NMR Spectra Of Complexes Research Articles

CRAFT (complete reduction to amplitude frequency table) – robust and time‐efficient Bayesian approach for quantitative mixture analysis by NMR

The intrinsic quantitative nature of NMR is increasingly exploited in areas ranging from complex mixture analysis (as in metabolomics and reaction monitoring) to quality assurance/control. Complex NMR spectra are more common than not, and therefore, extraction of quantitative information generally involves significant prior knowledge and/or operator interaction to characterize resonances of interest. Moreover, in most NMR-based metabolomic experiments, the signals from metabolites are normally present as a mixture of overlapping resonances, making quantification difficult. Time-domain Bayesian approaches have been reported to be better than conventional frequency-domain analysis at identifying subtle changes in signal amplitude. We discuss an approach that exploits Bayesian analysis to achieve a complete reduction to amplitude frequency table (CRAFT) in an automated and time-efficient fashion - thus converting the time-domain FID to a frequency-amplitude table. CRAFT uses a two-step approach to FID analysis. First, the FID is digitally filtered and downsampled to several sub FIDs, and secondly, these sub FIDs are then modeled as sums of decaying sinusoids using the Bayesian approach. CRAFT tables can be used for further data mining of quantitative information using fingerprint chemical shifts of compounds of interest and/or statistical analysis of modulation of chemical quantity in a biological study (metabolomics) or process study (reaction monitoring) or quality assurance/control. The basic principles behind this approach as well as results to evaluate the effectiveness of this approach in mixture analysis are presented.

Paramagnetic 18-Valence-Electron Alkylcyclopentadienylnickel(II) Bromide Dimers

The paramagnetic behavior of 18-electron cyclopentadienylnickel(II) complexes of the [CpNi(μ-Br)]2 type with two unpaired electrons per metal ion has been investigated by 1H and 13C NMR spectroscopy of [Cp‴Ni(μ-Br)]2 (1; Cp‴ = 1,3,4-tBu3C5H2), [3CpNi(μ-Br)]2 (2; 3Cp = 1,3,4-iPr3C5H2), and [4CpNi(μ-Br)]2 (3; 4Cp = 2,3,4,5-iPr4C5H). The tri-tert-butylcyclopentadienyl derivative 1 crystallizes in the triclinic space group P1 and has been investigated by X-ray crystallography. Solid-state magnetic susceptibility measurements of 3 revealed an effective magnetic moment at room temperature of 4.04 μB, confirming the presence of two d8 nickel(II) ions. While antiferromagnetic coupling via the bromo bridges is weak (J = −2.4 cm–1), zero-field splitting is substantial (D = +48.2 cm–1). NMR spectra of complexes 1–3 show signals with half-widths up to 3600 Hz within a spectral window exceeding 500 ppm (1H) or 2200 ppm (13C). An analysis of the spectra gave insight into the spin delocalization, the equilibrium orient...

Vibrational and electronic structural study of dinuclear Zn(II) halide complexes with 4-azabenzimidazole

Two zinc(II) halide complexes of 4-azabenzimidazole (4AB), [Zn2(4AB)4Cl2]Cl2 and [Zn2(4AB)4Br2]Br2, have been synthesized for the first time and characterized by elemental analysis, FT-IR (mid IR, far IR), Raman spectra, and DFT calculations. For the zinc chloride complex, 1H and 13C NMR spectra are also presented. The DFT calculations have been carried out at the B3LYP/6-31G(d) level. The optimized structures were resulted in dinuclear paddlewheel-like geometries around the zinc atoms. The ligands are coordinated to the metal centers in bidentate fashion.

