M6gbauer measurements of hexane-diammonium-tetrachloro-ferrate over the temperature range 78-320 K for powdered and single-crystal absorbers show a transition to the antiferromagnetically ordered state at (105.0 + 0.2) K. The center shift indicates an electronic ground state of 3d64s°< The quadrupole splitting implies that Fe(II) exists in a distorted octahedral field and that the ground state is a doublet, with negative electric field gradient. The recoilless fraction, the center shift and the quadrupole splitting reveal the existence of a structural phase change at (235 + 5) K. The Debye temperature of the lower temperature phase is (166 + 5) K and (155 + 3) K for the higher.
Transition to the ordered state takes place between 105 and 110 K where an increase of the spin correlation time is found. A three-dimensional transition associated with a weak ferromagnetic interaction as a result of canting of the spins is observed at about 102 K. At 77 K the effective magnetic field strength was found to be (225 _+ 3) kOe and to make an angle of 80 ° + 3 ° with the principle axis of the electric field gradient.