Observation of (31)P-(31)P Indirect Spin-Spin Coupling in Copper-Bis(phosphine) Complexes by Two-Dimensional Solid-State NMR

The first observations of (31)P-(31)P indirect spin-spin (J) coupling in copper(I) phosphine complexes are reported for solid Cu(PPh(3))(2)X (X = NO(3)(-), BH(4)(-)). Values of (2)J((31)P,(31)P), 157 +/- 5 and 140 +/- 5 Hz for Cu(PPh(3))(2)NO(3) and Cu(PPh(3))(2)BH(4), respectively, have been obtained from two-dimensional (2D) J-resolved (31)P NMR spectra obtained under slow magic-angle spinning (MAS) conditions. In both complexes, the two phosphine ligands are crystallographically equivalent; thus, the two (31)P nuclei have identical isotropic chemical shifts. Under rapid sample spinning conditions, the (31)P MAS NMR spectra exhibit relatively sharp overlapping asymmetric quartets arising from (1)J((63/65)Cu,(31)P) and residual (63/65)Cu-(31)P dipolar interactions. No evidence of (2)J((31)P,(31)P) is apparent from the spectra obtained with rapid MAS; however, under slow MAS conditions there is evidence of homonuclear J-recoupling. Peak broadening due to heteronuclear dipolar interactions precludes measurement of (2)J((31)P,(31)P) from standard 1D (31)P MAS NMR spectra. It is shown that this source of broadening can be effectively eliminated by employing the 2D J-resolved experiment. For the two copper(I) phosphine complexes investigated in this study, the peak widths in the f(1) dimension of the 2D J-resolved (31)P MAS NMR spectra are about three times narrower than those found in the corresponding 1D (31)P MAS NMR spectra.     

Determination of 31P chemical shielding tensors from NMR studies on single crystals of chlorotris(triphenylphosphine) rhodium(I)

The ³¹P chemical shielding tensors, and their direction cosines, of the three chemically different phosphorus nuclei in chlorotris(triphenylphosphine) rhodium(I) were determined in single-crystal studies using high-resolution cross-polarization NMR with proton decoupling. The tensors are not axially symmetric and the directions of the most shielded principal values for each of the three phosphorus nuclei are almost parallel to the corresponding PRh bonds.     

Phosphorus chemical shift tensors of phosphido ligands in ruthenium carbonyl compounds: (31)P NMR spectroscopy of single-crystal and powder samples and ab initio calculations

The phosphorus chemical shift (CS) tensors of several ruthenium carbonyl compounds containing a phosphido ligand, micro), bridging a Ru [bond] Ru bond were characterized by solid-state (31)P NMR spectroscopy. As well, an analogous osmium compound was examined. The structures of most of the clusters investigated have approximate local C(2v) symmetry about the phosphorus atom. Compared to the "isolated" PH(2)(-) anion, the phosphorus nucleus of a bridging phosphido ligand exhibits considerable deshielding. The phosphorus CS tensors of most of the compounds have spans ranging from 230 to 350 ppm and skews of approximately zero. Single-crystal NMR was used to investigate the orientation of the phosphorus CS tensors for two of the compounds, Ru(2)(CO)(6)(mu(2)-C [triple bond] C [bond] Ph)(mu(2)-PPh(2)) and Ru(3)(CO)(9)(mu(2)-H)(mu(2)-PPh(2)). The intermediate component of the phosphorus CS tensor, delta(22), lies along the local C(2) axis in both compounds. The least shielded component, delta(11), lies perpendicular to the Ru [bond] P [bond] Ru plane while the most shielded component, delta(33), lies perpendicular to the C [bond]P [bond] C plane. The orientation of the phosphorus CS tensor for a third compound, Ru(2)(CO)(6)(mu(2)-PPh(2))(2), was investigated by the dipolar-chemical shift NMR technique and was found to be analogous, suggesting it to be the same in all compounds. Ab initio calculations of phosphorus magnetic shielding tensors have been carried out and reproduce the orientations found experimentally. The orientation of the CS tensor has been rationalized using simple frontier MO theory. Splittings due to (99,101)Ru [bond] (31)P spin-spin coupling have been observed for several of the complexes. A rare example of (189)Os [bond] (31)P spin-spin splittings is observed in the (31)P MAS NMR spectrum of the osmium cluster, where (1)J((189)Os, (31)P) is 367 Hz. For this complex, the (189)Os nuclear quadrupolar coupling constant is on the order of several hundred megahertz.     

