Syntheses, characterizations and magnetic properties of two MII-diphosphonate coordination polymers decorated by N-heterocyclic group (M=Co, Fe)

Two 2-D diphosphonate coordination polymers (CPs), {[Co3(HL1-H)2(H2O)4]·2H2O}n 1 and {[Fe3(HL2-H)2(H2O)4]·6H2O}n 2, (H5L1 = (1-hydroxy-2-(imidazo[1,2-a]pyridin-3-yl)ethane-1,1-diyl)diphosphonic acid, H5L2 = 1-hydroxy-2-(3-pyridyl)ethylidene-1,1-diphosphonate acid), have been hydrothermally isolated and determined by single-crystal X-ray diffractions, elemental analysis, IR, powder X-ray diffractions (PXRD), TG-DSC. Both two compounds possess 2-D inorganic layer structures containing 1-D ladder-like inorganic chains with building blocks [M2O2]n and [MO6]n. Compound 1 is the first example of Co(II)-H5L1 diphosphonate. The photoluminescence studies show that both compounds display fluorescent emissions, 378.5, 431.5 nm for 1 and 321.5, 390 nm for 2 (λex = 235 nm), respectively. Magnetic results show that both 1 and 2 present ferro- (FM) and antiferro- (AFM) metamagnetic behavior aroused by spin canted antiferromagnetic coupling between metal(II) centers. Moreover, the studies on the zero-field alternating current (ac) magnetic susceptibility suggest that compound 2 displays slow magnetic relaxation property, being promising potential as magnetic materials.