NMR investigation of the structure of NiZrF6·.6H2O at low temperatures

Previous studies have shown that NiZrF₆.6H₂O can be described by an axial spin Hamiltonian with parameters g = 2.33 and $\text{D}\text{k}\text{= ?3.14}\text{K}$, and exhibits ferromagnetic ordering at T_c = 164mK. Our room temperature X-ray measurements confirm that NiZrF₆·.6H₂O is isomorphous with NiSnCl₆·.6H₂O and give lattice parameters of $\text{a = 6.55}\text{A}\text{?}$ and α = 96°09′. Proton NMR measurements show that there exist important molecular motions at room temperature and that the space group remains $\text{R}\text{3}$ down to liquid helium temperatures. The positions of all twelve protons have been determined and are found to lie on a sphere of radius 2.9 Å centered on the nickel ion.