Anuar Abras

New heptacoordinated tin complexes of 2,6-diacetylpyridine-bis(thiosemicarbazone), H2daptsc, and of 2,6-diacetylpyridine-bis(semicarbazone), H2dapsc. Crystal and molecular structures of [MeSnCl(Hdaptsc)]Cl·MeOH and [MeSnCl(H2dapsc)]Cl2·2H2O

Two new heptacoordinated organotin complexes, [MeSnCl(Hdaptsc)]Cl·MeOH (1) and MeSnCl(H2dapsc)]- Cl2·2H2O (2), have been prepared from MeSnCl3 and H2daptsc and H2dapsc, respectively. Single crystal X-ray diffraction studies showed them to be approximately pentagonal bipyramidal (PBP), with the organic ligands lying in the equatorial plane. H2daptsc and SnCl4 form a complex with the formula [ClSnCl(Hdaptsc)]Cl (3), which is presumed to have an analogous PBP structure. On the other hand, the complex obtained from H2dapsc and Me2SnCl2 is tentatively formulated as [(Me2SnCl2)2(H2dapsc)] (4), and 119Sn Mossbauer spectroscopic evidence suggests an octahedral coordination for the two tin atoms.

Structures, semi-empirical calculations and thermolyses of some five- and six-membered chelate organotin mercaptide complexes

Abstract Characterization of Ph 2 Sn(Cl)(MBT) ( 1 ) (HMBT=2-mercaptobenzothiazole) has been carried out by IR, Mossbauer, 1 H, 13 C and 119 Sn spectroscopies and by X-ray crystallography for 1 together with that of Ph 2 Sn(SCH 2 CH 2 S) ( 2 ). Compound 1 , unexpectedly obtained from the reaction between Ph 2 SnCl 2 and KMBT in a 1:2 mole ratio, has a trigonal-bipyramidal geometry, due to intramolecular SnN interactions, both in the solid state and in solution; the axial sites are occupied by N and Cl, N(24)SnCl(4)=155.27(17)°, the chelate bite angle, N(24)SNS(15), is 64.65(17)°. Compound 2 is essentially monomeric in the solid state and has a distorted tetrahedral structure; the bond angles at tin vary from 92.50(16)° [S(2)SnS(5)] to 116.4(6)° [C(6)SnC(12)]. The shortest intermolecular Sn⋯S contact in 2 is 3.885 A, just within the sum of the van der Waals’ radii for Sn and S (4.0 A). PM3 semi-empirical calculations for 2 indicated that the geometry at the tin center can be accounted for by a high degree of p-character in the tin bonding orbitals to sulfur; PM3 semi-empirical calculations on Ph 2 Sn(SCH 2 CH 2 CH 2 S) ( 3 ) indicated the geometry at tin to be less distorted from tetrahedral, with a SSnS angle of 99°; the calculations further indicated that the only stable conformation of the six-membered ring in 3 is the chair form.

The reaction of 2-formylpyridine thiosemicarbazone (HFPT) with tin tetrahalides. Crystal and molecular structure of [SnCl3(FPT)]

Abstract 2-Formylpyridine thiosemicarbazone (HFPT) reacts with the tin tetrahalides (X=Cl, Br, I) with abstraction of HX and the formation of tridentate N,N,S-bonded hexacoordinated species [SnX3(FPT)]. A single crystal X-ray diffraction study of the chloro complex establishes mer-isomerism. Mossbauer data of the products correlate very well with a rehybridization of tin from sp3 to d2sp3 upon complexation.

Spectroscopic studies of metal complexes containing π-delocalized sulfur ligands. Mössbauer and kinetic studies of iron(II) and iron(III) complexes of the antitumor agent 2-formylpyridine thiosemicarbazone

Abstract Mossbauer studies on the Fe(II) and Fe(III) complexes of 2-formylpyridine thiosemicarbazone (FPT) showed the complexes to be low spin and provided evidence of the reducing character of the ligand. In addition, kinetic measurements of the Fe(III) complex reduction by the ligand gave an expression for the initial rate of the type vi = k′A + k″AB, in which A stands for the concentration of the Fe(III) complex and B for the concentration of the reducing agent. From this equation one may infer the coexistence of two mechanisms, one expressed by the first term and occurring even in the absence of FPT. For the second term we propose an inner sphere mechanism in which the ligand is the reducing agent.

Organotin(IV) Derivatives of 2-Acetylpyridine-N(4)-Phenylthiosemicarbazone, HAP4P, and 2-Hydroxyacetophenone-N(4)-Phenylthiosemicarbazone, H2DAP4P: Crystal and Molecular Structure of [SnMe2(DAP4P)] and [SnBu2(DAP4P)]

The reactions of 2-acetylpyridine-N(4)-phenylthiosemicarbazone, HAP4P, and 2-hydroxyacetophenone-N(4)-phenylthiosemicarbazone, H2DAP4P, with R4-mSnXm (m = 2, 3; R = Me, nBu, Ph and X = Cl, Br) led to the formation of hexa- and penta-coordinated organotin(IV) complexes, which were studied by microanalysis, IR, 1H-NMR and Mossbauer spectroscopies. The molecular structures of [SnMe2(DAP4P)] and [SnnBu2(DAP4P)] were determined by single-crystal X-ray diffraction studies. In the compounds [SnClMe2(AP4P)] and [SnBrMe2(AP4P)], the deprotonated ligand AP4P- is N,N,S-bonded to the Sn(IV) atoms, which exhibit strongly distorted octahedral coordination. The structures of [SnMe2(DAP4P)] and [SnnBu2(DAP4P)] revealed that the DAP4P2- anion acts as a O,N,S-tridentate ligand. In these cases, the Sn(IV) atoms adopt a strongly distorted trigonal bipyramidal configuration where the azomethine N and the two C atoms are on the equatorial plane while the O and the S atoms occupy the axial positions.

