ARTICLE IN PRESSJOURNAL OF

Inorganic
Biochemistry
Journal of Inorganic Biochemistry xxx (2005) xxx–xxx
www.elsevier.com/locate/jinorgbio

Sulfur K-edge extended X-ray absorption ﬁne structure spectroscopyof homoleptic thiolato complexes with Zn(II) and Cd(II)Yuki Matsunaga a, Kiyoshi Fujisawa a,*, Naoko Ibi a, Mitsuharu Fujita a, Tetuya Ohashi a
Nagina Amir a, Yoshitaro Miyashita a, Ken-ichi Aika b, Yasuo Izumi b,*, Ken-ichi Okamoto aaGraduate School of Pure and Applied Sciences, Department of Chemistry, University of Tsukuba, Tsukuba 305-8571, Japan
Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Yokohama 226-8502, Japanb

Received 6 February 2005; received in revised form 6 November 2005; accepted 9 November 2005

Abstract
The sulfur K-edge extended X-ray absorption ﬁne structure (EXAFS) spectroscopy is applied to homoleptic thiolato complexes withZn(II) and Cd(II), (Et4N)[Zn(SAd)3] (1), (Et4N)2[{Zn(ScHex)2}2(l-ScHex)2] (2), (Et4N)2[{Cd(ScHex)2}2(l-ScHex)2] (3),
(Et4N)2[{Cd(ScHex)}4(l-ScHex)6] (4), [Zn(l-SAd)2]n (5), and [Cd(l-SAd)2]n (6) (HSAd = 1-adamantanethiol, HScHex = cyclohexanethiol). The EXAFS results are consistent with the X-ray crystal data of 1–4. The structures of 5 and 6, which have not been determined by
X-ray crystallography, are proposed to be polynuclear structures on the basis of the sulfur K-edge EXAFS, far-IR spectra, and elemental
analysis. Clear evidences of the S  S interactions (between bridging atoms or neighboring sulfur atoms) and the S  Cfar interactions (inwhich Cfar atom is next to carbon atom directly bonded to sulfur atom) were observed in the EXAFS data for all complexes and thus leadto the reliable determination of the structures of 5 and 6 in combination with conventional zinc K-edge EXAFS analysis for 5. This new
methodology, sulfur K-edge EXAFS, could be applied for the structural determination of in vivo metalloproteins as well as inorganic
compounds.
Ó 2005 Elsevier Inc. All rights reserved.
Keywords: Extended X-ray absorption ﬁne structure spectroscopy; Zinc(II); Cadmium(II); Molecular structure; M–S stretching

1. Introduction
Group 12 metal(II) complexes have not been paid muchattention in the fundamental studies on vibrational energies as well as charge transfer (CT) transition energies.
These metals consist of closed d10 electronic conﬁgurationand their ligands usually contain aromatic ring(s) or multiple bond(s) for the stabilization of Zn(II) and Cd(II) complexes. Therefore, it is diﬃcult to uniquely assign vibrationenergies and CT transition energies for the series of complexes. The crystal structures of many thiolato complexes
with Zn(II) and Cd(II) ions have been published [1–3]. In*
Corresponding authors. Tel.: +81 29 853 6922; fax: +81 29 853 6503
(K. Fujisawa), +81 45 924 5569 (Y. Izumi).
E-mail addresses: kiyoshif@chem.tsukuba.ac.jp (K. Fujisawa), yizumi@chemenv.titech.ac.jp (Y. Izumi).

0162-0134/$ - see front matter Ó 2005 Elsevier Inc. All rights reserved.
doi:10.1016/j.jinorgbio.2005.11.004

contrast, so far there have been only a few reports on systematic studies on the properties of group 12 metal(II) ions,using multinuclear nuclear magnetic resonance (NMR)
spectroscopy such as 67Zn NMR [4,5], 113Cd NMR [6],and 199Hg NMR [7] and resonance Raman spectroscopy[8]. In this situation, our strategy is to synthesize group
12 metal(II) complexes with ‘‘saturated’’ supporting
ligands which do not contain double/triple bond(s) andhave lower molecular weight. By using saturated supporting ligands, we recently reported the crystal structures
together with vibrational energies and CT energies [9,10].
For Zn(II) complexes with S-containing saturated ligands
such as 1-adamantanethiol (HSAd) and cyclohexanethiol(HScHex), the assignments of (Et4N)[Zn(SAd)3] (1) and(Et4N)2[{Zn(ScHex)2}2(l-ScHex)2] (2) were very easy forthe vibration energies by far-IR and Raman spectroscopies
and for the CT energies by UV–visible (UV–Vis) absorp-

