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Budnikov AS, Krylov IB, Ushakov IE, Subbotina IR, Monin FK, Nikishin GI, Efimov NN, Gorbunov DE, Gritsan NP, Tretyakov EV, Yu B, Terent'ev AO. Two Discoveries in One Crystal: σ-Type Oxime Radical as an Unforeseen Building Block in Molecular Magnetics and Its Spatial Structure. Inorg Chem 2023. [PMID: 37399244 DOI: 10.1021/acs.inorgchem.3c00947] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/05/2023]
Abstract
In the present work, the study of the unusual interaction between copper hexafluoroacetylacetonate and the diacetyliminoxyl radical resulted in two discoveries from different fields: the determination of the oxime radical spatial structure and the introduction of an oxime radical into the field of molecular magnetic material design. Oxime radicals are key plausible intermediates in the processes of oxidative CH-functionalization and in the synthesis of functionalized isoxazolines from oximes. Due to the lack of X-ray diffraction data for oxime radicals, the knowledge about their structure is based mainly on indirect approaches, spectroscopic methods (electron paramagnetic resonance and IR), and quantum chemical calculations. The structure of the oxime radical was determined for the first time by stabilizing the diacetyliminoxyl radical in the form of its complex with copper (II) hexafluoroacetylacetonate (Cu(hfac)2), followed by single-crystal X-ray diffraction analysis. Although oxime radicals are known to undergo oxidative coupling with acetylacetonate ligands in transition-metal complexes, a complex is formed with intact hfac ligands. X-ray diffraction studies have shown that the oxime radical is coordinated with copper ions through the oxygen atoms of the carbonyl groups without the direct involvement of the C═N-O• radical moiety. The structure of the coordinated diacetyliminoxyl is in good agreement with the density functional theory (DFT) prediction for free diacetyliminoxyl due to the very weak interaction of the radical molecule with copper ions. Remarkably, both weak ferromagnetic and antiferromagnetic interactions between Cu (II) and oxime radicals have been revealed by modeling the temperature dependence of magnetic susceptibility and confirmed by DFT calculations, rendering diacetyliminoxyl a promising building block for the design of molecular magnets.
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Affiliation(s)
- Alexander S Budnikov
- N. D. Zelinsky Institute of Organic Chemistry of the Russian Academy of Sciences, 47 Leninsky prosp., Moscow 119991, Russian Federation
| | - Igor B Krylov
- N. D. Zelinsky Institute of Organic Chemistry of the Russian Academy of Sciences, 47 Leninsky prosp., Moscow 119991, Russian Federation
| | - Ivan E Ushakov
- A. N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences, 28 Vavilova Str., Moscow 119991, Russian Federation
| | - Irina R Subbotina
- N. D. Zelinsky Institute of Organic Chemistry of the Russian Academy of Sciences, 47 Leninsky prosp., Moscow 119991, Russian Federation
| | - Fedor K Monin
- N. D. Zelinsky Institute of Organic Chemistry of the Russian Academy of Sciences, 47 Leninsky prosp., Moscow 119991, Russian Federation
| | - Gennady I Nikishin
- N. D. Zelinsky Institute of Organic Chemistry of the Russian Academy of Sciences, 47 Leninsky prosp., Moscow 119991, Russian Federation
| | - Nikolay N Efimov
- N. S. Kurnakov Institute of General and Inorganic Chemistry, Leninsky Prospect 31, Moscow 119991, Russia
| | - Dmitry E Gorbunov
- V. V. Voevodsky Institute of Chemical Kinetics and Combustion, Siberian Branch of the Russian Academy of Sciences, Novosibirsk 630090, Russian Federation
| | - Nina P Gritsan
- V. V. Voevodsky Institute of Chemical Kinetics and Combustion, Siberian Branch of the Russian Academy of Sciences, Novosibirsk 630090, Russian Federation
| | - Evgeny V Tretyakov
- N. D. Zelinsky Institute of Organic Chemistry of the Russian Academy of Sciences, 47 Leninsky prosp., Moscow 119991, Russian Federation
| | - Bing Yu
- Green Catalysis Center, College of Chemistry, Zhengzhou University, Zhengzhou 450001, China
| | - Alexander O Terent'ev
