Ferromagnetic ordering, anisotropy, and spin reorientation for the cyano-bridged bimetallic compound Mn-2(H2O)(5)Mo(CN)(7)center dot 4H(2)O (alpha phase)

The title compound has been synthesized by slow diffusion of aqueous soluti ons containing K-4-[Mo(CN)(7)]. 2H(2)O and [Mn(H2O)(6)](NO3)(2), respective ly. The compound crystallizes in the monoclinic system, space group P2(1)/c . The Mo site is surrounded by seven -C-N-Mn linkages in a distorted pentag onal bipyramid fashion. There are two distorted octahedral Mn sites, one wi th four and the other with three Mn-N-C-Mo linkages. The structure is three -dimensional and of low symmetry. It consists of ladders made of edge-shari ng lozenge motifs (MoCNMnNC)(2) running along the a direction. These ladder s are linked further along the b and c directions. Both temperature depende nces of the magnetic susceptibility and field dependences of the magnetizat ion have been investigated along the three crystallographic directions, a, b, and c*. The angular dependence of the magnetization in the ab plane as a function of the external field has also been measured. These single crysta l magnetic measurements have revealed that the compound orders ferromagneti cally at T-c = 51 K, without hysteresis effect. Two additional magnetic phe nomena have been detected. In zero field, another transition has been obser ved at 43 K, which disappears when applying a field higher than 100 Oe alon g the a direction. For a critical value of the field, H-c, applied along th e a direction, a field-induced spin reorientation has been observed. The b direction is the easy magnetization axis in low field; both the a and b dir ections are easy magnetization axes as the external field overcomes the cri tical value. From the magnetic data, a magnetic phase diagram has been esta blished. Finally, it has been found that when the compound is partially deh ydrated, the long-range ferromagnetic ordering was shifted up to 65 K. This partially dehydrated material presents a magnetic hysteresis loop with a c oercive field of 0.85 kOe at 5 K. The origins of the magnetic anisotropy al ong with the mechanism of the ferromagnetic interaction between low-spin Mo 3+ and high-spin Mn2+ ions through the cyano bridge have been discussed.