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

Two pairs of novel enantiomerically chiral clusters R/S=[(NaMnMn3L3)-Mn-II-L-III(mu(3)-O)] (R/S-1) and R/S-[(Na2Mn2MnIII)-Mn-II-L-6(6)(mu(3)-O)(2)] (R/S-2) have been obtained via the self-assembly of R/S-H2L Schiff base ligands and different auxiliary ligands (N-3(-), 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-[(NaMnMn3L3)-Mn-II-L-III(mu(3)-O)] (R-1 and S-1) with a trigonal bipyramid configuration were obtained, while another pair of enantiomeric clusters R/S-[Na2Mn2II-(Mn6L6)-L-III(mu(3)-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 [(NaMnMn3L3)-Mn-II-L-III(mu(3)-O)](2) via 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.