- N. D. Zelinsky Institute of Organic Chemistry of the Russian Academy of Sciences, 47 Leninsky prosp., Moscow 119991, Russian Federation
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2
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Kumar K, Singh R, Kaur V. Synthesis, structure and hydrolysis studies of pseudostannatranes: Kinetic studies of a hexanuclear tin(IV) hydroxo-cluster formed via reverse Kocheshkov reaction and partial hydrolysis of pseudostannatrane. Polyhedron 2022. [DOI: 10.1016/j.poly.2022.115812] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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3
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Xu Z, Gu S, Li Y, Wu J, Zhao Y. Recognition-Enabled Automated Analyte Identification via 19F NMR. Anal Chem 2022; 94:8285-8292. [PMID: 35622989 DOI: 10.1021/acs.analchem.2c00642] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Nuclear magnetic resonance (NMR) is an indispensable tool for structural elucidation and noninvasive analysis. Automated identification of analytes with NMR is highly pursued in metabolism research and disease diagnosis; however, this process is often complicated by the signal overlap and the sample matrix. We herein report a detection scheme based on 19F NMR spectroscopy and dynamic recognition, which effectively simplifies the detection signal and mitigates the influence of the matrix on the detection. It is demonstrated that this approach can not only detect and differentiate capsaicin and dihydrocapsaicin in complex real-world samples but also quantify the ibuprofen content in sustained-release capsules. Based on the 19F signals obtained in the detection using a set of three 19F probes, automated analyte identification is achieved, effectively reducing the odds of misrecognition caused by structural similarity.
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Affiliation(s)
- Zhenchuang Xu
- Key Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Ling-Ling Road, Shanghai 200032, China
| | - Siyi Gu
- Key Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Ling-Ling Road, Shanghai 200032, China
| | - Yipeng Li
- Key Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Ling-Ling Road, Shanghai 200032, China
| | - Jian Wu
- Instrumental Analysis Center, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Ling-Ling Road, Shanghai 200032, China
| | - Yanchuan Zhao
- Key Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Ling-Ling Road, Shanghai 200032, China.,Key Laboratory of Energy Regulation Materials, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Ling-Ling Road, Shanghai 200032, China
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4
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Kadilenko EM, Gritsan NP, Tretyakov EV, Fokin SV, Romanenko GV, Bogomyakov AS, Gorbunov DE, Schollmeyer D, Baumgarten M, Ovcharenko VI. A black-box approach to the construction of metal-radical multispin systems and analysis of their magnetic properties. Dalton Trans 2020; 49:16916-16927. [PMID: 33188374 DOI: 10.1039/d0dt03184d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
An interaction of M(hfac)2 (M = Mn or Ni) with N-(bis(4,4,5,5-tetramethyl-3-oxido-1-oxyl-4,5-dihydro-1H-imidazol-2-yl)methylene)-2-methyl-propan-2-amine oxide (a nitronyl nitroxide diradical with the >C[double bond, length as m-dash]N(O)-tert-Bu coupler) was investigated under various conditions. It was found that prolongation of reaction time caused transformation of the initial diradical into new diradicals with the unique >C[double bond, length as m-dash]N-OH coupling unit and formation of binuclear Mn(ii) and Ni(ii) complexes, which were characterized by X-ray diffraction analysis. The resulting binuclear heterospin complexes have a complicated magnetic structure with six paramagnetic centers and a number of exchange interaction channels between them, as well as between neighboring complexes. To adequately describe the magnetic properties of these complexes, high-level ab initio calculations of their electronic structure and parameters of the spin-Hamiltonian were carried out. The accuracy of the conventional broken-symmetry density functional theory approach in the calculation of the exchange interaction parameters was also verified.
