Chemical Shift Tensors Research Articles

Calcium binding environments probed by 43Ca NMR spectroscopy

Calcium is an important component of materials, metalloproteins, minerals, glasses, and small inorganic and organic complexes. However, NMR spectroscopy of the quadrupolar (43)Ca nuclide remains difficult primarily due to its low natural abundance and low resonance frequency. In this Perspective, experimental challenges and recent successes in the field are highlighted, with a focus on solid-state (43)Ca NMR spectroscopy. Solution (43)Ca NMR studies of calcium-binding biomolecules are also presented. The structural insights afforded from quadrupolar and chemical shift parameters are examined. For example: isotropic chemical shifts have been shown to correlate with the mean Ca-O distance and also with calcium coordination number; quadrupolar coupling constants and chemical shift tensor spans have been shown to be useful probes of polymorphism; and, distance measurements involving (43)Ca have been recently demonstrated. Lastly, challenges and opportunities for the future are considered.

Magnetic resonance tensors in Uracil: Calculation of 13C, 15N, 17O NMR chemical shifts, 17O and 14N electric field gradients and measurement of 13C and 15N chemical shifts

The experimental 13C NMR chemical shift components of uracil in the solid state are reported for the first time (to our knowledge), as well as newer data for the 15N nuclei. These experimental values are supported by extensive calculated data of the 13C, 15N and 17O chemical shielding and 17O and 14N electric field gradient (EFG) tensors. In the crystal, uracil forms a number of strong and weak hydrogen bonds, and the effect of these on the 13C and 15N chemical shift tensors is studied. This powerful combination of the structural methods and theoretical calculations gives a very detailed view of the strong and weak hydrogen bond formation by this molecule. Good calculated results for the optimized cluster in most cases (except for the EFG values of the 14N3 and 17O4 nuclei) certify the accuracy of our optimized coordinates for the hydrogen nuclei. Our reported RMSD values for the calculated chemical shielding and EFG tensors are smaller than those reported previously. In the optimized cluster the 6-311+G** basis set is the optimal one in the chemical shielding and EFG calculations, except for the EFG calculations of the oxygen nuclei, in which the 6-31+G** basis set is the optimal one. The optimal method for the chemical shielding and EFG calculations of the oxygen and nitrogen nuclei is the PW91PW91 method, while for the chemical shielding calculations of the 13C nuclei the B3LYP method gives the best results.

Density Functional Theory Calculations of 95Mo NMR Parameters in Solid-State Compounds

The application of periodic density functional theory-based methods to the calculation of (95)Mo electric field gradient (EFG) and chemical shift (CS) tensors in solid-state molybdenum compounds is presented. Calculations of EFG tensors are performed using the projector augmented-wave (PAW) method. Comparison of the results with those obtained using the augmented plane wave + local orbitals (APW+lo) method and with available experimental values shows the reliability of the approach for (95)Mo EFG tensor calculation. CS tensors are calculated using the recently developed gauge-including projector augmented-wave (GIPAW) method. This work is the first application of the GIPAW method to a 4d transition-metal nucleus. The effects of ultra-soft pseudo-potential parameters, exchange-correlation functionals and structural parameters are precisely examined. Comparison with experimental results allows the validation of this computational formalism.

15N NMR studies of layered nitride superconductor LixZrNCl

NMR measurements were carried out on pristine ZrNCl and LixZrNCl. From the 15N-Knight shift study, the isotropic Knight shift, the traceless chemical (orbital) shift tensor and the traceless Knight shift tensor were determined as Kiso=−71ppm, (σ1, σ2, σ3)=(−55, −55, 110)ppm and (K1, K2, K3)=(48, 48, −96)ppm, respectively. In the superconducting state, the fractional change of the 15N NMR shift for H∥ab was observed, evidencing that the pairing symmetry is a spin-singlet state.

