Synthesis and characterization of trinuclear square-planar NiII3 and CuII3 complexes of an extended phloroglucinol ligand: Experimental evidence for the relative contributions of benzene-like and radialene-like resonance structures

Feldscher, Bastian; Stammler, Anja; Bögge, Hartmut; Glaser, Thorsten

doi:10.1016/j.poly.2011.02.029

Cited by 29 publications

(63 citation statements)

References 75 publications

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“…2a). This splitting pattern corresponds to that observed for our N-protonated ligands [46,47,50,51]. The presence of four doublets for the vinylic protons is indicative of the presence of two different geometrical isomers (C 3h and C s , Scheme 7) [28, 30, 31, 33 -37, 46, 47, 50, 82, 83].…”

Section: Synthesis and Characterizationsupporting

confidence: 78%

“…These absorption maxima are also present in the UV/Vis spectra of other of our extended phloroglucinol ligands (Fig. 3) and have been assigned to the heteroradialene backbone [46,47].…”

Section: Synthesis and Characterizationsupporting

confidence: 62%

“…Especially, prominent features in the 1700 -1400 cm −1 region cannot be explained by established assignments and trends derived for imineand/or salen-type ligands and complexes [46,47,49,51,63]. However, the realization that the π system of the central phloroglucinol backbone is heavily distorted toward a heteroradialene structure prompted us to ask whether these spectroscopic features may serve as a convenient method to evaluate the electronic structure of the ligand as well as of the complexes without high-resolution single-crystal diffraction data and NMR spectroscopy, which is not practicable for paramagnetic complexes.…”

Section: Introductionmentioning

confidence: 83%

“…They were therefore included in geometrically generated positions. In order to evaluate the calculated properties of the trialdimine H 3 13 Me , the n-butyl derivative H 3 13 nBu was synthesized analogously to H 3 felden [46] and H 3 felddien [47] by a Schiff base condensation of butylamine and H 3 11. The 1 H NMR spectrum of H 3 13 nBu exhibits four doublets (J = 14 Hz) between 8.3 -8.0 ppm and two poorly resolved multiplets between 11.5 -10.8 ppm (Fig.…”

Section: Synthesis and Characterizationmentioning

confidence: 99%

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Electronic and Molecular Structures of Heteroradialenes: A Combined Synthetic, Computational, Spectroscopic, and Structural Study Identifying IR Spectroscopy as a Simple but Powerful Experimental Probe

Richthofen

Feldscher

Lippert

et al. 2013

Zeitschrift Für Naturforschung B

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The vicinity of a hydrogen bond donor (O-H) and a hydrogen bond acceptor (C=O or C=N-R) in salicylaldehydes and ortho-Schiff bases results in significant structural variations compared to the monosubstituted derivatives that are reflected in the electronic structure and thus in the spectroscopic properties. This interplay between intramolecular hydrogen bonding and multicenter π-electron delocalization is the origin of the concept of resonance-assisted hydrogen bonding (RAHB). Herein, the complexity is extended from one hydrogen bond donor-acceptor pair in salicylaldehyde and ortho-Schiff bases to three hydrogen bond donor-acceptor pairs in 2,4,6-tricarbonyl-and 2,4,6-triimine-substituted phloroglucinols (1,3,5-trihydroxybenzene), respectively. To evaluate the changes in the molecular and electronic structures, we have performed a comprehensive computational, spectroscopic, and structural study starting from monosubstituted benzene derivatives as references over ortho-disubstituted derivates to the sixfold-substituted derivatives. Whereas in salicylaldehydes, ortho-Schiff bases, and 2,4,6-tricarbonyl-phloroglucinols the phenolic O-protonated tautomers represent the energy minima, the N-protonated tautomers represent the energy minima in 2,4,6-triiminephloroglucinols. The analysis provides a keto-enamine resonance structure with six exocyclic double bonds to be dominant for these species reminiscent of [6]radialenes, which were termed heteroradialenes. These heteroradialenes are non-aromatic alicycles. However, the predominance of this resonance structure does not represent a sudden change going from the 2,4,6-tricarbonyl-to the 2,4,6-triimine-phloroglucinols, but a gradual increase of analogous resonance structure contributions is observed even in salicylaldehyde and ortho-Schiff bases demonstrating some hetero-orthoquinodimethane character. These changes are, besides in the molecular structures, well reflected in the IR spectra, which can therefore be used as a simple tool to probe the electronic structures in these systems. Interruption of the delocalized π system supporting the intramolecular hydrogen bond, i. e. going from 2,4,6-triimine-to 2,4,6-triamine-substituted phloroglucinols, reestablishes an O-protonated aromatic phloroglucinol system.

