Laser-induced NMR shift of a paramagnetic system

Perturbation theory on optical ac Stark effect is applied to study the NMR spectroscopy in paramagnetic systems. Application of the circularly or linearly polarized optical field would lead to shifts in the NMR lines, which is proportional to the laser intensity and the induced polarizability tensors by hyperfine interaction. The induced shift for 193Ir NMR spectrum of [IrBrg]2- is expected to be of the order of 1-10 Hz as resonance is approached with light intensity 10 W·cm-2. For the supersonic molecular beam samples 193IrC, the laser-induced NMR shift is estimated to be as large as 1-10 MHz near resonance.     

ESR spectra of paramagnetic palladium complexes

Binuclear nitrosopalladium complexes Pd₂(μ-COOR)₂(η²-CH₂C₆H₄NO)₂ (R = Me, CF₃, or Ph) were studied by ESR spectroscopy. Analysis of parameters of ESR spectra of the polycrystalline samples and their toluene solutions suggests partial izomerization of the nitroso ligands to the nitroxide form to result in the oxidation of palladium(II) to palladium(III). __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1746–1751, August, 2005.     

Peculiarities of NMR spectra of heterospin complexes

Experimental investigation and theoretical simulation of the unusual phenomenon of multiple broadening and narrowing of NMR signals due to the temperature variation of a solution of the stereochemically non-rigid heterospin Ni²⁺ complex with stable nitroxide were performed. The investigation of the temperature dependence of the NMR signals of stereochemically non-rigid heterospin systems can be used for choosing conditions for growing heterospin single crystals containing molecules in a definite conformation.     

A justification for using NMR model-free methods when investigating the solution structures of rhombic paramagnetic lanthanide complexes

The detailed analysis of the 1H NMR hyperfine shifts according to the model-free methods shows that the semi-rigid monometallic complexes [Ln(L)(NO3)3] (Ln = Eu-Yb) are isostructural in solution. The associated separation of contact and pseudo-contact contributions to the hyperfine NMR shifts in each rhombic lanthanide complex at room temperature provides paramagnetic susceptibility tensors whose principal magnetic axes match the expected symmetry requirements. Moreover, both axial (Delta chi(ax)) and rhombic (Delta chi(rh)) paramagnetic anisotropies display satisfactory linear dependence on Bleaney's factors, a correlation predicted by the approximate high-temperature expansion of the magnetic susceptibility limited to T(-2). Consequently, the simple, and chemically attracting NMR model-free methods are not limited to axial systems, and can be safely used for the investigation of the solution structures of any lanthanide complexes. Molecular-based structural criteria for the reliable estimation of paramagnetic susceptibility tensors by NMR are discussed, together with the assignment of the labels of the crystal-field and magnetic axes within Bleaney's approach.     

1H and 13C NMR spectra of N-substituted morpholines

(1)H and (13)C NMR data for N-substituted morpholines 1-20 were measured using 1D (DEPT, 1D NOE difference) and 2D NMR spectroscopic methods including (1)H-(1)H COSY, long-range (1)H-(1)H COSY, NOESY, gHMBC and gHMQC experiments. At room temperature the (1)H NMR spectra of protonated compounds 2 and 9 show the chair conformation for the morpholine ring. Spin-spin coupling constants were deduced from the resolution-enhanced proton spectra.     

19F and 1H NMR spectra of halocarbons

19F NMR chemical shifts and coupling constants are reported for 215 compounds. For 77 of these compounds, 1H NMR spectral data are also given. Long-range couplings, including 8J(F,F) and 5J(F,H), are reported. The complexity of halocarbon spectra owing to the presence of rotational isomers, asymmetric centers, long-range couplings, and chlorine isotope effects are illustrated, and the methods used for analyzing such complex spectra are briefly discussed.     

