Intersystem crossing observed by ultrasonic relaxation of the singlet-quintet spin equilibrium of iron(II) complexes in solution

Beattie, James K.; Binstead, Robert A.; West, Robert J.

doi:10.1021/ja00478a016

Cited by 78 publications

(41 citation statements)

References 5 publications

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“…[13][14][15] The volume of activation found for the binding of NO in the present study lies within this range of values and supports that Fe-NO bond formation can involve a contribution from the high-spin to lowspin transition. 17500 Ϯ 300 35 Ϯ 1 -47 Ϯ 5 -5 [b] 2620 Ϯ 160 12.5 Ϯ 0.7 -133 Ϯ 2 -6.7 Ϯ 0.3…”

Section: Kinetic Studies Of the Binding Of No To [Fe(s 4 Net 2 N)] Frsupporting

confidence: 85%

Mechanistic Information on the Reversible Binding of NO to Mono‐ and Dinuclear Fe^II Complexes of a Biomimetic S₄N Ligand

Shaban

Eldik

2010

Eur J Inorg Chem

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Structural and mechanistic information on the binding of NO to mono-and dinuclear [Fe II (S 4 NNEt 2 )] fragments as potential catalysts for the removal of NO from effluent gas streams have been obtained from concentration, temperature and pressure dependent kinetic measurements using stoppedflow techniques. The results indicate that the steric and electronic structure only affect the rate but not the nature of the binding mechanism by which NO coordinates to the selected complexes. Therefore, the sterically hindered dinuclear complex [Fe II (S 4 NNEt 2 )] 2 binds NO ca. eight times slower than

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Section: Kinetic Studies Of the Binding Of No To [Fe(s 4 Net 2 N)] Frsupporting

confidence: 85%

Mechanistic Information on the Reversible Binding of NO to Mono‐ and Dinuclear Fe^II Complexes of a Biomimetic S₄N Ligand

Shaban

Eldik

2010

Eur J Inorg Chem

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“…The thermal interconversion rates of the S = 0 and S = 2 states of Fe" complexes (29,30) have been found to lie in the 10-to 100-ns range. This rate depends sensitively on the energy difference between the interconverting spin states, but it is implausible that a high-spin complex could have been generated within 30 ps from a S = 0 photolysis product.…”

Section: Methodsmentioning

confidence: 97%

Picosecond resonance Raman spectroscopic evidence for excited-state spin conversion in carbonmonoxy-hemoglobin photolysis

Terner

Stong

Spiro

et al. 1981

Proc. Natl. Acad. Sci. U.S.A.

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The structure of the carbonmonoxy-hemoglobin (COHb) photoproduct has been studied on the picosecond time scale with resonance Raman spectroscopy, by tightly focusing the 30-ps pulses of a synchronously pumped mode-locked cavitydumped dye laser on ajet stream of COHb solution. The spectrum of the photoproduct is similar to that of deoxy Hb, but the frequencies 1603 cm-1 (depolarized), 1552 cm-' (anomalously polarized), and 1542 cm-t (depolarized) are 2-4 cm-' lower than those of deoxy Hb. Similar low frequencies are observed for a species believed to be the bis-tetrahydrofuran adduct of Fei" octaethylporphyrin, containing in-plane high-spin Fe",. These results indicate that in the COHb photoproduct the Fe" is already high-spin but is closer to the heme plane than in deoxy Hb. Photodissociation from a quintet ligand-field excited state of COHb is suggested. The frequency shifts relative to deoxy Hb persist when the laser pulses are lengthened to 20 ns. The apparently slow relaxation to the fully out-of-lane heme conformation of deoxy Hb is suggested to be associate with change of the globin tertiary structure.The efficient photodissociation of CO from carbonmonoxyhemoglobin (COHb) has long been exploited to study the kinetics of ligand binding to the freshly generated deoxy Hb (1). With the advent of lasers generating ultrashort pulses, the dynamics of the photodissociation itself have been under active investigation (2-10). The initial absorbance change upon laser excitation is very fast, the rise time being reported as <1 ps (2) or 11 ps (3); the difference is possibly related to the laser wavelength (3). It is presumed, although not proven, that CO dissociates in this fast process. The optical spectrum of the initial photolysis product (4) resembles that of deoxy Hb, but the absorption bands are broader. The broadened spectrum persists for at least 680 ps.The structure of this initial photoproduct is of considerable interest. It can be probed with resonance Raman (RR) spectroscopy, which is capable of monitoring heme structure inside heme proteins by virtue of the large enhancements observed for the porphyrin vibrational modes when the laser excitation wavelength is brought into resonance with the intense heme absorption bands (11). The frequencies of some of these modes vary in response to changes in heme geometry and electronic structure (12). The influence of porphyrin core expansion (13,14), and of electron donation into the porphyrin i7r* orbitals (12,15,16), have been well characterized. Three recent studies (5-7), using 5-to 10-ns laser pulses to photolyze COHb and simultaneously to generate RR spectra, have established that on this time scale the RR bands are characteristic of deoxy Hb. Lyons et al. (7), however, reported slight but definite frequency lowerings of the observed bands relative to deoxy Hb, and this has been confirmed by W. H. Woodruff (personal communication).We have now determined that this spectrum is already developed within 30 ps of COHb photolysis and that it persists to at ...

