Mo2 Paddlewheel Complexes Functionalized with a Single MLCT, S1 Infrared-Active Carboxylate Reporter Ligand: Preparation and Studies of Ground and Photoexcited States

From the reactions between Mo2(DAniF)3pivalate (DAniF = N,N′-di­(p-anisyl)­formamidinate) and the carboxylic acids LH, the title compounds Mo2(DAniF)3L have been prepared and characterized: compounds I (L = O2CCCPh), II (L = O2CC4H2SCCH), and III (L = O2CC6H4-p-CN). The new compounds have been characterized in their ground states by spectroscopy (1H NMR, ultraviolet–visible absorption, near-infrared absorption, and steady state emission), cyclic voltammetry, and density functional theory calculations. The compounds show strong metal Mo2 to ligand L δ−π* transitions in their visible spectra. The nature of the S1 1MLCT and T1 states has been probed by time-resolved (femtosecond and nanosecond) transient absorption and infrared spectroscopy. The observed shifts of the CC and CN vibrational modes are found to be consistent with the negative charge being localized on the single L in the S1 states, while the T1 states are 3Mo2 δδ*. The present results are compared to earlier studies of the photoexcited states of trans-Mo2(2,4,6-triisopropylbenzoate)2L2 compounds that have been assigned as either localized or delocalized.