119Sn Chemical Shifts Research Articles

Unsymmetrical Schiff Bases Efficient Ligands for the Synthesis of Organotin (IV) Complexes and 1,5‐Benzodiazepines with Anxiolytic Properties, Molecular Docking Studies

AbstractA series of organotin(IV) complexes were synthesized from an unsymmetrical diimine‐Schiff base ligand derived from dehydroacetic acid, salicylaldehydes (5‐R substituted R = H, F, Cl, Br, I, NO2, OCH3, CH3) and 1,2‐phenylenediamine. The reaction also led to the formation of 1,5‐benzodiazepines, catalyzed by the diorganotin(IV) derivative used. The compounds were characterized by IR, UV–vis, MS, and 1H, 13C and 119Sn NMR. The hexacoordination of the tin atom for complexes was suggested based on the 119Sn chemical shifts. X‐ray single‐crystal analysis was performed for the ligand H₂L 1 h and the 1,5‐benzodiazepine 3c. The 1,5‐benzodiazepines were screened for anxiolytic activity in mice using an elevated plus maze test with diazepam as a positive control. The 1,5‐benzodiazepines were screened for their anxiolytic activity in mice, using an elevated plus maze test with diazepam as a positive control. Benzodiazepines 3g and 3h presented an anxiolytic effect in mice at 1 mg/Kg (p.o.) without affecting their spontaneous motor activity, motor coordination, and muscle strength. Docking studies indicated that 1,5‐benzodiazepines interact with GABA‐A receptor binding site. Most ligands formed H‐bond with amino acid Phe43, Asp46, Asp475, Tyr123, Ser421, and/or Gln316 and exhibited Pi and Pi–Pi interactions with amino acid residues Tyr124, Phe319, Phe43, Phe325, Ala479, and Val120.

Structural characterization of tin in toothpaste by dynamic nuclear polarization enhanced 119Sn solid-state NMR spectroscopy

Stannous fluoride (SnF2) is an effective fluoride source and antimicrobial agent that is widely used in commercial toothpaste formulations. The antimicrobial activity of SnF2 is partly attributed to the presence of Sn(II) ions. However, it is challenging to directly determine the Sn speciation and oxidation state within commercially available toothpaste products due to the low weight loading of SnF2 (0.454 wt% SnF2, 0.34 wt% Sn) and the amorphous, semi-solid nature of the toothpaste. Here, we show that dynamic nuclear polarization (DNP) enables 119Sn solid-state NMR experiments that can probe the Sn speciation within commercially available toothpaste. Solid-state NMR experiments on SnF2 and SnF4 show that 19F isotropic chemical shift and 119Sn chemical shift anisotropy (CSA) are highly sensitive to the Sn oxidation state. DNP-enhanced 119Sn magic-angle turning (MAT) 2D NMR spectra of toothpastes resolve Sn(II) and Sn(IV) by their 119Sn chemical shift tensor parameters. Fits of DNP-enhanced 1D 1H → 119Sn solid-state NMR spectra allow the populations of Sn(II) and Sn(IV) within the toothpastes to be estimated. This analysis reveals that three of the four commercially available toothpastes contained at least 80% Sn(II), whereas one of the toothpaste contained a significantly higher amount of Sn(IV).

Synthesis, structure, and cytotoxicity of some triorganotin(iv) complexes of 3-aminobenzoic acid-based Schiff bases

