113Cd Nuclear Magnetic Resonance Research Articles

Structural and Electronic Studies of Substituted m-Terphenyl Group 12 Complexes.

The effects of para-substitution on the structural and electronic properties of four series of two-coordinate m-terphenyl Group 12 complexes (R-Ar#)2M (M = Zn, Cd, Hg; R = t-Bu 1–3, SiMe34–6, Cl 7–9, CF310–12, where R-Ar# = 2,6-{2,6-Xyl}2-4-R-C6H2 and 2,6-Xyl = 2,6-Me2C6H3) have been investigated. X-ray crystallography shows little structural variation across the series, with no significant change in the C–M–C bond distances and angles. However, considerable electronic differences are revealed by heteronuclear nuclear magnetic resonance (NMR) spectroscopy; a linear correlation is observed between the 113Cd, 199Hg, and 1H (2,6-Xyl methyl protons) NMR chemical shifts of the para-substituted complexes and the Hammett constants for the R-substituents. Specifically, an upfield shift in the NMR signal is observed with increasingly electron-withdrawing R-substituents. Density functional theory (DFT) calculations are employed to attempt to rationalize these trends.

Thermal property, structural characterization, and physical property of cation and anion in organic–inorganic perovskite [(CH2)3(NH3)2]CdCl4 crystal

Structural characteristics and molecular dynamics of the [(CH2)3(NH3)2] cation and CdCl6 anion in organic-inorganic perovskite [(CH2)3(NH3)2]CdCl4 near the phase transition temperature (TC) were studied by magic angle spinning (MAS) 1H nuclear magnetic resonance (NMR), MAS 13C NMR, and static 113Cd NMR experiments at different temperatures. The chemical shifts of 1H for CH2 and NH3 were nearly constant without anomalous change, whereas the 13C and 113Cd chemical shifts were changed with increasing temperature. These observations imply that the chemical environments of 1H do not change with temperature, while those of 13C and 113Cd were changed. In addition, from the spin-lattice relaxation times in the rotating frame (T1ρ) for 13C in the middle of the N–C–C–C–N bond, and the spin-lattice relaxation times in the laboratory frame (T1) for 113Cd in octahedron CdCl6, the molecular motions of these atoms below and above TC were discussed. The main effect causing the phase transition is a change in the environments of the 113Cd nuclei in the CdCl6 octahedra and in the environments of N–C–C–C–N groups in the [(CH2)3(NH3)2] cations. The study of the molecular dynamics was conducted to improve the relatively weak stability compared to the high efficiency of perovskite solar cells.

A review of cadmium sorption mechanisms on soil mineral surfaces revealed from synchrotron-based X-ray absorption fine structure spectroscopy: Implications for soil remediation

ABSTRACT The sorption of cadmium (Cd) is one of the most important chemical processes in soil, affecting its fate and mobility in both soil and water and ultimately controlling its bioavailability. In order to fundamentally understand the sorption/desorption of Cd in soil systems, X-ray absorption fine structure spectroscopy (XAFS) has been applied in numerous studies to provide molecular-level information that can be used to characterize the surface adsorption and precipitation reactions that Cd can undergo. This information greatly improves our current knowledge of the possible chemical reactions of Cd in soil. This paper critically reviews the mechanisms of Cd sorption/desorption at the mineral-water interface based on XAFS studies performed over the past twenty years. An introduction to the basic concepts of sorption processes is provided, followed by a detailed interpretation of XAFS theory and experimental data collection and processing, ending finally with a discussion of the atomic/molecular-scale Cd sorption mechanisms that occur at the soil mineral-water interface. Particular emphasis is placed on literature that discusses Cd adsorption and speciation when associated with iron, manganese, and aluminum oxides and aluminosilicate minerals. Multiple sorption mechanisms by which Cd is sorbed by these minerals have been found, spanning from outer-sphere to inner-sphere to surface precipitation, depending on mineral type, surface loading, and pH. In addition, the application of complementary techniques (e.g., 113Cd nuclear magnetic resonance (NMR) and molecular dynamics simulation) for probing Cd sorption mechanisms is discussed. This review can help to develop appropriate strategies for the environmental remediation of Cd-contaminated soils.

