1H NMR Spectroscopic Study of Paramagnetic Lanthanide(III) Texaphyrins. Effect of Axial Ligation

Lisowski, Jerzy; Sessler, Jonathan L.; Lynch, Vincent M.; Mody, Tarak D.

doi:10.1021/ja00113a016

Cited by 109 publications

(89 citation statements)

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“…Similar agreement factors were previously obtained for Ln III texaphyrins (0.066 < AF j < 0.259). [46] As expected for a nonaxial system, the D 1 and D 2 values obtained define very large c tensor anisotropies. [19] These results indicate that our ab initio calculations provide good models for the structure of these complexes in solution, particularly when solvent effects are taken into account.…”

Section: -Induced Shifts and Relaxation-rate Enhancement Effects:supporting

confidence: 71%

Lanthanide Chelates Containing Pyridine Units with Potential Application as Contrast Agents in Magnetic Resonance Imaging

Platas‐Iglesias

Mato‐Iglesias

Djanashvili

et al. 2004

Chemistry A European J

108

128

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A new pyridine-containing ligand, N,N'-bis(6-carboxy-2-pyridylmethyl)ethylenediamine-N,N'-diacetic acid (H(4)L), has been designed for the complexation of lanthanide ions. (1)H and (13)C NMR studies in D(2)O solutions show octadentate binding of the ligand to the Ln(III) ions through the nitrogen atoms of two amine groups, the oxygen atoms of four carboxylates, and the two nitrogen atoms of the pyridine rings. Luminescence measurements demonstrate that both Eu(III) and Tb(III) complexes are nine-coordinate, whereby a water molecule completes the Ln(III) coordination sphere. Ligand L can sensitize both the Eu(III) and Tb(III) luminescence; however, the quantum yields of the Eu(III)- and Tb(III)-centered luminescence remain modest. This is explained in terms of energy differences between the singlet and triplet states on the one hand, and between the 0-phonon transition of the triplet state and the excited metal ion states on the other. The anionic [Ln(L)(H2O)]- complexes (Ln=La, Pr, and Gd) were also characterized by theoretical calculations both in vacuo and in aqueous solution (PCM model) at the HF level by means of the 3-21G* basis set for the ligand atoms and a 46+4 f(n) effective core potential for the lanthanides. The structures obtained from these theoretical calculations are in very good agreement with the experimental solution structures, as demonstrated by paramagnetic NMR measurements (lanthanide-induced shifts and relaxation-rate enhancements). Data sets obtained from variable-temperature (17)O NMR at 7.05 T and variable-temperature (1)H nuclear magnetic relaxation dispersion (NMRD) on the Gd(III) complex were fitted simultaneously to give insight into the parameters that govern the water (1)H relaxivity. The water exchange rate (k(298)(ex)=5.0 x 10(6) s(-1)) is slightly faster than in [Gd(dota)(H2O)]- (DOTA=1,4,7,10-tetrakis(carboxymethyl)-1,4,7,10-tetraazacyclododecane). Fast rotation limits the relaxivity under the usual MRI conditions.

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Section: -Induced Shifts and Relaxation-rate Enhancement Effects:supporting

confidence: 71%

Lanthanide Chelates Containing Pyridine Units with Potential Application as Contrast Agents in Magnetic Resonance Imaging

Platas‐Iglesias

Mato‐Iglesias

Djanashvili

et al. 2004

Chemistry A European J

108

128

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“…The agreement factors and the correlation coefficients obtained for the aromatic protons are satisfying and can be compared to those found for similar mathematical treatments applied to [Ln(pyridine-2,6-dicarboxylato),13-(0.004 < A F < 0.27 [34]) and [Ln"' (texaphyrin)(NO,),] (0.06 < A F < 0.26 [35]). The difference between the sum of the predicted contact and dipolar contributions (Eqn.…”

Section: Me-c(5) Me-n(1') H-c(6'"') H-c(4"") H -C ( 3 ) H-c(7') H-c(6mentioning

confidence: 54%

Structural and Photophysical Properties of Pseudo‐Tricapped Trigonal Prismatic Lanthanide building blocks controlled by zinc(II) in heterodinuclear df complexes

