Thermochromic nitro–nitrito interconversion mediated by weak-linked amide in nickel (II) diaminodiamide complexes in the solid state

Abstract

The red-violet nickel (II) complex [Ni (C 8 H 18 N 4 O 2 ) (NO 2 ) 2 ]·H 2 O ( 3 ) was synthesized from an aqueous solution containing nickel chloride, sodium nitrite and 4,7-diazadecanediamide ( 1 ). The NO 2 − ions in compound 3 are bound to the metal center through the nitrogen atoms. On heating the solid sample of compound 3 , the nitro anion rotates to give nitrito coordination and changes the compound color from red-violet to blue. Significantly, the structure transformation along with the color change is a reversible process. For purposes of comparison, the green nickel (II) complex [Ni (C 10 H 22 N 4 O 2 ) (H 2 O) 2 ]·2 (NO 2 )·2H 2 O ( 4 ) was synthesized from an aqueous solution containing nickel chloride, sodium nitrite and 4,7-dimethyl-4,7-diazadecanediamide ( 2 ). The NO 2 − ions are not coordinated to the nickel metal center. On heating the solid complex 4 , neither color change nor spectral modifications were observed. The red-violet nickel (II) complex [Ni(C 8 H 18 N 4 O 2 )(NO 2 ) 2 ] · H 2 O ( 3 ) was synthesized from an aqueous solution containing nickel chloride, sodium nitrite and 4,7-diazadecanediamide. On heating the solid sample of compound 3 , the nitro anion rotates to give nitrito coordination and changes the compound color from red-violet to blue. ► The solid state thermochromic behavior assisted by the weak-linked amide group of Ni(II) diaminodiamide complexes was reported. ► The reversible nitro-nitrito interconversion in nickel(II) complex provide a new class of thermochromic materials with diaminodiamide ligands. ► The nickel(II) complex is of special interest in the design of devices for visual color change with temperature.