ARTICLE IN PRESS
2

Y. Matsunaga et al. / Journal of Inorganic Biochemistry xxx (2005) xxx–xxx

tion spectroscopy [11]. The sulfur chemistry is related tovarious ﬁelds such as organic, inorganic chemistry, biochemistry, and environmental science. Therefore, thesefundamental data of physicochemical properties for Zn(II)and Cd(II) complexes with saturated ligands should provide new insights into these research ﬁelds.
X-ray absorption spectroscopy (XAS) can characterize
the coordination environment around a target atom.
XAS has been applied to a variety of system such as inorganic compounds, catalysts, semiconductors, and biochemistry. Both metal K- and L-edges can be studied for theelectronic transitions from metal 1s and from metal 2p,
respectively. For example, the zinc K and LI,II,III absorption edges are at 9663 eV and at 1200, 1047, and1024 eV, respectively. Other options of the X-ray absorption edges are the ligand K- and L-edges which excite theelectron out of ligand 1s and 2p orbitals, respectively.
The ligand K-edge XAS has been used to deﬁne the covalency of the ligand–metal bond in bioinorganic chemistry[12,13].
For the study of metal sites that have an unﬁlled d orbital, metal K/L-edge X-ray absorption near edge structure(XANES) are very eﬀective. The pre-edge feature directly
reﬂects unﬁlled d orbital(s) condition of each metal site.
In contrast, as the Zn(II) and Cd(II) complexes containd10 electronic conﬁguration [14], metal K-edge XANES is
not direct to determine the site symmetry and electronic
state. On the other hand, extended X-ray absorption ﬁne
structure (EXAFS) provides detailed information about
the bonding of ligand(s). Thus, zinc K-edge EXAFS has
been applied to various ﬁelds, such as metalloproteins[14–18], semiconductor [19,20], medicine [21], and catalyst[22,23].
As the sulfur K-edge energy is relatively low (2471 eV)compared with that of metal, the photon ﬂux from synchrotron radiation is relatively low, and thus the measurements take relatively longer accumulation time. However,this method can provide direct information about sulfur
atom environment in proteins and metal complexes thatcannot be obtained by the complementary metal K-edge
measurements. The sulfur K-edge EXAFS has been
applied already to inorganic materials [24–29] and metalloprotein [14,30]. However, no sulfur K-edge EXAFS studies
of Zn(II) and Cd(II) complexes have been reported yet toour knowledge, in contrast, various Zn(II) and Cd(II) complexes mimicking biological systems do exist.
In our lower molecular weight complexes with saturated
supporting ligands, the sulfur atoms occupy relatively
higher weight ratio and the sulfur K-edge EXAFS measurements are easy. We discuss in this paper the sulfur
K-edge EXAFS data of Zn(II) and Cd(II) complexes withsaturated ligands such as 1, 2, (Et4N)2[{Cd(ScHex)2}2(lScHex)2] (3), and (Et4N)2[{Cd(ScHex)}4(l-ScHex)6] (4)and the determination of their bond distances from sulfur
atoms. The complementary zinc K-edge EXAFS of 1, 2,
and 5 are also described. We propose the structures of[Zn(l-SAd)2]n (5) and [Cd(l-SAd)2]n (6) based on their sul-

fur K-edge and far-IR spectra, and elemental analysis. We
also report the crystal structure of 4 and the M–S stretching vibration data for 3–6 in detail.
2. Results and discussion
2.1. General aspects
Complexes 1–3 were synthesized by the reported methods [11,31]. There are some diﬀerences in the reactivities
between Zn(II) and Cd(II) complexes. The three-coordinate Cd(II) complex ([Cd(SAd)3]) corresponding to 1
was not obtained. The complexes 2 and 3 have the samestructures as reported, conﬁrmed by UV–Vis, far-IR spectra, and elemental analysis. Tetranuclear Cd(II) complex 4
was obtained from the ﬁltrate after ﬁltration of 3. The tetranuclear Zn(II) complex ([{Zn(ScHex)}4(l-ScHex)6]2)
corresponding to 4 was not obtained. Complexes 5 and 6
were immediately formed as white powder after the addition of MCl2 (M = Zn(II) and Cd(II)) solution to the
NaSAd solution (MCl2:NaSAd = 1:2). Complexes 5 and6 were not dissolved in any solvents. Slow conversions
from 1 to 5 and from 3 to 4 were observed in solution.
Therefore, all complexes are studied in solid state in thispaper (see Scheme 1).
2.2. Crystal structures
The crystal structures of 1–3 were reported and theirsimpliﬁed models are shown in Fig. 1 [11,31]. Complex 1
has a three-coordinate planar structure with three 1-adamantanethiolate anions and 2 has a dinuclear structure
containing two ZnS3 units bridged by two sulfur atoms
from cyclohexanethiolate anions. In 1, three sulfur atoms
and one Zn(II) ion exist in the same plane (av. Zn–S:
2.262(4), av. S  S: 3.917(4), av. S–C: 1.844(9), av. S  Cfar:
2.770(9) Å) [11]. In this paper, Cfar is deﬁned as the carbon
atom next to the carbon atom which directly bonded to sulfur atom. The S–Zn–S angles in 1 are almost 120°, indicating a trigonal plane. In 2, the Zn2S6 core has a D2hsymmetry (av. Zn–S: 2.352(1), av. S  S: 3.864(2), av. S–
C: 1.831(5), av. S  Cfar: 2.779(5) Å) [11]. The Cd(II) complex 3 has a dinuclear structure as same as 2 (av. Cd–S:
2.550(4), av. S  S: 4.136(6), av. S–C: 1.848(17), av.
S  Cfar: 2.75(1) Å) [31].
The crystal structure of 4 is shown in Fig. 2. Selected distances and angles of 4 are summarized in Table 1. FourCd(II) ions and six sulfur atoms from cyclohexanethiolate

Scheme 1.

ARTICLE IN PRESS
Y. Matsunaga et al. / Journal of Inorganic Biochemistry xxx (2005) xxx–xxx

Fig. 1. Simpliﬁed structures of 1–6. ((for S  S, and (- - - - - - ) for S  Cfar).

