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Weeraratne ADKI, Hewa-Rahinduwage CC, Luo L, Verani CN. Electrochemical Quantification of Corrosion Mitigation on Iron Surfaces with Gallium(III) and Zinc(II) Metallosurfactants. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:14173-14180. [PMID: 33205971 DOI: 10.1021/acs.langmuir.0c01826] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
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 [GaIII(LN2O3)] (1) and [ZnII(LN2O2)H2O] (2) 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. Both complexes show some degree of mitigation, with a more pronounced activity in saline than in acidic medium.
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Affiliation(s)
- A D K Isuri Weeraratne
- Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United States
| | | | - Long Luo
- Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United States
| | - Cláudio N Verani
- Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United States
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2
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Weeraratne ADKI, Hewa-Rahinduwage CC, Gonawala S, Luo L, Verani CN. A Molecular Approach for Mitigation of Aluminum Pitting based on Films of Zinc(II) and Gallium(III) Metallosurfactants. Chemistry 2019; 25:14048-14053. [PMID: 31565813 DOI: 10.1002/chem.201903408] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Revised: 09/23/2019] [Indexed: 11/06/2022]
Abstract
The use of metallosurfactants to prevent pitting corrosion of aluminum surfaces is discussed based on the behavior of the metallosurfactants [ZnII (LN2O2 )H2 O] (1) and [GaIII (LN2O3 )] (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. Both metallosurfactants demonstrate superior anticorrosion activity due to the presence of redox-inactive 3d10 metal ions that enhance the structural resistance of the ordered molecular films and limit chloride mobility and electron transfer.
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Affiliation(s)
| | | | - Sunalee Gonawala
- Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, MI, 48202, USA
| | - Long Luo
- Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, MI, 48202, USA
| | - Cláudio N Verani
- Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, MI, 48202, USA
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3
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Basu D, Mazumder S, Kpogo KK, Verani CN. Influence of nitro substituents on the redox, electronic, and proton reduction catalytic behavior of phenolate-based [N 2O 3]-type cobalt(iii) complexes. Dalton Trans 2019; 48:14669-14677. [PMID: 31536091 DOI: 10.1039/c9dt03158h] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
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. A concerted experimental and theoretical approach sheds some light on these drastic differences.
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Affiliation(s)
- Debashis Basu
- Department of Chemistry, Wayne State University, Detroit, MI-48202, USA.
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Brand I, Juhaniewicz-Debinska J, Wickramasinghe L, Verani CN. An in situ spectroelectrochemical study on the orientation changes of an [Fe iiiL N2O3] metallosurfactant deposited as LB Films on gold electrode surfaces. Dalton Trans 2018; 47:14218-14226. [PMID: 29589614 DOI: 10.1039/c8dt00333e] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
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. potential curves upon repeated cycles. Here we evaluate the redox response associated with the reduction of the Feiii/Feii couple in a single monolayer, as well as in a 5-layer LB film of 1. We use polarization modulation infrared reflection absorption spectroscopy (PM IRRAS) to follow structural and orientation changes associated with such applied potential scans. We observe that the reduction of the Fe center becomes increasingly irreversible because an Fe-Ophenolate bond is cleaved. This transformation is accompanied by an almost vertical change in the orientation of metallosurfactant molecules in LB films.
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Affiliation(s)
- Izabella Brand
- Department of Chemistry, Carl von Ossietzky University of Oldenburg, 26111 Oldenburg, Germany.
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Weeraratne ADKI, Baydoun H, Shakya R, Niklas J, Xie L, Mao G, Stoian SA, Poluektov OG, Verani CN. Observation of current rectification by the new bimetallic iron(iii) hydrophobe [Fe(L N4O6)] on Au|LB-molecule|Au devices. Dalton Trans 2018; 47:14352-14361. [PMID: 30215065 DOI: 10.1039/c8dt03158d] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
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. We show that the metal-based reduction processes in (1) proceed sequentially, as observed for electronically coupled metal centers. This species forms a well-defined Pockels-Langmuir film at the air-water interface, with collapse pressure of 32 mN m-1. Langmuir-Blodgett monolayers were deposited on gold substrates and used to investigate current-voltage (I-V) measurements. This unprecedented bimetallic hydrophobe [FeIII2(LN4O6)] (1) shows unquestionable molecular rectification and displays a rectification ratio RR between 2 and 15.
