Reversible thermo- and mechanochromic behaviour in a 3D hydrogen bonded discrete complex

A 3D hydrogen-bonded Co(II) complex {Co(34pbz)2·(H2O)4}n (1), where 34pbz is 3-(4-pyridyl)benzoate, is found to exhibit thermo- and mechanochromic behaviour. The thermochromic behaviour in the temperature range of 30–120 °C may be attributed to the disruption of the supramolecular environments or metal to ligand charge transfer transitions. Above 150 °C this behaviour is attributed to loss of coordinated water molecules from the Co(II) which has the effect of altering the visible d–d electronic transitions. Interestingly, when crystals of 1 are ground, a purple colour is observed under ambient light. This mechanochromic property is ascribed to change in the crystal field around the Co(II) centre. These effects are fully reversible as suggested by PXRD and thermal analysis studies.

Graphical abstractA 3D hydrogen bonded Co(II) discrete complex of 3-(4-pyridyl)benzoate shows reversible thermochromic and mechanochromic behaviour. This phenomenon has been attributed to the disruptions of the supramolecular environments within the hydrogen bonded network.Figure optionsDownload full-size imageDownload as PowerPoint slide