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.

Crystals of a family of six one-dimensional (1D) coordination polymers of cadmium(II) with cyanopyridines [[CdX₂L₂]_n, where X = Cl, Br, or I and L = 3-cyanopyridine (3-CNpy) or 4-cyanopyridine (4-CNpy)] presented a variety of morphologies and mechanical responses with dominant two-dimensional (2D) anisotropic flexibility, which has not been previously reported. All mechanically adaptable crystals were 2D flexible and displayed a variety of direction-dependent responses; in addition to 2D isotropic flexibility observed for solely elastic materials, 2D anisotropic flexibility was noticed for both elastic and elastic → plastic crystals. The consequences of fine and controlled structural variations on mechanical behavior were additionally explored via microfocus single-crystal X-ray diffraction and complementary theoretical studies, revealing that the relative strength and direction of the hydrogen bonding interactions were the key parameters in delivering a specific mechanical response.

In order to link coordination complexes via halogen bonds and to test the limit of halogen-bond interactions in metal-containing crystalline solids, a series of thirteen new acac complexes of Co^II and Ni^II with small halogen-bearing aromatic ligands, namely 3-halopyridines, 2-halopirazines and 5-halopyrimidine were prepared. Ligands having a single aromatic ring were used to limit the influence of π–π stacking on the resulting crystal structure, while fine-tuning of the electron density at the halogen atom σ-hole was achieved via two routes: (i) by changing the position of the additional nitrogen heteroatom on the aromatic ring, and (ii) by utilizing different transition metal ions. The moderate ‘activation’ of the halogen atom produced the desired halogen interaction in a limited number of supramolecular events. Two supramolecular links, C–X⋯O and C–H⋯O, were shown to have a larger influence on the overall supramolecular assembly, and their role could be explained on the basis of calculated molecular electrostatic potential values. Slight electronic changes introduced by metal–cation exchange revealed an additional handle for achieving a switch between different supramolecular interactions and architectures.

A novel synthetic approach toward a poorly explored bioorganometallic consisting of ferrocene-1,1′-diamine bearing structurally and chirally diverse amino acid sequences is reported. Until now, ferrocene-1,1′-diamine was suitable for accommodating only identical amino acid sequences at its N-termini, leading to the symmetrically disubstituted homochiral products stabilized through a 14-membered intramolecular hydrogen-bonded ring as is seen in antiparallel β-sheet peptides. The key step of the novel synthetic pathway is the transformation of Ac–Ala––Fn–OH (5) (Fn = 1,1′-ferrocenylene) to orthogonally protected Ac–Ala––Fn–Boc (7). The spectroscopic analysis (IR, NMR, CD) of the novel compounds, corroborated with DFT studies, suggests the interesting feature of the ferrocene-1,1′-diamine scaffold. The same hydrogen-bonding pattern, i.e. a 14-membered hydrogen-bonded ring, was determined both in solution and in the solid state, thus making them promising, yet simple scaffolds capable of mimicking β-sheet peptides. In vitro screening of potential anticancer activity in Hep G2 human liver carcinoma cells and Hs 578 T human breast cancer cells revealed a cytotoxic pattern for novel compounds (150–500 μM) with significantly decreased cell proliferation.