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.

An atomistic mechanism for elasto-plastic bending in molecular crystals

“…In recent years, a growing number of crystalline phases have been reported wherein single crystals of small molecules [10][11][12][13][14] and coordination polymers [15][16][17][18] exhibit a remarkable degree of mechanical exibility. Both mechanically elastic (reversible) 19 and plastic (irreversible) 20 single crystals have been identied, and dened according to the spontaneity of shape recovery upon release of the deforming force.…”

Plastic bending in a semiconducting coordination polymer crystal enabled by delamination

“…A number of recent studies have shown that many organics 14 – 22 and a few CP crystals 4 , 9 – 13 and some coordination complexes 23 – 25 can be mechanically deformable, through both elastic and plastic bending. Atomistic-scale analysis via micro-focus X-ray diffraction and spectroscopic methods shows that a delicate balance of different kinds of intermolecular interactions is the main cause of the observed mechanical behavior 4 , 10 , 12 , 26 – 31 . For the elastic bending, two general structural features are found in these crystals.…”

Flexible organic crystals. Understanding the tractable co-existence of elastic and plastic bending

“…11,12 Not surprisingly, immense interest has been attached to comprehending the mechanical properties of molecular materials in recent times. [13][14][15][16][17] Momentous progress attained in this field owes much to the systematic and earnest efforts made to gain significant insights into precise mechanisms that govern the structural and mechanical properties of molecular materials. 18 Such understanding is imperative to attain predictable mechanical properties in crystalline materials.…”