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[摘要]：Crystals of the vanadyl phosphate hydrate Pb(VOPO4)(2)center dot 3H(2)O were synthesized by mild hydrothermal treatment and characterized by X-ray diffraction techniques, infrared spectroscopy, XPS, ICP,magnetic and heat capacity measurements. A new structure type (space group P2(1)/c (14), a = 10.292(4) angstrom, b = 7.552(3) angstrom, c = 12.557(5) angstrom, beta = 90.007(4)degrees, Z = 4 and V = 976.0(7) angstrom(3)) has been found. Pb(VOPO4)(2)center dot 3H(2)O exhibits a 3D open-framework structure where the lead and water molecules were located orderly in the channel. Magnetic measurements indicated the antiferromagnetic properties and the presence of predominant short-range interactions in the investigated temperature range of 2-300 K, which was further confirmed by heat capacity measurements. The magnetic exchange pathways between the V4+ magnetic ions are via the bridging phosphates and can therefore be classified as a V-O center dot center dot center dot O-V super-superexchange. Magnetic analysis shows that Pb(VOPO4)(2)center dot 3H(2)O is an interesting spin gapped antiferromagnet in a pure SSE system with a 3D open-framework crystal structure. Analysing the exchange couplings based on the extended Huckel tight binding calculations, it was possible to identify one dominant spin dimer interaction in Pb(VOPO4)(2)center dot 3H(2)O, which effectively produces a lower magnetic dimensionality. The magnetic data fit also shows that Pb(VOPO4)(2)center dot 3H(2)O can be taken to be a magnetic spin dimer system with inter-dimer coupling. It is a good example of effective magnetic dimensionality being reduced from the geometric characteristics of the crystal structure. In addition, a known compound beta-PbVO2PO4 can be synthesized with a different ratio of reactants, yet keeping all the other conditions the same as for Pb(VOPO4)(2)center dot 3H(2)O. Both compounds are formed as high quality crystals. For comparison, the infrared spectroscopy and XPS of beta-PbVO2PO4 and Pb(VOPO4)(2)center dot 3H(2)O are reported. |
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