Hydrated Cr(V) Peroxychromates M3CrO8·XH2O (M = Li, Na, Cs): Model 3d1 Systems Exhibiting Linear Chain Behavior and Antiferromagnetic Interactio
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- 作者：Brant Cage ; William Geyer ; Khalil A. Abboud ; and Nar S. Dalal
- 刊名：Chemistry of Materials
- 出版年：2001
- 出版时间：March 2001
- 年：2001
- 卷：13
- 期：3
- 页码：871 - 879
- 全文大小：242K
- 年卷期：v.13,no.3(March 2001)
- ISSN：1520-5002
文摘
A new class of Cr(V) peroxychromates, those containing waters of hydration (Li3CrO8·10H2O, Na3CrO8·14H2O and Cs3CrO8·3H2O), has been synthesized and characterizedby single-crystal X-ray diffraction, magnetic susceptibility, specific heat, and EPR techniques.The Li salt crystallizes into the orthorhombic (Cmcm) group, whereas the Na and Cs saltsexhibit the triclinic (P
) and monoclinic P2(1)/n space groups, respectively. Crystal structureanalysis indicated the availability of low-dimensional spin-exchange pathways. The orientation dependence of the EPR line width exhibited the (3 cos2 
- 1)4/3 behavior characteristicof linear chain compounds, with = 0 coinciding with the chain axis. Correlation of theEPR and X-ray data allowed for the explicit determination of the magnetic chain axes inthe crystal and molecular frameworks. Magnetic susceptibility, 
, measurements on orientedsingle crystals yielded negative values for the Curie-Weiss temperatures, indicatingdominant antiferromagnetic interactions. The data yielded the Curie constants that appearto be inversely related to the number of waters of hydration in the crystal structure; thisobservation is not yet understood. Correlation of the EPR line width, nearest neighbordistances, and Curie constants attested to the essential correctness of the linear chain spinexchange and dipolar fields in the Li and Cs salts, and to a lesser extent also for the Nasalt. The specific heat data indicated that all these compounds have the potential to be usefulfor devices requiring strong heat sinks as well as magnetic refrigerants in the 250 mKtemperature regime. They appear to be good as model systems for theoretical investigationson low-dimensional magnetic lattices and for understanding aspects of Cr(VI)-based catalysisand carcinogenesis.
) and monoclinic P2(1)/n space groups, respectively. Crystal structureanalysis indicated the availability of low-dimensional spin-exchange pathways. The orientation dependence of the EPR line width exhibited the (3 cos2 - 1)4/3 behavior characteristicof linear chain compounds, with = 0 coinciding with the chain axis. Correlation of theEPR and X-ray data allowed for the explicit determination of the magnetic chain axes inthe crystal and molecular frameworks. Magnetic susceptibility, , measurements on orientedsingle crystals yielded negative values for the Curie-Weiss temperatures, indicatingdominant antiferromagnetic interactions. The data yielded the Curie constants that appearto be inversely related to the number of waters of hydration in the crystal structure; thisobservation is not yet understood. Correlation of the EPR line width, nearest neighbordistances, and Curie constants attested to the essential correctness of the linear chain spinexchange and dipolar fields in the Li and Cs salts, and to a lesser extent also for the Nasalt. The specific heat data indicated that all these compounds have the potential to be usefulfor devices requiring strong heat sinks as well as magnetic refrigerants in the 250 mKtemperature regime. They appear to be good as model systems for theoretical investigationson low-dimensional magnetic lattices and for understanding aspects of Cr(VI)-based catalysisand carcinogenesis.