Molecular and electronic structures and photophysical properties of quadruply bonded dimetal complexes (M = Mo or W) supported by trans-arylethynylcarboxylate ligands where aryl = p-tolyl or 9-anthrancenyl.
From the reactions between M(2)(T(i)PB)(4), where T(i)PB = 2,4,6-triisopropylbenzoate and M = Mo or W, in toluene and each of the respective carboxylic acids (2 equiv) the quadruply MM bonded compounds trans-M(2)(T(i)PB)(2)(O(2)C-C[triple bond, length as m-dash]C-Ar)(2) have been prepared where Ar = p-tolyl and M = Mo, , and M = W, , and Ar = 9-anthracenyl, where M = Mo, , and M = W, . Single crystal X-ray crystallographic studies of and confirmed the trans substitution pattern about the Mo(2)(4+) unit and the centrosymmetric molecules have structural features that indicate extensive Lπ-Mo(2)δ-Lπ conjugation involving the arylethynylcarboxylates. The compounds are intensely colored as a result of the HOMO → LUMO, metal δ-to-ligand π* charge transfer (1)MLCT transition: (orange), (red), (blue) and (green). The compounds , , and have been characterized by UV-Vis-NIR absorption and emission spectroscopy, cyclic voltammetry, femtosecond (fs) and nanosecond (ns) transient absorption spectroscopy and by fs time-resolved infrared spectroscopy in the region of ν(C[triple bond, length as m-dash]C), ν(CO(2)) and from 1400-1000 cm(-1). Aided by density functional theory, (DFT) and time dependent DFT, the electronic structures of the ground state and the S(1) and T(1) states are described. The molybdenum compounds have short lived (1)MLCT states, ∼ 5.0 ps and ∼ 10.5 ps, that undergo intersystem crossing to long lived (3)MoMoδδ* states: ∼ 101 μs and ∼ 83 μs. The tungsten complexes show interesting time-resolved infrared spectra in the ν(C[triple bond, length as m-dash]C) region when compared with their ground state. Compound shows ν(C[triple bond, length as m-dash]C) at 1975 cm(-1) for the (1)MLCT state which decays with τ ∼ 0.7 ps to ν(C[triple bond, length as m-dash]C) at 2000 cm(-1) for the (3)MLCT state. For the (1)MLCT is characterized by ν(C[triple bond, length as m-dash]C) at 2150 cm(-1), τ ∼ 19 ps, and a very broad absorption with a maximum ∼1970 cm(-1) which is proposed to arise from a low energy electronic transition. The (3)MLCT state for shows no evidence of ν(C[triple bond, length as m-dash]C) and is suggested to have an electron localized principally on the anthracenyl portion of the ligand, a proposal that finds support from the nature of triplet transient absorption spectrum of .[1]References
- Molecular and electronic structures and photophysical properties of quadruply bonded dimetal complexes (M = Mo or W) supported by trans-arylethynylcarboxylate ligands where aryl = p-tolyl or 9-anthrancenyl. Alberding, B.G., Brown-Xu, S.E., Chisholm, M.H., Gallucci, J.C., Gustafson, T.L., Naseri, V., Reed, C.R., Turro, C. Dalton. Trans (2012) [Pubmed]
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