ELECTRON-SPIN-RESONANCE OF RHODIUM-VACANCY COMPLEXES IN SOLUTION-GROWN NACL-CRYSTALS

Three different paramagnetic [RhCl6](4-) complexes were detected in x- ray irradiated solution-grown NaCl single crystals: RhCl64- . nVac, n = 2, 1, 0. These complexes all have a 4d(7) ground state, with the unp aired electron spin mainly in a 4d(z2) orbital and differ only by the presence of two, one, or none next-nearest cation vacancy (Vac). The R hCl64- . 2Vac is formed at 77 K and partially converts into RhCl64- . 1Vac at about 190 K. At room temperature the RhCl64- . 0Vac is dominan t, but traces of the RhCl64- . 1Vac and RhCl64- . 2Vac centers remain. A thermally induced reorientation motion of the 4d(z2) molecular orbi tal is used to explain the temperature dependence of the RhCl64- . 1Va c electron spin resonance spectrum. (C) 1998 American Institute of Phy sics.