Synthesis, crystal structures and luminescence properties of Zn(ii) and Cd(ii) coordination compounds assembled from flexible bis(quinolyl) ligands with symmetrical spacers: the influence of coordinated anions†

This study is committed to the synthesis and characterization of a series of bi-, tri- and tetranuclear coordination compounds. These compounds are produced through the reactions of zinc(II) or cadmium(II) ions as coordination centers with flexible bis(quinolyl) ligands HL1 (N,N′-bis-quinolin-2-ylmethylene-carbohydrazide) or HL2 (N,N′-bis-quinolin-2-ylmethylene-carbonothioic dihydrazide), in conjunction with chloride, thiocyanate, iodide or hydroxyl anions serving as the coordinated counterions. These compounds are denoted as [Zn₃(L1)₂Cl(NCS)₃]·2DMF·H₂O (1), [Zn₄(L1)₂Cl_3.8I_0.2(OH)₂]·8H₂O (2), [Cd₂(L1)I₃(H₂O)(DMF)]·DMF·0.25H₂O (3), [Zn₃(L2)₂Cl₄]·3DMF·2H₂O (4), [Zn₃(L2)₂Cl(NCS)₃]·3DMF (5), [Zn₄(L2)₂Cl₄(OH)₂]·3DMF·2H₂O (6), and [Cd₄(L2)₂I₆]·2DMF (7). An array of analytical techniques including elemental analyses, infrared (IR) spectroscopy, thermogravimetric (TG) analysis, powder X-ray diffraction (XRD) and comprehensive single crystal structure analyses have been utilized to elucidate the nature of these compounds. The crystal structures of compounds 1 to 7 exhibit complex supramolecular networks, arranged in zero, one, two, or three dimensions, primarily mediated by various interactions such as intermolecular π⋯π, C–H⋯π, C–H⋯Cl, and C–H⋯S weak interactions, in addition to hydrogen bonding. The structural diversity highlights the key roles of the variable coordinating counterions and the coordination modes of the iodide anions in shaping the architectures of the coordination compounds. Furthermore, the luminescence characteristics of compounds 1 to 7 have been assessed in the solid state.