Lanthanide(III)chloride-tetrahydrofuran solvates: structural patterns within the series LnCl 3(THF) n, where n = 2,3,3.5 and 4: crystal and molecular structures of [PrCl( μ-Cl) 2(THF) 2] n, [Nd( μ-Cl) 3(H 2O)(THF)] n and GdCl 3(THF) 4

Abstract

Praseodymium(III), neodymium(III) and gadolinium(III) chloride adducts with tetrahydrofuran (THF) have been prepared and structurally characterized by X-ray crystallography. Removal of water from the corresponding hexahydrate LnCl 3(H 2O) 6 using thionyl chloride in the presence of excess THF provides light-green cubic crystals of [PrCl 3(THF) 2] n ( 1), blue block crystals of [NdCl 3(H 2O)(THF)] n ( 2) and colourless needle crystals of GdCl 3(THF) 4 ( 3). In 1 each praseodymium atom is seven-coordinate and is linked to (two) adjacent metal centres by double (μ-Cl) 2 halogen bridging units, resulting in a polymeric chain structure. The metal geometry approximates to distorted pentagonal bipyramidal with PrCl bridge 2.852(6)–2.891(5), PrCl terminal 2.668(6), PrO THF 2.51(1) (axial), 2.53(2) Å (equatorial). In 2 the structure is a two-dimensional cross-linked polymer in which each neodymium atom is connected to (three) others via double (μ-Cl) 2 halogen bridge bonds. he coordination sphere of each metal centre comprises six chlorine atoms [NdCl bridge 2.816(3)–2.938(3) Å] and two oxygen atoms belonging to a THF molecule [NdO, 2.548(6) Å] and a water molecule [NdO, 2.490(7) Å], respectively. Hydrogen bonding interactions involving halogen atoms and coordinated water molecules from adjacent metal units (intermolecular) are observed, OH3·Cl 3.147–3.350 Å. In 3 the molecular structure is based on a seven-coordinate pentagonal bipyramidal metal geometry in which two chlorides occupy the axial positions with the other chloride and the four solvate (THF) molecules making up the equatorial plane. GdCl 2.60(2)–2.66(2), GdO 2.40(2)–2.52(3) Å. In addition, general comments concerning structural relationships within the series LnCl 3(THF) n , where n = 2, 3, 3.5 and 4, are discussed.