Organometallic Molecules Research Articles

Benchmark Study of Electrochemical Redox Potentials Calculated with Semiempirical and DFT Methods

The calculation of redox potentials by semiempirical quantum mechanical (SQM) approaches is evaluated with a focus on the recently developed GFNn-xTB methods. The assessment is based on a data set comprising 313 experimental redox potentials of small to medium-sized organic and organometallic molecules in various solvents. This compilation is termed as ROP313 (reduction and oxidation potentials 313) and divided for analysis purposes into the organic subset OROP and the organometallic subset OMROP. Corresponding data for a few common density functional theory (DFT) functionals employing extended AO basis sets and small basis-set DFT composite schemes are computed for comparison. Continuum solvation models are used to calculate the important solvation free energy contribution. The results for ROP313 show that the GFNn-xTB methods provide a robust, efficient, and generally applicable workflow for the routine calculation of redox potentials. The GFNn-xTB methods outperform the PMx competitor for the OROP subset (mean absolute deviation from the experiment, MADGFN2-xTB = 0.30 V, MADGFN1-xTB = 0.31 V, PM6-D3H4 = 0.61 V, PM7 = 0.60 V), almost reaching low-cost DFT quality (MADB97-3c = 0.25 V) at drastically reduced computational cost (2-3 orders of magnitude). All SQM methods perform considerably worse for the OMROP subset. Here, the GFN2-xTB still yields semiquantitative results slightly better and more robustly than with the PMx methods (MADGFN2-xTB = 0.74 V, PM6-D3H4 = 0.78 V, PM7 = 0.82 V). The proposed workflow enables large-scale quantum chemical computations of organic and, to a lesser extent, organometallic molecule redox potentials on common laptop computers in seconds to minutes of computation time enabling, e.g., screening of extended compound libraries.

One‐Pot Intercalation Strategy for the Encapsulation of a CO‐Releasing Organometallic Molecule in a Layered Double Hydroxide

The photoactivatable CO‐releasing molecule (photoCORM) [Mo(CO)3(CNCH2COOH)3] (ALF795) has been incorporated into a Zn,Al layered double hydroxide (LDH) host by a coprecipitation synthesis strategy. Powder X‐ray diffraction (PXRD) of the resultant material Zn,Al‐ALF795 showed that the ALF795 guest molecules assembled into a monolayer to give a basal spacing of 16.0 Å. FTIR and 13C{1H} CP MAS NMR spectroscopy confirmed that the molecular structure of the tricarbonyl complex was retained upon intercalation. Scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDS) and elemental analyses confirmed the phase‐purity of Zn,Al‐ALF795. The myoglobin assay was used to demonstrate that intercalated ALF795 retains the photoactive behavior of the free CORM, with a substantial fraction (42 %) of the high CO payload (2.46 mmol g–1) being released after exposure to UV light for 3 h under simulated physiological conditions. In addition, gas chromatography was used to track sequential light‐ and H2O2‐triggered decarbonylation of free and intercalated ALF795. In biological buffer solution (HEPES), less than 2 % Mo leaching from Zn,Al‐ALF795 took place after 5 h, showing the strong capacity of the LDH host to retain the unaltered complex and decarbonylation fragments.

An Artemisinin‐Derivative–(NHC)Gold(I) Hybrid with Enhanced Cytotoxicity through Inhibition of NRF2 Transcriptional Activity

AbstractA family of hybrid complexes combining two biologically active motifs, an artemisinin derivative and a cationic bis(NHC)‐gold(I) unit, has been synthesized. One of these complexes, 2 a, has been analyzed by single‐crystal X‐ray diffraction. 2 a shows strong anticancer activities on a large panel of human cancer cell models (prostate, breast, lung, liver, bladder, bone, acute and chronic myeloid leukemias) with GI50 values in the nm range, together with a high selectivity. An original and distinctive mechanism of action, that is, through inhibition of the redox antioxidant NRF2 transcription factor (strongly associated with aggressiveness and resistance to cancer therapies) has been evidenced. 2 a could remarkably sensitize to sorafenib in HepG2 liver cells, in which dysregulated NRF2 signaling is linked to primary and acquired drug resistance. 2 a also inhibited NF‐κB and HIF transcriptional activities, which are also associated with progression and resistance in cancer. Our findings provide evidence that hybrid (NHC)gold(I) compounds represent a new class of organometallic hybrid molecules that may yield new therapeutic agents.

