Intra- and intermolecular interactions in a series of chlorido-tricarbonyl-diazabutadienerhenium(I) complexes: structural and theoretical studies

A series of new chlorido-tricarbonylrhenium(I) complexes bearing alkyl-substituted diazabutadiene (DAB) ligands, namely N,N'-bis(2,4-dimethylbenzene)-1,4-diazabutadiene (L1), N,N'-bis(2,4-dimethylbenzene)-2,3-dimethyl-1,4-diazabutadiene (L2), N,N'-bis(2,4,6-trimethylbenzene)-2,3-dimethyl-1,4-diazabutadiene (L3) and N,N'-bis(2,6-diisopropylbenzene)-1,4-diazabutadiene (L4), were synthesized and investigated. The crystal structures have been fully characterized by X-ray diffraction and spectroscopic methods. Density functional theory, natural bond orbital and non-covalent interaction index methods have been used to study the optimized geometry in the gas phase and intra- and intermolecular interactions in the complexes, respectively. The most important studied interactions in these metal carbonyl complexes are n→π*, n→σ* and π→π*. Among complexes 1-4, only 2 shows interesting intermolecular n→π* interactions due to lp(C[triple-bond]O)...π* and lp(Cl)...π* (lp = lone pair) contacts.