HEPTADENTATE LIGANDS FOR THE LANTHANIDES - THE 1ST STRUCTURALLY CHARACTERIZED EXAMPLE OF A LANTHANIDE HEPTADENTATE LIGAND COMPLEX - (TRIS(3-AZA-4-METHYL-6-OXOHEPT-4-EN-1-YL)AMINE)YTTERBIUM(III)

Several binary heptacoordinate-N4O3-ligand LnL complexes of the lanthanides have been prepared and characterized. The heptadentate ligands are the Schiff base condensation products of tris(2-aminoethyl)amine with 3 equiv of either acetylacetone (to form H-3trac) or a hydroxyacetophenone (to form H-3hatren or H-3datren). The complexes hydrolyze easily but most of the Ln(trac) complexes are stable enough to sublime. Crystals of Yb(trac) were isolated by sublimation, and its structure has been solved; it is the first structurally characterized example of a lanthanide heptadentate ligand complex. Crystals of Yb(trac) are monoclinic, a = 13.150 (5) angstrom, b = 16.125 (5) angstrom, c = 22.938 (5) angstrom, beta = 105.83 (2)-degrees, Z = 8, rho-c = 1.597 g cm-3, space group P2(1)/c. The structure was solved by the Patterson method and was refined by full-matrix least-squares procedures to R = 0.043 and R(w) = 0.053 for 4199 reflections with I greater-than-or-equal-to 3-sigma(I). The structure contains two crystallographically independent, but virtually identical (one LAMBDA and one DELTA), molecules of Yb(trac) having approximate C3 symmetry. The Yb atoms are coordinated by the three O atoms and four N atoms of the heptadentate trac3- ligand in a capped octahedral arrangement with Yb-O = 2.161(9)-2.199(9) angstrom and Yb-N = 2.41(1)-2.46(1) angstrom.