Antimony chains

Delocalization of the electrons along the antimony chains was assumed to be responsible for the bathochromic shift of the absorption from the yellow liquid to the red solid. Similar colour phenomena have also been observed for Me4Bi2 , a compound that is red or orange in solution in organic solvents and green in the crystalline state. 

A simple qualitative explanation of the colour effects of Me4Sb2 and Me4Bi2 is based on the assumption of p orbital overlap in the bismuth or antimony chains (Figure 3). The transition energy between the orbitals in the monomers is larger than the band gap in the polymer and thus the bathochromic shift of the edge of absorption between monomers in... 

The extent of delocalization of electrons, and hence the colours of the antimony chains, may also be influenced by the presence of different conformers and interaction of lone pairs. A more extended conjugation should be possible in all trans chains of the solid whereas gauche interactions in the liquid might interrupt the delocalization. IR and Raman spectroscopic investigations of liquid and solid tetramethyldistibane have been carried out. There are considerable spectral changes between the solid state spectra and the liquid. The possibility of the presence of both gauche and trans conformers in liquid tetramethyldistibane has, however, been discussed controversely - . 

The thermochromic effect of heterocyclic bistiboles has been the subject of several theoretical publications " " with focus on the unsaturated compounds. Band structures have been calculated for the antimony chain of... 

The reactivity of antimony rings towards distibanes has also been studied by NMR spectroscopy in benzene and by mass spectroscopy of neat liquids. With excess of distibanes the formation of short antimony chains (tristibanes) was observed (equation 20) after a few minutes reaction time. 

The standard synthesis method features side-chain chlorination of a methylpyridine (picoline), followed by exchange-fluoriaation with hydrogen fluoride or antimony fluorides (432,433). The fluoriaation of pyridinecarboxyHc acids by sulfur tetrafluoride (434) or molybdenum hexafluoride (435) is of limited value for high volume production operations due to high cost of fluorinating agent. 

At higher temperatures the stable form is valentinite, which consists of infinite double chains. The orthorhombic modification is metastable below 570 °C however, it is sufficientiy stable to exist as a mineral. Antimony trioxide melts in the absence of oxygen at 656°C and partially sublimes before reaching the boiling temperature, 1425°C. The vapor at 1500°C consists largely of Sb O molecules, but these dissociate at higher temperatures to form Sb202 molecules. 

Antimony Trisulfide. Antimony(III) sulfide (antimony sesquisulftde) [1345-04-6] SbS, exists as a black crystalline soHd, stibnite [1317-86-8] and as an amorphous red to yeUow-orange powder. Stibnite melts at 550°C and has Ai i° 298 175 kJ/mol (—41.8 kcal/mol)) A°29g, 182 J/(182 mol-K) [43.5 cal/(43.5 mol-K)] for the amorphous soHd AH° 298 1 147 kJ/mol (—35.1 kcal/mol) (38). The crystal stmcture of stibnite contains two distiucdy different antimony sites and consists of two parallel Sb S chains that are linked together to form cmmpled sheets (two per unit cell). 

Addition Chlorination. Chlorination of olefins such as ethylene, by the addition of chlorine, is a commercially important process and can be carried out either as a catalytic vapor- or Hquid-phase process (16). The reaction is influenced by light, the walls of the reactor vessel, and inhibitors such as oxygen, and proceeds by a radical-chain mechanism. Ionic addition mechanisms can be maximized and accelerated by the use of a Lewis acid such as ferric chloride, aluminum chloride, antimony pentachloride, or cupric chloride. A typical commercial process for the preparation of 1,2-dichloroethane is the chlorination of ethylene at 40—50°C in the presence of ferric chloride (17). The introduction of 5% air to the chlorine feed prevents unwanted substitution chlorination of the 1,2-dichloroethane to generate by-product l,l,2-trichloroethane. The addition of chlorine to tetrachloroethylene using photochemical conditions has been investigated (18). This chlorination, which is strongly inhibited by oxygen, probably proceeds by a radical-chain mechanism as shown in equations 9—13. 

