o-Iminobenzosemiquinonate and o-Imino-p-methylbenzosemiquinonate Anion Radicals Coupled VO2+ Stabilization

• Published in: Inorganic chemistry 2011-03, Vol.50 (6), p.2488-2500
• Main Authors: Roy, Amit Saha, Saha, Pinaki, Adhikary, Nirmal Das, Ghosh, Prasanta
• Format: Article
• Language: English
• Subjects: Benzoquinones - chemistry; Crystallography, X-Ray; Models, Molecular; Molecular Structure; Organometallic Compounds - chemical synthesis; Organometallic Compounds - chemistry; Quantum Theory; Vanadium Compounds - chemistry
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic102296p

The diamagnetic VO2+-iminobenzosemiquinonate anion radical (LR IS •−, R = H, Me) complexes, (L−)(VO2+)(LR IS •−): (L1 −)(VO2+)(LH IS •−)•3/2MeOH (1•3/2MeOH), (L2 −)(VO2+)(LH IS •−) (2), and (L2 − )(VO2+)(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→πdiimine* transition. The V−Ophenolato (cis to the VO) lengths, 1.940(2) and 1.984(2) Å, respectively, in 1•3/2MeOH and 3•1/2 LMe AP are consistent with the VO2+ description. The V−Oiminosemiquinonate (trans to the VO) 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 VO bond. Because of the stronger affinity of the paramagnetic VO2+ ion to the LH IS •− or LMe IS •−, the V−Niminosemiquinonate 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 (VO 3+ -amidophenolato (L R AP 2− ) coordination) of these complexes are unstable with respect to triplet perturbations. But BS (1,1) Ms = 0 (VO2+-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−)(VO2+)(LR IQ)]+ descriptions [VO2+-o-iminobenzoquinone (LR IQ) coordination], and one electron reduced anions are consistent with the [(L•2-)(VO3+)(LR AP 2-)]− descriptions [VO3+-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, b