Abstract
Two transition‐metal phosphites, Na~2~[M(HPO~3~)~2~] (M = Fe, Co) with a new structure type have been synthesised under mild hydrothermal conditions and the solid‐state structures have been elucidated by single‐crystal X‐ray diffraction studies. The structures are of a new type with the following data: orthorhombic, Pnma, a = 12.169(4), b = 5.441(2) and c = 9.146(3) Å for the iron species 1 and a = 12.091(3), b = 5.400(4) and c = 9.115(2) Å for the cobalt compound 2, with Z = 4. The crystal structures of these compounds are isotypic and built up from a 3D open framework with 4‐, 6‐ and 12‐membered polyhedral rings of vertex‐linked MO~6~ and HPO~3~ building units. The inorganic frameworks contains 12‐membered ring channel systems in which the sodium ions are located. The topology of this structure type is remarkably similar to that of the aeschynite CaTa~2~O~6~ with much larger channels. Magnetic measurements of Na~2~[Co(HPO~3~)~2~] show different magnetic features in the low‐temperature (5–30 K) and high‐temperature ranges (100–320 K) suggesting the possible existence of a complex magnetic structure. Antiferromagnetic ordering can be observed as a broadened cusp in χ^–1^ at θ = 2.6 K. For Na~2~[Fe(HPO~3~)~2~], the magnetic behavior follows the Curie–Weiss law with μ~eff~ = 5.41 μ~B~, fitted for 100–320 K. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)