In addition, for the sodium-antimony alloy, where the Zintl anions are Sb spiral chains, ab initio MD simulations are in progress. 

Mercury, tin, lead, arsenic, and antimony form toxic lipophilic organometallic compounds, which have a potential for bioaccumulation/bioconcentration in food chains. Apart from anthropogenic organometallic compounds, methyl derivatives of mercury and arsenic are biosynthesized from inorganic precursors in the natural environment. 

This bismuth-III structure is also observed for antimony from 10 to 28 GPa and for bismuth from 2.8 to 8 GPa. At even higher pressures antimony and bismuth adopt the body-centered cubic packing of spheres which is typical for metals. Bi-III has a peculiar incommensurate composite crystal structure. It can be described by two intergrown partial structures that are not compatible metrically with one another (Fig. 11.11). The partial structure 1 consists of square antiprisms which share faces along c and which are connected by tetrahedral building blocks. The partial structure 2 forms linear chains of atoms that run along c in the midst of the square antiprisms. In addition, to compensate for the... 

The structural chemistry of some metal dithiocarbamates, i.e. systematics, coordination modes, crystal packing, and supramolecular self-assembly patterns of nickel, zinc, cadmium, mercury,363 organotin,364 and tellurium,365 366 complexes has been thoroughly analyzed and discussed in detail. Supramolecular self-assembly frequently occurs in non-transition heavier soft metal dithiocarbamates. Thus, lead(II),367 bismuth(III)368 zinc,369 cadmium,370 and (organo)mercury371 dithiocarbamates are associated through M- S secondary bonds, to form either dimeric supermolecules or chain-like supramolecular arrays. The arsenic(III)372 and antimony(III)373 dithiocarbamates are... 

Although there seems little doubt that antimony trihalides play a chemical role in inhibition of free radical chain reactions in the flame zone, a comparison... 

In this regard, it should be noted at this point that one of the products identified by CGC/MS from these pyrolysis reactions was SbBr3- Furthermore, the data presented concerning the importance of the polymer substrate in the degradation of the DBDPO and the proposed chain radical transfer mechanism [7] would suggest that the condensed phase chemistry could be much more important in antimony oxide/organohalogen flame retardant systems than had been previously thought. 

The compound 4(Ph3SbI)2OI2 is obtained by the addition of I2 in acetonitrile/water to a solution of triphenyl-antimony. The crystal structure contains a one-dimensional chain 53 and (Ph3SbI)20 molecules which are not coordinated to I2. In the ID chain, the distance between the iodine of the (Ph3SbI)20 molecule and the diiodine... 

The esterification of TPA is catalyzed by protons and in standard industrial operations neither an additional esterification catalyst nor a polycondensation catalyst is added to the esterification reactor. Some new antimony-free polycondensation catalysts [125-128] also affect the speed of esterification significantly and it could be advantageous to add them directly into the slurry preparation vessel. Co-monomers, which should be randomly incorporated into the polymer chains, are usually fed into the slurry preparation vessel. How and when additives, catalysts, colorants and co-monomers are added influences the overall reaction rate and therefore affects the product quality. 

PET requires special flame-retardant chemistry since the antimony oxide synergist that is normally used in combination with brominated flame retardants causes de-esterification of the PET chain and concomitant molecular weight loss. In place of antimony oxide, PET requires a sodium antimonate synergist. Another problem with antimony trioxide is that it decreases the thermal stability of the brominated flame retardant which then produces hydrobromic acid which degrades the PET. 

THF can be polymerized only with cationic initiators, for example, boron trifluoride or antimony pentachloride. The initial step consists of the formation of a cyclic oxonium ion one of two activated methylene groups in the a-position to the oxonium ion is then attacked by a monomer molecule in an S 2-reaction, resulting in the opening of the ring. Further chain growth proceeds again via tertiary oxonium ions and not, as formerly assumed, via free carbonium ions ... 

Antimony trisulfide occurs in nature primarily as the mineral, stibnite, which consists of two parallel Sb4Se chains hnked together. It is used in fireworks in certain types of safety matches as a pigment in paints and in the manufacture of ruby glass. 

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