Charge Transfer Properties of Triarylamine Integrated Dimolybdenum Dyads

Three quadruply bonded dimolybdenum complexes equipped with a triarylamine pendant, [(DAniF)₃Mo₂(μ-O₂CC₆H₄N­(C₆H₄CH₃)₂] (DAniF = <i>N,N</i>′-di­(<i>p</i>-anisyl)­formamidinate; [<b>OO–ph–N</b>]), [(DAniF)₃Mo₂(μ-OSCC₆H₄N­(C₆H₄CH₃)₂] ([<b>OS–ph–N</b>]), and [(DAniF)₃Mo₂(μ-S₂CC₆H₄N­(C₆H₄CH₃)₂] ([<b>SS–ph–N</b>]), have been synthesized and characterized by single crystal X-ray diffraction. In electrochemical measurements, the redox couple for the organic amine group becomes irreversible, reflecting the substantially strong electronic interaction between the dimetal center and organic redox site. The potential difference for the two successive redox events, ca. Δ<i>E</i>_1/2(<i>E</i>_1/2(2)­(N/N^<b>•</b>+) – <i>E</i>_1/2(1)­(Mo₂^IV/V)), falls in the range of 0.5–0.8 V as estimated from the differential pulse voltammograms. For the monocation radicals [<b>OO–ph–N</b>]⁺, [<b>OS–ph–N</b>]⁺, and [<b>SS–ph–N</b>]⁺, obtained by chemical oxidation of the neutral precursor, a broad ligand (amine) to metal (Mo₂) charge transfer (LMCT) absorption band is observed in the near-IR region. Interestingly, analogous to the intervalence charge transfer (IVCT) bands for mixed-valence complexes, the LMCT absorption bands, which are solvent dependent, decrease in energy and bandwidth as the electronic coupling between the two redox sites increases in an order of increasing S content in the chelating group. The electronic coupling matrix elements (<i>H</i>_ab) are determined by optical analyses from the generalized Mulliken–Hush (GMH) theory, falling in the range of 400–800 cm^–1 in CH₂Cl₂. These results indicate that in these radical cations the charge is localized. Time-dependent DFT calculations show that the frontier molecular orbitals for these asymmetrical donor–acceptor systems have unbalanced distribution of electron density, and the LMCT bands arise from an electronic transition from the pendant ligand-based to metal-based molecular orbitals, corresponding to donor (N)–acceptor (Mo₂) charge transfer

Insight on the presence of dimethylammonium cation within anionic metal-organic supramolecular host: structural, Hirshfeld surface, optical and theoretical analysis

A new supramolecular metal-organic complex, [(DMA)+{Fe(IDA)2}-] (where H2IDA = iminodiacetic acid and DMA = dimethylammonium cation) (1), has been synthesized solvothermally at 90 °C from reaction of ferric(III) chloride hexahydrate with nitrilotriacetic acid (H3NTA) in stoichiometric ratio. The complex was characterized by single crystal X-ray diffraction (SCXRD) along with spectroscopic analyses. During the reaction process, H3NTA is degraded into IDA2- ligand. Structural analysis reveals that 1 is mononuclear and crystallizes in the monoclinic space group C2/c. Within the [Fe(IDA)2]- unit, Fe3+ shows six-coordinate distorted octahedral geometry. The [Fe(IDA)2]- units are connected by strong N1-H1···O4 hydrogen bonds to form anionic 2D supramolecular layers which are further connected by weak C-H···O hydrogen bonds to form a 3D metal-organic supramolecular host (MOSH) structure having 1D supramolecular channels along the crystallographic c-axis. DMA cations are present within the supramolecular channels through N2-H2···O2 hydrogen bonding interactions. Hirshfeld surface analysis and corresponding 2D fingerprint plots indicate that O···H interactions are the major supramolecular interactions present between MOSH and guest DMA cation. DFT calculations reveal that the HOMO and LUMO of the [Fe(IDA)2]- unit are composed of mixed metal-ligand orbitals. Both the absorption and emission spectra of the complex were studied in aqueous phase and the result was correlated with the TDDFT study.</p

Aromaticity-Driven Molecular Structural Variation and Electronic Configuration Alternation: An Example of Cyclic π Conjugation Involving a Mo–Mo δ Bond

We have synthesized and characterized the mixed-ligand dimolybdenum paddlewheel complex Na­[(DAniF)₃Mo₂(C₃S₅)] (Na­[<b>1</b>]; DAniF = <i>N</i>,<i>N</i>′-di-<i>p</i>-anisylformamidinate, dmit = 1,3-dithiole-2-thione-4,5-dithiolate), which has a six-membered chelating [Mo₂S₂C₂] ring created by equatorial coordination of the dmit (C₃S₅) ligand to the Mo₂ unit. One-electron oxidation of Na­[<b>1</b>] using Cp₂FePF₆ yields the neutral complex [(DAniF)₃Mo₂(C₃S₅)] ([<b>1</b>]), and removal of two electrons from Na­[<b>1</b>] using AgBPh₄ gives [(DAniF)₃Mo₂(C₃S₅)]­BPh₄ ([<b>1</b>]­BPh₄). In the crystal structures, [<b>1</b>]⁻ and [<b>1</b>] present dihedral angles of 118.9 and 142.3° between the plane defined by the Mo–Mo bond vector and the dmit ligand, respectively, while DFT calculations show that in [<b>1</b>]⁺ the Mo–Mo bond and the dmit ligand are coplanar. Complex [<b>1</b>] is paramagnetic with a <i>g</i> value of 1.961 in the EPR spectrum and has a Mo–Mo bond distance of 2.133(1) Å, increased from 2.0963(9) Å for [<b>1</b>]⁻. Consistently, a broad absorption band is observed for [<b>1</b>] in the near-IR region, which arises from charge transfer from the dmit ligand to the cationic Mo₂⁵⁺ centers. Interestingly, complex [<b>1</b>]⁺ has an aromatic [Mo₂S₂C₂] core, as evidenced by a large diamagnetic anisotropy, in addition to the coplanarity of the core structure, which shifts downfield the ¹H NMR signal of the horizontal methine proton (ArN–(C<i>H</i>)–NAr) but upfield those of the vertical protons, relative to the methine proton resonances for the precursor ([<b>1</b>]⁻). The magnetic anisotropy (Δχ = χ_⊥ – χ_∥) for the [Mo₂S₂C₂] ring in [<b>1</b>]⁺ is −105.5 ppm cgs, calculated from the McConnell equation, which is about 2-fold larger than that for benzene. The aromaticity of the [Mo₂S₂C₂] ring is supported by theoretical studies, including single-point calculations and gauge-including atomic orbital (GIAO) NMR spectroscopic calculations at the density functional theory (DFT) level. DFT calculations also show that the [Mo₂S₂C₂] core in [<b>1</b>]⁺ possesses a set of three highest occupied and three lowest unoccupied molecular orbitals in π character, corresponding to those of benzene in symmetry, and six π electrons that conform to the Hückel 4<i>n</i> + 2 rule for aromaticity. Therefore, this study shows that an aromatic [Mo₂S₂C₂] core is formed by coupling the δ orbital of the Mo≣Mo bond with the π orbital of the CC bond through the bridging atoms (S), thus validating the equivalency in bonding functionality between δ and π orbitals

TP Ex for analysis- Weekly paclitaxel baseline data- Revised.xlsx

Baseline data of    Weekly paclitaxel, carboplatin and cetuximab (PCC) combination followed by nivolumab in platinum-sensitive recurrent and /or metastatic squamous cell carcinoma of head and neck– a retrospective analysis from two institutions in Indi