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 [CoCl 4 ] 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_NH 3 _1 day ). This transformation was concomitant with the formation of [Co(NH 3 ) 6 ] 3+ from [CoCl 4 ] 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. An NDI-based Co( ii )-OIMH represents a new combination of functional materials, demonstrating both thermosalient effects in the solid state and sensing abilities for ammonia through changes in color and magnetism.