Tin dithiocarbamates: applications and structures

The uses and potential utility of tin/organotin dithiocarbamate, ^?S₂CNR′₂, compounds are reviewed. Various derivatives exhibit exciting potential as anti‐cancer agents, anti‐microbial agents and insecticides, e.g. against mosquito larvae. Tin dithiocarbamates have also proven useful as precursors for tin sulfide nanoparticles. There is a wealth of structural data available for such compounds and with the exception of the diorganotin bis(dithiocarbamate) compounds, R₂Sn(S₂CNR′₂)₂, compounds for which different structural motifs are evident, there is a certain degree of homogeneity in the molecular structures for each class of compound unless there are additional coordination sites on the R and/or R′ groups. Owing to the strong coordination potential of the dithiocarbamate ligand for tin, supramolecular aggregates involving secondary Sn…S interactions are the exception rather than the norm. Copyright © 2008 John Wiley & Sons, Ltd.     

Combined first-principles computational and experimental multinuclear solid-state NMR investigation of amino acids

13C, 14N, 15N, 17O, and 35Cl NMR parameters, including chemical shift tensors and quadrupolar tensors for 14N, 17O, and 35Cl, are calculated for the crystalline forms of various amino acids under periodic boundary conditions and complemented by experiment where necessary. The 13C shift tensors and 14N electric field gradient (EFG) tensors are in excellent agreement with experiment. Similarly, static 17O NMR spectra could be precisely simulated using the calculation of the full chemical shift (CS) tensors and their relative orientation with the EFG tensors. This study allows correlations to be found between hydrogen bonding in the crystal structures and the 17O NMR shielding parameters and the 35Cl quadrupolar parameters, respectively. Calculations using the two experimental structures for L-alanine have shown that, while the calculated isotropic chemical shift values of 13C and 15N are relatively insensitive to small differences in the experimental structure, the 17O shift is markedly affected.     

N → Sn coordination in the complexes of tin halides with pyridine: A comparison between Sn(II) and Sn(IV)

The experimentally well‐known complexation of tin(II) and tin(IV) halides with pyridine (py) leads to structures showing N → Sn coordination. In the present work, the complexes SnX_n·mpy (where X = F, Cl, Br, I; n = 2, 4; m = 1, 2) possessing this kind of coordination were studied using a computational quantum chemical approach. Various aspects in the theoretical picture of these complexes were examined to find similarities and differences in their N → Sn coordination. The aspects included, among others, the physical nature of intermolecular interactions, and their role in establishing the structure and energetic stabilization of the complexes. In this context, the effect of tin valency was inspected in great detail. As proven by several theoretical methods, a largely ionic character with a certain covalent component can be attributed to the studied N → Sn coordination, irrespective of tin valency. All complexes are destabilized by py‐py and three‐body interactions, but the Sn(II) complexes experience it to a greater extent. Marked differences are observed in the structural behavior of N → Sn and SnX_n during complex formation. This affects the energetics of complexation and, in consequence, the penta‐coordinated Sn(IV) center shows a higher propensity to expand its coordination number, compared with the tri‐coordinated Sn(II) center. The present study supplements the experimental characterization of SnX_n·mpy and, in general, it sheds light on the coordination of heteroaromatic nitrogen to tin. The survey of the Cambridge Structural Database revealed that such coordination occurred in a number of crystal structures.     

Ultrafast Magic‐Angle Spinning: Benefits for the Acquisition of Ultrawide‐Line NMR Spectra of Heavy Spin‐ Nuclei

The benefits of the ultrafast magic‐angle spinning (MAS) approach for the acquisition of ultrawide‐line NMR spectra—spectral simplification, increased mass sensitivity allowing the fast study of small amounts of material, efficient excitation, and application to multiple heavy nuclei—are demonstrated for tin(II) oxide (SnO) and the tin complex [(LB)Sn^IICl]⁺[Sn^IICl₃]^? [LB=2,6‐diacetylpyridinebis(2,6‐diisopropylanil)] containing two distinct tin environments. The ultrafast MAS experiments provide optimal conditions for the extraction of the chemical‐shift anisotropy tensor parameters, anisotropy, and asymmetry for heavy spin‐ nuclei.     

