Electron paramagnetic resonance characterization and electron spin relaxation of manganate ion in glassy alkaline LiCl solution and doped into Cs2SO4.

ABSTRACT

Manganate ion, MnO42-, has important roles in catalysis and potential roles in water treatment. EPR spectra of MnO42- in a glassy alkaline solution of concentrated LiCl at X-band and Q-band at 80 K exhibit g1 = 1.9776 ± 0.001, g2 = 1.9677 ± 0.001, g3 = 1.9560 ± 0.001 and A1 = 182 ± 9, A2 = 275 ± 15, and A3 = 400 ± 15 MHz. In Cs2SO4 the spectra were simulated with 1.908 ± 0.001, g2 = 1.909 ± 0.001, g3 = 1.937 ± 0.001 and A1 = 90 ± 20, A2 = 100 ± 20, and A3 = 400 ± 15 MHz. Simulations required large distributions in A values which suggests that hyperfine splittings are sensitive to differences in geometry. Continuous wave spectra are observable at 80 K in glassy alkaline LiCl, but only up to about 20 K in Cs2SO4. In glassy alkaline LiCl electron spin relaxation was measured at X-band using spin echo and inversion recovery from 4.2 to 60 K. Tm is 4.6 µs at 4.2 K and decreases at higher temperatures as it becomes driven by T1. T1 decreases from ca. 34 ms at 4.2 K to ca. 240 ns at 60 K. Tm and T1 in Cs2SO4 are too short to measure by electron spin echo. The distorted tetrahedral geometry of MnO42- results in faster relaxation than for other 3d1 spin systems that have square pyramidal (C4v) or distorted octahedral geometries.