Solid-state studies of α- and β-[Mo 2Cl 4(dppe) 2]—kinetics of the α → β isomerization reaction and solid-state 31P and 13C NMR spectra

Abstract

We have investigated the reaction in which the chelated (α) form of [Mo 2Cl 4(dppe) 2] isomerizes to the bridged (β) form in the solid state. The kinetic parameters for the solid-state reaction ( E a = 335±30 kJ mol −1, ΔS‡ = 340±30 J K −1) are substantially different from those measured for the isomerization in solution ( E a = 121±5 kJ mol −1, ΔS‡ = 16.2±0.8 J K −1). The 31P and 13C solid-state NMR spectra of the two isomers are presented and discussed. Of particular note is the 31P NMR spectrum of the β-isomer which is broad at room temperature and sharpens markedly on cooling. This temperature dependence is interpreted as being due to paramagnetism caused by the presence of the low-lying 3§§* state, which has significant population at room temperature.