The bonding situation in 1,3,2‐diazaphospholene derivatives as studied by solid‐state NMR spectroscopy

The ³¹P chemical shift (CS) tensors of the 1,3,2‐diazaphospholenium cation 1 and the P‐chloro‐1,3,2‐diazaphospholenes 2 and 3 and the ³¹P and ¹⁹F CS tensors of the P‐fluoro‐1,3,2‐diazaphospholene 4 were characterized by solid‐state ³¹P and ¹⁹F NMR studies and quantum chemical model calculations. The computed orientation of the principal axes system of the ³¹P and ¹⁹F CS tensors in the P‐fluoro compound was found to be in good agreement with experimentally derived values obtained from evaluation of P–F dipolar interactions. A comparison of the trends in the chemical shifts of 1 – 4 with further available literature data confirms that the unique high shielding of δ₁₁ in the cation 1 can be related to the effective π‐conjugation in the five‐membered heterocycle, and that a further systematic decrease in δ₁₁ for the P‐halogen derivatives 2 – 4 is attributable to the increased perturbation of the π‐electron distribution by interaction with the halide donor. Copyright © 2002 John Wiley & Sons, Ltd.     

溅射功率对氧化锡薄膜结构和电化学性能的影响

应用射频磁控溅射技术在硅基底上制备氧化锡薄膜,着重研究溅射功率对薄膜结构和电化学性能的影响.XRD,SEM分析及恒电流充放电测试表明,随着溅射功率的增大,薄膜的结晶程度提高;生长速率和晶粒尺寸增大;电池的贮锂容量减少,且首圈不可逆容量损失增大.溅射功率对薄膜的电化学性能有较大的影响.     

13C chemical shift tensors in MOF α-Mg3(HCOO)6: Which component is more sensitive to host-guest interaction?

Metal–organic frameworks (MOFs) are a class of important porous materials with many current and potential applications. Their applications almost always involve the interaction between host framework and guest species. Therefore, understanding of host–guest interaction in MOF systems is fundamentally important. Solid-state NMR spectroscopy is an excellent technique for investigating host–guest interaction as it provides information complementary to that obtained from X-ray diffraction. In this work, using MOF α-Mg₃(HCOO)₆ as an example, we demonstrated that ¹³C chemical shift tensor of organic linker can be utilized to probe the host–guest interaction in MOFs. Obtaining ¹³C chemical shift tensor components (δ₁₁, δ₂₂, and δ₃₃, where δ₁₁ ≥ δ₂₂ ≥ δ₃₃) in this MOF is particularly challenging as there are six coordinatively equivalent but crystallographically non-equivalent carbons in the unit cell with very similar local coordination environment. Two-dimensional magic-angle-turning experiments were employed to measure the ¹³C chemical shift tensors of each individual crystallographically non-equivalent carbon in three microporous α-Mg₃(HCOO)₆ samples with different guest species. The results indicate that the δ₂₂ component (with its direction approximately being co-planar with the formate anion and perpendicular to the C−H bond) is more sensitive to the adsorbate molecules inside the MOF channel due to the weak C−H···O hydrogen bonding or the ring current effect of benzene. The ¹³C isotropic chemical shift, on the other hand, seems much less sensitive to the subtle changes in the local environment around formate linker induced by adsorption. The approach described in this study may be used in future studies on host–guest interaction within MOFs.     

锌粉-硼砂-硼酸熔融-碘酸钾滴定法测定高硅锡精矿中的锡

针对高硅锡精矿中锡的测定时通常用锌粉-氢氧化钠熔融,精密度差,不能满足分析要求的问题,建立了锌粉-硼砂-硼酸熔融,盐酸浸取,铝粒将锡还原,碘酸钾滴定法测定高硅锡精矿中锡的分析方法。方法结果稳定,精密度好,相对标准偏差在0.19%~0.55%,加标回收率在96.9%~105%。分析结果能够满足高硅锡精矿中锡的测定要求。     

51V magic angle spinning NMR in VOPO4 phases

51V magic angle spinning NMR was applied to the alpha(II), beta and gamma phases of VOPO4 at three magnetic field strengths (4.7, 7.1, and 11.7 T). The 51V quadrupole and chemical shift tensors were determined by iterative fitting of the NMR lineshapes at the three magnetic field strengths. The applicability of the method is illustrated by comparison with literature data. Although determined chemical shift tensors are completely axially symmetric and of the same magnitude, all studied phases can clearly be distinguished by their quadrupole coupling tensor. Relationships between the 51V NMR data and structural characteristics such as crystal symmetries are discussed.     

[SnI8{Fe(CO)4}4]2+: Highly Coordinated Sn+III8 Subunit with Fragile Carbonyl Clips

[SnI₈{Fe(CO)₄}₄][Al₂Cl₇]₂ contains the [SnI₈{Fe(CO)₄}₄]²⁺ cation with an unprecedented highly coordinated, bicapped SnI₈ prism. Given the eightfold coordination with the most voluminous stable halide, it is all the more surprising that this SnI₈ arrangement is surrounded only by fragile Fe(CO)₄ groups in a clip‐like fashion. Inspite of a predominantly ionic bonding situation in [SnI₈{Fe(CO)₄}₄]²⁺, the I^????I^? distances are considerably shortened (down to 371 pm) and significantly less than the van der Waals distance (420 pm). The title compound is characterized by single‐crystal structure analysis, spectroscopic methods (EDXS, FTIR, Raman, UV/Vis, Mössbauer), thermogravimetry, and density functional theory methods.     