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Affiliation(s)
- E M Kadilenko
- V. V. Voevodsky Institute of Chemical Kinetics and Combustion, 3 Institutskaya Str., Novosibirsk 630090, Russia.
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5
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Pour YS, Safaei E, Wojtczak A, Jagličić Z. Valence tautomerism in catecholato cobalt Bis(phenolate) diamine complexes as models for Enzyme–substrate adducts of catechol dioxygenases. Polyhedron 2020. [DOI: 10.1016/j.poly.2020.114620] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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6
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Uemura K, Taoka M. Isolation and characterization of a tetranuclear Pt-FeFe-Pt intermediate en route to the trinuclear Pt-Fe-Pt cluster. Dalton Trans 2017; 46:14012-14020. [PMID: 28976522 DOI: 10.1039/c7dt02583a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
An intermediate compound, [{PtFe(piam)2(NH3)2(OCH3)}2(μ-OCH3)2](ClO4)2 (1, piam = pivalamidate), in the synthetic process to form [Pt2Fe(piam)4(NH3)4](ClO4)3 (2) by mixing cis-[Pt(piam)2(NH3)2]·2H2O and iron sources was successfully isolated and characterized by single-crystal X-ray analysis. In 1, the platinum and iron atoms are bridged by two piam ligands to afford a dinuclear Pt-Fe structure and are further linked to each other by methoxide bridges at the equatorial positions of iron atoms to form a tetranuclear Pt-FeFe-Pt complex. The Pt-Fe distances in 1 are 3.0010(16) and 2.9883(17) Å, which are significantly longer than those in 2 (2.5566(15) and 2.5718(15) Å). X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and magnetic susceptibility measurements revealed that the oxidation states are Pt(+2)-Fe(+3)Fe(+3)-Pt(+2) (1) and Pt(+2)-Fe(+3)-Pt(+2) (2) with high-spin (S = 5/2) configurations in iron atoms. The magnetic susceptibility of 1 has a χT value of 5.83 cm3 mol-1 K per Pt(+2)-Fe(+3)Fe(+3)-Pt(+2) unit at 300 K, which decreases down to 0.04 cm3 mol-1 K at 7 K due to antiferromagnetic coupling (J = -28 cm-1) of the two Fe(+3) centers. Compound 2 maintains its trinuclear structure in MeCN, exhibiting reversible one-electron reduction and oxidation, Pt(+2)-Fe(+2)-Pt(+2) ↔ Pt(+2)-Fe(+3)-Pt(+2), at E1/2 = -0.19 V (vs. Fc/Fc+). However, in MeOH, compound 2 is decomposed into a dinuclear structure of Pt-Fe involving an equilibrium between 1 and 2.
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Affiliation(s)
- Kazuhiro Uemura
- Department of Chemistry and Biomolecular Science, Faculty of Engineering, Gifu University, Yanagido 1-1, Gifu, 501-1193, Japan.
