A New Family of Bimetallic Framework Materials Showing Reversible Structural Transformations

Three new bimetallic framework compounds, namely, (([Cd3(tn)4][Co(CN)6]2)·5H2O)∞ (1), ([Cd(tn)]3[Cr(CN)6]2)∞ (2), and ([Cu2(tn)2][Ru(CN)6]·4H2O)∞ (3), have been prepared in a very simple manner from the ligand 1,3-diaminopropane (tn), the hexacyanometalates [Co(CN)6]3−, [Cr(CN)6]3− and [Ru(CN)6]4−, and a metal(II) sulfate (MIISO4: M = Cd2+, Cu2+). They have been characterized by IR, X-ray diffraction, elemental analysis and immersion calorimetry. All three compounds have three-dimensional structures, with both the organic ligand and the cyanide groups acting as bridges. Compounds 1 and 3 have channels occupied by water molecules of crystallization. All three complexes are stable indefinitely when exposed to the air at room temperature; however, when compounds 1 and 3 are heated, they lose the water molecules of crystallization. The powder X-ray diffractograms of these dried and as yet unknown species are different from those of the original compounds. However, in a humid atmosphere both dried compounds readsorb water molecules and revert to the original structures, as shown by powder X-ray diffraction measurements. The adsorption properties of compounds 1 and 3 were studied using immersion calorimetry and in situ powder X-ray diffraction. In the case of compound 3 the heat of the structural transformation on rehydration was found to be ca. 19 ± 3 J/g.