Spectroscopic studies of a square-pyramidal nitridochromium(V) complex

Azuma, Nagao; Ozawa, Takehiro; Tsuboyama, Sei

doi:10.1039/dt9940002609

Cited by 24 publications

(15 citation statements)

References 36 publications

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“…In the EPR spectra of [Cr V (N)(oep)], [Cr V (N)(ttp)], and [Cr V (N)(bpb)] additional signals due to hyperfine interactions with 14 N nuclei ( I = 1) are reported. , In contrast to the pyrrol nitrogens in oep and ttp the amine nitrogens of the ligand cyclam in 5a carry a bound hydrogen with a nuclear spin of 1 / 2 which gives rise to a super-super hyperfine interaction. Thus 9 of the expected 13 signals of an Cr V N 6 octahedron are split into doublets.…”

Section: Resultsmentioning

confidence: 99%

Molecular and Electronic Structure of Nitridochromium(V) Complexes with Macrocyclic Amine Ligands

et al. 1998

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Photolysis of red cis- and trans-[CrIII(cyclam)(N3)2](ClO4) (1a, 2a) (cyclam = 1,4,8,11-tetraazacyclotetradecane) in the solid state or aqueous solution by light affords the nitridochromium(V) complexes of cis- or trans-[CrV(N)(cyclam)(N3)](ClO4) (3a) and dinuclear [{trans-[CrV(N)(cyclam)]}2(μ-N3)](ClO4)3·3.5H2O (4a), respectively. 4a was converted to the bis(tetraphenylborate)−azide−2C2H5OH salt (4b). Crystallization of 4a from acetonitrileafter addition of AgClO4 and removal of AgN3yields octahedral trans-[CrV(N)(cyclam)(NCCH3)](ClO4)2 (5a). The crystal structures of 1a, 2b (which is the tetraphenylborate salt of 2a), 4a,b, 5a,b have been determined by single-crystal X-ray crystallography. All nitridochromium(V) compounds contain the trans-[CrV(N)(cyclam)]2+ fragment with an N⋮CrV moiety (1.56 ± 0.01 Å). The electronic spectra of d1 configurated complexes display three low-intensity d−d bands which have been assigned in C 4 v symmetry as (xy) ((xz,yz) 2B2 → 2E, (xy) → (x 2 − y 2) 2B2 → 2B1, and (xy) → (z 2) 2B2 → 2A1, where the molecular z-axis coincides with the N⋮Cr vector. Ligand-field parameters within the angular overlap model (AOM) of e σ cyclam = 7300−8600, e σ ax = 22 000, e σ ax = 21300−25000 cm-1 have been determined which reproduce the experimental electronic spectra well. Temperature-dependent magnetic susceptibility measurements and X-band EPR spectroscopy on solid samples of 4a containing a linear CrV−NNN−CrV moiety revealed a weak intramolecular antiferromagnetic exchange coupling which is nearly absent in 4b containing a bent azido bridge. A mechanism for this unexpected coupling in 4a is proposed.

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Section: Resultsmentioning

confidence: 99%

Molecular and Electronic Structure of Nitridochromium(V) Complexes with Macrocyclic Amine Ligands

et al. 1998

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“… a This work. b Reference 26. c Reference 24. d L is N , N ‘-bis(pyridine-2-carbonyl)- o -phenylenediamine; ref . e mT.…”

Section: Resultsmentioning

confidence: 99%

ESR Studies of Oxochromium(V) Porphyrin Complexes: Electronic Structure of the Cr^VO Moiety

