Reactions of lanthanoid metals with 3,5-diphenylpyrazole at elevated temperatures: synthesis and structures of both homoleptic, [Ln3(Ph2pz)9] (Ln = La, Nd), [Ln2(Ph2pz)6] (Ln = Er, Lu), and heteroleptic, [Ln(Ph2pz)3(Ph2pzH)2] (Ln = La, Nd, Gd, Tb, Er or Yb), pyrazolate complexes

Abstract

The direct reaction of lanthanoid metals with 3,5-diphenylpyrazole (Ph₂pzH) at 300 °C under vacuum in the presence of mercury gives the structurally characterized [Ln₃(Ph₂pz)₉] (Ln = La or Nd), [Ln₂(Ph₂pz)₆] (Ln = Er or Lu). Similar reactions provided heteroleptic [Ln(Ph₂pz)₃(Ph₂pzH)₂] (Ln = La, Nd, Gd, Tb, Er and Y). The last was obtained only from impure Ph₂pzH, but was subsequently prepared by treatment of [Yb(Ph₂pz)₃(thf)₂] with Ph₂pzH. Reactions of Yb with Ph₂pzH at 200 °C gave a poorly soluble divalent species which was converted by 1,2-dimethoxyethane into [Yb(Ph₂pz)₂(dme)₂]. Single crystal X-ray structures established a bowed trinuclear pyrazolate-bridged structure for [Ln₃(Ph₂pz)₉] (Ln = La or Nd), Ln⋯Ln⋯Ln being 135.94(1)° (La) and 137.41(1)° (Nd). There are two η²-Ph₂pz ligands on the terminal Ln atoms and one on the central metal with adjacent Ln atoms linked by one μ-η²:η² and one μ-η⁵ (to terminal Ln):η² pyrazolate group. Thus the terminal Ln atoms are formally nine-coordinate and the central Ln, ten-coordinate. By contrast, [Ln₂(Ph₂pz)₆] (Ln = Er or Lu) complexes are dimeric with two terminal (η²) and two bridging (μ-η²:η²) pyrazolates and eight-coordinate lanthanoids. All six heteroleptic complexes [Ln(Ph₂pz)₃(Ph₂pzH)₂] (Ln = La, Nd, Gd, Tb, Er or Yb) are isomorphous with three equatorial η²-Ph₂pz groups, transoid (N–Ln–N 158.18(6)–161.43(9)°) η¹-pyrazole ligands, and eight-coordinate Ln throughout.