A model for the interpretation of the absorption and circular dichroism spectra of tris(di-imine) complexes of iron(II) and ruthenium(II)

Daul, Claude; Schlaepfer, C. W.

doi:10.1039/dt9880000393

Cited by 15 publications

(11 citation statements)

References 3 publications

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“…The interpretation of these CD signals is controversial, however. In particular, the CD band at the longest wavelength, which is missing in the spectra of the corresponding Ru(II) and Os(II) complexes, has been interpreted to be due to a 3d–3d transition mixed with charge-transfer ones. , The second and third CD bands are due to two d−π* MLCT transitions, although recent TDDFT calculations have reversed the assignments of the first and third bands. , These latter reports, however, clearly demonstrate that TDDFT methods have an inherent difficulty in treating transitions involving strong participation from 3d electrons. In all cases, following these calculations, one can rule out the hypothesis that the origin of the visible CD bands of [Fe(phen) 3 ] 2+ and [Fe(bipy) 3 ] 2+ is due to exciton coupling of d−π* transitions, as they lack the proper symmetry and/or dipole strength requirements for ECCD. , …”

Section: Resultsmentioning

confidence: 99%

“…For octahedral D 3 -symmetric tris -bidentate metal complexes with transition dipoles oriented parallel to the edges spanned by the ligands, exciton theory predicts the Δ configuration is associated with a negative exciton couplet, and vice-versa . 47–49 A CD couplet is defined negative if the first or long-wavelength Cotton effect is negative. The similarity with the present Fe(II) complexes suggests the same correlation holds.…”

Section: Introductionmentioning

confidence: 99%

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In Situ Assembly of Octahedral Fe(II) Complexes for the Enantiomeric Excess Determination of Chiral Amines Using Circular Dichroism Spectroscopy

et al. 2012

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A method for discriminating between α-chiral primary amine enantiomers is reported. The method utilizes circular dichroism spectroscopy and a sensing ensemble composed of 2-formyl-3-hydroxyl pyridine (4) and Fe(II)(TfO)2. Aldehyde 4 reacts rapidly with chiral amines to form chiral imines, which complex Fe(II) to form a series of diastereomeric octahedral complexes that are CD active in both the UV and visible spectrum. NMR studies showed that, for enantiomerically pure imine complexes, the Δ-fac isomer is preferred. A statistical analysis of the distribution of stereoisomers accurately models the calibration curves for enantiomeric excess. CD signals appearing in the UV region were bisignate, and the null of the CD signals were coincident with maxima in the UV spectrum, consistent with exciton coupling. TTDFT and semi-empirical calculations confirmed that the CD signals in the UV region arise from coupling of the π-π* transitions in the imine chromophores, and can be used to accurately describe the sign and magnitudes of the curves. The CD signals in the visible region arise from metal-to-ligand charge transfer bands, and these signals can be used to determine the ee values of chiral amines with an average absolute error of ±5%. Overall, the strategy presented herein represents a facile in situ assembly that uses commercially available simple reagents to create large optical signals indicative of ee values.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

In Situ Assembly of Octahedral Fe(II) Complexes for the Enantiomeric Excess Determination of Chiral Amines Using Circular Dichroism Spectroscopy

et al. 2012

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“…The transfer term should be the origin of the intensity of the MLCT transitions between the d and π* orbitals with a large resonance integral, and therefore, the transition dipole moment is oriented along the CT direction. The intense MLCT absorption in tris(2,2‘-bipyridine) complexes of Fe(II), Ru(II), and Os(II) with a D 3 point group is ascribed to the transfer term in e → e transitions. − Recent theoretical investigation of the phosphorescence in [ fac -Ir(ppy) 3 ] and [Ru(bpy) 3 ] 2+ has revealed that the lowest triplet state borrows the transfer term of the 1 dπ* (b 1 → b 1 ) transition in the pseudo- C 2 v point group…”

Section: Resultsmentioning

confidence: 99%

Highly Phosphorescent Iridium Complexes Containing Both Tridentate Bis(benzimidazolyl)-benzene or -pyridine and Bidentate Phenylpyridine: Synthesis, Photophysical Properties, and Theoretical Study of Ir-Bis(benzimidazolyl)benzene Complex

