Designed synthesis and DFT study of R22(8) motifs in the solid state structures of trinuclear cobalt complexes of N2O2 donor Schiff bases using dicarboxylic acids as bridging co-ligands

Three trinuclear, linear, centrosymmetric, Co3 complexes, [Co{(mu-L1)(mu-Hsuc)Co(DMF)}2](ClO4)2 (1), [Co{(mu -L2) (mu-Hsuc)Co(DMF)}2](ClO4)2 (2) and [Co{(mu -L3)(mu- Hmal)Co(DMF)}2](ClO4)2 (3) have been synthesized using tetradentate N2O2 donor 'Schiff base' ligands, H2L1 {N,N'-bis(salicylidene)-1,3-diaminopropane}, H2L2{N,N'-bis (salicylidene)-2,2-dimethyl-1,3-diaminopropane}, H2L3 {N,N'-bis(5-chlorosalicylidene)-2,2-dimethyl-1,3-diaminopropane} and succinic acid (H2suc) or malonic acid (H2mal) as anionic co-ligands. The complexes have been characterized by spectroscopic measurements and their solid state structures have been determined by single crystal X-ray diffraction analysis. Some supra -molecular assemblies observed in the solid state of the complexes have been analysed using DFT calculations, in particular hydrogen bonding interactions. QTAIM computational tool has been used to characterize the interactions. Taking into consideration that each trinuclear complex is dicationic, the dimerization energy cannot be estimated using the supramolecular approach. Consequently, we have used the Lagrangian kinetic energy density (Gr) measured at the bond CPs that characterize the H -bonds to estimate the strength of the R22(8) motifs free from the pure Coulombic repulsion between the cations.