) for M–S, () for S–C, ()

3

ligand constitute a Cd4S6 adamantane-like cage. Each
Cd(II) ion consists of a tetrahedral conﬁguration, one terminal (the outside of adamantane-like cage) and threebridging cyclohexanethiolate ligands. The M4X10 complexes containing adamantane-like cages have beenreported for many metal ions and ligands. For example,
the structures of [(l-SPh)6(MSPh)4]2 (M = Mn(II), Fe(II),and Co(II)) have been determined [32–36]. For Zn(II) andCd(II) ions, the structures of [(l-SPh)6(MSPh)4]2 typecomplexes have been studied well as good structural models of metallothionein [37–39], including [M4(oSC6H4CH3)10]2 (M = Zn(II) and Cd(II)) [40], and[Zn4(SePh)10]2 [41]. [(l-SR)6(MX)4] type complexes werereported from a structural viewpoint. The terminal positions on the adamantane-like cage can be substituted byother ligands such as sulﬁde [S4M10(SPh)16]2 (M = Zn(II)and Cd(II)) [42,43], halogenide ions [(l-SPh)6(ZnX)4]2
(X = Cl, Br, and I) [44], [(l-SPh)6(ZnSPh)2(ZnCl)2]2
[45], [(l-S-iPr)6(CdBr)4]2 [46], [(l-EPh)6(CdBr)4]2
(E = S
and
Se)
[47],
and
phosphine[(l-SiPr)6(CdPPh3)2(CdOClO3)2] [48]. The complex substituted
by solvent, [(l-SPh)6Zn4(SPh)(CH3OH)] [49], was also
structurally characterized.
Bond distances of Cd–St (2.485(2)–2.502(3) Å) and Cd–
Sb (2.542(2)–2.576(3) Å) in 4 are in the same range as thoseof Cd–St (2.460(4)–2.480(3) Å) and Cd–Sb (2.533(3)–2.603(3) Å) in [Cd4(SPh)10]2 [39]. Bond distances ofSb  Sb (3.896(3)–4.355(3) Å) and Sb  St (4.052(4)–4.349(4) Å) in 4 are also in the same range as those ofSb  Sb (3.695(4)–4.434(4) Å) and Sb  St (3.96–4.36 Å) in[Cd4(SPh)10]2 [39]. On the other hand, bond angles of
St–Cd–Sb (101.84(7)–118.38(8)°) and Sb–Cd–Sb (99.35(7)–115.83(8)°) in 4 were not common to [Cd4(SPh)10]2 (St–Cd–Sb (102.0(1)–121.1(1)°) and Sb–Cd–Sb (91.5(1)–118.4(1)°)) [39]. This is due to the diﬀerences of using
ligands between alkyl and aromatic frameworks. Fromthese diﬀerences, the corresponding cluster such as[Zn4(ScHex)10]2 could not be synthesized by any experimental conditions [37–39]. Each Cd(II) center is a distorted
tetrahedral CdS4. Three sulfur atoms (S4, S5, and S6) andthree Cd(II) ions (Cd2, Cd3, and Cd4) constitute a chairlike Cd3(l-S)3 ring. This unit is related to metallothioneins;a mammalian Cd(II) substituted metallothionein contains a
Cd3(Cys-S)9 and a Cd4(Cys-S)11 units, both including a
Cd3(l-S)3 ring [1,37,39]. Comparing with 3, the bond distances in 4 (av. Cd–S: 2.547(7), av. Sb/St  Sb/St: 4.13(1),S–C: 1.827(19), S  Cfar: 2.75(3) Å) are almost the sameas those in 3 (av. Cd–S: 2.550(4), av. St  S 4.136(6), S–
C: 1.848(17), S  Cfar: 2.75(1) Å). This indicates that thesebond distances do not aﬀect on each structure.
2.3. Far-IR spectroscopy

Fig. 2. ORTEP diagram of the anion of (Et4N)2[{Cd(ScHex)}4(lScHex)6] (4). Non-H atoms are represented with 50% probability
ellipsoids: (a) the whole structure and (b) the framework of Cd4S10 unit.

The far-IR spectra of 4 along with 2 and 3, which contain cyclohexanethiolate ligand, are shown in Fig. 3. There
are many peaks arising from thiolate ligands below
360 cm1 because of the presence of terminal and bridging

ARTICLE IN PRESS
4

Y. Matsunaga et al. / Journal of Inorganic Biochemistry xxx (2005) xxx–xxx

Table 1
Selected distances (Å) and angles (°) for (Et4N)2[{Cd(ScHex)}4(l-ScHex)6] (4)Distances
Cd–StaCd1–S7
Cd2–S82.495(2)2.496(4)Cd3–S9
Cd4–S102.485(2)2.502(3)Cd1–S1Cd1–S2
Cd1–S3Cd2–S12.576(3)2.562(2)2.575(3)2.563(2)Cd2–S4Cd2–S5
Cd3–S2
Cd3–S4Cd  Cd
Cd1–Cd2
Cd1–Cd3

4.2077(9)4.2851(7)Sb  Sb
S1–S2
S1–S3
S1–S4
S1–S5

Mean

2.495(4)2.547(2)2.575(3)2.567(2)2.567(3)Cd3–S6
Cd4–S3
Cd4–S5
Cd4–S6Mean

2.559(3)2.568(2)2.572(3)2.542(2)2.564(3)

