Probing the effect of nitro-substituents in the modulation of LUMO energies for directional electron transport through 4d ruthenium(II)-based metallosurfactants.

Electron-withdrawing nitro-substituents were installed onto terpyridine- and phenanthroline-based metallosurfactants with 4d ruthenium(II), which were deposited as Langmuir-Blodgett monolayers aiming to study the feasibility of charge transport in Au|LB|Au junctions. The nitro groups are intended to modulate the energy of the frontier molecular orbitals to near to, or match that of Fermi levels in the gold electrodes. A series of heteroleptic metallosurfactants [Ru(COPh-terpy)(X-terpy)](PF) and [Ru(COPh-terpy)(X-phen)Cl]PF were synthesized, where COPh-terpy is the 4'-[4-(octadecyloxy)phenyl]-2,2':6',2''-terpyridine amphiphile common to all species, X-terpy is a terpyridine with-H (1) or-phenyl-NO (2) and X-phen is a phenanthroline with-H (3) or-NO (4) groups.

A bioinspired cobalt catalyst based on a tripodal imidazole/pyridine platform capable of water reduction and oxidation.

The prototypical drug carrier [Co(L)Cl]PF (1), where L is a tripodal amine bound to pyridine and methyl-imidazoles, had its electrocatalytic water splitting activity studied under different pH conditions. This species contains a high-spin 3d Co metal center, and is capable of generating both H from water reduction and O from water oxidation Turnover numbers reach 390 after 3 h for water reduction. Initial water oxidation activity is molecular, with TONs of 71 at pH 7 and 103 at pH 11.

Bioinspired oxidation of benzyl alcohol: The role of environment and nuclearity of the catalyst evaluated by multivariate analysis.

Inspired by copper-containing enzymes such as galactose oxidase and catechol oxidase, in which distinct coordination environments and nuclearities lead to specific catalytic activities, we summarize here the catalytic properties of dinuclear and mononuclear copper species towards benzyl alcohol oxidation using a multivariate statistical approach. The new dinuclear [Cu(μ-L)(μ-pz)] (1) is compared against the mononuclear [CuLCl] (2), where (L) and (L) are the respective deprotonated forms of 2,6-bis((bis(pyridin-2-ylmethyl)amino)methyl)-4-methylphenol, and 3-((bis(pyridin-2-ylmethyl)amino)methyl)-2-hydroxy-5-methylbenzaldehyde and (pz) is a pyrazolato bridge. Copper(II) perchlorate (CP) is used as control.

Electron transport through a (terpyridine)ruthenium metallo-surfactant containing a redox-active aminocatechol derivative.

Aiming to develop a new class of metallosurfactants with unidirectional electron transfer properties, a (terpyridine) ruthenium complex containing a semiquinone derivative L, namely [Ru(L)(L)Cl]PF (1), was synthesized and structurally characterized as a solid and in solution. The electronic and redox behaviour of 1 was studied experimentally as well as by means of DFT methods, and is indicative of significant orbital mixing and overlap between metal and ligands. The complex forms stable Pockels-Langmuir films at the air-water interface and allows for the formation of thin films onto gold electrodes to prepare nanoscale Au|LB 1|Au junctions for current-voltage (/) analysis.

Distinct Bimetallic Cooperativity Among Water Reduction Catalysts Containing [Co Co ], [Ni Ni ], and [Zn Zn ] Cores.

Three binuclear species [LCo (μ-Pz) ](ClO ) (1), [LNi (CH OH) Cl ]ClO (2), and [LZn Cl ]PF (3) supported by the deprotonated form of the ligand 2,6-bis[bis(2-pyridylmethyl) amino-methyl]-4-methylphenol were synthesized, structurally characterized as solids and in solution, and had their electrochemical and spectroscopic behavior established. Species 1-3 had their water reduction ability studied aiming to interrogate the possible cooperative catalytic activity between two neighboring metal centers. Species 1 and 2 reduced H O to H effectively at an applied potential of -1.

Dual anticancer and antibacterial activities of bismuth compounds based on asymmetric [NN'O] ligands.

Two new bismuth(III) complexes, [BiLCl] (1) and [BiLCl] (2), in which L is (2-hydroxy-4-6-di-tert-butylbenzyl-2-pyridylmethyl)amine and L is 2,4-diiodo-6-((pyridine-2-ylmethylamino)methyl)phenol, were synthesized and characterized by elemental and conductivity analyses, atomic absorption spectrometry, infrared and H NMR spectroscopies. The molecular structure of 1 reveals that the NN'O ligand forms a 1:1 complex with bismuth through coordination via the nitrogen of the aliphatic amine, the nitrogen of the pyridine ring and the oxygen of the phenolate. The coordination sphere is completed with two chloride anions in a distorted square pyramidal geometry.

