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.