Pseudocontact Contributions Research Articles

The π electron binding in pentacoordinated ferrous porphyrins

The contact and pseudocontact contribution to the hyperfine shift of the protons in high spin ( S = 2) pentacoordinated ferrous porphyrins has been re-evaluated, providing direct evidence for metal to porphyrin π back-bonding.

ChemInform Abstract: A NUCLEAR MAGNETIC RESONANCE INVESTIGATION OF BIS(OO′‐DIETHYL DITHIOPHOSPHATO)‐COMPLEXES OF THE LANTHANOIDS‐ SEPARATION OF CONTACT AND PSEUDO‐CONTACT CONTRIBUTIONS TO THE CHEMICAL SHIFTS

Chemischer InformationsdienstVolume 9, Issue 22 Physical Organic Chemistry ChemInform Abstract: A NUCLEAR MAGNETIC RESONANCE INVESTIGATION OF BIS(OO′-DIETHYL DITHIOPHOSPHATO)-COMPLEXES OF THE LANTHANOIDS- SEPARATION OF CONTACT AND PSEUDO-CONTACT CONTRIBUTIONS TO THE CHEMICAL SHIFTS A. A. PINKERTON, A. A. PINKERTONSearch for more papers by this authorW. L. EARL, W. L. EARLSearch for more papers by this author A. A. PINKERTON, A. A. PINKERTONSearch for more papers by this authorW. L. EARL, W. L. EARLSearch for more papers by this author First published: May 30, 1978 https://doi.org/10.1002/chin.197822057AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume9, Issue22May 30, 1978 RelatedInformation

A nuclear magnetic resonance investigation of bis(OO′-diethyl dithiophosphato)-complexes of the lanthanoids: separation of contact and pseudo-contact contributions to the chemical shifts

Measurements of 1H and 31P chemical shifts have been made at 26 and –40 °C for [AsPh4][Ln{S2P(OEt)2}4](Ln = La–Lu, excluding Pm and Gd). The results show that there are two structure types in solution, La–Dy and Ho–Lu. In both series the 1H shifts are dipolar in origin, but the 31P shifts have a large contact contribution. A new approach to the determination of the contact contribution has been developed, and hyperfine coupling constants of 1.52 and 0.86 MHz obtained for the two structure types. This is interpreted as a covalent contribution to the bonding.

Proton magnetic resonance in four-coordinated ferrous porphyrins

The N.M.R. spectra of ferrous four-coordinated octaethylporphyrin, deuteroporphyrin IX dimethylester, meso-tetraphenylporphin and mesotetra(αααα-o-pivalamidophenyl)porphin (the so-called ‘picket fence’ porphyrin) show that these paramagnetic complexes are in the same spin state in non-polar solvents. The isotropic paramagnetic shifts have been analysed using fluorine substituted tetraphenylporphins as probes for the estimation of the pseudocontact contribution to the observed shifts. The anisotropy of the pseudocontact interaction and the distribution pattern of the contact hyperfine interaction suggest that the spin state of these complexes corresponds to S=1. The electronic relaxation time for this configuration is very short, (T 1=5 × 10-13s), enabling the observation of high resolution spectra for these axially non-coordinated ferrous prophyrins.

Lanthanide shift reagents. II. Shift mechanisms

The lanthanide-induced NMR shifts in the complexes of Pr(fod) 3 with the model compounds 1,2-dimethoxyethane, 4,5-dimethylveratrole, and 1-methoxy-2-octyloxyethane are analyzed as a function of temperature. It is shown that a T −1 dependence is dominant, at variance with Bleaney's theory, which predicts a T −2 dependence. This rules out the application of the temperature dependence to separate Fermi contact and pseudocontact contributions to the induced shifts. Moreover, other methods currently used to accomplish this separation are inadequate for the systems investigated by us. In order to achieve, nevertheless, a separation of FC and PC contributions the lanthanide dependence of the shifts induced by Ln(fod) 3 in the rigid molecule, DMV was studied extensively. The data could be analyzed utilizing the full equation for the induced shift. It was found that for most lanthanides the Fermi contact interaction contributes considerably to the 1H and 13C shifts. The susceptibility tensors of the complexes investigated turn out to be nonaxial. Finally a criterion for the occurrence of apparent axial symmetry is presented and illustrated with some examples.

An analysis of N.M.R. shifts in lanthanide complexes

A method is developed to analyse a range of N.M.R. shifts in lanthanide complexes and to estimate the relative contact and pseudocontact contributions to the N.M.R. shifts for a specific N.M.R. nucleus in the lanthanide complexes.

