(CuL1)2CA]•CH3OH (1), [(CuL1)2CA]•CH3CN (1A), [(CuL2)2CA] (2) and [(CuL3)2CA] (3) (where, CA = chloranilate anion, HL1 = 2-[1-(2-dimethylamino-ethylimino)-methyl]-phenol, HL2 = 2-[1-(2-methylamino-ethylimino)-methyl]-phenol, HL3 = 2-[1-(methylamino)propan-2-ylimino)methyl)]phenol) have been synthesized by self-assembly of copper-Schiff base precursor together with chloranilate anion as the bridging ligand. Complexes are characterized by elemental analyses, IR spectroscopy, thermal analyses, and single crystal X-ray crystallography.The structural analyses reveal that complexes 1 and 1A are in syn- while 2 and 3 are in anti-conformation with respect to the metal coordinated Schiff-base ligands. The theoretical calculations show that for all three ligands, the anti conformations are energetically favorable and the unfavourable syn conformation in 1 or 1A is stabilized through CH•••π and hydrogen bonding interactions between the [(CuL1)2CA] unit and co-crystallised solvent molecule. M06-2X/def2-TZVP level of theory and NCI plot explicitly shows that unlike the case of 2 and 3, which form 1D supramolecular chain by chelate ring•••chelate ring π-stacking and cuprophilic interactions between the neighbouring dimers, in 1 and 1A, steric interactions between the neighbouring dimeric units, incorporated by one extra methyl group of the Schiff-base moiety restrict these structures to dimeric units.The variable-temperaturemagnetic susceptibility measurements suggest weak antiferro- and ferromagnetic coupling in 1(syn conformation) and 3(anti-conformation) with coupling constants −2.11 and 3 cm−1, respectively.