The effect of chlorine and fluorine substitutions on tuning the ionization potential of benzoate-bridged paddlewheel diruthenium(ii, ii) complexes?

Dalton Transactions Pub Date: 2015-03-20 DOI: 10.1039/C5DT00505A

Abstract

A series of paddlewheel diruthenium(II, II) complexes with various chlorine-substituted benzoate ligands (Cl-series) was synthesized as tetrahydrofuran (THF) adducts [Ru2(ClxPhCO2)4(THF)2]; where ClxPhCO2? = o-chlorobenzoate, o-Cl; m-chlorobenzoate, m-Cl; p-chlorobenzoate, p-Cl; 2,3-dichlorobenzoate, 2,3-Cl2; 2,4-dichlorobenzoate, 2,4-Cl2; 2,5-dichlorobenzoate, 2,5-Cl2; 2,6-dichlorobenzoate, 2,6-Cl2; 3,4-dichlorobenzoate, 3,4-Cl2; 3,5-dichlorobenzoate, 3,5-Cl2; 2,3,4-trichlorobenzoate, 2,3,4-Cl3; 2,3,5-trichlorobenzoate, 2,3,5-Cl3; 2,4,5-trichlorobenzoate, 2,4,5-Cl3; 3,4,5-trichlorobenzoate, 3,4,5-Cl3; 2,3,4,5-tetrachlorobenzoate, 2,3,4,5-Cl4. This Cl-series and the previously synthesized F-series together with four new fluorine-substituted derivatives, [Ru2(FxPhCO2)4(THF)2] (where FxPhCO2? = 2,3-difluorobenzoate, 2,3-F2; 2,4-difluorobenzoate, 2,4-F2; 2,5-difluorobenzoate, 2,5-F2; 2,3,5-trifluorobenzoate, 2,3,5-F3), were experimentally characterized with respect to solid-state structure, magnetic properties and electrochemistry. By tuning the substituents of the benzoate ligands using chlorine or fluorine atoms, the redox potential (E1/2) for [Ru2II,II]/[Ru2II,III]+ varied over a wide range of potentials from ?40 mV to 360 mV (vs. Ag/Ag+ in THF). This was dependent on (i) the number of ortho-substituents, i.e. non-, mono- and di-o-substituted groups, with quasi-Hammett parameters for ortho-Cl and -F substitutions (σo = ?0.272 and ?0.217, respectively) and (ii) the general Hammett constants, σm and σp, for each group. The HOMO energy level calculated on the basis of the atomic coordinates of the solid-state structure was strongly affected by Cl- and F-substitutions as well as the redox potential in solution, which emphasizes the steric contribution of ortho-substituents in the energy level giving a deviation of EHOMO < 0.3 eV and <0.55 eV for the Cl- and F-series, respectively.

Graphical abstract: The effect of chlorine and fluorine substitutions on tuning the ionization potential of benzoate-bridged paddlewheel diruthenium(ii, ii) complexes
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