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 (χMT–T and χM−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.