Computational spectroscopic investigation of the effect of nitrosyl bonding type on molecular properties in iron tetracarbonyl nitrosyl complex

eq-[Fe(CO)4(NO)]+ (C2v), ax-[Fe(CO)4(NO)]+ (C3v),eq-[Fe(CO)4(NO)]– (Cs) and ax-[Fe(CO)4(NO)]– (Cs) complex ions have been designed for iron tetracarbonyl nitrosyl. Experimental C–O stretching frequencies of the complex with C2v symmetry have been used to determine the optimal computation level. The optimal level for the complexes has been determined as BVP86/LANL2DZ/6-31G(d). Optimized structures of complex ions with C2v, C3v and Cs point groups have been found at the optimal computational level in the gas phase. During the optimization process, it is seen that the eq-[Fe(CO)4(NO)]– complex with Cs symmetry is transformed into the ax-[Fe(CO)4(NO)]– complex with the Cs symmetry. From the bond angles, IR spectra and 13C NMR spectra, it is predicted that the iron atom in each of the complexes is a triangular bipyramidal ligand field. From the C-O stretching frequencies in the carbonyl stretching region and the Fe-C bond force constants, it has been estimated that complex with C2v point group can be used as CO-releasing material (CORM). Optical conductivity (DE), hardness (h), Mulliken electronegativity (c) and electrophilicity index (w) values of the complexes have been calculated from the highest occupied molecular orbital energy (EHOMO) and lowest energy unoccupied molecular orbital energy (ELUMO) values. The calculated values show that the optical conductivity, softness, nucleophilicity index and basicity strength of the complex with Cs point group are higher than those of the other complexes.