Electronic absorption spectra of molybdenum(0) bisarene complexes, (η 6-Arene) 2Mo 0

Abstract

The UV and visible absorption spectra of (η 6-Arene) 2Mo 0 (Arene = benzene (I), toluene (II), m-xylene (III), mesitylene (IV)) in the vapor phase and in the pentane solution have been investigated. Rydberg series converging to the ionization limit have been found in the spectra of vaporous complexes. The sharpest Rydberg bands correspond to the transitions 4 d( a 1 g ) → Rnp( e 1 u ) and 4 d( a 1 g ) → Rnp( a 2 u ). The band arising from the 4 d( a 1 g ) → R5 s( a 1 g ) Rydberg transition has been found in the vapor-phase spectra of the II and III complexes. Some weak bands in the vapor-phase spectra have been tentatively assigned to the 4 d( a 1 g ) → Rnd transitions. Rydberg bands disappeared from the spectra on going from vapor phase to pentane solution. The ionization limits for I–IV are 5.525 ± 0.010, 5.375 ± 0.010, 5.250 ± 0.010, 5.137 ± 0.010 eV, respectively. These limits correspond to the ionization from the highest occupied molecular orbital 4 d( a 1 g ) and are consistent with the first ionization potentials determined by photoelectron spectroscopy for the complexes I, II, and IV.