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7
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Safaei E, Naghdi N, Jagličić Z, Pevec A, Lee YI. Synthesis and characterization of an iron(III) complex of an ethylenediamine derivative of an aminophenol ligand in relevance to catechol dioxygenase active site. Polyhedron 2017. [DOI: 10.1016/j.poly.2016.10.034] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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8
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Srivastav N, Mutneja R, Singh N, Singh R, Kaur V, Wagler J, Kroke E. Diverse Molecular Architectures of Si and Sn [4.4.3.0
1,6
]Tridecane Cages Derived from a Mannich Base Possessing Semi‐Rigid Unsymmetrical Podands. Eur J Inorg Chem 2016. [DOI: 10.1002/ejic.201600137] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Neha Srivastav
- Department of chemistry, Panjab University, Sector 14, Chandigarh 160014, India, http://chemistry.puchd.ac.in/show‐biodata.php?qstrempid=5532&qstrempdesigcode=10
| | - Ruchi Mutneja
- Department of chemistry, Panjab University, Sector 14, Chandigarh 160014, India, http://chemistry.puchd.ac.in/show‐biodata.php?qstrempid=5532&qstrempdesigcode=10
| | - Navjot Singh
- Department of chemistry, Panjab University, Sector 14, Chandigarh 160014, India, http://chemistry.puchd.ac.in/show‐biodata.php?qstrempid=5532&qstrempdesigcode=10
| | - Raghubir Singh
- Department of chemistry, DAV College, Sector 10, Chandigarh 160011, India, http://www.davchd.com
| | - Varinder Kaur
- Department of chemistry, Panjab University, Sector 14, Chandigarh 160014, India, http://chemistry.puchd.ac.in/show‐biodata.php?qstrempid=5532&qstrempdesigcode=10
| | - Jörg Wagler
- Institut für Anorganische Chemie, Technische Universität Bergakademie, Freiberg 09596 Freiberg, Germany
| | - Edwin Kroke
- Institut für Anorganische Chemie, Technische Universität Bergakademie, Freiberg 09596 Freiberg, Germany
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9
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Safak B, Yahsi Y, Gungor E, Kara H. Crystal structure and magnetic properties of dinuclear iron(III) complex with ONNO-donor ligand. J STRUCT CHEM+ 2016. [DOI: 10.1134/s0022476615080107] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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10
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Roberts AE, Schenk G, Gahan LR. A Heterodinuclear FeIIIZnIIComplex as a Mimic for Purple Acid Phosphatase with Site-Specific ZnIIBinding. Eur J Inorg Chem 2015. [DOI: 10.1002/ejic.201500351] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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11
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Badetti E, Gjoka B, Nagy EM, Bernardinelli G, Kündig PE, Zonta C, Licini G. Mononuclear Iron(III) Complexes as Functional Models of Catechol Oxidases and Catalases. Eur J Inorg Chem 2015. [DOI: 10.1002/ejic.201403225] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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12
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Coggins MK, Toledo S, Kovacs JA. Isolation and characterization of a dihydroxo-bridged iron(III,III)(μ-OH)2 diamond core derived from dioxygen. Inorg Chem 2013; 52:13325-31. [PMID: 24229319 PMCID: PMC3885352 DOI: 10.1021/ic4010906] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Dioxygen addition to coordinatively unsaturated [Fe(II)(O(Me2)N4(6-Me-DPEN))](PF6) (1) is shown to afford a complex containing a dihydroxo-bridged Fe(III)2(μ-OH)2 diamond core, [Fe(III)(O(Me2)N4(6-Me-DPEN))]2(μ-OH)2(PF6)2·(CH3CH2CN)2 (2). The diamond core of 2 resembles the oxidized methane monooxygenase (MMOox) resting state, as well as the active site product formed following H-atom abstraction from Tyr-OH by ribonucleotide reductase (RNR). The Fe-OH bond lengths of 2 are comparable with those of the MMOHox suggesting that MMOHox contains a Fe(III)2(μ-OH)2 as opposed to Fe(III)2(μ-OH)(μ-OH2) diamond core as had been suggested. Isotopic labeling experiments with (18)O2 and CD3CN indicate that the oxygen and proton of the μ-OH bridges of 2 are derived from dioxygen and acetonitrile. Deuterium incorporation (from CD3CN) suggests that an unobserved intermediate capable of abstracting a H-atom from CH3CN forms en route to 2. Given the high C-H bond dissociation energy (BDE = 97 kcal/mol) of acetonitrile, this indicates that this intermediate is a potent oxidant, possibly a high-valent iron oxo. Consistent with this, iodosylbenzene (PhIO) also reacts with 1 in CD3CN to afford the deuterated Fe(III)2(μ-OD)2 derivative of 2. Intermediates are not spectroscopically observed in either reaction (O2 and PhIO) even at low-temperatures (-80 °C), indicating that this intermediate has a very short lifetime, likely due to its highly reactive nature. Hydroxo-bridged 2 was found to stoichiometrically abstract hydrogen atoms from 9,10-dihydroanthracene (C-H BDE = 76 kcal/mol) at ambient temperatures.
