Kinetics of solid state nitrito-nitro bond isomerization in [Co(NH3)(5)ONO]Br-2 at high pressures

The kinetics of the solid state bond isomerization in [Co(NH3)(5)ONO]Br-2 i s 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 degrees C. The pressure dependence of the reaction rate c onstant is adequately described by the equation lnK = a + bP + cP(2). Altho ugh solid state isomerization is accompanied by an increase in molar volume , the hydrostatic pressure accelerates the reaction. The reason for this un usual effect-must be sought in the anisotropy of structure deformation in t he course of bond isomerization; the total increment in volume is comparati vely small (0.84%), but the structure is drastically compressed (by 3.4%) i n a number of crystallographic directions, and the crystal structure is com pressed under pressure in the same directions.