Photon Factory Activity Report 2004 #22 Part B (2005)
Materials Science

12C,10B/2004G283

Electronic states and local structures of photomagnetic CuMo cyanides
Xiao-Dong Ma1, Toshihiko Yokoyama*1,2,Toshiya Hozumi3, Kazuhito Hashimoto3, Shin-ichi Ohkoshi3
1Dept. Structural Molecular Science, Grad. Univ. of Adv. Studies (Sokendai), Okazaki 444-8585, Japan
2
Institute for Molecular Sciences, Myodaiji-cho, Okazaki 444-8585, Japan
3
Dept. Chem., Grad. School Sci., Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan

Introduction
Prussian-blue analogues often exhibit noble
magnetic properties such as photoinduced magnetizationand high Curie temperature. In this work, we haveinvestigated the local structures and the electronic states
mainly of the photoinduced phases of these two CuMo
cyanides of Cu2Mo(CN)8⋅8H2O (1) [1] and Cs0.5Cu1.75
Mo(CN)8⋅1.5H2O (2) [2] by means of XAFS. Usually,
the photoinduced phase at low temperature (LT) is
considered to be structurally identical to that of thecorresponding high-temperature phase. The photoinduced
phase is however an essentially new state for thesecompounds because the CuMo cyanides are in the LT
phase even at room temperature and are likely to
decompose with the temperature rise.

neighbor Mo-C and Cu-N shells are kept constant. The
latter implies enhancement of the static Debye-Waller
factors instead of the reduction of the coordination
number. The reduction of the coordination numbers for
the Mo-N, Mo-Cu, and Cu-Mo shells may be ascribed not
to the bond breaking but to the bond bending. One canqualitatively conclude that due to the photoirradiation theMo-CN bond is bent, while Cu-NC is kept rathercollinear.
References[1] S. Ohkoshi et al. Synthetic Metals, 122, 523 (2001).
[2] T. Hozumi et al. J. Am. Chem. Soc. 127, 3864 (2005).
* yokoyama@ims.ac.jp

Experimental
The XAFS measurements were performed at BL10B(transmission) and 12C (fluorescence). Fluorescence
XAFS spectra were taken for Cu and Mo K edges of (1)and (2) at 30 K. In order to measure the reliable spectra of
the photoinduced phase, fluorescence detection wasessential because the penetration depth of the visible lightis much smaller than that of the x rays.
Results and discussion
Figure 1 shows the Cu K-edge XANES spectra ofsamples (1) and (2) before and after photoirradiation,
together with the reference spectra of Cu2O and CuO. As
illustrated in the spectra of Cu2O and CuO, monovalent
Cu compounds show a typical resonance peak at ~8984
eV, while divalent Cu gives a weak 1s→3d dipoleforbidden absorption at ~8981 eV and a shoulder at~8990 eV. From Fig. 1, one can immediately conclude
that the Cu atoms in samples (1) and (2) are divalent
before photoirradiation, and monovalent Cu appears afterphotoirradiation.
Figure 2 shows the Mo and Cu K-edge EXAFS

Fig. 1: Cu K-edge XANES spectra of samples (1)(middle) and (2) (bottom), together with Cu2O andCuO.

k3χ(k) and their Fourier transforms of sample (2).
Overall, one can find that the features of the initial LT
and photoinduced phases are almost identical. Theinteratomic distances are almost the same between theinitial and the photoinduced phases. Differences between
the low-temperature and the photoinduced phases canhowever be detected in the amplitude in the EXAFS
oscillation. From the curve-fitting results, thecoordination numbers of the Mo-N, Mo-Cu, and Cu-Mo
shells are found to be reduced, while those of the Mo-C,Cu-N, and Cu-C shells as well as the first-nearest

Fig. 2: Mo and Cu K-edge EXAFS k3χ(k) and their
Fourier transforms of sample (2) before and after laser
irradiation.

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