Structural phase transitions and ferroelastic properties of perovskite-type layered (CH3NH3)2CdCl4

Herein, we perform a structural characterization of (CH3NH3)2CdCl4 by 1H and 13C magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectrometry, discussing the geometry around CH3NH3 cations. 1H MAS NMR determined two sets of protons in hydrogen-bonded CH3NH3 groups, exhibiting large T1ρ (L) and small T1ρ (S) values corresponding to long and short C-H/N-H bonds, respectively. The spin-lattice relaxation time of 113Cd in CdCl6 octahedra is shown to exhibit an anomaly near 283 K (TC2) due to the occurrence of a phase transition that is not governed by changes in the motion of CH3NH3 groups but is accompanied by the corresponding changes for Cd in CdCl6 units. The observed domain pattern corresponds to an exchange of a- and c-axes of the orthorhombic structure, with the resulting domain orientations viewed as the main reason for the occurrence of phase transitions, and changes in CdCl6 group motion observed by 113Cd NMR.

(113)Cd Nuclear Magnetic Resonance as a Probe of Structural Dynamics in a Flexible Porous Framework Showing Selective O2/N2 and CO2/N2 Adsorption.

Two new isomorphous three-dimensional porous coordination polymers, {[Cd(bpe)0.5(bdc)(H2O)]·EtOH}n (1) and {[Cd(bpe)0.5(bdc)(H2O)]·2H2O}n (2) [bpe = 1,2-bis(4-pyridyl)ethane, and H2bdc = 1,4-benzenedicarboxylic acid], have been synthesized by altering the solvent media. Both structures contain one-dimensional channels filled with metal-bound water and guest solvent molecules, and desolvated frameworks show significant changes in structure. However, exposure to the solvent vapors (water and methanol) reverts the structure back to the as-synthesized structure, and thus, the reversible flexible nature of the structure was elucidated. The flexibility and permanent porosity were further reinforced from the CO2 adsorption profiles (195 and 273 K) that show stepwise uptake. Moreover, a high selectivity for O2 over N2 at 77 K was realized. The framework exhibits interesting solvent vapor adsorption behavior with dynamic structural transformation depending upon the size, polarity, and coordination ability of the solvent molecules. Further investigation was conducted by solid state (113)Cd nuclear magnetic resonance (NMR) spectroscopy that unambiguously advocates the reversible transformation "pentagonal-bipyramidal CdO6N → octahedral CdO5N" geometry in the desolvated state. For the first time, (113)Cd NMR has been used as a probe of structural flexibility in a porous coordination polymer system.

Bis(Tetramethylselenophosphoramidoyl) Methylamine Complexes of Cd(Ii) and Zn(Ii): Synthesis and Multinuclear (31P, 77Se, and 113Cd) Nmr Characterization in Solution

Five new complexes ZnL2(ClO4)2 (1), CdL2(ClO4)2 (2), CdL2(BF4)2 (3), CdLCl2 (4), and CdL(NO3)2 (5) [L = ((Me2N)2PSe)2NMe] have been synthesized and characterized by elemental analysis, infrared (IR) and multinuclear (31P, 77Se, and 113Cd), and nuclear magnetic resonance (NMR) spectroscopy. The 31P and 77Se NMR data showed that the title ligand is coordinated in a bidentate fashion to the metal center via its both P=Se groups. The solution structure of the cadmium complexes was further confirmed by its 113Cd NMR spectra, which displayed a quintuplet for the perchlorate complex and a triplet for each of the nitrate and chloride complexes, respectively due to coupling with four (two ligands) and two (one ligand) equivalent phosphorus nuclei, consistent with a four-coordinate tetrahedral geometry for the cadmium center. The results are discussed and compared with the corresponding oxo and thio analogues.

