Translational diffusion of transition metal complexes Original Research Article

Capillary flow techniques have been used to measure DT, the translational diffusion constant at temperature T, for three transition metal complexes in several low-viscosity liquids. The translational radius, rt, for each of the complexes was obtained from DT using the Stokes–Einstein relation. The common value of rt of Ni(mnt)2− in n-butyl alcohol, acetonitrile (ACN), acetone, and ethyl alcohol (EtOH) indicates that the apparently different rotational radii (from ESR) in a series of polar solvents are due to solute–solvent interactions and not to solvation or ion pairing. Another complex, Ni(mnt)22−, was also studied in ACN; our values of DT for Ni(mnt)22− and Ni(mnt)2− in ACN are in agreement with electrochemical values. The reproducibility of our techniques was checked by using three different capillaries to make four separate determinations of DT for Ni(mnt)2− in EtOH; the values are in good agreement. Values of DT were measured for Mn(Cat–N–SQ)2, MnR2, in tetrahydrofuran, 2-methyltetrahydrofuran, diethyl ether, and acetone. This complex is of interest because of its screw-propeller geometry. The values of rt in our solvents are in agreement with each other and are consistent with ESR studies of the reorientational motion of MnR2.