short paper assignment on iron

8/11/2019 Short Paper Assignment on Iron

1/4

Chem 351 Binh Nguyen

Short Paper Assignment on Iron

Photophysical Properties of the complex [Fe(phen)2(TTF-dppz)]2+

The research article I have chosen for this assignment came out of the Hauser labin Switzerland and was published onInorganic Chemistry in 2013 under the title A

DonorAcceptor Tetrathiafulvalene Ligand Complexed to Iron(II): Synthesis,

Electrochemistry, and Spectroscopy of [Fe(phen)2(TTFdppz)](PF6)2.1The purpose of

the paper is to study light-induced electron transfer and the spin-crossover phenomena

by UV-Vis and Transient Absorption Spectroscopy.

Figure 1 below shows the structure of the complex of interest, [Fe(phen)2(TTF-

dppz)]2+. With three L2-type ligands, iron center is in its +2 oxidation state (or valence

number of 2) and therefore has 6 electrons in its metal-based d-orbitals. Assuming the

iron centers local symmetry is Oh, the iron center can exist in either low-spin (LS)

1A1g(t2g6) or high-spin (HS) 5T2g(t2g4eg2). Given the three diimine ligands, which are all

strong field ligands, iron(II) is expected to have a LS ground state. Figure 2 shows the

Molecular Orbitals diagram for the d-manifold MOs of Iron in this complex in both LS

and HS configurations.

Figure 1: Structure of [Fe(phen)2(TTF-dppz)]2+.

Figure 2: MOs diagram for both LS and HS configurations.

Fe2+

N

N

N

N

N

N N

N

S

S

S

S S

S

Low-spin 1A1g High-spin5T2g

t2g

eg

t2g

eg


2/4


3/4


Therefore, the authors decided to subtract the absorption of free TTF-dppz ligand (red

line) from that of [Fe(phen)2(TTF-dppz)]2+(black line) and found out that the MLCT

band is indeed a part of the broaden band at 17000 cm-1. Other transition bands are

assigned to the absorption of the ligands.

UV-Vis absorption spectra show some interesting light-induced electron

transfers, but are not particularly helpful in understanding the electronic structure of

the iron metal center in this case. So, the authors decided to take transient-absorption

spectroscopy, an extension of absorption spectroscopy, to follow the photophysical

processes by measuring the absorbance as a function of time. From transient absorption

spectra, we could obtain a global fit to calculate the decay, and therefore the lifetime, of

different excited states. The authors have drawn several interesting observations from

the spectra, but for the purpose of this assignment, I will only talk about the spin-crossover transition because of its relevancy to the topic of our class.

The HS->LS relaxation in a spin-crossover system has been shown to have a

typical range of 1 ns to 1.5 ns in previous works3. Figure 4 shows the transient spectra of

[Fe(phen)2(TTF-dppz)]2+ in dichloromethane on picosecond timescale with an

excitation wavelength of 400nm. The authors were able to show that the corresponding

relaxation time is 1.46 ns, which is typical for HS-LS relaxation of iron(II) LS complexes

following an ultrafast, light-induced population of HS state via the MLCT state.

Figure 4: Transient absorption spectra of [Fe(phen)2(TTF-dppz)]2+at 400nm. Source:

Hauser et al.


4/4


In this research article, the authors have studied the photophysical properties of

[Fe(phen)2(TTF-dppz)]2+, a LS spin complex that is similar to the series

[Ru(phen)3-x(TTF-dppz)x]2+ which is previously studied 4. They have shown the

complex is a light-induced spin-crossover system via a MLCT intermediate state.

Future direction might be to study the photophysical properties of similar cobalt(II)

and cobalt(III) complexes.

Reference

1. Dupont, N.; Ran, Y.; Liu, S.; Grilj, J.; Vauthey, E.; Decurtins, S.; Hauser, A.

Inorg. Chem.2013,52, 306312.

2.

Goze, C.; Leiggener, C.; Liu, S.-X.; Sanguinet, L.; Levillain, E.; Hauser, A.;

Decurtins, S. ChemPhysChem2007, 8, 1504.

3. Brady, C.; McGarvey, J. J.; McCusker, J. K.; Toftlund, H.; Hendrickson, D. N.

Top. Curr. Chem.2004, 235, 288.

4. Goze, C.; Leiggener, C.; Liu, S.-X.; Sanguinet, L.; Levillain, E.; Hauser, A.;

Decurtins, S. ChemPhysChem2007, 8, 1504.

short paper assignment on iron

Documents