Syntheses, Structures and Fluorescent Properties of Three Low-Dimensional Zn-II-Diphosphonate Coordination Polymers

By introducing the second organic ligand 2,2'-bipy (bipy), three low-dimensional examples of Zn(II)-diphosphonate coordination polymers based on 1-hydroxyethylidenediphosphonic acid (H5L=CH3C(OH)(PO3H2)(2)), [Zn-1.5(H2L)(bipy)(H2O)]center dot 3H(2)O (1), [Zn(H3L)(bipy)](2) (2), [Zn(H3L)(bipy)(H2O)]center dot H2O (3), have been hydrothermally obtained and characterized by powder X-ray diffraction (PXRD), IR, elemental analysis, TG-DSC. The single-crystal X-ray diffractions show that compound 1 possesses one-dimensional ladder-like double chain structure with two unique Zn(II) ions in 4- and 6-coordinated modes, respectively. Compound 2 displays zero-dimensional structure built from binuclear unit [ZnO3N2](2) by a double O-P-O bridge. Compound 3 also shows one-dimensional chain structure built from octahedron [ZnO4N2] by a single O-P-O bridge. Then H-bond or/and pi-pi interactions further expand the one- and zero-dimensional structures into the three-dimensional supramolecular frameworks. Fluorescent measurements reveal that the maximum emission peaks of 1 similar to 3 have a significant increase in intensity compared to that of the bipy ligand, centered at 374 nm for 1, 388 nm for 2 and 387 nm for 3, respectively. These peaks are mainly caused by intraligand pi*-pi emission state of the bipy ligand (lambda(em)=391 nm, lambda(ex)=252 nm). All the three compounds indicate a one-electron oxidation process based on electrochemical measurements and the donor ability of 1 similar to 3 has gone up, compared with the H5L and the bipy ligands. CCDC: 1001967, 1; 1001968, 2; 1001969, 3.