Spectroscopic and Density Functional Studies of the Dinitrosyl Metalloporphyrin Complexes Fe(P)(NO)<sub>2</sub> and Ru(P)(NO)<sub>2</sub>

Experimental evidence including infrared spectra for the formation of the dinitrosyl metalloporphyrin complexes M(P)(NO)<sub>2</sub> (M = Ru or Fe, P = tetraphenylporphyrin (TPP), octaethylporphyrin (OEP), or tetra-<i>m</i>-tolylporphryin (TmTP)) is described. Although observation of a single NO stretching band in the IR spectrum of each M(P)(NO)<sub>2</sub> complex first suggested a centrosymmetric (<i>D</i><sub>4</sub><i><sub>h</sub></i> or <i>C</i><sub>2</sub><i><sub>h</sub></i>) structure, DFT geometry optimizations and frequency calculations of model complexes indicate that the <i>trans</i>-<i>syn</i> (<i>C</i><sub>2</sub><i><sub>v</sub></i>) conformation should be more stable. The frequency calculations resolve the apparent ambiguity in the IR spectra in terms of the relative oscillator strengths of the predicted IR bands.