Interaction of Cd and Zn with biologically important ligands characterized using solid-state NMR and ab initio calculations

For the first time, coordination geometry and structure of metal binding sites in biologically relevant systems are studied using chemical shift parameters obtained from solid-state NMR experiments and quantum chemical calculations. It is also the first extensive report looking at metal-imidazole interaction in the solid state. The principal values of the (113)Cd chemical shift anisotropy (CSA) tensor in crystalline cadmium histidinate and two different cadmium formates (hydrate and anhydrate) were experimentally measured to understand the effect of coordination number and geometry on (113)Cd CSA. Further, (13)C and (15)N chemical shifts have also been experimentally determined to examine the influence of cadmium on the chemical shifts of (15)N and (13)C nuclei present near the metal site in the cadmium-histidine complex. These values were then compared with the chemical shift values obtained from the isostructural bis(histidinato)zinc(II) complex as well as from the unbound histidine. The results show that the isotropic chemical shift values of the carboxyl carbons shift downfield and those of amino and imidazolic nitrogens shift upfield in the metal (Zn,Cd)-histidine complexes relative to the values of the unbound histidine sample. These shifts are in correspondence with the anticipated values based on the crystal structure. Ab initio calculations on the cadmium histidinate molecule show good agreement with the (113)Cd CSA tensors determined from solid-state NMR experiments on powder samples. (15)N chemical shifts for other model complexes, namely, zinc glycinate and zinc hexaimidazole chloride, are also considered to comprehend the effect of zinc binding on (15)N chemical shifts.     

A free,tricoordinate stannylium cation

Tris(2,4,6-triisopropylphenyl)stannylium tetrakis(pentafluorophenyl)borate constitutes a free, tricoordinate tin cation according to its X-ray structure. There is no coordination between the cation and either solvent or anion, and there are no atoms at apical positions. DFT calculations confirm the structure and indicate that there is no agostic bonding between the ortho isopropyl methinyl hydrogens and the Sn atom. Calculation of the 119Sn chemical shift is in good agreement with the observed value.     

Revealing successive steps of deprotonation of L- phosphoserine through 13C and 31P chemical shielding tensor fingerprints

The effects of deprotonation on the (13)C and (31)P chemical shielding tensors of L-O-phosphoserine are revealed by using solid-state NMR spectroscopy and ab initio calculations. The characteristic changes in some principal elements of the (13)C and (31)P chemical shift tensors have been detected during successive steps of deprotonation of carboxyl, phosphate, and amide functional groups. The calculations carried out in a polarizable continuum taking into account the effects of the surroundings have shown their ability to reproduce correctly the changes of the principal values induced by deprotonation and to provide precious information, which is very difficult to obtain experimentally, about the concurrent changes in the orientation of chemical shielding tensors in the molecular frame. The experimentally observed subtle effects related to the deprotonation-induced modifications of intermolecular contacts involving hydrogen bonding as well as the influence of counterions on the (13)C and (31)P principal elements of the chemical shift tensors are also discussed.     

Nuclear magnetic resonance chemical shifts and quadrupole couplings for different hydrogen-bonding cases occurring in liquid water: a computational study

Nuclear magnetic resonance (NMR) parameters are determined theoretically for the oxygen and hydrogen/deuterium nuclei of differently hydrogen-bonded water molecules in liquid water at 300 K. The parameters are the chemical shift, the shielding anisotropy, the asymmetry parameter of shielding, the nuclear quadrupole coupling constant, and the asymmetry parameter of the nuclear quadrupole coupling. We sample instantaneous configurations from a Car-Parrinello molecular dynamics simulation and feed nuclear coordinates into a quantum chemical program for the calculation of NMR parameters using density-functional theory with the three-parameter hybrid exchange-correlation (B3LYP) functional. In the subsequent analysis, molecules are divided into groups according to the number of hydrogen bonds they possess, and the full average NMR tensors are calculated separately for each group. The classification of the hydrogen-bonding cases is performed using a simple distance-based criterion. The analysis reveals in detail how the NMR tensors evolve as the environment changes gradually from gas to liquid upon increasing the number of hydrogen bonds to the molecule of interest. Liquid-state distributions of the instantaneous values of the NMR properties show a wide range of values for each hydrogen-bonding species with significant overlap between the different cases. Our study shows how local changes in the environment, along with classical thermal averaging, affect the NMR parameters in liquid water. For example, a broken or alternatively extra hydrogen bond induces major changes in the NMR tensors, and the effect is more pronounced for hydrogen or deuterium than for oxygen. The data sheds light on the usefulness of NMR experiments in investigating the local coordination of liquid water.     