Abstract Six new triorganotin(iv) complexes of 3-aminobenzoic acid-based Schiff bases, 3-(R′-CH═N)C6H4COOSnR3 (1–6) (R′, R = 5-Br-2-HOC6H3, Ph (1); 3,5-Br2-2-HOC6H2, Ph (2); 4-NEt2-2-HOC6H3, Cy (3); 3-OCH3-2-HOC6H3, Cy (4); 2-HOC10H6, Ph (5); 2-HOC10H6, Cy (6)), have been synthesized by the one-pot reaction of equimolar 3-aminobenzoic acid, substituted 2-hydroxybenzaldehyde (or 2-hydroxy-1-naphthaldehyde) and triorganotin(iv) hydroxide, and characterized by elemental analysis, FT-IR, NMR spectroscopy, and X-ray single crystal diffraction. The NMR data (1 J(119Sn–13C) and 119Sn chemical shifts) suggested that these organotin(iv) complexes are all four-coordinated in CDCl3 solution. In the crystalline state, the tin atoms in 1–4 and 6 are four-coordinated and possess a distorted tetrahedral geometry. Complex 5 with crystalline solvents (CH3OH and CHCl3) exhibits a zigzag chain, and the five coordination atoms on the tin atom are arranged in a trigonal bipyramidal geometry in which the carboxylate oxygen atom and the phenolic oxygen atom of the adjacent ligand occupy the axial positions. In all complexes, the 3-(arylmethyleneamino)benzoate ligands are coordinated with tin atoms in monodentate mode. Their cytotoxicity against two human cancer cell lines (A549 and HeLa), UV-Vis, and fluorescence have been determined, and the results reveal that complexes 1–6 have higher cytotoxicity than cisplatin and may be explored for potential blue luminescent materials.

Synthesis, Characterization and Structural Aspects of Three New Nonsymmetrical Bimetallic Dibutyltin (IV) Derivatives

Abstract. Three new nonsymmetric bimetallic diorganotin compounds derived from hexadentate Schiff bases were obtained by reaction of 2,6-dihydroxybenzene-1,3-dicarbaldehyde with R-(-)-phenylglycinol, glycine and 2-amino-5-nitrophenol, in the presence of dibutyltin oxide. The full multinuclear NMR analysis, IR and elemental analyses allowed to establish the structures of all new compounds. In the three cases, the 119Sn chemical shifts are indicative of two different pentacoordinated tin atoms in solution. The molecular structure of compound 4 in the solid state shows two distinct tin atoms with different geometries, one is a distorted trigonal bipyramid with the oxygen atoms in the axial positions and the organic moieties and imine nitrogen in equatorial ones; while the other tin shows distorted octahedral geometry due to Sn(2)-O(4) intermolecular coordination, leading to a dimeric specie, with a Sn-O-Sn-O four-membered ring. The most interesting issue in the solid state is that only one of the tin atoms exhibits intermolecular coordination, in spite of the fact that the atoms are nearly equivalents. Resumen. El presente trabajo describe la síntesis de tres nuevos compuestos diorganoestaño derivados de bases de Schiff hexadentadas, los cuales fueron obtenidos por reacción de 2,6-dihidroxibenceno- 1,3-dicarbaldehido con R-(-)fenilglicinol, glicina y 2-amino-5-nitrofenol, en presencia de óxido de dibutilestaño. La estructura de los nuevos compuestos se estableció por Resonancia Magnética Nuclear Multinuclear, Infrarrojo y Análisis Elemental. Los desplazamientos de RMN de 119Sn de los tres compuestos, en solución, son característicos de átomos de estaño pentacoordinados. La estructura del compuesto 4, en estado sólido, muestra dos átomos de estaño con diferente geometría; uno de ellos de bipirámide trigonal distorsionada, donde los átomos de estaño ocupan posiciones axiales mientras que los sustituyentes orgánicos y el nitrógeno de la imina están en posiciones ecuatoriales; el otro estaño presenta una geometría de octaedro distorsionado debido a la coordinación intermolecular Sn(2)-O(4) que conduce a la formación de una especie dimérica formando un anillo de cuatro miembros. El aspecto más relevante en estado sólido es que sólo uno de los átomos de estaño presenta coordinación intermolecular a pesar de que los átomos son casi equivalentes.

Synthetic, structural and reaction chemistry of N-heterocyclic germylene and stannylene compounds featuring N-boryl substituents.

This study details the syntheses of N-heterocyclic germylenes and stannylenes featuring diazaborolyl groups, {(HCDippN)2B} (Dipp = 2,6-iPr2C6H3), as both of the N-bound substituents, with a view to generating electron rich and sterically protected metal centres. The energies of their key frontier orbitals - the group 14-centred lone pair and orthogonal pπ-orbital (typically the HOMO-2 and LUMO) have been probed by DFT calculations and compared with a related acyclic analogue, revealing (in the case of the stannylenes) a correlation with the measured 119Sn chemical shifts. The reactivity of the germylene systems towards oxygen atom transfer agents has been examined, with 2 : 1 reaction stoichiometries being observed for both Me3NO and pyridine N-oxide, leading to the formation of products thought to be derived from the activation of C-H bonds by a transient first-formed germanone.

