Photochemistry of the group VI hexacarbonyls in low temperature matrices. Part I. The pentacarbonyls of chromium, molybdenum, and tungsten

Abstract

I.r. and u.v. data are presented for the C_4v pentacarbonyl fragments produced by photolysis of chromium, molybdenum, and tungsten hexacarbonyls in inert-gas matrices at 20 K. Structures are deduced from i.r. intensity data. The hexacarbonyls can be regenerated with ease at 20 K by irradiation with light corresponding to the u.v. absorptions of the pentacarbonyls. Without irradiation the reverse reaction is just detectable at 42–45 K but only in the presence of an excess of carbon monoxide. The mechanism for the reversal is considered as is also the relevance of the matrix study to solution photochemistry. The splitting of the T_1u mode of the hexacarbonyls in the lowtemperature matrices is discussed and molecular distortion is presented as a probable explanation.