An Artemisinin-Derivative-(NHC)Gold(I) Hybrid with Enhanced Cytotoxicity through Inhibition of NRF2 Transcriptional Activity.

A family of hybrid complexes combining two biologically active motifs, an artemisinin derivative and a cationic bis(NHC)-gold(I) unit, has been synthesized. One of these complexes, 2 a, has been analyzed by single-crystal X-ray diffraction. 2 a shows strong anticancer activities on a large panel of human cancer cell models (prostate, breast, lung, liver, bladder, bone, acute and chronic myeloid leukemias) with GI50 values in the nm range, together with a high selectivity. An original and distinctive mechanism of action, that is, through inhibition of the redox antioxidant NRF2 transcription factor (strongly associated with aggressiveness and resistance to cancer therapies) has been evidenced. 2 a could remarkably sensitize to sorafenib in HepG2 liver cells, in which dysregulated NRF2 signaling is linked to primary and acquired drug resistance. 2 a also inhibited NF-κB and HIF transcriptional activities, which are also associated with progression and resistance in cancer. Our findings provide evidence that hybrid (NHC)gold(I) compounds represent a new class of organometallic hybrid molecules that may yield new therapeutic agents.

Structural Isomerism Effect in Platinum(II) Acetylide-Based Supramolecular Polymers.

The self-assembly of π-aromatic organic and organometallic molecules into long-range-ordered supramolecular polymers is dictated by a variety of molecular parameters and external conditions. In this work, structural isomerism, representing one of the potent molecular parameters, has been investigated to modulate the self-assembly behaviors. Two platinum(II) acetylide-based structural isomers, with different N-hexyl substitution positions on the inner benzotriazole core, have been designed. Thanks to the synergistic participation of hydrogen-bonding and π-π-stacking interactions, both platinum(II) acetylide-based compounds are prone to forming supramolecular polymers via a nucleation-elongation cooperative mechanism in apolar media. Thermal hysteresis phenomena are observed for both compounds, suggesting the different supramolecular polymerization pathways upon cooling and heating. Remarkably, in addition to the spectroscopic difference, these two supramolecular polymers display distinct thermostability and rheological moduli, ascribing to different binding enthalpies of the neighboring monomers. Overall, it is evident that a minor variation at the molecular level brings huge differences to the properties of long-range-ordered supramolecular polymers. The current study illustrates the importance of the structural isomerism effect for the rational design of π-functional supramolecular materials.

Chemoinformatic Resources for Organometallic Drug Discovery

Medicinal Organometallic Chemistry keeps contributing to drug discovery efforts including the development of diagnostic compounds. Despite the limiting issues of metal-based molecules, e.g., such as toxicity, there are drugs approved for clinical use and several others are under clinical and pre-clinical development. Indeed, several research groups continue working on organometallic compounds with potential therapeutic applications. For arguably historical reasons, chemoinformatic methods in drug discovery have been applied thus far mostly to organic compounds. Typically, metal-based molecules are excluded from compound data sets for analysis. Indeed, most software and algorithms for drug discovery applications are focused and parametrized for organic molecules. However, considering the emerging field of material informatics, the objective of this Commentary we emphasize the need to develop cheminformatic applications to further develop metallodrugs. For instance, one of the starting points would be developing a compound database of organometallic molecules annotated with biological activity. It is concluded that chemoinformatic methods can boost the research area of Medicinal Organometallic Chemistry.

