Incongruent Melting and Vitrification Behaviors of Anionic Coordination Polymers Incorporating Ionic Liquid Cations

Crystal Engineering of Cyanoborate-Bridged Cubane-Type Tetranuclear Ru Complex: Synthesis, Pseudopolymorphism, and Coordination Polymer Formation

Cyanoborate anions are versatile bridging ligands that lead to structurally diverse compounds from a crystal engineering perspective. Herein, we report the synthesis of a cubane-type tetranuclear Ru complex, [Ru4(Cp)4{B(CN)4}4] (1, Cp = C5H5), obtained by photoirradiation of [Ru(Cp)(C6H6)]B(CN)4 in solution or by the reaction of [CpRu(MeCN)3]+ with KB(CN)4. This complex served as a host for various solvents, generating different pseudopolymorphs, including 1·nCH2Cl2 (n = 1, 2, 3), 1·0.5C6H6, 1·C6H5Me, and 1·3THF upon recrystallization. Moreover, the four free cyano groups in 1 allow it to act as a bridging ligand, facilitating the formation of 1D and 2D coordination polymers through reactions with transition metal complexes.

Functional metal-organic liquids

For decades, the study of coordination polymers (CPs) and metal-organic frameworks (MOFs) has been limited primarily to their behavior as crystalline solids. In recent years, there has been increasing evidence that they can undergo reversible crystal-to-liquid transitions. However, their "liquid" states have primarily been considered intermediate states, and their diverse properties and applications of the liquid itself have been overlooked. As we learn from organic polymers, ceramics, and metals, understanding the structures and properties of liquid states is essential for exploring new properties and functions that are not achievable in their crystalline state. This review presents state-of-the-art research on the liquid states of CPs and MOFs while discussing the fundamental concepts involved in controlling them. We consider the different types of crystal-to-liquid transitions found in CPs and MOFs while extending the interpretation toward other functional metal-organic liquids, such as metal-containing ionic liquids and porous liquids, and try to suggest the unique features of CP/MOF liquids. We highlight their potential applications and present an outlook for future opportunities.

Organometallic Ionic Liquids Containing Sandwich Complexes: Molecular Design, Physical Properties, and Chemical Reactivities

Ionic liquids (ILs) are salts with low melting points and are useful as electrolytes and solvents. We have developed ILs containing cationic metal complexes, which form a family of functional liquids that exhibit unique physical properties and chemical reactivities originating from metal complexes. Our study explores the liquid chemistry in the field of coordination chemistry, where solid-state chemistry is currently the main focus. This review describes the molecular design, physical properties, and reactivities of organometallic ILs containing sandwich or half-sandwich complexes. This paper mainly covers stimuli-responsive ILs, whose magnetic properties, solvent polarities, colors, or structures change by the application of external fields, such as light, heat, and magnetic fields, or by reaction with coordinating molecules.