We present a method to evaluate the analytical gradient of reference interaction site model Moller-Plesset second order free energy with respect to solute nuclear coordinates. It is applied to calculate the geometries and energies in the equilibria of the Grignard reagent (CH3MgCl) in dimethylether solvent. The Mg-Mg and Mg-Cl distances as well as the binding energies of solvents are largely affected by the dynamical electron correlation. The solvent effect on the Schlenk equilibrium is examined. (c) 2007 Elsevier B.V. All rights reserved.