David Tudela

Metal-ion assisted reactions of oximes and reactivity of oxime-containing metal complexes

Abstract The syntheses, structures and solution chemistry of oxime- and oximato-containing metal complexes have been extensively studied and described in a large number of books and reviews. However, metal-ion assisted reactions of oximes and reactivity of oxime-containing metal complexes have received much less attention and no general overview of these processes has been presented. The goal of this review is to fill this gap. Along with consideration of experimental results illustrating a rich chemistry of coordinated oximes, an attempt is made to show general features of some reactions and to systematize reaction types. In order to provide a clearer picture of different reactivity modes, possible reaction pathways are discussed and evidence for these mechanisms is provided. In conclusion the article points out certain metal-ion assisted reactions which (from the viewpoint of the authors) need more attention.

Influence of Sn4+ on the structural and electronic properties of Ti1−xSnxO2 nanoparticles used as photocatalysts

Ti(1-x)Sn(x)O(2) nanocrystalline materials employed for photocatalysis have been characterised by means of X-ray diffraction, Raman, X-ray absorption (XANES and EXAFS) and UV-Vis spectroscopy and high resolution transmission electron microscopy. Single-phase samples with anatase or rutile type structures and similar tin contents permitted a separate study of the effect of Sn(4+) ions on these crystalline forms, whereas materials composed of anatase and rutile mixtures were used to investigate the distribution of the dopant cations when both phases coexist. The results obtained from the single-phase doped TiO(2) samples indicate that the presence of tin causes a different effect when doping anatase or rutile in both their structural and electronic properties. While a random substitution of Sn(4+) for Ti(4+) seems plausible for the rutile phase, some kind of gradient in Sn(4+) concentration is possible in anatase. On the other hand, when anatase and rutile coexist, effects of doping are visible in both phases. Regarding chemical composition, a homogeneous distribution of tin was found in both calcined and hydrothermal multiphase samples. Photocatalytic experiments show that both tin-doping and coexistence of different phases have a beneficial effect on the activity of the catalysts.

Mössbauer study of the cis−trans isomers of tin(IV) complexes. Some considerations about the sign of the electric-field gradient

Mossbauer spectra are reported for the cis–trans isomers of SnCl4L2[L =NN-dimethylacetamide (dma), NN-dimethylformamide (dmf), dimethyl sulphoxide (dmso), or tetrahydrothiophen (tht)] and SnBr4(dmf)2. The following octahedral partial quadrupole splitting values were obtained: tht =+0.09, dmso =+0.14, dmf =+0.18, and dma =+0.20 mm s–1. A correlation has been found between the quadrupole splitting and the values for ν(Sn–Cl)(from i.r. and Raman spectra) for trans-SnCl4L2.

Structure and reactivity of [PtX2 (ketoxime) 2] compounds. Cis-trans isomerization and X-ray structures of cis- [PtBr2 (Me2C=NOH) 2] and trans- [PtBr2 (Me2C=NOH) 2] · 2MeC (=O) NMe2

Abstract The solid state thermal isomerization of cis- [PtX2 (ketoxime) 2] (X = Cl, ketoxime = Me2C=NOH, (CH2) 4C = NOH, (CH2) 5C=NOH ; X = Br, ketoxime = Me2C=NOH) gives the corresponding trans-isomers in almost quantitative yields, thus showing that solid state isomerization is a general and convenient procedure for the synthesis of trans- [PtX2 (ketoxime) 2] complexes. X-ray structure analyses were performed for both cis- [PtBr2 (Me2C=NOH) 2] and the bis-dimethylacetamide solvate of trans- [PtBr2 (Me2C=NOH) 2] . The former compound crystallizes in the orthorhombic space group Pbca with a = 9.593 (1) , b = 14.827 (2) , c = 17.218 (2) A ; V = 2449.0 (8) A3, Z = 8, and ρcalcd = 2.718 cm−3. The latter complex crystallizes in the orthorhombic space group Pbca with a = 10.543 (2) , b = 17.676 (4) , c = 12.398 (2) A ; V = 2310.5 (8) A3, Z = 4, and ρcalcd = 1.941 g cm−3. These two compounds are the first structurally characterized representatives of neutral Pt complexes with ‘‘simple’’ oximes.

Vibrational and 119Sn Mössbauer spectra and X-ray crystal structure of ammonium tetrafluorodimethylstannate(IV)

Ammonium tetrafluorodimethylstannate(IV) has been prepared and characterized by IR, Raman and 119Sn Mossbauer spectroscopies. The Mossbauer parameters place this compound at the frontier between the dimethyltin(IV) compounds that gave rise to the quadrupole splitting (QS) vs. CSNC angle correlation, and the dimethyltin(IV) salts of strong protic acids and superacids. The Mossbauer QS, as well as the IR and Raman spectra, indicate that the CSNC angle is 180°. The IR-active v(SnF) Eu mode appears at 345 cm−1, and this mode is related to the Mossbauer QS for trans-[SnF4L2] because strong donors have a negative partial quadrupole splitting (pqs) and weaken the SnF bond. The IR spectrum also suggests the existence of normal (not polyfurcated) NH⋯F hydrogen bonds. The X-ray crystal structure contains two crystallographically independent centrosymmetric [Me2SnF4]2- anions, but only one kind of NH4+ cation. The cations and the anions are linked by nearly linear NH⋯F hydrogen bonds giving rise to a three-dimensional network. The average SnF distance is 2.127 A and the usefulness of covalent radii to predict accurate bond distances is challenged. An equation to calculate the average SnF distance in complexes [SnF4L2] from the Mossbauer QS is proposed.

