Electron spin resonance study of dioxygenyl ion salts. Influence of crystal field effects and relaxation

A low-temperature study of the magnetic properties of the molecular cations O2+, Br2+, and I2+

“…A phase transition at 255 + 3 K (30) results in a rhombohedra1 distortion of the cubic structure found at room temperature (6). This distortion is also evident from ESR studies down to 4 K (23,31) For personal use only.…”

“…As described by Goldberg et al (31), both crystal-field splitting and spin-orbit coupling contribute to the ground state in O2+[AsF6]-. In a pure 2n112g ground state the spin and orbital contributions cancel, and there is no first-order paramagnetism associated with this state (33).…”

“…In our study we chose not to correct the susceptibilities for TIP. A crystal-field analysis of ESR data for O2+[AsF6]-suggests the separation between the ground and first electronic excited state is 1480 cm-I, caused by both spin-orbit coupling and crystal-field splitting due to 02+ being in a site of orthorhombic or lower symmetry (31). In this case one is clearly not dealing with pure 211112g and 211312g states and it is not clear what the TIP correction should be.…”

“…The limited structural information available on 02+[AsF6]- (25,31,38) derived from powder diffraction data does not permit an accurate determination of the shortest 0...0 nonbonding contact distance. Estimates of 4.00 (30b) and 4.05 A (32) respectively, used to argue against O..-O interaction, are simply the unit cell length a. divided by 2 for the roomtemperature phase (25,31,38).…”

“…Estimates of 4.00 (30b) and 4.05 A (32) respectively, used to argue against O..-O interaction, are simply the unit cell length a. divided by 2 for the roomtemperature phase (25,31,38). The distance ao/2 describes the separation between the mass centers of the OZf cations, assumed to be in the most probable sites.…”