Multinuclear Magnetic Resonance Study Research Articles

Multinuclear MR and MRI study of lithium-ion cells using a variable field magnet and a fixed frequency RF probe

An exploratory multinuclear magnetic resonance (MR) and magnetic resonance imaging (MRI) study was performed on lithium-ion battery cells with 7Li, 19F, and 1H measurements. A variable field superconducting magnet with a fixed frequency parallel-plate radiofrequency (RF) probe was employed in the study. The magnetic field was changed to set the resonance frequency of each nucleus to the fixed RF probe frequency of 33.7 MHz. Two cartridge-like lithium-ion cells, with graphite anodes and LiNi0.5Mn0.3Co0.2O2 (NMC) cathodes, were interrogated. One cell was pristine, and one was charged to a cell voltage of 4.2 V. The results presented demonstrate the great potential of the variable field magnet approach in multinuclear measurement of lithium-ion batteries. These methods open the door for developing faster and simpler methods for detecting, quantifying, and interpreting MR and MRI data from lithium-ion and other batteries.

Direct Synthesis of Two-Dimensional SnSe and SnSe2 through Molecular Scale Preorganization.

Two-dimensional tin monoselenide (SnSe) and tin diselenide (SnSe2) materials were efficiently produced by the thermolysis of molecular compounds based on a new class of seleno-ligands. Main group metal chalcogenides are of fundamental interest due to their layered structures, thickness-dependent modulation in electronic structure, and small effective mass, which make them attractive candidates for optoelectronic applications. We demonstrate here the synthesis of stable tin selenide precursors by in situ reductive bond cleavage in the dimeric diselenide ligand (SeC2H4N(Me)C2H4Se)2 in the presence of SnCl4. New molecular precursors [SnIV(SeC2H4N(Me)C2H4Se)2], [SnIVCl2(SeC2H4N(Me)C2H4Se)], and [SnIV(SC2H4N(Me)C2H4S)(SeC2H4N(Me)C2H4Se)] were thoroughly characterized by multinuclear magnetic resonance studies and single-crystal X-ray diffraction analysis that revealed the Sn(IV) center to be octahedrally coordinated by two tridentate dianionic chelating ligands or trigonally pyramidally coordinated by one chelating ligand and two chlorido ligands. Preorganization of metal-selenium bonds in both compounds offered direct and reproducible synthetic access to two-dimensional tin chalcogenides (SnSe and SnSe2) via simple adjustment of the pyrolysis temperature. Additionally, SnSe2 and SnSxSe2-x particles could be successfully synthesized by microwave-assisted decomposition of the molecular precursors, which was unambiguously corroborated by both experimental and computational analyses that explained the formation of a selenium rich SnSxSe2-x phase from a single molecular precursor containing both Sn-Se and Sn-S bonds.

Multinuclear Magnetic Resonance Study of Sodium Salts in Water Solutions

The small amounts of gaseous 3He dissolved in low concentrated water solutions of NaCl, NaNO3 and NaClO4 were prepared and examined by 3He-, 23Na-, 35Cl- and 15N-NMR spectroscopy. This experimental data, along with new theoretical shielding factors, was used to measure the 23Na nuclear magnetic moment against that of helium-3 μ(23Na) = +2.2174997(111) in nuclear magnetons. The standard relationship between NMR frequencies and nuclear magnetic moments of observed nuclei was used. The nuclear magnetic shielding factors of 23Na cation were verified against that of counter ions present in water solutions. Very good agreement between shielding constants σ(3He), σ(23Na+), σ(35Cl‒), σ(35ClO4‒), σ(15NO3‒) in water at infinite dilution and nuclear magnetic moments was observed for all magnetic nuclei. It can be used as a reference nucleus for calculating a few other magnetic moments of different nuclei by the NMR method. An analysis of new and former μ(23Na) experimental data obtained by the atomic beam magnetic resonance method (ABMR) and other NMR measurements shows good replicability of all specified results. The composition of sodium water complexes was discussed in terms of chemical equilibria and NMR shielding scale.

