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

Abstract

Two enantiomeric Schiff base ligands R-/S-H₂Lin 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(μ₃-O)(N₃)_1.75Br_0.25(R-L)₃(MeOH)₂(H₂O)₂][NaMn₄(μ₃-O)(N₃)₂(R-L)₃(MeOH)₂(H₂O)₂]Br₄ (1R), [NaMn₄(μ₃-O)(N₃)_1.75Br_0.25(S-L)₃(MeOH)₂(H₂O)₂][NaMn₄(μ₃-O)(N₃)₂(S-L)₃(MeOH)₂(H₂O)₂]Br₄ (1S), [Cu₆(R-L)₂(R-HL)₂(N₃)₅(MeOH)]NO₃·2MeOH·H₂O (2R) and [Cu₆(S-L)₂(S-HL)₂(N₃)₅(MeOH)]NO₃·2MeOH·H₂O (2S), have been synthesized and characterized by single crystal X-ray crystallography and CD spectroscopy. Three Mn(III) in the Mn^IIMn^III₃ clusters of 1R and 1S are joined together through the μ₃-O bridge to form an oxo-centered Mn₃O unit. Three L²⁻ link four manganese atoms via the μ₂-O,N,O-bridging manner into a Mn^IIMn^III₃ 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 Cu₂(N₃)₂ unit capped on one of the faces of the Cu₄L₄ cubane via the μ_1,1-azide and phenolate bridges from the chiral ligands. Magnetic analysis reveals intracluster antiferromagnetic interaction between adjacent manganese ions in chiral oxo-centered Mn^IIMn^III₃ magnetic clusters for 1R and 1S, and dominating antiferromagnetic over weak ferromagnetic interactions in Cu₆ clusters in 2R and 2S.