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The mechanism of the gas-phase halogen-exchange reaction between boron- and aluminum-halides (i.e., BX3 + BX3 and AlX3 + AlX3, X = F, Cl, or Br) was discovered using density functional theory. The reaction takes place via a two-step mechanism with the intermediacy of a diamond-core structure analogous to diborane. Good agreement was found between the simulated reaction features and experimental observations, which demonstrate slow kinetics and an equilibrium process for boron species and dimer formation in the case of aluminum-halides. This computational and theoretical study also reveals and quantifies the effect of resonance on the thermodynamic stability of the central intermediate and conceptualizes the extreme stability difference (∼50 kcal mol−1) between boron and aluminum diamond-core bridge structures. Through an interaction energy decomposition analysis in combination with electronic structure analyses, we revealed that, beyond the resonance stabilization in free boron-halides, superior electrostatics in aluminum-halides results in the different reactivities, i.e., dimer formation for the latter species whereas substituent exchange for the former ones. [ABSTRACT FROM AUTHOR]

Life is all the more appealing thanks to the phenomenon of color. In general we understand color in the context of unabsorbed light reflecting from a surface; however, that may [...]

All living things, including humans, exist in complex interdependent relationships known as ecosystems. Destruction and degradation of natural ecosystems are the primary causes of declines in biodiversity, the key indicator [...]

One hundred and fifty years ago, 1869, the Russian Scientist Dimitri Mendeleev decided to forgo a planned trip to a cheese factory and, instead, jotted down his blossoming ideas on [...]

The tetrahedral geometry of organolead(IV) compounds can be readily transformed by using an organic ligand containing a dangling-arm oxygen functionality. The acidity of the Pb center results in so-called secondary bonding between O and Pb thereby pushing the geometry at Pb toward a trigonal bipyramidal (tbp) structure. Replacing a phenyl group by a chlorine atom dramatically enhances this phenomenon. Thus for (o-methoxybenzyl) triphenyllead (4), and (o-methoxybenzyl)diphenyllead chloride (5), the Pb--O internuclear distances are 3.362(4) and 2.845(3) [Angstrom], respectively; 83% (4) and 70% (5) of the sum of the van der Waals Pb and O radii. Within the group 14 element congeners the structural analysis of the (o-methoxybenzyl)triphenylE compounds, E = Si, Ge, Sn, and now Pb, demonstrates the relative acidities of E are Si < Ge < Sn < Pb. Keywords: hypercoordination, dangling-arm ligands, oxygen secondary bonding, group 14 Lewis acidity, Since the structural analysis of the pyridine adduct of trimethyltinchloride, Py[Me.sub.3]SnCl (Hulme 1963), there has been a consistent interest in the so-called hypercoordinated compounds of the heavy group 14 elements, [...]

The reaction between the Grignard reagent formed from Mg and 2‐bromobenzylmethyl ether and SnCl4 produced four products: [2‐(MeOCH2)C6H4]3SnBr (1), [2‐(MeOCH2)C6H4]2SnX2 (2, X2=Br2 (a) and BrCl (b)), [{2‐(MeOCH2)C6H4}3Sn]2 (3), and [{2‐(MeOCH2)C6H4}2SnBr]2O (4). In the case of 1, two of the three dangling arm O atoms coordinate to the central tin atom with O−Sn internuclear distances of 2.53 (O1) and 2.91 (O2) Å, the shorter interaction being trans to the Br atom, the other trans to a phenyl carbon atom. In the case of 2a the resulting hexacoordinate structure exhibits two very short O−Sn interactions of 2.42 and 2.50 Å, well below the sum of the VdW radii of O and Sn, 3.69 Å. The sterically crowded ditin compound 3 was obtained in trace amounts and the structure demonstrates no dangling O−Sn interactions. General changes in structure compared to other distannane systems are reflective of the great steric crowding. Distannoxane 4, has a Sn−O−Sn bond angle of 148.1(2)° which is larger compared to other distannoxane structures. The intermolecular interactions between Sn−O 2.470(3) and 2.521(3)Å and 2.665(3) and 2.629(3)Å for Sn1 and Sn2 respectively are responsible for a distorted octahedral geometry around the two tin atoms. The various 119Sn,13C and 1H NMR spectra are in accord with their structural analysis for 1 and 2, and in the solid state 13C NMR spectrum of 1 the dangling methylene group is observable whereas is solution there is a rapid dynamic equilibrium resulting in a single resonance for all methylene groups. [ABSTRACT FROM AUTHOR]

