SYNTHESES, Structures and Fluorescent Properties of Two Zn(II)-Diphosphonate Coordination Polymers

With the introduction of 2,2′-bipyridine (2,2′-bipy) agent, two new zinc coordination polymers (CPs), {[Zn6(HL-H)4(2,2′-bipy)4]·¼H2O}n 1 and {[Zn3(HL-H)2(H2O)4]·6H2O}n 2, have been hydrothermally obtained derived from diphosphonic acid, 1-hydroxy-2-(3-pyridyl)ethylidene-1,1-diphosphonic acid (H5L = (H4C5N)CH2C(OH)(PO3H2)2, HL-H = (H4C5N–H)CH2C(OH)(PO3)2), and determined by single-crystal X-ray diffractions, elemental analysis, IR, powder X-ray diffractions (PXRD). The single-crystal X-ray diffractions reveal that compound 1 owns a novel 1-D fishbone-like inorganic chain structure built from binuclear building blocks [Zn2(O–P–O)2]n via [ZnO4]n tetrahedron linkers. It is the first example that N-heterlcyclic amine 2,2′-bipy is used as the second ligand to construct the compound 1 with the diphosphonic acid ligand H5L. Both hydrogen bonding and π–π stacking interactions further extend the 1-D chain to the 3-D supramolecular network. Compound 2 exhibits a 2-D reticulate layer structure containing 4-, 8- and 16-membered rings created from 1-D ladder-like inorganic chain, and the organic pyridine rings in the structure point to voids defined by the 16-membered rings. Moreover, the room-temperature fluorescence measurements show that both the compounds display two fluorescent emissions centered at 379, 424 nm for 1 and 380, 424 nm for 2, respectively, caused by intraligand π*–π emission state of organic pyridine ring (λex = 235 nm). With the introduction of 2,2′-bipyridine (2,2′-bipy) agent, two new Zn(II)-phosphonate CPs, 1-D {[Zn6(HL-H)4(2,2′-bipy)4]·¼H2O}n 1 and 2-D {[Zn3(HL-H)2(H2O)4]·6H2O}n 2 (H5L = (H4C5N)CH2C(OH)(PO3H2)2, HL-H = (H4C5N–H)CH2C(OH)(PO3)2), have been hydrothermally obtained and characterized. The thermal stabilities and fluorescent properties of them have been investigated.