Electron paramagnetic resonance of chromium(III) ion in α, β and γ alums

Study on the phase transitions by nuclear magnetic resonance of alpha-type RbAl(SO4)2 x 12H2O and beta-type CsAl(SO4)2 x 12H2O single crystals

The thermodynamic properties, spin-lattice relaxation times, T(1), and spin-spin relaxation times, T(2), of the (27)Al, (87)Rb, and (133)Cs nuclei in MAl(SO(4))(2)x12H(2)O (M=Rb and Cs) crystals were investigated, and the two crystals were found to lose H(2)O with increases in temperature. From our results for T(1) and T(2), we conclude that the discontinuities near T(d) in the T(1) curves of the two crystals correspond to structural changes. In both crystals, below T(d) the water molecules surrounding the Al(3+) and M(+) nuclei form distorted octahedra, whereas above T(d) the water molecules around the Al(3+) and M(+) nuclei form regular octahedra and the environment of the Al(3+) and M(+) nuclei has cubic symmetry. Further, the T(1) for the (27)Al and (87)Rb nuclei in RbAl(SO(4))(2)x12H(2)O below T(d) were found to increase with increasing temperature, whereas the T(1) for the (27)Al and (133)Cs nuclei in CsAl(SO(4))(2)x12H(2)O were found to decrease. It is possible that this difference is due to the different characteristics of alpha- and beta-type crystals.

On the nature of the trigonal fields in hexaaquachromium(III) in guanidinium aluminum sulfate hexahydrate

Zeeman and site selective luminescence and excitation spectra in the region of the 2E<--4A2 transition are reported for the hexaaquachromium(III) complex in the trigonal ferroelectric guanidinium aluminum sulfate hexahydrate. The two prominent transitions are due to the R1 lines of the two sites of C3 and C3v point symmetry. The two R1 lines display g parallel = -3.1 and g parallel = -3.2, respectively, and show no measurable Zeeman shift or splitting with B perpendicular c. This behavior is consistent with the presence of a very large trigonal field. A peculiar feature of the present system is the conspicuous absence of any prominent R2 line. From the Zeeman data with B perpendicular c and a comparison of vibrational sidelines in excitation and luminescence it is concluded that the R2 level strongly interacts with vibrational levels.