Structure of metal adducts of anthracyclines probed by absorption,circular dichroism and paramagnetic NMR

A structural study of metal ion adducts of a new anthracycline disaccharide (MEN 10755) was undertaken. The trivalent lanthanide ion Yb(III) was employed as paramagnetic structural probe for ¹H NMR analysis. Through a comparative spectroscopic investigation [UV–Vis absorption and circular dichroism (CD), ¹H NMR], the isomorphism between its adducts with lanthanide ions (La³⁺, Yb³⁺, Lu³⁺) and calcium (one of the most representative biological cations) was verified. Solution behavior and cation binding were also investigated by means of optical titrations. In agreement with other anthracyclines, MEN 10755 was found to dimerize in aqueous solution [estimated K_dim (pH7.6) = 7 × 10³], but not in methanol. A prevalent complex Yb³⁺–MEN 10755 (1:1) in both buffered aqueous and methanolic solutions (estimated K_compl = 2100 M ^?1) was observed. A numerical analysis of the LIR and LIS ¹H NMR literature data for a similar adduct (Yb³⁺–daunorubicin) was performed using newly developed software, PERSEUS (Paramagnetic Enhanced Relaxation and Shifts for Eliciting Ultimate Structures), and the structure of the complex was characterized, locating definitely the binding site on the O‐11, O‐12 quinone system. The components of the anisotropic part of the magnetic susceptibility tensor were also determined. Finally, a study of the time‐dependent formation of an Yb³⁺–MEN 10755 complex through ¹H NMR, UV–Vis CD and induced NIR CD was carried out. Copyright © 2002 John Wiley & Sons, Ltd.     

Reaction of the acrylic acid and 1-vinylimidazole copolymer with CuCl2 in aqueous solution

The reaction of acrylic acid—1-vinylimidazole copolymer with CuCl₂ in an aqueous medium was investigated by potentiometric titration and UV and ESR spectroscopy. The complex formation involves both the azole units and the carboxy groups. The Cl^– ions are also incorporated in the inner sphere of the complexes, their removal by dialysis resulting in an increase in the coordination capacity of the carboxylate groups.     

NMR Spectroscopy of Paramagnetic Complexes

Serviceable NMR spectra can, with a few exceptions^[1,6], be recorded for paramagnetic complexes in solution. These spectra provide information about the structure of the complexes and the distribution of the unpaired electrons, and hence also about reactive centers in the molecule. The elucidation of intermolecular and intramolecular exchange phenomena, e.g. the determination of ligand exchange rate constants, the determination of rotation barriers, and the detection of contact complexes in solution, or even of occupation equilibria of the electrons, is possible in this way. It can be seen, therefore, that NMR studies on paramagnetic complexes can be a rich source of information.     

Synthesis, mechanism and NMR spectra of lanthanide complexes with a novel unsymmetrical Schiff base

Owing to its two unsymmetrical-NH_2 groups sited on different terminals, 2, 6-diaminocaproic acid (lysine) was used as a reactant for synthesizing a novel unsymmetrical Schiff base with salicylaldehyde on one side and ovanillin on the other for the first time. It is a new way to synthesize such a special unsymmetrical Schiff base. It is named "hetero bis-Schiff base" for distinguishing it from others. The synthesis method, formation mechanism as well as twelve new lanthanide complexes with the above ligand are reported and discussed herein. They were characterized by elementary analysis, molar conductivity, IR-spectra and especially by ~1H and ~(13)C NMR spectra. The results obtained may provide a new promising method for synthesizing similar unsymmetrical Schiff bases and their complexes.     

Molecular structure of paramagnetic <Emphasis Type="Italic">bis</Emphasis>-diisobutyl dithiophosphinate complexes of lanthanides(III) with 1,10-phenanthroline in solution by the data of NMR relaxation spectroscopy

NMR relaxation spectroscopy (RS) is used to examine the molecular structure of paramagnetic bis-diisobutyl dithiophosphinate complexes of lanthanides (by the example of europium and lutetium) with 1,10-phenanthroline in CDCl₃ solution. The results obtained are consistent with the results of studying the molecular structure of bis-diisobutyl dithiophosphinate complexes of yttrium with 1,10-phenanthroline in the crystalline phase by XRD.     

Molecular structures and ESR spectra of copper(ii) complexes with 2-hydroxypropiophenone acyldihydrazones

The dinuclear copper(ii) complexes with 2-hydroxypropiophenone acyldihydrazones (H₄L) having the composition [Cu₂L·mPy], where the L ligand contains the polymethylene chain with different lengths (from two to five units), were synthesized and studied. The crystal and molecular structures of the 2-hydroxypropiophenone adipoylhydrazone complex [Cu₂L·4Py]·Py were established by X-ray diffraction analysis. Copper atoms are 8.212 distant from each other, and their nearest environment has the tetragonal pyramidal geometry. The ESR spectra of solutions of the complexes based on acyldihydrazones of succinic, glutaric, and adipic acids contain seven HFS lines with the constant 40·10^–4 cm^–1 from two equivalent copper atoms. The spectra were interpreted as a result of the spin-spin exchange interaction of two unpaired electrons. An increase in the polymethylene chain length to five units prevents exchange interactions. The ESR spectrum of the complex with acyldihydrazone of pimelic acid contains a signal of four HFS lines with a _Cu = 73.4·10^–4 cm^–1, which is typical of mononuclear copper(ii) complexes.     

