Cryochemical Studies. 6. ESR Studies of the Reaction of Group 1B Metal Atoms with Arenes at 77 K in a Rotating Cryostat

Article abstract of DOI:10.1021/ja00349a002

Group 1B metal atoms have been deposited into inert hydrocarbon and reactive arene matrices at 77 K in a rotating cryostat and their electron spin resonance spectra have been examined.The spectra show that the metal atoms Cu, Ag, and Au(M) are trapped in adamantane and cyclohexane at 77 K with less perturbation of the singly occupied atomic orbital than atoms trapped in rare gas matrices.In the case of benzene, the spectra indicate formation of metal atom-monoligand complexes, M(C6H6).Cu(C6H6) has an anisotropic g tensor, an almost isotropic A tensor and ca. 70percent unpaired 4s spin population in the singly occupied molecular orbital (SOMO).Au(C6H6) and Ag(C6H6) have axially symmetric and isotropic parameters, respectively.The SOMO for the Ag and Au complexes have ca. 95percent unpaired s spin population.Substitution onto the benzene of electron withdrawing and donating substituents leads to complete destabilization of the copper complex and some loss of stability of the silver and gold complexes with little change in their ESR parameters.The difference between Cu(C6H6) and Ag(C6H6) (and Au(C6H6)) may arise from the higher energy level of the Cu 3d orbitals relative to the benzene orbitals.Bonding in Cu(C6H6) may involve interaction between 3d and 4p orbitals of the correct symmetry with the upper le_1g benzene orbitals and leads to a SOMO having metal 4p and 3d as well as 4s character.In Ag(C6H6) and Au(C6H6) bonding may involve interaction between 4d, 5p, 5d, and 6p orbitals with the lower la_2u benzene orbitals leading to an almost pure metal 5s and 6s SOMO.In most cases ESR spectra arising from metal atom clusters and microcrystallites are also observed.