From the reactions between M2(TiPB)4, where TiPB = 2,4,6-triisopropylbenzoate and two equivalents each of 2-furan carboxylic acid, FuCO2H, and 2-selenophene carboxylic acid, SpCO2H in toluene, the new compounds trans-M2(TiPB)2(O2CFu)2 (1a M = Mo, 2a M = W) and trans-M2(TiPB)2(O2CSp)2 (1b M = Mo, 2b M = W) were formed. These new compounds have been characterized by 1H NMR, steady-state UV-Vis-NIR absorption and emission spectroscopy, cyclic and differential pulse voltammetry, and fs and ns transient absorption spectroscopy. The compound Mo2(TiPB)2(O2CSp)2 (1b) has been characterized by single crystal X-ray crystallography. These data are compared with those previously reported for related 2-thiophene carboxylate derivatives: M2(TiPB)2(O2CTh)2. The physico–chemical data correlate well with electronic structure calculations performed on model compounds. All compounds have detectible S1 photoexcited states with lifetimes that vary from ∼5 ps to < 1 ps. The molybdenum compounds have T1 states with microsecond lifetimes that are assigned as MMδδ* whereas the T1 states for tungsten are 3MLCT with lifetimes on the order of nanoseconds. In all cases, shorter lifetimes were seen in complexes containing heavier atoms.
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