CRYSTAL-STRUCTURE, CONFORMATIONAL DIVERSITY AND SOLUTION NMR-SPECTROSCOPY OF 4 TRIS(INDENYL)LANTHANOID(III) TETRAHYDROFURAN ADDUCTS - [LN(C9H7)(3)CENTER-DOT-THF] (LN = LA, PR, ND, SM)

Four homologous tris(indenyl)lanthanoid(III) adducts, [Ln(C9H7)(3)THF] (THF = tetrahydrofuran), with Ln = La (1), Pr (2), Nd (3) and Sm (4) were prepared in excellent yields, and six single crystals, 1a, 1b, 2, 3a, 3b and 4 (1 and 3 being at least dimorphic) have been subjected t o detailed X-ray studies. The C-5-fragments of the C9H7 ligands are al most pentahapto-bonded, and either two or three C9H7 units adopt paddl e-wheel-like orientations. The crystals 1a, 2 and 3a contain two molec ules of different conformation, one molecule displaying one C9H7 benzo group in a transoid orientation relative to the THF ligand. A similar conformation, albeit with one cisoid benzo group, is realized in 1b. Three characteristic structural motifs, I(1a, 2, 3a), II (1b) and III (3b, 4), emerge from the present results, and appear to be consistent with earlier findings. Motif III is most remarkable in view of its hex agonal, chiral space group P6(3), owing to 'trigonally disordered' THF units. Solution H-1 NMR spectroscopy indicates three rapidly equilibr ating virtually equivalent C9H7 ligands, the La-139 NMR spectrum of 1 and the MCD spectrum of 2 admitting again eta(5)-coordination. The lon g-pending suggestion of predominantly eta(1)-coordinated C9H7 ligands in dissolved molecules of 4 seems to be no longer justified. (C) 1997 Elsevier Science S.A.