Structural Landscape of Zn(II) and Cd(II) Coordination Compounds with Two Isomeric Triimidazole Luminophores: Impact of Crystal Packing Patterns on Emission Properties

The interplay of different Zn(II) and Cd(II) salts with two luminescent triimidazole ligands, triimidazo[1,2-a:1′,2′-c:1″,2″-e][1,3,5]triazine (L1) and its positional isomer triimidazo[1,2-a:1′,2′-c:1″,5″-e][1,3,5]triazine (L2), in solvothermal synthetic conditions resulted in mono-, bi-, and polynuclear Zn(II) and Cd(II) coordination compounds with diverse metal/luminophore(L1,L2)/anion/water ratios, [Zn(H2O)6](NO3)2(L1)2 (1), [Zn(H2O)4(L1)2](NO3)2(H2O)2 (2), [Cd(H2O)4(L1)2](NO3)2(H2O)2 (3), [Zn(L1)(NO3)(H2O)3](NO3) (4), [Cd(L1)2(NO3)2(H2O)2] (5, 6), [Cd2(bdc)(L1)2(NO3)2(H2O)4]·2H2O (7), [Zn(H2O)4(L2)2](NO3)2 (8), [Cd(L2)2(NO3)2(H2O)] (9), [Zn(L2)2(CH3COO)2] (10), [Cd(L2)2(CH3COO)2(Im)0.75(H2O)0.25]·0.5(H2O) (11), [Zn(Cl)2(L1)(H2O)] (12), {[Zn(Cl)2(L1)]·1/6(L1·H2O)}n (13), and [Cd(L2)6]2[Cd(H2O)6](ClO4)6·7(H2O) (14). Herein, for the first time, the Zn and Cd coordination compounds with L1 and L2 luminophores as inner-sphere ligands have been obtained and structurally characterized. The structural landscape includes inclusion compound 1, supramolecular isomers 1-3, isomorphs 2 and 3, polymorphs 5 and 6, and one-dimensional coordination polymer 13. In discrete complexes, both luminophores coordinate to the metals in monodentate mode; in 13, L1 acts as a bidentate bridging ligand giving rise to the structure extension. Since the crystal packing and stacking patterns of the luminophore molecules are important factors underlying the aggregation induced emission, the finite and infinite stacking motifs registered in the crystal structures 1-14 are reported. All compounds reveal an emissive response upon irradiation under the UV-vis lamp. The best performing compounds in the series, namely, 4, 5, and 10, have been fully spectroscopically characterized.