The characterization of Co(urea)2Cl2·2H2O is reported. The crystal structure at ambient temperatures yields the following information: the chlorine, water, and urea group are coordinated, the urea being bound via the oxygen, to form an octahedral environment about the metal atom. Intermolecular hydrogen bonds between the coordinated chlorine and water ligands produce parallel infinite sheets which provide a two-dimensional exchange pathway. The sheets are separated by the urea ligands and may be considered as magnetically isolated from one another. Crystal data: space group P21/c, Z = 2, α = 7.397 (3) Å, b = 7.795(1) Å, c = 9.764(2) Å, β = 116.23(5) Å, V = 505 Å3, ρcalc = 1.87 g cm-3, ρobs = 1.88 g cm-3, R = 4.1% for 692 reflections. A λ anomaly in the specific heat was observed at 2.585 ± 0.005 K, and the critical parameters are characteristic of the two-dimensional Ising model. The zero-field susceptibilities have been measured over the temperature interval 1.2-30 K, and are consistent with antiferromagnetic ordering at 2.52 ± 0.05 K. The easy axis lies parallel to the monoclinic a axis, while hidden canting was observed parallel to the b axis. All the data have been analyzed consistently by the two-dimensional Ising model with the parameters ga = 7.0 ± 0.1, J/kB =- 2.1 ±0.05 K.



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© 1981 American Institute of Physics (AIP), All rights reserved.

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01 Jul 1981

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