Single Domain Metallothioneins: Supermetalation of Human MT 1a

Metallothioneins are a family of small, cysteine rich proteins that have been implicated in a range of roles including toxic metal detoxification, protection against oxidative stress, and as metallochaperones involved in the homeostasis of both essential zinc and copper. We report that human metallothionein 1a, well-known to coordinate 7 Zn(2+) or Cd(2+) ions with 20 cysteinyl thiols, will bind 8 structurally significant Cd(2+) ions, leading to the formation of the supermetalated Cd(8)-βα-rhMT 1a species, for which the structure is a novel single domain. ESI-mass spectrometry was used to determine the exact metalation status of the βα-rhMT. The derivative-shaped CD envelope of Cd(7)-βα-rhMT [peak extrema (+) 260 and (-) 239 nm] changed drastically upon formation of the Cd(8)-βα-rhMT with the appearance of a sharp monophasic CD band centered on 252 nm, a feature indicative of the loss of cluster symmetry. The structural significance of the eighth Cd(2+) ion was determined from a combination of direct and indirect (113)Cd nuclear magnetic resonance (NMR) spectra. In the case of Cd(8)-βα-rhMT, only four peaks were observed in the direct (113)Cd NMR spectrum. Significantly, while both of the isolated domains can be supermetalated forming Cd(4)-β-rhMT and Cd(5)-α-rhMT, Cd(8)-βα-rhMT and not Cd(9)-βα-rhMT was observed following addition of excess Cd(2+). We propose that both domains act in concert to coordinate the eighth Cd(2+) atom, and furthermore that this interaction results in a coalescence of the two domains leading to collapse of the two-domain structure. This is the first report of a possible single-"superdomain" metallothionein structure for Zn(2+) and Cd(2+) binding mammalian proteins. A computational model of a possible single-domain structure of Cd(8)-βα-rhMT is described.

Supermetalation of the β Domain of Human Metallothionein 1a

Metallothionein has been implicated in a number of functions, including toxic metal detoxification, as a metal chaperone and in metal ion homeostasis. In this paper, we demonstrate that the beta domain of human metallothionein 1a, well-known to bind three Zn(2+) or Cd(2+) ions with nine cysteinyl sulfurs, is also capable of binding an additional Cd(2+) ion, leading to the formation of the supermetalated Cd(4)-beta-rhMT 1a. This intermediate, either by itself or in concert with the alpha domain of human metallothionein, is a likely model for metal exchange with the apoenzyme, which is one of the key roles of metallothionein. Through electrospray ionization (ESI) mass spectrometry and circular dichroism (CD) and ultraviolet (UV) spectroscopy, we show that the addition of 4.4 molar equiv of CdSO(4) to a solution of Cd(3)-beta-rhMT 1a leads to the complete conversion to Cd(4)-beta-rhMT 1a. ESI mass spectrometry was used to determine the exact speciation of beta-rhMT 1a. While the UV absorption spectrum increased slightly, the CD spectrum of Cd(4)-beta-rhMT 1a showed significant changes with the appearance of a sharp monophasic peak at 252 nm in contrast to the derivative-shaped envelope of the Cd(3)-beta-rhMT 1a species [peak extrema at (+)262 and (-)236 nm], indicating disruption of the exciton coupling in the metal-thiolate cluster. Additionally, both direct and indirect (113)Cd nuclear magnetic resonance (NMR) spectra of the Cd(3)-beta-rhMT 1a and Cd(4)-beta-rhMT 1a species were recorded. The (113)Cd NMR spectrum of Cd(4)-beta-rhMT 1a contained four cadmium peaks in the tetrahedral thiolate region at 688.8, 650.3, 635.9, and 602.5 ppm. This represents the first report of both NMR data for isolated Cd(3)-beta-rhMT 1a and supermetalated Cd(4)-beta-rhMT 1a.

CdS Magic-Sized Nanocrystals Exhibiting Bright Band Gap Photoemission via Thermodynamically Driven Formation

