Three Co(II)-containing coordination polymers displaying solvent determined entanglement structures and different ammonia and amines selective sensing properties

Thermosalient effect of a naphthalene diimide and tetrachlorocobaltate hybrid and changes of color and magnetic properties by ammonia vapor

An organic-inorganic hybrid metal halide (OIMH), namely the electron-deficient naphthalene diimide (NDI) and [CoCl₄]^2- hybrid (1), showed potential as a sensor for ammonia and amines, in addition to magnetic changes upon vapochromism. Crystal 1 exhibited thermosalient behavior such as leaping and movement, at around 130 °C, which could be explained to be associated with the removal of water molecules from the crystal lattice as shown by TGA and DSC. Compound 1 changed from green to black within 5 minutes when exposed to ammonia vapor, which was attributed to the radical formation in the NDI moiety as evidenced by ESR, and this phenomenon was preserved even when other mono- and di-alkylamines were applied. The exposure of 1 to ammonia resulted in a subsequent color alteration, progressing from black to a gradually dark orange after one day (1_NH3_1 day). This transformation was concomitant with the formation of [Co(NH₃)₆]³⁺ from [CoCl₄]^2-, leading to a modification of the magnetic properties from paramagnetic Co(II) (S = 3/2) to diamagnetic Co(III) (S = 0). Based on these findings, compound 1 represents the first example of an OIMH that exhibits thermosalient behaviour, color change, and magnetic conversion upon exposure to ammonia.

Solvent-Modulated Self-Assembly of Naphthalenediimide-Based Cd(II) Complexes and the Controllable Photochromism via Conformational Isomerization

Rational regulation of the properties of photochromic materials is a challenging and meaningful work. In the present work, NDI-based complexes, namely, [Cd_0.5(NDI)(HBDC)]·H₂O (1) and a series of conformational isomers of {[Cd(NDI)_0.5(BDC)]·MeCN}_n (2), were synthesized by varying the solvent conditions (H₂BDC = terephthalic acid, NDI = N,N'-bis(3-pyridylcarbonylhydrazine)-1,4,5,8-naphthalene diimide). Complex 1 exhibits a 0D mononuclear structure without photochromic behavior due to the bad conjugation of the naphthalene diimide moiety. The conformational isomers of complex 2 manifest a 3D network, showing ultra-fast photo-induced intermolecular electron transfer photochromic behavior under X-ray, UV, and visible light. However, they show different photochromic rates and coloring contrast upon photoirradiation, which originates from their difference in the distances of lone pair(COO)···π(NDI). This was realized via controlling the solvent ratio in the reaction system. In addition, compared to UV/X-ray light, 2 exhibits greater sensitivity to visible light and is an organic-inorganic hybrid material with photomodulated luminescence. Based on the excellent performance, complex 2 can be applied to filter paper, showing potential applications as an inkless printing medium and selective perception of ammonia and amine vapors in the solid state via different visual color changes.