New Homoleptic Rare Earth 3,5‐Diphenylpyrazolates and 3,5‐Di‐tert‐butylpyrazolates and a Noteworthy Structural Discontinuity

Abstract

Direct thermally induced reactions between rare earth metals (Ln = Y,Ce, Dy, Ho, and Er) activated by Hg metal and 3,5‐diphenylpyrazole (Ph2pzH) or 3,5‐di‐tert‐butylpyrazole (tBu2pzH) yielded either homoleptic complexes [Lnn(R2pz)3n] or a heteroleptic complex [Ln(Ph2pz)3(Ph2pzH)2] From Ph2pzH, [Ce3(Ph2pz)9], [Dy2(Ph2pz)6], [Ho2(Ph2pz)6], and [Y(Ph2pz)3(Ph2pzH)2] were isolated. The first has a bowed trinuclear Ce3 backbone with two η2 pyrazolate ligands on the terminal metal atoms and one on the middle, and bridging by both μ‐η2:η2 and μ‐η2:η5 ligands between the terminal and the central Ce atoms. Although both the Dy and Ho complexes are dinuclear, the former has the rare μ‐η2:η1 bridging whilst the latter has μ‐η2:η2 bridging. Thus the dysprosium complex is seven‐coordinate and the holmium is eight‐coordinate, in contrast to any correlation with Ln3+ ionic radii, and the series has a remarkable structural discontinuity. The heteroleptic Y complex is eight coordinate with three chelating Ph2pz and two transoid unidentate Ph2pzH ligands. From tBu2pzH, dimeric [Ln2(tBu2pz)4] (Ln = Ce, Er) were isolated and are isomorphous with eight coordinate Ln atoms ligated by two chelating terminal tBu2pz and two μ‐η2:η2 tBu2pz donor groups. They are also isomorphous with previously reported La, Nd, Yb, and Lu complexes.