Tin chemical shift anisotropy in tin dioxide: On ambiguity of CSA asymmetry derived from MAS spectra

Two different axial symmetries of the 119Sn chemical shift anisotropy (CSA) in tin dioxide with the asymmetry parameter (η) of 0 and 0.27 were reported previously based on the analysis of MAS NMR spectra. By analyzing the static powder pattern, we show that the 119Sn CSA is axially symmetric. A nearly axial symmetry and the principal axis system of the 119Sn chemical shift tensor in SnO2 were deduced from periodic scalar-relativistic density functional theory (DFT) calculations of NMR parameters. The implications of fast small-angle motions on CSA parameters were also considered, which could potentially lead to a CSA symmetry in disagreement with a crystal symmetry. Our analysis of experimental spectra using spectral simulations and iterative fittings showed that MAS spectra recorded at relatively high frequencies do not show sufficiently distinct features in order to distinguish CSAs with η≈0 and η≈0.4. The example of SnO2 shows that both the MAS lineshape and spinning sideband analyses may overestimate the η value by as much as ∼0.3 and ∼0.4, respectively. The results confirm that a static powder pattern must be analysed in order to improve the accuracy of the CSA asymmetry measurements. The measurements on SnO2 nanoparticles showed that the asymmetry parameter of the 119Sn CSA increases for nm-sized particles with a larger surface area compared to μm-sized particles. The increase of the η value for tin atoms near the surface in SnO2 was also confirmed by DFT calculations.

73Ge, 119Sn and 207Pb: general cooperative effects of single atom ligands on the NMR signals observed in tetrahedral [MXnY4-n] (M = Ge, Sn, Pb; 1 ≤ n ≤ 4; X, Y = Cl, Br, I) coordination compounds of heavier XIV group elements.

An inverse linear relationship between 73Ge, 119Sn and 207Pb NMR chemical shifts and the overall sum of ionic radii of coordinated halido ligands has been discovered in tetrahedral [MXnY4-n] (M = Ge, Sn, Pb; 1 ≤ n ≤ 4; X, Y = Cl, Br, I) coordination compounds. This finding is consistent with a previously reported correlation found in octahedral, pentacoordinate and square planar platinum complexes. The effect of the coordinated halido ligands acting on the metal as shielding conducting rings is therefore confirmed also by 73Ge, 119Sn and 207Pb NMR spectroscopy.

Relativistic DFT calculations of structure and 119Sn NMR chemical shifts for bent M[sbnd]Sn[sbnd]C bonding in Power’s metallostannylenes of chromium, molybdenum, tungsten and iron and diaryl stannylenes