Multinuclear Magnetic Resonance Study on Aluminium Sec-butoxide Chelated with Ethyl Acetoacetate in Various Amounts

Reactive aluminum alkoxide (ASB, aluminium sec-butoxide) was chelated using β-diketone (EAA, ethyl acetoacetate) in order to gain control over rapid hydrolysis in the course of the sol-gel process. Derived chelates were analysed using several NMR spectroscopic techniques: one-dimensional 1H, 13C, 27Al NMR and two-dimensional COSY, HSQC and DOSY. The NMR analysis enabled identification of the formed chelate species, as well as determination of their quantitative relationships. Several complexation products were observed: tris-chelated monomer, Al(EAA)3, bis-chelated dimmer, Al2(OnBu)4(EAA) 2, tris-chelated dimmer, Al2(OnBu)3(EAA)3, tetra-chelated dimmer, Al2(OnBu)2(EAA)4, and monochelated trimer, Al3(OnBu)8(EAA). Of the formed oligomer compounds, this is the first evidence of Al2(OR)3L3 in any alkoxide and β-ketoester or β-diketone combination. Aluminium sec-butoxide and ethyl acetoacetate complexes Al2(OnBu)4(EAA) 2 and Al2(OnBu)2(EAA)4 were also observed for the first time. With the increase of the EAA/ASB ratio the coordination of aluminium shifts towards six, whereas above the EAA/ASB ratio of 2.5 solely six-coordinated aluminium exists.

Multinuclear magnetic resonance study on the occurrence of phosphorus in activated carbons prepared by chemical activation of lignocellulosic residues from the babassu production

Activated carbons with well-developed microporosity and containing dispersed nanostructured phosphorus compounds were produced by the chemical activation with H3PO4 of an abundant Brazilian lignocellulosic residue (endocarp of babassu coconut). The chemical nature of the phosphorus-containing species in the produced materials was studied by 1H, 13C and 31P solid-state NMR spectroscopy, including 2D 1H-31P correlation experiments and the use of 1H homonuclear decoupling. With this approach, it was possible to detect the formation of different phosphorus compounds (mostly containing phosphate groups) embedded into the porous carbon network and exhibiting strong dipolar coupling between 31P nuclei and 1H nuclei in hydrogen atoms bonded to aromatic carbons. The chemical activation with H3PO4 was found to be noticeably effective when starting from the raw lignocellulosic precursor, leading to the achievement of activated carbons with large surface area (up to 1900m2/g). Due to the natural occurrence of silicon compounds in the endocarp of babassu coconut, the chemical activation with H3PO4 was found to produce silicon pyrophosphate nanocrystals in addition to phosphate groups in non-crystalline clusters dispersed into the porous structure of the activated carbons, suggesting that these materials can be useful for applications as solid phosphoric acid catalysts.

Investigation of Dynamics in BMIM TFSA Ionic Liquid through Variable Temperature and Pressure NMR Relaxometry and Diffusometry

A comprehensive variable temperature, pressure and frequency multinuclear (1H, 2H, and 19F) magnetic resonance study was undertaken on selectively deuterated 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (BMIM TFSA) ionic liquid isotopologues. This study builds on our earlier investigation of the effects of increasing alkyl chain length on diffusion and dynamics in imidazolium-based TFSA ionic liquids. Fast field cycling 1H T1 data revealed multiple modes of motion. Through calculation of diffusion coefficient (D) values and activation energies, the low- and high-field regimes were assigned to the translational and reorientation dynamics respectively. Variable-pressure 2H T1 measurements reveal site-dependent interactions in the cation with strengths in the order MD3 > CD3 > CD2, indicating dissimilarities in the electric field gradients along the alkyl chain, with the CD2 sites having the largest gradient. Additionally, the α saturation effect in T1 vs. P was observed for all three sites, suggesting significant reduction of the short-range rapid reorientational dynamics. This reduction was also deduced from the variable pressure 1H T1 data, which showed an approach to saturation for both the methyl and butyl group terminal methyl sites. Pressure-dependent D measurements show independent motions for both cations and anions, with the cations having greater D values over the entire pressure range.

