77Se and 87Rb Solid state NMR study of the structure of Rb2[Pd(Se4)2].Se8

The structure of Rb(2)[Pd(Se(4))(2)].Se(8) has been investigated using (87)Rb magic angle spinning and static NMR and (77)Se magic angle spinning NMR. The number and the integrated intensities of the (87)Rb and (77)Se resonances are in full agreement with the crystallographic structure of the compound. The (87)Rb and (77)Se nuclear spin interaction parameters have been used to characterize the main structural units of the compound: infinite [Rb(Se(8))](x)(x+) columns and polymeric [Pd(Se(4))(2)](x)(2x-) sheet anions.     

Gold complexes containing organoselenium and organotellurium ligands

This article reviews the synthesis, structures, reactions and spectroscopic studies of gold complexes containing organoselenium and organotellurium ligands, i.e. compounds containing an Au–Se–C and Au–Te–C unit. The literature up to June 2009 has been covered. Appendix 1 lists important structural data of complexes which have been characterised by X-ray diffraction, whilst Appendix 2 contains a compilation of ⁷⁷Se and ¹²⁵Te NMR data for these compounds.     

The selenite-capped polyoxo-4-aurate(iii), [Au(III)(4)O(4)(Se(IV)O(3))(4)](4-)

The discrete heteropolyaurate [Au(III)(4)O(4)(Se(IV)O(3))(4)](4-) () represents only the second member of this class ever reported, and was synthesized via one-pot room temperature condensation in aqueous medium. was structurally characterized in the solid state and in solution by single-crystal XRD, TGA, FT-IR, (77)Se NMR, mass spectrometry and electrochemistry.     

Crystal structures and 77Se NMR spectra of molybdenum(IV) areneselenolates having intramolecular NH...Se hydrogen bonds

Salts of the monooxomolybdenum(IV,V) areneselenolates having intramolecular NH...Se hydrogen bonds, [Mo(IV)O(Se-2-RCONHC6H4)4]2- (R = t-Bu, CH3, CF3) and [Mo(V)O(Se-2-t-BuCONHC6H4)4]-, were synthesized and characterized by 1H nuclear magnetic resonance (NMR), 77Se NMR, electron spin resonance (ESR), UV-visible spectra, X-ray analysis, and electrochemical measurements. 77Se-1H correlated spectroscopy (COSY) indicated a significant correlation between amide 1H and selenolate 77Se atoms through an NH...Se hydrogen bond with 1J(77Se-1H) = 5.4 Hz coupling. The hydrogen bonds contribute to the positive shift in the Mo(V)/Mo(IV) redox potential. In the crystal structure of (PPh4)2[Mo(IV)O(Se-2-CH3CONHC6H4)4], an NH...O=Mo hydrogen bond was found. Ab inito calculations support the presence of intramolecular NH...O=Mo and NH...Se hydrogen bonds.     

有机硒化合物的^7^7Se NMR研究

本文测定了一系列二茂铁有机硒衍生物及几种烷基硒醚、芳基硒醚化合物的^7^7Se NMR谱。确定了这些化合物的^7^7Se NMR化学位移值。着重讨论了影响^7^7Se化学位移的因素。与硒直接相连取代基的链长、支链化程度以及吸电子能力的改变对^7^7Se NMR化学位移有着不同程度的影响。除此之外, 溶剂效应对二茂铁有机硒类化合物的^7^7Se NMR化学位移也有一定程度的影响。     

NMR Crystallography Enhanced by Quantum Chemical Calculations and Liquid State NMR Spectroscopy for the Investigation of Se-NHC Adducts**

N-heterocyclic carbene ligands (NHC) are widely utilized in catalysis and material science. They are characterized by their steric and electronic properties. Steric properties are usually quantified on the basis of their static structure, which can be determined by X-ray diffraction. The electronic properties are estimated in the liquid state; for example, via the ⁷⁷Se liquid state NMR of Se-NHC adducts. We demonstrate that ⁷⁷Se NMR crystallography can contribute to the characterization of the structural and electronic properties of NHC in solid and liquid states. Selected Se-NHC adducts are investigated via ⁷⁷Se solid state NMR and X-ray crystallography, supported by quantum chemical calculations. This investigation reveals a correlation between the molecular structure of adducts and NMR parameters, including not only isotropic chemical shifts but also the other chemical shift tensor components. Afterwards, the liquid state ⁷⁷Se NMR data is presented and interpreted in terms of the quantum chemistry modelling. The discrepancy between the structural and electronic properties, and in particular the π-accepting abilities of adducts in the solid and liquid states is discussed. Finally, the ¹³C isotropic chemical shift from the liquid state NMR and the ¹³C tensor components are also discussed, and compared with their ⁷⁷Se counterparts. ⁷⁷Se NMR crystallography can deliver valuable information about NHC ligands, and together with liquid state ⁷⁷Se NMR can provide an in-depth outlook on the properties of NHC ligands.     

