Tuning the Framework Topologies of Co^II-Doped Zn^II−Tetrazole-benzoate Coordination Polymers by Ligand Modifications: Structures and Spectral Studies

In our continuing efforts to explore the effects of ligand modifications on the structures and properties of their metal complexes, we studied the in situ [2 + 3] cycloaddition reactions of benzonitrile, o-phthalodinitrile, 3-cyanobenzoic acid, 4-cyanobenzoic acid with NaN₃ in the presence of Zn^II and/or Co^II salts under hydrothermal conditions, and obtained four new Co^II-doped Zn^II-tetrazole-benzoate coordination polymers with the formula of [Co_xZn_1−x(L^m)_y]_n [5-phenyl-1H-tetrazole (HL¹) for 1, 2-(1H-tetrazol-5-yl)benzoic acid (H₂L²) for 2, 3-(1H-tetrazol-5-yl)benzoic acid (H₂L³) for 3, and 4-(1H-tetrazol-5-yl)benzoic acid (H₂L⁴) for 4]. The structure of 1 shows a classical diamondoid net, while 2 and 3, take 2D layer structure with (4.6²)(4.6.4.6) topology and 3D SrAl₂ topology, respectively. The structure of 4 exhibits a four-connected 3D network with rare non-diamondoid 6⁶ topology. The coordination modes of the center metal and the ligands in the four complexes are almost the same, being tetrahedral or four-connected, but their topologies are quite different. Thus, the four structurally related ligands allow analysis of the effects of the disposition of a second functional carboxylate group on an aromatic ring and the twist angles of the carboxylate and tetrazoyl out of the plane of the aromatic ring on the overall structural topology of their complexes. Interestingly, the Co^II ions were doped into the Zn^II complexes, as confirmed by their macroscopical colors, inductively coupled plasma (ICP) analysis and UV−visible spectra. In addition, the photoluminescence of the four complexes in the solid state at room temperature was briefly studied.