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Please use this identifier to cite or link to this item: http://repository.iitr.ac.in/handle/123456789/24668
Title: Singlet diradical complexes of chromium, molybdenum, and tungsten with azo anion radical ligands from M(CO)6 precursors
Authors: Bandyopadhyay, Anasuya
Chatterjee S.
Castiñeiras A.
Sarkar B.
Singh P.
Fiedler J.
Záliš S.
Kaim W.
Goswami S.
Published in: Inorganic Chemistry
Abstract: The homoleptic diamagnetic complexes M(mer-L)2, M = Cr, Mo,W (1a,b, 2a,b, and 4a,b), were obtained by reacting the hexacarbonyls M(CO) 6 with the tridentate ligands 2-[(2-N-arylamino)phenylazo]pyridine (HL = NH4C5N=NC6H4N(H)C 6H4(H) (HLa) or NH4C 5N=NC6H4N(H)C6H4(CH 3) (HLb)) in refluxing n-octane. In the case of M = Mo, the dinuclear compounds [Mo(L)(pap)]2(μ-O) (3a,b) (pap = 2-(phenylazo)pyridine), were obtained as second products in moist solvent. X-ray diffraction analysis for Cr(Lb)2 (1b), Mo(L a)2 (2a), and W(La)2 (4a) reveals considerably distorted-octahedral structures with trans-positioned azo-N atoms and cis-positioned 2-pyridyl-N and anilido nitrogen atoms. Whereas the N azo-M-Nazo angle is larger than 170°, the other two trans angles are smaller, at about 155° (M = Cr, 1b) or 146° (M = Mo, W; 2a, 4a), due to the overarching bite of the mer-tridentate ligands. The bonds from M to the neutral 2-pyridyl-N atoms are distinctly longer by more than 0.08 Å than those to the anilido or azo nitrogen atoms, reflecting negative charge on the latter. The N-N bond distances vary between 1.339(2) Å for 1b and 1.373(3) Å for 4a, clearly indicating the azo radical anion oxidation state. Considering the additional negative charge on anilido-N, the mononuclear complexes are thus formulated as MIV(L •2-)2. The diamagnetism of the complexes as shown by magnetic susceptibility and 1H NMR experiments is believed to result from spin-spin coupling between the trans-positioned azo radical functions, resulting in a singlet diradical situation. The experimental structures are well reproduced by density functional theory calculations, which also support the overall electronic structure indicated. The dinuclear 3a with N-N distances of 1.348(10) Å for La and 1.340(9) Å for pap is also formulated as an azo anion radical-containing molybdenum(IV) species, i.e., [MoIV(L•2-)(pap•-)] 2(μ-O). All compounds can be reversibly reduced; the Cr complexes 1a,b are also reversibly oxidized in two steps. Electron paramagnetic resonance spectroscopy indicates metal-centered spin for 1a+ and 1a- and g ≈ 2 signals for 2a-, 3a+, 3a-, and 4a_. Spectroelectrochemistry in the UV-vis-NIR region showed small changes for the reduction of 2a, 3a, and 4a but extensive spectral changes for the reduction and oxidation of 1a. © 2007 American Chemical Society.
Citation: Inorganic Chemistry, 46(21): 8584-8593
URI: https://doi.org/10.1021/ic700584x
http://repository.iitr.ac.in/handle/123456789/24668
Issue Date: 2007
Keywords: chromium
ligand
molybdenum
tungsten
chemical model
chemistry
conformation
electrochemistry
electron spin resonance
magnetism
methodology
near infrared spectroscopy
nuclear magnetic resonance spectroscopy
spectrophotometry
ultraviolet spectrophotometry
X ray diffraction
Chromium
Electrochemistry
Electron Spin Resonance Spectroscopy
Ligands
Magnetic Resonance Spectroscopy
Magnetics
Models, Chemical
Molecular Conformation
Molybdenum
Spectrophotometry
Spectrophotometry, Ultraviolet
Spectroscopy, Near-Infrared
Tungsten
X-Ray Diffraction
ISSN: 201669
Author Scopus IDs: 36999801800
55769748540
7006710796
7202875667
57197739435
7103170393
35598070800
7102267983
7102060926
Author Affiliations: Sanyal, A., Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata 700 032, India
Chatterjee, S., Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata 700 032, India
Castiñeiras, A., Departamento de Química Inorgánica, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain
Sarkar, B., Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany
Singh, P., Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany
Fiedler, J., J. Heyrovský Institute of Physical Chemistry, v.v.i., Academy of Sciences of the Czech Republic, Dolejškova 3, CZ-18223 Prague, Czech Republic
Záliš, S., J. Heyrovský Institute of Physical Chemistry, v.v.i., Academy of Sciences of the Czech Republic, Dolejškova 3, CZ-18223 Prague, Czech Republic
Kaim, W., Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany
Goswami, S., Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata 700 032, India
Corresponding Author: Kaim, W.; Institut für Anorganische Chemie, Pfaffenwaldring 55, D-70550 Stuttgart, Germany; email: Kaim@iac.uni-stuttgart.de
Appears in Collections:Journal Publications [PE]

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