Straightforward Access to Tetrametallic Complexes with a Square Array by Oxidative Dimerization of Organometallic Wires

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.

Migration of Condensed Aromatic Hydrocarbons During Alkyne-Vinylidene Rearrangements

Diarylacetylenes ArC≡CAr featuring condensed aromatic hydrocarbon fragments (Ar) such as naphthalene, anthracene, phenanthrene and pyrene were converted into vinylidene ligands by 1,2-migration reactions within the coordination sphere of half-sandwich complexes [MII(dppe)Cp]+ (MII = RuII, FeII). Comparison of the extent of conversion of the alkyne substrates to the vinylidene complexes [Ru{=C=CAr2}(dppe)Cp]+ with those obtained from acetylenes functionalized by smaller groups (H, CH3, Ph) show that the molecular volume (VM) of the migrating group and relief of steric congestion plays a role during the rearrangement process. Conversely, the H-atoms from the larger condensed ring aryl groups that are in close proximity to the migrating sites also have a significant influence on the efficacy and extent of the reaction by restricting access of the alkyne to the metal center, resulting in a less effective migration reaction. This combination of competing steric factors (acceleration due to relief of steric congestion and restricted access of the alkyne moiety to the reaction site) is exemplified by the facile migration of 1-pyryl entities and the low yields of vinylidene products formed from 1,2-bis(9-anthryl)acetylene.

Towards the design of molecular cells for quantum cellular automata: critical reconsideration of the parameter regime for achieving functionality

In this article, we present a critical discussion of the parametric regimes required for reaching the functionality of the two-electron square-planar tetrameric mixed-valence (MV) complexes as molecular cells in quantum cellular automata (QCA). Previous studies on molecular QCA were restricted by the limit case of strong Coulomb interaction that was supposed to be the only way to ensure such two key requirements for functioning QCA cells as bistability and switchability. It was thus assumed that the site-to-site electron transfer energy t should be much smaller than the energy U of the Coulomb repulsion between the two excess electrons (strong-U limit defined by the inequality U ≫ t). Unlike those studies, here, we develop a generalized theoretical approach within which no restricting assumptions are implied on the relative strength of the intracell Coulomb interaction, electron transfer, the vibronic coupling with "breathing" modes of redox sites and the external electrostatic field of the driver cell acting on the working cell. We demonstrate that dominating Coulomb repulsion is not the only source of bistability and switchability, but such key features of QCA cell can be reached even in systems in which the strong-U limit is violated, provided that the vibronic coupling is strong enough. Such a reconsideration of the parameter regime for achieving proper functionality is expected to essentially enlarge the family of MV molecules, which can be used as molecular QCA cells.

Insight Into The Spin-Vibronic Problem of a Mixed Valence Magnetic Molecular Cell for Quantum Cellular Automata

The effects of the vibronic coupling in quantum cellular automata (QCA) based on the square planar mixed valence (MV) molecular cells comprising four paramagnetic centers (spin cores) and two excess mobile electrons are analyzed in the important particular case when the Coulomb energy gap between the ground antipodal diagonal-type two-electron configurations and the excited side-type configurations considerably exceeds both the one-electron transfer parameter (strong U-limit) and the vibronic stabilization energy. Under such conditions the developed model involves the second-order double exchange, the Heisenberg-Dirac-Van Vleck (HDVV) exchange and the vibronic coupling of the excess electrons with the molecular B_1g -vibration composed of four full-symmetric local vibrations. The latter interaction is shown to significant amplify the ability of the electric field produced by the driver-cell to polarize the excess electrons in the working cell, which can be termed "the effect of the vibronic enhancement of the cell-cell interaction". This effect leads to a redetermination of the conditions for switching between different spin-states, as well as to a significant change in the shapes of the cell-cell response functions. The obtained results demonstrate the importance of the vibronic coupling in all aspects (such as description of a free cell and cell-cell response) of the theory of molecular QCA based on MV clusters.

In Quest of Molecular Materials for Quantum Cellular Automata: Exploration of the Double Exchange in the Two-Mode Vibronic Model of a Dimeric Mixed Valence Cell

In this article, we apply the two-mode vibronic model to the study of the dimeric molecular mixed-valence cell for quantum cellular automata. As such, we consider a multielectron mixed valence binuclear d2−d1–type cluster, in which the double exchange, as well as the Heisenberg-Dirac-Van Vleck exchange interactions are operative, and also the local (“breathing”) and intercenter vibrational modes are taken into account. The calculations of spin-vibronic energy spectra and the “cell-cell”-response function are carried out using quantum-mechanical two-mode vibronic approach based on the numerical solution of the dynamic vibronic problem. The obtained results demonstrate a possibility of combining the function of molecular QCA with that of spin switching in one electronic device and are expected to be useful from the point of view of the rational design of such multifunctional molecular electronic devices.

Iron vs. ruthenium: syntheses, structures and IR spectroelectrochemical characterisation of half-sandwich Group 8 acetylide complexes

A synthetic ‘trick’ affording complexes [M(CCR)(dppe)Cp′] (M = Fe, Ru) in high purity directly from the reaction vessel is described.

