Solid-State Replacement in the Polyhedra of Cu2+, Ni2+, and Co2+ upon Dehydration/Rehydration Processes Associated with a Color Change in Three Isomorphous Materials with 5,5'-Indigodisulfonate

The significance of thermochromic materials in a wide range of applications makes their research and development highly desirable. Herein, three new thermochromic isomorphous supramolecular materials based on the 5,5'-indigodisulfonate ion of the indigo carmine dye, with formulas [Cu(H2O)6](C16H8N2O8S2)·2H2O (1), [Ni(H2O)6](C16H8N2O8S2)·2H2O (2), and [Co(H2O)6](C16H8N2O8S2)·2H2O (3), are reported. These materials exhibit thermochromic properties, with a color change from red-bronze to grayish-red after the first step of their dehydration process completed around 80 °C (conversion of 1 to [Cu(H2O)2(C16H8N2O8S2) (1')]), and then, this grayish-red color becomes lighter after the second step, which is completed around 230 °C (conversion of 1' to [Cu(C16H8N2O8S2)] (1d)). The 1, 1', and 1d phases have different crystal structures but similar tetragonal bipyramidal geometries around the copper ions. These dehydrated phases rehydrate by exposure to a higher humidity level. Solid-state UV-visible spectroscopy, thermogravimetric analysis, infrared spectroscopy, and X-ray powder diffraction analyses shed light on the structural and chemical changes accompanying the color change of 1, 2, and 3 to their partial dehydrated phases 1', 2', and 3', respectively. These transformations occur with the small modification of the charge transfer energy in the 5,5'-indigodisulfonate ions, indicating the potential of dye-based metall-organic materials for chromic properties.

Exploring Reversible Thermochromic Behavior in a Rare Ni(II)-MOF System

Thermochromic metal-organic frameworks (MOFs) are promising functional materials for a wide range of applications due to their ability to exhibit color variation under external temperature stimuli, yet the development of them with high cyclability and efficient regeneration processes remains challenging. Here, presented is a rare example of an ultrastable Ni(II)-MOF exhibiting an unprecedented reversible four-step color change between two complementary colors in a wide temperature range, which could be repeated for at least 500 cycles without losing crystallinity and thermochromic performance. Notably, the regeneration can be achieved within 1 min by simply letting the crystals cool naturally in the air, facilitated by the unique nature of the channels' inner surface. The reversible thermochromic behavior is owing to a series of reversible crystal structure changes with temperature, including the stepwise dehydration/rehydration process, and structural changes. This work facilitates the future development of more MOF-based reversible thermochromic materials with excellent performance and improved practical applicability.

A stimuli responsive multifunctional ZMOF based on an unorthodox polytopic ligand: reversible thermochromism and anion triggered metallogelation

A novel Cd(ii)-ZMOF with a unique sodalite topology has been successfully designed and synthesized using a flexible polytopic compartmental ligand. The microporous complex contains 1D hexagonal channels with large void space for the accommodation of guest molecules. This work demonstrates a new paradigm for designing and functionalizing zeolite-type frameworks. The triconnected linker forms coordination polymer gels in the presence of Cd2+ and the gelation was controlled by the presence of specific anions. They possess good thermal stability and exhibit thixotropic behavior. Optical properties revealed that the complex is exclusively thermochromic and undergoes a reversible transition at 80 °C, changing its color from yellow to orange red. Owing to the large voids in the framework, the complex can serve as a host for use in dye adsorption. Thus this paper offers a new MOF material with exceptional chromic behavior, gelation properties and adsorption capability for the development of high performance multifunctional materials.

Reversible Thermochromism of Nickel(II) Complexes and Single-Crystal-to-Single-Crystal Transformation

A molecular Ni(II)-NNN pincer complex (1) exhibited unprecedented reversible single-crystal-to-single-crystal transformation and color change upon heating and cooling due to a subtle change in the N-Ni(II) bond length and ligand conformation. UV-vis, thermogravimetric, differential scanning calorimetry, single-crystal structural data, temperature-dependent powder X-ray diffraction, and Raman and computational studies supported the structural change of the Ni(II) complex with temperature.

Modular triazine-based carborane-containing carboxylic acids - synthesis and characterisation of potential boron neutron capture therapy agents made of readily accessible building blocks

Based on a modular combination of s-triazine, the well-known 9-mercapto-1,7-dicarba-closo-dodecaborane(12) and commercially available carboxylic acids, namely thioglycolic acid, glycine, and N_α-Boc-l-lysine, several carboxylic acid derivatives were synthesised and fully characterised. The thioglycolic acid derivative was introduced into a peptide hormone by solid phase peptide synthesis. High activity and selective internalisation into peptide receptor-expressing cells was observed. With a very high boron content of twenty boron atoms, these derivatives are interesting as selective Boron Neutron Capture Therapy (BNCT) agents.

Syntheses of mono and bimetallic cyamelurate polymers with reversible chromic behaviour

MOPs and MMOPs were synthesized in water and their crystals exhibit switchable chromic behaviour and reversible solid-state structural transformations.

Naked-eye detection and thermochromic properties of Cu(ii)-3,3′-thiodipropionate complexes with benzimidazole

Two novel coordination complexes were synthesized and characterized. Solvent sensing and their thermochromic properties were studied. Complex 1 can be used as a naked-eye sensor for methanol. Complex 2 may be used as a DMF sensor. The thermochromic behaviors of complexes 1 and 2 were investigated.

A series of metal–organic frameworks containing diverse secondary building units derived from a flexible triazine-based tetracarboxylic ligand

Five new coordination polymers containing diverse SBUs derived from a flexible triazine-based tetracarboxylic acid have been solvothermally synthesized and characterized.