et al. 2006

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Novel mixed-ligand Ir(III) complexes, [Ir(L)(NwedgeC)X]n+ (L = N/\C/\N or N/\N/\N; X = Cl, Br, I, CN, CH3CN, or -CCPh; n = 0 or 1), were synthesized, where N/\CwedgeN = bis(N-methylbenzimidazolyl)benzene (Mebib) and bis(N-phenylbenzimidazolyl)benzene (Phbib), N/\N/\N = bis(N-methylbenzimidazolyl)pyridine (Mebip), and N/\C = phenylpyridine (ppy) derivatives. The X-ray crystal structures of [Ir(Phbib)(ppy)Cl] and [Ir(Mebib)(mppy)Cl] [mppy = 5-methyl-2-(2'-pyridyl)phenyl] indicate that the nitrogen atom of the ppy ligand is located trans to the coordinating carbon atom in Me- or Phbib, while the coordinating carbon atom in ppy occupies the trans position of Cl. [Ir(Mebip)(ppy)Cl]+ showed a quasireversible Ir(III/IV) oxidation wave at +1.05 V, while the Ir complexes, [Ir(Mebib)(ppy)Cl], were oxidized at +0.42 V versus Fc/Fc+. The introduction of an Ir-C bond in [Ir(Mebib)(ppy)Cl] induces a large potential shift of 0.63 V in a negative direction. Further, the oxidation potential of [Ir(Mebib)(Rppy)X] was altered by the substitution of R, R', and X groups. Compared to the oxidation potential, the first reduction potential revealed an almost constant value at -2.36 to -2.46 V for [Ir(L)(ppy)Cl] (L = Mebib and Phbib) and -1.52 V for [Ir(Mebip)(ppy)Cl. The UV-vis spectra of [Ir(Mebib)(R-ppy)X] show a clear singlet metal-to-ligand charge-transfer transition around 407 approximately 425 nm and a triplet metal-to-ligand charge-transfer transition at 498 approximately 523 nm. [Ir(Mebip)(ppy)Cl]+ emits at 610 nm with a luminescent quantum yield of Phi = 0.16 at room temperature. The phosphorescence of [Ir(Mebib)(ppy)X] was observed at 526 nm for X = CN and 555 nm for X = Cl with the high luminescent quantum yields, Phi = 0.77 approximately 0.86, at room temperature. [Ir(Phbib)(ppy)Cl] shows the emission at 559 nm with a luminescent quantum yield of Phi = 0.95, which is an unprecedentedly high value compared to those of other emissive metal complexes. Compared to the luminescent quantum yields of the Ir(ppy)2(L) derivatives and [Ir(Mebip)(ppy)Cl]+, the neutral Ir complexes, [Ir(L)(R-ppy)X] (L = Me- or Phbib), reveal very high quantum yields and large radiative rate constants (kr) ranging from 3.4 x 10(5) to 5.5 x 10(5) s(-1). The density functional theory calculation suggests that these Ir complexes possess dominantly metal-to-ligand charge-transfer and halide-to-ligand charge-transfer excited states. The mechanism for a high phosphorescence yield in [Ir(bib)(ppy)X] is discussed herein from the perspective of the theoretical consideration of radiative rate constants using perturbation theory and a one-center spin-orbit coupling approximation.

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“…This mixing results in an additional bonding (backbonding), since it stabilizes the HOMO e(dn;, rr~') and destabilizes the corresponding LUMO. The significance of this effect has already been stressed by Orgel [134] and later, for example, by Ceulemans and Vanquickenborne [135], Daul et al [138,139], and Ferguson and Herren [153]. It is assumed that the energy separation between the e and the al MOs (A in Fig.…”

Section: [Ru(bpy)~] ~+mentioning

confidence: 99%

“…11) is largely determined by this type of interaction. From [135,138,139,153,154], the corresponding value A is estimated to be of the order of 103 cm-L Obviously, the larger this backbonding or orbital mixture is, the more covalent is the complex, and consequently, less net charge transfer occurs upon excitation. In this context we want to mention the early conclusion given by Orgel [134], where he related already at that time the depression of the e orbital below the a~ orbital with an extensive delocalization of metal electrons into the ligands.…”

Section: [Ru(bpy)~] ~+mentioning

confidence: 99%

Characterization of excited electronic and vibronic states of platinum metal compounds with chelate ligands by highly frequency-resolved and time-resolved spectra

Yersin

Humbs

Strasser

1997

Topics in Current Chemistry

133

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The lowest excited electronic states of triplet character and related vibronic properties are discussed in detail on the basis of highly frequency-resolved and time-resolved emission and excitation spectra of per-protonated, per-deuterated, and partially deuterated [Pt(bpy)2] 2+, [Rh(bpy)3] 3+, [Ru(bpy)3] 2+, and [Os(bpy)3] ~+. Emphasis is placed on the use of the enormous amount of information displayed in well-resolved vibrational satellite structures. For comparison, IR data and Raman spectra are also used. In addition, data are given for [Ru(bpz)Pt(3-thpy) 2, Pt(2-thpy)(CO)(Cl), Pt(2-thpy) 2, Pt(qol)2, Pt(qtl)2. Trends and effects are also addressed, which are related to the amount of metal d-orbital mixing. In particular, we discuss the role of traps and sites in the context of high-resolution, site-selective, and line-narrowed spectra of chromophores doped into matrices; the interplay between states of ligand-centered 3rtrr* and ~MLCT character; localization versus delocalization behavior; radiative decay properties; zero-field splittings; spin-lattice relaxations via direct and Orbach mechanisms; Arrhenius behavior after time delay; Franck-Condon activities and Huang-Rhys factors; Franck-Condon versus Herzberg Teller activities and tunability of these activities under high magnetic fields; isotope marking and deuteration effects; aggregate formation of [Ru(bpy)3]2+; and radiationless energy transfer in neat [Ru(bpy)3](PF6) 2. These effects are in part treated in detail, but the aim is to use easy-to-follow descriptions. In particular, it is emphasized throughout this review that chemical tunability opens fascinating possibilities for controlled variation of physical properties.

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A model for the interpretation of the absorption and circular dichroism spectra of tris(di-imine) complexes of iron(II) and ruthenium(II)

Cited by 15 publications

References 3 publications

In Situ Assembly of Octahedral Fe(II) Complexes for the Enantiomeric Excess Determination of Chiral Amines Using Circular Dichroism Spectroscopy

In Situ Assembly of Octahedral Fe(II) Complexes for the Enantiomeric Excess Determination of Chiral Amines Using Circular Dichroism Spectroscopy

Highly Phosphorescent Iridium Complexes Containing Both Tridentate Bis(benzimidazolyl)-benzene or -pyridine and Bidentate Phenylpyridine: Synthesis, Photophysical Properties, and Theoretical Study of Ir-Bis(benzimidazolyl)benzene Complex

Characterization of excited electronic and vibronic states of platinum metal compounds with chelate ligands by highly frequency-resolved and time-resolved spectra

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