Spying on Fe ions and their role in modified aluminosilicates during the sorption of anions using solid-state NMR spectroscopy

Post-synthetic modifications of zeolites enable their possible use as adsorbents in separation and purification processes. Here, we present a multinuclear (29Si, 27Al, 31P) magnetic resonance study of solid samples of zeolite A (LTA) and hydroxysodalite (HS), their post-synthetic modification using FeSO4 solution, and the results of their analysis by NMR after the anion (PO43−) adsorption process. High-resolution 29Si and 27Al MAS NMR spectra provide valuable structural information on the oxidation of Fe2+ ions to Fe3+ species during the modification process, whereas 27Al 3Q/MAS solid-state NMR spectra of LTA and HS unveil a simultaneous dealumination process characteristic of acid leaching in aluminosilicate systems. 31P solid-state NMR spectra of LTA and HS, collected at “very-fast” spinning speed, revealed a dramatic change in the chemical shift values for the phosphates present, directly characteristic of FePO4 in the case of LTA, and phosphates of alkali and/or alkaline earth metals in the case of HS. Moreover, density functional theoretical (DFT) computations provide satisfactory agreement with the obtained 27Al and 29Si experimental data. This work demonstrates possible NMR approaches to the characterization of complex framework materials and provides key insights into aluminosilicate materials affected by unpaired electron(s).

Multinuclear solid-state magnetic resonance study of oxo-bridged diniobium and quadruply-bonded dimolybdenum carboxylate clusters

Carboxylate paddlewheels and their oxo-bridged analogues constitute ideal building blocks for the assembly of two- and three-dimensional framework materials. Here, we present a multinuclear (1H, 13C, 93Nb, 95Mo) magnetic resonance study of solid samples of Nb2OCl6(O2Ph)2 (1), Mo2(O2CMe)4 (2), and Mo2(O2CCHF2)4 (3). High-resolution proton and 13C CP/MAS NMR spectra provide valuable information on structure and crystal symmetry and on cocrystallized solvent. 93Nb solid-state NMR spectra of 1 provide quadrupolar coupling constants and chemical shift tensors which are characteristic of the axially asymmetric Nb-O-Nb bridging environment. 95Mo solid-state NMR spectra of 2 and 3 provide quadrupolar coupling constants and chemical shift tensors which are directly characteristic of the molybdenum-molybdenum quadruple bonds in these compounds. The quadruple bonds are characterized by particularly large 95Mo chemical shift tensor spans on the order of 5500ppm. Density functional theoretical computations provide good agreement with the 93Nb and 95Mo experimental data, with some exceptions noted. This work demonstrates possible NMR approaches to characterize more complex framework materials and provides key insight into the Mo-Mo quadruple bond.

Diastereoselective Ortho Lithiation of Phosphinimidic Amides: A Multinuclear Magnetic Resonance and Computational Study

The structure of the dianion (SP,RC)-10 formed in the diastereoselective N,Cortho dilithiation of the phosphinimidic amide (RC)-Ph2P(═NCO2Me)NHCH(Me)Ph (5; dr of 95:5) with tert-butyllithium in THF has been elucidated using multinuclear magnetic resonance methods, including 2D 7Li,nX-HMQC (nX = 15N, 31P) correlations. (SP,RC)-10 consists of a monomer in which C,N and N,O chelation of the lithium cations generates a system containing a five- and a six-membered metallacycle, respectively, sharing a P-N bond with the lithium atoms connected through the NCO moiety of the phosphazenyl group. Selective deprotonation of the pro-S P-phenyl ring of 5 was ascertained through NOE measurements. DFT computations at the M06-2X(SMD,THF)/6-311+G(d,p)//M06-2X/6-31G(d) level showed that the stereoselective ortho deprotonation process fulfills the features of the CIPE model. The P═N linkage of the N-lithiated species (RC)-8 acts as a directing metalation group via N···LitBu coordination. The mixed complex that is formed evolves to a more stabilized species due to the intramolecular coordination of the OMe group to the lithium cation of the base. Abstraction of the ortho proton proceeds with energy barriers of 12.4 and 13.3 kcal/mol for the pro-R and pro-S phenyl rings. The preference for the latter is explained in terms of the Curtin-Hammett principle.

