Cyclopalladated complexes of 2-phenylbenzothiazole with 4,4′-bipyridyl

Complexes [Pd(bt)(4,4'-bpy)OOCCH3], [Pd(bt)NO3](2)(m-4,4'-bpy), [Pd(bt)(m-4,4'-bpy)](4)(NO3)(4) (bt(-) is deprotonated form of 2-phenylbenzothiazole, bpy is 4,4'-bipyridyl) are prepared and characterized by H-1 NMR, electron absorption and emission spectroscopy, as well as by voltammetry. The upfield shift of the signal of proton in the ortho-position to the donor carbon atom of the cyclopalladated ligand in the complexes [(Delta delta = -(1.1-1.5) ppm] is assigned to the anisotropic effect of the ring current of the pyridine rings of the 4,4'-bipyridyl moiety, which are orthogonal to the coordination plane. Characteristic longwave absorption bands lambda = (387 +/- 4) nm and the low-temperature phosphorescence bands lambda = (512 +/- 3) nm in the complexes are assigned to the chromophore {Pd(bt)} metal complex fragment. The reduction waves in the complexes [E (1/2) = -(1.54 +/- 0.04) and E (p) = -(1.83 +/- 0.03) V] are assigned to the ligand-centered processes of the successive electron transfer to the pi* orbitals localized predominantly on the coordinated pyridine components of the 4,4'-bipyridyl moiety.