Optical and electronic properties of nickel(II) coordinated to chiral amino-alcohols. An experimental and theoretical study

Abstract

In this work it was investigated the experimental and theoretical properties of chiral acetyl aminoalcohols and their octahedral coordination compounds with nickel(II). Structural relaxation to determine the ground state (GS) were based on their X-ray crystal structures. DFT (Density Functional Theory) was applied for electronic exchange and correlation, PCM (polarizable continuum method) for the simulation of water solvent effects. The experimental circular dichroism (CD) for the studied diasteromers [Ni(S,S(+)Hcpse)2] 6 and [Ni(R,S(−) Hceph)2]∙7 compounds, with two chiral C atoms, presented CD spectra with mirror images and opposite Cotton effects. This was confirmed by the theoretical calculations, TD-DFT (Time-Dependent DFT), which allowed to assign the observed electronic transitions. The influence of the spatial orientation of the substituents at the chiral carbon atom, which may produce marked effects on the electronic properties, was analyzed by means of these two approaches. A similar study was carried on for the [Ni(R(−) Hcphen)2] 8 compound, with only one chiral C atom, as the C-methyl group is replaced by a C–H, in order to investigate the differences on the electronic properties of 6 and 7. The differences of 6, 7 and 8 are reflected on the dipole moments, stereochemistry and compositions of the orbitals involved in the electronic transitions in the CD spectra.