Multinuclear magnetic resonance study of equilibria between aluminum(III) and sulfur-containing amino acids in aqueous solutions

Aluminum(III) is generally found in small amounts in living organisms where it interacts with several biomolecules. Low mass biomolecules can form complexes associated with absorption and distribution processes of this toxic ion. However, investigating aluminum(III) complexes in solution poses singular difficulties, because it is highly hydrolyzable. Amino acids constitute possible ligands for aluminum(III). Methionine, cysteine and homocysteine are found in healthy human body. Penicillamine is a drug used in several circumstances, such as in treating metal poisoning. These four biomolecules share similar donor atoms involved in complexation reactions: a carboxylate oxygen, an amine nitrogen and sulfur. In this study, four binary complexes formed by aluminum(III) and amino acids in solution at a metal-to-ligand ratio of 1:1 were analyzed through potentiometry and multinuclear magnetic resonance (13C and 27Al). Potentiometry data consistently demonstrated complexion formation. Distributions of species revealed the coexistence of several species in ample pH ranges and pointed out the preferable value to perform the NMR analyses. 13C NMR data were used to confirm complexion formation, while 27Al NMR data indicated the geometric arrangement adopted by the complexes. Structures were proposed for each complex.

Direct observation of a lithiated oxirane: a synergistic study using spectroscopic, crystallographic, and theoretical methods on the structure and stereodynamics of lithiated ortho-trifluoromethyl styrene oxide

α-Lithiated epoxides, long considered “fleeting” intermediates in the reactions of epoxides with strong bases, have nowadays proven to be key synthons for asymmetric synthesis. In this study, the solution and the solid state structure of an α-lithiated aryloxirane, namely α-lithiated ortho-trifluoromethyl styrene oxide (1-Li), were determined. Single crystal X-ray diffraction analysis of 1-Li performed at 100 K applying the X-TEMP-2 device revealed a self-assembled heterochiral dimeric structure with a rare central six-membered (O–Li–C)2 planar core, which is unprecedented in Li/oxygen carbenoids. Multinuclear magnetic resonance (1H, 13C, 19F, 7Li) studies suggested that 1-Li exists in THF solution as a mixture of two interconverting diastereomeric dimeric aggregates, each one featuring a single σ-contact between lithium and a carbon atom. Line shape analysis provided activation parameters for both the dynamic interconversion of the two dimers and the enantiomerisation of 1-Li, which proved to be mostly entropy controlled. The structural assignment in solution was supported by density functional theory computations through the investigation of conformers of monomeric and dimeric complexes of 1-Li featuring different degrees of specific solvation. A mechanism based on the equilibration of six-membered homo- and heterochiral dimers was proposed to explain the configurational instability exhibited by 1-Li in THF.

A multinuclear magnetic resonance study of transformations of ruthenium(II) nitrosyl chloride complexes in aqueous solutions

Aqueous solutions of ruthenium nitrosyl chloride complexes have been studied by14N, 15N, 17O, 99Ru, and 35Cl NMR. Individual complex species have been identified and the corresponding chemical shifts have been determined. The primary aquation product of the pentachloronitrosylruthenate ion is the cis-[RuNO(H2O)Cl4]− complex, which subsequently undergoes isomerization. The equilibrium constants of interconversions of ruthenium nitrosyl chloride complexes in an aqueous solution at room temperature have been estimated.

Multinuclear magnetic resonance study of N-phenyl-aza-15-crown-5 complexes with lithium, sodium and caesium ions in nonaqueous solvents

Nuclear magnetic resonances of 7Li, 23Na and 133Cs nuclei were used to study the lithium, sodium and caesium ion complexes with N-phenyl-aza-15-crown-5 (PhA15C5) in nitromethane (NM), acetonitrile (AN) and AN–NM mixture solutions. The chemical shift data indicated that these cations form 1 : 1 cation : ligand complexes with PhA15C5. The formation constants of the resulting complexes were calculated from the computer fitting of the chemical shift–mole ratio data. The results show that the complex formation constants of PhA15C5 with these cations vary in the order of Na+ > Li+ ≫ Cs+. Complexation of the lithium ion was also studied in binary AN–NM mixtures. It was found that the stability of the resulting complexes increases by an increase in the amount of NM in the solvent mixture.