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Section: Synthesis and Characterizationsupporting

confidence: 78%

“…These absorption maxima are also present in the UV/Vis spectra of other of our extended phloroglucinol ligands (Fig. 3) and have been assigned to the heteroradialene backbone [46,47].…”

Section: Synthesis and Characterizationsupporting

confidence: 62%

Section: Introductionmentioning

confidence: 83%

Section: Synthesis and Characterizationmentioning

confidence: 99%

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Electronic and Molecular Structures of Heteroradialenes: A Combined Synthetic, Computational, Spectroscopic, and Structural Study Identifying IR Spectroscopy as a Simple but Powerful Experimental Probe

Richthofen

Feldscher

Lippert

et al. 2013

Zeitschrift Für Naturforschung B

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“…Our investigations of trinuclear Ni II , Cu II , and Fe III complexes based on these ligands indicate that the heteroradialene resonance structure still prevails in the coordinated deprotonated form of the ligands, although to a lower extent than in the free ligands. 154,183,190 The C−C bond lengths of the central phloroglucinol rings in the [Mn III 6 Cr III ] 3+ compounds 1−6 are in the range of 1.40− 1.44 Å, with a mean value of 1.42 Å, which is slightly higher than the mean C−C bond length in the terminal phenolates (1.40 Å) serving as an internal reference. This clearly indicates some heteroradialene character of the central phloroglucinol backbone in [Mn III 6 Cr III ] 3+ , which is supported by the electronic absorption spectra exhibiting two strong features in the 27 000−35 000 cm −1 region and by the FT-IR spectra showing three strong bands at 1560, 1535, and 1491 cm −1 , which are typical signatures for a heteroradialene contribution to the resonance hybrid of the central backbone.…”

Section: Inorganic Chemistrymentioning

confidence: 97%

Environmental Influence on the Single-Molecule Magnet Behavior of [Mn^III₆Cr^III]³⁺: Molecular Symmetry versus Solid-State Effects

et al. 2012

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The structural, spectroscopic, and magnetic properties of a series of [Mn(III)(6)Cr(III)](3+) (= [{(talen(t-Bu(2)))Mn(III)(3)}(2){Cr(III)(CN)(6)}](3+)) compounds have been investigated by single-crystal X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and electronic absorption spectroscopy, elemental analysis, electro spray ionization-mass spectrometry (ESI-MS) and matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS), cyclic voltammetry, AC and DC magnetic measurements, as well as theoretical analysis. The crystal structures obtained with [Cr(III)(CN)(6)](3-) as a counterion exhibit (quasi-)one-dimensional (1D) chains formed by hydrogen-bonded (1) or covalently linked (2) trications and trianions. The rod-shaped anion lactate enforces a rod packing of the [Mn(III)(6)Cr(III)](3+) complexes in the highly symmetric space group R3[overline] (3) with a collinear arrangement of the molecular S(6) axes. Incorporation of the spherical anion BPh(4)(-) leads to less-symmetric crystal structures (4-6) with noncollinear orientations of the [Mn(III)(6)Cr(III)](3+) complexes, as evidenced by the angle between the approximate molecular C(3) axes taking no specific values in the range of 2°-69°. AC magnetic measurements on freshly isolated crystals (1a and 3a-6a), air-dried crystals (3b-6b), and vacuum-dried powder samples (3c-6c) indicate single-molecule magnet (SMM) behavior for all samples with U(eff) values up to 28 K. The DC magnetic data are analyzed by a full-matrix diagonalization of the appropriate spin-Hamiltonian including isotropic exchange, zero-field splitting, and Zeeman interaction, taking into account the relative orientation of the D-tensors. Simulations for 3a-6a and 3c-6c indicate a weak antiferromagnetic exchange between the Mn(III) ions in the trinuclear subunits (J(Mn-Mn) = -0.70 to -0.85 cm(-1), Ĥ(ex) = -2∑(i

