W. Xue, M. C. Chan, Z. Su
Mar 25, 1998
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Organometallics
Abstract
Rhenium(I) N-heterocyclic carbene complexes of the have been prepared, where L−L = 4,4‘-dimethoxy-2,2‘-bipyridine (2), 4,4‘-bis(tert-butyl)-2,2‘-bipyridine (3), 2,2‘-bipyridine (4), 4,4‘-dichloro-2,2‘-bipyridine (5), 4,4‘-bis(carbomethoxy)-2,2‘-bipyridine (6), 5-phenyl-1,10-phenanthroline (7), and o-phenylenebis(diphenylphosphine) (8). The molecular structures of 4, 6, and 8 have been determined by X-ray analyses and show Re−C(carbene) bond distances of 2.171(7), 2.163(4), and 2.199(6) A, respectively. HF-SCF and MP2 calculations on the model (4m) show that the HOMO is nonbonding d(Re) and the LUMO is mainly π*(diimine) with partial pz(carbene) character. CIS calculations on the excited state of optimized 4m suggest that the lowest energy absorption originates from a HOMO to LUMO spin-forbidden transition. Complexes 2−7 are emissive at room temperature and 77 K. The room-temperature and 77 K luminescence data of 2−6 are consistent with emission from a 3MLCT state. The nature of the emission of 7 at room t...