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Abstract
This paper reviews the present status of unimolecular electronics (UME). The field started in the 1970s with a hope that some day organic molecules (∼2 nm in size), when used as electronic components, would challenge Si-based inorganic electronics in ultimate-high-density integrated circuits. The technological push to ever smaller inorganic device sizes (Moore's "law") was driven by a profit motive and by vast investments. UME, the underfunded pauper, may have lost that "race to the bottom", but some excellent science is left to be done.
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Affiliation(s)
- Robert Melville Metzger
- Laboratory for Molecular Electronics, Department of Chemistry and Biochemistry, University of Alabama, Box 870336, Tuscaloosa, AL 35487-0336, USA.
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Baydoun H, Burdick J, Thapa B, Wickramasinghe L, Li D, Niklas J, Poluektov OG, Schlegel HB, Verani CN. Immobilization of an Amphiphilic Molecular Cobalt Catalyst on Carbon Black for Ligand-Assisted Water Oxidation. Inorg Chem 2018; 57:9748-9756. [DOI: 10.1021/acs.inorgchem.7b03252] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- Habib Baydoun
- Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United States
| | - Jordyn Burdick
- Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United States
| | - Bishnu Thapa
- Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United States
| | - Lanka Wickramasinghe
- Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United States
| | - Da Li
- Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United States
| | - Jens Niklas
- Chemical Sciences & Engineering Division, Argonne National Laboratory (ANL), Lemont, Illinois 60439, United States
| | - Oleg G. Poluektov
- Chemical Sciences & Engineering Division, Argonne National Laboratory (ANL), Lemont, Illinois 60439, United States
| | - H. Bernhard Schlegel
- Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United States
| | - Cláudio N. Verani
- Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United States
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Johnson MS, Horton CL, Gonawala S, Verani CN, Metzger RM. Observation of current rectification by a new asymmetric iron(iii) surfactant in a eutectic GaIn|LB monolayer|Au sandwich. Dalton Trans 2018; 47:6344-6350. [PMID: 29633775 DOI: 10.1039/c8dt00562a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
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.
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Affiliation(s)
- Marcus S Johnson
- Laboratory for Molecular Electronics, Department of Chemistry and Biochemistry, University of Alabama, Box 870336, Tuscaloosa, AL 35487, USA.
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Wickramasinghe LD, Mazumder S, Kpogo KK, Staples RJ, Schlegel HB, Verani CN. Electronic Modulation of the SOMO–HOMO Energy Gap in Iron(III) Complexes towards Unimolecular Current Rectification. Chemistry 2016; 22:10786-90. [DOI: 10.1002/chem.201602444] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2016] [Indexed: 11/08/2022]
Affiliation(s)
| | - Shivnath Mazumder
- Department of Chemistry Wayne State University 5101 Cass Ave Detroit MI 48202 USA
| | - Kenneth K. Kpogo
- Department of Chemistry Wayne State University 5101 Cass Ave Detroit MI 48202 USA
| | | | - H. Bernhard Schlegel
- Department of Chemistry Wayne State University 5101 Cass Ave Detroit MI 48202 USA
| | - Cláudio N. Verani
- Department of Chemistry Wayne State University 5101 Cass Ave Detroit MI 48202 USA
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10
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Gonawala S, Baydoun H, Wickramasinghe L, Verani CN. Efficient water oxidation with electromodified Langmuir–Blodgett films of procatalytic [CoIII(N2O3)] metallosurfactants on electrodes. Chem Commun (Camb) 2016; 52:8440-3. [DOI: 10.1039/c6cc03263j] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Electromodified Langmuir–Blodgett films of a cobalt-based metallosurfactant support water oxidation at turnover numbers of up to 54 000 h−1.
