A nuclear quadrupole resonance investigation of the effect of pressure on molecular rotation in K2PtCl6

Abstract

The pressure dependences of the ³⁵Cl quadrupolar relaxation rate and nuclear quadrupole resonance frequency in K₂PtCl₆ are measured for hydrostatic pressures up to 5000 kg cm⁻² at six temperatures. The temperatures were selected so that the effects of pressure on the rotation of PtCl₆ groups could be investigated. The relaxation resulting from the molecular rotation is discussed in terms of the simple classical model of an activated process. An activation volume ΔV* = 25.6 cm³ mole⁻¹ for the rotation is deduced. The effect of the onset of the rotation on the nuclear quadrupole resonance frequency is noted. The results are shown to be consistent with earlier measurements on the ¹⁴N resonance in (CH₂)6N₄. The activation energy ΔE* for the rotation is shown to have a value between 12.6 and 18.8 kcal mole⁻¹.