CdS magic-sized nanocrystals (MSNs) exhibiting both band gap absorption and emission at 378 nm with a narrow bandwidth of approximately 9 nm and quantum yield (QY) of approximately 10% (total QY approximately 28%, in hexane) were synthesized via a one-pot noninjection approach. This CdS MSN ensemble is termed as Family 378. It has been acknowledged that magic-sized quantum dots (MSQDs) are single-sized, and only homogeneous broadening contributes to their bandwidth. The synthetic approach developed is ready and highly reproducible. The formation of the CdS MSQDs was carried out at elevated temperatures (such as 90-140 degrees C) for a few hours in a reaction flask containing bis(trimethylsilyl)sulfide ((TMS)(2)S) and Cd(OAc)(OA) in situ made from cadmium acetate dihydrate (Cd(OAc)(2).2H(2)O) and oleic acid (OA) in 1-octadecene (ODE). Low OA/Cd and high Cd/S feed molar ratios favor this formation, whose mechanism is proposed to be thermodynamically driven. (13)C solid-state cross-polarization magic-angle spinning (CP/MAS) nuclear magnetic resonance (NMR) demonstrates that the capping ligands are firmly attached to the nanocrystal surface via carboxylate groups. With the cross-polarization from (1)H of the alkyl chains to surface (113)Cd, (113)Cd NMR is able to distinguish the surface Cd (471 ppm) bonding to both -COO(-) and S and the bulk Cd (792 ppm) bonding to S only. DOSY-NMR was used to determine the size of Family 378 ( approximately 1.9 nm). The present study provides strategies for the rational design of various MSNs.

Single-Sized CdSe Nanocrystals with Bandgap Photoemission via a Noninjection One-Pot Approach

The manuscript addresses the synthesis and characterization of one colloidal CdSe single-sized nanocrystal ensemble exhibiting bandgap absorption and emission peaking at 463 and 465 nm, respectively, with full width at half-maximum of ca. 8 nm. This ensemble is called Family 463; also, these single-sized quantum dots (QDs) are termed as magic-sized quantum dots (MSQDs). A magic-sized quantum dot (MSQD) ensemble is similar to a regular quantum dot (RQD) ensemble but consisting of single-sized nanocrystals; meanwhile, MSQDs do not grow in size any more with longer reaction periods or higher temperature, after their well development during synthesis. The CdSe MSQDs were synthesized via a noninjection one-pot approach with long reaction periods at elevated temperature, with cadmium acetate dihydrate (Cd(OAc)2·2H2O) and elemental selenium as Cd and Se sources, respectively, one long-chain fatty acid as ligands, and 1-octadecene (ODE) as a reaction medium. Different carboxylic acids with the carbon-chain length ranging from C2 to C24, the number of which refers to the total number of carbons, were investigated. Deficient acid feed amount with respect to Cd is crucial for the formation of the CdSe MSQDs, leading to the resulting Cd precursor Cd(OAc)x(OOC−(CH2)n−CH3)2-x (with tunable activity). It was also found that the fatty acids of C12−C18, with low acid-to-Cd and high Cd-to-Se feed molar ratios and the growth temperature of 200−240 °C, are optimum for MSQD Family 463, regarding the yield, purity, and their bandgap photoluminescent (PL) efficiency. Interestingly, in the initial stage of the formation at the growth temperature of 140−160 °C, there may be an “isomer competing” process. 13C solid-state cross-polarization magic-angle spinning (CP/MAS) nuclear magnetic resonance (NMR) indicates that the capping carboxylate groups are firmly attached to the nanocrystals, which allows cross-polarization from 1H of the alkyl chains to 113Cd. Thus 113Cd NMR is able to distinguish surface (422 ppm) bonding to both −COO and Se and bulk (680 ppm) Cd species bonding to Se only. The CdSe MSQD Family 463 possesses long shelf-storage stability. The synthetic approach introduced here is ready and reproducible, featuring large-scale production. The present study on the growth kinetics of CdSe MSQD Family 463 brings insights for rational design strategies toward various MSQD ensembles with different sizes, via the choice of acids and their feed amount affecting the activity of the resulting Cd precursor.

