Photon Factory Activity Report 2016 #34 (2017)

BL-27A/2016G198

X-ray absorption spectroscopy of bis(dithiolene) complexes
Hiromi Ikeura-Sekiguchi1,* and Tetsuhiro Sekiguchi2
Research Institute for Measurement and Analytical Instrumentation (RIMA),
National Metrology Institute of Japan (NMIJ),
National Institute of Advanced Industrial Science and Technology (AIST),
Tsukuba, Ibaraki 305-8568, Japan
2
Japan Atomic Energy Agency (JAEA), Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan
1

2 Experiment
Experiments were performed at beamline BL-27A
with an InSb(111) double-crystal monochromator with anenergy resolution of ca. 0.8 eV around S K-edge. TheXAS spectra of polycrystalline TBA[NiIII(mnt)2] andNiII(S2C2Ph2)2 (mnt = maleonitriledithiolate, TBA = tetra
n-butyl ammonium, as shown inset of Fig. 1) were
measured using monitoring sample drain current near theS K-edge (2465–2505 eV) and normalized to the incident
flux with thin aluminum films. Such energies werechosen to excite the S 1s core electron to 3p and 4p
unoccupied orbitals.
3 Results and Discussion
Fig. 1 shows S K-edge XAS spectra ofpolycrystalline neutral form of Ni(S2C2Ph2)2 and oneelectron oxidized form of [NiIII(mnt)2]. Based on
previous study [3], peak A is assigned to S 1s → b1g*(Ni3dxy* ‒ Lxy) transition. Peak B and C are assigned to S 1s→σ*(S–C–CN) and S 1s → σ*(S–C) transitions,respectively. Peak D is attributed to S 1s → 4p. Featuresof peak A in both samples are resemble in each other but
the peak position of [NiIII(mnt)2] is slightly shifted tohigher energy (∼0.3eV) than that of NiII(S2C2Ph2)2. Thisshift would be caused by difference in Ni oxidation states,
where effective nuclear charge (Zeff) of Ni is larger for the[NiIII(mnt)2].
Although a chemical component [Ni(mnt)2] in theTBA[NiIII(mnt)2] is similar to that in [(nC4H5)N][NiIII(mnt)2] [3], it was found that S K-edge XAS
features are different. Especially, SOMO (SinglyOccupied Molecular Orbital) at lower energy position ofpeak A has not been observed in the TBA[NiIII(mnt)2].
This suggests that ligand π*contribution in SOMO may
be much smaller in the TBA[NiIII(mnt)2]. However, ingeneral, such different contribution is not plausible for thesame chemicals. Therefore, further consideration isneeded to understand this contradiction. Also a low-lying
out-of-plane ligand π* orbital corresponding to S 1s →b3g*(Lyz) transition emerging between peaks A and B has
not been observed, differently from the XAS of the [(nC4H5)N][NiIII(mnt)2] [3].

ABCD

Imtensity (arb. units)

1 Introduction
Metal dithiolene complexes have been extensively
investigated for more than half a century [1] because of
their unique chemical and physical properties and also
variety of applications such as photo energy conversion,
non-linear optics, and electronic or photonic devices [2].
Nevertheless, oxidation states of the complexes are stillless understood due to redox non-innocent nature ofligands. Therefore in order to investigate the oxidation or
chemical states of Ni dithiolene complexes, we usedsulfur K-edge X-ray absorption spectroscopy (XAS).

2465

2470

2475 2480
Energy (eV)2485

Fig. 1: S K-edge XAS spectra of polycrystalline samplesof NiII(S2C2Ph2)2 (black solid line, black chemicalformula) and TBA[NiIII(mnt)2] (blue dot line, bluechemical formula).
Acknowledgements
We thank the staff of the Photon Factory and BL27A(JAEA) for supporting experiments.
References[1] G.N. Schrauzed, and V. Mayweg, J. Am. Chem. Soc.,
84 , 3221(1962).
[2] B.G Bonneval, K.I.M-C Ching, F. Alary, T-T. Bui,and L. Valade, Coord. Chem. Rev., 254, 1457 (2010).
[3] T. Hatsui, Y. Takata, and N. Kosugi, J. SynchrotronRad. 6, 379 (1999).
*ikeura-sekiguchi@aist.go.jp