Diimines mixed-ligand diimine dithiolates

Mixed-ligand diimine dithiolate complexes of Zn(II) were among the first compounds classified as having a LLCT excited state (131). The complexes Zn(phen)(tdt) (41), Zn(bpy)(tdt) (42), and Zn(biq)(tdt) (43), where biq = 2,2 -biquinoline, were reported to have absorption bands at wavelengths of 475 nm (80 M-1 cm-1), 465 nm (65 A/-1 cm-1), and 590 nm (40 M-1 cm-1), respectively. The LLCT transition is attributed to a HOMO that is localized on the dithiolene and a LUMO that is localized on the diimine, with a clear relationship to the MMLL CT transition described for the square-planar M(di-imine)(dithiolate) complexes (M = Ni, Pd, Pt) described in Section II.C. However, the relative orientations of the two planar ligands in the <78 square planar and the dw pseudotetrahedral complexes are quite different, and have a profound influence on the absorption and emission properties. 

Diaz, G.E., S. Diez, M.M. Campos-VaUette, and J.I. Zink (1979). Vibrational analysis of metal diimine dithiolate mixed ligand complexes. Spectrochim. Acta A 55, 979. 

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