cis- and trans-Isomerism in Manganese(II) Complexes with Acylpyrazolonepyridine

The reaction between 1-(5-hydroxy-1-methyl-3-(pyridin-2-yl)-1H-pyrazol-4-yl)ethan-1-one (L) and manganese(II) acetate afforded two new manganese(II) complexes with trans and cis configurations of the acylpyrazolone ligands—trans-L2Mn(MeOH)2 (trans-I) and cis-L2Mn(MeOH)2 (cis-I),—characterized by elemental analysis and X-ray diffraction (CCDC nos. 2408806 and 2408805, respectively). The less stable (cis-I) complex was obtained by introducing 2,2′-bipyridine into the reaction, presumably leading to the formation of an intermediate heteroleptic complex with L and 2,2′-bipyridine. The resulting isomeric complexes exhibit different molecular geometries and supramolecular organization in the crystal but convert into the more stable (trans-I) isomer in DMF solution. According to magnetometry and EPR spectroscopy, they display slightly different magnetic properties.