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-κ ² -Me₂N(CH₂)₂NMe₂-closo-3,1,2-RuC₂B₉H₁₁] display low temperature (77 K) phosphorescences with single-exponential decays (λ_em = 455 nm (τ = 1.65 ms) and λ_em = 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 (λ_em = 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 (λ_em ≈ 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.

ACKNOWLEDGEMENTS

None of the work described here would have been possible without the dedicated contributions form my graduate students, Justin H. Orlando and Matthew J. Fischer, along with the much appreciated effort of undergraduate research assistants listed in the cited articles. Collaborations with researchers at other institutions have been vital in developing comprehensive, integrated descriptions of the complexes described. These include: Nigam P. Rath (X-ray crystallography, University of Missouri–St Louis); Michael J. Shaw (spectroelectrochemistry, Southern Illinois University at Edwardsville); Aleksander Siemiarczuk (time-resolved fluorescence measurements, Photon Technology Inc., Ontario, Canada). I am also indebted to my faculty colleagues at Saint Louis University, Steven W. Buckner and Shelley D. Minteer, for helpful discussions and advice. I am grateful to the following for financial support: Saint Louis University; US government; Lynntech, Inc. Above all I am thankful to my former mentor, F. Gordon A. Stone, for providing me with the inspiration to work with these fascinating complexes.

Notes

Dedicated to the memory of Judith M. Stone (1928–2008), beloved wife of Prof. F. Gordon A. Stone.

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Notes on contributors

Paul A. Jelliss

Paul A. Jelliss is an associate professor in the Department of Chemistry at Saint Louis University. His research interests include synthesis, characterization and unusual structures and properties of organometallic complexes, especially metallacarboranes. He has published articles in Inorganic Chemistry, Organometallics, Inorganica Chimica Acta, and the Journal of Materials Chemistry as well as chapters in Specialist Periodical Reports and Comprehensive Organometallic Chemistry III.