CHEMICAL BONDING AND ELECTRONIC-STRUCTURE IN THE IONIC SPECIES CRNO2-ELECTRON AB-INITIO MULTI CONFIGURATION SELF-CONSISTENT-FIELD CALCULATIONS( AND [CR(H2O)(5)NO](2+) BY ALL)

In the present work we present results of all electron ab initio multi configuration self consistent field (CASSCF) calculations of six elec tronic states of the linear ion CrNO2+ and of eight electronic states of the ion [Cr(H2O)(5)NO](2+). The predicted electronic ground state o f CrNO2+ is (4) Pi and that of the [Cr(H2O)(5)NO](2+) ion is (2)A(2). For both ions the electronic ground state is well separated from the h igher lying electronic states. For both ions and for all the electroni c states investigated the net charge on chromium is in the range +1.65 e to +1.84e. This indicates that the oxidation state of chromium is ap proximately +2 in both CrNO2+ and [Cr(H2O)(5)NO](2+). In both ions a c ovalent chemical bond has been formed in between the Cr2+ ion and the NO ligand. The chemical bonds in both ions are due to the formation of bonding and antibonding molecular orbitals particularly in between th e orbitals Cr 3d pi and NO p pi. The bond order is approximately one in between Cr and N in the (4) Pi ground state of CrNO2+, and it is ap proximately one and a half in the (2)A(2) ground state of the [Cr(H2O) (5)NO](2+) ion. The low spin ground state, (2)A(2), of [Cr(H2O)(5)NO]( 2+) as compared to the high spin ground state, (4) Pi, of CrNO2+ is as cribed to a substantial energy splitting between the Cr 3d delta partn ers caused by the H2O ligand molecules.