Role of non-covalent interactions to dictate chiral selective self-assembly in Ni(II), Cu(II) and Cd(II) complexes of a racemic 1,2-dihydroquinazolinone ligand

Managing chirality at supramolecular level is an important aspect in crystal packing of chiral organic and organometallic molecules. Herein molecular structure of Ni(II), Cu(II) and Cd(II) complexes of a racemic 1,2-dihydroquinazolin-4(1H)-one ligand is described. The Cd(II) complexes exhibit intriguing structural features viz. capped octahedral geometry with seven coordination, and the presence of bridging as well as end-on azido ligand coordination to one metal center. Homo/heterochiral self-assembly in the complexes is dictated by strong NH⋯N, NH⋯O, NH⋯Cl hydrogen bonds as well as non-classical CH⋯O, CH⋯N, NH⋯π hydrogen bonds and parallel displaced π⋯π stacking interaction. Chiral self-recognition or self-discrimination process in the crystal packing is governed by the nature and strength of the participating non-covalent interactions.

Role of charge transfer in hybridization-induced spin transition in metal-organic molecules

The spin-crossover in organometallic molecules constitutes one of the most promising routes towards the realization of molecular spintronic devices. In this article, we explore the hybridization-induced spin-crossover in metal-organic complexes. We propose a minimal many-body model that captures the essence of the spin-state switching in a generic parameter space, thus providing insight into the underlying physics. Combining the model with density functional theory (DFT), we then study the spin-crossover in isomeric structures of Ni-porphyrin (Ni-TPP). We show that metal-ligand charge transfer plays a crucial role in the determination of the spin-state in Ni-TPP. Finally, we propose a spin-crossover mechanism based on mechanical strain, which does not require a switch between isomeric structures.

Mechanistic Study of Nucleation Enhancement in Atomic Layer Deposition by Pretreatment with Small Organometallic Molecules

Thermal atomic layer deposition (ALD) of metals on metal oxide surfaces typically suffers from nucleation delays that result in poor-quality films. The poor nucleation may be caused by a lack of su...

Evolution of Magnetic Anisotropy of an Organometallic Molecule in a Mechanically Controlled Break Junction: The Roles of Connecting Electrodes

The precise control of local spin states in magnetic organometallic molecules by means of a mechanically controlled break junction (MCBJ) is a cutting edge frontier of single molecule science. For instance, a fine-tuning of the magnetic anisotropy of a Co(tpy–SH)2 molecule has been achieved experimentally by sandwiching the molecule between two electrodes and gradually enlarging their separation. However, an accurate simulation of such a process has remained rather challenging, which is largely due to the complex structure of the composite junction as well as the static electron correlation originating from the nearly degenerate d-orbitals of the cobalt atom. In this work, by employing an embedding method which combines the high-level complete active space self-consistent field (CASSCF) method and a density functional theory (DFT) method, we carefully simulate the evolution of magnetic anisotropy of the Au–Co(tpy–S)2–Au junction during the mechanical stretching process. It is found that the presence of th...

Highly Robust Organometallic Small-Molecule-Based Nonvolatile Resistive Memory Controlled by a Redox-Gated Switching Mechanism.

Although organic small-molecule-based memory devices (OSMDs) have been demonstrated to show great potential for the application in next-generation data-storage technology, progress toward their further development has been hugely hindered by the ambiguity of their electrical switching mechanism. Thus, purposely fabricating OSMDs with a definite switching behavior is very urgent. Here, we reported a redox-gated nonvolatile rewritable memory device using an organometallic small molecule as an active material. By introducing the redox-active ferrocene into an organic skeleton, the target small molecule exhibits reliable and robust FLASH-type bistable electrical characteristics with a clear redox-controlled switching mechanism, which leads to low operational voltages, good endurance, and long retention. Our study offers a proof-of-concept strategy to design controllable OSMDs with excellent performances.

Tunable Magnetism of Organometallic Nanoclusters by Graphene Oxide On-Surface Chemistry

Assembly of interacting molecular spins is an attractive candidate for spintronic and quantum computing devices. Here, we report on-surface chemical assembly of aminoferrocene molecules on a graphene oxide (GO) sheet and their magnetic properties. On the GO surface, organometallic molecules having individual spins through charge transfer between the molecule and the sheet are arranged in nanoclusters having diameters of about 2 nm. The synthetic fine tuning of the reaction time enables to change the interspacing between the nanoclusters, keeping their size intact. Their magnetism changes from paramagnetic behavior to collective one gradually as the interspacing decreases. The creation of collective nature among weakly interacting molecular spins through their nanoscale arrangement on the GO surface opens a new avenue to molecular magnetism.