Toward multifunctional molecular cells for quantum cellular automata: exploitation of interconnected charge and spin degrees of freedom

We discuss the possibility of using mixed-valence (MV) dimers comprising paramagnetic metal ions as molecular cells for quantum cellular automata (QCA). Thus, we propose to combine the underlying idea behind the functionality of QCA of using the charge distributions to encode binary information with the additional functional options provided by the spin degrees of freedom. The multifunctional ("smart") cell is supposed to consist of multielectron MV dn-dn+1-type (1 ≤ n ≤ 8) dimers of transition metal ions as building blocks for composing bi-dimeric square planar cells for QCA. The theoretical model of such a cell involves the double exchange (DE), Heisenberg-Dirac-Van Vleck (HDVV) exchange, Coulomb repulsion between the two excess electrons belonging to different dimeric half-cells and also the vibronic coupling. Consideration is focused on the topical case in which the difference in Coulomb energies of the two excess electrons occupying nearest neighboring and distant positions significantly exceeds both the electron transfer integral and the vibronic energy. In this case the ground spin-state of the isolated square cell is shown to be the result of competition of the second-order DE producing a ferromagnetic effect and the HDVV exchange that is assumed to be antiferromagnetic. In order to reveal the functionality of the magnetic cells, the cell-cell response function is studied within the developed model. The interaction of the working cell with the polarized driver-cell is shown to produce an antiferromagnetic effect tending to suppress the ferromagnetic second-order DE. As a result, under some conditions the electric field of the driver cell is shown to force the working cell to exhibit spin-switching from the state with maximum dimeric spin values to that having minimal spin values.

Zwitterionic Mixed-Valence Species for the Design of Neutral Clocked Molecular Quantum-Dot Cellular Automata

Mixed-valence compounds can be used for the design of molecular quantum-dot cellular automata (QCA). Here, we investigate the QCA properties of a three-dot "Y"-shaped functionalized zwitterionic neutral closo-carborane model 1-(3,5-{Cp(dHpe)Fe-C≡C-}₂(C₆H₃))-10-Cp(dHpe)Fe-C≡C-closo-1-CB₉H₈ (1) (Cp = cyclopentadienyl (η⁵-C₅H₅) and dHpe = 1,2-bis(phosphino)ethane (H₂PCH₂CH₂PH₂)) as a neutral clocked molecular half-cell. DFT results clearly demonstrate that 1 can display simultaneously the two most basic properties necessary for clocked QCA operation, i.e., bistable switching behavior and clocked control. This is possible due to the three stable states (two active and one null) of 1, corresponding to occupation of each of the three iron-ethynyl groups by the positive charge. In addition, the proximal electronic bias effects can be overcome by the zwitterionic nature of 1, which could be imposed by external counterions, rendering these effects more predictable.

Understanding the singlet–triplet energy splittings in transition metal-capped carbon chains

Density functional theory and molecular orbital analysis suggest that the odd–even alternation of singlet–triplet energy separations is a general feature of transition metal-capped carbon chains, determined primarily by the carbon chains.

Metal coordination to a dimetallaoctatetrayne

The reactions of the ditungstaoctatetrayne [(Tp*)(CO)₂W([triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash])W(CO)₂(Tp*)] with several metal complexes have been investigated. Addition of [Co₂(CO)₈] occurs across the internal C[triple bond, length as m-dash]C bonds, whereas [AuCl(SMe₂)] initially delivers 'AuCl' across the W[triple bond, length as m-dash]C carbyne bonds before undergoing further reaction to oxidise the tungsten and replace the carbonyl ligands with chloride in [(Tp*)Cl₂W([triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash])WCl₂(Tp*)] with retention of the ditungstaoctatetrayne bridge. Reaction with [AuCl(PR₃)] (R = Ph, Cy) in the presence of AgPF₆ prevents this oxidation and adds [AuPR₃]⁺ across the W[triple bond, length as m-dash]C bonds to give dicationic derivatives. Finally, the reaction with [Pt(nbe)₃] (nbe = norbornene, bicyclo[2.2.1]hept-2-ene) and 1,5-cyclooctadiene (COD) adds a 'Pt(COD)' unit to one or both tungsten-carbon bonds, allowing both the mono- and diplatinum complexes to be isolated.

Diruthenium(ii)-capped oligothienylethynyl bridged highly soluble organometallic wires exhibiting long-range electronic coupling

