Cp*W(dmit)2]•: An Organometallic 15-Electron Neutral Radical (d1) with Optical Limiting Properties in Solution and an Antiferromagnetic Ground State in the Solid State

Abstract

The synthesis of the organometallic d2 [Cp*W(dmit)2]1– complex (where Cp* is pentamethylcyclopentadienyl and dmit is 1,3-dithiole-2-thione-4,5-dithiolate), and its oxidation to the paramagnetic d1 [Cp*W(dmit)2]• species, is described and their X-ray crystal structures given. Geometrical evolutions upon oxidation, characterized by a variable folding of the WS2C2 metallacycles along the S–S hinge, are rationalized by density functional theory (DFT) calculations and by comparison with the molybdenum analogs; as is also the evolution in the UV-vis-NIR absorption spectra. In solution, only the d1 complexes exhibit positive optical density variations in transitory nanosecond spectroscopy after 10 ns laser pulses. A weak optical limiting effect was observed on these d1 species, stronger in the W than in the Mo complex. In the solid state, the interacting, paramagnetic [Cp*W(dmit)2]• species (θCurie–Weiss = –20 K) orders antiferromagnetically below TNéel = 4.5 K with a spin-flop field, BSF(W) of 8000 G. Compared with the molybdenum analog, the weaker θCurie–Weiss(W) and TNéel(W) values, and larger BSF(W) values reflect weaker intermolecular interactions due to a decreased spin density on the dithiolene ligands and stronger spin–orbit coupling with the W atom, as confirmed by DFT calculations on the d2 and d1 Mo and W complexes.