Identifying critical unrecognized sugar–protein interactions in GH10 xylanases from Geobacillus stearothermophilus using STD NMR

(1)H solution NMR spectroscopy is used synergistically with 3D crystallographic structures to map experimentally significant hydrophobic interactions upon substrate binding in solution under thermodynamic equilibrium. Using saturation transfer difference spectroscopy (STD NMR), a comparison is made between wild-type xylanase XT6 and its acid/base catalytic mutant E159Q--a non-active, single-heteroatom alteration that has been previously utilized to measure binding thermodynamics across a series of xylooligosaccharide-xylanase complexes [Zolotnitsky et al. (2004) Proc Natl Acad Sci USA 101, 11275-11280). In this study, performing STD NMR of one substrate screens binding interactions to two proteins, avoiding many disadvantages inherent to the technique and clearly revealing subtle changes in binding induced upon mutation of the catalytic Glu. To visualize and compare the binding epitopes of xylobiose-xylanase complexes, a 'SASSY' plot (saturation difference transfer spectroscopy) is used. Two extraordinarily strong, but previously unrecognized, non-covalent interactions with H2-5 of xylobiose were observed in the wild-type enzyme but not in the E159Q mutant. Based on the crystal structure, these interactions were assigned to tryptophan residues at the -1 subsite. The mutant selectively binds only the β-xylobiose anomer. The (1)H solution NMR spectrum of a xylotriose-E159Q complex displays non-uniform broadening of the NMR signals. Differential broadening provides a unique subsite assignment tool based on structural knowledge of face-to-face stacking with a conserved tyrosine residue at the +1 subsite. The results obtained herein by substrate-observed NMR spectroscopy are discussed further in terms of methodological contributions and mechanistic understanding of substrate-binding adjustments upon a charge change in the E159Q construct.

Synthesis and characterization of trianionic pincer-type complexes of tantalum(V) including solid (X-ray) and solution (NMR) state assignment of an intraligand N–H—F hydrogen bonding interaction

Tanatalum(V) complexes ligated with a trianionic ONO3− pincer-type ligand were synthesized and characterized. Using the ONO trianionic pincer ligand precursor 2,2′-(azanediylbis(3-methyl-6,1-phenylene))bis(1,1,1,3,3,3-hexafluoropropan-2-ol) [CF3-ONO]H3 (1) and various sources of Ta(V), the following pincer complexes were synthesized: (I) anionic trichloride complex {[CF3-ONO]TaCl3}{HNEt3}·(HNEt3Cl)x (2), (II) diamido-amine complex [CF3-ONO]Ta(NMe2)2(HNMe2) (3-NHMe2) and its amine free version [CF3-ONO]Ta(NMe2)2 (3), (III) the neutral trichloride [CF3-ONHO]TaCl3 (4), (IV) the neutral dichloride [CF3-ONO]TaCl2(THF) (5), and (V) the dibenzyl complex [CF3-ONO]TaBn2 (6). Characterization methods include the complete assignment (where possible) for 1H, 13C, 19F, and 15N NMR spectra for complexes 2–6, and single crystal X-ray diffraction characterization for complexes 2, 3, and 4. Interesting aspects regarding the interplay of the ligand in its dianionic form versus its trianionic form, and an unusual H⋯F hydrogen bonding interaction within complex 4 were discovered from these synthetic pursuits.

Solid‐State NMR Correlation Experiments and Distance Measurements in Paramagnetic Metalorganics Exemplified by Cu‐Cyclam

We show how to record and analyze solid-state NMR spectra of organic paramagnetic complexes with moderate hyperfine interactions using the Cu-cyclam complex as an example. Assignment of the (13)C signals was performed with the help of density functional theory (DFT) calculations. An initial assignment of the (1)H signals was done by means of (1)H-(13)C correlation spectra. The possibility of recording a dipolar HSQC spectrum with the advantage of direct (1)H acquisition is discussed. Owing to the paramagnetic shifting the resolution of such paramagnetic (1)H spectra is generally better than for diamagnetic solid samples, and we exploit this advantage by recording (1)H-(1)H correlation spectra with a simple and short pulse sequence. This experiment, along with a Karplus relation, allowed for the completion of the (1)H signal assignment. On the basis of these data, we measured the distances of the carbon atoms to the copper center in Cu-cyclam by means of (13)CR2 relaxation experiments combined with the electronic relaxation determined by EPR.