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Gonawala S, Leopoldino VR, Kpogo K, Verani CN. Langmuir–Blodgett films of salophen-based metallosurfactants as surface pretreatment coatings for corrosion mitigation. Chem Commun (Camb) 2016; 52:11155-8. [DOI: 10.1039/c6cc04563d] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Langmuir–Blodgett films of metallosurfactants prevent up to 30% of acidic and saline corrosion, showing potential as surface pretreatment coatings.
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Affiliation(s)
| | - Verônica R. Leopoldino
- Department of Chemistry
- Wayne State University
- USA
- Department of Chemical Engineering
- Universidade Federal de São João del Rei
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12
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Chakraborty C, Pandey RK, Hossain MD, Futera Z, Moriyama S, Higuchi M. Platinum(II)-Based Metallo-Supramolecular Polymer with Controlled Unidirectional Dipoles for Tunable Rectification. ACS APPLIED MATERIALS & INTERFACES 2015; 7:19034-19042. [PMID: 26285226 DOI: 10.1021/acsami.5b03434] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
A platinum(II)-based, luminescent, metallo-supramolecular polymer (PolyPtL1) having an inherent dipole moment was synthesized via complexation of Pt(II) ions with an asymmetric ligand L1, containing terpyridyl and pyridyl moieties. The synthesized ligand and polymer were well characterized by various NMR techniques, optical spectroscopy, and cyclic voltammetry studies. The morphological study by atomic force microscopy revealed the individual and assembled polymer chains of 1-4 nm height. The polymer was specifically attached on Au-electrodes to produce two types of film (films 1 and 2) in which the polymer chains were aligned with their dipoles in opposite directions. The Au-surface bounded films were characterized by UV-vis, Raman spectroscopy, cyclic voltammetry, and atomic force microscopy study. The quantum mechanical calculation determined the average dipole moment for each monomer unit in PolyPtL1 to be about 5.8 D. The precise surface derivatization permitted effective tuning of the direction dipole moment, as well as the direction of rectification of the resulting polymer-attached molecular diodes. Film 1 was more conductive in positive bias region with an average rectification ratio (RR = I(+4 V)/I(-4 V)) ≈ 20, whereas film 2 was more conducting in negative bias with an average rectification ratio (RR = I(-4 V)/I(+4 V)) ≈ 18.
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Affiliation(s)
- Chanchal Chakraborty
- Electronic Functional Materials Group, National Institute for Materials Science (NIMS) , Tsukuba 305-0044, Japan
- International Center for Materials Nanoarchitectonics (MANA), NIMS , Tsukuba, Japan
- JST-CREST , Chiyoda-ku, Tokyo 102-0076, Japan
| | - Rakesh K Pandey
- Electronic Functional Materials Group, National Institute for Materials Science (NIMS) , Tsukuba 305-0044, Japan
| | - Md Delwar Hossain
- Electronic Functional Materials Group, National Institute for Materials Science (NIMS) , Tsukuba 305-0044, Japan
| | - Zdenek Futera
- International Center for Materials Nanoarchitectonics (MANA), NIMS , Tsukuba, Japan
| | - Satoshi Moriyama
- International Center for Materials Nanoarchitectonics (MANA), NIMS , Tsukuba, Japan
- JST-CREST , Chiyoda-ku, Tokyo 102-0076, Japan
| | - Masayoshi Higuchi
- Electronic Functional Materials Group, National Institute for Materials Science (NIMS) , Tsukuba 305-0044, Japan
- JST-CREST , Chiyoda-ku, Tokyo 102-0076, Japan
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Affiliation(s)
- Robert M. Metzger
- Laboratory for Molecular
Electronics, Department of Chemistry, The University of Alabama, Box 870336, Tuscaloosa, Alabama 35487-0336, United States
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Basu D, Allard MM, Xavier FR, Heeg MJ, Schlegel HB, Verani CN. Modulation of electronic and redox properties in phenolate-rich cobalt(iii) complexes and their implications for catalytic proton reduction. Dalton Trans 2015; 44:3454-66. [DOI: 10.1039/c4dt03337j] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The redox, spectroscopic and catalytic activity of a series of cobalt complexes with phenolate-rich environments was investigated. The complex [CoIII(LCl)MeOH] shows considerable proton reduction in MeCN:HOAc with TON = 10.8.