Organometallic molecular wires with π-conjugation along their molecular backbones are of considerable interest for application in molecular-scale electronics. In this regard, thienylethynyl-based π-conjugated oligomers of three, five and seven thienylethynyl units with -C[triple bond, length as m-dash]C-H termini have been successfully synthesized through stepwise Pd(0)/Cu(i)-catalyzed Sonogashira coupling. The corresponding highly soluble diruthenium(ii) diacetylide complexes (O1-Ru2, O3-Ru2, O5-Ru2 and O7-Ru2, respectively) have been prepared by the reaction of cis-Ru(dppe)2Cl2 and NaPF6 in DCM with the corresponding rigid rod-like thienylethynyl oligomers with one, three, five and seven thienylethynyl π-conjugated segments containing alkynyl termini (O1, O3, O5 and O7). These Ru(ii)-Cl capped diacetylide complexes have been further functionalized by incorporating a phenylacetynyl moiety to afford [Ru(ii)-C[triple bond, length as m-dash]C-Ph]-capped diacetylide organometallic wires (O1-Ru2-Ph, O3-Ru2-Ph, O5-Ru2-Ph and O7-Ru2-Ph). The photophysical properties of the highly soluble thienylethynyl-based oligomers and Ru(ii)-organometallic wires have been explored to understand their electronic properties. Electrochemical studies of the binuclear ruthenium(ii)-alkynyl complexes showed highly interesting results, revealing long-range electrochemical communication between the two remote Ru(ii) termini connected even with five and seven thienylethynyl units. DFT computational studies further support the long range electrochemical communication between the redox active metal termini through heavy participation of the thienylethynyl bridge in the corresponding mono-oxidized mixed valence species of the organometallic wire-like complexes.

Optimised Syntheses of the Half-Sandwich Complexes FeCl(dppe)Cp*, FeCl(dppe)Cp, RuCl(dppe)Cp*, and RuCl(dppe)Cp

Thanks to their synthetic versatility, the half-sandwich metal chlorides MCl(dppe)(η5-C5R5) [M = Fe, Ru; dppe = 1,2-bis(diphenylphosphino)ethane, R = H (cyclopentadiene, Cp), CH3 (pentamethylcyclopentadiene, Cp*)] are staple starting materials in many organometallic laboratories. Here we present an overview of the synthetic methods currently available for FeCl(dppe)Cp*, FeCl(dppe)Cp, RuCl(dppe)Cp*, and RuCl(dppe)Cp, and describe in detail updated and optimised multigram syntheses of all four compounds.

Electronic structure of modelized vs. real carbon-chain containing organometallic dinuclear complexes: similarities and differences

DFT calculations were carried out on the homo- and hetero-bimetallic model wires [(η(5)-C5H5)(dpe)Fe-C≡C-C6H4-C≡C-Fe(dpe)(η(5)-C5H5)] (1'), [(η(7)-C7H7)(dpe)Mo-C≡C-C6H4-C≡C-Mo(dpe)(η(7)-C7H7)] (2'), and [(η(5)-C5H5)(dpe)Fe-C≡C-C6H4-C≡C-Mo(dpe)(η(7)-C7H7)] (3') used to tentatively mimic [(η(5)-C5Me5)(dppe)Fe-C≡C-C6H4-C≡C-Fe(dppe)(η(5)-C5Me5)] (1), [(η(7)-C7H7)(dppe)Mo-C≡C-C6H4-C≡C-Mo(dppe)(η(7)-C7H7)] (2), and [(η(5)-C5Me5)(dppe)Fe-C≡C-C6H4-C≡C-Mo(dppe)(η(7)-C7H7)] (3), respectively in order to analyze the similarities and the differences between models and real compounds previously theoretically and experimentally studied, with respect to their molecular structures and properties. A comparison of the metrical data computed for the models and the real systems shows some slight discrepancy between the metal-ancillary ligand distances - shorter distances are observed in the formers - but comparable metal-Cα and Cα-Cβ distances. Incidentally, distances computed for the model molecules match more closely those measured experimentally. Replacement of a dppe ligand tethered to the metal centers by a dpe group does not much alter the electronic properties. Therefore, overall, data obtained for the Mo2 models 2' compare rather well with those computed for the real systems 2. Larger alteration is noticed when Cp* is substituted by Cp, even if the general trends observed for the real iron species 1 and 3 are kept overall for the iron models 1' and 3'. Indeed, the smaller electron-donor properties of Cp affect somewhat the nodal properties of the HOMOs (less metallic character) and increase the HOMO-LUMO gaps and the ionization potentials. Despite this, similarities between models and real compounds largely overtake differences. It is shown that calculations on models provide quite acceptable results.

Crystal structure of paddle-wheel sandwich-type [Cu2{(CH3)2CO}{μ-Fe(η(5)-C5H4C N)2}3](BF4)2·(CH3)2CO

The mol-ecular structure of (acetone-κO)tris-(μ-ferrocene-1,1'-dicarbo-nitrile-κ(2) N:N')dicopper(I) bis-(tetra-fluorido-borate) acetone monosolvate, [Cu2Fe3(C6H4N)6(C3H6O)](BF4)2·C3H6O, consists of two Cu(I) ions bridged by a ferrocene-1,1'-dicarbo-nitrile moiety in a paddle-wheel-architectured sandwich complex with two BF4 (-) units as counter-ions. One of the latter is equally disordered over two sets of sites. The two Cu(I) ions are complexed in a trigonal-planar manner by three nitrile N-donor atoms. Further inter-actions by the O atom of an acetone mol-ecule to one of the Cu(I) atoms and a weak η(2),π-inter-action of two atoms of a cyclo-penta-dienyl ring to the other Cu(I) atom complete a distorted trigonal-pyramidal environment for each of the metal ions. A further acetone mol-ecule is also present as a solvent mol-ecule. The crystal packing is consolidated by several π-π inter-actions.