Influence of Central Metalloligand Geometry on Electronic Communication between Metals: Syntheses, Crystal Structures, MMCT Properties of Isomeric Cyanido‐Bridged Fe 2 Ru 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)Fe II NCRu II (phen) 2 CN‐Fe II (dppe)Cp][PF 6 ] 2 ( cis / trans ‐ 1 [PF 6 ] 2 ), cis / trans ‐[Cp(dppe)Fe II NCRu II (phen) 2 CNFe III ‐(dppe)Cp][PF 6 ] 3 ( cis / trans ‐ 1 [PF 6 ] 3 ) and cis / trans ‐[Cp(dppe)Fe III NCRu II (phen) 2 CN‐Fe III (dppe)Cp][PF 6 ] 4 ( cis / trans ‐ 1 [PF 6 ] 4 ) have been synthesized and characterized. Electrochemical measurements show the presence of electronic interactions between the two external Fe II  atoms of the cis‐ and trans ‐isomeric complexes cis / trans ‐ 1 [PF 6 ] 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 [PF 6 ] 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 Ru II ‐CN‐Fe II subunit to a Fe III d orbital with some contributions from the co‐ligands. Moreover, the NIR transition energy in trans ‐ 1 [PF 6 ] 3 is lower than that in cis ‐ 1 [PF 6 ] 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 [PF 6 ] 4 possesses lower vicinal Ru II →Fe III MMCT transition energy than cis ‐ 1 [PF 6 ] 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.