Influence of Central Metalloligand Geometry on Electronic Communication between Metals: Syntheses, Crystal Structures, MMCT Properties of Isomeric Cyanido-Bridged Fe2Ru Complexes, and TDDFT Calculations.

To investigate how the central metalloligand geometry influences distant or vicinal metal-to-metal charge-transfer (MMCT) properties of polynuclear complexes, c is- and trans-isomeric heterotrimetallic complexes, and their one- and two-electron oxidation products, cis/ trans- [Cp(dppe)FeIINCRuII(phen)2CN-FeII(dppe)Cp][PF6]2 ( cis/ trans- 1[PF6]2), cis/ trans-[Cp(dppe)FeIINCRuII(phen)2CNFeIII-(dppe)Cp][PF6]3 ( cis/ trans- 1[PF6]3) and cis/ trans-[Cp(dppe)FeIIINCRuII(phen)2CN-FeIII(dppe)Cp][PF6]4 ( cis/ trans- 1[PF6]4) have been synthesized and characterized. Electrochemical measurements show the presence of electronic interactions between the two external FeII atoms of the cis- and trans-isomeric complexes cis/ trans- 1[PF6]2. The electronic properties of all these complexes were studied and compared by spectroscopic techniques and TDDFT//DFT calculations. As expected, both mixed valence complexes cis/ trans- 1[PF6]3 exhibited different strong absorption signals in the NIR region, which should mainly be attributed to a transition from an MO that is delocalized over the RuII-CN-FeII subunit to a FeIII d orbital with some contributions from the co-ligands. Moreover, the NIR transition energy in trans- 1[PF6]3 is lower than that in cis- 1[PF6]3, which is related to the symmetry of their molecular orbitals on the basis of the molecular orbital analysis. Also, the electronic spectra of the two-electron oxidized complexes show that trans- 1[PF6]4 possesses lower vicinal RuII→FeIII MMCT transition energy than cis- 1[PF6]4. Moreover, the assignment of MMCT transition of the oxidized products and the differences of the electronic properties between the cis and trans complexes can be well rationalized using TDDFT//DFT calculations. [ABSTRACT FROM AUTHOR]