Kinetics of solid state nitrito-nitro bond isomerization in [Co(NH3)5ONO]Br2 at high pressures

The kinetics of the solid state bond isomerization in Co(NH₃)₅ONO]Br₂ is studied by quantitative IR spectroscopy in diamond anvils at pressures of 1.0, 2.0, 3.0, and 4.0 GPa and atmospheric pressure and at temperatures of 7, 16, 25, and 34°C. The pressure dependence of the reaction rate constant is adequately described by the equation inK = a + bP + cP². Although solid state isomerization is accompanied by an increase in molar volume, the hydrostatic pressure accelerates the reaction. The reason for this unusual effect must be sought in the anisotropy of structure deformation in the course of bond isomerization; the total increment in volume is comparatively small (0.84%), but the structure is drastically compressed (by 3.4%) in a number of crystallographic directions, and the crystal structure is compressed under pressure in the same directions. Translated fromZhumal Strukturnoi Khimii, Vol. 39, No. 5, pp. 934–946, September–October, 1998.