Hydrated Cr(V) peroxychromates M(3)CrO8 center dot XH2O (M = Li, Na, Cs): Model 3d(1) systems exhibiting linear chain behavior and antiferromagnetic interactions

A new class of Cr(V) peroxychromates, those containing waters of hydration (Li-3-CrO8 10H2O, Na3CrO8. 14H(2)O and Cs3CrO8. 3H(2)O), has been synthesiz ed and characterized by single-crystal X-ray diffraction, magnetic suscepti bility, specific heat, and EPR techniques. The Li salt crystallizes into th e orthorhombic (Cmcm) group, whereas the Na and Cs salts exhibit the tricli nic (P (1) over bar) and monoclinic P2(1)/n space groups, respectively. Cry stal structure analysis indicated the availability of low-dimensional spin- exchange pathways. The orientation dependence of the EPR line width exhibit ed the (3 cos(2) theta - 1)(4/3) behavior characteristic of linear chain co mpounds, with theta = 0 coinciding with the chain axis. Correlation of the EPR and X-ray data allowed for the explicit determination of the magnetic c hain axes in the crystal and molecular frameworks. Magnetic susceptibility chi, measurements on oriented single crystals yielded negative values for t he Curie-Weiss temperatures, indicating dominant antiferromagnetic interact ions. The chi data yielded the Curie constants that appear to be inversely related to the number of waters of hydration in the crystal structure; this observation is not yet understood. Correlation of the EPR line width, near est neighbor distances, and Curie constants attested to the essential corre ctness of the linear chain spin exchange and dipolar fields in the Li and C s salts, and to a lesser extent also for the Na salt. The specific heat dat a indicated that all these compounds have the potential to be useful for de vices requiring strong heat sinks as well as magnetic refrigerants in the 2 50 mK temperature regime. They appear to be good as model systems for theor etical investigations on low-dimensional magnetic lattices and for understa nding aspects of Cr(VI)-based catalysis and carcinogenesis.