Dimers unbridged

The lifetime of Pyr +oPyr seemed to depend on the structure of the parent dimer. It was observed that the presence of a trimethylene bridge linking both pyrimidine units at N(l) and N(l ), as in the mixed thymine-uracil dimer 4 and in the thymine dimer 5, leads to significant stabilization of the corresponding dimer radical cation, whereas in unbridged dimers a maximum lifetime of 10-1°-10-9 s was proposed for their dimer radical cations [6]. It was further shown that in bridged pyrimidines dimers of types 4 and 5 the interconversion of dimer and... 

Most bis(dithiolene) Fe and Co complexes are found as strongly joined M S dimers (see Section IH.A.4, Table III, and Fig. 12) with square-pyramidal geometry about the central metal atom. In the M S dimers, the five-membered dithiolene rings are more distorted than with unbridged monomeric units as determined from dihedral (A), Cj—M—c2, and ligand bend (r ) angles. 

The Rh-Rh bond in the product is susceptible to disproportionation, and the equilibrium is rapidly established in solution. The equilibrium constants for reaction (1) are strongly solvent-dependent, with high dielectric constant solvents favoring the binuclear species. Flowever, the binuclear species can be isolated in pure, crystalline form the structure of [(p-CH3C6H4NC)8Rh2l2] [PFe]2 consists of an unbridged dimer with axial iodide ligands. ... 

The photochemically studied group VIIA dimers are mainly the Mj(CO),o complexes and their derivatives which contain unbridged, single metal-metal bonds. As with the group VIA dimers, flash photolysis and kinetic studies argue for an additional photoproduced intermediate besides the expected M(CO)j radicals, but the radical species still dominate the photochemistry of these compounds. ... 

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