Abstract Dispersion corrected density functional theory calculations of the metallostannylene complexes [(η 5 -C 5 H 5 )(CO) 3 M(SnC 6 H 3 -2,6-Ar 2 )] ( 1 – 6 ; M = Cr, Mo, W; Ar = Mes, Trip), [(η 5 -C 5 H 5 )(CO) 2 Fe(SnC 6 H 3 -2,6-Dip 2 )] ( 7 ) and [(η 5 -C 5 H 5 )(CO) 2 Fe(SnC 6 H 3 -2,6-Trip 2 )] ( 8 ) and monomeric diaryl stannylenes [Sn(C 6 H 2 -2,6-Mes 2 -4-Cl) 2 ] ( 9 ), [Sn(C 6 H 2 -2,6-Mes 2 -4-SiMe 3 ) 2 ] ( 10 ), [Sn(C 6 H-2,6-Mes 2 -3,5-iPr 2 ) 2 ] ( 11 ), [Sn(C 6 H 3 -2,6-Mes 2 ) 2 ] ( 12 ) and [Sn(C 6 H 3 -2,6-Dip 2 ) 2 ] ( 13 ) (Mes = C 6 H 2 -2,4,6-Me 3 ; Trip = C 6 H 2 -2,4,6- i Pr 3 ; Dip = C 6 H 2 -2,6- i Pr 2 ) have been carried out at the BP86-D3(BJ)/TZ2P/ZORA level of theory. The calculated geometrical parameters of the studied metallostannyles (Power et al., Organometallics 21 (2002) 5622; 30 (2011) 6316) and diaryl stannylenes (Power et al., Organometallics 34 (2015) 2222) are in good agreement with the available experimental values. The bent geometries at tin are consistent with the presence of a divalent Sn(II) center. The M-Sn-C bond angles in metallostannylenes are smaller than C Sn C bond angles in diaryl stannylenes. The lengthening of M − Sn bonds and decrease in M Sn C bond angles are found in the solvent (benzene) phase geometries optimized. The 119 Sn NMR chemical shifts (ppm) have been calculated with the direct implementation of the gauge including atomic orbitals (GIAO) method. The calculated 119 Sn chemical shifts with ZORA spin orbit level in gas phase yield reliable results. While switching from ZORA spin orbit level to ZORA scalar level results 119 Sn upfield shift of ca. 300–400 ppm. Due to greater percentage s character of Sn lone pair in the chromium complexes [(η 5 -C 5 H 5 )(CO) 3 M(SnC 6 H 3 -2,6-Mes 2 )] ( 1 ) and [(η 5 -C 5 H 5 )(CO) 3 M(SnC 6 H 3 -2,6-Trip 2 )] ( 4 ), the upfield 119 Sn NMR chemical shifts are observed. The relationship between computed ( δ calcd ) 119 Sn NMR chemical shifts and 1 / ΔE (LUMO-HOMO)) clearly exhibit a linear trend. The difference between 119 Sn NMR chemical shifts of metallostannylenes ( 1 – 8 ) and diaryl stannylenes ( 9 – 13 ) has been analyzed. The Sn C bonds in diaryl stannylenes are weaker than the Sn C bonds in metallostannylenes. The Sn nuclei are more shielded in diaryl stannylenes than in metallostannylenes. As a consequence, the upfield values of 119 Sn NMR chemical shifts are observed for diaryl stannylenes both experimentally and theoretically. Upfield 119 Sn chemical shifts, which deviate much from the experimental values, are observed for optimized geometries of metallostannylenes in solvent (benzene) phase. The decrease in asymmetric parameter ( η ) causes a downfield 119 Sn NMR chemical shift accompanied by an increase in 119 Sn chemical shift anisotropy.

Multinuclear NMR and crystallographic study of diorganotin valproates – Part II

Abstract The reactions of SnR2Cl2 {R = Me, Bu and Ph} and sodium valproate, NaO2CCH(CH2CH2CH3)2, NaOVp yielded three diorganotin valproates [{(Me2SnOVp)2O}2] (1), [{(Bu2SnOVp)2O}2] (2) and [{PhSn(O)OVp}6] (3). These stannoxanes have been authenticated in terms of infrared, 1H and 13C NMR, and solution- and solid-state 119Sn NMR and 119Sn Mossbauer spectroscopy. In addition the crystallographic structures of complexes (1)–(3) have been determined by X-ray diffraction. Complexes (1) and (2) displayed two major signals in the 119Sn NMR spectra in solution corresponding to the exo and endocyclic SnR2 moiety of the stannoxanes. Other minor resonances have been also observed due to dynamic processes in solution. However in the 119Sn MAS-NMR experiments only two down field signals were detected for complex (1), according to the presence of the exo and endocyclic organotin fragments, but with different resonance in comparison with the chemical shift obtained in solution. On the other hand little difference was observed in the 119Sn chemical shift of complex (3) since only one resonance was detected in solution- or in the solid-state experiments, and the signals are very close to each other.

Synthesis and structural study of bis-, tris- and tetra-[1,3,5]-dithiazinanyl silanes and stannanes