Multimode jetting unlocks a trade-off between nanostructure morphology and composition in focused electron beam induced deposition

An ability to accelerate the growth rate while simultaneously controlling shape and composition of deposits is fundamental to expanding the utility of electron beam assisted deposition for “direct write” nanostructure fabrication from gas phase precursors. We report on novel tunable mode of Focused Electron Beam Induced Deposition (FEBID) as enabled by the switchable use of reactive (O2) and inert (Ar) “assist” gases directed at high impingement energy and momentum to a deposition site concurrently with a supply of a precursor in a dual-nozzle FEBID arrangement. Organometallic molecules introduced into a deposition chamber in a free-molecular flow regime through a conventional gas injection nozzle, yielding a broad uniform substrate coverage by the precursor in a quasi-equilibrium adsorbed state. Simultaneously, a supersonic micro-jet from a micron-scale capillary placed in close proximity to a deposition site produces a low Knudsen number continuous flow impingement of energized “assist” gas, which perturbs the precursor state to facilitate different chemical reaction pathways. This process enables modulation of deposition outcomes, e.g., enhanced vertical growth rate (aspect ratio) of nanostructures when using argon micro-jet while locally removing parasitic carbonaceous by-products of organometallic precursor decomposition reaction by e-beam through interactions with oxygen micro-jet. Such in-situ/in operando (during growth and on-demand switchable) modulation of FEBID allows for rapid and precisely controllable deposition for a desired outcome, such as tuning metal-to-carbon composition and maintaining shape fidelity in fabricating high-aspect ratio composite nanostructures, which extends the capabilities of FEBID as a robust multi-dimensional, multi-purpose nanoscale 3D printing tool.

(Invited) Recent Progress in Organic-Based Aqueous Flow Batteries

The ability to store large amounts of electrical energy is of increasing importance with the growing fraction of electricity generation from intermittent renewable sources such as wind and solar. Flow batteries show promise because the designer can independently scale the power (electrode area) and energy (arbitrarily large storage volume) components of the system by maintaining all electro-active species in fluids. Wide-scale utilization of flow batteries is limited by the abundance and cost of these materials, particularly those utilizing redox-active metals such as vanadium or precious metal electrocatalysts. We have developed high performance flow batteries based on the aqueous redox behavior of small organic and organometallic molecules, e.g. [1-10]. These redox active materials can be inexpensive and exhibit rapid redox kinetics and long lifetimes, although short lifetimes are more common [7]. We have developed new protocols for measuring capacity fade rates and have discovered that the capacity fade rate is typically determined by the molecular calendar life, which can depend on state of charge, but is independent of the number of charge-discharge cycles imposed [7]. We will report the performance of the few chemistries with long enough calendar life, or the potential for acquiring long enough calendar life [9], for practical application in stationary storage. [1] B. Huskinson, M.P. Marshak, C. Suh, S. Er, M.R. Gerhardt, C.J. Galvin, X. Chen, A. Aspuru-Guzik, R.G. Gordon and M.J. Aziz, "A metal-free organic-inorganic aqueous flow battery", Nature 505, 195 (2014), http://dx.doi.org/10.1038/nature12909[2] K. Lin, Q. Chen, M.R. Gerhardt, L. Tong, S.B. Kim, L. Eisenach, A.W. Valle, D. Hardee, R.G. Gordon, M.J. Aziz and M.P. Marshak, "Alkaline Quinone Flow Battery", Science 349, 1529 (2015), http://dx.doi.org/10.1126/science.aab3033[3] K. Lin, R. Gómez-Bombarelli, E.S. Beh, L. Tong, Q. Chen, A.W. Valle, A. Aspuru-Guzik, M.J. Aziz, and R.G. Gordon, "A redox flow battery with an alloxazine-based organic electrolyte", Nature Energy 1, 16102 (2016). http://dx.doi.org/10.1038/nenergy.2016.102[4] E.S. Beh, D. De Porcellinis, R.L. Gracia, K.T. Xia, R.G. Gordon and M.J. Aziz, "A Neutral pH Aqueous Organic/Organometallic Redox Flow Battery with Extremely High Capacity Retention", ACS Energy Letters 2, 639 (2017). http://dx.doi.org/10.1021/acsenergylett.7b00019[5] Z. Yang, L. Tong, D.P. Tabor, E.S. Beh, M.-A. Goulet, D. De Porcellinis, A. Aspuru-Guzik, R.G. Gordon, and M.J. Aziz, "Alkaline benzoquinone aqueous flow battery for large-scale storage of electrical energy” Advanced Energy Materials 2017, 1702056 (2017). http://dx.doi.org/10.1002/aenm.201702056[6] D.G. Kwabi, K. Lin, Y. Ji, E.F. Kerr, M.-A. Goulet, D. DePorcellinis, D.P. Tabor, D.A. Pollack, A. Aspuru-Guzik, R.G. Gordon, and M.J. Aziz, “Alkaline Quinone Flow Battery with Long Lifetime at pH 12” Joule 2, 1907 (2018). https://doi.org/10.1016/j.joule.2018.07.005[7] M.-A. Goulet & M.J. Aziz, “Flow Battery Molecular Reactant Stability Determined by Symmetric Cell Cycling Methods”, J. Electrochem. Soc. 165, A1466 (2018). http://dx.doi.org/10.1149/2.0891807jes[8] Y. Ji, M.-A. Goulet, D.A. Pollack, D.G. Kwabi, S. Jin, D. DePorcellinis, E.F. Kerr, R.G. Gordon, and M.J. Aziz, “A phosphonate-functionalized quinone redox flow battery at near-neutral pH with record capacity retention rate” Advanced Energy Materials 2019 1900039; https://doi.org/10.1002/aenm.201900039[9] M.-A. Goulet, L. Tong, D.A. Pollack, D.P. Tabor, E.E. Kwan, A. Aspuru-Guzik, R.G. Gordon, and M.J. Aziz, “Extending the lifetime of organic flow batteries via redox state management” Journal of the American Chemical Society 141, in press (2019); https://doi.org/10.1021/jacs.8b13295[10] http://aziz.seas.harvard.edu/electrochemistry

