Ligand Dependence of Magnetic Dimensionality in Chromium(IV) Complexes: Layered vs Three-Dimensional Antiferromagnets
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- 作者：Chris M. Ramsey ; Brant Cage ; Philan Nguyen ; Khalil A. Abboud ; and Nar S. Dalal
- 刊名：Chemistry of Materials
- 出版年：2003
- 出版时间：January 14, 2003
- 年：2003
- 卷：15
- 期：1
- 页码：92 - 99
- 全文大小：252K
- 年卷期：v.15,no.1(January 14, 2003)
- ISSN：1520-5002
文摘
X-ray diffraction and thermomagnetic measurements were made on two chromium(IV)complexes, Cr(dien)(O2)2·H2O and Cr(NH3)3(O2)2, with the view of understanding how theligands might change the magnetic dimensionality in such compounds. The magneticsusceptibility (
(T)) of Cr(dien)(O2)2·H2O was analyzed according to the quadratic Heisenbergmodel, H = -2J
i,j S(i)·S(j) - g
Hi Sz(i), which yielded J010 = -2.71 K, J100 = -2.86 K, J001= -2.88 K, g010 = 1.92, g001 = 1.96, and g100 = 1.82, where the indices coincide with alignmentof the crystal axes relative to the magnetic field. The heat capacity (Cp) and entropy datasupport this analysis and show it to be a layered, two-dimensional antiferromagnet. Incontrast, (T) and Cp(T) measurements on Cr(NH3)3(O2)2 showed it to be a classical three-dimensional antiferromagnet with sharp 
-type transitions at 8.80 and 8.46 K, respectively.Only 38% of the magnetic entropy is removed above TN = 8.46 K, implying that nominalshort-range interactions occur, but the system is dominated by three-dimensional magneticexchange. The data reveal how the ligand as well as lattice hydration affect the spindimensionality of Cr(IV) compounds.
(T)) of Cr(dien)(O2)2·H2O was analyzed according to the quadratic Heisenbergmodel, H = -2Ji,j S(i)·S(j) - gHi Sz(i), which yielded J010 = -2.71 K, J100 = -2.86 K, J001= -2.88 K, g010 = 1.92, g001 = 1.96, and g100 = 1.82, where the indices coincide with alignmentof the crystal axes relative to the magnetic field. The heat capacity (Cp) and entropy datasupport this analysis and show it to be a layered, two-dimensional antiferromagnet. Incontrast, (T) and Cp(T) measurements on Cr(NH3)3(O2)2 showed it to be a classical three-dimensional antiferromagnet with sharp -type transitions at 8.80 and 8.46 K, respectively.Only 38% of the magnetic entropy is removed above TN = 8.46 K, implying that nominalshort-range interactions occur, but the system is dominated by three-dimensional magneticexchange. The data reveal how the ligand as well as lattice hydration affect the spindimensionality of Cr(IV) compounds.