Elucidating the Origins of a Range of Diverse Flexible Responses in Crystalline Coordination Polymers

Abstract

The mechanical adaptability of a family of six one-dimensional crystalline coordination polymers (CPs) of cadmium ([CdX2(3-X′py)2]n; 1: X = Br, X′ = Cl, 2: X = I, X′ = Cl, 3: X = I, X′ = Br, 4: X = Cl, X′ = I, 5: X = Br, X′ = I, and 6: X, X′ = I) to applied external force was examined, and a plethora of flexible responses was noticed. While two of the six CPs (4 and 6) were slightly elastic, the remaining four CPs (1–3 and 5) presented variable plastic deformation; three of these (1–3) displayed exceptional crystal flow, and one (2) demonstrated unprecedented ductility of crystalline metal–organic material. The feature was examined by theory and custom-designed experiments, and it was shown that specific and directional intermolecular interactions are not only the most influential structural feature in determining the type of mechanical responses (i.e., elastic vs plastic), with interlocking of adjacent molecules playing only a supportive role, but also an unavoidable tool for dialing-in a diversity of plastic responses in Cd(II) coordination polymers.