A spin-frustrated cobalt(II) carbonate pyrochlore network

The crystal structure of the cobalt(II) carbonate-based compound cobalt(II) dicarbonate tris-odium chloride, Co(CO ₃) ₂Na ₃Cl, grown from a water-ethanol mixture, exhibits a three-dimensional network of corner-sharing {Co ₄(μ3-CO ₃) ₄} tetra-hedral building blocks, in which the Co ^II centres define a pyrochlore lattice and reside in a slightly distorted octa-hedral Co(O-CO ₂) ₆ environment. The space outside the hexa-gonal framework defined by these inter-linked groups is occupied by Na ⁺ and Cl ^- ions. Anti-ferromagnetic coupling between adjacent Co ^II centres, mediated by carbonate bridges, results in geometric spin frustration which is typical for pyrochlore networks. The Co and Cl atoms reside on the special position 3̄, one Na atom on position 2 and a carbonate C atom on position 3.