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Item type:Publication, Access status: without files , Field-induced conductance switching by charge-state alternation in organometallic single-molecule junctionsCharge transport through single molecules can be influenced by the charge and spin states of redox-active metal centres placed in the transport pathway. These intrinsic properties are usually manipulated by varying the molecule's electrochemical and magnetic environment, a procedure that requires complex setups with multiple terminals. Here we show that oxidation and reduction of organometallic compounds containing either Fe, Ru or Mo centres can solely be triggered by the electric field applied to a two-terminal molecular junction. Whereas all compounds exhibit bias-dependent hysteresis, the Mo-containing compound additionally shows an abrupt voltage-induced conductance switching, yielding high-to-low current ratios exceeding 1,000 at bias voltages of less than 1.0â €...V. Density functional theory calculations identify a localized, redox-active molecular orbital that is weakly coupled to the electrodes and closely aligned with the Fermi energy of the leads because of the spin-polarized ground state unique to the Mo centre. This situation provides an additional slow and incoherent hopping channel for transport, triggering a transient charging effect in the entire molecule with a strong hysteresis and large high-to-low current ratios.Publicationtype: Journal Article19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Structural and electronic variations of sp/sp² carbon-based bridges in di- And trinuclear redox-active iron complexes bearing Fe(diphosphine₂X (X = I, NCS) moieties(2015-01-26); ; ; Starting from the mononuclear precursor trans-Fe(depe)2I2 (depe = 1,2-bis(diethylphosphino)ethane), four dinuclear complexes IFe(depe)2-R-Fe(depe)2I, with R = 1,4-(-C≡C-C6H4-C≡C-) 1, 1,3-(-C≡C-C6H4-C≡C-) 2, 4,4′-(-C≡C-C6H4-C6H4-C≡C-) 3, and 2,5-(- C≡C-thiophene-C≡C-) 4, as well as a trinuclear complex, {I-Fe(depe)2(C≡C-)}3(1,3,5-C6H3)} 5, were prepared in a facile way by transmetalation from stannylated precursors. Substitution of the terminal iodides applying an excess of NaSCN yielded the corresponding isothiocyanate complexes 6-10 in very good yields. All complexes 1-10 are intrinsically functional due to the redox-active Fe centers embedded in a structurally rigid and covalent sp/sp2 framework. 1-10 were characterized by NMR, IR, and Raman spectroscopy, as well as elemental analyses. X-ray diffraction studies were carried out for 1, 2, 4, 5, 6, 8, and 9. Cyclic voltammetry was employed to explore the redox behavior of 1-10. The 1,4-(-C≡C-C6H4-C≡C-) and the 2,5-(-C≡C-thiophene-C≡C-) bridged compounds 1, 4, 6, and 9 exhibit two fully reversible oxidation waves, while the 1,3-(-C≡C-C6H4-C≡C-) and 4,4′-(-C≡C-C6H4-C6H4-C≡C-) bridged dinuclear complexes and the trinuclear complexes show only one reversible oxidation wave corresponding to 2 e- and 3 e- processes, respectively. Calculations were carried out for truncated model complexes to determine the HOMO/LUMO energies. The DFT results confirmed that by changing the sp/sp2 bridging ligand, tuning of the energies of the molecular orbitals and modifying of the HOMO-LUMO gap ΔE(H-L) and the chemical hardness are possible. (Chemical Equation Presented).Publicationtype: Journal Article11 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Organometallic single-molecule electronics : tuning electron transport through X(diphosphine)₂FeC₄Fe(diphosphine)₂X building blocks by varying the Fe-X-Au anchoring scheme from coordinative to covalent(2014-10-15); ; ; ; A series of X(depe)2FeC≡C-C≡CFe(depe)2X complexes (depe =1,2-bis(diethylphosphino)ethane; X = I 1, NCMe 2, N2 3, C2H 4, C2SnMe3 5, C4SnMe3 6, NCSe 7, NCS 8, CN 9, SH 10, and NO2 11) was designed to study the influence of the anchor group on organometallic molecular transport junctions to achieve high-conductive molecular wires. The FeC4Fe core is electronically functional due to the redox-active Fe centers and sp-bridging ligands allowing a strong electronic delocalization. 1-11 were characterized by elemental analyses, X-ray diffraction, cyclic voltammetry, NMR, IR, and Raman spectroscopy. DFT calculations on model compounds gave the HOMO/LUMO energies. 5-9 were investigated in mechanically controllable break-junctions. For 9, unincisive features at 8.1 × 10-7 G0 indicate that sterical reasons prevent stable junctions to form or that the coordinative binding motif prohibits electron injection. 