The synthesis and structural study of 23 new bis-, tris-, tetra-(dithiazinan-2-yl)silanes and stannanes is reported. The compounds were obtained by reaction of 5-alkyl-[1,3,5]-dithiazinanes (alkyl ¼ Me, i Pr, t Bu) with t BuLi followed by addition of R 0 nSiCl4� n or R 0 nSnCl4� n (n ¼ 0e2, R 0 ¼ Me and Ph) in THF. Structures were determined by 1 H, 13 C, 29 Si or 119 Sn NMR, mass spectrometry and X-ray diffraction analyses. Conformation of compounds in the solid state is discussed. The silanyl and stannanyl groups are in equatorial position in bis and tris-dithiazinanyl compounds in solution. The X-ray diffraction of tetra-(Nisopropyl-dithiazinan-2-yl)stannane showed that the tin atom is bound to two dithiazinanyl groups by equatorial bonds and to other two by axial bonds. Atomic distances indicate sulfuresilicon and sulfuretin short contacts. NMR data, in particular 29 Si and 119 SN chemical shifts and 1 J( 13 C, 119 Sn) coupling constants, indicate the presence of weak S/Si and S/Sn interactions in the compounds. Ab-initio calculations were performed for (eq,eq,eq,eq), (ax,ax,ax,ax) and (eq,eq,ax,ax) conformers in order to find the most stable structures in tetra-(5-methyl-[1,3,5]-dithiazinan-2-yl)silane and tetra-(5-methyl-[1,3,5]-dithiazinan-2-yl) stannane.

Combined NMR and DFT Study on the Complexation Behavior of Lappert’s Tin(II) Amide

The complexation chemistry of the stannylene Sn{N[Si(CH3)3]2}2, first reported by Lappert in the 1970s, was investigated by 119Sn NMR chemical shift measurements. To this end, experimental NMR data and theoretical density functional theory (DFT) calculations were combined to get an insight into the interaction between the stannylene and various solvent molecules with σ- and/or π-coordinating power. Small variations in the measured 119Sn chemical shifts revealed a donor–acceptor interaction with the solvent molecules. In comparison to the noncoordinating solvent cyclohexane taken as a reference, a weak coordination was observed with aromatic solvent molecules (benzene and toluene) and a much stronger coordination with the σ-donors THF and pyridine. Pyridine was confirmed to be the strongest donor, as evidenced by its large upfield chemical shift Δδ(119Sn) of 635 ppm. The experimental chemical shifts were reproduced by DFT (NMR) calculations, demonstrating similar trends in the interaction strength with the σ- and π-donors. The stannylene Sn{N[Si(CH3)3]2}2 showed the ability to react with Fe(CO)5 and Fe2(CO)9 in the molar ratio 1/1 to provide L2SnFe(CO)4 complexes. With a molar excess of Fe2(CO)9, L2Sn[Fe(CO)4]2 was generated irreversibly. Upon prolonged UV irradiation in the presence of W(CO)6, in the molar ratio 1/1, a mixture of L2SnW(CO)5 and two (L2Sn)2W(CO)4 complexes was generated.

Performance of ONIOM in the investigations of tri-n-butyltin compounds

Abstract The performance of ONIOM was systematically assessed in the calculations of various properties for six conformers of tri- n -butyltin chloride and tri- n -butylmethyltin. Three ONIOM combinations of levels of theory, namely ONIOM(B3PW91/IGLO:HF/3-21G * ), ONIOM(B3PW91/IGLO:PM3) and ONIOM(B3PW91/IGLO:UFF), were used and for each combination three ONIOM partitioning schemes of the investigated molecules were probed. The results of such molecular properties as structural parameters, relative conformational energies, dipole moments, vibrational frequencies and chemical shifts obtained by the ONIOM combinations were compared in a statistical manner with the reference data calculated using B3PW91/IGLO. It was found that ONIOM(B3PW91/IGLO:HF/3-21G * ) and ONIOM(B3PW91/IGLO:PM3) reproduce the structural parameters of the investigated conformers accurately when the core layer contains the (–CH 2 CH 2 CH 2 ) 3 SnX or (–CH 2 CH 2 ) 3 SnX fragment (X = Cl, Me). ONIOM(B3PW91/IGLO:HF/3-21G * ) with the (–CH 2 CH 2 ) 3 SnX core is recommended for fast predictions of relative conformational energies, dipole moments and vibrational frequencies. A good agreement with the reference results of 119 Sn, 13 C and 1 H NMR chemical shifts was obtained only in one case, namely for ONIOM(B3PW91/IGLO:HF/3-21G * ) and the largest possible core layer.

