Structure and basic magnetic properties of the honeycomb lattice   compounds Na2Co2TeO6 and Na3Co2SbO6
  The synthesis, structure, and basic magnetic properties of Na2Co2TeO6 and Na3Co2SbO6 are reported. The crystal structures were determined by neutron powder diffraction. Na2Co2TeO6 has a two-layer hexagonal structure (space group P6322) while Na3Co2SbO6 has a single-layer monoclinic structure (space group C2/m). The Co, Te, and Sb ions are in octahedral coordination, and the edge sharing octahedra form planes interleaved by sodium ions. Both compounds have full ordering of the Co2+ and Te6+/Sb5+ ions in the ab plane such that the Co2+ ions form a honeycomb array; the stacking of the honeycomb arrays differ in the two compounds. Both Na2Co2TeO6 and Na3Co2SbO6 reveal antiferromagnetic ordering at low temperatures, with a metamagnetic transition displayed by Na3Co2SbO6. 
L. Viciu, Q. Huang, E. Morosan, H.W. Zandbergen, N. I. Greenbaum, T.   McQueen, and R.J. Cava