Fluorescent Heteroleptic Zirconium and Hafnium Complexes

Kuhlmann, L.; Methling, R.; Simon, J.; Neumann, B.; Stammler, H.-G.; Strassert, C. A.; Mitzel, N. W.

Abstract

Five new heteroleptic zirconium and hafnium complexes were synthesized. The complexes carry chloro ligands as well as differently substituted phenoxy benzoxazole ligands [HL1 = 2-(2′-hydroxyphenyl)benzoxazole, HL2 = 2-(2′-hydroxynaphthyl)benzoxa-zole, HL3 = 2-(2′-hydroxy-3′,5′-di-tert-butylphenyl)benzoxazole]. They were characterized by 1H and 13C{1H} NMR spectroscopy as well as by elemental analyses and X-ray diffraction experiments. The molecular structures in the crystals show distorted octahedral or capped trigonal prismatic coordination spheres. The intermolecular interactions influencing the packing patterns are mainly H···Cl contacts. For the hafnium complex [Cl2Hf(L3)2] a dynamic behavior in solution was examined using temperature dependent 1H NMR spectroscopy. The photo-physical data show that in all cases fluorescence arises from a short-lived excited state, the emission maxima being located in the blue spectral region.