ChemInform Abstract: CONTACT VS. PSEUDOCONTACT CONTRIBUTIONS TO LANTHANIDE‐INDUCED SHIFTS IN THE NUCLEAR MAGNETIC RESONANCE SPECTRA OF ISOQUINOLINE AND OF ENDO‐NORBORNENOL

Chemischer InformationsdienstVolume 7, Issue 40 Physical Organic Chemistry ChemInform Abstract: CONTACT VS. PSEUDOCONTACT CONTRIBUTIONS TO LANTHANIDE-INDUCED SHIFTS IN THE NUCLEAR MAGNETIC RESONANCE SPECTRA OF ISOQUINOLINE AND OF ENDO-NORBORNENOL OTTO A. GANSOW, OTTO A. GANSOWSearch for more papers by this authorPAUL A. LOEFFLER, PAUL A. LOEFFLERSearch for more papers by this authorRAYMOND E. DAVIS, RAYMOND E. DAVISSearch for more papers by this authorROBERT E. LENKINSKI, ROBERT E. LENKINSKISearch for more papers by this authorM. ROBERT III WILLCOTT, M. ROBERT III WILLCOTTSearch for more papers by this author OTTO A. GANSOW, OTTO A. GANSOWSearch for more papers by this authorPAUL A. LOEFFLER, PAUL A. LOEFFLERSearch for more papers by this authorRAYMOND E. DAVIS, RAYMOND E. DAVISSearch for more papers by this authorROBERT E. LENKINSKI, ROBERT E. LENKINSKISearch for more papers by this authorM. ROBERT III WILLCOTT, M. ROBERT III WILLCOTTSearch for more papers by this author First published: October 5, 1976 https://doi.org/10.1002/chin.197640033AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume7, Issue40October 5, 1976 RelatedInformation

Contact vs. pseudocontact contributions to lanthanide-induced shifts in the nuclear magnetic resonance spectra of isoquinoline and of endo-norbornenol

Contact vs. pseudocontact contributions to lanthanide-induced shifts in the nuclear magnetic resonance spectra of isoquinoline and of endo-norbornenol

On the theory of the pseudocontact contribution to the N.M.R. shifts in paramagnetic systems

(1976). On the theory of the pseudocontact contribution to the N.M.R. shifts in paramagnetic systems. Molecular Physics: Vol. 31, No. 6, pp. 1933-1939.

On the theory of N.M.R. screening constants int21andt25transition metal ion complexes—The pseudocontact contribution

The pseudocontact contribution to the N.M.R. shift arising from the interaction of the electron spin and orbital angular momenta with the N.M.R. nucleus is calculated for the case of a d 1 transition metal ion in a crystal field of octahedral symmetry and for a d 5 transition metal ion in a strong crystal field of octahedral symmetry. The results are applicable for not only long-range dipolar coupling but for short-range coupling including the special case when the N.M.R. nucleus is the transition metal ion. Also, the pseudocontact contribution to the N.M.R. shift is calculated for two cases when the crystal field has a specific tetragonal and a trigonal component. Bonding effects are examined for the case of a d 5 transition metal ion and the 14N N.M.R. results for the Fe(CN)6 3- ion are interpreted as arising dominantly from the interaction with the nitrogen nucleus of the unpaired electrons in the nitrogen p-orbital of the 2 T 2 molecular orbital.

Deuterium nuclear magnetic resonance of deuterium-labeled diacetyldeuterohemin incorporated into sperm whale myoglobin.

The heme derivative 2,4-diacetyldeuterohemin deuterated in the methyl groups of the acetyl moieties was reconstituted with sperm whale apomyoglobin and the two labeled methyl groups in the protein environment were observed by deuterium nuclear magnetic resonance spectroscopy. The results were compared to the free hemin form as the dimethyl ester in chloroform and in a pyridine-water mixture, as well as in the zinc complex form. Under most conditions the two methyl resonances overlie each other to a large degree. Resonance width at half-height is of the order of 25 Hz for the protein and approximately one-third as much for the free hemin at 16 degrees and is little affected by conversion to paramagnetic derivatives. Chemical shifts for the oxy- and carbonmonoxymyoglobins are very similar. In cyanoferrimyoglobin a positive pseudo-contact contribution of 3.04 ppm was computed to explain a relative upfield shift offset in part by a small negative contact shift contribution. The cyanoferrimyoglobin resonance was sensitive to the presence of phosphate buffer as well as to cyclopropane. The aquoferrimyoglobin form shows distinct resonances for the two methyl groups, with the downfield resonance considerably broadened. The expected effects of temperature on chemical shift were observed, the paramagnetic derivatives showing an effect and carbonmonoxymyoglobin showing none. The relaxation behavior was gauged from the line widths and from measurements of spin-lattice relaxation time, T1. The effective rotational correlation time is of the order of 50 ps for the liganded myoglobin forms. The temperature dependence of the line widths may imply an increased retational freedom with increasing temperature. The broadening observed in the aquoferrimyoglobin case is indicative of restricted internal rotational motion of one of the methyl groups. The method is suitable for probing the more mobile structures in proteins and retains its value in the neighborhood of paramagnetic centers.

