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)

• Published in: Inorganic chemistry 2000-05, Vol.39 (11), p.2397-2404
• Main Authors: Yang, Wenyu, Schmider, Hartmut, Wu, Qingguo, Zhang, You-sheng, Wang, Suning
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic991436m

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)Cl2, 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 1 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 λ = 422, 426, and 432 nm, respectively. The blue luminescence of the complexes is due to a π* → π 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 1H NMR spectroscopic analysis.