Molten phases of metal−organic networks offer exciting opportunities for using coordination chemistry principles to access liquids and glasses with unique and tunable structures and properties. Here, we discuss general thermodynamic strategies to provide an increased enthalpic and entropic driving force for reversible, low-temperature melting transitions in extended coordination solids and illustrate this approach through a systematic study of a series of bis(acetamide)-based networks with record-low melting temperatures. The low melting temperatures of these compounds are the result of weak coordination bonds, conformationally flexible bridging ligands, and weak electrostatic interactions between spatially separated cations and anions, which collectively reduce the enthalpy and increase the entropy of fusion. Through a combination of crystallography, spectroscopy, and calorimetry, enthalpic trends are found to be dictated by the strength of coordination bonds and hydrogen bonds within each compound, while entropic trends are strongly influenced by the degree to which residual motion and positional disorder are restricted in the crystalline state. Extended X-ray absorption fine structure (EXAFS) and pair distribution function (PDF) analysis of Co(bba) 3 [CoCl 4 ] [bba = N,N′-1,4-butylenebis(acetamide)], which features a record-low melting temperature for a three-dimensional metal−organic network of 124 °C, provide direct evidence of metal−ligand coordination in the liquid phase, as well as intermediate-and extended-range order that support its network-forming nature. In addition, rheological measurements are used to rationalize differences in glass-forming ability and relaxation dynamics. These results provide new insights into the structural and chemical factors that influence the thermodynamics of melting transitions of extended coordination solids, as well as the structure and properties of coordination network-forming liquids.

“Open” sites on the nodes of UiO-66 are converted to catalytically active Zr-OOH and can coordinate with solvent/products.

Glassy phases of framework materials feature unique and tunable properties that are advantageous for gas separation membranes, solid electrolytes, and phase-change memory applications. Here, we report a new guanidinium organosulfonate hydrogen-bonded organic framework (HOF) that melts and vitrifies below 100 °C. In this low-temperature regime, non-covalent interactions between guest molecules and the porous framework become a dominant contributor to the overall stability of the structure, resulting in guest-dependent melting, glass, and recrystallization transitions. Through simulations and X-ray scattering, we show that the local structures of the amorphous liquid and glass phases resemble those of the parent crystalline framework.

Cyanea nozakii is a common bloom-forming Scyphomedusa in coastal waters of China. To understand the diet of this jellyfish and its trophic relationship with other zooplankton groups, stable isotope δ13C and δ15N values of C. nozakii in the bloom area within the northern East China Sea (ECS) in August 2017 were analyzed. We examined: first, the size-based variation in C. nozakii stable isotope values, second, the contributions of different food sources to the C. nozakii diet, and possible size-based dietary shifts in individual C. nozakii and, third, the contribution of gelatinous prey to the C. nozakii diet. Isotope values of differently sized C. nozakii ranged from −18.81 to −16.88‰ for δ13C and from 8.23 to 10.46‰ for δ15N. A significant change in δ15N values implies that the trophic position and the diet of C. nozakii changed as body size increased. The MixSIAR model indicated that C. nozakii underwent a dietary shift during growth, from a seston-dominant diet in smaller medusae to a zooplankton-dominant diet in larger medusae. Copepods were an important food source for C. nozakii, irrespective of size. The mean proportions of gelatinous zooplankton increased significantly in the C. nozakii diet with increasing C. nozakii diameter, suggesting that larger C. nozakii consumed more gelatinous prey. The diet of larger C. nozakii included 9.54% Nemopilema nomurai and 9.53% small medusae. The results suggest that intraguild predation among these jellyfish exist in the northern ECS.