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Affiliation(s)
| | | | - Julie A. Kovacs
- The Department of Chemistry, University of Washington: Box 351700 Seattle, WA 98195-1700
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13
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Kushch LA, Yagubskii EB, Simonov SV, Shibaeva RP, Suturina EA, Gritsan NP, Sadakov AV, Sulimenkov IV. Transformation of the [Mn
II
2
Mn
III
2
(hmp)
6
]
4+
Core into [Co
III
2
Mn
II
2
(hmp)
6
]
4+
in the Reaction of the [Mn
4
(hmp)
6
(NO
3
)
2
(H
2
O)
2
] Cluster with [CoX
4
]
2–
(X = Cl, Br). Eur J Inorg Chem 2013. [DOI: 10.1002/ejic.201300652] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Lyudmila A. Kushch
- Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russia, http://www.icp.ac.ru
| | - Eduard B. Yagubskii
- Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russia, http://www.icp.ac.ru
| | - Sergey V. Simonov
- Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russia
| | - Rimma P. Shibaeva
- Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russia
| | - Elizaveta A. Suturina
- Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, 630090 Novosibirsk, Russia, http://www.kinetics.nsc.ru
| | - Nina P. Gritsan
- Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, 630090 Novosibirsk, Russia, http://www.kinetics.nsc.ru
| | - Andrei V. Sadakov
- P. N. Lebedev Physical Institute, Russian Academy of Sciences, Leninskii av., 53, 119333 Moscow, Russia
| | - Il'ya V. Sulimenkov
- Branch of Institute for Energy Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russia
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14
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Heidari S, Safaei E, Wojtczak A, Cotič P, Kozakiewicz A. Iron(III) complexes of pyridine-based tetradentate aminophenol ligands as structural model complexes for the catechol-bound intermediate of catechol dioxygenases. Polyhedron 2013. [DOI: 10.1016/j.poly.2013.02.067] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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15
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Whiteoak CJ, Gjoka B, Martin E, Belmonte MM, Escudero-Adán EC, Zonta C, Licini G, Kleij AW. Reactivity Control in Iron(III) Amino Triphenolate Complexes: Comparison of Monomeric and Dimeric Complexes. Inorg Chem 2012; 51:10639-49. [DOI: 10.1021/ic3008624] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Christopher J. Whiteoak
- Institute of Chemical Research of Catalonia (ICIQ),
Av. Països Catalans 16, 43007 Tarragona, Spain
| | - Blerina Gjoka
- Dipartimento di Scienze Chimiche, Università di Padova, Via Marzolo 1, 35131,
Padova, Italy
| | - Eddy Martin
- Institute of Chemical Research of Catalonia (ICIQ),
Av. Països Catalans 16, 43007 Tarragona, Spain
| | - Marta Martínez Belmonte
- Institute of Chemical Research of Catalonia (ICIQ),
Av. Països Catalans 16, 43007 Tarragona, Spain
| | - Eduardo C. Escudero-Adán
- Institute of Chemical Research of Catalonia (ICIQ),
Av. Països Catalans 16, 43007 Tarragona, Spain
| | - Cristiano Zonta
- Dipartimento di Scienze Chimiche, Università di Padova, Via Marzolo 1, 35131,
Padova, Italy
| | - Giulia Licini
- Dipartimento di Scienze Chimiche, Università di Padova, Via Marzolo 1, 35131,
Padova, Italy
| | - Arjan. W. Kleij
- Institute of Chemical Research of Catalonia (ICIQ),
Av. Països Catalans 16, 43007 Tarragona, Spain
- Catalan Institute of Research and Advanced Studies (ICREA), Pg. Lluís Companys 23, 08010 Barcelona, Spain
