Three Metal(II) Diphosphonates with d 10 Electron Configuration: Structural, Fluorescent and Electrochemical Studies

Abstract

By introducing the second ligand 1,10-phenanthroline (phen), three low-dimensional examples of CdII/ZnII diphosphonates based on 1-hydroxyethylidenediphosphonic acid (H5L = CH3C(OH)(PO3H2)2), [Cd2(H3L)2(phen)2(H2O)2] 1, {[Zn3(H2L)2(phen)2]·2H2O}n 2 and [Zn2(H3L)2(phen)2]·(HOCH2CH2OH) 3, have been hydro- or solvo-thermally obtained and characterized by powder X-ray diffraction (PXRD), elemental analysis, IR, TG-SDTA. The single-crystal X-ray diffractions show that both compounds 1 and 3 display zero-dimensional structures built from binuclear units [M2(OPO)2] n (M = CdII/ZnII) via a double O–P–O bridge, and compound 2 possesses one-dimensional fish-bone inorganic chain structure with three types of coordination modes of Zn(II) ions. Then H-bond or/and π–π stacking interactions further expand the low-dimensional structures into the three-dimensional supramolecular frameworks. Fluorescent measurements reveal that the maximum emission peaks (371.5, 391.5 nm for 2 and 376.5, 392.5 nm for 3) of 2–3 have a significant increase in intensity compared to those of the phen ligand (λ em = 362.5, 379 nm, λ ex = 335 nm), which are mainly caused by intraligand π*–π emission state of the phen ligand. The results of electrochemical measurements indicate the donor ability of 1–3 has gone up, compared with the ligands (H5L and phen). Three examples of CdII/ZnII diphosphonates have been hydro- or solvo-thermally obtained. Two Zn(II) diphosphonates with 1,10-phenanthroline indicate a significant increase in intensity of fluorescence. The results of electrochemical measurements indicate the donor ability of CdII/ZnII diphosphonates increase, compared with the ligands H5L and phen.