Reactivity and Mechanisms of Photoactivated Heterometallic [Ru Ni ] and [Ru Ni Ru ] Catalysts for Dihydrogen Generation from Water.

Two heterometallic photocatalysts were designed and probed for water reduction. Both [(bpy) Ru Ni (L )](ClO ) (1) and [(bpy) Ru Ni (L ) Ru (bpy) ](ClO ) (2) can generate the low-valent precursor involved in hydride formation prior to dihydrogen generation. However, while the bimetallic [Ru Ni ] (1) requires the presence of an external photosensitizer to trigger catalytic activity, the trimetallic [Ru Ni Ru ] (2) displays significant coupling between the catalytic and light-harvesting units to promote intramolecular multielectron transfer and perform photocatalysis at the Ni center.

Electrochemical Quantification of Corrosion Mitigation on Iron Surfaces with Gallium(III) and Zinc(II) Metallosurfactants.

We have recently described a new potential use for Langmuir-Blodgett films of surfactants containing redox-inert metal ions in the inhibition of corrosion and have shown good qualitative results for both iron and aluminum surfaces. In this study we proceed to quantify electrochemically the viability of gallium(III)- and zinc(II)-containing metallosurfactants [Ga(L)] () and [Zn(L)HO] () as mitigators for iron corrosion in saline and acidic media. We evaluate their charge transfer suppression and then focus on potentiodynamic polarization and impedance spectroscopy studies, including detailed SEM data to interrogate their metal dissolution/oxygen reduction rate mitigation abilities.

A Molecular Approach for Mitigation of Aluminum Pitting based on Films of Zinc(II) and Gallium(III) Metallosurfactants.

The use of metallosurfactants to prevent pitting corrosion of aluminum surfaces is discussed based on the behavior of the metallosurfactants [Zn (L )H O] (1) and [Ga (L )] (2). These species were deposited as multilayer Langmuir-Blodgett films and characterized by IR reflection absorption spectroscopy and UV/Vis spectroscopy. Scanning electron microscopy images, potentiodynamic polarization experiments, and electrochemical impedance spectroscopy were used to assess corrosion mitigation.

Influence of nitro substituents on the redox, electronic, and proton reduction catalytic behavior of phenolate-based [NO]-type cobalt(iii) complexes.

We report on the synthesis, redox, electronic, and catalytic behavior of two new cobalt(iii) complexes, namely [CoIII(L1)MeOH] (1) and [CoIII(L2)MeOH] (2). These species contain nitro-rich, phenolate-based pentadentate ligands and present dramatically distinct properties associated with the position in which the -NO2 substituents are installed. Species 1 displays nitro-substituted phenolates, and exhibits irreversible redox response and negligible catalytic activity, whereas 2 has fuctionalized phenylene moieties, shows much improved redox reversibility and catalytic proton reduction activity at low overpotentials.

Molecular rectifiers based on five-coordinate iron(iii)-containing surfactants.

In this article we review the state-of-the-art of metallorganic-based molecular rectification with an emphasis on our research in five-coordinate FeIII-containing surfactants. We place rectification in the broader context of molecular electronics, and include the description of methodology used in electrode|LB film|electrode assemblies, concluding with an outlook on future directions for metallosurfactants.

Observation of current rectification by the new bimetallic iron(iii) hydrophobe [Fe(L)] on Au|LB-molecule|Au devices.

Targeting the development of stimulus-responsive molecular materials with electronic functionality, we have synthesized and studied the redox and electronic properties of a new bimetallic iron hydrophobe [FeIII2(LN4O6)] (1). The new H6LN4O6 ligand displays bicompartmental topology capable of accomodating two five-coordinate HSFeIII ions bridged by tetraaminobenzene at a close distance of ca. 8 Å.

Immobilization of an Amphiphilic Molecular Cobalt Catalyst on Carbon Black for Ligand-Assisted Water Oxidation.

We have prepared the amphiphilic molecular catalyst [Co(L)(pyrr)]ClO (1), where L is the deprotonated form of N, N'-[4,5-bis(octadecyloxy)-1,2-phenylene]dipicolinamide. Species 1 can be anchored onto a carbon black support to yield the assembly 1@CB, which can catalyze water oxidation at an affordable onset overpotential of 0.32 V, with a current density of 10 mA/cm at 0.