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“…Among the field of SCO complexes, the influence of different types of N-or O-donor on metal ions spin states is more subtle, and harder to quantify from available solution-phase data. On one hand, SCO equilibria in [Fe(HBpz 3 ) 2 ] (in thf or a chlorinated solvent [33,34] [86] (Scheme 6). Thus, replacement of pyridyl by pyrazinyl donors stabilizes the low-spin state of these complexes to a small extent.…”

Section: Influence Of Ligand Donor Types On Metal Ion Spin Statementioning

confidence: 99%

The Effect of Ligand Design on Metal Ion Spin State—Lessons from Spin Crossover Complexes

2016

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Abstract:The relationship between chemical structure and spin state in a transition metal complex has an important bearing on mechanistic bioinorganic chemistry, catalysis by base metals, and the design of spin crossover materials. The latter provide an ideal testbed for this question, since small changes in spin state energetics can be easily detected from shifts in the spin crossover equilibrium temperature. Published structure-function relationships relating ligand design and spin state from the spin crossover literature give varied results. A sterically crowded ligand sphere favors the expanded metal-ligand bonds associated with the high-spin state. However, steric clashes at the molecular periphery can stabilize either the high-spin or the low-spin state in a predictable way, depending on their effect on ligand conformation. In the absence of steric influences, the picture is less clear since electron-withdrawing ligand substituents are reported to favor the low-spin or the high-spin state in different series of compounds. A recent study has shed light on this conundrum, showing that the electronic influence of a substituent on a coordinated metal ion depends on its position on the ligand framework. Finally, hydrogen bonding to complexes containing peripheral N-H groups consistently stabilizes the low-spin state, where this has been quantified.

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Intersystem crossing observed by ultrasonic relaxation of the singlet-quintet spin equilibrium of iron(II) complexes in solution

Cited by 78 publications

References 5 publications

Mechanistic Information on the Reversible Binding of NO to Mono‐ and Dinuclear Fe^II Complexes of a Biomimetic S₄N Ligand

Mechanistic Information on the Reversible Binding of NO to Mono‐ and Dinuclear Fe^II Complexes of a Biomimetic S₄N Ligand

Picosecond resonance Raman spectroscopic evidence for excited-state spin conversion in carbonmonoxy-hemoglobin photolysis

The Effect of Ligand Design on Metal Ion Spin State—Lessons from Spin Crossover Complexes

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Intersystem crossing observed by ultrasonic relaxation of the singlet-quintet spin equilibrium of iron(II) complexes in solution

Cited by 78 publications

References 5 publications

Mechanistic Information on the Reversible Binding of NO to Mono‐ and Dinuclear FeII Complexes of a Biomimetic S4N Ligand

Mechanistic Information on the Reversible Binding of NO to Mono‐ and Dinuclear FeII Complexes of a Biomimetic S4N Ligand

Picosecond resonance Raman spectroscopic evidence for excited-state spin conversion in carbonmonoxy-hemoglobin photolysis

The Effect of Ligand Design on Metal Ion Spin State—Lessons from Spin Crossover Complexes

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Mechanistic Information on the Reversible Binding of NO to Mono‐ and Dinuclear Fe^II Complexes of a Biomimetic S₄N Ligand

Mechanistic Information on the Reversible Binding of NO to Mono‐ and Dinuclear Fe^II Complexes of a Biomimetic S₄N Ligand