Solid-state NMR spectra of paramagnetic silica-based materials: observation of 29Si and 27Al nuclei in the first coordination spheres of manganese ions

Some silica-based solids, prepared by the sol/gel method in the presence of high Mn2+ concentrations, have been characterized by the 29Si, 27Al MAS NMR spectra and 29Si T1 measurements. The single-pulse 29Si and 27Al MAS NMR spectra have shown broad spinning sideband patterns that are interpreted in terms of anisotropic bulky magnetic susceptibility (BMS) and dipole-field effects. In the absence of paramagnetic isotropic shifts, the 29Si and 27Al nuclei observed in the single-pulse NMR spectra have been assigned to nuclei remote from paramagnetic centers. It has been demonstrated that the 29Si and 27Al nuclei, which are in the vicinity of the manganese ions, can be detected by the Hahn-echo MAS NMR experiments at different carrier frequencies.     

Dynamic 15N NMR studies of iron phosphine complexes containing coordinated dinitrogen

The ¹⁵N‐labelled iron dinitrogen complexes trans‐[FeH(N₂)(PP)₂]⁺[BPh₄]^? (PP = dppe, depe, dmpe) and cis‐[FeH(N₂)(PP₃)]⁺[BPh₄]^? were prepared in situ by exchange of unlabelled coordinated dinitrogen with ¹⁵N₂. ¹⁵N NMR chemical shifts and coupling constants are reported. The ¹⁵N spectra exhibit separate signals for the metal‐bound and terminal nitrogen atoms of the coordinated N₂. The ¹⁵N resonances display ¹⁵N, ¹⁵N coupling as well as ³¹P, ¹⁵N coupling and long‐range ¹⁵N, ¹H coupling when there is a metal‐bound hydrido ligand. Exchange between free and coordinated dinitrogen was monitored by magnetization transfer between ¹⁵N‐labelled sites using an inversion–transfer–recovery experiment. Exchange between the metal‐bound and terminal nitrogen atoms of coordinated N₂ was also monitored by magnetization transfer and this could proceed by N₂ dissociation or by an intramolecular process. Copyright © 2003 John Wiley & Sons, Ltd.     

47, 49Ti NMR spectra of half-sandwich titanium(IV) complexes

The 47, 49Ti chemical shifts, resonance line half-widths (Deltanu1/2) and energies of the first electronic charge-transfer transitions (lambdamax1.CT) of Cp'TiX3, where Cp' = eta5-C5H5 (Cp), eta5-C5H4Me (MeCp), eta5-C5HMe4 (Me4Cp), eta5-C5Me5 (Me5Cp), eta5-C5H4SiMe3 (SiCp), eta5-C5H4SnMe3 (SnCp) and eta5-C5H4SiMe2Cl (Si'Cp) and X = Cl, Br, I and OBut, half-sandwich complexes are reported. For the compounds studied, a direct linear relationship between delta(49Ti) and lambdamax1.CT was found.     

Vanadium NMR of organovanadium complexes

A brief (and simplified) introduction into the background theory of NMR parameters (shielding, scalar coupling constants, and relaxation times) pertinent to the quadrupolar nucleus ⁵¹V is provided. General trends are discussed in the light of electronic and steric factors, medium effects, temperature and isotope effects influencing these parameters, in particular ⁵¹V shielding. Data are reported on vanadium complexes containing at least one vanadium-to-carbon bond, including alkyl, alkylidene and alkylidyne complexes, complexes containing η²- and η³-bonded ligands, carbonyl and isonitrile complexes, as well as η⁵-cyclopentadienyl and related vanadium compounds. DFT supported correlations between substituent effects and shielding, applicable to catalyst design, are included. The review focuses on solution NMR, but NMR in the crystalline solid state and in mesophases is also briefly addressed.     

