Effect of molecular motion on electron spin phase memory times for copper(II) complexes in doped solids

Abstract

Electron spin phase memory times,T m, as a function of temperature were measured for Cu(II) bis(diethyldithiocarbamate), Cu(Et2dtc)2; Cu(II) bis(diethyldithiophosphate), Cu(Et2dtp)2; Cu(II) bis(diphenyldithiophosphate), Cu(Ph2dtp)2; Cu(II) tetratolylporphyrin, CuTTP; vanadyl 5-(4-carboxyphenyl)-10,15,20-tritolylporphyrin, VOTTP-COOH; and Ag(II) tetratolylporphyrin, AgTTP, doped into powdered samples of closely-related diamagnetic hosts. For the three metalloporphyrins, the electron spin relaxation rate (1/T m) increased monotonically with increasing temperature. However the temperature dependence of the relaxation rate was not monotonic for the three other Cu(II) complexes. For Cu(Et2dtc)2 and Cu(Et2dtp)2 the temperature dependence of 1/T m between about 85 and 130 K is attributed to the effects of methyl rotation, with activation energies of 1.0 kcal/mole. Between 120 and 250 K the 1/T m data for Cu(Ph2dtp)2 exhibit effects that are attributed to motion of the phenyl rings.