The chemical behaviour of di(2-pyridyl)sulphide, dps. Crystal and molecular structure of μ-di(2-pyridyl)sulphidebis(trans-dichlorotriethylphosphine platinum(II)), [{Pt(PEt3)Cl2}2μ-dps] and its reactivity towards stannylated species

The coordinating ability of the ligand di(2-pyridyl)sulphide, dps, was studied in several situations. Dps behaved as a bidentate chelating agent with SnX4 (X=Cl or Br) and also with Pd and Pt (PdCl2 and K2PtCl4), whereas with [Pt2(PR3)2Cl4], (R = Et or Ph), it formed bridging complexes: [{Pt(PR3)Cl2}2μ-dps]. The crystal and molecular structure of [{Pt(PEt3)Cl2}2μ-dps] was determined. This complex, as well as [M(dps)Cl2], (M = Pd or Pt), underwent reactions with SnCl2, which inserts into the M–Cl bonds producing heterobimetallic products, which are important in catalysis.

Mössbauer effect study of natural chromites of Brazilian and Philippine origin

Mössbauer spectroscopy has been used to study nine natural chromite samples from deposits throughout Brazil and one sample from Philippine. It was possible to identify three different groups of chromite spinels, depending on the iron distribution over tetrahedral and octahedral sites. Using the Mössbauer Fe3+/Fe2+ ratio, chemical analysis and x-ray data a chemical formula was proposed for each group.

New Heptacoordinated Organotin(IV) Complexes Derivatives of 2,6-diacetylpyridinebis(2-furanoylhydrazone), H2dapf, and 2,6-diacetylpyridinebis(2-thenoylhydrazone), H2dapt: Crystal and Molecular Structure of [Me2Sn(Hdapt]Br.H2O

The reaction of the ligands H2dapf and H2dapt, with R4-mSnXm (m = 2, 3; R = Me, Ph and X = Cl, Br) led to the formation of eight new heptacoordinated organotin(IV) complexes, which were studied by microanalysis, IR, NMR and Mossbauer spectroscopy to investigate their structural properties. The methyl derivative [Me2Sn(Hdapt)]Br.H2O was also studied by single crystal X-ray diffraction. It crystallizes in the monoclinic system, space group P21/c, with a = 21.920(3), b = 7.4470(5), c = 16.805(2) A, b = 110.18(1)o, Z = 4. The structure determination revealed a monocationic complex of Sn(IV) in a distorted bipyramidal geometry [Me2Sn(Hdapf)]+, with Br- as counter ion and one molecule of water helping the crystal packing. Mossbauer parameters of the complex [Me2Sn(Hdapf)]2[Me2SnCl4] have evidenced two Sn(IV) sites, as observed in the crystal structure determination. Also a correlation between Mossbauer and X-ray data based on the point-charge model is discussed.

Mössbauer and solid-state NMR spectroscopic studies of tin-modified rhenium-based metathesis catalysts

Mossbauer and solid-state NMR spectroscopic studies have been carried out on Re2O7/SiO2–Al2O3/SnR4 metathesis catalysts (R = Me, Et or n-Bu). The effects of both the rhenium loading and the SnR4 alkyl group are presented. The amounts of gas released upon the interaction between Re2O7/SiO2–Al2O3 and SnR4 do not correspond to a simple stoichiometry while chemical reactivity suggests the presence of minor amounts of a rhenium–alkylidene species. Mossbauer and NMR data suggest two kinds of tin sites, with the tin atom linked to the surface by one or two Sn—O bonds. The effects of exposure to air and catalyst regeneration on the tin environment have also been investigated. The nature of the tin-containing surface species is discussed.

Effects of the addition of Nb2O5 to rhenium-based olefin metathesis catalysts

Abstract The effects of the addition of Nb 2 O 5 to 6 wt.% Re 2 O 7 /Al 2 O 3 metathesis catalysts were investigated. At least until 9 wt.% Nb 2 O 5 loadings both tetrahedral and octahedral aluminum sites are evenly involved in the reaction between alumina and niobium oxide. Up to 12 wt.% Nb 2 O 5 no significative influence was observed in the catalytic activity of the resulting systems. For higher niobia loadings, however, the catalytic activity decreased quickly. In such conditions a second rhenium species, probably [Nb]-OReO 3 was detected by TPR. 119 Sn Mossbauer analyses showed that the reaction between the niobia-modified systems and SnBu 4 ([Sn]:[Re] = 0.55) led to the formation of only one kind of rhenium-tin site, with the tin atom attached to the surface by two SnO bonds. In contrast to what happens with the unmodified system, no physisorbed SnBu 4 was observed.