Synthesis, structure, and 13C and 31P CP/MAS NMR of crystalline modifications of the polynuclear thallium(I) O,O′-dicyclohexyl phosphorodithioate complex [Tl{S2P(O-cyclo-C6H11)2}] n

Two crystalline modifications (Ia and Ib) of the polynuclear thallium (I) O,O′-dicyclohexyl phosphorodithioate complex [Tl{S2P(O-cyclo-C6H11)2}]n have been synthesized and characterized by CP/MAS NMR (13C, 31P). From full 31P CP/MAS NMR spectra, the χ2 plots were constructed to calculate the 31P chemical shift anisotropy 31P − δaniso = (δzz − δiso) and asymmetry parameters η = (δyy − δxx)/(δzz − δiso). The data obtained for the O,O′-dicyclohexyl phosphorodithioate (Dtph) groups (in both modifications) are evidence that the 31P chemical shift tensors are intermediate between rhombic and axially symmetric. However, whereas the rhombic component dominates for Ia, the tensor for Ib is close to axially symmetric (for δzz < δyy ≈ δxx). The same pattern of the MAS spectra corresponding to negative δaniso (δzz < δyy < δxx) points to a bridging or terminal/bridging coordination mode of the Dtph groups. X-ray crystallography shows that complex Ib has a polynuclear structure (of the chain polymer type). The chains are composed of alternating structurally nonequivalent noncentrosymmetric binuclear molecules [Tl2{S2P(O-cyclo-C6H11)2}2]. All Dtph ligands have the terminal/μ3-bridging coordination mode.

Polymeric thallium(I) O,O′-diisopropyl dithiophosphate [Tl{S2P(O-iso-C3H7)2}] n : Synthesis, structure, and 13C and 31P CP/MAS NMR spectra

The crystalline polymeric thallium(I) O,O′-diisopropyl dithiophosphate [Tl{S2P(O-iso-C3H7)2}] n (I) was obtained and examined by solid-state 13C and 31P CP/MAS NMR spectroscopy. Diagrams of the χ2 statistic were constructed from the complete 31P MAS NMR spectra and used to calculate the 31P chemical shift anisotropy (δaniso = (δ zz − δiso)) and the asymmetry parameter (η = (δ yy − δ xx )/(δ zz − δiso)). The 31P chemical shift tensor has a nearly axial symmetry (η = 0.22, δ zz < δ yy ≈ δ xx ). The MAS NMR spectral patterns correspond to the negative sign of δaniso (δ zz < δ yy < δ xx ), which indicates bridging or chelating-bridging coordination of the dithiophosphate ligands (Dtph). X-ray diffraction analysis revealed a polymeric structure of compound I. The polymer chain consists of alternating mononuclear [Tl{S2P(O-iso-C3H7)2}] molecules with opposite spatial orientations. The Dtph ligands are coordinated in a mixed, chelating-μ3-bridging fashion. The shape of the 31P NMR signal was interpreted in terms of the 31P-203,205Tl coupling pattern proposed from crystallographic data.

Orientational Order of Fluorinated Mesogens Containing the 1,3,2-Dioxaborinane Ring: A Multidisciplinary Approach

Orientational order properties of two fluorinated liquid crystals containing the 1,3,2-dioxaborinane ring have been investigated by means of optical, dielectric, and (13)C and (19)F NMR spectroscopies. The optical birefringence and dielectric anisotropy values determined in the mesomorphic phases were analyzed in terms of well-established theoretical models to obtain the order parameters relative to the principal axis of the polarizability tensor and molecular dipole moment, respectively. A large set of data, including (13)C and (19)F chemical shift anisotropies and (13)C-(19)F and (1)H-(19)F couplings relative to nuclei on the aromatic rings, was acquired in the NMR experiments and analyzed to determine local order parameters (principal order parameter and biaxiality) for different rigid fragments of the mesogen aromatic core using advanced DFT methods for the calculation of geometrical parameters and chemical shift tensors. A critical analysis of the dependence of the order parameters on the data set employed and on the theoretical assumptions and approximations has also been performed. The orientational order parameters obtained using the different techniques are compared and discussed in relation to the reference frame associated with the anisotropic properties monitored.

Analysis of the amide 15N chemical shift tensor of the Cα tetrasubstituted constituent of membrane-active peptaibols, the α-aminoisobutyric acid residue, compared to those of di- and tri-substituted proteinogenic amino acid residues