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Affiliation(s)
- Debashis Basu
- Department of Chemistry
- Wayne State University
- Detroit
- USA
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15
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Basu D, Mazumder S, Shi X, Baydoun H, Niklas J, Poluektov O, Schlegel HB, Verani CN. Ligand Transformations and Efficient Proton/Water Reduction with Cobalt Catalysts Based on Pentadentate Pyridine‐Rich Environments. Angew Chem Int Ed Engl 2014. [DOI: 10.1002/ange.201409813] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Debashis Basu
- Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, MI 48202 (USA) http://chem.wayne.edu/veranigroup/
| | - Shivnath Mazumder
- Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, MI 48202 (USA) http://chem.wayne.edu/veranigroup/
| | - Xuetao Shi
- Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, MI 48202 (USA) http://chem.wayne.edu/veranigroup/
| | - Habib Baydoun
- Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, MI 48202 (USA) http://chem.wayne.edu/veranigroup/
| | - Jens Niklas
- Argonne National Laboratory, Chemistry Division, E117, 9700 South Cass Ave. Argonne, IL 60439 (USA)
| | - Oleg Poluektov
- Argonne National Laboratory, Chemistry Division, E117, 9700 South Cass Ave. Argonne, IL 60439 (USA)
| | - H. Bernhard Schlegel
- Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, MI 48202 (USA) http://chem.wayne.edu/veranigroup/
| | - Cláudio N. Verani
- Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, MI 48202 (USA) http://chem.wayne.edu/veranigroup/
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Basu D, Mazumder S, Shi X, Baydoun H, Niklas J, Poluektov O, Schlegel HB, Verani CN. Ligand transformations and efficient proton/water reduction with cobalt catalysts based on pentadentate pyridine-rich environments. Angew Chem Int Ed Engl 2014; 54:2105-10. [PMID: 25533319 DOI: 10.1002/anie.201409813] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2014] [Revised: 11/25/2014] [Indexed: 11/10/2022]
Abstract
A series of cobalt complexes with pentadentate pyridine-rich ligands is studied. An initial Co(II) amine complex 1 is prone to aerial oxidation yielding a Co(III) imine complex 2 that is further converted into an amide complex 4 in presence of adventitious water. Introduction of an N-methyl protecting group to the ligand inhibits this oxidation and gives rise to the Co(II) species 5. Both the Co(III) 4 and Co(II) 5 show electrocatalytic H2 generation in weakly acidic media as well as in water. Mechanisms of catalysis seem to involve the protonation of a Co(II)-H species generated in situ.