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Aromatic Versus Heteroradialene Character in Extended Thiophloroglucinol Ligands and their Trinuclear Nickel(II) Complexes

Feldscher¹,

Stammler²,

Bögge³

et al. 2014

Chemistry An Asian Journal

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Extended phloroglucinol ligands and complexes are best described as nonaromatic heteroradialenes. Herein, the electronic structures of extended thiophloroglucinol ligands and their Ni(II) 3 complexes are evaluated by comparison to their phloroglucinol analogs by means of NMR, FTIR, UV/Vis, and structural parameters. To provide a full set of compounds for this comparison of S versus O substitution, a new triplesalen ligand, its Ni(II) 3 complex, and a new thiophloroglucinol were synthesized. (1) H and (15) N NMR chemical shifts and coupling constants prove that the thiophloroglucinol ligands exist as the N-protonated and not the O-protonated tautomer. (13) C and (15) N NMR chemical shifts and structural parameters further demonstrated that the extended thiophloroglucinol ligands must be described with a predominant thione-enamine (heteroradialene) character despite the participation of a CS double bond. In the Ni(II) 3 complexes, this heteroradialene character is reduced but still predominant.

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Synthesis and characterization of trinuclear square-planar NiII3 and CuII3 complexes of an extended phloroglucinol ligand: Experimental evidence for the relative contributions of benzene-like and radialene-like resonance structures

Cited by 29 publications

References 75 publications

Electronic and Molecular Structures of Heteroradialenes: A Combined Synthetic, Computational, Spectroscopic, and Structural Study Identifying IR Spectroscopy as a Simple but Powerful Experimental Probe

Electronic and Molecular Structures of Heteroradialenes: A Combined Synthetic, Computational, Spectroscopic, and Structural Study Identifying IR Spectroscopy as a Simple but Powerful Experimental Probe

Environmental Influence on the Single-Molecule Magnet Behavior of [Mn^III₆Cr^III]³⁺: Molecular Symmetry versus Solid-State Effects

Aromatic Versus Heteroradialene Character in Extended Thiophloroglucinol Ligands and their Trinuclear Nickel(II) Complexes

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Synthesis and characterization of trinuclear square-planar NiII3 and CuII3 complexes of an extended phloroglucinol ligand: Experimental evidence for the relative contributions of benzene-like and radialene-like resonance structures

Cited by 29 publications

References 75 publications

Electronic and Molecular Structures of Heteroradialenes: A Combined Synthetic, Computational, Spectroscopic, and Structural Study Identifying IR Spectroscopy as a Simple but Powerful Experimental Probe

Electronic and Molecular Structures of Heteroradialenes: A Combined Synthetic, Computational, Spectroscopic, and Structural Study Identifying IR Spectroscopy as a Simple but Powerful Experimental Probe

Environmental Influence on the Single-Molecule Magnet Behavior of [MnIII6CrIII]3+: Molecular Symmetry versus Solid-State Effects

Aromatic Versus Heteroradialene Character in Extended Thiophloroglucinol Ligands and their Trinuclear Nickel(II) Complexes

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Environmental Influence on the Single-Molecule Magnet Behavior of [Mn^III₆Cr^III]³⁺: Molecular Symmetry versus Solid-State Effects