Interligand transmetallic charge-transfer transitions in mixed-ligand chelates

In chelates of divalent zinc which have two different aromatic ligands, a new absorption band is observed in the visible region. This new band is interpreted as arising from a π→π* interligand transmetallic charge-transfer (ITCT) transition. The nature of this type of charge-transfer transition in a chelate molecule, using a molecular orbital model, is examined. Experimental results for the chelates (3,4-toluenedithiolato)(1,10-phenanthroline)zinc(II), (3,4-toluenedithiolato)(2,2′-dipyridyl)zinc(II),and (3,4-toluenedithiolato)(2,2′-biquinoline)zinc(II) are presented.