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Affiliation(s)
- Debashis Basu
- Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, MI 48202 (USA) http://chem.wayne.edu/veranigroup/
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Wickramasinghe LD, Mazumder S, Gonawala S, Perera MM, Baydoun H, Thapa B, Li L, Xie L, Mao G, Zhou Z, Schlegel HB, Verani CN. The Mechanisms of Rectification in Au|Molecule|Au Devices Based on Langmuir-Blodgett Monolayers of Iron(III) and Copper(II) Surfactants. Angew Chem Int Ed Engl 2014; 53:14462-7. [DOI: 10.1002/anie.201408649] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Revised: 09/18/2014] [Indexed: 11/08/2022]
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Wickramasinghe LD, Mazumder S, Gonawala S, Perera MM, Baydoun H, Thapa B, Li L, Xie L, Mao G, Zhou Z, Schlegel HB, Verani CN. The Mechanisms of Rectification in Au|Molecule|Au Devices Based on Langmuir-Blodgett Monolayers of Iron(III) and Copper(II) Surfactants. Angew Chem Int Ed Engl 2014. [DOI: 10.1002/ange.201408649] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Verani CN, Driscoll J, Keyes PH, Heeg MJ. Cationic Copper(II)-containing Surfactants: Molecular Structures, Film Morphology, and Influence on the Alignment of Nematic Mesogens. Inorg Chem 2014; 53:5647-55. [DOI: 10.1021/ic5004098] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Cláudio N. Verani
- Department of Chemistry and ‡Department of Physics and Astronomy, Wayne State University, 5101 Cass Avenue, Room 161, Detroit, Michigan 48202, United States
| | - Jeffery Driscoll
- Department of Chemistry and ‡Department of Physics and Astronomy, Wayne State University, 5101 Cass Avenue, Room 161, Detroit, Michigan 48202, United States
| | - Paul H. Keyes
- Department of Chemistry and ‡Department of Physics and Astronomy, Wayne State University, 5101 Cass Avenue, Room 161, Detroit, Michigan 48202, United States
| | - Mary Jane Heeg
- Department of Chemistry and ‡Department of Physics and Astronomy, Wayne State University, 5101 Cass Avenue, Room 161, Detroit, Michigan 48202, United States
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Rajput A, Sharma AK, Barman SK, Koley D, Steinert M, Mukherjee R. Neutral, cationic, and anionic low-spin iron(III) complexes stabilized by amidophenolate and iminobenzosemiquinonate radical in N,N,O ligands. Inorg Chem 2014; 53:36-48. [PMID: 24387744 DOI: 10.1021/ic401985d] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A brownish-black complex [Fe(III)(L)2] (1) (S = 0), supported by two tridentate redox-active azo-appended o-amidophenolates [H2L = 2-(2-phenylazo)-anilino-4,6-di-tert-butylphenol], has been synthesized and structurally characterized. In CH2Cl2 1 displays two oxidative and two reductive 1e(-) redox processes at E1/2 values of 0.48 and 1.06 V and -0.42 and -1.48 V vs SCE, respectively. The one-electron oxidized form [1](+) isolated as a green solid [Fe(III)(L)2][BF4] (2) (S = 1/2) has been structurally characterized. Isolation of a dark ink-blue one-electron reduced form [1](-) has also been achieved [Co(III)(η(5)-C10H15)2][Fe(III)(L)2] (3) (S = 1/2). Mössbauer spectral parameters unequivocally establish that 1 is a low-spin (LS) Fe(III) complex. Careful analysis of Mössbauer spectral data of 2 and 3 at 200 and 80 K reveal that each complex has a major LS Fe(III) and a minor LS Fe(II) component (redox isomers): [Fe(III){(L(ISQ))(-•)}2](+) and [Fe(II){(L(IBQ))(0)}{(L(ISQ))(-•)}](+) (2) and [Fe(III){(L(AP))(2-)}2](-) and [Fe(II){(L(ISQ))(-•)}{(L(AP))(2-)}](-) (3). Notably, for both at 8 K mainly the major component exists. Broken-Symmetry (BS) Density Functional Theory (DFT) calculations at the B3LYP level reveals that in 1 the unpaired electron of LS Fe(III) is strongly antiferromagnetically coupled with a π-radical of o-iminobenzosemiquinonate(1-) (L(ISQ))(-•) form of the ligand, delocalized over two ligands providing 3- charge (X-ray structure). DFT calculations reveal that the unpaired electron in 2 is due to (L(ISQ))(-•) [LS Fe(III) (SFe = 1/2) is strongly antiferromagnetically coupled to one of the (L(ISQ))(-•) radicals (Srad = 1/2)] and 3 is primarily a LS Fe(III) complex, supported by two o-amidophenolate(2-) ligands. Time-Dependent-DFT calculations shed light on the origin of UV-vis-NIR spectral absorptions for 1-3. The collective consideration of Mössbauer, variable-temperature (77-298 K) electron paramagnetic resonance (EPR), and absorption spectral behavior at 298 K, and DFT results reveals that in 2 and 3 the valence-tautomerism is operative in the temperature range 80-300 K.
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Affiliation(s)
- Amit Rajput
- Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur 208 016, India
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