The Electron Transfer Process in Mixed Valence Compounds with a Low‐lying Energy Bridge in Different Oxidation States

Abstract

Mixed‐valence compounds with the iso‐cyanidometal‐ligand bridge in different oxidation states are used as models for the investigation of the electron‐transfer process. We synthesized a series of trimetallic isocyanidometal‐bridged compounds with [Fe–CN–Ru–NC–Fe]n+ (n=2–4), in which the one‐electron oxidation product (N3+) and two‐electron oxidation product (N4+) compounds possess an isocyanidometal bridge whose energy is, respectively lower and slightly higher than the terminal metal centers energies. For the N3+ compounds, the bridge state (FeII–RuIII–FeII) and mixed‐valence states (FeIII–RuII–FeII or FeII–RuII–FeIII) could be simultaneously observed on the IR timescale. For the N4+ compounds, as the donor becomes stronger the electron transfer bridge excited state (FeIII–RuII–FeIII) becomes more and more stable, and even becomes ground state due to the strong electronic coupling between Fe and Ru.

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 similar phenomena has been reported by our previous work. [23] In addition, the energy of MM'CT for the three two-electron oxidation complexes decreases in the order of 4 . Moreover, the energy of MM'CT for N[PF 6 ] 4 (N = 1, 2, 3) are solvent independent which can be found from Figure S18 and Table S10, implying that the three two-electron oxidation complexes may belong to Class II-III or Class III mixed valence complexes.…”

Influence of Substitution Effect on MMCT in Mixed‐Valence Cyanido‐Bridged FeII−CN−Ru2III,III−NC−FeII System

“…As shown in Figure 5 and Figure S8, each of complexes 1 – 8 exhibits two quasi‐reversible one‐electron redox processes in the positive potential range (E>0). From Table 4, the first redox potentials of 1 – 8 are close to the relevant precursors CpFe II (dppe)CN (E 1/2 =0.48 V), CpMe 4 Fe II (dppe)CN (E 1/2 =0.30 V) and CpMe 5 Fe II (dppe)CN (E 1/2 =0.25 V) [15] with a reasonable increase, respectively. Thus, they can be assigned to the redox of the CpMe n Fe II (dppe)CN fragment in 1 – 8 .…”

“…It also should be noted that the Fe−P bond length of 1 (2.1834(12) Å) are comparable to that of the precursor CpFe II (dppe)CN (2.1803(7) Å) [14] . However, the Fe−P distances of 2 (2.2115(17) Å) and 3 (2.224(2) Å) elongate by about 0.02 and 0.03 Å with respect to the precursors CpMe 4 Fe II (dppe)CN (2.1907(12) Å) and CpMe 5 Fe II (dppe)CN (2.1952(9) Å), [15] respectively, suggesting clearly the increase of oxidation state of the terminal Fe II in the order of 1 < 2 < 3 . Based on above crystallographic analysis, it can be found that the intramolecular electron interactions between the terminal Fe II and the central Ru 2 III,III exists and is enhanced by the increase of electron‐donating ability of the CpMe n ligand in complexes 1 (n=0), 2 (n=4) and 3 (n=5).…”

“…Taking complexes 1 – 3 for example, a new absorption band with respect to the precursor Ru 2 (DMBA) 4 (NO 3 ) 2 can be observed at 14906 cm −1 for 1 , 9000 cm −1 for 2 , and 8883 cm −1 for 3 , respectively. Due to the absence of any absorption below 25000 cm −1 for CpMe n Fe II (dppe)CN fragment, [15] the new absorption bands can be assigned as the absorption of MMCT from Fe II to Ru 2 III,III . Complex 9 displays very different electron absorption with respect to 1 – 8 , which suggests a dissociation as confirmed by the CV measurement.…”

“…Methanol was dried by distilling over magnesium. The complexes Ru 2 (DMBA) 4 (NO 3 ) 2 , Ru 2 (MeO‐DMBA) 4 (NO 3 ) 2 , Ru 2 (CF 3 ‐DMBA) 4 (NO 3 ) 2 , CpMe n Fe II (dppe)CN (n=0,4,5) were prepared according to literature procedures [15,19,20] . All other reagents were available commercially and used without further purification.…”