Extended X-ray absorption fine structure and multiple-scattering simulation of nickel dithiolene complexes Ni[S2C2(CF3)2]2n (n =-2,-1, 0) and an olefin adduct Ni[S2C2(CF3)2]2(1-hexene)

A series of Ni dithiolene complexes Ni[S2C2(CF3)](2)(n) (n = -2, -1, 0) (1, 2, 3) and a 1-hexene adduct Ni[S2C2(CF3)(2)](2)(C6H12) (4) have been examined by Ni Kedge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectroscopies. Ni XANES for 1-3 reveals clear pre-edge features and approximately +0.7 eV shift in the Ni K-edge position for 'one-electron' oxidation. EXAFS simulation shows that the Ni-S bond distances for 1, 2 and 3 (2.11-2.16 angstrom) are within the typical values for square planar complexes and decrease by similar to 0.022 angstrom for each 'one-electron' oxidation. The changes in Ni K-edge energy positions and Ni-S distances are consistent with the 'non-innocent' character of the dithiolene ligand. The Ni-C interactions at similar to 3.0 angstrom are analyzed and the multiple-scattering parameters are also determined, leading to a better simulation for the overall EXAFS spectra. The 1-hexene adduct 4 presents no pre-edge feature, and its Ni K-edge position shifts by -0.8 eV in comparison with its starting dithiolene complex 3. Consistently, EXAFS also showed that the Ni-S distances in 4 elongate by similar to 0.046 angstrom in comparison with 3. The evidence confirms that the neutral complex is 'reduced' upon addition of olefin, presumably by olefin donating the pi-electron density to the LUMO of 3 as suggested by UV/visible spectroscopy in the literature.