EPR and electrochemical studies of bimetallic seventeen-electron molybdenum species exhibiting unusually large interactions across bipyridyl bridging ligands

1990 ◽  
pp. 940 ◽  
Author(s):  
Sean L. W. McWhinnie ◽  
Christopher J. Jones ◽  
Jon A. McCleverty ◽  
David Collison ◽  
Frank E. Mabbs
Keyword(s):  
Electrochemical Studies ◽  
Bridging Ligands

Modulation of Internuclear Communication in Multinuclear Ruthenium(II) Polypyridyl Complexes

2003 ◽  
Vol 68 (8) ◽  
pp. 1467-1487 ◽  
Author(s):  
Wesley R. Browne ◽  
Frances Weldon ◽  
Adrian Guckian ◽  
Johannes G. Vos
Keyword(s):  
Ground State ◽  
Weak Interactions ◽  
Electrochemical Studies ◽  
Protonation State ◽  
Ruthenium Polypyridyl ◽  
Bridging Ligands ◽  
Polypyridyl Complexes ◽  
Bridging Ligand ◽  
Dinuclear Ruthenium ◽  
Ruthenium Polypyridyl Complexes

The syntheses and characterisation of a series of mononuclear and dinuclear ruthenium polypyridyl complexes based on the bridging ligands 1,3-bis-[5-(2-pyridyl)-1H-1,2,4-triazol-3-yl]benzene, 1,4-bis-[5-(2-pyridyl)-1H-1,2,4-triazol-3-yl]benzene, 2,5-bis-[5-(2-pyridyl)-1H-1,2,4-triazol-3-yl]thiophene, 2,5-bis-[5-pyrazinyl-1H-1,2,4-triazol-3-yl]thiophene are reported. Electrochemical studies indicate that in these systems, the ground state interaction is critically dependent on the nature of the bridging ligand and its protonation state, with strong and weak interactions being observed for thiophene- and phenylene-bridged complexes, respectively.

Binuclear Iron and Ruthenium Complexes with Bis(diazene) or Bis(diazenido) Bridging Ligands:  Synthesis, Characterization, X-ray Crystal Structure, and Electrochemical Studies

1996 ◽  
Vol 35 (21) ◽  
pp. 6245-6253 ◽  
Author(s):  
Gabriele Albertin ◽  
Stefano Antoniutti ◽  
Alessia Bacchi ◽  
Emilio Bordignon ◽  
Giancarlo Pelizzi ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Ruthenium Complexes ◽  
Electrochemical Studies ◽  
Bridging Ligands ◽  
X Ray ◽  
Binuclear Iron

Electrochemical studies of bi- and polymetallic complexes featuring acetylide based bridging ligands

2005 ◽  
Vol 9 (11) ◽  
pp. 717-731 ◽  
Author(s):  
Paul J. Low ◽  
Rachel L. Roberts ◽  
Richard L. Cordiner ◽  
František Hartl
Keyword(s):  
Electrochemical Studies ◽  
Bridging Ligands ◽  
Polymetallic Complexes

Preparations, Structures, and Electrochemical Studies of Aryldiazene Complexes of Rhenium:  Syntheses of the First Heterobinuclear and Heterotrinuclear Derivatives with Bis(diazene) or Bis(diazenido) Bridging Ligands

2000 ◽  
Vol 39 (15) ◽  
pp. 3265-3279 ◽  
Author(s):  
Gabriele Albertin ◽  
Stefano Antoniutti ◽  
Alessia Bacchi ◽  
Giovanni B. Ballico ◽  
Emilio Bordignon ◽  
...  
Keyword(s):  
Electrochemical Studies ◽  
Bridging Ligands

Electrochemical studies of a series of dirhodium(II) complexes with acetate and acetamidate bridging ligands

1984 ◽  
Vol 23 (1) ◽  
pp. 2-3 ◽  
Author(s):  
T. P. Zhu ◽  
M. Q. Ahsan ◽  
T. Malinski ◽  
K. M. Kadish ◽  
J. L. Bear
Keyword(s):  
Electrochemical Studies ◽  
Bridging Ligands

