Preparation and X-Ray Crystal Structures of Tetrahydrofuran-Complexed Rare Earth Chlorides — a Structurally Rich Series

Abstract

Anhydrous lanthanoid metal chlorides LnCl₃(thf)_n (Ln = La, Ce, Nd, Sm, n = 2; Ln = Tb, Ho, n = 2·5; Ln = Dy, Tm, n= 2·7; Ln = Gd, Yb, Lu, n = 3; Ln = Er, n = 3·5) have been prepared in excellent yield by the direct reaction of the lanthanoid metal powders with hexachloroethane in tetrahydrofuran (thf), and (Ln = Eu, n = 0·8; Ln = La, n = 1·7; Ln = Pr, n = 2; Ln = Gd, n = 2·5; Ln = Er, n = 3) in good yield except for EuCl3(thf)_0·8 from bulk metal. [YbCl₃(thf)₂]₂ was prepared by prolonged treatment of solid YbCl₃(thf)₃ with pentane. The X-ray crystal structures of [LnC₃(thf)₂] (Ln = La, Ce or Pr), [LnCl₃(thf)_3.5] (Ln = Gd or Er), [YbCl₃(thf)₃] and [LaCl₃(thf)(H₂O)] have been determined. For [LaCl₃(thf)₂], a square antiprismatic single-stranded polymer, ... La(-Cl)₃(thf)₃La(-Cl)₃(thf)₂ ..., is the first eight-coordinate LnCl₃(thf)_n complex. The metal is surrounded by two sets of three bridging chlorines and cis thf oxygens. [LnCl₃(thf)₂] (Ln = Ce, Pr) have seven-coordinate structures with doubly chloride-bridged linear chains, ... LnCl(µ-Cl)₃(thf)₂LnCl(µ-Cl)₂(thf)₂ ... where the lanthanoid atom exists in a pentagonal bipyramidal environment, the pentagonal bipyramidal plane being defined by four chloride atoms and one oxygen atom of the thf ligand, and the axial positions being occupied by a chloride and a thf oxygen atom. [LnCl₃(thf)_3.5] (Ln = Gd, Er) crystallize as discrete ion pairs, [LnCl₂(thf)₅]⁺ [LnCl₄(thf)₂]¯. The lanthanoid atom in the cation displays pentagonal bipyramidal geometry with two apical chloride atoms and five equatorial thf ligands while the anion has quasi-regular octahedral stereochemistry with trans thf ligands. [LaCl₃(thf)(H₂O)] displays an eight-coordinate two-dimensional polymeric array with six bridging chlorides per lanthanum atom. Far-infrared spectra have been recorded for a number of products and used as a basis for structural proposals, particularly for products with fractional thf.