In protein NMR spectroscopy the chemical shift provides important information for the assignment of residues and a first structural evaluation of dihedral angles. Furthermore, angular restraints are obtained from oriented samples by solution and solid-state NMR spectroscopic approaches. Whereas the anisotropy of chemical shifts, quadrupolar couplings and dipolar interactions have been used to determine the structure, dynamics and topology of oriented membrane polypeptides using solid-state NMR spectroscopy similar concepts have been introduced to solution NMR through the measurements of residual dipolar couplings. The analysis of (15)N chemical shift spectra depends on the accuracy of the chemical shift tensors. When investigating alamethicin and other peptaibols, i.e. polypeptides rich in alpha-aminoisobutyric acid (Aib), the (15)N chemical shift tensor of this C(alpha)-tetrasubstituted amino acid exhibits pronounced differences when compared to glycine, alanine and other proteinogenic residues. Here we present an experimental investigation on the (15)N amide Aib tensor of N-acetyl-Aib-OH and for the Aib residues within peptaibols. Furthermore, a statistical analysis of the tensors published for di- (glycine) and tri-substituted residues has been performed, where for the first time the published data sets are compiled using a common reference. The size of the isotropic chemical shift and main tensor elements follows the order di- < tri- < tetra-substituted amino acids. A (15)N chemical shift-(1)H-(15)N dipolar coupling correlation NMR spectrum of alamethicin is used to evaluate the consequences of variations in the main tensor elements for the structural analysis of this membrane peptide.

Intermolecular shielding contributions studied by modeling the (13)C chemical-shift tensors of organic single crystals with plane waves.

In order to predict accurately the chemical shift of NMR-active nuclei in solid phase systems, magnetic shielding calculations must be capable of considering the complete lattice structure. Here we assess the accuracy of the density functional theory gauge-including projector augmented wave method, which uses pseudopotentials to approximate the nodal structure of the core electrons, to determine the magnetic properties of crystals by predicting the full chemical-shift tensors of all (13)C nuclides in 14 organic single crystals from which experimental tensors have previously been reported. Plane-wave methods use periodic boundary conditions to incorporate the lattice structure, providing a substantial improvement for modeling the chemical shifts in hydrogen-bonded systems. Principal tensor components can now be predicted to an accuracy that approaches the typical experimental uncertainty. Moreover, methods that include the full solid-phase structure enable geometry optimizations to be performed on the input structures prior to calculation of the shielding. Improvement after optimization is noted here even when neutron diffraction data are used for determining the initial structures. After geometry optimization, the isotropic shift can be predicted to within 1 ppm.

Experimental and theoretical investigations of selenium nuclear magnetic shielding tensors in Se–N heterocycles

A preliminary study involving solid-state 77Se NMR spectroscopy and first principles calculations of 77Se NMR parameters in Se–N heterocycles is reported. 77Se CP/MAS NMR spectra of the ring systems reveal expansive selenium chemical shift (CS) tensors, which are extremely sensitive to molecular geometry, symmetry, ligand substitution, and intermolecular contacts. For systems with known crystal structures, hybrid density functional theory (DFT) calculations of selenium nuclear magnetic shielding (NMS) tensors were carried out, and tensor orientations in the molecular frames examined. Additional DFT calculations of selenium NMS tensors are presented, along with a detailed analysis of pairs of occupied and virtual molecular orbitals that give rise to the Se NMS tensors. A new naturalized local molecular orbital (NLMO) analysis under the same DFT framework is also discussed. Collectively, the NMR data and first principles calculations provide understanding of the influences of electronic structure, bonding, and intermolecular interactions on the selenium NMS tensors, allowing for (i) prediction of unknown molecular structures and (ii) insight into the positions of the stereochemically active selenium lone pairs.

Combined solid state NMR and ONIOM studies of reversible crystalline phase reaction for nickel coordination compounds

Ni(II) with bis(acetylacetone)ethylenediamine ligand forms complexes which crystallizes as semi-hydrate with C2/c space group in monoclinic system and anhydrous form with Pna2(1) space group in orthorhombic system. 13C and 15N CP/MAS experiments were employed for structural characterization of both forms and searching of process of reversible water exchange in the crystal lattice. Comparative analysis of 13C and 15N principal elements of chemical shift tensors for ligand and complexes showed the sensitivity of δ ii elements both for complexation and phase reaction processes. Theoretical 13C and 15N NMR shielding parameters σ ii were computed employing ONIOM approach and correlated with experimental δ ii data. The applicability of ONIOM in structural analysis of coordination compounds (CC) is discussed.