Solution and solid state NMR studies of some selenium analogues of auranofin (an anti-arthritic gold drug)

Three mixed ligand complexes of gold(I) with phosphines and selenones, [Et₃PAuSe=C<]Br as analogues of auranofin (Et₃PAuSR) have been prepared and characterized by elemental analysis, IR and NMR methods. A decrease in the IR frequency of the C=Se mode of selenones upon complexation is indicative of selenone binding to gold(I) via a selenone group. An upfield shift in ¹³C NMR for the C=Se resonance of the selenones and downfield shifts in ³¹P NMR for the R₃P moiety are consistent with the selenium coordination to gold(I). ¹³C solid state NMR shows the chemical shift difference between free and bound selenone to gold(I) for ImSe and DiazSe to be ca 10 and 17?ppm respectively. Large ⁷⁷Se NMR chemical shifts (55?ppm) upon complexation in the solid state for [Et₃PAuDiazSe]Br compared to [Et₃PAuImSe]Br (10?ppm) indicates the former to be more stable and the Au–Se bond to be stronger than in the latter complex.     

Solution and solid-state NMR studies of some cadmium-selenone complexes

Cadmium(II) complexes of Imidazolidine-2-selenone (ImSe) and its derivatives have been prepared with the general formula Cd(RImSe)2Cl2 (where R=Me, Et, Pr, etc.). These complexes are characterized by elemental analysis, IR and NMR (1H, 13C, 77Se and 113Cd) spectroscopy. An upfield shift in C=Se resonance of selenones in 13C NMR and in 77Se and high-frequency shifts in N-H resonances in 1H are consistent with the selenium coordination to Cd(II). The 77Se nucleus in Cd(ImSe)2Cl2 is shielded by 38 ppm on coordination, relative to the free ligand. The principal components of the 77Se, 113Cd and 13C shielding tensors for the complexes were determined from solid-state NMR data. Large selenium chemical shift anisotropies were observed for these complexes.     

77Se-NMR einiger titanocendiselenolen-metallacyclen

The first ⁷⁷Se NMR was carried out on a titanocene diselenopyrocatechol derivative with Se bonded directly to the transition metal. Surprisingly, the Ti metallacycle shows, compared with Zr, a reversed shielding effect by proceeding from the non-cyclic Se system to the five-membered Se,Se′ co-ordinated heterocycle. This reflects the different bonding system in Ti and Zr bis (cyclopentadienyl) dichalcogenolene complexes. The results are discussed on the basis of the ⁷⁷Se NMR spectra, the dynamic ¹H NMR spectra (¹H DNMR), and the V. B. and M. O. bonding theories.     

Efficient chiral discrimination by 77Se NMR

[reaction: see text] Several (77)Se NMR experiments were performed by titrating a sample of selenides with the chiral shift reagent methylbenzylamine (MBA), followed by acquisition of (77)Se NMR spectra. Eventually, we observed the appearance of two anisochronous resonances, with a relatively large separation, from 37 to 56 Hz, corresponding to the formation of the diastereomeric complexes. This methodology avoids derivatization processes, and the studied compound can be easily recovered from the NMR tube.     

13C and 77Se NMR of some organometallic derivatives with Ti,Zr and Hf

¹³C and ⁷⁷Se NMR was carried out on dicyclopentadienyl derivatives of Ti, Zr and Hf with selenium bonded directly to the metal. Although ¹³C NMR is not sensitive to different substitution, ⁷⁷Se NMR is valuable and reflects the influence of the different organic substituents and the nature of the metals bonded to the selenium atom.     

