Crystal Structure and Magnetic Properties of a New Chiral Manganese(ll) Three-Dimensional Framework: Na3[Mn3(HCOO)9].

A structural and magnetic characterization of a trinuclear chiral Mn(ll) formate three-dimensional framework exhibiting a triangular arrangement is presented. Compound Na[sub3][Mn[sub3](HCOO)[sub9]] was obtained by solvothermal synthesis and crystallizes in the chiral cubic space group P2[sub1]3 and is well described by a Δ conformation. The structure displays triangular Mn[sub3] building blocks, in which the metal centers are bonded byformate ligands in a syn-anti mode (Mn-Mn 5.697(1) Å). The coordination sphere of manganese(ll) is completed by six oxygen atoms from six formate ligands, resulting in an octahedral geometry. Magnetic susceptibility measurements showed antiferromagnetic interactions at high temperature and a strongly field dependent magnetic behavior below 40 K. At fields higher than 1 .0 kOe only the antiferromagnetic interactions can be observed. At applied fields lower than 1.0 kOe magnetic susceptibility becomes irreversible with maxima observed at 22 and 34 K. These maxima suggest a weak ferromagnetic behavior because of spin canting, allowed by the presence of the noncentrosymmetric syn-anti HCOO bridges linking the Mn sites. This non-collinear antiferromagnetism and irreversible behavior can be due to the existence of a high degree of frustration in this unique lattice composed of linked triangular arrangements of interacting magnetic centers. [ABSTRACT FROM AUTHOR]