Application of Solid-State 209Bi NMR to the Structural Characterization of Bismuth-Containing Materials

Herein, we report the first detailed study of (209)Bi solid-state NMR (SSNMR) spectroscopy of extremely broad central transition powder patterns. (209)Bi ultrawideline SSNMR spectra of several bismuth-containing materials (bismuth oxyhalides, bismuth nitrate pentahydrate, nonaaquabismuth triflate, and bismuth acetate) were acquired at field strengths of 9.4 and 21.1 T using frequency-stepped techniques. The (209)Bi SSNMR experiments at 9.4 T yield powder patterns with breadths ranging from 0.9 to 14.6 MHz, from which quadrupolar coupling constants, C(Q)((209)Bi), between 78 and 256 MHz, were extracted via analytical simulations. The breadths of the quadrupolar-dominated spectra and overall experimental times are greatly reduced for experiments conducted at 21.1 T, which yield high signal-to-noise spectra in which the smaller effects of bismuth chemical shift anisotropy can be clearly observed. The (209)Bi electric field gradient (EFG) and chemical shift (CS) tensor parameters extracted from these spectra are correlated to the molecular structures at the bismuth sites, via first principles calculations of (209)Bi EFG and CS tensors performed using CASTEP for periodic solids and Gaussian 03 for molecular clusters. The rapidity with which (209)Bi SSNMR spectra can be acquired at ultrahigh fields, the sensitivity of the (209)Bi NMR parameters to the bismuth environment, and the predictive power of theoretically calculated NMR interaction tensors suggest that (209)Bi SSNMR may be useful for the characterization of a variety of Bi-containing materials and compounds.

A 13C solid-state NMR analysis of vitamin D compounds

13C cross-polarization/magic-angle spinning (CP/MAS) solid-state NMR spectroscopy has been employed to analyze four vitamin D compounds, namely vitamin D3 (D3), vitamin D2 (D2), and the precursors ergosterol (Erg) and 7-dehydrocholesterol (7DHC). The 13C NMR spectrum of D3 displays a doublet pattern for each of the carbon atoms, while that of Erg contains both singlet and doublet patterns. In the cases of 7DHC and D2, the 13C spectra display various multiplet patterns, viz. singlets, doublets, triplets, and quartets. To overcome the signal overlap between the 13C resonances of protonated and unprotonated carbons, we have subjected these vitamin D compounds to 1D 1H-filtered 13C CP/MAS and { 1H}/ 13C heteronuclear correlation (Hetcor) NMR experiments. As a result, assisted by solution NMR data, all of the 13C resonances have been successfully assigned to the respective carbon atoms of these vitamin D compounds. The 13C multiplets are interpreted due to the presence of s- cis and s- trans configurations in the α- and β-molecular conformers, consistent with computer molecular modeling determined by molecular dynamics and energy minimization calculations. To further characterize the ring conformations in D3, we have successfully extracted chemical shift tensor elements for the 13C doublets. It is demonstrated that 13C solid-state NMR spectroscopy provides a robust and high sensitive means of characterizing molecular conformations in vitamin D compounds.

Revisiting HgCl 2: A solution- and solid-state 199Hg NMR and ZORA–DFT computational study

The 199Hg chemical-shift tensor of solid HgCl 2 was determined from spectra of polycrystalline materials, using static and magic-angle spinning (MAS) techniques at multiple spinning frequencies and field strengths. The chemical-shift tensor of solid HgCl 2 is axially symmetric ( η = 0) within experimental error. The 199Hg chemical-shift anisotropy (CSA) of HgCl 2 in a frozen solution in dimethylsulfoxide (DMSO) is significantly smaller than that of the solid, implying that the local electronic structure in the solid is different from that of the material in solution. The experimental chemical-shift results (solution and solid state) are compared with those predicted by density functional theory (DFT) calculations using the zeroth-order regular approximation (ZORA) to account for relativistic effects. 199Hg spin–lattice relaxation of HgCl 2 dissolved in DMSO is dominated by a CSA mechanism, but a second contribution to relaxation arises from ligand exchange. Relaxation in the solid state is independent of temperature, suggesting relaxation by paramagnetic impurities or defects.

