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

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Title o-Iminobenzosemiquinonate and
o-Imino-p-methylbenzosemiquinonate Anion
Radicals Coupled VO2þ Stabilization
 
Creator Saha Roy, Amit
Saha, Pinaki
Das Adhikary, Nirmal
Ghosh, Prasanta
 
Subject Chemistry
 
Description 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-
 
Date 2011
 
Type Article
PeerReviewed
 
Format application/pdf
 
Identifier http://www.eprints.iicb.res.in/107/1/INORGANIC_CHEMISTRY%2C50(6)%2C_2488%2D2500%2C2011[79].pdf
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.
 
Relation http://dx.doi.org/10.1021/ic102296p
http://www.eprints.iicb.res.in/107/