Reversible nitro–nitrito inter-conversion in a simple mono-nuclear nickel(II) complex [NiII{C6H4(NH2)2}2(NO2)2] in the solid state

A simple mono-nuclear nickel(II) complex [NiII{C6H4(NH2)2}2(NO2)2] (1) has been synthesized from an aqueous solution containing nickel chloride, sodium nitrite and ortho-phenylenediamine (opda). When crystals of compound 1 are heated in the temperature range of 110–120 °C for 5 min, their brown color changes to blue, that is accompanied by the conversion of nitro group (N-coordinated) in compound 1 into nitrito group (O-coordinated) in compound [NiII{C6H4(NH2)2}2(ONO)2] (2). On cooling, the nitrito compound 2 goes back to parent nitro-compound 1.

Graphical abstractCompound [NiII(C6H4(NH2)2)2(NO2)2] (1) exhibits the thermochromism in solid state driven by reversible linkage isomerization of –NO2 to –ONO. This is accompanied by color change from red to blue as is evidenced from the pictures of crystals at different stages.Figure optionsDownload full-size imageDownload as PowerPoint slide