Fluorine Nuclear Magnetic Relaxation Study of K₂SbF₅: Anisotropic Reorientation of the Square Pyramidal Ions

Fluorine-19 spin-lattice relaxation time of crystalline K 2 SbF 5 was measured at 10.0 and 26.6 MHz between 77 and 397 K. Angular dependence of T 1 was also examined using a single crystal at 298 K. Magnetic dipolar relaxation due to axial reorientation of the square pyramidal ion SbF 5 2- was observed, its activation energy being 30 kJ mol -1 . A theoretical expression of T 1 due to reorientation of a square pyramidal ion is derived, which is described as a superposition of the two BPP functions with different time constants, τ c and 2π c . Low temperature relaxation behavior was explained in terms of spin diffusion to paramagnetic impurities.