Cd1–Cd4
Cd2–Cd3

4.2698(9)4.3535(9)Cd2–Cd4
Cd3–Cd4Mean

4.203(1)4.3329(9)4.275(1)4.286(3)4.275(4)3.896(3)4.327(3)

S2–S3
S2–S4
S2–S6
S3–S5

3.934(3)3.985(3)4.123(3)4.355(3)

S3–S6
S4–S5
S4–S6
S5–S6
Mean

4.101(3)4.218(3)4.076(4)3.928(4)4.125(4)Sb  St
S1–S7
S2–S7
S3–S7
S1–S8

4.217(3)4.169(3)4.083(4)4.018(4)

S4–S8
S5–S8
S2–S9
S4–S9

4.149(4)4.275(5)4.338(3)4.152(3)S6–S9
S3–S10S5–S10
S6–S10Mean

4.193(3)4.052(4)4.349(4)4.109(3)4.175(5)S–C
S1–C11S2–C21S3–C31
S4–C41

1.842(9)1.86(1)
1.839(9)1.825(8)S5–C51
S6–C61S7–C711.85(1)1.84(2)
1.85(1)S8–C81S9–C91
S10–C101Mean

1.77(1)1.80(1)1.79(2)
1.83(2)

Cd–SbaAngles
St–Cd–Sb
S1–Cd1–S7
S2–Cd1–S7
S3–Cd1–S7
S1–Cd2–S8

112.50(8)111.05(8)107.27(8)105.16(9)S4–Cd2–S8
S5–Cd2–S8
S2–Cd3–S9
S2–Cd3–S4

110.70(9)114.87(9)118.38(8)101.84(7)S2–Cd3–S6
S3–Cd4–S10
S5–Cd4–S10
S6–Cd4–S10
Mean

107.10(8)106.09(8)117.95(9)109.11(8)110.17(9)Sb–Cd–Sb
S1–Cd1–S2
S1–Cd1–S3
S2–Cd1–S3
S1–Cd2–S4

113.06(7)112.21(8)99.96(8)99.35(7)S1–Cd2–S5
S4–Cd2–S5
S2–Cd3–S4
S2–Cd3–S6

114.75(7)110.84(8)101.84(7)107.10(8)S4–Cd3–S6
S3–Cd4–S5
S3–Cd4–S6
S5–Cd4–S6
Mean

105.32(8)115.83(8)106.76(8)100.35(8)107.28(8)Cd–Sb–Cd
Cd1–S1–Cd2
Cd1–S2–Cd3

109.94(8)113.34(9)Cd1–S3–Cd4
Cd2–S4–Cd3

112.25(8)116.69(9)Cd2–S5–Cd4
Cd3–S6–Cd4
Mean

109.47(9)116.3(1)113.0(1)at, terminal ligand; b, bridging ligand.

sulfur atoms. The stretching vibration m(Cd–St) and m(Cd–Sb) bands in the spectrum of 3 (Fig. 3 (b)) are assigned at
352 and 220 cm1, respectively [11]. The spectra of 2
(Fig. 3 (a)) and 3 were very similar and the two bands corresponding to m(M–S) shifted to lower energy from 2 (357
and 235 cm1) to 3 (352 and 220 cm1).
The structural change from 3 to 4 (Fig. 3 (c)) is reﬂectedin the spectra. As for (Me4N)2[Cd4(SPh)10], the Cd4S10 core

has a Td symmetry and it is expected to show metal–ligand
stretching vibrations with A1 (Raman active) and T2 (IRand Raman active) symmetry due to the four terminal
ligands, and A1 (Raman active) + E (Raman active) + T1
(Raman active) + 2T2 (IR and Raman active) symmetry
due to the six bridging ligands [50]. In addition, the spectrum of 4 is broadened compared to that of 3 in the whole
region. By comparing with the far-IR and Raman spectra,

ARTICLE IN PRESS
Y. Matsunaga et al. / Journal of Inorganic Biochemistry xxx (2005) xxx–xxx

Fig. 3. Far-IR spectra: (a) (Et4N)2[{Zn(ScHex)2}2(l-ScHex)2] (2), (b)(Et4N)2[{Cd(ScHex)2}2(l-ScHex)2] (3), and (c) (Et4N)2[{Cd(ScHex)}4(lScHex)6] (4).

5Waller factors, and coordination numbers are summarizedin Table S1 (see Supporting Information). For 1 and 2, the
EXAFS best ﬁt data reproduced well the Zn–S bond distances and the interactions between Zn(II) ions and carbon
atoms near sulfur atoms: Zn–S bond distances (2.259 Å for
1 and 2.345 Å for 2) and Zn  C bond distances (3.567 Å
for 1 and 3.677 Å for 2) comparing with the values in crystal structures. In particular, the interaction between two
Zn(II) ions was observed for 2 at 3.326 Å with the coordination number of one. This peak strongly suggests the
dinuclear structure in 2. The EXAFS data of 5 was ﬁt wellwhen a structure model of a polynuclear bridged by sulfur
atoms of 1-adamantanethiolate ions was assumed. The
peak at 3.298 Å should be Zn  Zn based on the ﬁt(Fig. S3). The ﬁtting of 5 without Zn  Zn interaction gave
a worse F value (18.993%) and the ﬁt did not reproduce thepeak in the range from 2.5 to 3.0 Å (data not shown). FarIR and elemental analysis further support that 5 contains
common [Zn(SAd)2] framework. We also conclude that
this relatively stronger Zn  Zn interaction is very usefulassignment by zinc K-edge EXAFS data for determining
the structure as reported [11].
2.5. Sulfur K-edge EXAFS spectroscopy

