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
B. Cage et al., 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, CHEM MATER, 13(3), 2001, pp. 871-879
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.