Synthesis of [NH<sub>4</sub>]MnCl<sub>2</sub>(OAc) and [NH<sub>4</sub>]<sub>2</sub>MnCl<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub> by Solvothermal Dehydration and Structure/Property Correlations in a One-Dimensional Antiferromagnet
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The utility of the solvothermal dehydration strategy whereby superheated acetonitrile reacts with water of hydration to form ammonium acetate is demonstrated in the synthesis of [NH4]MnCl2(OAc), I, and [NH4]2MnCl4(H2O)2, II, from MnCl2·4H2O. The structure of I is shown to crystallize in the monoclinic space group C2/c (No. 15) with a = 15.191(6) Å, b = 7.044(2) Å, c = 13.603(6) Å, β = 107.31°, V = 1389.7(9) cm-1, and Z = 8. The structure of II crystallizes in the space group I4/mmm (No. 139) with a = 7.5250(5) Å, b = 8.276(2) Å, V = 468.6(1) cm-1, and Z = 2. Both structures exhibit extensive hydrogen bonding that controls both local Mn−Cl bonding and the interchain organization. I is shown to be a one-dimensional Heisenberg antiferromagnet with an intrachain exchange constant J/k = −2.39 K. This structure exhibits exchange coupling intermediate between the well-studied triply and doubly chloride-bridged one-dimensional manganese Heisenberg antiferromagnets. The structure/property correlation demonstrates a linear dependence of the exchange constant on the Mn−Cl−Mn bond angle, α, for α < 94°.