Fig. 4. Far-IR spectra: (a) [Zn(l-SAd)2]n (5) and (b) [Cd(l-SAd)2]n (6).

the bands at 352 and 303 cm1 in 4 were assigned to m(Cd–St), and the newly formed band at 247 cm1 was assigned
to m(Cd–Sb).
The structures of 5 and 6 were studied by far-IR spectra.
Each spectrum shows similar patterns as shown in Fig. 4.
Three strong bands shifted toward lower energy side from
Zn(II) complex 5 to Cd(II) complex 6. Two of them at 367
and 294 cm1 in the spectrum of 5, which show larger shifts(diﬀerence 8–14 cm1) rather than the third one (diﬀerence
4 cm1), are assigned to m(Zn–S). In the spectrum of 6, thebands at 359 and 280 cm1 are assigned to m(Cd–S). Elemental analysis supported that 5 and 6 have the same composition containing an [M(SAd)2] framework.
2.4. Zinc K-edge EXAFS spectroscopy
The zinc K-edge EXAFS spectra were measured for 1, 2,
and 5. The k3-weighted EXAFS oscillation data and its
associated Fourier transforms in comparison with each ﬁtting data are shown in Figs. S1–S3 (see Supporting Information). The obtained interatomic distances, Debye–

The sulfur K-edge EXAFS Fourier transforms of 1–6
are shown in Figs. 5–10 with corresponding spectral ﬁts.
The obtained interatomic distances, Debye–Waller factors,
and coordination numbers are summarized in Table 2. The
EXAFS results of 1–4 are in good agreement with the crystallographic data. It is worthy to notice that S  S interactions were observed clearly for all the spectra. For 1, S  S
interactions between neighboring sulfur atoms (S1  S2,
S1  S3, and S2  S3 in Fig. 1) appeared at 3.914 Å in
Fig. 5, in good agreement with the crystal data (av.
3.917(4) Å). S  S interactions in the spectra of 2
(3.827 Å, Fig. 6) includes not only between terminal sulfur
atoms (S2  S3) but also between bridging and terminal
sulfur atoms (S1  S2 and S1  S3) and between bridging
sulfur atoms (S1  S1 0 ), all in good agreement with crystallographic data (av. 3.864(2) Å). In the case of 3 (Fig. 7), theS  S interaction was observed at 4.149 Å, which is in good
agreement with the crystallographic data (av. 4.136(6) Å)[31]. In the crystal structure of 4 (Fig. 2), S  S distances(including Sb  Sb and Sb  St) range widely from3.896(3) Å (S1  S4) to 4.355(3) Å (S3  S5). The EXAFS
data ﬁtting of 4 improves when the S  S interactions are
divided into two parts as the shorter S  S interactions(3.896(3)–4.109(3) Å) and the longer one (4.123(3)–4.355(3) Å). The shorter and longer S  S interactions are
ﬁt at 3.992 and 4.263 Å, respectively (Fig. 8), consistent
with the average distance of crystallographic data (av.
4.018(4) and av. 4.245(5) Å).
The S  S interaction of 1 was found to be longer thanthat of 2 (3.914 Å for 1, 3.827 Å for 2). This trend is dueto the structural diﬀerence: 1; planar and 2; tetrahedral.
The S  S interactions of 2 include two types: the shorter

ARTICLE IN PRESS
6

Y. Matsunaga et al. / Journal of Inorganic Biochemistry xxx (2005) xxx–xxx

Fig. 5. Sulfur K-edge EXAFS Fourier transform of 1; experimental (solidline) and the ﬁt (dash line) data. (Inset: the k3-weighted sulfur K-edge
EXAFS of 1; experimental (solid line) and the ﬁt (dash line) data.)

Fig. 8. Sulfur K-edge EXAFS Fourier transform of 4; experimental (solidline) and the ﬁt (dash line) data. (Inset: the k3-weighted sulfur K-edge
EXAFS of 4; experimental (solid line) and the ﬁt (dash line) data.)

Fig. 6. Sulfur K-edge EXAFS Fourier transform of 2; experimental (solidline) and the ﬁt (dash line) data. (Inset: the k3-weighted sulfur K-edge
EXAFS of 2; experimental (solid line) and the ﬁt (dash line) data.)

Fig. 9. Sulfur K-edge EXAFS Fourier transform of 5; experimental (solidline) and the ﬁt (dash line) data. (Inset: the k3-weighted sulfur K-edge
EXAFS of 5; experimental (solid line) and the ﬁt (dash line) data.)

Fig. 7. Sulfur K-edge EXAFS Fourier transform of 3; experimental (solidline) and the ﬁt (dash line) data. (Inset: the k3-weighted sulfur K-edge
EXAFS of 3; experimental (solid line) and the ﬁt (dash line) data.)

