Tuning the magnetic properties of transition metal MOFs by metal–oxygen

M. C. BERNINI; A.E. PLATERO-PRATS; N. SNEJKO; E. GUTIERREZ-PUEBLA; A. LABRADOR; R. SAEZ-PUCHE; J. ROMERO; M. A. MONGE

CRYSTENGCOMM

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2012 vol. 14 p. 5493 - 5504

1466-8033

Five novel metal organic frameworks, belonging to three structural types, have been obtained hydrothermally. Three of them, with formula [M3(hfipbb)2(OH)2(H2O)] (M = Mn, Co, Ni; hfipbb = 4,49-(hexafluoroisopropylidene)bis(benzoate) dianion) belong to the first structural type. The crystal structure of the Mn-based compound was obtained from single crystal synchrotron X-ray diffraction data, while the isostructural compounds of Co and Ni were studied by means of Rietveld analysis using powder X-ray diffraction data. The magnetic behavior of the compounds with M = Co and Ni is characterized by the onset of long-range ferromagnetic order at very low temperature with Curie temperatures near 8 and 2.5 K, respectively. Such spontaneous magnetization seems to be preceded by low-dimensional magnetic interactions, due to the nature of the secondary building units (SBUs) of the structure, which are triple chains built by M3O14 units. Structural and topological analyses of [Mn2(hfipbb)2(H2hfipbb)] and [Co2(hfipbb)2(H2hfipbb)] (2 and 3 structural types, respectively; H2hfipbb = 4,49-(hexafluoroisopropylidene)bis(benzoic acid)) demonstrate that the packing of the rod-shaped SBUs in 2 prevents the framework interpenetration giving rise to a bnn net whereas 3 is a 2-fold interpenetrated pcu net with isolated paddle-wheel clusters as SBUs pcu. Concerning the magnetic behavior of 2 and 3, antiferromagnetic interactions observed at very low temperature (magnetic susceptibility maximum at 2.8 and 18 K, respectively) are confined to the secondary building units.