Control of dominant conduction orbitals by peripheral substituents in paddle-wheel diruthenium alkynyl molecular junctions

Controlling Redox and Wirelike Charge-Delocalization Properties of Dinuclear Mixed-Valence Complexes with MCp*(dppe) (M = Fe, Ru) Termini Bridged by Metalloporphyrin Linkers

Four dinuclear organometallic molecular wire complexes with diethynylmetalloporphyrin linkers 1 MM' , [5,15-bis{MCp*(dppe)ethynyl}-10,20-diarylporphinato]M' (Cp* = η5-C5Me5; dppe = 1,2-bis(diphenylphosphino)ethane; M/M' = Fe/Zn (1 FeZn ), Ru/Zn (1 RuZn ), Fe/Ni (1 FeNi ), Ru/Ni (1 RuNi ); aryl = 3,5-di-tert-butylphenyl), are synthesized and characterized by NMR, CV, UV-vis-NIR, and ESI-TOF mass spectrometry techniques. Electrochemical investigations combined with electronic absorption spectroscopic studies reveal strong interactions among the electron-donating, redox-active MCp*(dppe) termini and the metalloporphyrin moieties. The monocationic species of the four complexes obtained by chemical oxidation have been characterized as mixed-valence Class II/III or Class III compounds according to the Robin-Day classification despite the long molecular dimension (>1.5 nm), as demonstrated by their intense intervalence charge transfer bands (IVCT) in the near IR region. DFT calculations indicate large spin densities on the metalloporphyrin moieties. Furthermore, the wirelike performance can be finely tuned by coordination of appropriate nitrogen donors to the axial sites of the metalloporphyrin.

Manipulating the charge transport via incorporating a cobalt bridge into a single-molecule junction

Cobalt-bridged organometallic molecular wires (p-Co-p, p-Co-m and m-Co-m) are synthesized, and their charge transport properties are studied. The experimental results show that the quantum interference (QI) effects of cobalt-bridged organometallic wires are determined by the anchoring group. Interestingly, the cobalt-bridge reduces the conductance of the junctions and tunes the QI effect of the wires. These results demonstrate the unique property of metal-bridged organometallic molecular wires and their potential applications in molecular electronics.

Metal-Carbodithioate-Based 3D Semiconducting Metal-Organic Framework: Porous Optoelectronic Material for Energy Conversion

Solar energy conversion requires the working compositions to generate photoinduced charges with high potential and the ability to deliver charges to the catalytic sites and/or external electrode. These two properties are typically at odds with each other and call for new molecular materials with sufficient conjugation to improve charge conductivity but not as much conjugation as to overly compromise the optical band gap. In this work, we developed a semiconducting metal-organic framework (MOF) prepared explicitly through metal-carbodithioate "(-CS₂)_nM" linkage chemistry, entailing augmented metal-linker electronic communication. The stronger ligand field and higher covalent character of metal-carbodithioate linkages─when combined with spirofluorene-derived organic struts and nickel(II) ion-based nodes─provided a stable, semiconducting 3D-porous MOF, Spiro-CS₂Ni. This MOF lacks long-range ordering and is defined by a flexible structure with non-aggregated building units, as suggested by reverse Monte Carlo simulations of the pair distribution function obtained from total scattering experiments. The solvent-removed "closed pore" material recorded a Brunauer-Emmett-Teller area of ∼400 m²/g, where the "open pore" form possesses 90 wt % solvent-accessible porosity. Electrochemical measurements suggest that Spiro-CS₂Ni possesses a band gap of 1.57 eV (σ = 10^-7 S/cm at -1.3 V bias potential), which can be further improved by manipulating the d-electron configuration through an axial coordination (ligand/substrate), the latter of which indicates usefulness as an electrocatalyst and/or a photoelectrocatalyst (upon substrate binding). Transient-absorption spectroscopy reveals a long-lived photo-generated charge-transfer state (τ_CR = 6.5 μs) capable of chemical transformation under a biased voltage. Spiro-CS₂Ni can endure a compelling range of pH (1-12 for weeks) and hours of electrochemical and photoelectrochemical conditions in the presence of water and organic acids. We believe this work provides crucial design principles for low-density, porous, light-energy-conversion materials.