Piguet

Rivara‐Minten

Hopfgartner

et al. 1995

Helvetica Chimica Acta

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(18.V.95), An efficient combination of electrospray mass spectrometry (ES-MS), spectrophotometric and 'H-NMR titrations in solution is used to characterize the assembly of the segmental ligand 2-{ 6-[1-(3,S-dimethoxybenzyl)-azole] (L') with Zn" and 4f metal ions, Ln"'. Ligand L2 reacts with Zn(ClO,), in MeCN to give successively [Zn(L2),I2', where the metal ion is coordinated by the tridentate binding units of the ligands, and the double-helical head-to-head complex [Zn2(L2)2]4'. When L2 reacts with Ln(CIO,), (Ln = La, Eu, Lu), La"' only leads to a well-defined cylindrical CI-symmetrical homodinuciear head-to-tail complex [La2(L2),16' in solution, while chemical-exchange processes prevent the 'H-NMR characterization of [Eu2(L2)$', and Lu"' gives complicated mixtures of complexes. However, stoichiometric amounts of Ln"' (Ln = La, Ce, Pr, Nd, Sm, Eu, Tb, Y, Lu), Zn", and L2 in a 1 :I : 3 ratio lead to the selective formation of the C,-symmetrical heterodinuclear complexes [LnZn(L2)3]S+ under thermodynamic control. Detailed NOE studies show that the ligands are wrapped about the C, axis defined by the metal ions, and the separation of dipolar and contact contributions to the 'H-NMR paramagnetic shifts of the axial complexes [LnZn(L2)3]S+ (Ln = Ce, Pr, Nd, Sm, Eu) in MeCN establishes that Zn" occupies the pseudo-octahedral capping coordination site defined by the three bidentate binding units, while Ln"' lies in the resulting 'facial' pseudo-tricapped trigonal prismatic site produced by the three remaining tridentate units. Photophysical measurements show that [LnZn(L*),]'+ (Ln = Eu, Tb) are only weakly luminescent because of quenching processes associated with the C,-cylindrical structure of the complexes. The use of 3d metal ions to control and design isomerically pure 'facial' tricapped trigonal prismatic lanthanide building blocks is discussed together with the calculation of a new nephelauxetic parameter associated with heterocyclic N-atoms coordinated to Ln'".Introduction. - [7]. However, the recent development of selective self-assembly processes between segmental ligands and metal ions leading to programmed architectures [8] [9] has reached a point where it is now possible to tailor

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“…The significantly smaller Dy 3+ ion (with 91 pm ionic radius 42 ) fits even better into the cavity of the texaphyrin ring, having an average d(La-N) value of 236 pm and a very small d(OOP) (7.3 pm). 49 In 40 the 1:1 porphyrin complexes of Nd 3+ , the size of which (98.3 pm ionic radius) is closer to that of La 3+ , d(Nd-N) was determined to be 245 pm. 50 Since these complexes contained a tripodal axial ligand (a phosphite derivative) pulling the metal center out of the cavity, the value of d(OOP) in these cases was measured to be 130 44 In the latter complex the deeper insertion of the metal center into the cavity of the ligand moderately pushes apart the N atoms, resulting in the diagonal N- the HgP and BiP + complexes (40 and 38 pm, respectively).…”

Section: Monoporphyrin Complexesmentioning

confidence: 94%

Equilibrium, photophysical and photochemical examination of anionic lanthanum(iii) mono- and bisporphyrins: the effects of the out-of-plane structure

2012

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Lanthanum(III) ion forms kinetically labile complexes with the 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin anion (H2TSPP 4-), the compositions and formation constants of which significantly depend on the presence of potential axial ligands (at 0.01 M). Deviating from the chloride ion, acetate coordinating to the metal center hinders the formation of bisporphyrin complex. In these 10 lanthanum(III) complexes, the metal center, due to its large ionic radius (103.2 pm), is located out of the ligand plane, distorting it. Accordingly, the absorption and fluorescence spectra of these coordination compounds display special properties characteristic of the so-called sitting-atop (SAT) or out-of-plane (OOP) porphyrin complexes. Metalation significantly decreases the quantum yield of the fluorescence from the S1 excited state. Quantum chemical calculations (DFT) confirm the considerable OOP 15 displacement of the La(III) center (about 120 pm in the monoporphyrin complexes). The monoporphyrins display efficient fluorescence (0.03), while the bisporphyrin does not emit. Differing from the normal (in-plane) metalloporphyrins, excitation of these lanthanum(III) porphyrins leads to an irreversible ligandto-metal charge transfer (LMCT) followed by the opening of the porphyrin ring, which is also typical of OOP complexes. Dissociation releasing free-base porphyrin can also be observed upon irradiation of the 20 monoporphyrin in acetate solution, while in the presence of chloride ions interconversions of the monoand bisporphyrins may also take place beside the irreversible photoredox reaction.

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1H NMR Spectroscopic Study of Paramagnetic Lanthanide(III) Texaphyrins. Effect of Axial Ligation

Cited by 109 publications

References 0 publications

Lanthanide Chelates Containing Pyridine Units with Potential Application as Contrast Agents in Magnetic Resonance Imaging

Lanthanide Chelates Containing Pyridine Units with Potential Application as Contrast Agents in Magnetic Resonance Imaging

Structural and Photophysical Properties of Pseudo‐Tricapped Trigonal Prismatic Lanthanide building blocks controlled by zinc(II) in heterodinuclear df complexes

Equilibrium, photophysical and photochemical examination of anionic lanthanum(iii) mono- and bisporphyrins: the effects of the out-of-plane structure

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