Syntheses, structures, and fluxionality of blue luminescent zinc(II) complexes:: Zn(2,2′,2"-tpa)Cl2, Zn(2,2′,2"-tpa)2(O2CCF3)2, and Zn(2,2′,3"-tpa)4(O2CCF3)2 (tpa = tripyridylamine)

Three novel Zn(II) complexes containing either 2,2',2"-tripyridylamine (2,2',2"-tpa) or 2,2',3"-tripyridylamine (2,2',3"-tpa) have been synthesized and structurally characterized. Compound 1, Zn(2,2',2"-tpa)Cl-2, has a tetrahedral geometry while compounds 2, Zn(2,2',2"- tpa)(2)(O2CCF3)(2), and 3, Zn(2,2',3 "-tpa)(4)(O2CCF3)(2), have an octahedral geometry. The 2,2',2"-tpa ligand in I and 2 functions as a bidentate ligand, chelating to the zinc center, while the 2,2",3"-tpa ligand in 3 functions as a terminal ligand, binding to the zinc center through the 3-pyridyl nitrogen atom. All three compounds emit a blue color in solution and in the solid state. The emission maxima for the three compounds in solution are at lambda = 422, 426, and 432 nm, respectively. The blue luminescence of the complexes is due to a pi* --> pi transition of the tpa ligand as established by an ab initio calculation on the free Ligand 2,2',2"-tpa and complex 1. Compounds 1 and 2 are fluxional in solution owing to an exchange process between the coordinate and noncoordinate 2-pyridyl rings of the 2,2',2"-tpa ligand. Compound 2 is also fluxional owing to a cis-trans isomerization process, as determined by variable-temperature H-1 NMR spectroscopic analysis.