A Pyridinic Fe-N4 Macrocycle Effectively Models the Active Sites in Fe/N-Doped Carbon Electrocatalysts

2020 ◽  
Author(s):  
Travis Marshall-Roth ◽  
Nicole J. Libretto ◽  
Alexandra T. Wrobel ◽  
Kevin Anderton ◽  
Nathan D. Ricke ◽  
...  
Keyword(s):  
Oxygen Reduction ◽  
Active Sites ◽  
Catalytic Properties ◽  
Reduction Reaction ◽  
Iron Phthalocyanine ◽  
Electrochemical Studies ◽  
Onset Potential ◽  
Nitrogen Doped Carbon ◽  
Iron Active Sites

Iron- and nitrogen-doped carbon (Fe-N-C) materials are leading candidates to replace platinum in fuel cells, but their active site structures are poorly understood. A leading postulate is that iron active sites in this class of materials exist in an Fe-N<sub>4</sub> pyridinic ligation environment. Yet, molecular Fe-based catalysts for the oxygen reduction reaction (ORR) generally feature pyrrolic coordination and pyridinic Fe-N<sub>4</sub> catalysts are, to the best of our knowledge, non-existent. We report the synthesis and characterization of a molecular pyridinic hexaazacyclophane macrocycle, (phen<sub>2</sub>N<sub>2</sub>)Fe, and compare its spectroscopic, electrochemical, and catalytic properties for oxygen reduction to a prototypical Fe-N-C material, as well as iron phthalocyanine, (Pc)Fe, and iron octaethylporphyrin, (OEP)Fe, prototypical pyrrolic iron macrocycles. N 1s XPS signatures for coordinated N atoms in (phen<sub>2</sub>N<sub>2</sub>)Fe are positively shifted relative to (Pc)Fe and (OEP)Fe, and overlay with those of Fe-N-C. Likewise, spectroscopic XAS signatures of (phen<sub>2</sub>N<sub>2</sub>)Fe are distinct from those of both (Pc)Fe and (OEP)Fe, and are remarkably similar to those of Fe-N-C with compressed Fe–N bond lengths of 1.97 Å in (phen<sub>2</sub>N<sub>2</sub>)Fe that are close to the average 1.94 Å length in Fe-N-C. Electrochemical studies establish that both (Pc)Fe and (phen<sub>2</sub>N<sub>2</sub>)Fe have relatively high Fe(III/II) potentials at ~0.6 V, ~300 mV positive of (OEP)Fe. The ORR onset potential is found to directly correlate with the Fe(III/II) potential leading to a ~300 mV positive shift in the onset of ORR for (Pc)Fe and (phen<sub>2</sub>N<sub>2</sub>)Fe relative to (OEP)Fe. Consequently, the ORR onset for (phen<sub>2</sub>N<sub>2</sub>)Fe and (Pc)Fe is within 150 mV of Fe-N-C. Unlike (OEP)Fe and (Pc)Fe, (phen<sub>2</sub>N<sub>2</sub>)Fe displays excellent selectivity for 4-electron ORR with <4% maximum H<sub>2</sub>O<sub>2</sub> production, comparable to Fe-N-C materials. The aggregate spectroscopic and electrochemical data establish (phen<sub>2</sub>N<sub>2</sub>)Fe as a pyridinic iron macrocycle that effectively models Fe-N-C active sites, thereby providing a rich molecular platform for understanding this important class of catalytic materials.<p><b></b></p>

Tuning the Redox Activity of Metal−Organic Frameworks for Enhanced, Selective O2 Binding

