Novel Gallium Phosphate Framework Encapsulating Trinuclear Mn3(H2O)6O8 Cluster:  Hydrothermal Synthesis and Characterization of Mn3(H2O)6Ga4(PO4)6

2000-03-17T00:00:00Z (GMT) by Kuei-Fang Hsu Sue-Lein Wang
A new manganese gallium phosphate, Mn3(H2O)6Ga4(PO4)6, has been synthesized under hydrothermal conditions at 150 °C and characterized by single-crystal X-ray diffraction, thermogravimetric analysis, magnetic susceptibility, and electron paramagnetic resonance (EPR) spectroscopy. It crystallized in the monoclinic space group, P21/n, with a = 8.9468(4) Å, b = 10.1481(5) Å, c = 13.5540(7) Å, β = 108.249(1)°, and Z = 2. The compound is unusual in that it is not only the first nonorganically templated MnGaPO phase but also the first instance where edge-shared trinuclear manganese−oxygen clusters are encapsulated in a metal phosphate lattice. The trimer involves a central Mn(H2O)4O2 octahedron, which links to two Mn (H2O)2O4 octahedra at trans edges. The Mn3(H2O)6O8 clusters reside in tunnels built from GaO5 trigonal bipyramids and PO4 tetrahedra. Our magnetic study revealed that superexchange interactions occurred between the neighboring MnII centers. A good fit of the magnetic susceptibility data for the isolated trimers was obtained by using a derived expression based on Van Vleck's equation. Unlike all existing linear trinuclear MnII complexes, the χΜT product in the range 8−4 K remains at a constant value corresponding to one spin S = 5/2 per three MnII centers. The Curie behavior at such low temperatures has been confirmed by EPR data. According to the thermogravimetric analysis/differential thermal analysis (TGA/DTA) results, the title compound is thermally stable up to ca. 200 °C.