7 and 8 with the hitherto unexploited coordinatively binding end groups NCSe and NCS yielded currents of 1.3 × 10-9 A (7) and 1.8 × 10-10 A (8) at ±1.0 V. The SnMe3 in 5 and 6 splits off, yielding junctions with covalent C-Au bonds and currents of 6.5 × 10-7 A (Au-5′-Au) or 2.1 × 10-7 A (Au-6′-Au). Despite of a length of almost 2 nm, the Au-5′-Au junction reaches 1% of the maximum current assuming one conductance channel in quantum point contacts. Additionally, the current noise in the transport data is considerably reduced for the covalent C-Au coupling compared to the coordinative anchoring of 7-9, endorsing C-Au coupled organometallic complexes as excellent candidates for low-ohmic molecular wires.Publicationtype: Journal Article28 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , High-conductive organometallic molecular wires with delocalized electron systems strongly coupled to metal electrodes(2014-10-08); ; ; ; Besides active, functional molecular building blocks such as diodes or switches, passive components, for example, molecular wires, are required to realize molecular-scale electronics. Incorporating metal centers in the molecular backbone enables the molecular energy levels to be tuned in respect to the Fermi energy of the electrodes. Furthermore, by using more than one metal center and sp-bridging ligands, a strongly delocalized electron system is formed between these metallic "dopants", facilitating transport along the molecular backbone. Here, we study the influence of molecule-metal coupling on charge transport of dinuclear X(PP)2FeC4Fe(PP)2X molecular wires (PP = Et2PCH2CH2PEt2); X = CN (1), NCS (2), NCSe (3), C4SnMe3 (4), and C2SnMe3 (5) under ultrahigh vacuum and variable temperature conditions. In contrast to 1, which showed unstable junctions at very low conductance (8.1 × 10-7 G0), 4 formed a Au-C4FeC4FeC4-Au junction 4′ after SnMe3 extrusion, which revealed a conductance of 8.9 × 10-3 G0, 3 orders of magnitude higher than for 2 (7.9 × 10-6 G0) and 2 orders of magnitude higher than for 3 (3.8 × 10-4 G0). Density functional theory (DFT) confirmed the experimental trend in the conductance for the various anchoring motifs. The strong hybridization of molecular and metal states found in the C-Au coupling case enables the delocalized electronic system of the organometallic Fe2 backbone to be extended over the molecule-metal interfaces to the metal electrodes to establish high-conductive molecular wires.Publicationtype: Journal Article19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Stepwise construction of an iron-substituted rigid-rod molecular wire: targeting a tetraferra-tetracosa-decayne(American Chemical Society (ACS), 2013-02-13); ; ; ; trans-Fe(depe)2I2 (depe =1,2-bis(diethylphosphino) ethane) was employed to stepwise incorporate Fe(II) centers into a rigid-rod butadiyne based 5,10,15,20-tetraferratetracosa-1,3,6,8,11,13,16,18,21,23- decayne. The iterative synthesis first connects two Fe(II) centers via a central butadiynediyl ligand to provide I-Fe(depe)2-C4-Fe(depe) 2-I (2), then extends the system by substituting the terminal halides of 2 to yield Me3SiC4-Fe(depe)2-C 4-Fe(depe)2-C4SiMe3 (3). Further modification of the termini gives the deprotected and stannylated compounds RC4-Fe(depe)2-C4-Fe(depe)2-C 4R (4 and 5; R = H, Sn(CH3)3, respectively). Transmetalation with two more mononuclear units furnishes the homometallic tetranuclear compound I-Fe(depe)2-C4-Fe(depe) 2-C4-Fe(depe)2-C4-Fe(depe) 2-I (6), to which two more butadiynyl units were attached to give Me3SiC4-Fe(depe)2-C4-Fe(depe) 2-C4-Fe(depe)2-C4-Fe(depe) 2-C4SiMe3 (7). All compounds were characterized by NMR, IR, and Raman spectroscopies and by elemental analyses. X-ray diffraction studies were carried out on the dinuclear complexes revealing highly symmetrical rigid-rod structures. Cyclic voltammetric studies showed that compounds 2-7 undergo reversible and well-defined oxidations with high K c values indicating thermodynamically stable mixed valence species. While the number of the oxidation waves of compounds 2, 6, and 7 are equivalent to the number of metal centers, the dinuclear complexes 3, 4, and 5 exhibit three reversible oxidation waves, one at significantly more positive potential. Two redox waves were attributed to the oxidation of the metal centers, while the remaining one is due to the oxidation of the butadiynediyl ligand. The electronic properties of complexes 2, 3, and 7 were investigated by spectroelectrochemical measurements.Publicationtype: Journal ArticleScopus© Citations 51 21