Neutron powder diffraction study of the layer organic–inorganic hybrid iron(II) methylphosphonate-hydrate, Fe[(CD3PO3)(D2O)]

The crystal and magnetic structures of the hybrid organic–inorganic layer compound Fe[(CD3PO3)(D2O)] have been studied by neutron powder diffraction as a function of temperature down to 1.5 K. The neutron diffraction pattern recorded at 200 K shows that the fully deuterated compound crystallizes in one of the two known forms of the undeuterated Fe[(CH3PO3)(H2O)]. The crystal structure is orthorhombic, space group Pmn21, with the following unit-cell parameters: a=5.7095(1) Å, b=8.8053(3) Å and c=4.7987(1) Å; Z=2. The crystal structure remains unchanged on cooling from 200 to 1.5 K. Moreover, at low temperature, Fe[(CD3PO3)(D2O)] shows a commensurate magnetic structure (k=(0,0,0)). As revealed by bulk susceptibility measurements on Fe[(CH3PO3)(H2O)], the magnetic structure corresponds to a canted antiferromagnet with a critical temperature TN=25 K. Neutron powder diffraction reveals that below TN=23.5 K the iron magnetic moments in Fe[(CD3PO3)(D2O)] are antiferromagnetically coupled and oriented along the b-axis, perpendicular to the inorganic layers. No ferromagnetic component is observable in the neutron powder diffraction experiment, due to its too small value (<0.1μB).