Self-assembly and characterization of Ca–Zn heterometallic MOFs with 4,5-imidazoledicarboxylate

Self-assembly of Ca2+, Zn2+ and 4,5-imidazoledicarboxylic acid (H3imdc) via hydrothermal conditions under controlled pH affords three new and unusual heterometallic metal–organic frameworks (MOFs): [Ca2Zn2(imdc)2(Ac)(OH)(H2O)] (1), [CaZn2(imdc)2(im)2(H2O)2]·1.8H2O (2), [CaZn(Himdc)2(H2O)] (3), (Ac = acetate; im = imidazole) and characterized by elemental analysis, IR, powder X-ray diffraction (PXRD), and single-crystal X-ray diffraction. X-ray single-crystal structural analyses revealed that Zn(II) ions all coordinate with two imdc ligands no matter whether it is in a five or six coordination environment, while Ca(II) ions in 1–3 are all eight-coordinated. The Zn(II) ion with imdc ligands makes up a 2-D layer in 1, 1-D chain in 2, and 0-D elongated bridge in 3, respectively, which further connected the Ca(II) ion with the carboxylate oxygen atoms to form 3-D MOFs in 1, 2, a 2-D framework in 3. The total Schäfli symbol of the topologies of the heterometallic complexes 1–3 are {4;62}{4;64;8}{42;63;85}{43;62;8}{44;64;82}{44;65;85;10}{4}{62;8}, {123}{12}2{4;122}{4;125} and {4;82}{42;6;82;10}{46;64}{8}, respectively. The three Ca(II)/Zn(II) heterometallic complexes showed blue emission arising from intraligand π–π∗ transition.