FeII and CoII Complexes with Click‐Derived Tripodal Ligands: Influence of the Peripheral Substituents on Geometric Structures and Magnetic Properties

Schweinfurth, David; Demeshko, Serhiy; Sommer, Michael; Dechert, Sebastian; Meyer, Franc; Sarkar, Biprajit

doi:10.1002/ejic.201501385

Cited by 11 publications

(13 citation statements)

References 57 publications

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“…If this is attributed entirely to TIP, then the admixture of excited states is very large (χ TIP ≈ 3.4 × 10 –3 cm 3 mol –1 ). We note that large TIP has been reported in systems where other excited spin-states are accessible, − and is evident in frozen solution for Fe(II) triazacyclononane complexes …”

Section: Resultsmentioning

confidence: 52%

A Synthetically Tunable System To Control MLCT Excited-State Lifetimes and Spin States in Iron(II) Polypyridines

et al. 2017

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2,2':6',2″-Terpyridyl (tpy) ligands modified by fluorine (dftpy), chlorine (dctpy), or bromine (dbtpy) substitution at the 6- and 6″-positions are used to synthesize a series of bis-homoleptic Fe(II) complexes. Two of these species, [Fe(dctpy)] and [Fe(dbtpy)], which incorporate the larger dctpy and dbtpy ligands, assume a high-spin quintet ground state due to substituent-induced intramolecular strain. The smaller fluorine atoms in [Fe(dftpy)] enable spin crossover with a T of 220 K and a mixture of low-spin (singlet) and high-spin (quintet) populations at room temperature. Taking advantage of this equilibrium, dynamics originating from either the singlet or quintet manifold can be explored using variable wavelength laser excitation. Pumping at 530 nm leads to ultrafast nonradiative relaxation from the singlet metal-to-ligand charge transfer (MLCT) excited state into a quintet metal centered state (MC) as has been observed for prototypical low-spin Fe(II) polypyridine complexes such as [Fe(tpy)]. On the other hand, pumping at 400 nm excites the molecule into the quintet manifold (MLCT ← MC) and leads to the observation of a greatly increased MLCT lifetime of 14.0 ps. Importantly, this measurement enables an exploration of how the lifetime of theMLCT (or MLCT, in the event of intersystem crossing) responds to the structural modifications of the series as a whole. We find that increasing the amount of steric strain serves to extend the lifetime of theMLCT from 14.0 ps for [Fe(dftpy)] to the largest known value at 17.4 ps for [Fe(dbtpy)]. These data support the design hypothesis wherein interligand steric interactions are employed to limit conformational dynamics and/or alter relative state energies, thereby slowing nonradiative loss of charge-transfer energy.

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Section: Resultsmentioning

confidence: 52%

A Synthetically Tunable System To Control MLCT Excited-State Lifetimes and Spin States in Iron(II) Polypyridines

et al. 2017

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“…[49a], [49b] It was also seen that if analogous complexes of 45 2+ crystallize with solvents, the solvent molecules destroy the C–H ··· π interactions and prevent SCO in that molecule (Figure ). [49a] Additionally, changing the peripheral substituents on the tripodal ligand and moving to tpta instead of tbta (Figure ) leads to the observance of a different first coordination sphere (coordination only through the triazole donors) at the central iron(II) atom and this complex does not show SCO either . Thus, the observance of SCO in these complexes seems to be critically related to the use of the tbta ligand and accordingly to the formation of the C–H ··· π interactions on the secondary coordination sphere.…”

Section: Discussionmentioning

confidence: 99%

“…Thus, the observance of SCO in these complexes seems to be critically related to the use of the tbta ligand and accordingly to the formation of the C–H ··· π interactions on the secondary coordination sphere. [49a], [49b], …”

Section: Discussionmentioning

confidence: 99%

Metal Complexes of Click-Derived Triazoles and Mesoionic Carbenes: Electron Transfer, Photochemistry, Magnetic Bistability, and Catalysis

Schweinfurth

Hettmanczyk

Suntrup

et al. 2017

Z. Anorg. Allg. Chem.

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159

104

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Abstract. Even though the existence of 1,2,3-triazoles has been known for more than a century, the recent discovery of a copper(I) catalyzed version of this reaction has attributed unprecedented importance to these compounds. Coordination and organometallic chemists have benefited from this modular synthetic route, and have accessed ligands based on both the triazoles as well as the triazolylidenes. The wide variation of steric and electronic properties that can be achieved for this ligand class has made them useful for generating metal complexes

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“…19,20 This interesting property was dependent on the peripheral substituents of tbta. 21 Furthermore, tbta is a useful coligand for investigating magnetic exchange in di-Co(II) complexes. 22 From among the many paramagnetic 3d ions, Co(II) has played a significant role in recent years with respect to molecular magnetism.…”

Section: ■ Introductionmentioning

confidence: 99%

“…The magnetic anisotropy of Ni(II) and Co(II) complexes with such ligands has been investigated. More significantly, Fe(II) and Co(II) complexes specifically with [(1-benzyl-1 H -1,2,3-triazol-4-yl)methyl]-amine (tbta) ligands display temperature induced spin crossover behavior. , This interesting property was dependent on the peripheral substituents of tbta . Furthermore, tbta is a useful coligand for investigating magnetic exchange in di-Co(II) complexes …”

Section: Introductionmentioning

confidence: 99%

Tuning Magnetic Anisotropy Through Ligand Substitution in Five-Coordinate Co(II) Complexes

et al. 2017

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Understanding the origin of magnetic anisotropy and having the ability to tune it are essential needs of the rapidly developing field of molecular magnetism. Such attempts at determining the origin of magnetic anisotropy and its tuning are still relatively infrequent. One candidate for such attempts are mononuclear Co(II) complexes, some of which have recently been shown to possess slow relaxation of their magnetization. In this contribution we present four different five-coordinated Co(II) complexes, 1-4, that contain two different "click" derived tetradentate tripodal ligands and either Cl or NCS as an additional, axial ligand. The geometric structures of all four complexes are very similar. Despite this, major differences are observed in their electronic structures and hence in their magnetic properties as well. A combination of temperature dependent susceptibility measurements and high-frequency and -field EPR (HFEPR) spectroscopy was used to accurately determine the magnetic properties of these complexes, expressed through the spin Hamiltonian parameters: g-values and zero-field splitting (ZFS) parameters D and E. A combination of optical d-d absorption spectra together with ligand field theory was used to determine the B and Dq values of the complexes. Additionally, state of the art quantum chemical calculations were applied to obtain bonding parameters and to determine the origin of magnetic anisotropy in 1-4. This combined approach showed that the D values in these complexes are in the range from -9 to +9 cm. Correlations have been drawn between the bonding nature of the ligands and the magnitude and sign of D. These results will thus have consequences for generating novel Co(II) complexes with tunable magnetic anisotropy and hence contribute to the field of molecular magnetism.

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FeII and CoII Complexes with Click‐Derived Tripodal Ligands: Influence of the Peripheral Substituents on Geometric Structures and Magnetic Properties

Cited by 11 publications

References 57 publications

A Synthetically Tunable System To Control MLCT Excited-State Lifetimes and Spin States in Iron(II) Polypyridines

A Synthetically Tunable System To Control MLCT Excited-State Lifetimes and Spin States in Iron(II) Polypyridines

Metal Complexes of Click-Derived Triazoles and Mesoionic Carbenes: Electron Transfer, Photochemistry, Magnetic Bistability, and Catalysis

Tuning Magnetic Anisotropy Through Ligand Substitution in Five-Coordinate Co(II) Complexes

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