Crystal structure of triphenyltin fluoride

Triphenyltin fluoride has been studied by powder and single-crystal X-ray diffraction. Powder studies show that the polymeric chain of SnPh3F propagates along the c axis with a repeat distance of ca. 4.29 A. The colourless crystals are trigonal, space group Pc1 (no. 165), with a= 10.358(1), c= 8.583(1)A and Z= 2. The F atom lies at an inversion centre, giving rise to a crystallographically imposed rod (class 1) polymer with identical Sn–F distances of 2.1458(3)A. X-Ray powder diffraction and variable-temperature Mossbauer spectroscopy fail to distinguish between rod (class 1) and zigzag (class 2) triorganotin(IV) polymers.

Vibrational and 119Sn Mössbauer spectra of tin(IV) halide complexes with 1,3-dimethylurea and 1,3-dimethylthiourea

Tin(IV) halide complexes with 1,3-dimethylurea (dmu) and 1,3-dimethylthiourea (dmtu) have been prepared and characterised by IR, Raman and 119Sn Mossbauer spectroscopies. The previously reported isomer shift (IS) values of SnBr4(dmtu)2 and SnI4(dmtu)2 have been revised to 0.98 and 1.32 mm s−1, respectively. The IS increases with decreasing electronegativity of the halogen atoms, and on going from dmu to dmtu complexes. The variation of the IS of SnX4L2 complexes with the electronegativity of the halogen X and the donor atom of the ligand L is studied. The IS can be used to get information about the atoms bonded to tin. The shifts of v(CE) (EO, S) and vas(NCN) with respect to the free ligands, in the IR spectra of the complexes, indicate that the dmu and dmtu ligands coordinate through the O and S atoms, respectively. The structure of the complexes is discussed in terms of the Mossbauer quadrupole splitting and the tin-halogen stretching vibrations in the IR and Raman spectra.

Correlation between the Mössbauer quadrupole splitting and the Sn–Cl distance for tin(IV) chloride complexes

The Sn–Cl distances in octahedral SnCl4L2 compounds are linearly related to the Mossbauer partial quadrupole splitting data; the correlation can be used to predict Sn–Cl distances, and has allowed us to detect an error in the published crystal structure of tetrachlorobis(1,3-diethylthiourea)tin(IV) which was confirmed in a redetermination.

Structural chemistry of triorganotin fluorides. The crystal structure of tricyclohexyltin fluoride revisited

The crystal structure of tricyclohexyltin fluoride has been redetermined to be polymeric. The compound crystallizes in the trigonal P3c1 space group with a= 11.103(2), c= 8.708(1)A and Z= 2. The Sn–F–Sn bridges are linear and asymmetric with Sn–F distances of 2.051(10) and 2.303(10)A. These distances are rationalised in terms of the structure-correlation method which assumes bond-order conservation and Paulings relationship between bond length and bond order. The polymeric structure is consistent with the physical properties of Sn(C6H11)3F and variable-temperature Mossbauer spectroscopic data. It is proposed that, for rod-polymeric triorganotin fluorides, the repeat distance can give information about the Sn–F distances.

Surface CuO, Bi2O3, and CeO2 Species Supported in TiO2-Anatase: Study of Interface Effects in Toluene Photodegradation Quantum Efficiency

The enhancement of active triggered by surface deposition of Cu, Bi, and Ce containing oxidic species onto a high surface area anatase is analyzed through the calculation of the quantum efficiency for toluene photodegradation under UV and Sunlight-type illumination. To this end, series of Cu, Bi, and Ce containing oxides supported on anatase were synthesized having a growing content of the Cu, Bi, and Ce surface species and characterized with X-ray diffraction and photoelectron, UV-visible, and photoluminescence spectroscopies as well as transmission electron microscopy. Utilizing the surface concentration of Cu, Bi, and Ce species as a tool, we analyzed the influence of the system physicochemical properties affecting quantum efficiency in anatase-based materials. First, employing small surface concentrations of the Cu, Bi, and Ce species deposited onto (the unperturbed) anatase, we provided evidence that all steps of the photocatalytic event, including light absorption, charge recombination, as well as surface interaction with the pollutant and chemical output as to activity and selectivity have significance in the quantitative assessment of the enhancement of the efficiency parameter. Second, we analyzed samples rendering maximum quantum efficiency within all these series of materials. The study indicates that maximum enhancement over anatase displays a magnitude strongly dependent on the efficiency level of calculation and would thus require the use of the most accurate one, and that it occurs through a balance between optoelectronic and chemical properties of the composite materials. The (Cu, Bi, Ce) oxide-anatase interface plays a major role modulating the optoelectronic properties of the solids and thus the efficiency observable.