Substituent Effect in 2-Benzoylmethylenequinoline Difluoroborates Exhibiting Through-Space Couplings. Multinuclear Magnetic Resonance, X-ray Diffraction, and Computational Study

The series of nine 2-benzoylmethylenequinoline difluoroborates have been synthesized and characterized by multinuclear magnetic resonance, X-ray diffraction (XRD), and computational methods. The through-space spin-spin couplings between (19)F and (1)H/(13)C nuclei have been observed in solution. The NMR chemical shifts have been correlated to the Hammett substituent constants. The crystal structures of six compounds have been solved by XRD. For two derivatives the X-ray wave function refinement was performed to evaluate the character of bonds in the NBF(2)O moiety by topological and integrated bond descriptors.

Synthesis and characterization of new lead(II) complexes of Schiff bases derived from amino acids

Some new lead(II) complexes of the general formula Pb(L)2, where HL = Schiff bases derived from the condensation of isatin and chloroisatin with phenylalanine (HL1/HL4), isoleucine (HL2/HL5), and glycine (HL3/HL6), have been synthesized and characterized by elemental analysis, molar conductance, electronic, infrared, and multinuclear magnetic resonance (1H and 13C) studies. In all cases, the Pb atom is in a four-coordinated environment with two bidentate deprotonated Schiff bases binding as monoanionic ligands through the oxygen and azomethine nitrogen. The 3D molecular modeling and analysis for bond lengths and bond angles have also been carried out for one of the representative compounds, [Pb(L3)2] to substantiate the proposed structures.

Multinuclear Magnetic Resonance and DFT Studies of the Poly(chlorotrifluoroethylene-alt-ethyl vinyl ether) Copolymers

Chlorotrifluoroethylene (CTFE) and ethyl vinyl ether (EVE) were reacted under radical conditions to produce the poly(CTFE-co-EVE) alternating copolymer, and a full 13C, 1H, and 19F NMR structural interpretation is offered. All spectra were characterized by broad signals resulting from the overlapping of different chemical shifts. This observation was rationalized by considering a complex mixture of diastereomerically related compounds, hence allowing an average assignment to be determined. A density functional theory (DFT) computational study of the isotropic magnetic shieldings with the GIAO and CSGT methods was performed to explore the diasteriomeric relationships between the single building blocks and their mutual influences along the polymer chain. The calculated results totally support the assignment of the experimental chemical shifts of two diasteriomeric sets of resonances indicating chiral center inversion, and not spin−spin J coupling interactions, as the main cause of spectral complexity.

2-Lithio-3,3-dimethyl-2-oxazolinyloxirane: Carbanion or Azaenolate? Structure, Configurational Stability, and Stereodynamics in Solution

Chemical studies have shown that, in ethereal solvents, oxiranyllithium Li-1 is configurationally unstable either on the macroscopic (Hoffmann's text) or microscopic time scale at low temperature (175 K). An optically pure sample of oxazolinyloxirane 1, once deprotonated, racemized within 1 min at -130 degrees C in THF/Et(2)O (3:2) (t(1/2) = 6.05 s); the application of the Eyring equation suggested a barrier to inversion for Li-1 of 8.8 kcal/mol at -130 degrees C. Despite this, Li-1 exhibited an unusual thermal stability undergoing a successfully deuterium incorporation (>98%) also at 25 degrees C with a little decomposition. The structure, configurational stability, and stereodynamics in solution of alpha-lithiated oxazolinyloxirane Li-1 have been also synergically investigated by means of in situ IR and NMR spectroscopy. IR spectroscopic studies showed that lithiation of 1 is complete at -98 degrees C within 1 min and is accompanied by a decrease of the CN wavenumber by only 60 cm(-1), so supporting the idea that the structure of Li-1 may be more similar to that of an "organolithium" rather than an "azaenolate". In addition to this, multinuclear magnetic resonance studies suggested that at least in a range of concentration of 0.08-0.3 M, Li-1 mainly exists in THF as a monomeric eta(3)-aza-allyl coordinated species rapidly equilibrating, on the NMR time scale, with a complex mixture of diastereomeric oxazoline-bridged dimeric species variously intraaggregated. An exchange mechanism by which monomers would interchange their Li atoms via one of the above dimeric species and which may be responsible for the fast racemization Li-1 undergoes as soon as is generated has been proposed.

