13 research outputs found
Synthesis and Characterization of a High-Symmetry Ferrous Polypyridyl Complex: Approaching the <sup>5</sup>T<sub>2</sub>/<sup>3</sup>T<sub>1</sub> Crossing Point for Fe<sup>II</sup>
Electronic structure theory predicts
that, depending on the strength
of the ligand field, either the quintet (<sup>5</sup>T<sub>2</sub>) or triplet (<sup>3</sup>T<sub>1</sub>) term states can be stabilized
as the lowest-energy ligand-field excited state of low-spin octahedral
d<sup>6</sup> transition-metal complexes. The <sup>3</sup>T<sub>1</sub> state is anticipated for second- and third-row metal complexes and
has been established for certain first-row compounds such as [Co(CN)<sub>6</sub>]<sup>3–</sup>, but in the case of the widely studied
Fe<sup>II</sup> ion, only the <sup>5</sup>T<sub>2</sub> state has
ever been documented. Herein we report that 2,6-bis(2-carboxypyridyl)pyridine
(dcpp), when bound to Fe<sup>II</sup>, presents a sufficiently strong
ligand field to Fe<sup>II</sup> such that the <sup>5</sup>T<sub>2</sub>/<sup>3</sup>T<sub>1</sub> crossing point of the d<sup>6</sup> configuration
is approached if not exceeded. The electrochemical and photophysical
properties of [Fe(dcpp)<sub>2</sub>]<sup>2+</sup>, in addition to
being of fundamental interest, may also have important implications
for solar energy conversion strategies that seek to utilize earth-abundant
components
Synthesis and Characterization of a High-Symmetry Ferrous Polypyridyl Complex: Approaching the <sup>5</sup>T<sub>2</sub>/<sup>3</sup>T<sub>1</sub> Crossing Point for Fe<sup>II</sup>
Electronic structure theory predicts
that, depending on the strength
of the ligand field, either the quintet (<sup>5</sup>T<sub>2</sub>) or triplet (<sup>3</sup>T<sub>1</sub>) term states can be stabilized
as the lowest-energy ligand-field excited state of low-spin octahedral
d<sup>6</sup> transition-metal complexes. The <sup>3</sup>T<sub>1</sub> state is anticipated for second- and third-row metal complexes and
has been established for certain first-row compounds such as [Co(CN)<sub>6</sub>]<sup>3–</sup>, but in the case of the widely studied
Fe<sup>II</sup> ion, only the <sup>5</sup>T<sub>2</sub> state has
ever been documented. Herein we report that 2,6-bis(2-carboxypyridyl)pyridine
(dcpp), when bound to Fe<sup>II</sup>, presents a sufficiently strong
ligand field to Fe<sup>II</sup> such that the <sup>5</sup>T<sub>2</sub>/<sup>3</sup>T<sub>1</sub> crossing point of the d<sup>6</sup> configuration
is approached if not exceeded. The electrochemical and photophysical
properties of [Fe(dcpp)<sub>2</sub>]<sup>2+</sup>, in addition to
being of fundamental interest, may also have important implications
for solar energy conversion strategies that seek to utilize earth-abundant
components
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Probing Reaction Dynamics of Transition-Metal Complexes in Solution via Time-Resolved Soft X-ray Spectroscopy
We report the first time-resolved soft x-ray measurements of solvated transition-metal complexes. L-edge spectroscopy directly probes dynamic changes in ligand-field splitting of 3d orbitals associated with the spin transition, and mediated by changes in ligand-bonding
Photo-Induced Spin-State Conversion in Solvated Transition Metal Complexes Probed via Time-Resolved Soft X-ray Spectroscopy
Solution-phase photoinduced low-spin to high-spin conversion in the Fe-II polypyridyl complex [Fe(tren(py)(3))](2+) (where tren(py)3 is tris(2-pyridylmethyliminoethyl)amine) has been studied via picosecond soft X-ray spectroscopy. Following (1)A(1) -> (MLCT)-M-1 (metal-to-ligand charge transfer) excitation at 560 nm, changes in the iron L-2- and L-3-edges were observed concomitant with formation of the transient high-spin T-5(2) state. Charge-transfer multiplet calculations coupled with data acquired on low-spin and high-spin model complexes revealed a reduction in ligand field splitting of similar to 1 eV in the high-spin state relative to the singlet ground state. A significant reduction in orbital overlap between the central Fe-3d and the ligand N-2p orbitals was directly observed, consistent with the expected ca. 0.2 angstrom increase in Fe-N bond length upon formation of the high-spin state. The overall occupancy of the Fe-3d orbitals remains constant upon spin crossover, suggesting that the reduction in a-donation is compensated by significant attenuation of pi-back-bonding in the metal ligand interactions. These results demonstrate the feasibility and unique potential of time-resolved soft X-ray absorption spectroscopy to study ultrafast reactions in the liquid phase by directly probing the valence orbitals of first-row metals as well as lighter elements during the course of photochemical transformations
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Probing Reaction Dynamics of Transition-Metal Complexes in Solution via Time-Resolved X-ray Spectroscopy
We report measurements of the photo-induced Fe(II) spin crossover reaction dynamics in solution via time-resolved x-ray absorption spectroscopy. EXAFS measurements reveal that the iron?nitrogen bond lengthens by 0.21+-0.03 Angstrom in the high-spin transient excited state relative to the ground state. XANES measurements at the Fe L-edge show directly the influence of the structural change on the ligand-field splitting of the Fe(II) 3d orbitals associated with the spin transition
Femtosecond Soft X-ray Spectroscopy of Solvated Transition-Metal Complexes : Deciphering the Interplay of Electronic and Structural Dynamics
We present the first implementation of femtosecond soft X-ray spectroscopy as an ultrafast direct probe of the excited-state valence orbitals in solution phase molecules. This method is applied to photoinduced spin crossover of [Fe(tren(py)(3))](2+), where the ultrafast spin state conversion of the metal ion, initiated by metal-to-ligand charge transfer excitation, is directly measured using the intrinsic spin state selectivity of the soft X-ray L-edge transitions. Our results provide important experimental data concerning the mechanism of ultrafast spin state conversion and subsequent electronic and structural dynamics, highlighting the potential of this technique to study ultrafast phenomena in the solution phase
Femtosecond Soft X-ray Spectroscopy of Solvated Transition-Metal Complexes: Deciphering the Interplay of Electronic and Structural Dynamics
We present the first implementation of femtosecond soft X-ray spectroscopy as an ultrafast direct probe of the excited-state valence orbitals in solution-phase molecules. This method is applied to photoinduced spin crossover of [Fe(tren(py)<sub>3</sub>)]<sup>2+</sup>, where the ultrafast spin-state conversion of the metal ion, initiated by metal-to-ligand charge-transfer excitation, is directly measured using the intrinsic spin-state selectivity of the soft X-ray L-edge transitions. Our results provide important experimental data concerning the mechanism of ultrafast spin-state conversion and subsequent electronic and structural dynamics, highlighting the potential of this technique to study ultrafast phenomena in the solution phase