Dimer units

Both aluminium tribromide and triodide are dimeric in the solid state. As expected the solids dissolve in non-polar solvents without the break-up of these dimeric units. 

Figure 7.22 (a) Structure of the dimeric unit in the solvated complex [Ga(/) -C6H6)2][GaCl4].3QH6 indicating the... 

Figure 15.25 Molecular structure and dimensions of (a) the adduct SgO-SbCl at —100", and (b) the dimeric unit Sb 20->.2SbCl5 in Sb12Oj.2SbCI5.3CS) at —115 C. (c) Possible dipolar addition of 2SfO to form S12O2.

Figure 4.16 The structure of Au(S2CNPr2) showing the association of dimeric units into chains.

Due to the steric requirement of these substituents the formation of a columnar structure with infinite M M interactions is inhibited, and only the association of pairs of molecular units is allowed. The Ni Ni distance is 3.21 A [164]. If the same compound is crystallized in the presence of benzimidazole, the [Ni(dmg-BF2)2]2 dimer units are sandwiched between sheets of benzimidazole molecules due to n-n interactions resulting in an increased Ni Ni separation of 3.358 A [165]. With anthracene the n-n interactions seem to be stronger, because in this case the parent dimer molecule is cleaved. Each monomer now has a conformation of type B (Fig. 32) and is sandwiched by anthracene molecules [166]. Compound 121 has the same configuration [163d]. 

Yagi laid the foundation for the enzymology of CODH when he discovered an enzymatic activity in sulfate-reducing bacteria that oxidizes CO to CO2 (118). Twenty-five years later, the first CODH was purified to homogeneity (119, 120). The homogeneous C. thermo-aceticum CODH was shown to contain 2 mol of nickel, 12 iron, 1 zinc, and 14 acid-labile inorganic sulfide per afS dimeric unit (120). 

FIGURE 6.31 Spiro polymerization of a, spiro polymers 41 carrying spiro dimer units linked by alkyl chains. Reduction of 41 converts the spiro dimer units into ethano-dimer units, resulting in polytocopherols 42. 

Scheme 5 a Flavin-H-phosphonate and formacetal-linked thymine dimer phospho-ramidite used for the synthesis of the flavin and dimer containing DNA-strands 7-12. b Representation of a reduced flavin- and formacetal-linked cyclobutane pyrimidine dimer containing DNA strand, which upon irradiation (hv) and electron transfer (ET) performs a cycloreversion (CR) of the dimer unit, c Depiction of the investigated oligonucleotides... 

Scheme 6 a Incorporation of a silyl-spaced dimer into DNA, and treatment of the DNA strand with fluoride furnished DNA strand containing a dimer-unit with an open backbone. b Schematic representation of the light (ho) induced excess electron transfer (ET) from the reduced flavin to the dimer, followed by cycloreversion (CR). c The five DNA duplexes 13-17 containing the flavin donor and the dimer acceptor at increasing distances, together with the measured repair yields after irradiation for 1 min... 

Fig. 8. A stereographic view of the corresponding dimeric unit of Fig. 7. Reprinted with permission from Z. Naturforsch. 33 b, 11 (1978). Copyright by Verlag Zeitschr. fur Naturforsch.

While in the first case (Eq. (13)) the dimeric unit, which is formed due to nitrogen-tin interactions (Chapter 4), is converted to the simple adduct 40 by the stronger base pyridine, the second case illustrates that the polymer 21 can be dissolved in a coordinating solvent. 

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