Photon Factory Activity Report 2014 #32 (2015) B

9C/2013G009

Coordination structures of transition-metal ions in ionic liquids.
1Masayasu IIDA,1 Chisayo NAKAYAMA,1 and Masafumi HARADA*2
Department of Chemistry, Faculty of Natural Science, Nara Women’s University, Nara 630-8506,
Japan
2
Department of Clothing Environmental Science, Faculty of Human Life and Environment,
Nara Women’s University, Nara 630-8506, Japan

Introduction
A series of protic ionic liquids (= PILs) comprisingchelate amines have been prepared by our research groupand the characteristic interactions of some transition
metal ions in such unique type PILs have been studied.
[1] In order to see the effect of the number of amines in
the head group on the interactions, we herein newly
prepared the PILs with diethylenetriamine chelate. Afterdissolving some kinds of copper(II) salts, we determinedthe coordination structures around the copper(II) ion in
the PILs using EXAFS spectroscopy.
Experimental
The PILs were obtained by a neutralization of preparedN-hexyldiethylenetriamine(=Hexdien)or
2ethylhexyldiethylenetriamine (= EtHexdien) with HTf2N(= bis(trifluoromethanesulfonyl)amide acid) or withHTFA(= trifluoroacetic acid). The PILs thus obtained areabbreviated as HHexdien(Tf2N), HHexdien(TFA),
HEthexdien(Tf2N), and HEthexdien(TFA) hereafter.
Copper salts of CuCl2, Cu(Tf2N)2, and Cu(TFA)2 wereadded to the PILs or to the neat Hexdien (or EtHexdien),
liquid and the interactions of Cu2+ with the PILs werecompared with those of the neat Hexdien (or EtHexdien)liquid. The analogous Hexdien and EtHexdien copper(II)complexes were also synthesized, and then theirstructures in solid state and in molecular solvents werestudied using EXAFS for comparison.
EXAFS measurements were performed at room
temperature in a transmission mode at BL-9C. The solid
samples were mixed with boron nitride to make a tablet
specimen. The PILs were sealed into polyethylene bags
for measurements; the metal concentration in solution
To extract thewas adjusted to 0.10 mol kg-1.
backscattering amplitude and phase shift functions for thecurve-fitting, the reference compound (Cu(dien)2Br2 㻌 insolid) was used in this experiment. The structuralparameters for the respective copper(II) samples were
determined referred to those for the copper(II) referencecompounds and to the results of VIS absorption spectra.
Results and Discussion
The Fourier transformed |F(r)| of the k3Ȯ(k) curve wasobtained for Cu(dien)2Br2 in solid state as a standard,
whose crystalline structure has been determined. Thecopper(II) ion in the dien PILs as well as those in theisolated dien complexes shows a characteristic peakowing to a weak second shell contribution of carbon,
together with a single monatomic first shell of nitrogen oroxygen. Differently from the en complexes, a series of
the hexdien complexes were not simply classified into thetwo groups based on the intensities of FT spectra.
Therefore, we at first determined the Debye-Waller (Vasbelow) parameters from the analysis of the FT spectrum
for the reference Cu(dien)2Br2 complex and then the
curve-fittings for the copper(II) ion in the PILs and in thefree ligands were performed so as to the D-W parameters
have the similar values as that for the reference complex.
On the basis of the VIS absorption spectra, the CNvalues
could be roughly estimated.[2] However, as the nitrogenand oxygen atoms are not discriminated on the EXAFS
analysis, we herein analyzed the FT spectra by taking theinitial CN values in the solutions same as those for thereference dien complex. Some of the results are listed inTable1. There is a trend that in the PILs the CN values
for the Cu-N bonds are larger and the Vvalues areslightly smaller compared to those in the neat ligands.
The parameters for the Cu-C bond may have larger errors
due to the smaller and overlapped peak
Table 1. EXAFS parameters determined from thecurve-fittings of the copper(II) FT spectra.
([Cu2+] = 0.1 mol kg-1 for solutions)
SystemMedium
Solid

Neat
LigandHexdien(Tf2N)-PIL
EtHexdien(Tf2N)-PIL[Cu(dien)2]Br2Solid(STD)
Cu(Tf2N)2 in
HexdienCu(Tf2N)2 in
EthexdienCu(Tf2N)2 in
HHexen(Tf2N)Cu(Tf2N)2 in
HEthexdien(Tf2N)

10 r /nm

CN10䃢
/ nm
Cu-N(eq)2.04 4.0(fix) 0.09
Cu-N(ax)
2.42 2.0(fix) 0.12
Cu-C
2.92 8.0(fix)㻌 0.11
Cu-N(eq)
2.04
3.8
0.10
Cu-N(ax)
2.40
1.7
0.15
Cu-C
2.91
8.8
0.11
Cu-N(eq) 2.04
3.6
0.10
Cu-N(ax) 2.43
1.7
0.14
Cu-C
2.91
8.0
0.11
Cu-N(eq) 2.08
4.5
0.09
Cu-N(ax) 2.43
2.3
0.12
Cu-C
2.94
7.4
0.11
Cu-N(eq) 2.03
4.3
0.09
Cu-N(ax) 2.33
1.7
0.12
Cu-C
2.95
7.1
0.10
BondR(%)
1.0

1.9
2.2

0.9
2.9

References[1] S. Takemura, S. Kawakami, M. Harada, M. Iida, Inorg.
Chem., 53, 9667-9678 (2014).
[2] C. Nakayama and M. Iida, “the 5th Symposium on Ionic
Liquids of Japan”, 1P21, Yokohama (2014).

* harada@cc.nara-wu.ac.jp