2019 ◽  
Author(s):  
Andrew Rosen ◽  
M. Rasel Mian ◽  
Timur Islamoglu ◽  
Haoyuan Chen ◽  
Omar Farha ◽  
...  
Keyword(s):  
Density Functional ◽  
Metal Organic Frameworks ◽  
Redox Activity ◽  
Screening Methods ◽  
Bridging Ligands ◽  
Metal Centers ◽  
Computational Screening ◽  
Open Metal Sites ◽  
Metal Organic ◽  
Unsaturated Metal Sites

<p>Metal−organic frameworks (MOFs) with coordinatively unsaturated metal sites are appealing as adsorbent materials due to their tunable functionality and ability to selectively bind small molecules. Through the use of computational screening methods based on periodic density functional theory, we investigate O<sub>2</sub> and N<sub>2</sub> adsorption at the coordinatively unsaturated metal sites of several MOF families. A variety of design handles are identified that can be used to modify the redox activity of the metal centers, including changing the functionalization of the linkers (replacing oxido donors with sulfido donors), anion exchange of bridging ligands (considering μ-Br<sup>-</sup>, μ-Cl<sup>-</sup>, μ-F<sup>-</sup>, μ-SH<sup>-</sup>, or μ-OH<sup>-</sup> groups), and altering the formal oxidation state of the metal. As a result, we show that it is possible to tune the O<sub>2</sub> affinity at the open metal sites of MOFs for applications involving the strong and/or selective binding of O<sub>2</sub>. In contrast with O<sub>2</sub> adsorption, N<sub>2</sub> adsorption at open metal sites is predicted to be relatively weak across the MOF dataset, with the exception of MOFs containing synthetically elusive V<sup>2+</sup> open metal sites. As one example from the screening study, we predict that exchanging the μ-Cl<sup>-</sup> ligands of M<sub>2</sub>Cl<sub>2</sub>(BBTA) (H<sub>2</sub>BBTA = 1<i>H</i>,5<i>H</i>-benzo(1,2-d:4,5-d′)bistriazole) with μ-OH<sup>-</sup> groups would significantly enhance the strength of O<sub>2</sub> adsorption at the open metal sites without a corresponding increase in the N<sub>2</sub> affinity. Experimental investigation of Co<sub>2</sub>Cl<sub>2</sub>(BBTA) and Co<sub>2</sub>(OH)<sub>2</sub>(BBTA) confirms that the former exhibits only weak physisorption, whereas the latter is capable of chemisorbing O<sub>2</sub> at room temperature. The chemisorption behavior is attributed to the greater electron-donating character of the μ-OH<sup>-</sup><sub> </sub>ligands and the presence of H-bonding interactions between the μ-OH<sup>-</sup> bridging ligands and the O<sub>2</sub> adsorbate.</p>

Exchange-Biasing in a Dinuclear Dysprosium(III) Single-Molecule Magnet with a Large Energy Barrier for Magnetization Reversal

2019 ◽  
Author(s):  
Tian Han ◽  
Marcus J. Giansiracusa ◽  
Zi-Han Li ◽  
You-Song Ding ◽  
Nicholas F. Chilton ◽  
...  
Keyword(s):  
Single Molecule ◽  
Magnetization Reversal ◽  
Energy Barrier ◽  
Magnetic Hysteresis ◽  
Large Energy ◽  
Magnetic Studies ◽  
Bridging Ligands ◽  
Single Molecule Magnet ◽  
Exchange Biasing

A dichlorido-bridged dinuclear dysprosium(III) single-molecule magnet [Dy<sub>2</sub>L<sub>2</sub>(<i>µ</i>-Cl)<sub>2</sub>(THF)<sub>2</sub>] has been made using a diamine-bis(phenolate) ligand, H<sub>2</sub>L. Magnetic studies show an energy barrier for magnetization reversal (<i>U</i><sub>eff</sub>) around 1000 K. Exchange-biasing effect is clearly seen in magnetic hysteresis with steps up to 4 K. <i>Ab</i> initio calculations exclude the possibility of pure dipolar origin of this effect leading to the conclusion that super-exchange <i>via</i> the chloride bridging ligands is important.

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