Symmetry breaking in self-assembled M 4 L 6 cage complexes

Here we describe the phenomenon of symmetry breaking within a series of M4L6 container molecules. These containers were synthesized using planar rigid bis-bidentate ligands based on 2,6-substituted naphthalene, anthracene, or anthraquinone spacers and Fe(II) ions. The planarity of the ligand spacer favors a stereochemical configuration in which each cage contains two metal centers of opposite handedness to the other two, which would ordinarily result in an S4-symmetric, achiral configuration. Reduction of symmetry from S4 to C1 is achieved by the spatial offset between each ligand's pair of binding sites, which breaks the S4 symmetry axis. Using larger Cd(II) or Co(II) ions instead of Fe(II) resulted, in some cases, in the observation of dynamic motion of the symmetry-breaking ligands in solution. NMR spectra of these dynamic complexes thus reflected apparent S4 symmetry owing to rapid interconversion between energetically degenerate, enantiomeric C1-symmetric conformations.

Coordination studies of copper(II), nickel(II), cobalt(II) and zinc(II) salts with pyridyl–tetrazole ligands containing alkyl or alkyl halide pendant arms

The reaction of 2-(2H-tetrazol-5-yl)pyridine (L1) with 1,n-dibromoalkane (n=3, 4, 6 or 8) results in the formation of the isomers 2-(n″-bromoalkyl-(1-tetrazol-5-yl)pyridine (L2A-D) and 2-(n″-bromoalkyl-(2-tetrazol-5-yl)pyridine (L3A-D). The reaction of L1 with 1-bromoalkanes also resulted in the formation of isomeric materials, namely 2-(n″-alkyl-(1-tetrazol-5-yl)pyridine (L4A-C) and 2-(n″-alkyl-(2-tetrazol-5-yl)pyridine (L5A-C). Complexation reactions of these ligands with the transition metal salts CuCl2·2H2O, Co(NCS)2, NiCl2·2H2O and ZnCl2 were carried out in methanol and resulted in complexes containing a 1:1 metal:ligand stoichiometry except in the cases of the cobalt complexes where a 1:2 metal:ligand stoichiometry was obtained. The 1H NMR spectra of the zinc complexes showed that the ligands containing the pendant arm in the 2-N position of the tetrazole ring bind the zinc ion more strongly than those containing the pendant arm in the 1-N position. The X-ray structures of two cobalt salts, Co(L5A)2(NCS)2 and Co(L5C)2(NCS)2, are also discussed.

Molecular Indium(III) Phosphonates Possessing Ring and Cage Structures. Synthesis and Structural Characterization of [In2(t-BuPO3H)4(phen)2Cl2] and [In3(C5H9PO3)2(C5H9PO3H)4(phen)3]·NO3·3.5H2O

Two novel indium(III) phosphonates, [In2(t-BuPO3H)4(phen)2Cl2] (1) and [In3(C5H9PO3)2(C5H9PO3H)4(phen)3]·NO3·3.5H2O (2) with phen = 1,10-phenanthroline, have been synthesized by solvothermal reactions involving indium(III) salts and organophosphonic acids. 1 is a dinuclear compound where the two indium centers are bridged by a pair of isobidentate phosphonate ligands, [t-BuP(O)2OH](-), resulting in an eight-membered (In2P2O4) puckered ring. Compound 2 is trinuclear; the In3 platform is held together by two bicapping tripodal phosphonate ligands from the top and bottom of the indium plane. In addition, two bridging monoanionic phosphonate ligands serve to bind two pairs of indium centers. Both 1 and 2 also contain monodentate monoanionic phosphonate ligands. The solid-state MAS (31)P NMR spectrum of complex 1 shows two signals at 21.9 and 29.3 ppm. Compound 2 contains signal maxima at 25.8 and 28.9 ppm, with a shoulder at 31.5 ppm. Room temperature solid-state fluorescence spectra of 1 and 2 are characterized by strong emission bands at 385 nm (λex = 350 nm) and 395 nm (λex = 350 nm), respectively, which are red-shifted with respect to the emission of free phenanthroline.

