Magnetic study of .ALPHA.- and .BETA.-diamminecopper(II) chlorides and bromides.

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The magnetic susceptibilities, χ, of α- and β-Cu(NH3)2X2(X=Cl, Br) were measured from 4.2 to 360 K. Those of β-Cu(NH3)2X2 obeyed the Curie-Weiss law above 50 K. The Weiss constants and effective Bohr magneton numbers are −3.5(±1) K and 1.75(±0.01) for X=Cl, and −9.7 K and 1.82 for X=Br. α-Cu(NH3)2Cl2 showed a rounded maximum for χ at 30 K. A linear Heisenberg model with the parameters, J=−23.5(±1) K and g=2.03(±0.03), gave good agreement with observations. α-Cu(NH3)2Br2 had a peak for χ at 47(±2) K. This temperature is probably a Neèl temperature. The strong magnetic interaction of the α-form compounds is related to the compressed coordination octahedron of [Cu(NH3)2X4]2−. All samples used were solid solutions of Cu(NH3)2X2 and NH4X. An analysis of χ suggests that the Cu2+ cations in α-Cu(NH3)2Cl2 are distributed inhomogeneously over a short range. A similar inhomogeneity was also found for the β-Cu(NH3)2X2 samples. In this sense, the β-form may be better described as a solid solution of α-Cu(NH3)2X2 and NH4X rather than as a dimorph.
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