Neutron Diffraction Study of Iron(II) Chloride Tetrahydrate, FeCl2· 4H2O

A three‐dimensional neutron diffraction study has revealed the positions of hydrogen atoms in a 55.9% deuterated crystal of iron(II) chloride tetrahydrate (${\mathrm{FeCl}}_2\text{· 4}{\mathrm{H}}_2\mathrm{O}$ ). The space group is P2₁/c with Z=2 and unit cell parameters: a=5.885(3), b=7.180(6), c=8.514(4) Å, and β=111.09(2)°. The conventional R factor is 0.027, assuming a partially disordered model and anisotropic extinction. Hydrogen atom positions corresponding to a minimum of calculated electrostatic energy are compared with those from the crystal structure. Previous attempts to determine hydrogen positions in ${\mathrm{FeCl}}_2\text{· 4}{\mathrm{H}}_2\mathrm{O}$ from NMR spectra are analyzed in the light of the results obtained in this study.