A new oxofluoride Co15F2(TeO3)14 has been prepared by optimized hydrothermal synthesis involving a complex mineralization process. The crystal structure consists of a three-dimensional network of CoO5(O,F) octahedra, distorted CoO5 square pyramids, TeO3 trigonal pyramids and grossly distorted TeO3+3 octahedra, which are linked by sharing corners and edges. The Te(iv) lone pairs are accommodated within novel pyritohedron-shaped [(TeO3)14]28- units. This special framework provides a much larger free space that allows Te atoms to vibrate with a large amplitude, which leads to extremely low lattice thermal conductivity. Magnetic susceptibility data for Co15F2(TeO3)14 show antiferromagnetic ordering below 9.6 K with a substantial orbital component to the effective magnetic moment. An S = 3/2 honeycomb-like spin network was carefully analyzed by experimental techniques and first principles calculations.
M. L., J. J., B.Z., Y. Z., T. Z., H. Y., and Y. J. acknowledge support from the National Natural Science Foundation of China (Award No. 21671185). The regional computational cluster supported by Lille University, CPER Nord-Pas-de-Calais/
CRDER, France Grille CNRS and FEDER is thanked for providing computational resources.