Synthesis, structure, and properties of a new Co(II) diphosphonate based on auxiliary ligand 2,2'-bipyridine

ABSTRACTThe example of Co(II)-N-heterocyclic complex based on 1-hydroxyethylidenediphosphonic acid (H5L = CH3C(OH)(PO3H2)2), namely [Co2(H3L)2(2,2′-bipy)2] 1, has been solvothermally isolated using the second ligand 2,2'-bipyridine (2,2'-bipy) and characterized by powder X-ray diffraction (PXRD), elemental analysis, IR, and thermal gravimetric analyses. The single-crystal X-ray diffractions show that complex 1 possesses a 0-D structure built from binuclear unit [Co2(O–P–O)2] by μ2-(O–P–O) bridge. Then, H-bonding and π–π stacking interactions further expand this 0-D structure into a 3-D supramolecular framework. Fluorescent measurements reveal that the maximum emission peak is centered at 421.5 nm, mainly deriving from intraligand π*–π transition state of the second ligand 2,2'-bipy (λem = 419.5 nm, λex = 235 nm). Magnetism data indicate that 1 exhibits ferromagnetic behavior within binuclear Co(II) unit via μ2-(O–P–O) bridge in syn-anti mode.