Zinc, Cadmium, and Mercury 1,2-Benzenedithiolates with Intramolecular NH···S Hydrogen Bonds

Mononuclear Zn, Cd, and Hg 1,2-benzenedithiolates with intramolecular NH...S hydrogen bonds, [M(II){1,2-S2-3,6-(RCONH)2C6H2}2](2-) (R = CH 3, t-Bu; M = Zn, Cd, Hg), were synthesized and characterized by X-ray analysis and spectral measurements. The presence of intramolecular NH...S hydrogen bonds was established by the IR spectra. (199)Hg and (113)Cd nuclear magnetic resonance showed a stabilized four-thiolate coordinated structure and suggested the influence of the NH...S hydrogen bonds to ppi(Hg)-ppi(S) interactions. The NH stretching bands show that the NH...S hydrogen bonds in Cd and Hg complexes are stronger than those in the corresponding Zn complex. These results are supported by theoretical calculations. The experimental and theoretical results suggested that the NH...S hydrogen bond influences the efficient capture of toxic Cd and Hg ions by metallothioneins.

Characterization of Cd Translocation and Identification of the Cd Form in Xylem Sap of the Cd-Hyperaccumulator Arabidopsis halleri

Arabidopsis halleri is a Cd hyperaccumulator; however, the mechanisms involved in the root to shoot translocation of Cd are not well understood. In this study, we characterized Cd transfer from the root medium to xylem in this species. Arabidopsis halleri accumulated 1,500 mg kg(-1) Cd in the shoot without growth inhibition. A time-course experiment showed that the release of Cd into the xylem was very rapid; by 2 h exposure to Cd, Cd concentration in the xylem sap was 5-fold higher than that in the external solution. The concentration of Cd in the xylem sap increased linearly with increasing Cd concentration in the external solution. Cd transfer to the xylem was completely inhibited by the metabolic inhibitor carbonyl cyanide 3-chlorophenylhydrazone (CCCP). Cd concentration in the xylem sap was decreased by increasing the concentration of external Zn, but enhanced by Fe deficiency treatment. Analysis with 113Cd-nuclear magnetic resonance (NMR) showed that the chemical shift of 113Cd in the xylem sap was the same as that of Cd(NO3)2. Metal speciation with Geochem-PC also showed that Cd occurred mainly in the free ionic form in the xylem sap. These results suggest that Cd transfer from the root medium to the xylem in A. halleri is an energy-dependent process that is partly shared with Zn and/or Fe transport. Furthermore, Cd is translocated from roots to shoots in inorganic forms.

Spectroscopical identification of residues of subunit G of the yeast V-ATPase in its connection with subunit E

A critical point in the V(1) sector and entire V(1)V(O) complex is the interaction of stalk subunits G (Vma10p) and E (Vma4p). Previous work, using precipitation assays, has shown that both subunits form a complex. In this work, we have analysed the N-terminal segment of subunit G (G(1-59)) of the V(1)V(O) ATPase from Saccharomyces cerevisiae by using nuclear magnetic resonance (NMR) spectroscopy. Analyses of (1)H-(15)N heteronuclear single quantum coherence (HSQC) spectra of G(1-59) in the absence and presence of the N-terminal peptides E(1-18) and E(18-38) as well as the produced and purified C-terminal segment (E(39-233)) shows specific interactions only with the peptide fragment E(18-38). The binding of this peptide occurs via the residues M(1), V(2), S(3), and K(5) as well for V(22), S(23), K(24), A(25) and R(26) of G(1-59). The specific E(18-38)/G(1-59) binding has been confirmed by fluorescence correlation spectroscopy data. The E(18-38) peptide has been studied by CD spectroscopy and NMR. The 3D structure of this peptide adopts a stable helix-hinge-helix formation in solution. A model structure of the E(18-38)/G(1-59) complex reveals the orientation of E(18-38) relative to G(1-59) via salt-bridges of the polar residues and van der Waals forces at the very N-terminus of both segments.

Cd(O 2C(CH 2) 2CO 2)]: An unprecedented 3D hybrid organic–inorganic topology

The [Cd(O 2C(CH 2) 2CO 2)] has been hydrothermally prepared and structurally characterized using single-crystal X-ray diffraction. It crystallizes in the monoclinic system, S.G.: I 2/a, a=6.515(2) Å, b=4.889(3) Å, c=30.769(3) Å, β=94.34(8) Å. The structure exhibited alternating infinite chains of edge-sharing CdO 6 octahedra which progress parallel to the a-axis and four corner-sharing CdO 6 octahedra layers which progress in the ( a, b) plane, pillared by succinate anion. The topology leads to intersecting hydrophobic channels along (1 1 0) and (1¯ 1 0) directions. The preparation, structural, thermal and infrared spectroscopic characterizations and 113Cd NMR (nuclear magnetic resonance) are presented.

