Spectral study of the nitrogen monoxide interaction with sublimed layers of meso-mono-4-pyridyl-tri-phenyl- and meso-mono-3-pyridyl-tri-phenyl-porphyrinatocobalt(II)

Abstract

The low-temperature interaction of NO(15NO ) with sublimed layers of meso-mono-4-pyridyl-tri-phenyl- and meso-mono-3-pyridyl-tri-phenyl-porphyrinatocobalt(II) ( CoM4PyTPP (I) and CoM3PyTPP (II), respectively) has been investigated by means of FTIR and UV-visible spectroscopy. In addition to the stable five-coordinate nitrosyl complexes that are similar to the closely-related meso-tetraphenylporphyrinatocobalt(II)-nitrosyl Co(TPP)(NO) complex, a new type of complex with coordinated NO (15 NO ) has been found for the layers that were maintained at room temperature overnight before addition of nitric oxide at low temperature. The ν{ NO (15 NO )} in this species are more than 20 cm−1 lower than in five-coordinate compounds. These adducts are assigned to six-coordinate nitrosyl complexes, in which the fifth coordination site is occupied by the pyridyl group of the adjacent I (II) molecules. Warming the layers containing six-coordinate nitrosyl complexes of I almost completely transforms them to stable five-coordinate nitrosyl species indicating oligomers' disruption rather than loss of nitric oxide. In the case of II, however, a noticeable fraction of the six-coordinate species is left upon warming. Introducing new portions of NO to these layers at low temperature leads to formation of additional quantities of the six-coordinate species. Hence, part of six-coordinate complexes in II decomposed upon warming by releasing NO instead of by breaking Co -pyridyl bonds, therefore leaving free the sixth coordination sites in these layers. This result suggests a good possibility for creating solid state NO storage devices in which nitrogen monoxide can be kept and easily released by warming of the system.