Fig. 10. Sulfur K-edge EXAFS Fourier transform of 6; experimental(solid line) and the ﬁt (dash line) data. (Inset: the k3-weighted sulfur Kedge EXAFS of 6; experimental (solid line) and the ﬁt (dash line) data.)

distance of Sb  Sb at 3.594(2) Å and the longer distancesof Sb  St and St  St ranging from 3.849(7) to 4.088(2) Å[11]. For the analogous complexes [{Zn(SR)2}2(l-SR)2]2

(SR = SPh and SEt), the average S  S interaction is3.835(9) Å for SR = SPh and 3.848(8) Å for SR = SEt[51,52]. Similarly to 2, Sb  Sb distance was at 3.891(1) ÅARTICLE IN PRESS
Y. Matsunaga et al. / Journal of Inorganic Biochemistry xxx (2005) xxx–xxx

7

Table 2
Coordination number (CN), interatomic distances (r, Å), Debye–Waller factors (r2, Å2) and goodness of ﬁt parameter (F, %) obtained from the best ﬁts tothe sulfur K-edge EXAFS data for 1–6
Complex

Pair atomCNr (Å)

r2 (Å2)

Fa (%)

Average bond distanceb (Å)

Reference(Et4N)[Zn(SAd)3] (1)

Zn
S
C
Cfar

1
2
1
3

2.257
3.914
1.858
2.759

0.00340.00380.00350.0031

1.106

2.262(4)3.917(4)1.844(9)2.770(9)[11](Et4N)2[{Zn(ScHex)2}2(l-ScHex)2] (2)

Zn
S
C
Cfar

1.33
3.67
1
1

2.361
3.827
1.845
2.796

0.00350.00260.00380.00211.741

2.352(1)3.864(2)1.831(5)2.779(5)[11](Et4N)2[{Cd(ScHex)2}2(l-ScHex)2] (3)

Cd
S
C
Cfar

1.33
3.67
1
2

2.555
4.149
1.851
2.726

0.00350.00090.00360.00382.255

2.550(4)4.136(6)1.848(17)2.75(1)[31](Et4N)2[{Cd(ScHex)}4(l-ScHex)6] (4)

Cd
S
S
C
Cfar

1.67
4.8
4.8
1
2

2.543
3.992
4.263
1.836
2.761

0.00360.00370.00300.00380.05062.056

2.547(7)4.018(4)4.245(5)1.827(10)2.75(3)This work[Zn(l-SAd)2]n (5)

Zn
S
C
Cfar

2
5
1
3

2.390
3.544
1.834
2.876

0.00170.00340.00450.0213

6.242

This work[Cd(l-SAd)2]n (6)

Cd
S
C
Cfar

2
5
1
3

2.566
3.713
1.828
2.895

0.00090.01460.00050.0306

6.786

This workabPP
F = { (k3vobs  k3vcalc)2/ (k3vobs)2}1/2.
Bond distances in crystallographic data.

and longer Sb  St and St  St ranging from 3.9507(6) to
4.3955(6) Å in the crystal structure of 3. The averageS  S interaction of [{Cd(SPh)2}2(l-SPh)2]2 is 4.130(9) Å[51]. The S  S interactions of 4, having a Cd4S6 adamantane-like cage, span a wide range 3.992 and 4.263 Å. Thus,
the presence of M2(l-SR)2 core is predicted when the S  S
interaction was at 3.8 and 4.1 Å for unknown Zn(II) andCd(II) complexes, respectively. This S  S interaction by
sulfur K-edge EXAFS could determine the equivalent
structural information instead of measuring Zn  Zn interaction by zinc K-edge EXAFS. In addition, S  Cfar interaction in Fig. 5 for 1 (2.759 Å), in Fig. 6 for 2 (2.796 Å) and
Fig. 7 for 3 (2.726 Å), also contributes to settle these results
by sulfur K-edge EXAFS.
The structures of 5 and 6 were determined based on theS  S and S  Cfar distance values by the sulfur K-edge
EXAFS ﬁts. The structure of 5 and 6 includes the[M(SAd)2] framework from far-IR and elemental analysis
as described above. In the XAS spectrum of 6, an edge
was observed at 2850 eV, which should originate fromtrace amounts of chloride ions used in the synthesis. Thus,
the spectrum limited in the 2520–2820 eV region was usedthroughout the ﬁts for 6. The ﬁttings of 5 and 6 agreed
fairly well with experimental data with small F values(6.242% for 5 and 6.786% for 6) as shown in Fig. 9 for 5
and Fig. 10 for 6. Moreover, for both complexes, the pres-ence of S  S was convincing. The obtained S  S interaction distances of 5 and 6 (3.544 Å for 5 and 3.713 Å for6, respectively) are shorter than those of 2 (3.827 Å), 3(4.149 Å),[{M(SPh)2}2(l-SPh)2]2
(M = Zn(II)(3.835(9) Å) and Cd(II) (4.130(9) Å)), and [{Zn(SEt)2}2(lSEt)2]2 (3.848(8) Å) [52]. These results suggest that structures of 5 and 6 contain only Sb  Sb interaction similar toSb  Sb of 2 (4.594(2) Å [11]) and 3 (3.891(1) Å [31]), andare much shorter than the Sb  St and St  St. Thus, 5
and 6 are found to polynuclear structures. The S–M distance and S  S interaction of 6 (Cd(II) complex) arelonger than those of 5 (Zn(II) complex). When the ﬁtting
was carried out without S  S interaction, F values arehigher, 9.739% for 5, 19.616% for 6 (data not shown).
These data rule out the possibility of 5 and 6 being a mononuclear. The S–C and S  Cfar distances are almost thesame. Therefore, it is conﬁrmed that these EXAFS curve
ﬁt data can be applied to clarify unknown structure.
For the ﬁt of zinc K-edge EXAFS of 5, three waves ﬁt
was performed. Complementarily, four waves nicely ﬁt in
the sulfur K-edge EXAFS for the same complex. The
Zn–S bond was monitored by both from zinc 1s absorption(2.40 Å, Table S1) and from S 1s absorption (2.39 Å, Table2). The distance values obtained were essentially identical.
Thus in general, the sulfur K-edge EXAFS analyses in thispaper are reliable.

