Chiral transition metal clusters from two enantiomeric schiff base ligands. Synthesis, structures, CD spectra and magnetic properties

Two enantiomeric Schiff base ligands R-/S-H2L in situ generated from the condensation of o-vanillin with R- or S-2-phenylglycinol were applied to assemble chiral multinuclear transition metal magnetic clusters for the first time. Four new enantiomerically pure chiral clusters, [NaMn4(mu(3)-O)(N-3)(1.75)Br-0.25-(R-L)(3)(MeOH)(2)(H2O)(2)][NaMn4(mu(3)-O)(N-3)(2)(R-L)(3)(MeOH)(2)(H2O)(2)]Br-4 (1R), [NaMn4(mu(3)-O)(N-3)(1.75)Br0.25-(S-L)(3)(MeOH)(2)(H2O)(2)][NaMn4(mu(3)-O)(N-3)(2)(S-L)(3)(MeOH)(2)(H2O)(2)]Br-4 (1S),[Cu-6(R-L)(2)-(R-HL)(2)(N-3)(5)(MeOH)]NO3 center dot 2MeOH center dot H2O (2R) and [Cu-6(S-L)(2)(S-HL)(2)(N-3)(5)(MeOH)]NO3 center dot 2MeOH center dot H2O (2S), have been synthesized and characterized by single crystal X-ray crystallography and CD spectroscopy. Three Mn(III) in the (MnMn3III)-Mn-II clusters of 1R and 1S are joined together through the mu(3)-O bridge to form an oxo-centered Mn3O unit. Three L2- link four manganese atoms via the mu(2)-O,N, O-bridging manner into a (MnMn3III)-Mn-II cluster in a distorted tetrahedral geometry. Enantiomeric 2S and 2R are hexanuclear copper(II) clusters composed of a cubane-like Cu4L4 part with a dinuclear Cu-2(N-3)(2) unit capped on one of the faces of the Cu4L4 cubane via the mu(1,1)-azide and phenolate bridges from the chiral ligands. Magnetic analysis reveals intracluster antiferromagnetic interaction between adjacent manganese ions in chiral oxo-centered (MnMn3III)-Mn-II magnetic clusters for 1R and 1S, and dominating antiferromagnetic over weak ferromagnetic interactions in Cu-6 clusters in 2R and 2S.