Observation of current rectification by a new asymmetric iron(iii) surfactant in a eutectic GaIn|LB monolayer|Au sandwich.

In this paper we expand on the search for molecular rectifiers of electrical current and report on a hexacoordinate metallosurfactant [FeIII(LN3O)(OMe)2], where (LN3O)- is the deprotonated form of the new asymmetric ligand 2-((E)-((4,5-bis(2-methoxyethoxy)-2-(((E)-pyridin-2-ylmethylene)amino)phenyl)imino)methyl)-4,6-di-tert-butyl-phenol. This species rectifies current when deposited as a Langmuir-Blodget film in a "EGaIn/Ga2O3|LB|Au" sandwich with rectification ratios ranging from 25 to 300 at 1 Volt.

An in situ spectroelectrochemical study on the orientation changes of an [FeL] metallosurfactant deposited as LB Films on gold electrode surfaces.

In this paper we analyze the changes in molecular orientation triggered by electrochemical reduction of an iron-containing surfactant in Langmuir-Blodgett films deposited onto gold electrodes. The metallosurfactant [Feiii(LN2O3)] (1) is an established molecular rectifier capable of unidirectional electron transfer between two electrodes. A gradual decrease in the activity is observed in sequential current vs.

A pentadentate nitrogen-rich copper electrocatalyst for water reduction with pH-dependent molecular mechanisms.

The new pentadentate 3d complex [Cu(L)](PF) (1) based on a nitrogen-rich framework acts as an electrocatalyst toward dihydrogen production from water. This species is active at pHs 7 and 2.5 yielding respective TON values of 1670 and 3900.

Bimetallic Cooperativity in Proton Reduction with an Amido-Bridged Cobalt Catalyst.

The bimetallic catalyst [Co (L )(bpy) ]ClO (1), in which L is an [NN' O ] fused ligand, efficiently reduced H to H in CH CN in the presence of 100 equiv of HOAc with a turnover number of 18 and a Faradaic efficiency of 94 % after 3 h of bulk electrolysis at -1.6 V (vs. Ag/AgCl).

Deactivation of a Cobalt Catalyst for Water Reduction through Valence Tautomerism.

The activity of the water reduction catalyst [Co (L )(pyr) ]PF (1), where (L ) is a bis-amido pyridine ligand and pyr is pyrrolidine, is investigated. Catalyst 1 has an overpotential of 0.54 V and a high observed TOF of 23 min , albeit for a relatively short time.

Efficient electro/photocatalytic water reduction using a [Ni(NPy)] complex.

The pyridine-rich complex [Ni(L)(MeCN)](ClO) (1) acts as an efficient electro- and photocatalyst in the generation of H from water. Observed TONs reach 1050 for electrocatalysis and a remarkable 3500 for photocatalysis. Experimental and DFT data support the ligand-reduced [NiL˙] as the catalytically active species, contrasting with the [CoL] observed for cobalt catalysts.

Langmuir-Blodgett films of salophen-based metallosurfactants as surface pretreatment coatings for corrosion mitigation.

Salophen-based metallosurfactants are successfully used as pretreatment LB films for corrosion mitigation in acidic and saline media. Passivation of electron transfer is clearly demonstrated in gold electrodes, while 99.5% iron substrates treated with such films show up to an impressive 30% corrosion mitigation.

Efficient water oxidation with electromodified Langmuir-Blodgett films of procatalytic [Co(III)(N2O3)] metallosurfactants on electrodes.

Electromodified Langmuir-Blodgett films of a phenolate-rich [Co(III)(L(N2O3))H2O] metallosurfactant support water oxidation at an overpotential of 0.5 V. Gradual enhancement of catalytic activity is observed between 1 and 9 deposited layers.

Electronic Modulation of the SOMO-HOMO Energy Gap in Iron(III) Complexes towards Unimolecular Current Rectification.

Amphiphilic five-coordinate iron(III) complexes with {N2 O2 Cl} and {N2 O3 } coordination spheres are studied to elucidate the roles of electronic structure on the mechanisms for current rectification. The presence of an apical chlorido or phenolato ligand plays a crucial role, and the [Fe(III) {N2 O2 Cl}] species supports an asymmetric mechanism while its [Fe(III) {N2 O3 }] counterpart seems to allow for unimolecular mechanism. The effects of electron-donating and electron-withdrawing substituents in the ligand frameworks are also considered.