Coordination architectures of 2-(1H-tetrazol-5-yl)pyrazine with group IIB metal ions: luminescence and structural dependence on the metal ions and preparing conditions

Abstract

The influence of the nature of metal ions and reaction conditions on the formation of group IIB metal coordination architectures of a tetrazole ligand, 2-(1H-tetrazol-5-yl)pyrazine (HL), and the luminescent properties of some complexes have been investigated. At room temperature, the reactions of Zn(NO₃)₂∙6H₂O (or ZnCl₂) and Cd(NO₃)₂∙6H₂O with HL gave rise to two reported complexes, [M(L)₂(H₂O)₂] (1 and 2, Acta Crystallogr., Sect. C, 2006, 62, m614; Acta Crystallogr., Sect. E, 2006, 62, m2841), respectively. However, under hydrothermal conditions, the same reactions yield 1 and another complex, {[Cd₂(L)₄](H₂O)_0.25}_n (3), respectively. In both preparation conditions mentioned above, the HL ligand reacts with Hg(OAc)₂ (or HgBr₂) to give complexes, [Hg(L)₂]_n (4), [Hg(L)₂]_n (5) and [Hg(L)Br]_n (6) with different structures. 1 and 2 have a similar mononuclear structure and in the crystal structure such molecules are further assembled together to form a 3-D α-Pt topological framework with O–H⋯N hydrogen bonds. 4 possesses a 1-D chain structure, in which the Cd(II) center is six-coordinated, with all coordination sites being occupied by N atoms of the ligands. Furthermore, such chains are interlinked via π⋯π interactions to form a 3-D framework. 4 has a 2-D (6,3) topological structure, in which the Hg(II) center is six-coordinated to six N atoms of L, and the L ligand takes a chelating-bridging mode similar to that in 3. 5 has a 2-D (4,4) topological layer structure with the metal center being six-coordinated, and the six coordination sites are held by N atoms from four L ligands, taking different coordination modes. Moreover, such planes are generated to form a 3-D structure via two kinds of π⋯π interactions. 6 is a 2-D layer with the Hg(II) coordinating to a Br atom and three N atoms of three tetrazole rings from different L ligands. This result shows that the metal ions and reaction conditions have significant influence on the group IIB metal complexes of this multifunctional ligand, and the intramolecular/intermolecular weak interactions are likely to play important roles in the formation of such complexes, especially linking the discrete subunits or low-dimensional entities into high-dimensional frameworks. In addition, the luminescent studies of HL and 1, 2, 3 and 6 indicate that they display blue emissions with different densities in the solid state at room temperature.