Luminescent η5-pentamethylcyclopentadienyl tantalum(V) complexes:: synthesis, characterization, and emission spectroscopy

A series of eta(5)-pentamethylcyclopentadienyl tantalum(V) complexes have been prepared and their electronic and emission spectra examined. Compounds of the form Cp*TaX4 (where X = Cl, Br, OC6F5) and Cp*TaCl2X2 (where X = OC6Cl5, 2,6-OC6H3Cl2), as well as CpTaX4, have been found to luminesce at 77 K in frozen glasses (only Cp*TaCl4, reported previously, luminesces at ambient temperature in both solid and fluid solution). The shifts in luminescence maxima with ligand variation lead to the conclusion that the emissive state is a ligand-to-metal charge transfer in which the highest occupied orbital is based on the donor atom of one of the monodentate ligands and the lowest unoccupied orbital is Ta-based. (C) 2002 Elsevier Science B.V. All rights reserved.