Phosphorus Chemical Shift Tensors of Phosphole Derivatives Determined by (31)P NMR Spectroscopy of Powder Samples

The results of a systematic solid-state (31)P NMR study of 5-phenyldibenzophosphole, DBP, its chalcogenides, and some of its transition metal complexes are reported. Phosphorus chemical shift tensors have been obtained from (31)P NMR spectra of stationary samples and of samples spinning about the magic angle. The spans of the phosphorus chemical shift tensors for DBP and its chalcogenides are comparable to those of the corresponding compounds of triphenylphosphine; however, the asymmetry of the tensors for the DBP series reflects the reduced local symmetry at phosphorus. For the complexes (DBP)M(CO)(5) and cis-(DBP)(2)M(CO)(4), where M is a group 6 transition metal (Cr, Mo, W), the most shielded component of the phosphorus shift tensor is found to be relatively independent of the metal or complex, delta(33) = -41 +/- 8 ppm, and is thought to lie along or close to the P-M bond axis direction. In contrast, delta(11) and delta(22) show considerable variation but decrease systematically on descending the group from Cr to W. Group 10 metal complexes, (DBP)(2)MX(2), have also been investigated, including several trans geometric isomers of nickel, cis and trans isomers of palladium, and cis isomers of platinum. The phosphorus shift tensors are nonaxially symmetric with spans in the range 50 -150 ppm. The phosphorus shift tensors of the two nonequivalent DBP ligands of (DBP)(2)PtX(2) (X = Cl, Br) exhibit quite different principal components. The intermediate component of the shift tensor is thought to lie along the Pt-P bond in these complexes. Some of the complexes exhibit interesting MAS-frequency-dependent (31)P NMR spectra.     

An 17O NMR and quantum chemical study of monoclinic and orthorhombic polymorphs of triphenylphosphine oxide

Solid-state (17)O NMR spectroscopy is employed to characterize powdered samples of known monoclinic and orthorhombic modifications of (17)O-enriched triphenylphosphine oxide, Ph(3)PO. Precise data on the orientation-dependent (17)O electric field gradient (EFG) and chemical shift (CS) tensors are obtained for both polymorphs. While the (17)O nuclear quadrupolar coupling constants (C(Q)) are essentially identical for the two polymorphs (C(Q) = -4.59 +/- 0.01 MHz (orthorhombic); C(Q) = -4.57 +/- 0.01 MHz (monoclinic)), the spans (Omega) of the CS tensors are distinctly different (Omega = 135 +/- 3 ppm (orthorhombic); Omega = 155 +/- 5 ppm (monoclinic)). The oxygen CS tensor is discussed in terms of Ramsey's theory and the electronic structure of the phosphorus-oxygen bond. The NMR results favor the hemipolar sigma-bonded R(3)P(+)-O(-) end of the resonance structure continuum over the multiple bond representation. Indirect nuclear spin-spin (J) coupling between (31)P and (17)O is observed directly in (17)O magic-angle-spinning (MAS) NMR spectra as well as in (31)P MAS NMR spectra. Ab initio and density-functional theory calculations of the (17)O EFG, CS, and (1)J((31)P,(17)O) tensors have been performed with a variety of basis sets to complement the experimental data. This work describes an interesting spin system for which the CS, quadrupolar, J, and direct dipolar interactions all contribute significantly to the observed (17)O NMR spectra and demonstrates the wealth of information which is available from NMR studies of solid materials.     

A solid-state NMR investigation of single-source precursors for group 12 metal selenides; M[N(iPr2PSe)2]2 (M = Zn, Cd, Hg)

