Structural Diversity in Copper(II) Complexes with NNO Tridentate Schiff Bases and Chlorido Ligands: The Realm of N−H···O and N−H···Cl Hydrogen Bonds and Their Steric and Electronic Modulations

In this paper, we investigated the N−H···O and N−H···Cl hydrogen bonds (H-bonds) in determining the crystal packing in copper(II) complexes with NNO tridentate Schiff bases and chlorido ligands of general formula [Cu(GLnR1,R2)(Cl)]. The ligands derive from the monocondensation of G-substituted salicylaldehydes with modulated electronic character (G-salH, G = NO2, H, and OMe) and aliphatic diamines with either variable length or steric hindrance of the chain (Ln: L1 = ethylene bridge, en; L2 = propylene bridge, tn; and L3 = 2,2-dimethylpropylene bridge, Me2tn) and different degrees of alkylation of the coordinated amino group (R1, R2 = H and Me). Structural data from both single crystal and powder X-ray diffraction studies were successfully obtained for nearly all synthesized compounds, and they all crystallize with no solvent molecules, allowing the study of the H-bonds among [Cu(GLnR1,R2)(Cl)] units without solvent interference. The synergism among the different steric and electronic factors, together with the tendency of copper(II) to modulate its coordination environment from square planar to square pyramidal or trigonal bipyramidal with the addition of a fifth position, reveals an intriguing structural diversity, which can also be envisaged with the help of multivariate analysis.