Dimethylphosphinato and dimethylarsinato complexes of group 13 metals and their chemistry

Dimethylphosphinato M(Me2PO2)3 and dimethylarsinato (cacodylato) M(Me2AsO2)3 complexes of group 13 metals (M=Al, Ga, In, Tl) have been prepared in good yields from dimethylphosphinic and dimethylarsinic acids or sodium dimethylarsinate. The phosphinato and the gallium and indium cacodylato complexes are most likely polymeric, while the aluminum and thallium cacodylato ones are monomeric based on their thermal behavior. From aqueous solutions the hydrated complexes Al(Me2PO2)3·3H2O, Ga(Me2PO2)3·H2O, Al(Me2AsO2)3·H2O, and In(Me2AsO2)3·3H2O were isolated. Pyridine does not form addition compounds with any phosphinato and cacodylato complexes, In(Me2AsO2)3 was rearranged, and Al(Me2AsO2)3 gave Al(Me2AsO2)2(OH). The NMR spectra of the cacodylato complexes in D2O, CD3OD, and CDCl3 revealed the existence of several species in solution. All cacodylato complexes were decomposed by thiols, e.g., cysteine giving cystine and Me2As-SCH2CH(NH3 +)COO−.

Induced production of depsipeptides by co-culturing Fusarium tricinctum and Fusarium begoniae

A co-culture of Fusarium tricinctum and Fusarium begoniae induced the production of two new linear depsipeptides, subenniatins A and B (1–2), which were not detected when either of the two fungi was cultured alone. The structures of the new compounds were unambiguously determined by analysis of 1D, 2D NMR, and mass spectra, as well as by chemical transformation. Complex NMR spectra were observed for compounds 1 and 2, which were attributed to the presence of rotamers as revealed by 1D NOE and ROESY measurements. Structurally, compounds 1 and 2 are biogenetic building blocks of the cytotoxic enniatins B, B1, A1, and A, which are the major metabolites of F. tricinctum when this fungus is cultured alone. Compounds 1 and 2 were found to be inactive in cytotoxic and antibacterial assays.

Nanoparticles of novel organotin(IV) complexes bearing phosphoric triamide ligands

Four novel organotin(IV) complexes containing phosphoric triamide ligands were synthesized and characterized by multinuclear (1H, 31P, 13C) NMR, infrared, ultraviolet and fluorescence spectroscopy as well as elemental analysis. The 1H NMR spectra of complexes 1–4 proved that the Sn atoms adopt octahedral configurations. The nanoparticles of the complexes were also prepared by ultrasonication, and their SEM micrographs indicated identical spherical morphologies with particles sizes about 20–25 nm. The fluorescence spectra exhibited blue shifts for the maximum wavelength of emission upon complexation.

Rattler Site Selectivity and Covalency Effects in Type-I Clathrates

Type-I germanium clathrates comprised of Ga/Ge tetrakaidecahedra and dodecahedra cages that host alkaline earth atoms exemplify the properties of good thermoelectrics where the guest-atom anharmonic vibrations play a major role. However, while the host lattice–guest atom interaction is essential for this class of materials it is at the same time difficult to investigate due to the random Ga/Ge site occupation in the host lattice. In the present 71Ga NMR study of Sr8Ga16Ge30 and Ba8Ga16Ge30 samples we extract different Ga crystallographic site contributions from otherwise complex NMR spectra by exploring differences in their spin–lattice relaxation rates. Such approach opens a unique possibility for a site-selective study that directly proves non-negligible interaction of the anisotropic rattling motions of endohedral Sr with Ga atoms occupying the specific \(24k\) sites of larger tetrakaidecahedral cages. This interaction affects electron–phonon coupling and modifies the local chemical environment — possi...

ChemInform Abstract: Two‐Dimensional Higher Quantum Correlation and Resolved Techniques for the Analyses of Complex 1H NMR Spectra of Scalar‐Coupled Spins

AbstractReview: 94 refs.