Relations between 77Se NMR chemical shifts of (phenylseleno)-benzenes and their molecular structures derived from nine X-ray crystal structures

An extensive library of 77Se chemical shifts have been generated from the NMR measurements on substituted (phenylseleno)benzenes, including 33 new compounds. The variation in chemical shifts cover 265 ppm ranging from 446 to 181 ppm. Crystal structures have been determined for nine selected representatives of the substituted (phenylseleno)-benzenes. The analysis of the crystal structures supported that through-space interactions between selenium and the ortho-substituent observed in the crystal structures also are likely to be present in solution. The variation in the 77Se NMR chemical shifts can be rationalised from the intramolecular interactions with the substituent in the ortho-position. Furthermore it appears that these ortho-effects are roughly additive, and that it is the actual interactions and not the resulting conformational constraints that are responsible for the variations in the 77Se NMR chemical shifts.     

Gold(I) Complexation with Trialkyl/Triaryl Phosphine Selenide Ligands

Abstract

A number of phosphine selenide ligands and their gold(I) complexes of general formula R₃P?Se?Au?X (where X is Cl^?, Br^? and CN^? and R = phenyl, cyclohexyl and tolyl) were prepared. The complexes were characterized by elemental analysis, IR and ³¹P NMR spectroscopic methods. In the IR spectra of all complexes a decrease in frequency of P?Se bond upon coordination was observed, indicating a decrease in P?Se bond order. ³¹P NMR showed that the electronegativity of the substituents is the most important factor determining the ³¹P NMR chemical shift. It was observed that phosphorus resonance is more downfield in alkyl substituted phosphine selenides, as compared to the aryl substituted ones. Ligand disproportionation in the complex Cy₃P?SeAuCN in solution to form [Au(CN)₂]^? and [(Cy₃P?Se)₂Au]⁺ was investigated by ¹³C and ¹⁵N NMR spectroscopy.     

Surface Sites and Ligation in Amine-capped CdSe Nanocrystals**

Converting colloidal nanocrystals (NCs) into devices for various applications is facilitated by designing and controlling their surface properties. One key strategy for tailoring surface properties is thus to choose tailored surface ligands. In that context, amines have been universally used, with the goal to improve NCs synthesis, processing and performances. However, understanding the nature of surface sites in amine-capped NCs remains challenging, due to the complex surface compositions as well as surface ligands dynamic. Here, we investigate both surface sites and amine ligation in CdSe NCs by combining advanced NMR spectroscopy and computational modelling. Notably, dynamic nuclear polarization (DNP) enhanced ¹¹³Cd and ⁷⁷Se 1D NMR helps to identify both bulk and surface sites of NCs, while ¹¹³Cd 2D NMR spectroscopy enables to resolve amines terminated sites on both Se-rich and nonpolar surfaces. In addition to directly bonding to surface sites, amines are shown to also interact through hydrogen-bonding with absorbed water as revealed by ¹⁵N NMR, augmented with computations. The characterization methodology developed for this work provides unique molecular-level insight into the surface sites of a range of amine-capped CdSe NCs, and paves the way to identify structure-function relationships and rational approaches towards colloidal NCs with tailored properties.     

Four‐component relativistic DFT calculations of 77Se NMR chemical shifts: A gateway to a reliable computational scheme for the medium‐sized organoselenium molecules

A versatile high‐accuracy computational scheme for the ⁷⁷Se nuclear magnetic resonance (NMR) chemical shifts of the medium‐sized organoselenium compounds is suggested within a framework of a full four‐component relativistic density functional theory (DFT). The main accuracy factors (DFT functionals, relativistic geometry, vibrational corrections, and solvent effects) are addressed. The best result is achieved with NMR‐oriented KT2 functional of Keal–Tozer characterized by a fairly small error of only 30 ppm for the span of about 1700 ppm (<2%). © 2015 Wiley Periodicals, Inc.     

A Study of Competitive Coordination of Benzochalcogenazole Ligands by Heteronuclear NMR Spectroscopy

Complexes of 2-methyl(phenyl)benzo-1,3-tellurazole and 2-methyl(phenyl)benzo-1,3-selenazole with tungsten pentacarbonyl and boron trifluoride were studied by heteronuclear NMR spectroscopy (¹H, ¹³C, ⁷⁷Se, and ¹²⁵Te). The coordination mode of the ambident ligand can be determined from the coordination shifts of the ¹²⁵Te and ⁷⁷Se NMR signals: upfield at coordination via Te and Se atoms and downfield at N coordination.     

