Stereospecific assembly of chiral Λ-Cr(III)-Δ-Ln(III)- oxalatobridged dinuclear 3d-4f complexes (Ln = Yb or Dy) and near infrared circular dichroism in the 4f→4f transitions

Stereospecific formation of the chiral heterodinuclear 3d-4f complexes (Λ-Δ)-[(acac)₂Cr(ox)Ln(HBpz₃)₂] (acac^- = acetylacetonate, ox^2- = oxalato, HBpz ₃^- = hydrotris(pyrazol-1-yl)borato; Ln = Yb: 1, Dy: 2 where (Λ-Δ) implies the absolute configuration around the octahedral Cr and square antiprismatic Ln moiety, respectively) was demonstrated by comparing the near infrared circular dichroism (NIR CD) in the 4f→4f transitions and/or the single crystal X-ray analysis with those of a diastereomeric mixture of the mononuclear Λ-, and Δ-[Yb(HBpz ₃)₂(S-pba)] 3 (S-pba = S-(+)-2-phenylbutyrate) complex. The NIR CD spectra for the 4f→4f transitions of the 3d-4f (Λ-Δ)-Cr(ox)Ln complexes 1 and 2 with configurational chirality around the Ln ion with no asymmetric carbon were observed for the first time in CH₂Cl₂. This observation is supported by the selection rule for the optical activity of the 4f→4f transitions. The first solution NIR magnetic circular dichroism (MCD) of the racemic Cr(ox)Yb and Cr(ox)Dy complexes is also reported.