The first solid-state NMR investigation of dichalcogenoimidodiphosphinato complexes, M[N(R(2)PE)(2)](n), is presented. The single-source precursors for metal-selenide materials, M[N((i)Pr(2)PSe)(2)](2) (M = Zn, Cd, Hg), were studied by solid-state (31)P, (77)Se, (113)Cd, and (199)Hg NMR at 4.7, 7.0, and 11.7 T, representing the only (77)Se NMR measurements, and in the case of Cd[N((i)Pr(2)PSe)(2)](2)(113)Cd NMR measurements, to have been performed on these complexes. Residual dipolar coupling between (14)N and (31)P was observed in solid-state (31)P NMR spectra at 4.7 and 7.0 T yielding average values of R((31)P,(14)N)(eff) = 880 Hz, C(Q)((14)N) = 3.0 MHz, (1)J((31)P,(14)N)(iso) = 15 Hz, alpha = 90 degrees , beta = 26 degrees . The solid-state NMR spectra obtained were used to determine the respective phosphorus, selenium, cadmium, and mercury chemical shift tensors along with the indirect spin-spin coupling constants: (1)J((77)Se,(31)P)(iso), (1)J((111/113)Cd,(77)Se)(iso), (1)J((199)Hg,(77)Se)(iso), and (2)J((199)Hg,(31)P)(iso). Density functional theory magnetic shielding tensor calculations were performed yielding the orientations of the corresponding chemical shift tensors. For this series of complexes the phosphorus magnetic shielding tensors are essentially identical, the selenium magnetic shielding tensors are also very similar with respect to each other, and the magnetic shielding tensors of the central metals, cadmium and mercury, display near axial symmetry demonstrating an expected deviation from local S(4) symmetry.     

A chelate-stabilized ruthenium(sigma-pyrrolato) complex: resolving ambiguities in nuclearity and coordination geometry through 1H PGSE and 31P solid-state NMR studies

Reaction of RuCl2(PPh3)3 with LiNN' (NN' = 2-[(2,6-diisopropylphenyl)imino]pyrrolide) affords a single product, with the empirical formula RuCl[(2,6-iPr2C6H3)N=CHC4H3N](PPh3)2. We identify this species as a sigma-pyrrolato complex, [Ru(NN')(PPh3)2]2(mu-Cl)2 (3b), rather than mononuclear RuCl(NN')(PPh3)2 (3a), on the basis of detailed 1D and 2D NMR characterization in solution and in the solid state. Retention of the chelating, sigma-bound iminopyrrolato unit within 3b, despite the presence of labile (dative) chloride and PPh3 donors, indicates that the chelate effect is sufficient to inhibit sigma --> pi isomerization of 3b to a piano-stool, pi-pyrrolato structure. 2D COSY, SECSY, and J-resolved solid-state 31P NMR experiments confirm that the PPh3 ligands on each metal center are magnetically and crystallographically inequivalent, and 31P CP/MAS NMR experiments reveal the largest 99Ru-31P spin-spin coupling constant (1J(99Ru,31P) = 244 +/- 20 Hz) yet measured. Finally, 31P dipolar-chemical shift spectroscopy is applied to determine benchmark phosphorus chemical shift tensors for phosphine ligands in hexacoordinate ruthenium complexes.     

Sur la non-equivalence des liaisons CH du groupement methyle dans les complexes cristallises de trans-bromotetracarbonyle methyle carbyne de chrome

The syntheses, ³¹P{¹H} NMR spectra, and a structure of “mixed” 1,5-cyclo-octadienebis(tertiary phosphine)dirhodium complexes possess a rhodiumrhodium bond, briding diphenylphosphido and two different stereochemistries around the rhodium atoms. One rhodium is tetrahedral and surrounded by four phosphorus atoms and the other rhodium (bonded to COD) is nearly planar.     

Comparing main group and transition-metal square-planar complexes of the diselenoimidodiphosphinate anion: a solid-state NMR investigation of M[N(iPr2PSe)2]2 (M = Se, Te; Pd, Pt)

A comparison of the square-planar complexes of group 10 (Pd(II), Pt(II)) and 16 (Se(II), Te(II)) centers with the tetraisopropyldiselenoimidodiphosphinate anion, [N((i)Pr2PSe)2](-), is made on the basis of the results of a solid-state (31)P, (77)Se, (125)Te, and (195)Pt NMR investigation. Density functional theory calculations of the respective chemical shift and (14)N electric field gradient tensors in these compounds complement the experimental results. The NMR spectra were analyzed to determine the respective phosphorus, selenium, tellurium, and platinum chemical shift tensors along with numerous indirect spin-spin coupling constants. Special attention was given to observed differences in the NMR parameters for the transition metal and main-group square-planar complexes. Residual dipolar coupling between (14)N and (31)P, not observed in the solid-state (31)P NMR spectra of the Pd(II) and Pt(II) complexes, was observed at 4.7 and 7.0 T for M[N((i)Pr 2PSe)2]2(M = Se, Te) yielding average values of R((31)P, (14)N)eff = 890 Hz, CQ((14)N) = 2.5 MHz, (1) J( (31)P, (14)N) iso= 15 Hz, alpha = 90 degrees , beta = 17 degrees . The span, Omega, and calculated orientation of the selenium chemical shift tensor for the diselenoimidodiphosphinate anion is found to depend on whether the selenium is located within a pseudoboat or distorted-chair MSe 2P 2N six-membered ring. The largest reported values of (1)J((77)Se, (77)Se) iso, 405 and 435 Hz, and (1)J((125)Te, (77)Se)iso, 1120 and 1270 Hz, were obtained for the selenium and tellurium complexes, respectively; however, in contrast a correspondingly large value of (1)J((195)Pt, (77)Se)iso was not found. The chemical shift tensors for the central atoms, Se(II) and Te(II), possess positive skews, while for Pt(II) its chemical shift tensor has a negative kappa. This observed difference for the shielding of the central atoms has been explained using a qualitative molecular orbital approach.     

