| Popis: |
Pressure and temperature variations of the spin-Hamiltonian parameters and electron paramagnetic resonance (EPR) linewidths of non-central Jahn–Teller [CuF4F4]6− complexes in SrF2 crystal were studied by continuous-wave EPR. It was found that the static spin-Hamiltonian parameters, found at T = 85 K and at normal pressure (g∥ = 2.491, g⊥ = 2.083, a∥ = 360, a⊥ = 26, Ax'' = 96, Ay'' = 99, Az'' = 403 and βexp = 17°), are slightly changed with hydrostatic pressure and, at T = 85 K and P = 550 MPa, become equal to g∥ = 2.489, g⊥ = 2.083, a∥ = 348, a⊥ = 27, Ax'' = 99, Ay'' = 102, Az'' = 406 and βexp = 20° (a and A values in megahertz, x''-, y''-and z''-axes are eigenvectors of the super-hyperfine tensor A, βexp is the experimental value of the angle between the C4 symmetry axis of the complex and the x''-axis). With increasing temperature the well-resolved EPR spectrum of the complex is transformed continuously into a single broad line both at normal pressure and at a hydrostatic pressure of 550 MPa. But in the first case the coalescence point corresponds to 220–230 K while in the second case it is 195–205 K. Treatment using the linear combination of atomic orbitals representation of molecular orbitals (LCAO MO) model was performed to establish some relations between variations of the spin-Hamiltonian parameters and pressure-induced changes in the molecular structure of the complex. To get some additional information about the molecular structure of the complex and variations of its structural parameters with pressure, treatment using the rigid-ion model was performed. Experimental and theoretical results are discussed in the framework of the Jahn–Teller model of the complex. |
