Chiral [NaMnIIMnIII3] and [Na2MnII2MnIII6] clusters constructed by chiral multidentate Schiff-base ligands: synthesis, structures, CD spectra and magnetic properties

Abstract

Two pairs of novel enantiomerically chiral clusters R/S-[NaMn^IIMn^III₃L₃(μ₃-O)] (R/S-1) and R/S-[Na₂Mn^II₂Mn^III₆L₆(μ₃-O)₂] (R/S-2) have been obtained via the self-assembly of R/S-H₂L Schiff base ligands and different auxiliary ligands (N₃⁻, dca⁻) with divalent manganese salt in an air-exposed methanol–ethanol solution. The structures of R/S-1 and R/S-2 were characterized by single-crystal X-ray diffraction analysis and powder X-ray diffraction. When the dicyanamide anion serves as an auxiliary ligand in the assembling reaction system, a pair of enantiomeric clusters R/S-[NaMn^IIMn^III₃L₃(μ₃-O)] (R-1 and S-1) with a trigonal bipyramid configuration were obtained, while another pair of enantiomeric clusters R/S-[Na₂Mn^II₂Mn^III₆L₆(μ₃-O)₂] (R-2 and S-2) were formed in the case of the azide. Interestingly, the skeleton configuration of R/S-2 can be described as a 3-fold EO-azide bridging double trigonal bipyramid of [NaMn^IIMn^III₃L₃(μ₃-O)]₂via Mn^II vertices. Circular dichroism (CD) spectra demonstrated the enantiomeric nature of the two pairs of clusters. Detailed direct current (DC) magnetic susceptibility studies in the temperature range 2–300 K suggested that R-1 and R-2 showed predominantly antiferromagnetic interactions between the manganese centers.