TEMPERATURE AND ORIENTATION DEPENDENCE OF ELECTRON-SPIN RELAXATION INMOLYBDENUM(V) PORPHYRINS

Electron spin lattice relaxation rates were measured by saturation rec overy for three xo(5,10,15,20-tetratolylporphyrinato)molybdenum(V) com plexes, O=Mo(TTP)X, X=Cl-, OH-, OEt(-). For O=Mo(TTP)(OEt) in glassy s olution between 15 and 130 K the temperature dependence of 1/T-1 is co nsistent with a two-photon Raman process. For each of the complexes at 100 K 1/T-1 is faster when the magnetic field is in the molecular pla ne than when it is perpendicular to the molecular plane, which is attr ibuted to orientation dependence of intramolecular vibrations. The ori entation-dependent values of 1/T-1 are approximately the same for isot opes with I=0 or I=5/2, which indicates that molybdenum nuclear hyperf ine interaction is not a major factor in the electron spin-lattice rel axation rate, Phase memory relaxation rates were measured by electron spin echo, Below about 90 K 1/T-m is weakly temperature dependent and becomes more strongly temperature dependent at higher temperature as 1 /T-1 approaches 1/T-m and as the host lattice softens, For isotopes wi th I=5/2 at 100 K 1/T-m is faster at molecular orientations for which the resonant field is more strongly dependent on small changes in mole cular orientation.