Replacement of 2,2'-Bipyridine by 1,4-Diazabutadiene Acceptor Ligands: Why the Bathochromic Shift for (NN̂)IrCl(C5Me5)+ Complexes but the Hypsochromic Shift for (NN̂)Ir(C5Me5)?. Inorganic Chemistry, (42)17:5185--5191, 2003. [PUMA: bipyridine charge complex;DFT complex HOMO LUMO hypsochromic shift;orbital DFT iridium transfer bathochromic cationic cyclopentadienyl chloro interaction diazabutadiene]