Bisaryl and Bisalkynyl Diruthenium (III,III) Compounds Based on an Electron-Deficient Building Block

Reported herein is a new series of diruthenium(III,III) bisalkynyl and bisaryl diruthenium(III,III) compounds supported with 2-amino-3-(trifluoromethyl)pyridinate (amtfmp). Using Ru₂(amtfmp)₄Cl₂ from a modified preparation, cis 2:2 Ru₂(amtfmp)₄(C≡CPh)₂ (1), cis 2:2 Ru₂(amtfmp)₄(Ph)₂ (2), and 3:1 Ru₂(amtfmp)₄(Ph)₂ (3) were synthesized via a lithium-halogen exchange reaction using LiC₂Ph and LiPh, respectively. Compounds 1-3 are all Ru₂(III,III) species with a ground-state configuration of π⁴δ²(π*)⁴ (S = 0) and were characterized via mass spectrometry, electron absorption and ¹H/¹⁹F NMR spectroscopies, and voltammetry. The molecular structures of 1-3 were established using single-crystal X-ray diffraction analysis, and preliminary density functional theory analysis was performed to elaborate the electronic structures of 1 and 2. Comparisons of the electrochemical properties of 1-3 against the Ru₂(amtfmp)₄Cl₂ starting material reveal cathodic shifts of the Ru₂^7+/6+ oxidation and the Ru₂^6+/5+ and Ru₂^5+/4+ reduction potentials. In comparison to related Ru₂(III,III) bisalkynyl and bisaryl compounds, the electrode potentials for 1-3 are anodically shifted up to ca. 0.95 V, highlighting the strong electron-withdrawing nature of the amtfmp ligand.

Phenylene as an efficient mediator for intermetallic electronic coupling

The new compound [(NC)Ru₂(ap)₄]₂(μ-1,4-C₆H₄) (ap = 2-anilinopyridinate) was prepared to address the open question of whether a 1,4-phenylene bridge can mediate intermetallic electronic coupling. As a manifestation of strong coupling, hole delocalization between the Ru₂ centers on the IR time scale (10^-14 s) was established using spectroelectrochemistry. An orbital mechanism for coupling was elaborated with DFT analysis.

Diruthenium aryl compounds - tuning of electrochemical responses and solubility

Reported herein are the two new series of diruthenium aryl compounds: Ru₂(DiMeOap)₄(Ar) (1a-6a) (DiMeOap = 2-(3,5-dimethoxyanilino)pyridinate) and Ru₂(m-ⁱPrOap)₄(Ar) (1b-5b) (m-ⁱPrOap = 2-(3-iso-propoxyanilino)pyridinate), prepared through the lithium-halogen exchange reaction with a variety of aryl halides (Ar = C₆H₄-4-NMe₂ (1), C₆H₄-4-^tBu (2), C₆H₄-4-OMe (3), C₆H₃-3,5-(OMe)₂ (4), C₆H₄-4-CF₃ (5), C₆H₅ (6)). The molecular structures of these compounds were established with X-ray diffraction studies. Additionally, these compounds were characterized using electronic absorption and voltammetric techniques. Compounds 1a-6a and 1b-5b are all in the Ru₂⁵⁺ oxidation state, with a ground state configuration of σ²π⁴δ²(π*δ*)³ (S = 3/2). Use of the modified ap ligands (ap') resulted in moderate increases of product yield when compared to the unsubstituted Ru₂(ap)₄(Ar) (ap = 2-anilinopyridinate) series. Comparisons of the electrochemical properties of 1a-6a and 1b-5b against the Ru₂(ap')Cl starting material reveals the addition of the aryl ligand cathodically shifted the Ru₂^6+/5+ oxidation and Ru₂^5+/4+ reduction potentials. These oxidation and reductions potentials are also strongly dependent on the p-substituent of the axial aryl ligands.