Identification of Pt(II) and Pd(II) stereoisomeric complexes with aminobutyric acid by NMR and IR spectroscopy

Complexes of Pd(II) with aminobutyric acid AmH = NH₂CH(CH₂CH₃)COOH, namely, trans-[Pd(AmH)₂Cl₂] with monodentate (via the NH₂ group) AmH ligands and cis-, trans-Pd(Am)₂ with bidentate (via NH₂ and COO groups) ligands have been synthesized for the first time. Elemental analysis and IR and NMR spectroscopy were used to identify the synthesized compounds. The NMR spectra of the Pd(II) complexes were interpreted by comparing them with the NMR spectra of the analogous complexes of Pt(II). For Pt(II) and Pd(II) complexes with aminobutyric acid used as examples, an approach to identification of diastereomer bis-aminoacid complexes in specimens with racemic aminoacids by NMR spectroscopy is demonstrated.     

ESR spectra of copper(ii) complexes with 2-hydroxy-5-methyl- and 5-chloro-2-hydroxyacetophenone acyldihydrazones

ESR spectra of binuclear copper(ii) complexes with 2-hydroxy-5-methyl- and 5-chloro-2-hydroxyacetophenone acyldihydrazones (H₄L) [Cu₂L·2Py], in which the coordination polyhedra are linked by the polymethylene chain with different lengths (from one to five units), were studied. The spectra of the complexes based on acyldihydrazones of malonic, succinic, glutaric, and adipic acids exhibit weak exchange interactions between the paramagnetic sites. These interactions induce seven HFS lines from two equivalent copper nuclei with the constant 40·10^–4 cm^–1 in the ESR spectra of liquid solutions. An increase in the polymethylene chain length to five units prevents the exchange interactions, and the ESR spectrum of the complex based on heptadioic acyldihydrazone contains the signal of four HFS lines with the constant 72·10^–4 cm^–1, which is common for the copper(ii) monomeric compounds.     

Physicochemical characterization of the dimeric lanthanide complexes [en{Ln(DO3A)(H2O)}2] and [pi{Ln(DTTA)(H2O)}2]2-: a variable-temperature 17O NMR study

The Gd(III) complexes of the two dimeric ligands [en(DO3A)2] {N,N'-bis[1,4,7-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecan-10-yl-methylcarbonyl]-N,N'-ethylenediamine} and [pi(DTTA)2]8- [bisdiethylenetriaminepentaacetic acid (trans-1,2-cyclohexanediamine)] were synthesized and characterized. The 17O NMR chemical shift of H2O induced by [en{Dy(DO3A)}2] and [pi{Dy(DTTA)}2]2- at pH 6.80 proved the presence of 2.1 and 2.2 inner-sphere water molecules, respectively. Water proton spin-lattice relaxation rates for [en{Gd(DO3A)(H2O)}2] and [pi{Gd(DTTA)(H2O)}2]2- at 37.0 +/- 0.1 degrees C and 20 MHz are 3.60 +/- 0.05 and 5.25 +/- 0.05 mM(-1) s(-1) per Gd, respectively. The EPR transverse electronic relaxation rate and 17O NMR transverse relaxation time for the exchange lifetime of the coordinated H2O molecule and the 2H NMR longitudinal relaxation rate of the deuterated diamagnetic lanthanum complex for the rotational correlation time were thoroughly investigated, and the results were compared with those reported previously for other lanthanide(III) complexes. The exchange lifetimes for [en{Gd(DO3A)(H2O)}2] (769 +/- 10 ns) and [pi{Gd(DTTA)(H2O)}2]2- (910 +/- 10 ns) are significantly higher than those of [Gd(DOTA)(H2O)]- (243 ns) and [Gd(DTPA)(H2O)]2- (303 ns) complexes. The rotational correlation times for [en{Gd(DO3A)(H2O)}2] (150 +/- 11 ps) and [pi{Gd(DTTA)(H2O)}2]2- (130 +/- 12 ps) are slightly greater than those of [Gd(DOTA)(H2O)]- (77 ps) and [Gd(DTPA)(H2O)]2- (58 ps) complexes. The marked increase in relaxivity (r1) of [en{Gd(DO3A)(H2O)}2] and [pi{Gd(DTTA)(H2O)}2]2- result mainly from their longer rotational correlation time and higher molecular weight.