Structural Systematics of Lanthanide(III) Picrate Solvates: Molecular, Mononuclear Ln(pic)3(trimethylphosphate)3 Arrays

Abstract

Adducts of the form Ln(pic)3(tmp)3 (Ln=lanthanide(iii); pic=picrate=2,4,6-trinitrophenoxide; tmp=trimethylphosphate, (MeO)3PO) have been prepared for extremal Ln=La, Lu and some intermediate members, also Y, and characterised by single crystal X-ray structure determinations as unsolvated, mononuclear, molecular species. The lanthanide atom has nine-coordinate, tri-capped trigonal prismatic stereochemistry in all cases, the picrate components behaving as O,O′-bidentate ligands chelating through the phenoxy- and an adjacent O-nitro oxygen atom, thus: [Ln(tmp-O)3(pic-O,O′)3]. Two isomeric forms are found, one mer in which the three unidentate tmp-O ligands coordinate in cis-sites spanning the upper and lower triangles and a capping site of the coordination sphere, and fac, in which all three unidentate ligands occupy the mutually cis-sites of one triangular face. The mer isomer has been described as an isomorphous series in a monoclinic P21/c, Z 4, form, for Ln=La, Ce, Pr, Nd, Sm, Gd, Lu, and Y, presumptively accessible for the full gamut of Ln. The fac-isomer also crystallises in a monoclinic P21/c form, Z 8, two independent molecules of similar stereochemistry here comprising the asymmetric unit and described for Ln=Eu, Lu(isomorphous); it has also been described in a triclinic P, Z 2 form for Ln=La.