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.     

Double Chalcogen Bonds: Crystal Engineering Stratagems via Diffraction and Multinuclear Solid-State Magnetic Resonance Spectroscopy

Group 16 chalcogens potentially provide Lewis-acidic σ-holes, which are able to form attractive supramolecular interactions with electron rich partners through chalcogen bonds. Here, a multifaceted experimental and computational study of a large series of novel chalcogen-bonded cocrystals, prepared using the principles of crystal engineering, is presented. Single-crystal X-ray diffraction studies reveal that dicyanoselenadiazole and dicyanotelluradiazole derivatives work as promising supramolecular synthons with the ability to form double chalcogen bonds with a wide range of electron donors including halides and oxygen- and nitrogen-containing heterocycles. Extensive ⁷⁷Se and ¹²⁵Te solid-state nuclear magnetic resonance spectroscopic investigations of cocrystals establish correlations between the NMR parameters of selenium and tellurium and the local chalcogen bonding geometry. The relationships between the electronic environment of the chalcogen bond and the ⁷⁷Se and ¹²⁵Te chemical shift tensors were elucidated through a natural localized molecular orbital density functional theory analysis. This systematic study of chalcogen-bond-based crystal engineering lays the foundations for the preparation of the various multicomponent systems and establishes solid-state NMR protocols to detect these interactions in powdered materials.     

Density Functional Study on Adsorption of NO on AuSe (010) Surface

NO molecule adsorption on (010) surface of gold selenide (AuSe) has been studied with a periodic slab model by means of the GGA‐PW91 exchange‐correlation functional within the framework of density functional theory (DFT). Four different on‐top adsorption sites Au(1), Au(2), Se(1) and Se(2) were considered for α‐AuSe and three on‐top adsorption sites Au(1), Au(2) and Se(1) for β‐AuSe. N‐end and O‐end adsorptions of NO were investigated for the above sites. The results show that N‐end adsorptions are preferred for α‐ and β‐AuSe and O‐end adsorptions are not feasible and thought as physisorption with the weak adsorption energies from 6.0 to 10.8 kJ/mol. For the N‐end adsorptions on α‐ and β‐AuSe (010) surfaces, Au(2) sites are most favorable with the adsorption energies 89.0 and 78.0 kJ/mol for α‐ and β‐AuSe, respectively. However, the adsorptions at Au1 sites are very weak with the adsorption energies of 27.8 and 7.5 kJ/mol, respectively. In case of the adsorption of N‐down orientations of NO at Se sites for α‐ and β‐AuSe (010) surfaces, the adsorption activities of Se(1) and Se(2) sites on the α‐AuSe (010) surface and Se(1) site on the β‐AuSe (010) surface are almost the same with the adsorption energies 51.2, 52.7 and 49.2 kJ/mol. The geometric optimizations for adsorption configurations were calculated along with accounting for stretching frequency and density of states in our work.     

MP2 calculation of 77Se NMR chemical shifts taking into account relativistic corrections

The main factors affecting the accuracy and computational cost of the Second‐order Möller‐Plesset perturbation theory (MP2) calculation of ⁷⁷Se NMR chemical shifts (methods and basis sets, relativistic corrections, and solvent effects) are addressed with a special emphasis on relativistic effects. For the latter, paramagnetic contribution (390–466 ppm) dominates over diamagnetic term (192–198 ppm) resulting in a total shielding relativistic correction of about 230–260 ppm (some 15% of the total values of selenium absolute shielding constants). Diamagnetic term is practically constant, while paramagnetic contribution spans over 70–80 ppm. In the ⁷⁷Se NMR chemical shifts scale, relativistic corrections are about 20–30 ppm (some 5% of the total values of selenium chemical shifts). Solvent effects evaluated within the polarizable continuum solvation model are of the same order of magnitude as relativistic corrections (about 5%). For the practical calculations of ⁷⁷Se NMR chemical shifts of the medium‐sized organoselenium compounds, the most efficient computational protocols employing relativistic Dyall's basis sets and taking into account relativistic and solvent corrections are suggested. The best result is characterized by a mean absolute error of 17 ppm for the span of ⁷⁷Se NMR chemical shifts reaching 2500 ppm resulting in a mean absolute percentage error of 0.7%. Copyright © 2015 John Wiley & Sons, Ltd.