Coordination chemistry of lanthanides with multidentate ligands
Creators: name: Yang, Li Wei
Publisher: name: University of British Columbia
Year: 2009

description: A number of potentially heptadentate N₄0₃ and nonadentate/dinucleating N₆0₃ ligands are reported: tris(((2-hydroxy-3-methoxybenzyl)amino)ethyl)amine (H₃ (H₃(3-MeOaea)), 2-(2’ -hydroxyphenyl)-1,3-di[3’-aza-4’ -(2”-hydroxy-5“-halophenyl)-prop-4’ - en-1’-yl]-1,3-imidazolidine (H₃Xapi, X = H, Cl, Br), N, N’, N”’-tris(2- hydroxybenzyl)triethylenetetraamine (H₃ (1,2 ,4-btt)), and its acetone adduct 1 -(2’- hydroxybenzyl)-2,2-dimethyl-3-[3’ ,6’ -diaza-3 -(2”-hydroxybenzyl)-7’ -(2”-hydroxy phenyl)-heptyl]- 1,3-imidazolidine (H₃ (1,2,4-ahi)), H₃dha₃tren, and I ,4,7-tris(((2- hydroxy-5-bromobenzyl)amino)propyl)- I ,4,7-triazacyclononane (H₃Brapt). The Schiff base ligands H₃Xapi (X = H, Cl, Br) are the products of the condensation reaction of triethylenetetraamine (trien) with 3 equiv of unsubstituted or substituted salicylaldehyde. The Schiff base H₃ (dha₃tren) is prepared by the reaction of the tripodal tris(2- aminoethyl)amine (tren) and dehydroacetic acid. All the amine phenol ligands H₃ (3- MeOaea), H₃ (1,2,4-btt) and H₃ (1,2,4-ahi), and H₃Brapt are the KBH₄ reduction products of the Schiff bases derived from the reactions of tren with 3 equiv of o-vanillin, trien with 3 equiv of salicylaldehyde, and 1,4,7-tris(3-aminopropyl)-1,4,7-triazacyclononane (taptacn) with 3 equiv of 5-bromosalicylaldehyde, respectively. A series of mononuclear, homodinuclear, and heterodinuclear (with copper) lanthanide complexes with the aforementioned ligands were synthesized. The reactions of lanthanide nitrates with one equiv of N₄0₃ ligands produce mononuclear ninecoordinated complexes, [Ln(H₃L)(N0₃)₃] (H₃L = N₄0₃ ligands), wherein the ligand adopts a tridentate capping coordination mode. The N₆0₃ ligand H₃Brapt reacts with lanthanide triflates to give 1:1 complexes. In the presence of a base (sometimes in the absence of a base), other different coordination geometries are formed (depending on the ligand framework, rigidity, cavity size, and donor atom number): the six-coordinate bis(Iigand) bicapped complexes [Ln(H₃ (3-MeOaea)) ₂](N0₃)₃; the mononuclear seven coordinate encapsulated complexes Ln(1,2,4-btt) (obtained from the reactions of lanthanide salts withH₃ (l,2,4-ahiD; the homodinuclear sandwich complexes [Ln(Xapi)] ₂; an Nd-H₃dha₃ren polymer; and a heterodinuclear complex LaCu(Brapt)(N0₃)₂. The ligands and the metal complexes were fully characterized by a variety of techniques: elemental analysis, UV/vis, IR and NMR spectroscopy, and mass spectrometry; the structures of several ligands and metal complexes were determined by single crystal X-ray diffraction. Crystals of [Ln(H₃ (3-MeOaea)) ₂](NO₃)₃-xH₂O.yMeOH (Ln = Pr, x = 5.56, y = 0.44; and Ln = Gd, x = 5.96, y = 0.66) are isomorphous. In both complexes, the three phenolate 0 atoms of each of the two tridentate amine phenol ligands coordinate to the metal ions in a slightly distorted octahedral geometry, while the secondary amine N atoms are protonated and uncoordinated. In the ligandH₃api structure, strong intramolecular hydrogen bonding occurs between the hydroxy hydrogen atoms and the azomethine (or secondary) nitrogen atoms. The structure of Yb(1,2,4-btt) has a distorted pentagonal bipyramidal coordination geometry around the Y³⁺ ion, which is coordinated by an N₄O₃ donor set. In the structure of [La(Brapi)] ₂ the rigid backbones of both ligands force the chelating arms to spread wide to bridge the two metal ions, which gives a new eight-coordinated sandwich dimeric structure. Spontaneous conversion of the capped species to this new sandwich dimer, together with the evidence of variable-temperature 1H NMR of [La(Clapi)] ₂ in DMSO-d₆ indicates that these new sandwich complexes are very stable (at least kinetically) and extremely rigid. The X-ray structure of the polymer [Nd(NO₃)₃H₃dha₃treb]n reveals that two neodymium atoms form a dinuclear center through four bridging nitrate groups, and the ligand serves to link these neighbouring dinuclear centers to form a polymer in a three dimensional array. Each neodymium atom is coordinated by nine oxygen atoms, one from each of two separate H₃(dha₃tren) ligands, and the remaining seven from five nitrate groups which utilize three different coordination modes. The geometry around each of the metal ions is best viewed as a monocapped square antiprism. The crystal structure of the hydrolyzed H₃dha₃tren is also reported, indicating that the ligand has a keto-enamine form.