Magnetic force microscopy revealing long range molecule impact on magnetic tunnel junction based molecular spintronics devices

Commercially successful magnetic tunnel junction can harness the unmatched capabilities of molecular device elements by solving decade-old fabrication issues. Utilization of magnetic tunnel junction as a testbed for molecules also enables unprecedented magnetic studies of molecular spintronics devices. This paper utilizes magnetic force microscopy (MFM) to vividly show that organometallic molecules when bridged between two ferromagnetic electrodes along the magnetic tunnel junction edges, transformed the magnetic electrodes itself. Molecules impacted several hundred-micron areas of ferromagnetic electrodes at room temperature. Complementary, magnetic resonance and magnetometer studies supported the dramatic MFM results. Molecule induced changes in the magnetic electrodes impacted the transport of the magnetic tunnel junction and stabilized as much as six orders smaller current at room temperature. Magnetic tunnel junction based molecular devices can be a gateway to a vast range of commercially viable futuristic logic and memory devices that are controlled by the molecular quantum states near room temperature.

Insertion of CO2 Mediated by a (Xantphos)NiI–Alkyl Species

AbstractThe incorporation of CO2 into organometallic and organic molecules represents a sustainable way to prepare carboxylates. The mechanism of reductive carboxylation of alkyl halides has been proposed to proceed through the reduction of NiII to NiI by either Zn or Mn, followed by CO2 insertion into NiI‐alkyl species. No experimental evidence has been previously established to support the two proposed steps. Demonstrated herein is that the direct reduction of (tBu‐Xantphos)NiIIBr2 by Zn affords NiI species. (tBu‐Xantphos)NiI‐Me and (tBu‐Xantphos)NiI‐Et complexes undergo fast insertion of CO2 at 22 °C. The substantially faster rate, relative to that of NiII complexes, serves as the long‐sought‐after experimental support for the proposed mechanisms of Ni‐catalyzed carboxylation reactions.

Insertion of CO2 Mediated by a (Xantphos)NiI -Alkyl Species.

