Crystallographic and theoretical study of the atypical distorted octahedral geometry of the metal chromophore of zinc(II) bis((1R,2R)-1,2-diaminocyclohexane) dinitrate

Abstract

The topic of the study is crystallographic experimental and theoretical electron density analyses of entitled complex zinc(II) bis((1R,2R)-1,2-diaminocyclohexane) dinitrate (1), showing an atypical of ZnII-ion octahedral geometry of the metal chromophore (ZnO2N4.) The ligand 1,2-diaminocyclohexane (L) is characterized by a diversity of coordination modes with transition metal ions. Also, it has been broadly used to design of new metal-organic anticancer medications, for instance, looking at its PtII-complex (oxaliplatin) at clinical trials. Its coordination capability of ZnII-ion reveals mainly complexes with a distorted Td* geometry of the metal chromophore, including cases of complexes of simply N-substituted derivatives of the ligand. These empirical arguments arise a very important question: What are the governing molecular and environmental factors causing for the observed geometry of the chromophore in complex (1)? In order to address this question, we shed light on correlation among molecular structure ⇔ electronic structure ⇔ nature of metal-to-ligand bond (ML) ⇔ energetics of ML bond ⇔ thermodynamics of ZnII–metal organics of 1,2-diaminocyclohexane. A comparative analysis between octahedral complex (1) and classical tetrahedral coordination compounds of ZnII–ion with 1,2-diaminocyclohexane and ethylenediamine (en) is carried out. High resolution crystallographic data are used. Static and molecular dynamics ab initio methods and those based on density functional theory are employed. The methods of atoms in molecules (AIM) and natural bond orbital (NBO) are utilized, as well.