New bis-di-organotin compounds derived from aminoacid-imine-hexadentate ligands. Multifunctional evaluation as corrosion inhibitors, antibacterials and asphaltene dispersants/inhibitors

Abstract A new class of bis -di-organotin (IV) compounds were synthesized in good yields ( ca. 80%) by a one-step five molecules reaction in which intervene two molecular equivalents of leucine, one of 5,5′-methylene- bis -salicylaldehyde and either two of di- n -butyltin (IV) or diphenyltin (IV) oxides, that independently provided two bis -di-organotin derivatives. The structures of these two compounds were established by 1 H, 13 C and 119 Sn NMR, as well as by IR and elemental analysis. In both cases the 119 Sn chemical shifts are characteristic of pentacoordinated atoms in solution of non-coordinating solvent (CDCl 3 ). Once characterized, the novel compounds were tested as corrosion inhibitors at 25, 50 and 100 mg L −1 on mild steel surfaces in sour brine by linear polarization resistance and potentiodynamic curves. These experiments prove that these derivatives present top efficiencies of 54% and 68% for butyl and phenyl moieties, respectively. In addition, these two compounds were tested in vitro against Bacillus subtilis (Gram-positive, strain ATCC 6633), Escherichia coli (Gram-negative, strain DH5) and Pseudomonas fluorescens strains to assess their bactericidal activities, being more effective for the E. coli strain, at concentrations as low as 25 mg L −1 . Moreover, in order to correlate different activities and ascertain homologous action mechanisms, the two derivatives were tested for their asphaltene inhibition/dispersion activity. The results suggest that the presence of the four n -butyl moieties provide the needed amphiphillic balance to obtain better efficiencies in the tested activities.

Probing Cation and Vacancy Ordering in the Dry and Hydrated Yttrium-Substituted BaSnO3 Perovskite by NMR Spectroscopy and First Principles Calculations: Implications for Proton Mobility

Hydrated BaSn(1-x)Y(x)O(3-x/2) is a protonic conductor that, unlike many other related perovskites, shows high conductivity even at high substitution levels. A joint multinuclear NMR spectroscopy and density functional theory (total energy and GIPAW NMR calculations) investigation of BaSn(1-x)Y(x)O(3-x/2) (0.10 ≤ x ≤ 0.50) was performed to investigate cation ordering and the location of the oxygen vacancies in the dry material. The DFT energetics show that Y doping on the Sn site is favored over doping on the Ba site. The (119)Sn chemical shifts are sensitive to the number of neighboring Sn and Y cations, an experimental observation that is supported by the GIPAW calculations and that allows clustering to be monitored: Y substitution on the Sn sublattice is close to random up to x = 0.20, while at higher substitution levels, Y-O-Y linkages are avoided, leading, at x = 0.50, to strict Y-O-Sn alternation of B-site cations. These results are confirmed by the absence of a "Y-O-Y" (17)O resonance and supported by the (17)O NMR shift calculations. Although resonances due to six-coordinate Y cations were observed by (89)Y NMR, the agreement between the experimental and calculated shifts was poor. Five-coordinate Sn and Y sites (i.e., sites next to the vacancy) were observed by (119)Sn and (89)Y NMR, respectively, these sites disappearing on hydration. More five-coordinated Sn than five-coordinated Y sites are seen, even at x = 0.50, which is ascribed to the presence of residual Sn-O-Sn defects in the cation-ordered material and their ability to accommodate O vacancies. High-temperature (119)Sn NMR reveals that the O ions are mobile above 400 °C, oxygen mobility being required to hydrate these materials. The high protonic mobility, even in the high Y-content materials, is ascribed to the Y-O-Sn cation ordering, which prevents proton trapping on the more basic Y-O-Y sites.