ARTICLE IN PRESS
8Y. Matsunaga et al. / Journal of Inorganic Biochemistry xxx (2005) xxx–xxx

3. Conclusion

4.1. Synthesis

The complexes with saturated sulfur containing ligands,
1–4, were studied using the sulfur K-edge EXAFS spectroscopy. Both S   S and S  Cfar interactions were detected
clearly in the EXAFS analysis of 1–4. We showed that thisinformation could be used reliably for determining thestructures either mononuclear or polynuclear. The structures of 5 and 6 can be determined by ﬁtting the sulfur
K-edge EXAFS, coupled with far-IR spectra and elemental
analysis. The S  S interaction was observed in both
EXAFS spectra which further supports that 5 and 6 havea polynuclear structure. It also indicates that the applied
parameters should relate to each expected structure. To
conﬁrm the feasibility of sulfur K-edge EXAFS to homoleptic thiolato complexes having closed d10 electronic conﬁguration, obtained data was compared to the results ofzinc K-edge EXAFS spectroscopy as well-establishedmethod. The two methodologies were found to give complementary, consistent bonding information. In summary,the information obtained from the sulfur K-edge EXAFS
spectroscopy would be useful for determining structuresof various Zn(II) and Cd(II) complexes in combination
with other spectroscopic data.

Complexes 1 and 2 were synthesized by the method
reported earlier [11]. 1-Adamantanethiol (HSAd) was synthesized by the same procedure following Refs. [54,55].
NaSAd and NaScHex were formed by the reaction of
HSAd and HScHex with 0.8 eq. of NaH in diethyl ether,respectively.
(Et4N)2[{Cd(ScHex)2}2(l-ScHex)2](3)
and(Et4N)2[{Cd(ScHex)}4(l-ScHex)6] (4). The synthesisof 3 was carried out by the reported method [31] by usingof CdCl2 Æ 2.5H2O (0.228 g, 1.0 mmol), NaScHex (0.443 g,
3.20 mmol), and Et4NCl (0.183 g, 1.10 mmol) in the mixed
solvent of acetonitrile and ethanol. The colorless crystals of
3 were formed from diethyl ether and acetonitrile. The colorless crystals of 4 suitable for X-ray analysis were formed
from the solution after 3 was removed at 30 °C (0.430 g,
21% yield). For 3; Anal. Calcd. for C52H106N2Cd2S6: C,
53.08; H, 9.08; N, 2.38%. Found: C, 52.81; H, 9.00; N,
2.51%. IR m/cm1 (KBr): 3423m, 2918vs, 1487m, 1443m,
1394m, 1171m, 997m, 784m. far-IR m/cm1 (CsI): 514w,
439w, 352vs, 333m, 315m, 301m, 220m, 209m, 181m.
UV–Vis k/nm (CH3CN): 246. For 4; Anal. Calcd. for
C72H154N2Cd4S10O2 (4 Æ 2H2O): C, 46.74; H, 8.39; N,
1.51%. Found: C, 46.87; H, 7.95; N, 1.39%. IR m/cm1(KBr): 3435m, 2922vs, 2848s, 1482w, 1445m, 1260m,
1200m, 1172m, 997m, 817w, 729w. far-IR m/cm1 (CsI):
514m, 474w, 438w, 352vs, 337m, 303m, 247m, 227w.
Raman shift m/cm1: 515w, 438w, 364s, 357vs, 338m,
321m, 307m, 292m, 235m, 219m, 195m, 176m. UV–Vis k/
nm (CH3CN): 212.
[Zn(l-SAd)2]n (5). ZnCl2 (0.307 g, 2.25 mmol) dissolved in methanol (15 mL) was added to the NaSAd(0.942 g, 4.95 mmol) solution in methanol (15 mL). The
white powder was immediately formed. After stirring the
mixture for several hours, the solution was concentrated
to dryness. The residue was washed with dichloromethane,water and methanol (0.507 g, 56% yield). Anal. Calcd. for
C21H34S2OZn (5 Æ CH3OH): C, 58.38; H, 7.93%. Found:C, 58.59; H, 7.56%. IR m/cm1 (KBr): 2903vs, 2847m,
1448w, 1297w, 1101w, 1037m, 830w, 684w. far-IR m/
cm1 (CsI): 476m, 367vs, 294vs, 268m, 168s. Raman shiftm/cm1: 479m, 402m, 372s, 253vs. UV–Vis k/nm (solid):
219.
[Cd(l-SAd)2]n(6).
CdCl2 Æ 2.5H2O(0.280 g,
1.23 mmol) dissolved in methanol (15 mL) was added to
the NaSAd (0.499 g, 2.62 mmol) solution in methanol(15 mL). The white powder was immediately formed. After
stirring the mixture for several hours, the solution was concentrated to dryness. The residue was washed with waterand methanol (0.330 g, 56% yield). Anal. Calcd. for
C20H30CdS2Cl0.5Na0.5 (6 Æ 0.5NaCl): C, 50.44; H, 6.35%.
Found: C, 50.69; H, 6.41%. IR m/cm1 (KBr): 2908vs,
2846m, 1448w, 1295w, 1101w, 1036m, 827w, 682w. farIR m/cm1 (CsI): 476m, 359vs, 280vs, 264m, 152s. Raman
shift m/cm1: 481w, 449s, 400w, 362m, 258vs. UV–Vis k/
nm (solid): 254.