The incorporation of CO2 into organometallic and organic molecules represents a sustainable way to prepare carboxylates. The mechanism of reductive carboxylation of alkyl halides has been proposed to proceed through the reduction of NiII to NiI by either Zn or Mn, followed by CO2 insertion into NiI -alkyl species. No experimental evidence has been previously established to support the two proposed steps. Demonstrated herein is that the direct reduction of (tBu-Xantphos)NiII Br2 by Zn affords NiI species. (tBu-Xantphos)NiI -Me and (tBu-Xantphos)NiI -Et complexes undergo fast insertion of CO2 at 22 °C. The substantially faster rate, relative to that of NiII complexes, serves as the long-sought-after experimental support for the proposed mechanisms of Ni-catalyzed carboxylation reactions.

Redox-Active Ferrocene grafted on H-Terminated Si(111): Electrochemical Characterization of the Charge Transport Mechanism and Dynamics

Electroactive self-assembled monolayers (SAMs) bearing a ferrocene (Fc) redox couple were chemically assembled on H-terminated semiconducting degenerate-doped n-type Si(111) substrate. This allows to create a Si(111)|organic-spacer|Fc hybrid interface, where the ferrocene moiety is covalently immobilized on the silicon, via two alkyl molecular spacers of different length. Organic monolayer formation was probed by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) and X-ray photoelectron spectroscopy (XPS) measurements, which were also used to estimate thickness and surface assembled monolayer (SAM) surface coverage. Atomic force microscopy (AFM) measurements allowed to ascertain surface morphology and roughness. The single electron transfer process, between the ferrocene redox probe and the Si electrode surface, was probed by cyclic voltammetry (CV) measurements. CVs recorded at different scan rates, in the 10 to 500 mV s−1 range, allowed to determine peak-to-peak separation, half-wave potential, and charge-transfer rate constant (KET). The experimental findings suggest that the electron transfer is a one electron quasi-reversible process. The present demonstration of surface engineering of functional redox-active organometallic molecule can be efficient in the field of molecular electronics, surface-base redox chemistry, opto-electronic applications.

Isomeric platinum organometallics derived from pyrimidine, pyridazine or pyrazine and their potential as antitumor drugs

Two new organometallic compounds (1 and 2) containing multiple platinum(II) centers have been synthesized. 1 and 2 are structural isomers having the same molecular formula but they are different either in terms of the N-heterocycle present in the center or relative orientation of the two pendant arms bearing the alkynyl-Pt(PEt3)2I units. 1 and 2 have been characterized using FTIR, NMR, HRMS and elemental analyses, besides structural characterization of one of the complex (1) using single crystal XRD. The cytotoxic potential of 1 and 2 and a previously reported di-PtII organometallic molecule (3) have been studied against four cancer cell lines – HT-29 (colon carcinoma), MCF-7, MDA-MB-231 (breast cancer) and SK-HEP-1 (human hepatic adenocarcinoma). Comparison of IC50 values suggests that these Pt(II) based organometallic compounds have antiproliferative activity that is comparable with that of cisplatin.

Preparation and Antitumoral Activity of Au-Based Inorganic-Organometallic Nanocomposites.

The synergy between gelator molecules and nanostructured materials is currently a novel matter of study. The possibility to carefully design the skeleton of the molecular entity as well as the nanostructure's morphological and chemical features offers the possibility to prepare a huge variety of nanocomposites with properties potentially different than just the sum of those of the individual building blocks. Here we describe the synthesis and characterization of nanocomposites made by the unconventional combination of phosphine-Au(I)-alkynyl-based organometallic gelating molecules and plasmonic Au nanoparticles. Our results indicate that the interaction between the two moieties leads to a significant degree of aggregation in both hydrophilic and hydrophobic media, either when using DAPTA or PTA-based organometallic molecules, with the formation of a sponge-like hybrid powder upon solvent evaporation. The biological activity of the nanocomposites was assessed, suggesting the existence of a synergetic effect evidenced by the higher cytotoxicity of the hybrid systems with respect to that of any of their isolated counterparts. These results represent a preliminary proof-of-concept for the exploitation of these novel nanocomposites in the biomedical field.