Synthesis, X-ray structures and NIR chiroptical properties of a series of dinuclear lanthanide(iii) complexes [Ln₂(μ-(S- or RS-pba))₄(HBpz₃)₂] novel configurational chirality due to non-bonding Ln⋯O interactions

Two series of mononuclear [Ln^III(S- or RS-pba)(HBpz₃)₂] (Ln = Tm, Er, Ho) and dinuclear [Ln₂(μ-(S- or RS-pba))₄(HBpz₃−)₂] (Ln = Yb, Ho, Gd, Dy, Nd) complexes (pba = RS- and/or S-2-phenyl butyrate, HBpz₃ = hydrotris(pyrazol-1-yl)borate) were prepared and their X-ray structures and NIR chiroptical properties investigated. Synthesis with a molar ratio 1 ∶ 2 ∶ 1 of Ln ∶ KHBpz₃ ∶ pba results in the formation of either mono- or dinuclear complexes, depending on the Ln(iii) ionic radii: mononuclear complexes from Yb(iii) to Ho(iii) and dinuclear ones from Dy(iii) to Nd(iii). Only the dinuclear complexes for all of the Ln(iii) studied were formed with a molar ratio 1 ∶ 1 ∶ 2 of Ln ∶ KHBpz₃ ∶ pba. X-Ray structural analysis confirmed dinuclear structures with CH⋯π interactions and linear B⋯Ln⋯Ln⋯B arrangements for the Ln(μ-RS-pba)₄Ln(HBpz₃)₂ (Yb, Ho, Dy, Gd and Nd) complexes and a skew bent arrangement of B⋯Ln⋯Ln⋯B leading to configurational chirality in the Dy(μ-S-pba)₄Dy(HBpz₃)₂ complex. Comparison of NIR chiroptical spectra in the 4f–4f transitions with those of the corresponding Cr–Ln complexes, [(acac)₂Cr(ox)Ln(HBpz₃)₂] suggests that the 4f–4f CD intensities arise from configurational chirality, probably due to the skew bent B⋯Ln⋯Ln⋯B disposition.