Density functional theory studies on the structures and vibrational spectroscopic characteristics of nickel, copper and zinc naphthalocyanines.

Molecular geometries and electronic structure calculations and spectroscopic assignments for metallonaphthalocyanines NiNc, CuNc and ZnNc are performed on the optimized geometries at B3LYP/6-31G* level. The order of the bond lengths of the NM bonds is computed to be NiNc < CuNc < ZnNc. The Mulliken atomic charges of the central M vary in the same order as the bond lengths. The metal dependent frequencies of IR-active and Raman-active vibrational modes decrease in the order of NiNc > CuNc > ZnNc, which is in reverse sequence of the N-M bond length. The strongest Raman lines predicted at 1570 (NiNc), 1546 (CuNc) and 1525 (ZnNc) cm-1 are highly sensitive to the metal ion. Comparison of the calculated properties of MNcs and MPcs (metallphthalocyanines) compounds reveals some interesting and meaningful results due to extension of the conjugated systems.