Effect of pressure on the nitro-nitrito linkage isomerism in solid Ni(en)2(NO2)2

The equil. between red dinitro and violet dinitrito forms of Ni(en)2(NO2)2 was studied by observing the shift and decrease of the 500 and 800 nm bands (room temp. to 124°) at 1-30 kbars. A red → violet transition occurs at 98-116° and the large temp. interval suggests a high kinetic barrier (heat of conversion 1.47 ± 0.07 kcal/mol). Increasing pressure favors the nitro form. The complex Ni(N,N-dieten)2(NO2)2 (N,N'-diethylethylenediamine = N,N'-dieten) remains in the nitrito form ≤75 kbar due to larger steric factors.