Structure-directing role of CH⋯X (X = C, N, S, Cl) interactions in three ionic cobalt complexes: X-ray investigation and DFT study using QTAIM Vr predictor to eliminate the effect of pure Coulombic forces

Abstract

Three cobalt complexes, namely [Co^III(HL¹)₂(N₃)₂]ClO₄ (1), [Co^III(L²)(HL²)(N₃)]ClO₄·1.5H₂O (2), and [Co^III(L³)(HL³)(NCS)]₂ [Co^IICl₂(NCS)₂] (3), where HL¹ = 2-(3-(dimethylamino)propyliminomethyl)-6-methoxyphenol, HL² = 2-(2-(dimethylamino)ethyliminomethyl)-4,6-dichlorophenol, and HL³ = 2-(2-(dimethylamino)ethyliminomethyl)-6-methoxyphenol, as potential tridentate N₂O-donor Schiff base ligands, were synthesized and characterized using elemental analysis, IR and UV-vis spectroscopy, and single-crystal X-ray diffraction studies. All three were found to be monomeric ionic complexes. Complex 1 crystallizes in the orthorhombic space group Pbcn, whereas both complexes 2 and 3 crystallize in triclinic space groups, P. Further, 1 and 2 are cationic complexes of octahedral cobalt(III) with perchlorate anions, whereas complex 3 contains a cationic part of octahedral cobalt(III) and an anionic part of tetrahedral cobalt(II). Hydrogen-bonding interactions involving aromatic and aliphatic CH bonds as H-bond donors and the pseudo-halide co-ligands as H-bond acceptors were established, which are important aspects governing the X-ray packing. These interactions were analyzed theoretically using the quantum theory of atoms in molecules (QTAIM) and non-covalent interaction plot (NCI plot) analyses. Moreover, energy decomposition analysis (EDA) was performed to analyze the stabilization of the complexes in terms of the electrostatic, dispersion, and correlation forces.