Photon Factory Activity Report 2016 #34 (2017)
BL-9C/2015G087

Guest molecule inserted spin crossover complexes:
Fe[4-(3-Pentyl)pyridine]2[Au(CN)2]2･n Guest
Yusuke Ueki,1 Jun Okabayashi,2* and Takafumi Kitazawa1
1
2

Department of Chemistry, Toho University, 2-2-1 Miyama, Funabashi, Chiba 274-8510, Japan
Research Center for Spectrochemistry, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, JapanThe spin crossover (SCO) complexes represent
some kinds of functional molecular materials
possessing the specific electronic configurations
between high-spin (HS) and low-spin (LS) states intransition metals from 3d4 to 3d7 by external stimuli
such as temperature, light, pressure, and guest
molecules insertion. The Hofmann-type complexes arecomposed of linear units [MI(CN)2] (MI = Cu, Ag, andAu) or planar units [MII(CN)4] (MII = Ni, Pd, and Pt),
which are investigated by many research groups [1].
Recently, the SCO complex accommodated the guest
molecules in Fe[4-(3-Pentyl)pyridine]2[Au(CN)2]2 ･n
Guest, where the Guest is 4-(3-Pentyl)pyridine, hasbeen synthesized [2]. However, precise electronic andstructural properties have not been investigatedexplicitly in the SCO clathrate compound. In this study,
we aim to investigate the electronic and structuralproperties
acrossthespintransitionin
Fe[4-(3-Pentyl)pyridine]2[Au(CN)2]2 ･ guest (guest =chlorobenzene:
1,o-dichlorobenzene:
2,m-dichlorobenzene: 3, p-dichlorobenzene: 4) by using
temperature-dependent X-ray absorption fine structure(XAFS) and extended XAFS (EXAFS) [3].
The guest molecule inserted complexes into hoststructure Fe[4-(3-Pentyl)pyridine]2[Au(CN)2]2 weresynthesized by the liquid reaction using the Mohl’s saltof Fe(NH4)2(SO4)2･6H2O, ascorbic acid, K[Au(CN)2],
guest molecules and 4-(3-Pentyl)pyridine, which weremixed with all reagents together in air. The powder
samples were prepared rapidly by this reaction.
Temperature-dependent XAFS and EXAFS wereperformed at BL-9C, Photon Factory (KEK). The
sample used for XAFS measurements was diluted by
BN powder and formed into pellets. The samples werecooled by the conventional closed He ion cryostat
from room temperature to 20 K.
The crystal structures of o-dichlorobenzene
clathrate (1) and p-dichlorobenzene clathrate (4) were
determined by the single-crystal X-ray diffraction(XRD). The magnetic properties measured bysuperconducting quantum interference device(SQUID) shown in Fig. 1 reveals the spin transition
depending on the guest molecule shape. The spinstates converted from the HS state at room
temperature to the LS state at low temperature around200 K. The clathrate 4 achieved the highest spintransition temperature.
Figure 2 shows the temperature-dependent XAFS
spectra of Fe[4-(3-Pentyl)pyridine]2[Au(CN)2]2 ･o-dichlorobenzene for Fe K-edge and Au L3-edge. Inthe Fe K-edge XAFS spectra shown in Fig. 2 (left), themain peak positions shift toward higher photon energy

side with decreasing temperature, which can be
explained by the HS-LS transitions through thechanges of the crystal field strength by temperature.
Figure 2 (right) displays the Au L3-edge XAFSspectra. Contrary to Fe K-edge XAFS spectra, the peak
positions of the Au L3-edges remain unchanged acrossthe SCO transition, which suggests that the Au atomsdo not contribute to the SCO transition directly.
The insertion of guest molecules into the hoststructure promotes the spin transition because of theincrease of chemical pressure from the guest insertionand host-guest interaction. We also found that the
spin transition temperature depends on the guest
molecule sizes of o-, m-, p- clathrates. The guest
molecule shape influences the host structure and thespin transition temperature. In the case of para-type
guest molecule, the highest spin transition
temperature was achieved through the host-guest
hybridization [3].

Fig.
1,Magneticpropertiesof
Fe[4-(3-Pentyl)pyridine]2[Au(CN)2]2 ･ n Guest, Guest =chlorobenzene:
1,o-dichlorobenzene:
2,m-dichlorobenzene: 3, p-dichlorobenzene: 4) measured bySQUID.

Fig. 2, Temperature-dependent XAFS spectra ofFe[4-(3-Pentyl)pyridine]2[Au(CN)2]2 ･ o-dichlorobenzene,
for the Fe K-edge (left) and the Au L3-edge (right).
[1] M. Neville et al., Inorg. Chem., 55, 10490 (2016).
[2] T. Kosone and T. Kitazawa, Inorg. Chim. Acta. 439,159 (2016).
[3] Y. Ueki, J. Okabayashi, T. Kitazawa, Chem. Lett. 46,
747 (2017).

*e-mail: jun@chem.s.u-tokyo.ac.jp