Reactions between 8-RS-BODIPY (R = Me, 1) and alkyl and aryl thiols were readily accomplished in dichloromethane to provide a synthetic pathway to a range of new 8-organothio-BODIPYs in good yield. The new alkyl 8-RS-BODIPYs (R = Et, 2; Pr, 3; Bu, 4; [sup.t]Bu, 5; n-dodecyl, 6) exhibit absorption and emission properties essentially unchanged from those of 1 whereas the arylthio analogs (R = Ph, 7; 2,6-[Me.sub.2][C.sub.6][H.sub.3], 8; p-Me[C.sub.6][H.sub.4], 9; p-MeO[C.sub.6][H.sub.4],10) exhibit no fluorescence with the exception of 7, and then only in hexane. In common with other related 8-substituted BODIPYs, the new 8-alkylthio-BODIPY dyes show decreasing fluorescence intensity as solvent polarity increases. Compounds 2, 3, 7, and 8 were characterized via single-crystal X-ray analysis; the alkyl derivatives 2 and 3 exhibited planar BODIPY cores with co-planar organothio- substituents whereas the aryl derivatives exhibited both BODIPY core deformation and significant twisting about the S-C (8) bond removing co-planarity between the aryl group and the distorted BODIPY core. These deformations coincide with the significantly reduced emission properties. Key words: BODIPY, fluorescence, thiolation, structure. Nous avons effectue sans dificulte les reactions entre le 8-RS-BODIPY (R = Me, 1) et des alkylmercaptans ou des arylmercaptans dans le dichloromethane afin d'offrir une voie de synthese permettant d'acceder a une serie de 8-organothio-BODIPY avec unbon rendement. Les nouveaux derives alkyle 8-RS-BODIPY (R = Et, 2; Pr, 3; Bu, 4; [sup.t]Bu, 5; n-dodecyl, 6) presentent essentiellement les memes proprietes d'absorption et d'emission que celles du compose 1, tandis que dans la serie d'analogues arylthio (R = Ph, 7; 2,6-[Me.sub.2][C.sub.6][H.sub.4], 8; p-Me[C.sub.6][H.sub.4], 9; p-MeO[C.sub.6][H.sub.4],10) seul le compose 7 revele une fluorescence, et ce, seulement dans l'hexane. A l'instar d'autres composes apparentes de type BODIPY substitues en position 8, les nouveaux pigments de formule 8-alkylthio-BODIPY presentent une decroissance de l'intensite de la fluorescence en fonction de l'augmentation de la polarite du solvant. Nous avons caracterise les composes 2,3,7 et 8 par analyse des rayons X sur cristal unique; les derives alkyle 2 et 3 presentaient une conformation planaire du noyau BODIPY et une disposition coplanaire du substituant organothio, tandis que les derives aryle presentaient une deformation du noyau BODIPY et une torsion importante de la liaison S-C(8), se traduisant par une suppression de la coplanarite entre le groupement aryle et le noyau BODIPY deforme. Ces deformations coincident avec la reduction considerable des proprietes d'emission. [Traduit par la Redaction] Mots-cles: BODIPY, fluorescence, thiolation, structure., Introduction Boron dypyrromethene (BODIPY) molecules are of current interest due to such properties as strong photostability, high quantum yield emission, and high extinction coefficients. (1,2,3) These features may be tweaked [...]

The reaction between Ta(OEt)(sub 5) and 1,1,3,3-tetramethyl-1,3-disiloxanediol, (HOSiMe2OSiMe2OH), produces new siloxy complexes in which the dimeric nature of Ta(OEt)(sub 5) is maintained with both bridging ethoxide and disiloxanediolato bridges. The structural and spectroscopic characterization, catalytic properties and thermal transformations of these new complexes are discussed.