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16
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Shongwe MS, Al-Zaabi UA, Al-Mjeni F, Eribal CS, Sinn E, Al-Omari IA, Hamdeh HH, Matoga D, Adams H, Morris MJ, Rheingold AL, Bill E, Sellmyer DJ. Accessibility and selective stabilization of the principal spin states of iron by pyridyl versus phenolic ketimines: modulation of the 6A1 ↔ 2T2 ground-state transformation of the [FeN4O2]+ chromophore. Inorg Chem 2012; 51:8241-53. [PMID: 22808945 DOI: 10.1021/ic300732r] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Several potentially tridentate pyridyl and phenolic Schiff bases (apRen and HhapRen, respectively) were derived from the condensation reactions of 2-acetylpyridine (ap) and 2'-hydroxyacetophenone (Hhap), respectively, with N-R-ethylenediamine (RNHCH(2)CH(2)NH(2), Ren; R = H, Me or Et) and complexed in situ with iron(II) or iron(III), as dictated by the nature of the ligand donor set, to generate the six-coordinate iron compounds [Fe(II)(apRen)(2)]X(2) (R = H, Me; X(-) = ClO(4)(-), BPh(4)(-), PF(6)(-)) and [Fe(III)(hapRen)(2)]X (R = Me, Et; X(-) = ClO(4)(-), BPh(4)(-)). Single-crystal X-ray analyses of [Fe(II)(apRen)(2)](ClO(4))(2) (R = H, Me) revealed a pseudo-octahedral geometry about the ferrous ion with the Fe(II)-N bond distances (1.896-2.041 Å) pointing to the (1)A(1) (d(π)(6)) ground state; the existence of this spin state was corroborated by magnetic susceptibility measurements and Mössbauer spectroscopy. In contrast, the X-ray structure of the phenolate complex [Fe(III)(hapMen)(2)]ClO(4), determined at 100 K, demonstrated stabilization of the ferric state; the compression of the coordinate bonds at the metal center is in accord with the (2)T(2) (d(π)(5)) ground state. Magnetic susceptibility measurements along with EPR and Mössbauer spectroscopic techniques have shown that the iron(III) complexes are spin-crossover (SCO) materials. The spin transition within the [Fe(III)N(4)O(2)](+) chromophore was modulated with alkyl substituents to afford two-step and one-step (6)A(1) ↔ (2)T(2) transformations in [Fe(III)(hapMen)(2)]ClO(4) and [Fe(III)(hapEen)(2)]ClO(4), respectively. Previously, none of the X-salRen- and X-sal(2)trien-based ferric spin-crossover compounds exhibited a stepwise transition. The optical spectra of the LS iron(II) and SCO iron(III) complexes display intense d(π) → p(π)* and p(π) → d(π) CT visible absorptions, respectively, which account for the spectacular color differences. All the complexes are redox-active; as expected, the one-electron oxidative process in the divalent compounds occurs at higher redox potentials than does the reverse process in the trivalent compounds. The cyclic voltammograms of the latter compounds reveal irreversible electrochemical generation of the phenoxyl radical. Finally, the H(2)salen-type quadridentate ketimine H(2)hapen complexed with an equivalent amount of iron(III) to afford the μ-oxo-monobridged dinuclear complex [{Fe(III)(hapen)}(2)(μ-O)] exhibiting a distorted square-pyramidal geometry at the metal centers and considerable antiferromagnetic coupling of spins (J ≈ -99 cm(-1)).
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Affiliation(s)
- Musa S Shongwe
- Department of Chemistry, College of Science, Sultan Qaboos University, PO Box 36, Al-Khod 123, Muscat, Sultanate of Oman.
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