Photochemistry of tetracarbonylnitrosylmanganese in frozen gas matrices at 20 K. Infrared spectroscopic evidence for tricarbonylnitrosylmanganese, tricarbonyl(dinitrogen)nitrosylmanganese, and a species formed by metal-to-nitrosyl photoelectron transfer

Abstract

Infrared evidence is presented for the formation of a four-co-ordinate species [Mn(CO)₃(NO)], apparently capable of existing in two distinct structural modifications, on u.v. photolysis of [Mn(CO)₄(NO)] in argon and methane matrices, and for the formation of a five-co-ordinate species [Mn(CO)₃(N₂)(NO)] in nitrogen matrices at 20 K. Further loss of CO probably gives [Mn(CO)₂(NO)] and [Mn(CO)(NO)] in methane and [Mn(CO)₂(N₂)₂(NO)] in nitrogen matrices. Infrared evidence is also presented for the formation of a species [Mn(CO)₄(NO*)], where the asterisk denotes a nitrosyl group having an unusually low value of ν(NO)(at ca. 1 460 cm^–1), on photolysis of [Mn(CO)₄(NO)] with visible radiation in both argon and methane matrices. It is concluded that [Mn(CO)₄(NO*)] belongs to a class of compounds in which photoelectron transfer has occurred with the nitrosyl ligand (NO*) accepting additional electron density from the metal atom. The results are related to the postulates of co-ordin-atively unsaturated and expanded-co-ordination-shell species as intermediates in the thermal and photochemical substitution reactions of [Mn(CO)₄(NO)] in solution.