Bonding in a triamidoamine-supported chromium(III) carbonyl

Abstract

Cr(III) metal ion in low spin triamidoamine-supported chromium(III) carbonyl complex {[(RN)3N]CrCO, 1} has a unique feature of S=1/2 being unusual for a Cr(III) metal ion, which is high spin with S=3/2 in most complexes and this gives us the basis for this theoretical study. The primary preoccupation has been to determine the electronic ground state and other low-energy state with much emphasis places on the bonding scheme of the conformation obtained at this ground state. DFT calculations elucidated this bonding scheme paying special attention on the Cr-CO metal-ligand π backbonding. Varying the auxiliary ligand (where R= H, CH3, or C6H5) gave significant changes on the results obtained for the metal-ligand backbonding. Their molecular structures were described revealing a trigonal bipyramidal coordination geometry of the chromium center with all structures having Cr-CO bond angle of 180o being the most stable. Calculations with the highly efficient OLYP, BLYP, OPBE and PW91 DFT functionals with a variation of the spin occupations gave interesting results. An electronic structural analysis of these structures at their different spin occupations indicated that besides the electronic ground state other low-energy states do exist. From a broader perspective, comparison of the results obtained with variation of DFT exchange functionals, spin occupation, auxiliary groups, their respective changes affected on the geometry (bond angles and bond lengths) and on their electronic structures gave a better understanding of the bonding scheme of this complex.