Mn(ii) coordination polymers assembled from 8 or 9-connected trinuclear secondary building units: topology analysis and research of magnetic properties

Abstract

Two new Mn(II) coordination polymers, namely {[Mn₃L₂(pbbm)]·CH₃CN}_n (1) and [Mn₃L₂(CH₃CN)₂]_n (2) (pbbm = 1,1′-(1,5-pentane)bis-benzimidazole) have been prepared using a 3,4-bi(4-carboxyphenyl)benzoic acid (H₃L) ligand under solvothermal conditions. Single-crystal X-ray diffraction studies indicate that 1 and 2 are both three-dimensional frameworks composed of trinuclear Mn(II) subunits. A topological analysis manifests that 1 is a 3-nodal (3,4,9)-connected new topology with a Schläfli symbol of (3·4²)(3·4²·6³) (3⁴·4⁶·5⁶·6¹⁴·7⁶); while 2 is a 4,8-c flu network topology with a Schläfli symbol of (4⁶)(4¹²·6¹²·8⁴). 1 and 2 possess excellent chemical resistance to boiling water and organic solvents. Variable temperature magnetization measurements (χ_MT–T and χ_M⁻¹–T) make it clear that both complexes display ferrimagnetic interactions in the low-temperature region. The values from field-dependent magnetization measurements, M(H), do not reach clear saturation because of the magnetic anisotropy of the polycrystalline sample. Using alternating current (AC) susceptibility measurements, frequency-dependent peaks do not appear in all in-phase (χ′) and out-of-phase (χ′′) curves, indicating that there is no slow relaxation behavior of the magnetization. Markedly, the field-cooled (FC) and zero-field-cooled (ZFC) data of 1 display a divergence over the temperature range of 40–3.5 K, which could be on account of long-range magnetic ordering, or the impact of superparamagnetic behavior. Especially, 2 is based on a typical –J₁J₁J₂– sequence, featuring a ferrimagnetic chain with a (5/2, 10/2) spin topology.