New molecular conductors with iron bis(dicarbollide) anion – synthesis, crystal structure and electrical conductivity
Abstract
SbVO 4 series of compounds could be used as a catalyst for the production of 20% cheaper acrylonitrile by the ammoxidation of propane compared to current method producing 810 6 ton/year. In the non-stoichiometric series described as Sb 0.9 V 0.9+x 0.2-x O 4 (0x0.2), cation vacancies () are introduced in the basic rutile type-structure following the mechanism: 4V 3+ 3V 4+ + , while antimony remains as Sb 5+ . The reduced phase richest in V 3+ has been reported to be Sb 0.9 V 1.1 O 4 , which shows by electron diffraction superlattice reflections characteristic of a 2-fold rutile superstructure along c. However the X-ray powder diffraction pattern showed only basic rutile reflections (a r = 4.6085(1), c r = 3.0867(1) , S.G. P4 2 /mnm). The careful reciprocal lattice study by electron diffraction has revealed the following unit cell for the rutile superstructure: a =2a r , b = 2b r , c = 2c r . (subindex r refers to the basic rutile unit cell). Its space group, I4 1 md, was determined by means of CBED. A structural model based on alternating Sb and V cations ordering along c in the chains of edge-sharing octahedra was proposed. No cation vacancies have been observed for this reduced phase, while for the compounds synthesized in oxidizing conditions the presence of vacancies has been confirmed. In fact, electron diffraction experiments have shown that vacancies order in the basic rutile structure giving rise to a modulated structure on the other end member of the series, namely Sb 0.9 V 0.9 O 4 . On the other hand, our magnetic susceptibility studies indicate for the first time possible magnetic ordering. Thus for the magnetic structure determination we performed the study of 3 different samples of the series Sb 0.9 V 0.9+x 0.2-x O 4 by using neutron diffraction: 1) a reduced phase rich on V 3+ which shows the nuclear superstructure by Sb-V ordering.