Proton nmr line broadening studies of DMSO in Cr(en)33+-DMSO solutions were conducted between 20 and 90°. The resulting data were interpreted using the Swift-Connick relationship. The dominant contribution to line broadening in the temperature range 20-50° was a second coordination sphere exchange process. Above 70°, the dominant process was a first coordination sphere exchange process of partially dissociated Cr(en)33+. The kinetic parameters for the first and second coordination sphere processes respectively were found to be ΔH‡° = 25 kcal/mol, k0 = 1.4 sec-1 and ΔH‡′ = 6.6 kcal/mol, k′ = 1.2 × 103 sec-1. A discussion is given of the possibility of electron transfer through second coordination sphere bonding.