Octahedral monomeric molybdenum(III)

The first magneto-optical study of the 4 A 2g → 2 T 2g absorption, 2 E g → 4 A 2g and 2 T 2g → 2 T 1g, 2 E g luminescences of MoCl3- 6 in Cs2NaYCl6, as well as the absorption spectrum of the spin-allowed 4 T 2g and 4 T 1g ligand field states, are reported. Magneto-optical methods have allowed difficulties in a previous assignment to be resolved. Coupling of almost all electronic origins to α1g, t 2u and both t 1u MoCl3- 6 internal modes, as well as t 1u lattice modes, is established, uniquely, from the sign of the magnetic circular dichroism and magnetic circular polarization of luminescence spectra. In addition, coupling to a t 1u internal mode of the host YCl3- 6 unit is observed. Moderate coupling to the e g Jahn-Teller mode occurs for the 2 T 2g(U′), 2T1g(U′) and 2 E g(U′) origins, particularly the former, but is very weak or absent for the 2 T 2g(E″) and 2 T 1g(E′) origins. A comparison of the relative dipole strengths induced by t 1u and t 2u vibrations, as well as the sign of the MCPL for the 2 E g → 4 A 2g transition, are consistent with the intensity for the 4 A 2g → 2 E g, 2 T 1g, 2 T 2g transitions being borrowed primarily from the 4 T 2g state via spin-orbit coupling. The observed 2 T 1g and 2 T 2g spin-orbit splittings of 102 and 75cm-1, respectively, are reduced by approximately one third from those calculated, and this reduction is attributed to a Jahn-Teller effect.