Bridging unit

Figure C3.2.9. Both nearest neighbour and nonnearest neighbour coupling interactions mediate superexchange between tire temrinal pi-electron groups of rigid dienes witlr saturated bridging units. From [31],...

Uses. Dental solders and fluxes are used to join orthodontic wires, fasten attachments to partial dentures, repair castings units, and join crown and bridge units either before or after the appHcation of porcelain. They may also be used to repair fixed and removable dental appHances. 

When ring fusions and/or bridges are present in addition to spiro linkages, the fused or bridged units are first named individually (by any of the available methods) and the names are then cited (in square brackets and in alphabetical order) with the prefix spiro- or dispiro-, etc. Points of spiro attachment are indicated between the names of the components, with primes as necessary (examples 64-66). This method is also applicable to structures like (62) and (63) but is more cumbersome. 

Figure 3.10 Stniciural details of the bridging units between pairs of bases in separate strands of the double helix of DNA (a) the thymine-adenine pair (b) the cytosine-guanine pair.

A dramatic discovery in this area was made in 1996 when a dicopper-dioxygen adduct was found to have two isomeric forms which featured either a side-on bridging unit Cu(/r ), ) -02)-Cu) " or a cyclic (Cu(/r-0)2Cu) " core depending on whether it was crystallized from CH2CI2 or thf, respectively. The two forms could be readily interconverted by reversible 0-0 bond cleavage and reformation, the 0-0 distance being 141 pm and 229 pm in the two isomers.The... 

This compound has been investigated by several groups,379- 384 but due to its practical insolubility it has not been fully characterized. Another approach to obtain phthalocyanine network polymers is with the use of crown ethers385 or other groups like di oxy -para-p h enyle n e3 8 6 as bridging units between the macrocycles. Some attempts to obtain metal phthalocyanine substructures arranged as ladder polymers have also been proposed (see below).344... 

The situation is the contrary for the electrochemical behavior of the two cycles. These show distinct cyclic voltammograms due to the altered spatial distribution of the three electroactive CpFe groups. The differences in the electrochemistry of 83 and 84 are not dramatic but significant and their interpretation is not straightforward. A cycle with smaller bridging units such as 85, forcing the... 

Di- and oligomtclear complexes with dinucleating ligands incorporating diazine, diazole, and triazenido bridging units... 

Di(ethynyl)gold moieties can be used as bridging units between transition metals as demonstrated for square-grid complexes with Pt(dppe) acceptor components.96... 

X-ray studies confirm Bi2(ju,-OR)2 centrosymmetric dimers 4 in the solid state (24). Terminal alkoxides are generally bound more tightly than bridging units [terminal Bi-0 2.064(7) A bridging Bi-0 2.188(7) and 2.688(7) A], The bismuth oxide alkoxide cluster compounds [Bi6(p,3-07)(p,3-OC6F5) Bi(OC6F6)4 3(sol)2] [sol]2 (sol = thf or toluene) were also isolated as minor products (25). Both structures contain the unusual octahedral I Bi, (/x3-07 X/x3-OCeF.-) I" cores 5, which... 

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