Influence of the electronic effect of an ancillary ligand on MMCT and LMCT in localized cyanide-bridged complexes containing non-innocent ligands

For bimetallic MV complexes with non-innocent ligands, the MMCT energy in the localized system decreases significantly while the LMCT energy in the delocalized moiety increases slightly as the electronic effect of ancillary ligands is enhanced.

Influence of Fine Ligand Substitution Modification of the Isocyanidometal Bridge on Metal-to-Metal Charge Transfer Properties in Class II-III Mixed Valence Complexes

The synthesis and characterization of Class II-III mixed valence complexes have been an interesting topic due to their special intermediate behaviour between localized and delocalized mixed valence complexes. To investigate the influence of the isocyanidometal bridge on metal-to-metal charge transfer (MMCT) properties, a family of new isocyanidometal-bridged complexes and their one-electron oxidation products cis-[Cp(dppe)Fe-CN-Ru(L)₂ -NC-Fe(dppe)Cp][PF₆ ]_n (n=2, 3) (Cp=1,3-cyclopentadiene, dppe=1,2-bis(diphenylphosphino)ethane, L=2,2'-bipyridine (bpy, 1[PF₆ ]_n ), 5,5'-dimethyl-2,2'-bipyridyl (5,5'-dmbpy, 2[PF₆ ]_n ) and 4,4'-dimethyl-2,2'-bipyridyl (4,4'-dmbpy, 3[PF₆ ]_n )) have been synthesized and fully characterized. The experimental results suggest that all the one-electron oxidation products may belong to Class II-III mixed valence complexes, supported by TDDFT calculations. With the change of the substituents of the bipyridyl ligand on the Ru centre from H, 5,5'-dimethyl to 4,4'-dimethyl, the energy of MMCT for the one-electron oxidation complexes changes in the order: 1³⁺ <2³⁺ <3³⁺ , and that for the two-electron oxidation complexes decreases in the order 1⁴⁺ >3⁴⁺ >2⁴⁺ . The potential splitting (ΔE_1/2 (2)) between the two terminal Fe centres for N[PF₆ ]₂ are the largest potential splitting for the cyanido-bridged complexes reported so far. This work shows that the smaller potential difference between the bridging and the terminal metal centres would result in the more delocalized mixed valence complex.

Tuning metal to metal charge transfer properties in cyanidometal-bridged complexes by changing the auxiliary ligand on the bridge

In order to investigate the influence of the auxiliary ligand of the cyanidometal bridge on metal to metal charge transfer (MMCT) in cyanidometal-bridged complexes, two groups of heterotrimetallic cyanidometal-bridged complexes, trans-[Cp*(dppe)Fe-NC-Ru(L)2-CN-Fe(dppe)Cp*][PF6]n (L = bpy, 1(PF6)n; L = 4,4'-dmbpy, 2(PF6)n; n = 2, 3, 4) (Cp* = 1,2,3,4,5-pentamethylcyclopentadiene, dppe = 1,2-bis(diphenylphosphino)ethane, bpy = 2,2'-bipyridine, 4,4'-dmbpy = 4,4'-dimethyl-2,2'-bipyridyl) were synthesized and fully characterized. The MMCT of the one-electron oxidation mixed valence complexes is mainly attributed to RuII and FeII → FeIII MMCT transitions, and the MMCT of the two-electron oxidation complexes is mainly attributed to RuII → FeIII MMCT transitions. The energy of the MMCT of the four complexes decreases with the increase of the electron donating ability of the auxiliary ligand of the cyanidometal bridge. The IR, EPR, and Mössbauer spectra, and the solvent independence of MMCT characterizations indicate that the one-electron oxidation mixed valence complexes may belong to Class II-III systems, and the two-electron oxidation complexes may be localized at low temperature but delocalized at room temperature on the EPR timescale.