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Titolo:
H-1 NMR in solution and solid state structural study of lanthanide(III) cryptates
Autore:
Platas, C; Avecilla, F; de Blas, A; Geraldes, CFGC; Rodriguez-Blas, T; Adams, H; Mahia, J;
Indirizzi:
Univ Coimbra, Fac Ciencias & Tecnol, Dept Bioquim, P-3000 Coimbra, Portugal Univ Coimbra Coimbra Portugal P-3000 t Bioquim, P-3000 Coimbra, Portugal Univ Coruna, Dept Quim Fundamental & Ind, La Coruna, Spain Univ Coruna LaCoruna Spain pt Quim Fundamental & Ind, La Coruna, Spain Univ Sheffield, Dept Chem, Sheffield S3 7HF, S Yorkshire, England Univ Sheffield Sheffield S Yorkshire England S3 7HF S Yorkshire, England Univ Coruna, Serv Xerais Apoio Invest, La Coruna, Spain Univ Coruna La Coruna Spain Serv Xerais Apoio Invest, La Coruna, Spain
Titolo Testata:
INORGANIC CHEMISTRY
fascicolo: 13, volume: 38, anno: 1999,
pagine: 3190 - 3199
SICI:
0020-1669(19990628)38:13<3190:HNISAS>2.0.ZU;2-F
Fonte:
ISI
Lingua:
ENG
Soggetto:
NUCLEAR-MAGNETIC-RESONANCE; AGREEMENT FACTOR-R; SHIFT-REAGENTS; PSEUDOCONTACT MODEL; CRYSTAL-STRUCTURE; COMPLEXES; SPECTROSCOPY; RELAXATION; MACROCYCLE; LIGANDS;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
45
Recensione:
Indirizzi per estratti:
Indirizzo: Geraldes, CFGC Univ Coimbra, Fac Ciencias & Tecnol, Dept Bioquim, Apartado3126, P-3000 Coimbra, Portugal Univ Coimbra Apartado 3126 Coimbra Portugal P-3000 ortugal
Citazione:
C. Platas et al., "H-1 NMR in solution and solid state structural study of lanthanide(III) cryptates", INORG CHEM, 38(13), 1999, pp. 3190-3199

Abstract

We present here a detailed structural comparison, both in the solid state and in aqueous solution, of a complete series of lanthanide cryptate complexes of a Schiff base axial macrobicyclic ligand L of general formula [LnL][NO3](3). xH(2)O (Ln = La-Lu, Y); the macrobicyclic receptor L is an azacryptand N[(CH2)(2)N=CH-R-CH=N(CH2)(2)](3)N (R = m-C6H2OH-2-Me-5). The crystal structures of the Ce, Nd, and Eu complexes, chemical formulae [CeL(NO3)](NO3)(2). 1.5H(2)O . 0.5CH(3)CH(2)OH (3), [NdL(NO3)](NO3)(2). 3H(2)O (5), and [EuL(NO3)](NO3)(2). H2O . CH3OH (7), as well as that of [YL(NO3)][Y(NO3)(3)(H2O)(2)EtOH](NO3)(2). EtOH . CH3CN (16), have been determined by single-crystal X-ray crystallography. The four crystals crystallize in the triclinicspace group P (1) over bar with Z = 2; a = 10.853(3) Angstrom, b = 12.746(3) Angstrom, c = 17.907(5) Angstrom, alpha = 98.09(2)degrees, beta = 89.99(2)degrees, gamma = 96.34(2)degrees, for 3; a = 10.835(2) Angstrom, b = 12.544(3) Angstrom, c = 17.701(2) Angstrom, alpha = 82.220(10)degrees, beta = 89.240(10)degrees, gamma = 84.45(2)degrees for 5; a = 10.896(2) Angstrom, b = 12.566(4) Angstrom, 17.688(3) Angstrom, alpha = 81.23(2)degrees, beta = 89.500(10)degrees gamma = 84.72(3)degrees for 7; and a = 12.723(2) Angstrom,b = 14.047(3) Angstrom, c = 16.943(2) Angstrom, alpha = 66.07(2)degrees, beta = 79.838(12), gamma = 81.616(14)degrees for 16. In light of their crystal structures, it can be stated that all of them adopt very similar structures, with the nine-coordinated metal ion bound asymmetrically to seven donor atoms in the ligand cavity and also to two oxygen atoms of a bidentate nitrate anion. The macrobicycle cavity adapts to the lanthanide contraction, while preserving the pseudo-triple-helix conformation around the metal ion. The coordination geometry of the metal atom is best considered as a slightly distorted monocapped dodecahedron. The aqueous solution structures of the paramagnetic complexes were thoroughly characterized from the proton NMR LIS and LIR data, with, particular attention to the changes induced by the lanthanide contraction, and agree quite well with the crystal structures ofthe Nd and Y complexes. The experimental Ln-donor distances decrease progressively along the lanthanide series both in the solid and solution structures, but no drastic structural changes occur. The gradual contraction and distortion of the coordination polyhedron along the series cause a variationof the crystal field parameter A(2)degrees < r(2)> and the hyperfine constants A(i) of the lanthanides in the middle of the series, leading to "breaks" in the contact-pseudo-contact shift separation plots of the proton LIS values. However, this affects only slightly the geometric terms G(i) of the protons and not at all their R-ik ratios. The conformational rigidity of the five-membered chelate rings formed by the metal-bound ethylenediamino moieties of the bound cryptand increases upon lanthanide contraction. The Delta G double dagger value for the delta <-> lambda conformational interconversion process of those rings is 70 +/- 3 kJ for the Y complex.

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Documento generato il 02/12/20 alle ore 03:42:13