LUMINESCENT METALLACARBORANES

Abstract

Metallacarborane complexes comprising MC x B y (x = 1–3, y = 3–10) polyhedral frameworks are not well known for their photophysical properties. While the subject of metallacarborane luminescence remains a hitherto under-explored topic, we have recently discovered surprising optoelectronic responses from a small clutch of rhenium-and ruthenium-carborane species. Thus the complexes [3,3,3-(CO)3-8-I-closo-3,1,2-ReC2B9H10]− and [3-CO-3,3-κ2-Me2N(CH2)2NMe2-closo-3,1,2-RuC2B9H11] display low temperature (77 K) phosphorescences with single-exponential decays (λem = 455 nm (τ = 1.65 ms) and λem = 450 nm (τ = 0.77 ms), respectively), while the structurally novel complex [7,10-μ-H-7-CO-7,7-(PPh3)2-isonido-7,8,9-ReC2B7H9] is photoemissive in solution at ambient temperatures (λem = 442 nm) with a variable biexponential dual fluorescent decay in frozen (77 K) glass. We have also observed frozen glass and solid state blue emission (λem ≈ 400 nm) from the complex [3,3-(CO)2-3-NO-closo-3,1,2-ReC2B9H11]. This work provides an opportunity to collate these results together and examine the related underlying causes for these emissions by interpretation of photophysical, electrochemical and spectroelectrochemical measurements. The results are related to the only other observed luminescence for a metallacarborane with an inclusive metal vertex, reported for the complex [commo-3,3′-Ni(1,2-C2B9H11)2], by virtue of a dynamic element leading to polyhedral skeletal reorganization of the metallacarborane framework in the excited state.