On the Electronic Structure of Mesitylnickel Complexes of α‐Diimines — Combining Structural Data, Spectroscopy and Calculations

New organometallic nickel complexes of the type [(α‐diimine)Ni(Mes)Br] and [(α‐diimine)Ni(Mes) 2 ] (Mes = mesityl = 2,4,6‐trimethylphenyl) were prepared and characterised spectroscopically in detail. A combination of spectroscopic techniques (XRD, EXAFS, absorption, resonance Raman) and quantum chemical (DFT) calculations reveals the interplay of the diimine ligands and the mesityl or bromine co‐ligands with the nickel centre. The low‐lying electronic transitions are assigned as mixed MLCT/L′LCT or MLCT/XLCT due to low‐lying accepting π*‐orbitals centred on the diimine ligands and mixed metal/co‐ligand MOs as donor levels. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)