An Investigation of 1:1 Adducts of Gallium Trihalides with Triarylphosphines by Solid‐State 69/71Ga and 31P NMR Spectroscopy

Several 1:1 adducts of gallium trihalides with triarylphosphines, X₃Ga(PR₃) (X=Cl, Br, and I; PR₃=triarylphosphine ligand), were investigated by using solid‐state ^69/71Ga and ³¹P NMR spectroscopy at different magnetic‐field strengths. The ^69/71Ga nuclear quadrupolar coupling parameters, as well as the gallium and phosphorus magnetic shielding tensors, were determined. The magnitude of the ⁷¹Ga quadrupolar coupling constants (C_Q(⁷¹Ga)) range from approximately 0.9 to 11.0 MHz . The spans of the gallium magnetic shielding tensors for these complexes, δ₁₁?δ₃₃, range from approximately 30 to 380 ppm; those determined for phosphorus range from 10 to 40 ppm. For any given phosphine ligand, the gallium nuclei are most shielded for X=I and least shielded for X=Cl, a trend previously observed for In^III–phosphine complexes. This experimental trend, attributed to spin‐orbit effects of the halogen ligands, is reproduced by DFT calculations. The signs of C_Q(^69/71Ga) for some of the adducts were determined from the analysis of the ³¹P NMR spectra acquired with magic angle spinning (MAS). The ¹J(^69/71Ga,³¹P) and ΔJ(^69/71Ga, ³¹P) values, as well as their signs, were also determined; values of ¹J(⁷¹Ga,³¹P) range from approximately 380 to 1590 Hz. Values of ¹J(^69/71Ga,³¹P) and ΔJ(^69/71Ga,³¹P) calculated by using DFT have comparable magnitudes and generally reproduce experimental trends. Both the Fermi‐contact and spin‐dipolar Fermi‐contact mechanisms make important contributions to the ¹J(^69/71Ga,³¹P) tensors. The ³¹P NMR spectra of several adducts in solution, obtained as a function of temperature, are contrasted with those obtained in the solid state. Finally, to complement the analysis of NMR spectra for these adducts, single‐crystal X‐ray diffraction data for Br₃Ga[P(p‐Anis)₃] and I₃Ga[P(p‐Anis)₃] were obtained.     

Insight into the structure of silver cyanide from (13)C and (15)N solid-state NMR spectroscopy

The structure of silver cyanide has been investigated by solid-state multinuclear magnetic resonance spectroscopy. Carbon-13 and nitrogen-15 NMR spectra of magic-angle-spinning (MAS) and stationary powder samples of isotopically enriched Ag(13)CN, Ag(13)C(15)N, and AgC(15)N have been acquired at the external applied magnetic field strengths 4.7, 7.05, and 9.4 T. Axially symmetric carbon and nitrogen chemical shift (CS) tensors provide evidence for linearity of the polymeric (-Ag-CN-)(n)() chains. A two-site model is required to successfully simulate the (13)C MAS NMR line shape, which is dominated by indirect nuclear spin-spin coupling between (109/107)Ag and (13)C nuclei. In combination with relativistic zeroth-order regular approximation density functional theory (ZORA-DFT) calculations on model AgCN fragments, the (13)C MAS NMR results show that 30 +/- 10% of the silver sites are disordered, that is, either -NC-Ag-CN- or -CN-Ag-NC-, and 70 +/- 10% of the silver sites are ordered, that is, -NC-Ag-NC-. Effective dipolar coupling data extracted from (13)C NMR spectra of stationary samples allow an upper limit of 1.194 A to be placed on the carbon-nitrogen internuclear distance. After incorporation of the effects of anisotropic indirect nuclear spin-spin coupling and motional averaging on the NMR-derived distance, a corrected value of r(CN) = 1.16 +/- 0.03 A is obtained. This work provides an example of the type of information which may be obtained from solid-state NMR studies of disordered materials and how such information may complement that available from diffraction studies.     

