Freezing of molecular rotation in a paramagnetic crystal studied by <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi mathvariant="normal">P</mml:mi><mml:mprescripts /><mml:none /><mml:mn>31</mml:mn></mml:mmultiscripts></mml:math> NMR

We present a detailed $^{31}$P nuclear magnetic resonance (NMR) study of the molecular rotation in compound [Cu(pz)$_{2}$(2-HOpy)$_{2}$](PF$_{6}$)$_{2}$, where pz = C$_4$H$_4$N$_2$ and 2-HOpy C$_5$H$_4$NHO. Here, freezing PF$_6$ modes is revealed by several steplike increases temperature-dependent second spectral moment, with accompanying broad peaks longitudinal transverse spin-relaxation rates. An analysis based on Bloembergen-Purcell-Pound (BPP) theory quantifies related activation energies as $E_{a}/k_{B}$ 250 1400 K. Further, anisotropy moment absorption line was calculated for rigid lattice, well presence sets reorientation modes, excellent agreement experimental data. Whereas frequency shift enhancement rates driven respect to dipole fields stemming from Cu ions, determined intramolecular interaction $^{19}$F moments distinct modes.