Translational diffusion of transition metal complexes

Capillary flow techniques have been used to measure D-T, the translational diffusion constant at temperature T, for three transition metal complexes i n several low-viscosity liquids. The translational radius, r(t), for each o f the complexes was obtained from D-T using the Stokes-Einstein relation, T he common value of r(t) of Ni(mnt)(2)(-) in n-butyl alcohol, acetonitrile ( ACN), acetone, and ethyl alcohol (EtOH) indicates that the apparently diffe rent rotational radii (from ESR) in a series of polar solvents are due to s olute-solvent interactions and not to solvation or ion pairing. Another com plex, Ni(mnt)(2)(2-), was also studied in ACN; our values of D-T forNi(mnt) (2)(2-) and Ni(mnt)(2)(-) in ACN are in agreement with electrochemical valu es. The reproducibility of our techniques was checked by using three differ ent capillaries to make four separate determinations of D-T for Ni(mnt)(2)( -) in EtOH; the values are in good agreement. Values of D-T were measured f or Mn(Cat-N-SQ)(2), MnR2, in tetrahydrofuran, 2-methyltetrahydrofuran, diet hyl ether, and acetone. This complex is of interest because of its screw-pr opeller geometry. The values of r(t) in our solvents are in agreement with each other and are consistent with ESR studies of the reorientational motio n of MnR2. (C) 1999 Elsevier Science B.V. All rights reserved.