Structural characterization of silver dialkylphosphite salts using solid‐state 109Ag and 31P NMR spectroscopy,IR spectroscopy and DFT calculations

High‐resolution solid‐state ¹⁰⁹Ag and ³¹P NMR spectroscopy was used to investigate a series of silver dialkylphosphite salts, Ag(O)P(OR)₂ (R = CH₃, C₂H₅, C₄H₉ and C₈H₁₇), and determine whether they adopt keto, enol or dimer structures in the solid state. The silver chemical shift, CS, tensors and |J(¹⁰⁹Ag, ³¹P)| values for these salts were determined using ¹⁰⁹Ag (Ξ = 4.652%) NMR spectroscopy. The magnitudes of J(¹⁰⁹Ag, ³¹P) range from 1250 ± 10 to 1318 ± 10 Hz and are the largest reported so far. These values indicate that phosphorus is directly bonded to silver for all these salts and thus exclude the enol structure. All ³¹P NMR spectra exhibit splittings due to indirect spin–spin coupling to ¹⁰⁷Ag (I = 1/2, NA = 51.8%) and ¹⁰⁹Ag (I = 1/2, NA = 48.2%). The ¹J(¹⁰⁹Ag, ³¹P) values measured by both ¹⁰⁹Ag and ³¹P NMR spectroscopy agree within experimental error. Analysis of ³¹P NMR spectra of stationary samples for these salts allowed the determination of the phosphorus CS tensors. The absence of characteristic P?O stretching absorption bands near 1250 cm^?1 in the IR spectra for these salts exclude the simple keto tautomer. Thus, the combination of solid‐state NMR and IR results indicate that these silver dialkylphosphite salts probably have a dimer structure. Values of silver and phosphorus CS tensors as well as ¹J(¹⁰⁹Ag, ³¹P) values for a dimer model calculated using the density functional theory (DFT) method are in agreement with the experimental observations. Copyright © 2010 John Wiley & Sons, Ltd.     

A spectroscopic study of calcium surface sites and adsorbed iron species at aqueous fluorapatite by means of 1H and 31P MAS NMR

Assignments of the protolytic speciation at the calcium hydroxyl surface sites of synthetic fluorapatite and the chemical interactions between fluorapatite-maghemite and fluorapatite-Fe2+ ions have been studied by means of 1H and 31P single-pulse and 31P CP MAS NMR. Three possible forms of calcium hydroxyl surface sites have been suggested and assigned to [triple bond] CaOH, [triple bond]Ca(OH)2-, and [triple bond]CaOH2+, and their mutual ratios were found to vary as a function of pH. Due to their paramagnetic properties, iron species and Fe2+ ions adsorbed at the fluorapatite surface display a broad spinning sideband manifold in the single-pulse 31P MAS NMR spectra. The resonance lines in the 31P CP MAS NMR spectra originating from the bulk phosphate groups PO4(3-) and phosphorus surface sites [triple bond]POx and [triple bond]POxH decrease with increasing Fe2+ ion adsorption. When iron species originating from maghemite are adsorbed at the fluorapatite surface, no 31P NMR signal is detected, which supports the hypothesis that surface reactions occur between the phosphorus surface sites of fluorapatite and iron species.     

Phosphine and phosphonite complexes of a ruthenium(II) porphyrin. 1. Synthesis,structure, and solution state studies