Synthesis and Spectroscopic Studies of Ru(II) Complexes of 1,2,4-Triazoles, 1,2,4-Triazines and Pyrimidine Derivatives

Coordination modes of metal complexes with organic ligands with heteroatom N, S or O are well known. The usefulness of metal complexes with such ligands exhibit remarkable biological activity against certain microbes, viruses and tumors. The presence of heteroatom in such ligands play a key role when coordinated with transition metal atom for example 1,2,4-triazine derivative of Pd(II) and Pt(II) show mono-dentate or bidentate behaviour. Similarly derivatives of 1,2,4-triazoles and 1,2,4-tiazine act as bidentate and exhibit tautomerism or ambidentate nature on coordination with metal atom. For example 3-alkyl-4-amino-5-thiol derivative of 1,2,4triazole show a 5-membered ring complex on coordination with Co(II) or Ni(II). We have previously reported that Ru(II) forms very stable six membered complexes with ligands containing heteroatom N, S and O. These heteroatom's act as an electron donor to metal. Now we report the preparation of Ru(II) complexes with 1,2,4-triazoles, 1,2,4-triazines and pyrimidine derivatives (Scheme I-IV). Ruthenium(II) in these complexes acts as an electron acceptor. This enhanced its ability to coordinate with electron donor ligand to yield a stable and electron rich compound of low ionization energy. The complexes (1a), (2a), (3a), (4a), (6a) show their tautomeric nature on coordination with metal Ru(II) while in complex 5a the ligand acts as an ambidentate nature (Scheme-IV). The IR spectra of all these complexes show only two metal terminal (Ru-CO) band near 2000 cm and are in cis disposition. All the ligands form a six membered ring structure around the metal Ru(II). IR and H NMR spectra of complexes are shown in Tables 1 and 2, respectively. The elemental Synthesis and Spectroscopic Studies of Ru(II) Complexes of 1,2,4-Triazoles, 1,2,4-Triazines and Pyrimidine Derivatives

Tuning structure and properties of Pd and Pt camphor derived complexes

Seven new camphor palladium or platinum compounds with novel metal coordination environments were obtained by convenient choice of the experimental conditions in particular the solvent. cis-[PtCl2(PhNC10H14O)2]) and [Pd(MeNNC10H14O)2] were structurally characterized by X-ray diffraction analysis while [{PtCl2(Me2NC10H13NSO2)}2], [{PdCl2(YNC10H14O)}2] (Y=NMe2, NPh2) and [Pd(PhNNC10H14O)2] were formulated by elemental analysis and spectroscopic techniques. Relevant aspects of the IR and NMR spectra of complexes [Pd(YNC10H14O)2] (Y=MeN, PhN) are discussed with the help of DFT calculations.Evaluation of the properties of the new complexes as catalysts for activation of 4-pentyn-1-ol towards formation of cyclization products showed that [{PdCl2(Ph2NNC10H14O)}2] is more efficient than [PdCl2(Me2NNC10H14O)2] which is one of the more efficient camphor derived catalysts reported before. In contrast the chelate complexes [Pd(YNC10H14O)2] (Y=MeN, PhN) display no catalytic activity.

Atomic Contributions from Spin‐Orbit Coupling to 29Si NMR Chemical Shifts in Metallasilatrane Complexes

