Three M(II)-diphosphonate coordination polymers with N-heterocyclic group (M = Ni, Fe, Mg): Synthesis, characterization and magnetic properties

Three new divalent metal organic frameworks (MOFs) derived from phosphonate coordination polymer, [Ni3(H2L)2(H2O)4]·3H2O 1, [Fe(H3L)(H2O)] 2 and [Mg3(H2L)2(H2O)4]·2H2O 3, (ligand: H5L=1-hydroxy-2-(3-pyridyl)ethylidene-1,1-diphosphonate acid, (H4C5N)CH2C(OH)(PO3H2)2), have been hydrothermally obtained and determined by single-crystal X-ray diffractions, elemental analysis, IR, XRD, TG–DTA. Fluorescent measurements reveal that compounds all display two fluorescent emissions centered at 377nm and 422nm for 1, 382nm and 424nm for 2 as well 383nm and 425nm for 3, respectively, caused by intraligand π*–π emission state of organic pyridine ring (λex=234nm). Magnetism data indicate that compound 1 exhibits spin canted antiferromagnetic exchange coupling between Ni(II) centers, while compound 2 shows alternating ferromagnetic and antiferromagnetic interactions between Fe(II) centers.