New Hybrid Semiconductor Materials Based on Viologen Salts of Bimetallic Fe–Pt and Fe–Au Carbonyl Clusters: First Structural Characterization of the Diradical π‐Dimer of the Diethylviologen Monocation and EPR Evidence of its Triplet State

Abstract

The synthesis, structure, spectroscopic characterization and electrical resistivity of the [EtV](2)[Fe(4)Pt(CO)(16)], [EtV][Fe(3)Pt(3)(CO)(15)].THF, [EtV][Fe(4)Au(CO)(16)](2)2.THF (EtV=1,1'-diethyl-4,4'-bipyridilium cation) and [NEt(4)](2)[Fe(4)Au(CO)(16)] is reported. The crystal structure of [EtV](2)[Fe(4)Pt(CO)(16)] is based on infinite stacks of [(EtV)(*+)](2) pi-dimers rotated by 90 degrees and isolated [Fe(4)Pt(CO)(16)](2-) ions. Within each pi-dimer, the [EtV](*+) radical ions are perfectly eclipsed and the distance between their mean planes is 3.275 A. The EPR spectrum of the solid material at room temperature clearly indicates the presence of a significantly populated triplet state of the pi-dimer, by showing signals both at Deltam=1 and Deltam=2. The solid-state structure of [EtV][Fe(3)Pt(3)(CO)(15)].THF is based on the ionic packing of [EtV](2+) and [Fe(3)Pt(3)(CO)(15)](2-) ions, inferred from a comparison of their molecular parameters with literature data. Significant electron transfer could have been expected to give [EtV](*+)[Fe(3)Pt(3)(CO)(15)](*-) on the basis of their formal redox potentials. In spite of their different stoichiometries, the structures of [EtV][Fe(4)Au(CO)(16)](2).2 THF and [NEt(4)](2)[Fe(4)Au(CO)(16)] both contain an isomer of the monoanion [Fe(4)Au(CO)(16)](-) in solution (previously characterized in the solid state as a [NMe(3)CH(2)Ph](2)[Fe(4)Au(CO)(16)]Cl mixed salt). Resistivity measurements on pellets of powdered samples of the above compounds indicate that their tetrasubstituted ammonium salts, and complex [EtV][Fe(4)Au(CO)(16)](2)2.THF, largely behave as insulators. However, the [EtV](2)[Fe(4)Pt(CO)(16)] and [EtV][Fe(3)Pt(3)(CO)(15)].THF samples respectively display resistivities 3 and 4 orders of magnitude less than those of their corresponding ammonium salts and could be classified as semiconductor materials.

Synthesis and Characterization of Heterobimetallic Carbonyl Clusters with Direct Au‐Fe and Au···Au Interactions Supported byN‐Heterocyclic Carbene and Phosphine Ligands

“…2) Iron carbonyl clusters with naked Au connecting atoms. At the moment, the only species belonging to this category is [Fe 4 Au(CO) 16 ] – , which may be viewed as composed of a central Au III ion bonded to two [Fe 2 (CO) 8 ] 2– iron cluster anions …”

Chemically and Electrochemically Triggered Assembly of Viologen Radicals: Towards Multiaddressable Molecular Switches

“…The existence of multivariant orientations in ion radical associates has already been demonstrated in studies based on experimental X‐ray diffraction data. Twisted complexes have, for instance, already been reported with thianthrene, tetracyanopyrazine, and naphthalene derivatives83–85 but to our knowledge, such arrangements have neither been observed nor considered with viologen π‐dimers for which the sole structure reported so far corresponds to a fully “eclipsed” conformation 86. Our results thus point out the clear importance of the substituents introduced on the terminal nitrogen atoms of the pyridinyl radicals.…”

“…Unfortunately, from an experimental point of view, none of the data collected in solution with the N‐protonated and N‐methylated compounds support the existence of two different species in solution. The stronger argument in favor of the formation of a similar dimer is that the absorption spectra corresponding to the species produced by electrochemical reduction of 6 H 2 4+ and 6 Me 2 4+ exhibit fully identical features, the most remarkable one being the broad signal centered at 833 nm, which is a diagnostic signature13, 86, 91 attributed to the formation of [ 6 H 2 ]${{{\alpha =23\hfill \atop {\rm dim}\hfill}}}$ and [ 6 Me 2 ]${{{\alpha =19\hfill \atop {\rm dim}\hfill}}}$ , wherein the association corresponds to the most commonly found parallel mode. Some insights into the reasons for such a discrepancy found between the experimental and theoretical results have been obtained by noting that increasing the polarity of the solvent leads to stabilization of the most polar “parallel” isomers [ 6 H 2 ]${{{\alpha =23\hfill \atop {\rm dim}\hfill}}}$ and [ 6 Me 2 ]${{{\alpha =19\hfill \atop {\rm dim}\hfill}}}$ (see data collected in Table 3).…”

Gold/Iron Carbonyl Clusters for Tailored Au/FeOx Supported Catalysts

“…Both these isomers were structurally characterized, and an equilibrium constant K~10 −2 in solution was established [27]. In the present case, interaction with the TiO 2 support likely shifts the equilibrium toward the [AuFe 4 (CO) 14 (μ-CO) 2 ] − isomer after deposition.…”