New members of a novel class of metallasilatrane complexes [X-Si-(μ-mt)(4)-M-Y], with M=Ni, Pd, Pt, X=F, Cl, Y=Cl, Br, I, and mt=2-mercapto-1-methylimidazolide, have been synthesized and characterized structurally by X-ray diffraction and by (29)Si solid-state NMR. Spin-orbit (SO) effects on the (29)Si chemical shifts induced by the metal, by the sulfur atoms in the ligand, and by heavy halide ligands Y=Cl, Br, I were investigated with the help of relativistic density functional calculations. Operators used in the calculations were constructed such that SO coupling can selectively be switched off for certain atoms. The unexpectedly large SO effects on the (29)Si shielding in the Ni complex with X=Y=Cl reported recently originate directly from the Ni atom, not from other moderately heavy atoms in the complex. With respect to Pd, SO effects are amplified for Ni owing to its smaller ligand-field splitting, despite the smaller nuclear charge. In the X=Cl, Y=Cl, Br, I series of complexes the Y ligand strongly modulates the (29)Si shift by amplifying or suppressing the metal SO effects. The pronounced delocalization of the partially covalent M←Y bond plays an important role in modulating the (29)Si shielding. We also demonstrate an influence from the X ligand on the (29)Si SO shielding contributions originating at Y. The NMR spectra for [X-Si-(μ-mt)(4)-M-Y] must be interpreted mainly based on electronic and relativistic effects, rather than structural differences between the complexes. The results highlight the sometimes unintuitive role of SO coupling in NMR spectra of complexes containing heavy atoms.

Non-covalent interaction in metal cation-directed assembly of supramolecular architectures: Synthesis, characterization and crystal structures

Three new complexes [Zn(NCS)2L2] (1), [Hg(SCN)2L2] (2) and [Mn(NCS)2L4] (3), have been synthesized by the self-assembly of 4-imidazolychalcone (abbreviated as L) with M(SCN)2 (M=Hg2+, Zn2+, Mn2+). The complexes have been characterized by spectroscopic and crystallographic methods. 1H NMR spectra of complexes 1–3 present that metal ions have effect on the chemical shifts of protons of coordinated groups. Three complexes illustrate different molecular structures due to the different coordinated modes of the metal ions. In the title complexes, the coordination geometries of Zn, Hg and Mn ions are tetrahedral N4, N2S2 and octahedral N6, respectively. Finally, hydrogen bonding interactions assemble the different coordination units into higher-dimensional frameworks. The results show that the metal ion and weak non-covalent interactions play important roles in the construction of the final supramolecular structures.

Binding of nitrophenol isomers to calix[n]arene (n = 4, 6) hosts

Electronic structure, 1H NMR and vibrational spectra of complexes between nitrophenol isomer and calix[n]arene (n=4 or 6) are obtained from density functional theory. Nitrophenol interacts laterally with calix[4]arene portals and reveals shielding of all aromatic guest protons in the calculated 1H NMR spectra. The intense OH stretching vibration at the 3287cm−1 of calix[4]arene on complexation splits into two bands separated by ∼30cm−1. On the other hand, CX[6] host favors encapsulation of nitrophenol isomer via hydrogen bonded interactions. Complexation of p-nitrophenol with CX[6] engenders up-field signals for aromatic protons on confining within the host cavity while those of o- or m-nitrophenol isomers exhibit both shielding as well as deshielding thereby leading to distinct 1H NMR signals. Interaction energy of nitrophenol toward CX[6] host follows the order: p-nitrophenol>m-nitrophenol>o-nitrophenol, which is reflected in the frequency downshift of OH stretching (host) from OH···O interactions.

Alder‐ene addition of maleic anhydride to polyisobutene: nuclear magnetic resonance evidence for an unconventional mechanism

AbstractIn this work, the thermal Alder‐ene functionalization of highly reactive, vinylidene‐terminated, polyisobutene (PIB) with stoichiometric amounts of maleic anhydride at 200 °C was investigated by NMR spectroscopy. The thorough interpretation of the complex NMR spectra of PIB derivatives collected at different reaction times (from 4 to 21 h) was based on the combined use of one‐ and two‐dimensional techniques which allowed the precise structure of all the reaction products as well as their relative content to be ascertained. The analysis evidenced the formation of large amounts of derivatives generated by the classic Alder‐ene mechanism and involving the more reactive vinylidene ‘exo’ double bonds of PIB. More interestingly, the investigation also the investigation allowed also to detect the formation of a noteworthy amount of not expected structure generated by the thermal maleination of the less reactive PIB ‘endo’ β‐form provided by the isomerization of residual PIB ‘exo’ α‐form during the functionalization reaction. Copyright © 2012 Society of Chemical Industry