Diorganotin(IV) complexes of polyaromatic azo‐azomethine ligand derived from salicylaldehyde and ortho‐aminophenol: Synthesis, characterization, and molecular structures

AbstractThe diorganotin(IV) complexes of methyl 2‐{4‐hydroxy‐3‐[(2‐hydroxy‐phenylimino)‐methyl]‐phenylazo}‐benzoate (H2L) were obtained by the reaction of ortho‐aminophenol, R2SnO (R = Me, nBu, or Ph) and methyl 2‐[(E)‐(3‐formyl‐4‐hydroxy)diazenyl]benzoate (H2PL2) in ethanol, which led to diorganotin(IV) compounds of composition [Me2SnL]2 (1), nBu2SnL (2), and Ph2SnL (3) in good yield. The 1H, 13C, and 119Sn NMR, IR, the mass spectrometry along with elemental analyses allowed establishing the structure of ligand (H2L) and compounds 1–3. In all the three cases, 119Sn chemical shifts are indicators of five‐coordinated Sn atoms in a solution state. The crystal structures of ligand H2L and complexes 1 and 2 were determined by a single crystal X‐ray diffraction study. In the solid state, the ligand H2L exists as a keto‐enamine tautomeric form. The molecular structure of complex 1 in the solid state shows a distorted octahedral geometry around a tin atom due to additional coordination with an oxygen atom from a neighboring molecule leading to a four‐membered ring with Sn‐O···Sn‐O intermolecular coordination, leading to a dimeric species. On the other hand, complex 2 is a monomer with trigonal bipyramidal geometry surrounding the tin atom. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 23:457–465, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.21037

Possible intermolecular association in triphenyltin chloride in the solution state as detected by NMR spectroscopy

NMR measurements ((119)Sn chemical shift, line width and (13)C relaxation) were made on triphenyltin chloride in two solutions, 2.5 and 0.75 mol% in CDCl(3), at several temperatures. The (13)C spin-lattice relaxation time and NOE data for the phenyl carbons provide the corresponding correlation times for the overall molecular reorientational motion and the internal rotation of the phenyl groups. The results are indicative of a weak intermolecular association of the triphenyltin chloride molecules in solution and are discussed with reference to a model for intermolecular phenyl ring π-π stacking interactions.

119Sn MAS NMR and first-principles calculations for the investigation of disorder in stannate pyrochlores

The local structure and cation disorder in Y(2)Ti(2-x)Sn(x)O(7) pyrochlores, materials proposed for the encapsulation of lanthanide- and actinide-bearing radioactive waste, is studied using (119)Sn (I = 1/2) NMR spectroscopy. NMR provides an excellent probe of disorder, as it is sensitive to the atomic scale environment without the need for any long-range periodicity. However, the complex and overlapping spectral resonances that often result can be difficult to interpret. Here, we demonstrate how (119)Sn DFT calculations can be used to aid the spectral interpretation and assignment, confirming that Sn occupies only the six-coordinate pyrochlore B site, and that the Sn chemical shift is sensitive to the number of Sn/Ti on the neighbouring B sites. Although distinct resonances are resolved experimentally when the Ti content is low, there is significant spectral overlap for Ti-rich compositions. We establish that this is a result of two competing contributions to the Sn chemical shift; an upfield shift resulting from the incorporation of the more polarizing Ti(4+) cation onto the neighbouring B sites, and a concomitant downfield shift arising from the decrease in unit cell size. Despite the considerably easier spectral acquisition, the lower resolution in the (119)Sn spectra hinders the extraction of the detailed structural information previously obtained using (89)Y NMR. However, the spectra we obtain are consistent with a random distribution of Sn/Ti on the pyrochlore B sites. Finally, we consider whether an equilibrium structure has been achieved by investigating materials that have been annealed for different durations.

Novel bis(β-diketonato)diorganotin(IV) derivatives containing bulky 4-acyl-5-pyrazolonato ligands: Influence of the steric hindrance of the acyl moiety on the solid state structures of tin complexes and their behaviour in solution

