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

10B/2004G094

Dynamic change in framework structures of Cu-complex material
Yoshiyuki HATTORI*1, Hiroshi KAJIRO2, Hiroshi NOGUCHI3, Yohko NOBUHARA3,Takehisa KONISHI4, Hirofumi KANOH3,4, Katsumi KANEKO3,4
1
Institute of research and innovation, Takada, Kashiwa, Chiba 277-0861, Japan
2
Advanced technology research lab., Nippon steel corporation, Futtsu, Chiba 293-8511, Japan
3
Graduate school of science, Chiba Univ., Inage, Chiba 263-8522, Japan
4
Department of chemistry, Faculty of science, Chiba Univ., Inage, Chiba 263-8522, Japan
LPC retain the Oh symmetry around a Cu atom
irrespective of the removal of water molecules. Theseresults suggest that the bpy pillar ligands coordinate to Cu
ions instead of water molecules. The nearest-neighboratomic distances of the heat-treated LPC were also shownin Table 1. The curve fitting results also suggest that theCu ions are coordinated by the bpy units to form the 2D
square grid layers and that the BF4 ions act as pillars tohold tow layers together.
as synthesisheat-treated

FT amplitude

Introduction
Coordination polymers with designated frameworks areof interest due to their characteristic structural properties.
Their frameworks with nanopores are suitable for thestorage of a wide range of molecules such as methane orhydrogen. Li and Kaneko have found that the Cucomplex material [Cu(bpy)(BF4)2(H2O)2(bpy)]n (LPC)
shows a gate effect on CO2 adsorption that means thesteep increase of the amount adsorbed at specific relative
pressure[1].
Although the characteristic adsorption
properties can be found after the heat treatment to remove
the water molecules, the LPC cannot retain its singlecrystallinity upon the removal of water molecules. Theseresults suggest that the dynamic change in thecoordination structures will be occurred by the removableof water molecules. In this work, we have characterized
the dynamic behavior of the frameworks in the LPC by
XAFS techniques.
Experimental
The LPC materials were prepared by the addition of anaqueous solution of copper(II) tetrafluoroborate to amethanol solution of 4,4’-bipyridine (bpy). The detailpreparation methods are described elsewhere [2]. The
LPCs were heated at 378 K in vacuo to remove watermolecules in their frameworks. The LPCs were kept in
XAFS cell with Kapton film windows. The XAFS
spectra were recorded in transmission mode at BL-10B
beam line.
Results and Discussion
Figure 1 shows the Fourier transforms (FTs) of χ(k)extracted from the EXAFS spectra of the as synthesis andthe heat-treated LPCs. The changes in the FT wereobserved after the heat-treatment to give the dehydratedforms. In order to investigate the coordination structures,the structural parameters have been calculated by curve
fitting method. The results of best-fitted data for atomic
distances of the first shell were tabulated in Table1. The
results of the local structures for the as synthesis LPC are
almost consistent with those calculated from XRD data ofthe single crystal. The XANES spectra of the as synthesis
and the heat-treated LPC show main peaks at the energy
range from 8980 to 9000 eV. These peaks are assigned tothe dipole-allowed transition from 1s to 4p states inmolecular orbital. The XANES spectra of the heattreated LPC did not drastically change compared withthat of the as synthesis LPC, indicating the heat-treated

01

23R/Å

456Figure 1. The Fourier transforms of χ(k) extracted fromEXAFS spectra for as synthesis and heat-treated LPCs.
Table 1. Nearest-neighbour atomic distances of assynthesis (RLPC) and heat-treated (RHT) LPCs. The RXRD
denotes the distances calculated from the single-crystal
XRD analysis.
RLPC /Å
RXRD/ ÅRHT/ Å
Cu-O
1.97
1.97
Cu-N
1.99
1.99
1.99
Cu-F
2.41
2.39
2.19
References[1] D. Li and K. Kaneko, Chem. Phys. Lett. 335, 50(2001).
[2] A. J. Blake et al., J. Chem. Soc., Dalton Trans., 913(1997).
* hattori@iri.or.jp

Users' Report169