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

Abstract Self-assembly of Ca 2+ , Zn 2+ and 4,5-imidazoledicarboxylic acid (H 3 imdc) via hydrothermal conditions under controlled pH affords three new and unusual heterometallic metal–organic frameworks (MOFs): [Ca 2 Zn 2 (imdc) 2 (Ac)(OH)(H 2 O)] ( 1 ), [CaZn 2 (imdc) 2 (im) 2 (H 2 O) 2 ]·1.8H 2 O ( 2 ), [CaZn(Himdc) 2 (H 2 O)] ( 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 Schafli symbol of the topologies of the heterometallic complexes 1 – 3 are {4;6 2 }{4;6 4 ;8}{4 2 ;6 3 ;8 5 }{4 3 ;6 2 ;8}{4 4 ;6 4 ;8 2 }{4 4 ;6 5 ;8 5 ;10}{4}{6 2 ;8}, {12 3 }{12} 2 {4;12 2 }{4;12 5 } and {4;8 2 }{4 2 ;6;8 2 ;10}{4 6 ;6 4 }{8}, respectively. The three Ca(II)/Zn(II) heterometallic complexes showed blue emission arising from intraligand π–π ∗ transition.