Synthesis, structure and magnetic properties of the first two-dimensional infinite sheet-like mixed-valence manganese(II,III) complex with bridging salicylate and pyridine-2-carboxylate ligands

Abstract

A two-dimensional infinite sheet-like mixed-valence manganese(II,III) complex [{Na₂Mn₄(sal)₄(pyca)₄-(MeOH)₂}_n]·2nH₂O (H₂sal = salicyclic acid and Hpyca = pyridine-2-carboxylic acid) has been prepared and characterized by X-ray crystallography and magnetic measurements. The structure consists of a [Mn₄(sal)₄(pyca)₄(MeOH)₂]_n^2n– anion, 2nNa⁺ cations and 2n non-coordinated H₂O. In every [Mn₄(sal)₄(pyca)₄(MeOH)₂]^2– unit there are two six-co-ordinate Mn^III[Mn(1) and Mn(2)] located at symmetry centres, and two six-co-ordinate Mn^II[Mn(3) and Mn(3′)]. Atoms Mn(1) and Mn(3)[or Mn(2) and Mn(3)] are connected by a salicylate (pyridine carboxylate) carboxylate in a syn-anti configuration, while Mn(3) and Mn(3′) are bridged by two oxygen atoms of two pyridine carboxylates. The Na⁺ cation is six-co-ordinated, having contacts with six oxygens of carboxylate groups of Mn(1), Mn(2) and Mn(3) polyhedral units. The magnetic behaviour of the complex in the temperature range 1.4–300 K has been interpreted in terms of a dimer unit [Mn^II₂(pyca)₂] and two manganese(III) polyhedral units assuming the Mn^III to obey a Curie–Weiss law, and the values obtained for J, g and θ were –0.98 cm^–1, 2.00 and –5.66 K (–3.93 cm^–1), respectively.