We have investigated the effect of complexation of different phosphorus ligands on the stability, solid state structure, and spectroscopic properties (NMR, IR, UV-vis) of a 5,15-diphenyl-substituted ruthenium porphyrin, (MeOH)Ru(II)(CO)(DPP) 2 [DPP = 5,15-bis(3',5'-di-tert-butyl)phenyl-2,8,12,18-tetraethyl-3,7,13,17-tetramethylporphyrin]. The ligands used are PPh(3), diphenyl(phenylacetenyl)phosphine (DPAP), bis(diphenylphosphino)acetylene (DPPA), tris(phenylacetenyl)phosphine [(PA)(3)P], and diethyl (phenylacetenyl)phosphonite [PAP(OEt)(2)]. The mono-phosphine complexes (PR(3))Ru(II)(CO)(DPP) are readily formed in solution in quantitative yields. The complexes display association constants ranging from 1.2 x 10(4) M(-1) for PPh(3) to 4.8 x 10(6) M(-1) for PAP(OEt)(2). The weak association of PPh(3) does not correlate with its pK(a), delta((31)P), or cone angle value and is attributed to steric effects. Due to their kinetic lability, which is shown by 2D NMR spectroscopy, and the weakening of the carbonyl ligand via a trans effect, the mono-phosphine complexes could not be isolated. IR spectroscopy gives the relative order of pi-acceptor strength as PPh(3) < DPAP, DPPA < (PA)(3)P < PAP(OEt)(2), whereas the relative order of the sigma-donor strength is PPh(3) < (PA)(3)P < DPAP, DPPA < PAP(OEt)(2), based on the calculated pK(a) values and on the (31)P((1)H) NMR chemical shifts of the ligands. The chemical shift differences in the (31)P9(1)H)) NMR spectra upon ligand binding display a linear correlation with the calculated pK(a) values of the protonated ligands HPR(3)(+); we propose that the pK(a), and probably other electronic properties, of a specific phosphorus ligand can be estimated on the basis of the chemical shift difference Deltadelta((31)P) upon complexation to a metalloporphyrin. The bis-phosphine complexes can be isolated in pure form by crystallization from CHCl(3)-MeOH solutions using excess ligand. Association of the second ligand is in the same order of magnitude as the first binding for the phosphines, but the second phosphonite binding is decreased by a factor of about 100. The solid state structures show only marginal differences in the geometrical parameters. The calculated and the crystallographic cone angles of the ligands generally do not match, apart from the values obtained for PAP(OEt)(2).     

Synthesis and characterisation of a new class of phosphine-phosphonite ferrocenediyl dinuclear rhodium complexes

We previously reported the easy access to mixed ferrocenediyl ligands bearing phosphine and phosphonite moieties. Using this strategy, a new enantiopure phosphine-menthylphosphonite ferrocenediyl has been synthesised. This mixed ligand leads to original unsymmetrical dinuclear rhodium coordination-complexes. One example of this new class of “quasi-close bridging A frame” dinuclear rhodium complexes, fully characterised by multinuclear ¹H, ¹³C, ³¹P and ¹⁰³Rh NMR and optical rotation measurements, is presented. Preliminary tests have shown an activity improvement in the hydroformylation of oct-1-ene using the phosphine-menthylphosphonite ferrocenediyl auxiliary compared to known phosphine-phosphonite ligands.     

Solid-state 23Na NMR study of sodium lariat ether receptors exhibiting cation-pi interactions

Noncovalent cation-pi interactions are important in a variety of supramolecular and biochemical systems. We present a 23Na solid-state nuclear magnetic resonance (SSNMR) study of two sodium lariat ether complexes, 1 and 2, in which a sodium cation interacts with an indolyl group that models the side chain of tryptophan. Sodium-23 SSNMR spectra of magic-angle spinning (MAS) and stationary powdered samples have been acquired at three magnetic field strengths (9.4, 11.75, 21.1 T) and analyzed to provide key information on the sodium electric field gradient and chemical shift (CS) tensors which are representative of the cation-pi binding environment. Triple-quantum MAS NMR spectra acquired at 21.1 T clearly reveal two crystallographically distinct sites in both 1 and 2. The quadrupolar coupling constants, CQ(23Na), range from 2.92 +/- 0.05 MHz for site A of 1 to 3.33 +/- 0.05 MHz for site B of 2; these values are somewhat larger than those reported previously by Wong et al. (Wong, A.; Whitehead, R. D.; Gan, Z.; Wu, G. J. Phys. Chem. A 2004, 108, 10551) for NaBPh4, but very similar to the values obtained for sodium metallocenes by Willans and Schurko (Willans, M. J.; Schurko, R. W. J. Phys. Chem. B 2003, 107, 5144). We conclude from the 21.1 T data that the spans of the sodium CS tensors are less than 20 ppm for 1 and 2 and that the largest components of the EFG and CS tensors are non-coincident. Quantum chemical calculations of the NMR parameters substantiate the experimental findings and provide additional insight into the dependence of CQ(23Na) on the proximity of the indole ring to Na+. Taken together, this work has provided novel information on the NMR interaction tensors characteristic of a sodium cation interacting with a biologically important arene.     

