On a new structural type of fluorine compounds : Crystal and magnetic structures of a high pressure form of PdF2

A new structural type of MF₂ fluorine compounds has been studied using neutron diffraction. The structure of the high pressure form of Pd difluoride has been shown to derive from the fluorite type by a rhombohedral distortion of the cubic environment of the cations. The coordination number of the cations is VI + II : the six nearest neighbor fluorine atoms form a distorted octahedron with $\text{M}\text{?}\text{F}{}_1\text{? 2.18}\text{A}\text{?}$, while two further anions correspond to $\text{M}\text{?}\text{F}{}_2\text{? 3.17}\text{A}\text{?}$. Distances and angles have been compared with those of other Pd compounds. The structure of the high pressure form of PdF₂ has been refined via neutron diffraction ($\text{a}\text{= 5.329}\text{A}\text{?}$, space group Pa3 or P2₁3). This phase orders antiferromagnetically below 190 ± 5 K and the magnetic structure has been determined on the basis of both collinear and noncollinear models. The magnetic data have been compared with results obtained for other d⁸ or d⁹ difluorides.