Electromerism

Electromerism is a type of isomerism between a pair of molecules (electromers, electro-isomers) differing in the way electrons are distributed among the atoms and the connecting chemical bonds.[1] In some literature electromerism is equated to valence tautomerism,[2] a term usually reserved for tautomerism involving reconnecting chemical bonds.[3]

One group of electromers are excited electronic states but isomerism is usually limited to ground state molecules. Another group of electromers are also called redox isomers: metal ions that can exchange their oxidation state with their ligands (see non-innocent ligand). One of the first instances was a cobalt bis(quinone) complex described by Buchanan and Pierpont in 1980 [4] with a cobalt(II) complex in chemical equilibrium with the cobalt(III) complex. Ligands commonly found are based on dioxolenes, phenoxyl radicals and polychlorotriphenylmethyl radicals. Metalloporphyrins have also been studied. A set of electromers not requiring redox-active ligands have been described [5][6] as well as a set without a metal [7]

References
  1. Bally, T. (2010). "Isomerism: The same but different" (PDF). Nature Chemistry. 2 (3): 165–166. Bibcode:2010NatCh...2..165B. doi:10.1038/nchem.564. PMID 21124473.
  2. Evangelio, E.; Ruiz-Molina, D. (2005). "Valence Tautomerism: New Challenges for Electroactive Ligands". European Journal of Inorganic Chemistry. 2005 (15): 2957. doi:10.1002/ejic.200500323.
  3. Jones, L. W. (1917). "Electromerism, A Case of Chemical Isomerism Resulting from a Difference in Distribution of Valence Electrons" (PDF). Science. 46 (1195): 493–502. Bibcode:1917Sci....46..493J. doi:10.1126/science.46.1195.493. PMID 17818241.
  4. Buchanan, R. M.; Pierpont, C. G. (1980). "Tautomeric catecholate-semiquinone interconversion via metal-ligand electron transfer. Structural, spectral, and magnetic properties of (3,5-di-tert-butylcatecholato)(3,5-di-tert-butylsemiquinone)(bipyridyl)cobalt(III), a complex containing mixed-valence organic ligands". Journal of the American Chemical Society. 102 (15): 4951. doi:10.1021/ja00535a021.
  5. Puschmann, F.; Harmer, J.; Stein, D.; Rüegger, H.; De Bruin, B.; Grützmacher, H. (2010). "Electromeric rhodium radical complexes". Angewandte Chemie International Edition in English. 49 (2): 385–389. doi:10.1002/anie.200903201. PMID 19957252.
  6. Puschmann, F.F.; Grützmacher, H.; de Bruin, B. (2010). "Rhodium(0) Metalloradicals in Binuclear C−H Activation". Journal of the American Chemical Society. 132 (1): 73–75. doi:10.1021/ja909022p. PMID 20000835.
  7. Müller, B.; Bally, T.; Gerson, F.; De Meijere, A.; Von Seebach, M. (2003). ""Electromers" of the tetramethyleneethane radical cation and their nonexistence in the octamethyl derivative: interplay of experiment and theory". Journal of the American Chemical Society. 125 (45): 13776–13783. doi:10.1021/ja037252v. PMID 14599217.
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