A solid state nuclear magnetic resonance study on the thermolytic synthesis of CdS nanoparticles in a polystyrene matrix

We report on the optimization of the thermolytic synthesis of cadmium sulfide (CdS) nanoparticles in a polystyrene (PS) matrix. The annealing conditions were tuned on the basis of the indications coming from solid state 113Cd and 13C Nuclear Magnetic Resonance (NMR) experiments. 113Cd NMR provided direct evidence of CdS nanoparticles formation. Semi-quantitative 13C NMR experiments demonstrated that good quality samples are obtained by heating up precursor/polystyrene films to 270 °C in vacuum. X-ray diffraction (XRD) and wide angle X-ray scattering (WAXS) experiments revealed structural details of CdS nanoparticles, their average size ranging from 1 to more than 7 nm as a function of the annealing conditions.

Identification of the form of Cd in the leaves of a superior Cd-accumulating ecotype of Thlaspi caerulescens using 113Cd-NMR

Thlaspi caerulescens (Ganges ecotype) is a known Cd hyperaccumulator, however, the ligands which coordinate to Cd ions in the leaves have not been identified. In the present study, the chemical form of Cd was investigated by using 113Cd-nuclear magnetic resonance (NMR) spectroscopy. Plants were grown hydroponically with a highly enriched 113Cd stable isotope. Measurements of 113Cd-NMR with intact leaves showed a signal at the chemical shift of around -16 ppm. Crude leaf sap also gave a similar chemical shift. Purification by gel filtration (Sephadex G-10), followed by cationic and anionic exchange chromatography, showed that Cd occurred only in the anionic fraction, which gave the same chemical shift as intact leaves. Further purification of the anionic fraction, combined with 113Cd- and 1H-NMR studies, revealed that only the fraction containing malate showed a chemical shift similar to the intact leaves. These results indicate that Cd was coordinated mainly with malate in the leaves of T. caerulescens. The malate concentration in the leaves was not affected by increasing Cd concentration in the solution, suggesting that malate synthesis is not induced by Cd. Because the Cd-malate complex is relatively weak, we suggest that the complex forms inside the vacuoles as a result of an efficient tonoplast transport of Cd and a constitutively high concentration of malate in the vacuoles, and that the formation of the Cd-malate complex may lead to a decrease of subsequent Cd efflux to the cytoplasm.

Solid-State 93Nb, 19F, and 113Cd Nuclear Magnetic Resonance Study of Niobium Oxyfluorides: Characterization of Local Distortions and Oxygen/Fluorine Ordering

