Abstract

The redox systems [(NC) 5Fe(μ-L)Fe(CN) 5]) 6−/5−/4− with L=pyrazine ( 1 n ), 4,4′-bipyridine ( 2 n ) or 1,2-bis(4-pyridyl)ethene ( 3 n ), and [(NC) 4Fe(μ-bmtz)Fe(CN) 4] 5−/4−/3− ( 4 n ) with bmtz=3,6-bis(2-pyrimidyl)-1,2,4,5-tetrazine were studied in acetonitrile and other aprotic solvents. The comproportionation constants K c for the mixed-valent diiron(III, II) intermediates vary from less than 10 for 3 5− via 10 6.5 for 1 5− to 10 14.1 for 4 3−. Intervalence charge transfer band maxima lie between 1270 nm ( 2 5−) and 2475 nm ( 1 5−). In comparison with previous results from aqueous solutions, the system 1 n in particular shows increased metal–metal interaction. UV–Vis and IR spectroelectrochemistry suggest a localized/delocalized borderline sitation for 1 5− in acetonitrile, with only slightly weaker metal–metal coupling than in the related Creutz–Taube ion. The results illustrate how the established strong solvent sensitivity of cyanoiron complexes can be exploited in mixed-valence chemistry.

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