Synthesis, structure, and 13C and 31P CP/MAS NMR of the tetraphenylantimony(V) di-iso-propyl phosphorodithioate complex [Sb(C6H5)4{S2P(O-iso-C3H7)2}] and its solvated form [Sb(C6H5)4{S2P(O-iso-C3H7)2}] · 1/2C6H6: An example of the monodentate coordination of dithio ligands

The crystalline tetraphenylantimony(V) O,O′-di-iso-propyl phosphorodithioate complex [Sb(C6H5)4{S2P(O-i-C3H7)2}](I) and its solvated form [Sb(C6H5)4{S2P(O-i-C3H7)2}] · 1/2C6H6(II) were synthesized. Solid compounds I and II were studied by MAS NMR (13C, 31P). The 31P NMR chemical shift anisotropy 31P δaniso = (δzz − δiso) and asymmetry parameter η = (δyy − δxx)/(δzz − δiso) were calculated using χ2 plots constructed on the basis of the 31P MAS NMR data. The O,O′-di-iso-propyl phosphorodithioate ligands in both complexes are characterized by predominantly the axially symmetric 31P chemical shift tensor (for the case δzz < δxx ≈ δyy) with close values of anisotropy parameters (δaniso and η), which reflects their identical S-monodentate structural function. X-ray crystallography showed that II has a trigonal-bipyramidal molecular structure with the uncommon monodentate coordination of the Dtph ligands through an S atom in an axial position of the trigonal bipyramid and the benzene molecule in the outer sphere.

Characterization of cooperative effects in linear α-glycylglycine clusters

The aspects of N–H⋯O CNH, N–H⋯O CO and C–H⋯O CNH interactions are analyzed by applying ab initio and DFT methods as well as Bader theory. We investigated geometry, binding energies, 17O, 15N chemical shift tensors, and Atoms in Molecules (AIM) properties of α-glycylglycine (α-glygly) clusters, via MP2, B3LYP and PW91 XC methods. Dimer stabilization energies and equilibrium geometries are studied in various levels of theory. MP2 and DFT calculations reveal that for α-glygly clusters, stability of N–H⋯O and C–H⋯O hydrogen bonds are enhanced significantly as a result of cooperativity effects. Furthermore, a covalent nature is also detected for some hydrogen bondings. The n-dependent trend of 17O and 15N chemical shift tensors was reasonably correlated with cooperative effects in hydrogen-bond interactions. Regarding the various N–H⋯O CNH, N–H⋯O CO and C–H⋯O CNH hydrogen bondings, capability of the α-glygly clusters for electron localization at the N–H⋯O and C–H⋯O bond critical points, depends on the cluster size. This leads to cooperative changes in the hydrogen-bond length and strength as well as 17O and 15N chemical shift tensors.

Measurement and calculation of 13C and 15N NMR chemical-shift tensors of a push–pull ethylene

Methyl 3-dimethylamino-2-cyanocrotonate (MDACC) has a remarkably weak carbon–carbon double bond. It has strong electron-withdrawing groups on one end and electron-donating groups on the other: a so-called push–pull ethylene. To investigate this unusual electronic structure, we have determined the crystal structure and measured both the 13C and 15N NMR chemical-shift tensors. These measurements are supplemented by shielding-tensor calculations done with density functional methods. The large difference (approximately 100 ppm) between isotropic chemical shifts of the two alkenyl carbons reflects a large charge release from the electron-donating side of C=C double bond to the electron-withdrawing groups. Comparison of the calculated orientations of the principal components of the alkenyl carbons obtained from ab initio calculations shows that the primary changes in charge density occur in the molecular plane. On the other hand, smaller charge density changes above and below the plane of the C=C double bond establish the conjugation of donor and acceptor groups with π* and π molecular orbitals of the central double bond, respectively, which lowers the barrier to rotation about this bond.

Solid State NMR Study and Density Functional Theory (DFT) Calculations of Structure and Dynamics of Poly(p-xylylenes)

High resolution solid state (13)C nuclear magnetic resonance (SS NMR) measurements were carried out on poly(p-xylylene) (PPX). The samples comprised vapor-deposited specimens as well as pure alpha and beta polymorphs of this polymer. The measurements were performed using cross-polarization and magic angle spinning (CP/MAS) techniques. Density functional theory gauge-including-atomic-orbital (DFT GIAO) calculations of NMR shielding parameters (13)C sigma(ii) were performed for the optimized geometry and structure of a xylylene trimer, acquired from the X-ray data, including intermolecular interactions. Two-dimensional phase adjusted spinning sideband (2D PASS) correlation was employed for the assignment of the values of the principal elements (13)C delta(ii) of the chemical shift tensor (CST). A comparative analysis of shielding (sigma(ii)) versus chemical shift (delta(ii)) parameters showed substantial differences between the molecular dynamics of alpha and beta polymorphs. This observation was further supported by the measurements of (13)C T(1) relaxation times and the analysis of cross-polarization kinetics. Frequency switched Lee-Goldburg heteronuclear correlation (FSLG HETCOR) for the (1)H-(13)C system was used in order to analyze molecular packing in both polymorphs. As a result of all of the above measurements, new insight into the mechanism of thermal phase transition from the alpha to the beta polymorph of poly(p-xylylene) is presented.

