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

• Three MOFs based on diphosphonate coordination polymer are obtained.
• The fluorescent measurements reveal all the three compounds display two fluorescent emission peaks.
• Magnetism data indicate compound 1 is a canted antiferromagnet and compound 2 is a metamagnet.

Three new divalent metal organic frameworks (MOFs) derived from diphosphonate coordination polymers, [Ni3(H2L)2(H2O)4]·3H2O 1, [Fe(H3L)(H2O)] 2 and [Mg3(H2L)2(H2O)4]·2H2O 3, (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, PXRD, TG–DTA. The single-crystal X-ray diffractions reveal that compound 1 owns a novel 2-D layer structure constructed by 1-D ladder-like inorganic chain with magnetic topology building blocks [Ni4(O–P–O)4]n via pyridine moieties linkage. Compounds 2 and 3 are the first examples of Fe(II) and Mg(II) phosphonates based on ligand H5L, respectively. Compound 2 exhibits a 3-D supramolecular network built from 1-D ladder-like inorganic chain with 4- and 8-membered rings through hydrogen bonds, the organic pyridine ring holding close to both sides of the chain. Compound 3 displays a reticulate 2-D layer structure containing 8- and 16-membered rings built from novel 1-D right-handed helical chain. Moreover the room-temperature fluorescent measurements reveal that all the compounds display two fluorescent emissions centered at 377 nm and 422 nm for 1, 382 nm and 424 nm for 2 as well 383 nm and 425 nm for 3, respectively, caused by intraligand π*–π emission state of organic pyridine ring (λex = 234 nm). 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 within 1-D topology Fe(II)-chain, showing promising potential as magnetic materials.

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 377 nm and 422 nm for 1, 382 nm and 424 nm for 2 as well 383 nm and 425 nm for 3, respectively, caused by intraligand π*–π emission state of organic pyridine ring (λex = 234 nm). 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.Figure optionsDownload as PowerPoint slide