Chemical bonding and electronic structure in the ionic species CrNO 2 and [Cr(H 2O) 5NO] 2+ by all electron ab initio multi configurations self consistent field calculations

Abstract

In the present work we present results of all electron ab initio multi configuration self consistent field (CASSCF) calculations of six electronic states of the linear ion CrNO 2+ and of eight electronic states of the ion [Cr(H 2O) 5NO] 2+. The predicted electronic ground state of CrNO 2+ is 4Π and that of the [Cr(H 2O) 5NO] 2+ ion is 2A 2. For both ions the electronic ground state is well separated from the higher lying electronic states. For both ions and for all the electronic states investigated the net change on chromium is in the range +1.65 e to 1.84 e. This indicates that the oxidation state of chromiumo is approximately +2 in both CrNO 2+ and [Cr(H 2O) 5NO] 2+. In both ions a covalent chenical bond has been formed in betwenn the Cr 2+ ion and the NO ligand. The chemical bonmds in both ions are due to the formation of bonding and antibonding molecular orbitals particularly in between the orbitals Cr 3dπ and NO pπ ∗ . The bond order is approximately one in between Cr and N in the 4Π ground state of CrNO 2+, and it is approximately on and a half in the 2A 2 ground state of the [Cr(H 2O) 5NO] 2+ ion. The low spin ground state, 2A 2, of [Cr(H 2O) 5NO] 2+ as compared to the high spin ground state, 4Π , of CrNO 2+ is ascribed to a substantial energy splitting between Cr 3d° partners caused by the H 2O ligand molecules.