Using hyperbolic secant pulses to assist characterization of chemical shift tensors for half‐integer spin quadrupolar nuclei in MAS powder samples

Determination of the NMR anisotropic magnetic shielding parameters from magic angle spinning, MAS, powder samples containing half-integer spin quadrupolar nuclei is achieved by analysis of the difference spectrum obtained with and without application of a hyperbolic secant pulse. Application of a hyperbolic secant pulse to any spinning sideband associated with the central transition, m(I) = 1/2 to m(I) = - 1/2, results in 'saturation' of the entire central transition manifold. Similarly, if one spinning sideband associated with the m(I) = 3/2 to m(I) = 1/2 and m(I) = - 1/2 to m(I) = - 3/2 satellite transitions is perturbed, the entire satellite manifold associated with these transitions is 'saturated' while the central transition is enhanced by population transfer. Three 'difference spectrum' techniques are employed to selectively yield the spinning sidebands associated predominantly from the central transition. The success of these difference techniques is first demonstrated by examining (51)V NMR spectra of three metavanadate salts and (59)Co NMR spectra of Co(acac)(3). The vanadium and cobalt chemical shift tensors in these compounds have spans between 400 and 1400 ppm. Because the hyperbolic secant techniques proposed here yielded results that are in good agreement with earlier reports, they have been applied to characterize the (51)V chemical shift tensor of the dimer of bis(N, N-dimethylhydroxamido)-hydroxooxovanadate, {V(O)(ONMe(2))(2)}(2)O, whose chemical shift tensor has not been previously reported.

A13C and15N Solid-State NMR Study of Structural Disorder and Aurophilic Bonding in AuIand AuIIICyanide Complexes

Solid-state nuclear magnetic resonance has been used to study several cyanoaurates. Carbon-13 and nitrogen-15 NMR spectra of samples enriched with isotopically labeled 13C,15N cyanide ligands were recorded for stationary samples and samples spinning at the magic angle. Several salts of the dicyanoaurate(I) anion, M[Au(CN)2], where M = n-butylammonium, potassium, and thallium, were studied via solid-state NMR. A gold(III) cyanide, K[Au(CN)4], was also investigated. Carbon-13 and nitrogen-15 chemical shift tensors are reported for each salt, as are the measured 13C,15N direct dipolar coupling constants together with the related derived cyanide bond lengths, r(C,N). The value for r(C,N) in [(n-C4H9)4N][Au(CN)2], 1.17(5) A, was determined to be more realistic than a previously reported X-ray diffraction value of 1.03(4) A. Large 13C NMR line widths from Tl[Au(CN)2], 250-315 Hz, are attributed to coupling with 197Au (I = 3/2) and/or 203/205Tl (I = 1/2), as confirmed by measurements of the transverse relaxation constant, T2. Investigation of the carbon-13 chemical shifts for cyanide ligands bound to gold involved in a variety of metallophilic bonding environments demonstrates that the chemical shift is sensitive to metallophilic bonding. Differences in Au-Tl metallophilic bonding are shown to cause a difference in the isotropic carbon-13 chemical shift of up to 15.7 ppm, while differences in Au-Au aurophilic bonding are found to be responsible for a change of up to 5.9 ppm. The disordered polymeric material gold(I) monocyanide, AuCN, was also investigated using 13C and 15N SSNMR. Two-dimensional 13C,13C double-quantum dipolar-recoupling spectroscopy was used to probe connectivity in this material. The 13C NMR site multiplicity in AuCN is explained on the basis of sensitivity of the carbon-13 chemical shift to aurophilic bonding of the directly bonded gold atom. This assignment allows estimation of the position of the linear [-M-CN-]infinity chain's position with respect to the neighboring polymer chain. For the samples studied, a range of 7 +/- 2% to 25 +/- 5% of the AuCN chains are found to be "slipped" instead of aligned with the neighboring chains at the metal position.