o-Iminobenzosemiquinonate and o-Imino-p-methylbenzosemiquinonate Anion Radicals Coupled VO2þ Stabilization

Saha Roy, Amit and Saha, Pinaki and Das Adhikary, Nirmal and Ghosh, Prasanta (2011) o-Iminobenzosemiquinonate and o-Imino-p-methylbenzosemiquinonate Anion Radicals Coupled VO2þ Stabilization. Inorganic Chemistry, 50. pp. 2488-2500.

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    Abstract

    The diamagnetic VO2þ-iminobenzosemiquinonate anion radical (LR IS •-, R = H, Me) complexes, (L-)(VO2þ)(LR IS •-): (L1 -)(VO2þ)(LH IS •-)•3/2MeOH (1•3/2MeOH), (L2 -)(VO2þ)(LH IS •-) (2), and (L2 -)(VO2þ)(LMe IS •-)•1/2 LMe AP (3•1/2 LMe AP), incorporating tridentate monoanionic NNO-donor ligands {L = L1 - or L2 -, L1H = (2-[(phenylpyridin-2-yl-methylene) amino]phenol; L2H = 1-(2-pyridylazo)-2-naphthol; LH IS •- = o-iminobenzosemiquinonate anion radical; LMe IS •- = o-imino-p-methylbenzosemiquinonate anion radical; and LMe AP = o-amino-p-methylphenol} have been isolated and characterized by elemental analyses, IR, mass,NMR, and UV-vis spectra, including the single-crystal X-ray structure determinations of 1•3/2MeOH and 3•1/2 LMe AP. Complexes 1•3/2MeOH, 2, and 3•1/2 LMe AP absorb strongly in the visible region because of intraligand (IL) and ligand-to-metal charge transfers (LMCT). 1•3/2MeOH is luminescent (λext, 333 nm; λem, 522, 553 nm) in frozen dichloromethane- toluene glass at 77 K due to πdiimine f πdiimine* transition. The V-Ophenolato (cis to the VdO) lengths, 1.940(2) and 1.984(2) Å, respectively, in 1•3/2MeOH and 3•1/2 LMe AP are consistent with the VO2þ description. The V-Oiminosemiquinonate (trans to the VdO) lengths, 2.1324(19) in 1•3/2MeOH and 2.083(2) Å in 3•1/2 LMe AP, are expectedly ∼0.20 Å longer due to the trans influence of the VdO bond. Because of the stronger affinity of the paramagnetic VO2þ ion to the LH IS •- or LMe IS •-, the VNiminosemiquinonate lengths, 1.908(2) and 1.921(2) Å, respectively, in 1•3/2MeOH and 3•1/2 LMe AP, are unexpectedly shorter. Density functional theory (DFT) calculations using B3LYP, B3PW91, and PBE1PBE functionals on 1 and 2 have established that the closed shell singlet (CSS) solutions (VO3þ-amidophenolato (LR AP 2-) coordination) of these complexes are unstable with respect to triplet perturbations. But BS (1,1)Ms = 0 (VO2þ-iminobenzosemiquinonate anion radical (LR IS •-) coordination) solutions of these species are stable and reproduce the experimental bond parameters well. Spin density distributions of one electron oxidized cations are consistent with the [(L-)(VO2þ)(LR IQ)]þ descriptions [VO2þ-o-iminobenzoquinone (LR IQ) coordination], and one electron reduced anions are consistent with the [(L•2-)(VO3þ)(LR AP 2-)]- descriptions [VO3þ-amidophenolato (LR AP 2-) coordination], incorporating the diimine anion radical (L1 •2-) or azo anion radical (L2 3-). Although, cations and anions are not isolable, but electro-and spectro-electrochemical experiments have shown that 3þ and 3- ions are more stable than 1þ, 2þ and 1-, 2- ions. In all cases, the reductions occur with simultaneous two electron transfer, may be due to formation of coupled diimine/azo anion radical- VO2þ species as in [(L•2-)(VO2þ)(LR AP 2-)]2-

    Item Type: Article
    URI: http://www.eprints.iicb.res.in/id/eprint/107
    Subjects: Chemistry
    Divisions: Indian Institute of Chemical Biology
    Depositing User: Ms Sutapa Ganguly
    Date Deposited: 29 Sep 2011 11:37
    Last Modified: 29 Sep 2011 11:53
    Official URL: http://dx.doi.org/10.1021/ic102296p
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