Measurement, employing 1H and 13C spin-lattice relaxation times, of the temperature dependence of the correlation time for rotational reorientation (τR)of diamagnetic transition-metal Bis- and Tris-acetylacetonate complexes

Doddrell, D. M.; Bendall,; O'connor, Aj; Pegg, David T.

doi:10.1071/ch9770943

Cited by 13 publications

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“…In order to check the accuracy of the determined average interionic distances, rotational correlation times were estimated by two independent NMR methodologies: 13 C relaxation measurements63−65 and the dependence of 1 H‐ 1 H cross‐relaxation on the temperature. The latter methodology is based on nonlinear fitting of the experimental σ IS values against T (see Figure 8), in which the dependence of the rotational correlation time on temperature is introduced by means of Equation (6 ), where E R is the activation energy for rotational reorientation, τ 0 is a constant, and k is the Boltzmann constant 66,67 …”

Section: Quantitative Nmr Investigationsmentioning

confidence: 99%

Elucidation of the Solution Structures of Transition Metal Complex Ion Pairs by NOE NMR Experiments

2002

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Our results from structural investigations of transition metal complex ion pairs in solution by homonuclear and heteronuclear 1D‐ and 2D‐NOE NMR spectroscopy are reviewed. Both model (A) and catalytically active (B) complexes have been taken into account; their general formulas are: trans‐[ML2(N,X)(Y)(Z)]+A− (A) {M = FeII, RuII and OsII, L = PMe3, Y = CO, Z = COMe, A− = BPh3R−, CF3SO3−, BF4−, PF6− and B[3,5‐(CF3)2C6H3]4−; M = IrIII, L = PR3, Y = Z = H and A− = BPh4−, CF3SO3−, BF4−, PF6−} and [M′(N,X)(R,olefin)]+A− (B) {M′ = Pt, R = Me, olefin = ethene, propene and CH2=CHCOOMe, A− = BF4−; M′ = Pd, (R,olefin) = η1,η2‐5‐methoxycyclooctenyl, A− = BPh4−, CF3SO3−, BF4−, PF6−, SbF6− and B[3,5‐(CF3)2C6H3]4−}, where N,X = bis(pyrazolyl)methane, bipyridine, α‐diimines, α‐diamines or α‐oxo imines. The detection of dipolar interionic interactions in 1H‐NOESY and 19F,1H‐HOESY NMR spectra allowed relative anion‐cation orientations to be determined, these being well defined in most cases, with one orientation predominating in solution. We often found that the anion approaches the complexes from the side of the N,X‐ligands, due to an accumulation of positive charge at the junction of the moieties containing the N‐ and X‐donor atoms. In square‐planar complexes B, the apparently favoured apical positions were often protected either by electronic factors [N,X = bis(2‐pyridyl)amine or bis(pyrazolyl)methane] or by a combination of electronic and steric factors (N,X = α‐diimines). For M′ complexes, bearing Ar−N=C(Me)−C(Me)=N−Ar ligands, the position of the counter‐anion is finely modulated by the steric hindrance of the ortho‐aryl substituents. The accessibility of the metal centre, which is directly associated with the catalytic performances of the complexes, was determined by using the counteranion as a probe. Finally, average interionic distances were estimated for model complexes A, bearing unsymmetrical BPh3R− counter‐anions, based on the quantification of interionic NOEs. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2003)

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Section: Quantitative Nmr Investigationsmentioning

confidence: 99%

Elucidation of the Solution Structures of Transition Metal Complex Ion Pairs by NOE NMR Experiments

2002

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“…[4] where E, is an activation energy that should be related to the barrier to rotation (43). The relationship between E, and the barrier to rotation has been discussed by a number of workers (43)(44)(45)(46)(47).…”

Section: (B) Temperature Dependence Of ' 4~ Ti (3-80°c)mentioning

confidence: 99%

A nuclear magnetic resonance study of aqueous solutions of several nitrate salts

Nicholas¹,

Wasylishen²

1987

Can. J. Chem.

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A. MARTIN DE P. NICHOLAS and RODER~CK E. WASYLISHEN. Can. J. Chem. 65, 951 (1987).Rotational correlation times for the end-over-end rotation of the C3 symmetry axis of the nitrate anion in the temperature range 3-80°C are studied by nuclear magnetic resonance spectroscopy for a variety of nitrate salts in aqueous solution. The counterion is found to retard the rotation of the anion in the following order: sc3+ > La3+ > pb2+ > Ca", s r 2 + > ~l~+ , K + , Nai, (CH3)?N+ > Zn2+, Mg2+, Li+, NH4+, H 3 0 + . This relative order is discussed in terms of the association of the nitrate ion with the cation. Oxygen-17 nmr spin-lattice relaxation times in combination with I4N nmr T I values are used to derive rotational diffusion constants for the in-plane rotations of the nitrate anion. In all cases the in-plane rotations are found to be slower than the corresponding end-over-end motion.A. MARTIN DE P. NICHOLAS et RODERICK E. WASYLISHEN. Can. J. Chem. 65, 951 (1987).Operant 21 des temperatures allant de 3 B 80°C et faisant appel a la spectroscopie rmn d'une variCt6 de nitrates en solution aqueuse, on a determine les temps de corrClation rotationnelle pour la rotation d'un bout j. l'autre de l'axe de rotation C3 de I'anion nitrate. On a trouvC que le contre ion retarde la rotation de l'anion dans l'ordre suivant : Sc3+ > La3+ > Pb2+ > Ca2+, Sr2+ > A I~' , K', Na+, (CH3),N+ > ~n " , M~~+ , Li', NH,', H30'. Ondiscute de cet ordre relatif enfonction de l'association de I'ion nitrate avec le cation. On a utilisC les temps de relaxation spin-rCseau de la rmn du 170 de concert avec les valeurs T I de la rmn du I4N pour obtenir les valeurs des constantes de diffusion rotationnelle pour les rotations dans le plan de l'anion nitrate.Dans tous les cas, on a trouve que les rotations dans le plan sont plus lentes que le mouvement correspondant d'un bout i l'autre.[Traduit par la revue] IntroductionNuclear magnetic resonance spectroscopy is one of several techniques available for studying the rotations of ions in solution (1-4). The ease of application and sensitivity of this method make it an attractive choice, especially for studying more dilute solutions. Recently we have shown (5) the importance of using I4N and 170 nmr spin-lattice relaxation measurements to studv the rotations of the nitrate and carbonate anions in aqueous solution in the presence of the sodium cation. We found rotations of the carbonate ion to be more hindered than those of the nitrate anion because of stronger cation-anion pairing and stronger anion-solvent interactions (hydrogen bonding). Some evidence for ion association was found for NaN03 at solute concentrations of 1 M; however, ion pairing is much more important for the divalent carbonate anion.