Abstract New (Q)2SnR2 derivatives (HQ in general; in detail: HQ CHPh 2 = 4-diphenylacetyl-3-methyl-1-phenyl-5-pyrazolone; HQBn = 3-methyl-1-phenyl-4-phenylacetyl-5-pyrazolone; HQnaph = 3-methyl-4-naphthoyl-1-phenyl-5-pyrazolone; R = CH3, C2H5, C6H11, n- and t-C4H9, C6H5,) have been synthesised and characterised by analytical and spectral techniques. Variable temperature NMR studies of ( Q CHPh 2 ) 2 SnR 2 derivatives (R = CH3 and C2H5) in chlorohydrocarbon solvents indicate a fluxional behaviour, with rapid interconversion between six- and five-coordinate species, the latter containing a bidentate acylpyrazolonate and a monodentate one. The X-ray crystal structures of the diorganotin(IV) derivatives ( Q CHPh 2 ) 2 SnMe 2 , ( Q CHPh 2 ) 2 SnEt 2 , (QBn)2SnMe2 and ( Q naph ) 2 SnBu n 2 , inclusive of a representative of each Qx family, show the metal centres in a skewed trans octahedral configuration. The 4-acyl moiety of the β-diketonate donor exerts a steric effect which is correlated to structural behaviour in the solid and solution state. A solid state 119Sn CPMAS NMR study of the (QBn)2SnR2 (R = CH3, C2H5, t-C4H9 and C6H5) complexes shows a marked deshielding effect and upfield movement of the 119Sn isotropic chemical shift (δiso) through this series. The 119Sn chemical shift spans (Ω) are the largest reported for directly oxo-coordinated Sn(IV) systems, although the markedly reduced Ω value for the (QBn)2SnPh2 complex may be indicative of a cis octahedral coordination, in contrast to the trans octahedral coordination characterising the other complexes of this suite.

Study on the transannular bond formation and hypercoordination in tin and germanium spirometallocanes

[D(CH 2 CH 2 S) 2 MSNH(C 6 H 4 ) (M = Ge, Sn; D = O, S)] spirocycles were synthesized to analyze the influence of the transannular bond on the hypercoordination of group 14 elements. The germaspirocycles were pentacoordinated. [O(CH 2 CH 2 S) 2 GeSNH(C 6 H 4 )] exhibits an intramolecular hydrogen bond between the amine group and the oxygen, which determines the axial atom. D(CH 2 CH 2 S) 2 MSNH(C 6 H 4 ) (M = Ge, Sn; D = O, S) spirocycles were synthesized to analyze the influence of the decrease of the radius of the metal and the change of the hardness of donor atom on the strength of the transannular bond and the hypercoordination of group 14 elements. The compounds were characterized by IR, Raman and NMR ( 1 H, 13 C and 119 Sn) spectroscopy, EI mass spectrometry and elemental analysis. Monocrystal X-ray diffraction analyses were made for the germanium compounds. The germaspirocycles were five-coordinated and had distorted trigonal bipyramid geometry. In contrast with most of the reported analogous germocanes, the transannular bond is stronger when the donor atom is oxygen, rather than sulfur. O(CH 2 CH 2 S) 2 GeSNH(C 6 H 4 ) exhibits an intramolecular hydrogen bond formation between the amine group and the transannular oxygen. The presence of this hydrogen bond determines whether the sulfur (O⋯Ge–S) or the nitrogen (S⋯Ge–N) of the five-member ring is the axial atom. According to the 119 Sn chemical shift, both stannospirocycles were five-coordinated and therefore the presence of the transannular interaction in solution could be suggested.

Quantum-chemical calculations of spectroscopic, electric and thermochemical properties of some n-butyltin compounds

Abstract Some n -butyltin compounds were studied using DFT and semiempirical methods. The range of the investigated molecules covered various combinations of hydride, halide, alkoxy, carboxylate, and/or sulfonate substituents and at least one n -butyl group, all bonded to Sn(IV). The 119 Sn and 1 H chemical shifts were determined both in the gas phase and in chloroform, using the B3PW91//IGLO-II/III method and the PCM. It was found that the influence of chloroform on the 119 Sn chemical shifts is small, which is in line with the non-coordinating and unreactive nature of this solvent. The gas-phase 119 Sn chemical shifts were interpreted in terms of some group properties such as group electronegativity, hardness, and softness. For the majority of the investigated molecules, the group hardness correlates well with the δ ( 119 Sn) values. Dipole moments, Sn–H vibrational frequencies, and thermochemical properties were calculated for five selected molecules, namely, n -Bu 2 SnHX (X = H, Cl, O 2 CMe, O 3 SMe) and n -Bu 3 SnH, by means of B3PW91 and B3LYP combined with two different mixtures of basis sets, as well as by means of the PM6 semiempirical method. It was shown that Gibbs free energy evaluated for the reaction of the homolytic cleavage of the Sn–H bond in these five molecules remains in line with their experimentally observed reactivity.