The local structures and oxygen/fluorine ordering of Cdpy 4 NbOF 5 (py = C 5 H 5 N) and [pyH] 2 [Cdpy 4 (NbOF 5 ) 2 ] have been investigated with 1 9 F, 1 1 3 Cd, and 9 3 Nb solid-state NMR spectroscopy. The 9 3 Nb magic-angle spinning (MAS) NMR spectra acquired at an ultrahigh magnetic field strength (19.6 T) and at ultrahigh spinning speeds (∼43 kHz) of both compounds are dominated not only by the quadrupolar interaction but also by the chemical shielding (CS) interaction, consistent with highly asymmetric environments for niobium. A methodology is presented to extract the nuclear quadrupole coupling constant C Q , the asymmetry parameter η, and the isotropic chemical shift δ i s o in the presence of a large chemical shift anisotropy (CSA). The CS tensor was then obtained from the simulations of the 9 3 Nb (I = 9/2) static NMR spectrum. The separations between the centerband of the central transition and sidebands of the ′ 3/2 ↔ ′ 5/2 satellite transition in the 9 3 Nb MAS NMR spectra are sensitive to the value of C Q ( 9 3 Nb), while the line shapes are mainly determined by η and the relative orientation between the electric field gradient (EFG) and CS tensors. Thus, simulations of the MAS NMR spectra provided additional constraints on the fitting of all these parameters. The 9 3 Nb MAS NMR spectra acquired at lower field and lower spinning speeds, where the spinning sidebands are not separated from the centerband, were also reproduced in the simulations. The following parameters were determined for the two compounds at room temperature: C Q = 36.0(5)/33.2(5) MHz, η = 0.50(5)/0.40(5), δ i s o ( 9 3 Nb) = -1310(10)/-1320(10) ppm, Ω = 1000(20)/1100(20) ppm, K = 1.00(5)/0.8(1), a = 0(20)°/ 60(20)°, β = 0(2)°/5(2)°, y = 0(20)°/0(20)° for Cdpy4NbOF5/[pyH] 2 [Cdpy 4 (NbOF 5 ) 2 ], respectively. A very distorted multiplet in the solid-state 1 9 F MAS NMR spectra was observed, which arises from J-coupling [ 1 J( 9 3 Nb, 1 9 F) = 362(2) and 350(5) Hz, for Cdpy 4 NbOF 5 and [pyH] 2 [Cdpy 4 (NbOF 5 ) 2 ], respectively] and residual dipolar coupling between the 1 9 F and 9 3 Nb nuclei. Only one 1 1 3 Cd NMR resonance is observed for Cdpy 4 -NbOF 5 , which, together with the 1 9 F NMR, suggests that the O-substitution is not random. On the basis of the 1 1 3 cd NMR, the NbOF 5 octahedra are most likely oriented in opposite directions in different chains so as to allow the acentric NbOF 5 octahedra to occupy a center of inversion in the crystal structure of this compound determined by X-ray diffraction (the interchain cancellation mechanism proposed by Heier et al., in J. Solid State Chem. 1997, 133, 576-579).

Superconductivity and magnetic fluctuations in Cd(2))Re(2)O(7) via Cd nuclear magnetic resonance and re nuclear quadrupole resonance.

We report Cd nuclear magnetic resonance (NMR) and Re nuclear quadrupole resonance (NQR) studies on Cd(2)Re(2)O(7), the first superconductor among pyrochlore oxides (T(c) approximately 1 K). The Re NQR spectrum at zero magnetic field below 100 K rules out any magnetic or charge order. The spin-lattice relaxation rate below T(c) exhibits a pronounced coherence peak and follows the weak-coupling BCS theory with nearly isotropic energy gap. The results of Cd NMR point to a moderate ferromagnetic enhancement at high temperatures followed by a rapid decrease of the density of states below the structural transition temperature of 200 K.

A MAS NMR structural study of cadmium phosphate glasses

Cadmium phosphate glasses, of general formula xCdO(1− x)P 2O 5 (0.25⩽ x⩽0.6), have been prepared by melting in alumina crucibles, with resulting dissolution of up to 6.4 mol% Al 2O 3. The local structure in these glasses has been studied using 31P, 27Al and 113Cd nuclear magnetic resonance. The distribution of [PO 4]Q n species as a function of composition has been shown to follow the simple binary model. The rate of change of the chemical shift of the 31P species in the Q 2 environment depends on the bond order, which in turn reflects the extent of double bonding between phosphorus and oxygen.

Formula omitted] and [formula omitted] NMR and XPS characterization of PbO–PbCl 2–CdCl 2 glasses

A structural characterization of PbO–PbCl 2–CdCl 2 oxychloride glasses was achieved using 207 Pb and 113 Cd nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS). 207 Pb static NMR spectra exhibit two broad components, whose intensity change with oxygen–chlorine substitution in the glass composition. 207 Pb phase-adjusted spinning sidebands (PASS) NMR shows that the lead first co-ordination sphere in PbO–PbCl 2–CdCl 2 glasses contains both oxygen and chlorine atoms and that the Pb bonding environment varies from an ionic environment to a more covalent bonding state. From the study of crystalline Pb 3O 2Cl 2, the correlation between 207 Pb isotropic and anisotropic chemical shift is extended to oxychloride compounds. Oxygen 1s photoelectron spectra contain two components that are consistent with a glass formation through Pb–O–Pb bonds. 113 Cd NMR spectra show that Cd is mainly ionically bonded to chlorine and acts as network modifier for all glass compositions.