PULSED ELECTRON-PARAMAGNETIC-RESONANCE OF HIGH-SPIN COBALT(II) COMPLEXES

Electron paramagnetic resonance (EPR) data were obtained for Co(H2O)62 + and six Co(II) complexes with 0, 1, or 2 water molecules in the firs t coordination sphere. Continuous wave (CW) spectra confirmed that the complexes are high spin with zero-field splitting greater than the X- band EPR quantum. Two- and three-pulse electron spin echoes were recor ded at about 6 K. The electron spin phase memory time, T(m), varied th rough the spectrum, with longer values observed at higher magnetic fie ld. The electron spin lattice relaxation time, T1, measured by saturat ion recovery was approximately independent of position in the spectrum but was strongly temperature dependent. In D2O:glycerol-d3 solution, the depth of the deuteron modulation fell into two classes: complexes with directly bound water exhibited substantially deeper modulation th an complexes without directly bound water. Fourier transforms of the t wo-pulse electron spin echo envelope,modulation in H2O:glycerol soluti on reveal frequencies near twice the proton Larmor frequency that dist inguish between first and second coordination sphere water. Two comple xes containing imidazole bound to Co(II) exhibit characteristic nitrog en modulation frequencies in Fourier transforms of 3-pulse ESEEM data.