Multinuclear magnetic resonance studies of the reactions of the antitumor complexes cis-Pt(L) 2X 2 and cis-Pt(NH 3)(L)X 2 (L = cyclobutylamine and cyclopentylamine) with guanosine and other bases and crystal structures of Pt(cyclopentylamine) 2I 2

The crystal structures of two Pt(cyclopentylamine) 2I 2 compounds were determined by X-ray diffraction methods. Both crystals contain disordered cyclopentylamine ligands. Crystal I contains two independent trans-Pt(cyclopentylamine) 2I 2 molecules and all the C atoms are disordered on two positions. The second crystal ( II) is most interesting since it contains both cis- and trans-Pt(cyclopentylamine) 2I 2 isomers in the same unit cell. It was prepared from the recrystallization of the cis isomer in acetone. The C atoms of the trans molecule in crystal II are disordered on two positions, while only one position was determined in the cis molecule, although some of the C thermal factors are quite high. The reactions of cis-Pt(amine) 2X 2 and cis-Pt(NH 3)(amine)X 2 (amine = cyclobutylamine and cyclopentylamine) with guanosine in water were studied in different Pt:guanosine proportions by multinuclear ( 1H, 195Pt and 15N) magnetic resonance spectroscopy. The presence of several species in solution was observed. For the mixed-cyclobutylamine compound, 15N NMR has shown that some of the NH 3 ligands have been displaced from the coordination sphere in the presence of an excess of guanosine. The reactions of the two mixed-ligand complexes cis-Pt(NH 3)(amine)Cl 2 with 9-methylguanine, inosine and 9-methylhypoxanthine were also studied in water and the results are discussed.

DFT and multinuclear magnetic resonance studies of diazenedicarboxylates and related compounds

A number of diazenedicarboxylates have been studied by multinuclear magnetic resonance ((17)O, (15)N, (13)C) and compared with analogous fumaric, maleic, and phthalic diesters; the investigation of selected compounds of these classes was complemented by density functional theory (DFT) calculations using a polarizable continuum model (PCM) for the solvent, employing the PBE0 functional together with the 6-311G(d,p) basis set for geometry optimization, and the 6-311 + G(2d,p) basis set for calculating the NMR shielding using the gauge-including atomic orbital (GIAO) method. This combined approach provided important information about the preferred conformations in chloroform and their influence on the NMR parameters.

Multinuclear magnetic resonance studies of the hydrolyzed and aquated species of the antitumor complexes cis-Pt(cyclobutylamine) 2X 2 and cis-Pt(NH 3)(cyclobutylamine)X 2 and antitumor testing of mixed -amine Pt(II) compounds

The aquated and hydrolyzed species formed from the complexes cis-Pt(cba) 2I 2 and cis-Pt(NH 3)(cba)I 2 (cba = cyclobutylamine) were studied by multinuclear ( 195Pt, 15N and 1H) magnetic resonance spectroscopy. The iodo ligands were removed with AgNO 3. In acidic medium, the aqueous product consists of the diaqua and the aqua -nitrato cations, although some monohydroxo -bridged dimers are formed after several hours, especially for the mixed -ligand compound. In basic medium, the main species are the dihydroxo compounds. At neutral pD, several species exist in solution, especially with the mixed -amine system, which contained also a small quantity of the symmetric cis-Pt(cba) 2 complexes. Difficulties were encountered because of the insolubility of several oligomeric species, contrary to the cis-Pt(NH 3) 2 system, probably due to the greater lipophilicity of cba compared to NH 3. Monohydroxo -bridged dimers are formed in large quantities and the stereochemistry of the mixed -amine species was determined by 15N NMR spectroscopy. For the latter system, the cyclic dihydroxo -bridged dimers are the predominant species at neutral pD after a few hours. After an extended period of time, most of the oligomers precipitate, leaving the more soluble monohydroxo -bridged dimers as the major species in solution. The preliminary antitumor testing results on several dichloro mixed -ligand compounds are listed. The results on further testing on the most active compound cis-Pt(NH 3)(cba)Cl 2 are also included.