Zinc(II) complexes of 3,5-bis(4-pyridyl)-1H-1,2,4-triazole: Synthesis, the role of counter-anions in the formation of a type of crystal structure, and luminescence properties

Abstract

Four Zinc(II) coordination compounds, i.e. [Zn(4bpt)(piv)]<inf>n</inf>∙1.5nDMSO∙2nH₂O (1, 4Hbpt – 3,5-bis(4-pyridyl)-1,2,4-triazole, piv – pivalate-anion), [Zn₂(4bpt)₂Br₂(H₂O)]<inf>n</inf>∙∙3nDMF∙3nH₂O (2) and [Zn(4Hbpt)X₂]<inf>n</inf>∙2nDMF (X = Cl (3), Br (4)) have been synthesized and characterized by elemental and thermal analysis, IR spectroscopy and single-crystal X-ray diffraction methods. Structural analysis demonstrated that the influence of counter anions plays an important role in determining the resultant structure: 3D networks for 1 and 2 with topological type of srs and 3,4-c respectively, and chain polymers for 3 and 4. The photoluminescent properties and mechanisms, studied by means of solid state absorption, excitation/emission spectra, time-resolved lifetime techniques, indicate that the emissions of both compounds originate from a combination of exciplex and charge-transfer complex. Interestingly, compound 2 exhibit excitation-dependent emissions, which can be used to fine-tune their emission wavelengths.