Syntheses, Structures and Magnetic Properties of Two Novel Cu(II) Diphosphonate Coordination Polymers with N-Heterocyclic Auxiliary Ligand

Abstract

By introducing the second organic N-heterocyclic ligand 2,2′-bipyridine (2,2′-bipy), two binuclear examples of Cu(II)-diphosphonate coordination polymers based on 1-hydroxyethylidenediphosphonic acid (H₅L=CH₃C(OH)(PO₃H₂)₂), [Cu₂(H₄L)₂(H₃L)(2,2′-bipy)₂] 1 and [Cu(H₃L)(2,2′-bipy)] 2, have been hydrothermally obtained and characterized by powder X-ray diffraction, elemental analysis, IR, TG-DSC. The single-crystal X-ray diffractions show that both the two compounds possess zero-dimensional binuclear structures built through a single O–P–O bridge for 1 and a double O–P–O bridge for 2 in syn–anti fashion. Then H-bond and π–π interactions further expand the two zero-dimensional binuclear structures into three-dimensional supramolecular frameworks. Fluorescent measurements reveal that the maximum emission peaks of 1–2 centered at 423.5 nm for 1 and 423 nm for 2, respectively, are mainly caused by intraligand π*–π emission state of N-heterocyclic ligand 2,2′-bipy (λ _ex = 233 nm). The further magnetic study shows the two coordination polymers exhibit ferromagnetic behaviors derived from O–P–O bridges in syn–anti mode between the metal centers.