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)(H2D)(6) using thionyl chloride in the presence of excess THF provides light-green cubic crystals of [PrCl3(THF)(2)](n) (1), blue block crystals of [NdCl3(H2O)(THF)](n) (2) and colourless needle crystals of GdCl3(THF)(4) (3). In 1 each praseodymium atom is seven-coordinate and is linked to (two) adjacent metal centres by double (mu-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) Angstrom (equatorial). In 2 the structure is a two-dimensional cross-linked polymer in which each neodymium atom is connected to (three) others via double (mu-Cl)(2) halogen bridge bonds. The coordination sphere of each metal centre comprises six chlorine atoms [Nd-Cl-bridge 2.816(3)-2.938(3) Angstrom] and two oxygen atoms belonging to a THF molecule [Nd-O, 2.548(6) Angstrom] and a water molecule [Nd-O, 2.490(7) Angstrom], respectively. Hydrogen bonding interactions involving halogen atoms and coordinated water molecules from adjacent metal units (intermolecular) are observed, O-H ... Cl 3.147-3.350 Angstrom. 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) Angstrom. In addition, general comments concerning structural relationships within the series LnCl(3)(THF)(n), where n = 2, 3, 3.5 and 4, are discussed. (C) 1997 Elsevier Science Ltd
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