Isotropic NMR Shifts in Imidazole, 2‐Methyl Imidazole and n‐Methyl Imidazole Complexed with Copper (II) β‐Diketonates

AbstractIsotropic nuclear magnetic resonance shifts have been measured for imidazole (Im), 2‐methyl imidazole (2MeIm) and N‐methyl imidazole (NMeIm) adducts with Cu(AA)2, Cu(TFA), and Cu(HFA)2, where AA, TFA and HFA are anion of acetylacetone, trifluoroacetylacetone and hexafluoroacetylacetone, respectively, in deuteriochloroform solution. The pseudocontact contribution to the isotropic shifts are negligibly small and Ferrmi contact interaction is dominant in these copper complexes. The normal temperature effect and appreciable spin delocalization suggest that the imidazole and substituted imidazole adducts with Cu(chelate)2 are all six‐coordinated octahedral complexes, and consistent with our results of spectrophotometric study. In these imidazole complexes, the magnitude of the contact shifts lie in the order Cu(HFA)2>Cu(TFA)2>Cu(AA)2, which is the same as that of the stability constants for the pyridine type adduct formation found from spectrophotometric studies. For a given Cu(chelate)2, the basicity of ligand for adduct formation is in the order NMeIm>Im>2MeIm.

Contact and pseudo-contact lanthanide-induced shifts in the nuclear magnetic resonance spectrum of quinoline

Contact shifts produced by trisdipivaloylmethanatogadolinium [Gd(dpm)3] are used to analyse the observed 1H and 13C lanthanide-induced shifts of quinoline with Ln(dpm)3 complexes (Ln = Pr, Nd, Eu, Dy, Ho, Er, and Yb). The analysis gives varying contact and pseudo-contact contributions for the lanthanides, the former depending on 〈Sz〉 and the degree of covalency of the Ln–N bond, and the latter in agreement with theory.

Separation of contact and pseudo-contact contributions to shifts induced by lanthanide(III) ions in nuclear magnetic resonance spectra

A method for the separation of pseudo-contact and contact contributions to the shifts of n.m.r. lines has been devised. The method is tested on the 31P resonance of LnIII complexes of cytidine 5′-monophosphate.

Proton magnetic resonance studies of flavoquinone-metal complexes.

A detailed magnetic resonance investigation of the metal ion interaction with flavoquinones has been carried out with the purpose of obtaining the stoichiometry, stability and (sub) molecular structure of the complexes. The isotropic shifts of the paramagnetic chelates are analysed in terms of contact and pseudocontact contribution. It is shown that the flavoquinone-metal binding is mainly of σ-type regardless of the nature of the ion.

Nuclear magnetic resonance shifts in solution due to lanthanide ions

The pseudocontact contribution to the NMR shifts for lanthanide complexes in solution is derived from the anisotropy in the susceptibility. Provided that the molecular geometry is independent of temperature and of the lanthanide ion, the shift should vary as T −2 and in a predicted way from ion to ion. For Sm 3+, 4 f 5 and Eu 3+, 4 f 6 effects of excited states give a more complex temperature dependence; for the former ion a term in T −1 predominates, and for the latter the dependence is rather faster than T −1 near room temperature. For other ions such effects give corrections at room temperature of a few per cent for the light lanthanons, falling to less than 1% for the heaviest lanthanons.

Pseudo-contact contributions to lanthanide-induced nuclear magnetic resonance shifts

For a magnetically anisotropic lanthanide complex the pseudo-contact contributions to the induced shift may, under certain definable conditions for internal rotations, still be proportional to an expression of the type (3 cos2θ– 1)γ–3 even when the susceptibility tensor is not axially symmetric.

Evidence for Contact and Pseudo-Contact Contributions in Lanthanide-Induced 31P N.M.R. Shifts

Evidence for Contact and Pseudo-Contact Contributions in Lanthanide-Induced 31P N.M.R. Shifts

Isotropic NMR shifts in transition metal complexes: The calculation of the fermi contact and pseudocontact terms

The Fermi contact and pseudocontact contribution to isotropic NMR shifts in paramagnetic complexes are considered for the following cases, for which formulae customarily used are not strictly applicable: (1) there is an appreciable contribution to the magnetic moment of the complex from unquenched orbital angular momentum; (2) there is appreciable orbital contribution (induced by spin-orbit effects) from spin density at the ligand nucleus; (3) there is appreciable mixing of the ground electronic state and thermally populated excited states by the applied magnetic field. An approximate density matrix treatment is developed to handle these situations. The following examples are discussed as illustrations: octahedral ( t 2 g ) 1 and ( t 2 g ) 5 complexes and complexes in which zero-field splitting occurs.

Contact shift studies of some paramagnetic octahedral complexes: Diphenylsulfoxide complexes of iron(II), cobalt(II), and nickel(II)

The proton NMR isotropic shifts of the octahedral diphenylsulfoxide (DPSO) complexes, M(DPSO) 6(ClO 4) 2, of Fe(II), Co(II), and Ni(II), in CDCl 3 are reported. From a consideration of the magnitude and concentration dependence of these isotropic shifts, it is concluded that the pseudocontact contribution to the isotropic shifts is very important for Co(DPSO) 6 2+ but not for Ni(DPSO) 6 2+ and Fe(DPSO) 6 2+. Also in the latter two complexes, the unpaired spin is probably delocalized within the ligand by a combination of both σ and π-mechanisms.