NMR studies of dynamic behavior of dialkyl(acetylacetonato)bis(tertiary phosphine)cobalt(III) and related complexes in solution

The ¹H, ³¹P and ¹³C NMR spectra of cis-dialkyl(acetylacetonato)bis(tertiary phosphine)cobalt(III) complexes were obtained in several solvents. These complexes have an octahedral configuration with trans tertiary phosphine ligands. The coordinated tertiary phosphine ligands are partly dissociated in solution. One of the phosphine ligands in CoR₂(acac)(PR₃′)₂ can be readily displaced with pyridine bases to give pyridine-coordinated complexes. From observation of the ¹H and ³¹P NMR spectra several kinetic and thermodynamic data for exchange reactions and displacement reactions of tertiary phosphines were obtained.     

A solid-state 17O NMR study of L -phenylalanine and L -valine hydrochlorides

We have presented an experimental investigation of the oxygen-17 chemical shielding (CS) and electric-field-gradient (EFG) tensors for alpha-COOH groups in polycrystalline amino acid hydrochlorides. The 17O CS and EFG tensors including the relative orientations between the two NMR tensors are determined in [17O]-L-phenylalanine hydrochloride and [17O]-L-valine hydrochloride by the analysis of the 17O magic-angle-spinning (MAS) and stationary NMR spectra obtained at 9.4, 11.7, 16.4, and 21.8 T. The quadrupole coupling constants (CQ) and the span of the CS tensors are found to be 8.41-8.55 MHz and 7.35-7.41MHz, and 548-570 ppm and 225-231 ppm, for carbonyl and hydroxyl oxygen atoms, respectively. Extensive quantum chemical calculations using density functional theory (DFT) have been also carried out for a hydrogen-bonding model. It is demonstrated that the behavior of the dependence of hydrogen-bond distances on 17O NMR tensors for the halogen ions is different from those for the water molecule.     

K-39 quadrupolar and chemical shift tensors for organic potassium complexes and diatomic molecules

Solid-state potassium-39 NMR spectra of two potassium complexes of crown-ether-based organic ligands (1.KI and 2) have been acquired at 11.75 and 21.1 T and interpreted to provide information on the 39K quadrupolar and chemical shift tensors. The analyses reveal a large potassium chemical shift tensor span of 75+/-20 ppm for 1.KI. This appears to be the first such measurement for potassium in an organic complex, thereby suggesting the utility of potassium chemical shift tensors for characterizing organic and biomolecular K+ binding environments. Compound 2 exhibits a cation-pi interaction between K+ and a phenyl group, and therefore, the 39K NMR tensors obtained for this compound must be partly representative of this interaction. Analyses of potassium-39 spin-rotation data for gaseous 39K19F and 39K35Cl available from molecular beam experiments performed by Cederberg and co-workers reveal the largest potassium CS tensor spans known to date, 84.39 and 141 ppm, respectively. Collectively, the results obtained highlight the potential of ultrahigh-field potassium-39 solid-state NMR spectroscopy and, in particular, the wide range of the anisotropy of the potassium CS tensor when organic and diatomic systems are considered.     

Solid-state 17O NMR study of the electric-field-gradient and chemical shielding tensors in polycrystalline amino acids

We have presented a systematic experimental investigation of carboxyl oxygen electric-field-gradient (EFG) and chemical shielding (CS) tensors in crystalline amino acids. Three 17O-enriched amino acids were prepared: L-aspartic acid, L-threonine, and L-tyrosine. Analysis of two-dimensional 17O multiple-quantum magic-angle spinning (MQMAS), MAS, and stationary NMR spectra yields the 17O CS, EFG tensors and the relative orientations between the two tensors for the amino acids. The values of quadrupolar coupling constants (CQ) are found to be in the range of 6.70-7.60 MHz. The values of deltaiso lie in the range of 268-292 ppm, while those of the delta11 and delta22 components vary from 428 to 502 ppm, and from 303 to 338 ppm, respectively. There is a significant correlation between the magnitudes of delta22 components and C--O bond lengths. Since C--O bond length may be related to hydrogen-bonding environments, solid-state 17O NMR has significant potential to provide insights into important aspects of hydrogen bonds in biological systems.