1997

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ESR spectra of oxochromium(V) porphyrins were obtained to investigate the electronic structure of the Cr(V)=O moiety. At room temperature, the chlorooxochromium(V) meso-tetramesitylporphyrin complex 1-Cl exhibits an isotropic ESR signal, split into nine signals due to hyperfine coupling with four equivalent( 14)N, at g = 1.982. A small isotropic satellite signal, split into a quartet due to hyperfine coupling by the (53)Cr isotope is also observed. At 77 K, 1-Cl shows an anisotropic ESR signal with g( parallel) = 1.986 and g( perpendicular) = 1.980 and small satellite g( parallel) signals arising from hyperfine coupling with the (53)Cr isotope. The ESR parameters of 1-Cl, obtained from ESR spectral simulation, show that the pi-bonding character of the Cr(V)=O bond is not as strong as that of the Cr(V)&tbd1;N bond. To explore substituent effects on the bond character of the Cr(V)=O moiety, ESR spectra of perchloratooxochromium(V) porphyrins having various electronegative substituents were recorded. With an increase in electronegativity of the meso-substituent, the g( perpendicular) value and the (53)Cr hyperfine coupling constant (|a((53)Cr)|) are increased. These changes suggest an increase in the pi-bonding character of the Cr(V)=O moiety with an increase in the electronegativity of the meso-substituent. Furthermore, the hyperfine coupling constant of the oxo ligand, |a((17)O)|, obtained from ESR spectra of (17)O-labeled oxochromium(V) porphyrin is increased with an increase in electronegativity of the meso-substituent. This indicates that the radical character of the oxo ligand is increased by the electronegative meso-substituent. These data suggest that the pi-antibonding orbital of Cr=O is destabilized with an increase in electronegativity of the meso-substituent, which may facilitate bond breaking of the Cr=O moiety in an epoxidation reaction.

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“…The line separating those of groups 8 and 9 is called the oxo wall . The instability of M–O complexes of groups 9–11 is due to the high electron number in the antibonding metal–oxygen orbitals of the complexes. − Accordingly, Ir–oxo complexes, which are parts of group 9, can neither be observed nor detected in experiments despite the high importance of understanding the formation mechanism and the electronic structures of Ir–oxo complexes.…”

Section: Introductionmentioning

confidence: 99%

Computational Study on the Light-Induced Oxidation of Iridium–Aqua Complex to Iridium–Oxo Complex over WO₃(001) Surface

et al. 2019

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An iridium aqua complex [Ir III (η 5 -C 5 Me 5 ){bpy-(COOH) 2 }(H 2 O)] 2+ under visible light irradiation has been experimentally reported to form an iridium−oxo (Ir−oxo) complex [Ir V (η 5 -C 5 Me 5 ){bpy(COOH) 2 }(O)] 2+ , which oxidizes H 2 O to O 2 . However, the mechanism for the formation of this Ir−oxo complex remains unclear, due to the difficulties in observing the unstable Ir− oxo complex and computing light-induced systems having different numbers of electrons. In this study, we perform density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to investigate more in detail our previously proposed deprotonation and light-induced oxidation reactions composing the formation of the Ir−oxo complex. In particular, we discuss effects of light irradiation and WO 3 support on the formation of the Ir−oxo complex. We suggest two distinct mechanisms, that is, direct and indirect for the light-induced oxidation. In the direct mechanism electrons are directly transferred from the occupied π* orbitals of Ir III −OH or Ir IV =O • to the conduction band of the WO 3 surface, whereas in the indirect mechanism electrons are first excited from the valence band to the conduction band of the WO 3 surface due to the UV light, and then the resultant electron hole oxidizes the Ir complex. In the direct mechanism, in particular, we found that the lowest energy of the anode's conduction band determines the adsorption wavelength of the light irradiation, enabling us to predict alternative semiconductor anodes for more efficient formation of the Ir−oxo complex.

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Spectroscopic studies of a square-pyramidal nitridochromium(V) complex

Cited by 24 publications

References 36 publications

Molecular and Electronic Structure of Nitridochromium(V) Complexes with Macrocyclic Amine Ligands

Molecular and Electronic Structure of Nitridochromium(V) Complexes with Macrocyclic Amine Ligands

ESR Studies of Oxochromium(V) Porphyrin Complexes: Electronic Structure of the Cr^VO Moiety

Computational Study on the Light-Induced Oxidation of Iridium–Aqua Complex to Iridium–Oxo Complex over WO₃(001) Surface

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Spectroscopic studies of a square-pyramidal nitridochromium(V) complex

Cited by 24 publications

References 36 publications

Molecular and Electronic Structure of Nitridochromium(V) Complexes with Macrocyclic Amine Ligands

Molecular and Electronic Structure of Nitridochromium(V) Complexes with Macrocyclic Amine Ligands

ESR Studies of Oxochromium(V) Porphyrin Complexes: Electronic Structure of the CrVO Moiety

Computational Study on the Light-Induced Oxidation of Iridium–Aqua Complex to Iridium–Oxo Complex over WO3(001) Surface

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Product

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ESR Studies of Oxochromium(V) Porphyrin Complexes: Electronic Structure of the Cr^VO Moiety

Computational Study on the Light-Induced Oxidation of Iridium–Aqua Complex to Iridium–Oxo Complex over WO₃(001) Surface