Studies of the Mechanism of a Single-Crystal-to-Single-Crystal Reversible Dehydration of a Copper Carboxylate Framework

The open-framework copper carboxylate chloride [Cu7Cl2(THFTC)2(OH)4(H2O)2](H2O)4 (THFTC = tetrahydrofuran-2,3,4,5-tetracarboxylate) was synthesized hydrothermally and was characterized structurally and magnetically. The centrosymmetric three-dimensional framework has channels filled with water. Single crystals kept under vacuum at different temperatures (room temperature, 65 °C, and 105 °C) remain single while the structure is dehydrated in steps accompanied by distortions of the framework and repositioning of the water molecules and chlorine atoms. The dehydrated compounds are acentric and have two distinct channels with different inner environments. These single-crystal-to-single-crystal transformations are reversible evidenced by the structural studies of the dehydrated single crystals after exposure to humid air. Magnetic measurements showed antiferromagnetic coupling between the Cu2+ ions. Homometallic ferrimagnetism is observed below Tc of 2.4 and 3.4 K for the as-synthesized and the dehydrated samples, respectively.