13C NMR chemical shifts of carbonyl groups in substituted benzaldehydes and acetophenones: substituent chemical shift increments

13C NMR Substituent chemical shift (SCS) increments have been determined for the carbonyl carbon of a variety of substituted benzaldehydes and acetophenones. The 13C NMR chemical shift of the carbonyl carbon can be predicted for many di- and trisubstituted benzaldehydes and acetophenones through simple additivity of the SCS increments. The magnitude and sign of the SCS increments have been explored using Hartree-Fock 6-31G* calculations to determine the natural atomic charges of the carbonyl carbon. When a substituent capable of intermolecular hydrogen bonding is present, deviations from additivity on the order of 2 ppm are observed in dilution experiments; deviations of up to 6 ppm can result from intramolecular hydrogen bonding.     

Chemical shift driven geometry optimization

A new method for refinement of 3D molecular structures by geometry optimization is presented. Prerequisites are a force field and a very fast procedure for the calculation of chemical shifts in every step of optimization. To the energy, provided by the force field (COSMOS force field), a pseudoenergy, depending on the difference between experimental and calculated chemical shifts, is added. In addition to the energy gradients, pseudoforces are computed. This requires the derivatives of the chemical shifts with respect to the coordinates. The pseudoforces are analytically derived from the integral expressions of the bond polarization theory. Single chemical shift values attributed to corresponding atoms are considered for structural correction. As a first example, this method is applied for proton position refinement of the D-mannitol X-ray structure. A crystal structure refinement with 13C chemical shift pseudoforces is carried out.     

Accurate Backbone 13C and 15N Chemical Shift Tensors in Galectin-3 Determined by MAS NMR and QM/MM: Details of Structure and Environment Matter

Chemical shift tensors obtained from solid-state NMR spectroscopy are very sensitive reporters of structure and dynamics in proteins. While accurate ¹³C and ¹⁵N chemical shift tensors are accessible by magic angle spinning (MAS) NMR, their quantum mechanical calculations remain challenging, particularly for ¹⁵N atoms. Here we compare experimentally determined backbone ¹³C^α and ¹⁵N^H chemical shift tensors by MAS NMR with hybrid quantum mechanics/molecular mechanics/molecular dynamics (MD-QM/MM) calculations for the carbohydrate-binding domain of galectin-3. Excellent agreement between experimental and computed ¹⁵N^H chemical shift anisotropy values was obtained using the Amber ff15ipq force field when solvent dynamics was taken into account in the calculation. Our results establish important benchmark conditions for improving the accuracy of chemical shift calculations in proteins and may aid in the validation of protein structure models derived by MAS NMR.     

N7‐ and N9‐substituted purine derivatives: a 15N NMR study

The ¹⁵N NMR chemical shifts of N⁷‐ and N⁹‐substituted purine derivatives were investigated systematically at the natural abundance level of the ¹⁵N isotope. The NMR chemical shifts were determined and assigned using GSQMBC, GHMBC, GHMQC and GHSQC experiments in solution. ¹⁵N cross‐polarization magic angle spinning data were recorded for selected compounds in order to study the principal values of the ¹⁵N chemical shifts. Geometric parameters obtained by using RHF/6–31G** and single‐crystal x‐ray structural analysis were used to calculate the chemical‐shielding constants (GIAO and IGLO) which were then used to assign the nitrogen resonances observed in the solid‐state NMR spectra and to determine the orientation of the principal components of the shift tensors. Copyright © 2002 John Wiley & Sons, Ltd.     

119Sn Chemical Shifts in five- and six-coordinate organotin chelates

¹¹⁹Sn chemical shifts, δ(¹¹⁹Sn), relative to Me₄Sn in five- and six-coordinate organotin chelates were measured by means of FT NMR spectroscopy. ¹¹⁹Sn resonances were found to lie between ca. ?90 and ?330 ppm in the five-coordinate compounds and between ca. ?125 and ?515 ppm in the six-coordinate derivatives. thus δ(¹¹⁹Sn) moves upfield by 60–150 ppm with a change of the coordination number of tin from four to five and by 130–200 ppm from five to six. the δ(¹¹⁹Sn) values were shifted depending on the nature of chelating ligands and this shift was discussed in terms of the bonding between the ligand and tin. Replacement of methyl groups attached to tin by phenyl groups in five- and six-coordinate compounds induces upfield shifts in δ(¹¹⁹Sn) parallel to those found in four-coordinate organotin halides.