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

Two series of mononuclear [LnIII(S- or RS-pba)(HBpz3)2](Ln = Tm, Er, Ho ) and dinuclear [Ln2{(mu)-(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...(pi) interactions and linear B...Ln...Ln...B arrangements for the Ln((mu)-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((mu)-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.