Neutron powder diffraction of the layer organic-inorganic iron(II) methylphosphonate- hydride, 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)AÚ , b = 8.8053(3)AÚ and c = 4.7987(1)AÚ ; 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[(CD3PO3)(D2O)], 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 (<0.1 mB).