The rare-earth binding properties of two hydrophobic carbamoylmethylphosphine oxide (CMPO) ligands, the normal bidentate variety, a tridentate extractant and tributyl phosphate are evaluated. The results show that as the ionic radius of the lanthanide ion decreases, a pair of the carbamoylmethylphosphine ligands is able to completely solvate a bound metal ion thereby weakening the nitrate-metal interaction.

The series of compounds (o-[CH.sub.3][SC.sub.6][H.sub.4])[CH.sub.2] [EPh.sub.3] (E = Si (1), Ge (2), Sn (3), and Pb (4)) have been synthesized and characterized by NMR spectroscopy and by single crystal X-ray diffraction. Compounds 1 and 2 are isostructural with a triclinic crystal system and P-1 space group; however, morphotropic steps occur between Ge and Sn, and Sn and Pb. While the E-S distances in 1 and 2 are 3.985 and 3.974 [Angstrom], respectively, ~100% of the sum of the respective van der Waals (vdW) radii, there is a notable distortion from tetrahedral geometry about E. Compound 3 is also triclinic with P-1 symmetry, but has two molecules in the unit cell that demonstrate a distorted tetrahedral geometry and intramolecular Sn-S distances of 3.699 and 3.829 [Angstrom], 88% and 91% of the sum of the vdW radii. Compound 4 has a Pb-S distance of 3.953 [Angstrom] (91% of E vdW radii). The structure of the Grignard coupling product [[o-(SC[H.sub.3])[C.sub.6][H.sub.6]C[H.sub.2]].sub.2] is also reported. Key words: intramolecular self-assembly, silicon, germanium, tin, lead, sulfur.

We have reinvestigated the solid state structure of 1,l'-bis- (ferrocenyldimethylsilyl) ferrocenylene, [([[eta].sup.5]-FcSi[Me.sub.2][C.sub.5][H.sub.4]).sub.2], Fe, Fc = ([[eta].sup.5] -[C.sub.5][H.sub.5])Fe([[eta].sup.5]-[C.sub.5][H.sub.4]). Using a DSC technique we observed a reversible phase transition for this compound at 169(3)K with [DELTA]H = 1.1 kJ/mol, and [DELTA]S = 6.54 J/mol K. A single crystal X-ray diffraction study has demonstrated that this phase change involves a transformation from a high temperature phase, space group P[2.sub.1]/c, Z = 2, to a triclinic low temperature phase, space group P[bar]1, Z = 4. The phase transition involves the loss of the molecular crystallographic center of symmetry and rotations about the terminal and central cyclopentadienyl ring pairs. The results are compared to those reported for ferrocene. Key words: solid state, phase transition, silyleneferrocenylene.

A review of research into silicon-silicon (Si-Si) bond activation by transition metal complexes is presented. The review focuses on two aspects of such research: metal complexes that contain a Si-Si linkage and the use of metal complexes as catalysts in Si-Si bond transformations. Many of the studies reviewed were performed since 1985, and the outlook for further research in the field is bright.

Photochemical treatment of transition metal substituted disilanes in inert hydrocarbon solvents results in the discharge of the SiMeAr and SiMe2 fragments to produce FpSiMe2Ar and FpSiMe3. Photolysis of Fp-disilanes induces some direct Si-Si cleavage in which fortuitous H2O plays a role. Siloxane materials are formed when SiMe2 reacts units CO in the presence of metal complexes.

The tetrahedral geometry of organolead(IV) compounds can be readily transformed by using an organic ligand containing a dangling-arm oxygen functionality. The acidity of the Pb center results in so-called secondary bonding between O and Pb thereby pushing the geometry at Pb toward a trigonal bipyramidal (tbp) structure. Replacing a phenyl group by a chlorine atom dramatically enhances this phenomenon. Thus for (o-methoxybenzyl) triphenyllead (4), and (o-methoxybenzyl)diphenyllead chloride (5), the Pb--O internuclear distances are 3.362(4) and 2.845(3) Å, respectively; 83% (4) and 70% (5) of the sum of the van der Waals Pb and O radii. Within the group 14 element congeners the structural analysis of the (o-methoxybenzyl)triphenylE compounds, E = Si, Ge, Sn, and now Pb, demonstrates the relative acidities of E are Si < Ge < Sn < Pb. [ABSTRACT FROM AUTHOR]