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

Abstract

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-2'-bipyridyl (5,5'-dmbpy, 2[PF 6 ] n ) and 4,4'dimethyl-2,2'-bipyridyl (4,4'-dmbpy, 3[PF 6 ] n )) have been synthesized and fully characterized. The experimental resultssuggest 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: 1 3 + < 2 3 + < 3 3 + , and that for the two-electron oxidation complexes decreases in the order 1 4 + > 3 4 + > 2 4 + . The potential splitting (ΔE 1/2 (2)) between the two terminal Fe centres for N[PF 6 ] 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.

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

“…Similar phenomena were also observed in other cyanide-bridged MV complexes. 32,75–78 However, it should be noted that the average Ru–P bond lengths of the binuclear complexes change slightly compared to those of the corresponding precursors 1a–3a . These crystal data suggest that for all the binuclear complexes the ruthenium in the CpMe n Ru(dppe)CN part only gently interacts with the central metal in the part.…”

Investigation of the electron transfer properties between metal centers in binuclear and trinuclear cyanido-bridged mixed valence complexes with cis/trans-configuration

“…12 and Table 6, the UV-vis-NIR spectra of cis -1[PF 6 ] and cis -1[PF 6 ] 2 exhibit similar electronic transition absorption bands in the UV-vis area from 17 500 to 30 000 cm −1 , which can be assigned to the dπ → π* metal to ligand charge transfer (MLCT) according to the TDDFT calculations and the previous works in our group. 16,20,52 However, only the UV-vis-NIR spectrum of cis -1[PF 6 ] 2 shows one electronic transition absorption band (11 858 cm −1 ) in the vis-NIR area, which can be assigned to the Ru II → Fe III MMCT according to the TDDFT calculations (see below).…”

“…So far, a large number of polynuclear cyanido-bridged mixed valence complexes have been synthesized and characterized. 13–32 Baraldo's group synthesized a series of trimetallic cyanido-bridged mixed valence complexes, trans -[Ru(L) 4 {(μ-CN)Ru(py) 4 Cl} 2 ] 3+ , by changing the ancillary ligand on the central Ru from pyridine (py) and 4-methoxypyridine (MeOpy) to 4-dimethylaminopyridine (dmap), and the complex [Ru(dmap) 4 {(μ-CN)Ru(py) 4 Cl} 2 ] 3+ is the first Class III cyanido-bridged mixed valence complex. 33,34 Most recently, our group has reported two groups of trinuclear cyanidometal-bridged complexes with cis / trans configuration for the investigation of the influence of the cis / trans -configuration of the cyanidometal bridge and its ancillary ligand on the electron transfer properties between metal centers.…”

A Class III asymmetric binuclear cyanido-bridged mixed-valence complex

“…[35][36][37] For the first reversible redox wave that appeared (0.048 V), the potential is higher than the previously reported mononuclear complex [Ru(bpy) 2 Cl 2 Á2H 2 O] (À0.13 V vs. Cp 2 Fe +/0 ). 38 Meanwhile, the second reversible redox wave (0.697 V) has a significantly higher potential than the isolated mononuclear complex [Cp*(dppe)Ru(CN)] (Fig. S5, 0.236 V vs. Cp 2 Fe +/0 , ESI †).…”