Magnetic anisotropy in cyano-bridged bimetallic ferromagnets synthesized from the [Mo(CN)(7)](4-) precursor

The goal of this feature article is to introduce the dimension 'magnetic an isotropy' in the field of molecule-based magnets. For that, we have focused on three cyano-bridged (MnMoIII)-Mo-II compounds synthesized from the [Mo- III(CN)(7)](4-) precursor. The pentagonal bipyramid structure of this precu rsor is not compatible with a cubic lattice, as found in the Prussian blue phases. In this precursor, Mo-III has low-spin configuration, with a local spin S-Mo = 1/2, and a strongly anisotropic g tensor, Two of the compounds have a three-dimensional structure, Their formulas are Mn-2(H2O)(5)Mo(CN)(7 ). nH(2)O, with n = 4 for the a phase, and n = 4.75 for the beta phase, One of the compounds, of formula K2Mn3(H2O)(6)[Mo(CN)(7)](2). 6H(2)O, has a tw o-dimensional structure, with K+ cations and water molecules located betwee n double-sheet layers, The compounds crystallize in the monoclinic system, and the lattice symmetries are very low. For the three compounds, we have s ucceeded in growing well shaped single crystals suitable for magnetic aniso tropy measurements, and we have investigated the magnetic properties as fol lows: first, we have determined the magnetic axes by looking for the extrem es of the magnetization in the three crystallographic planes ab, be, and ac , Then, we have measured the temperature and field dependences of the magne tization in the de mode along the three magnetic axes. These measurements h ave revealed the existence of several magnetically ordered phases for the t hree-dimensional compounds, and of field-induced spin reorientations for th e three compounds. For the very first time in the field of molecular magnet ism, we have been able to determine the magnetic phase diagram for each com pound. We have obtained additional information from magnetic data recorded in the ac mode, with both zero and non-zero static fields. Finally, we have found that when the non-coordinated water molecules are released, the long -range magnetic ordering temperatures are shifted toward higher temperature s. Irrespective of the structural details, the Mo-III-C-N-Mn-II interaction has been found to be ferromagnetic, We have discussed this unexpected resu lt, and proposed a mechanism accounting for this, We have also discussed th e factors governing the magnetic anisotropy of the compounds.