Zinc structures

C.C.I.T.T. Study Group VI working party on corrosion by alternating currents (C. Cabrillac). A bibliography with over 60 references giving particular emphasis on buried lead, iron, aluminium and zinc structures, I.T.U., Geneva... 

For a liver alcohol dehydrogenase (LADH) model an NS2O coordination sphere is required. The chelating aldehydes are ideal for the formation of this donor set when combined with bis(pentafluoro-thiophenolato)zinc. Structural data on the complexes with one equivalent of 6-methylpyridine-2-carbaldehyde, 6-methoxypyridine-2-carbaldehyde, 2-(dimethylamino)benzal-dehyde) demonstrate that the coordination sphere for LADH has been reproduced to a close approximation and the corresponding alcohol complexes have also been characterized.354 Other thiophenols have been used to form such complexes but have not been structurally characterized.304... 

By analogy to the zinc structure, the coordination sphere around the silver(II) ion was anticipated to contain four sulfur atoms from two dialkyl dithiocarbamates in a square planar arrangement. Dimerization would occur by interaction via two Ag—S bridges (8S).538... 

Electrodeposition is used to fabricate ramified structures with high surface areas [51-55], in particular zinc structures. 

As a second example we may consider the element zinc, for which the three configurations shown below may be written. ZnA has no vacant metallic orbitals and corresponds to a purely covalent non-metallic structure of covalency 6. ZnB and Znc, however, both possess vacant orbitals. Separate zinc structures corresponding to these different configurations are not known, but the assumption that in the actual structure there is some contribution from each accounts elegantly for the fact that the crystal structure is not truly close packed. We shall revert to this point later when we discuss the metal structures in detail ( 7.19). 

As mentioned earlier, octahedral zinc structures are not uncommon, and one feature which seems to occur in most of these systems is the presence of co-ordinated water molecules. This is well illustrated by two structures... 

Figure Bl.8.4. Two of the crystal structures first solved by W L Bragg. On the left is the stnicture of zincblende, ZnS. Each sulphur atom (large grey spheres) is surrounded by four zinc atoms (small black spheres) at the vertices of a regular tetrahedron, and each zinc atom is surrounded by four sulphur atoms. On the right is tire stnicture of sodium chloride. Each chlorine atom (grey spheres) is sunounded by six sodium atoms (black spheres) at the vertices of a regular octahedron, and each sodium atom is sunounded by six chlorine atoms.

Sabinene and carene are isomeric natural products with the molecular formula CjoHig (a) Ozonolysis of sabinene followed by hydrolysis in the presence of zinc gives compound A What IS the structure of sabinene" What other compound is formed on ozonolysis" (b) Ozonoly SIS of A carene followed by hydrolysis in the presence of zinc gives compound B What is the structure of A carene" ... 

This cleavage reaction is more often seen in structural analysis than in synthesis The substitution pattern around a dou ble bond is revealed by identifying the carbonyl containing compounds that make up the product Hydrolysis of the ozonide intermediate in the presence of zinc (reductive workup) permits aide hyde products to be isolated without further oxidation... 

Ambrettohde is obtained from hibiscus and has a musk like odor Its preparation from a compound A is outlined in the table that follows Write structural formulas ignonng stereochem istry for compounds B through G in this synthesis Hint Zinc as used in step 4 converts vici nal dibromides to alkenes )... 

Analogously, pyrazolyl-aluminate and -indate ligands have been prepared <75JCS(D)749) and their chelating properties evaluated with cobalt, nickel, copper and zinc. Gallyl derivatives of pyrazoles and indazoles have been extensively studied by Storr and Trotter e.g. 75CJC2944) who determined several X-ray structures of these compounds. These derivatives exist in the solid state as dimers, such as (212) and (288). A NMR study in acetone solution showed the existence of a slow equilibrium between the dimer (212) and two identical tautomers (289) and (290) (Section 4.04.1.5.1) (81JOM(215)157). 

Liquid-Metal Corrosion Liquid metals can also cause corrosion failures. The most damaging are liqmd metals which penetrate the metal along grain boundaries to cause catastrophic failure. Examples include mercury attack on aluminum alloys and attack of stainless steels by molten zinc or aluminum. A fairly common problem occurs when galvanized-structural-steel attachments are welded to stainless piping or eqmpment. In such cases it is mandatoty to remove the galvanizing completely from the area which will be heated above 260°C (500°F). 

One feature of oxides is drat, like all substances, they contain point defects which are most usually found on the cation lattice as interstitial ions, vacancies or ions with a higher charge than dre bulk of the cations, refened to as positive holes because their effect of oxygen partial pressure on dre electrical conductivity is dre opposite of that on free electron conductivity. The interstitial ions are usually considered to have a lower valency than the normal lattice ions, e.g. Zn+ interstitial ions in the zinc oxide ZnO structure. 

---