Self-consistent-field-Xα-scattered-wave molecular orbital calculation of [CpMoS(μ-S)]2, a molecule that undergoes a photochemically induced isomerization

A self-consistent-field-Xα-scattered-wave molecular orbital calculation was carried out on the CpMoS(μ-S)]₂(Cp = η⁵-C₅H₅) complex. The calculated results were used to rationalize the observed photochemical isomerization of the title complex to CpMo(μ-S)]μ-S₂]. It is proposed that a terminal sulfur (S_t) → Mo charge-transfer excitation is responsible for the isomerization, which is an intramolecular redox; i.e. Mo(V) is reduced to Mo(IV) and S²⁻ is oxidized to S₂²⁻ , a result consistent with the charge-transfer character of the excitation. Specifically, the transition responsible for the isomerization is proposed to be 16b_u → 18a_g (¹A_g → ¹B_u). The 18a_g orbital is primarily Mo in character but it is also Mo---S_t π-antibonding; cleavage of the Mo---S_t π-bond facilitates the isomerization.