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Kinetik intramolekularer Reaktionen aus Relaxationszeitmessungen

1981

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Beispiel Nr die Kombination von R6ntgcn-und Ncutronenbeugung zur Ermittlung dcr Paar-Korrelationsfunktionen in AcetoNtril: H. Bertagnolli, M. Zeidler, Mol. Phys. 35, 177 (1978). Ncucrc Arbeit iibcr fliissiges Wasser: E. Kalman. G. Palinkas, P. Kovacs, ibid. 34, 502; 525 (1977). (531 Das bekanntestc auf der Hartree-Fock-Methode beruhende Verfahren zur Berechnung von (pcriodiihen) Festk6rperstrukturcn trilgt den Namen .Die genaucstc storungstheoretische Berechnung der Wechsclwirkung zwischen zwei Wassermolckiilcn wurde von B. Jeziorski, M. Van Hemert. Mol. Phys. 31, 713 (1976) durchgcfihrt. Diese Arbcit entklt auch eine schr genaue Hartree-Fock-Bcrechnung dcs Wasserdmcrs. Der Dispersionsbcitrag wurde mit eincr Formcl aus der St6rungsthcorie berechnct. Vemachlassigt wurden hingegen andere Beitrage der Elcktronenkorrelation, wie die Veranderungcn der Eigenschaften der Monomere, wclche die Gesamtwechsclwirkung nicht unwcscntlich beeinflussen. 1581 Eine cmpirischc, scchsdimcnsionale Potentialfunktion fur das Wasscrdimcr schlugen L. L. Shipman, H. A. Scheraga, J. Phys. Chem. 78,909 (1974), vor. Sic wurde ausNhrlich gctestet und gibt die bckannten, aus ab-initio-Rechnungcn 1311 und Mikrowellenspektrum 1281 crhaltenen Bcfunde gut wicder: L. L. Shipman, J. C. Owicki, H. A. Scheraga, ibid. 78, 2055 (1974). 1591 Encrgieaufteilung in den Komplcxionen H20.Li+ .OH2 und H 0 H . F -. HOH A. K q f e n , A. Beyer, P. Schusfer, noch unvcroffentlicht. Die kubisch-flilchenzentrierte (fa) und hexagonal dichtcstc (hcp) Kugelpackung wcisen die gleiche Zahl an ersten und zweiten Nachbarn auf. Die weiter entfernten Nachbarn Nhren zu ciner minimalen energetischcn Bcvonugung der hcp-Struktur [48].Die Bestimmung der Spin-Gitter-Relaxationszeit ( T ) bietet eine Alternative zu den ublichen NMR-Linienformanalysen, um die Kinetik intramolekularer Reaktionen zu untersuchen; obendrein kann der durch NMR-Spektroskopie erfaBbare Bereich sowohl nach hohen als auch nach niedrigen Energiebarrieren hin ausgedehnt werden. Die Dipol-Dipolund die Quadrupol-Relaxationszeiten sprechen auf sehr schnelle Vorgange wie die Rotation von Methylgruppen an. Die Analyse der Relaxation im rotierenden Koordinatensystem ( KP) gibt Information iiber die Kinetik vieler Prozesse, insbesondere iiber diejenigen, fur die der dynamische Bereich zu schnell fur Linienform-Methoden ist. Sattigungsiibertragung und die Koaleszenz von Relaxationszeiten bei hohen Temperaturen kdnnen zur Bestimmung hoher Energiebarrieren genutzt werden. Die Moglichkeiten und Grenzen dieser Methoden werden beschrieben.

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Measurement, employing 1H and 13C spin-lattice relaxation times, of the temperature dependence of the correlation time for rotational reorientation (τR)of diamagnetic transition-metal Bis- and Tris-acetylacetonate complexes

Cited by 13 publications

References 0 publications

Elucidation of the Solution Structures of Transition Metal Complex Ion Pairs by NOE NMR Experiments

Elucidation of the Solution Structures of Transition Metal Complex Ion Pairs by NOE NMR Experiments

A nuclear magnetic resonance study of aqueous solutions of several nitrate salts

Kinetik intramolekularer Reaktionen aus Relaxationszeitmessungen

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