4. Experimental
ZnCl2 and CdCl2 Æ 2.5H2O were obtained from Wako
Pure Chemical Int. Ltd. CDCl3 was purchased from Cambridge Isotope Laboratories Inc. All chemical reagentswere used without further puriﬁcation. Preparation andhandling of all the complexes were performed under anargon atmosphere by employing standard Schlenk line
techniques. Ethanol and methanol were commercially spectroscopic grade and used after bubbling argon gas. Acetonitrile and dichloromethane were distilled from CaH2 andP2O5 prior to use, respectively. Diethyl ether was carefully
puriﬁed by reﬂuxing/distilling under an argon atmosphere
over sodium benzophenone ketyl [53].
IR or far-IR spectra were recorded on KBr pellets in theregion of 4600–400 cm1 or CsI pellets in the region of
650–100 cm1 using a JASCO FT/IR-550 spectrophotometer, respectively. FT-Raman spectra were measured using
KBr or neat pellets on a Perkin–Elmer Spectrum GX spectrophotometer. Abbreviations used in the description ofvibration data are as follows: vs, very strong; s, strong;m, medium, w, weak. UV–Vis spectra of solution state
were recorded with a JASCO V-570 spectrophotometer atroom temperature using a quartz cell (1 mm path length)
in the region of 200–500 nm. UV–Vis spectra of solid state
were recorded using the ﬁne powder mull samples, whichwere prepared by ﬁnely grinding the solid materials, witha JASCO V-560 spectrophotometer in the region of 200–
500 nm. These were suspended in mineral oil (poly(dimethylsiloxane), Aldrich) and spread between quartz plates.
Elemental analysis (C, H, N) was performed by the Chemical Analysis Center of the University of Tsukuba.

ARTICLE IN PRESS
Y. Matsunaga et al. / Journal of Inorganic Biochemistry xxx (2005) xxx–xxx

4.2. Crystallography
Crystal data and reﬁnement parameters for 4 are given
in Table 3. The diﬀraction data were measured on a Rigaku/MSC Mercury CCD system with graphite monochromated Mo Ka (k = 0.71069 Å) radiation at 61 °C. The
crystal was mounted on glass ﬁber by epoxy glue. The unit
cell parameters of the crystal were retrieved using Rigaku
Daemon software and reﬁned using CrystalClear on all
observed reﬂections [56]. Data using 0.5° intervals in /and x for 20 s/frame were collected with a maximum resolution of 0.77 Å (744 oscillation images). The highly redundant data sets were reduced using CrystalClear andcorrected for Lorentz and polarization eﬀects. An empiricalabsorption correction was applied. Structures were solved
by direct-methods using the program SIR 92 [57]. The position of the metal atoms and their ﬁrst coordination sphere
were located from the E-map; other non-hydrogen atoms
were found in alternating diﬀerence Fourier syntheses(DIRDIF-99) [58] and least-squares reﬁnement cycles andduring the ﬁnal cycles, were reﬁned anisotropically (CrystalStructure) [59,60]. Hydrogen atoms were placed in calculated positions.
4.3. Measurements of zinc and sulfur K-edge EXAFSThe zinc and sulfur K-edge EXAFS data of 1–6 wererecorded on bending magnet beam line 7C and 9A[61,62], respectively, at KEK Photon Factory, Tsukuba,
Japan. Ring operation conditions were 2.5 GeV and 440–
300 mA. Double Si(1 1 1) crystals were used as the monochromator. For the curve ﬁt analyses, the empirical parameters of backscattering amplitudes and phase shifts for 5
and 6 were extracted from the EXAFS data for 2 and 3
Table 3
Crystallographic data of (Et4N)2[{Cd(ScHex)}4(l-ScHex)6] (4)Complex4 Æ 4.5MeCN
FormulaC85H163.50Cd4N6.50S10
FW2047.01
Crystal system
Monoclinic
Space group
P21/n (No. 14)
a (Å)
14.879(6)b (Å)
29.413(11)c (Å)
24.720(9)b (°)
110.988(4)V (Å3)
10,101.0(66)Z
4
Dcalc (g cm3)
1.346
l (Mo Ka) (cm1)
10.80
Temperature (°C)
61
2h Range (°)
6–55
Reﬂections collected81,032
Unique reﬂections
22,525Rint
0.063
Number of observations
12,159 (I > 2r(I))
Number of variables
966
Final R, Rwa
0.060, 0.086
1.01/0.78
Maximum/minimum peak (e Å3)
P
P
P
P
a
R = iFo|  |Fci/ |Fo|;Rw ¼ ½ð wðjF o j  jF c jÞ2 = wF 2o Þ1=2 ,2
w = 1/r (|Fo|).

9(see below). Sample preparation was carried out underambient condition. To avoid any artifacts of sample preparations, we checked the data reproducibility and tried toobtain the best spectra by more than three independentmeasurements for zinc K-edge and more than ﬁve independent measurements for sulfur K-edge. The zinc K-edge
EXAFS data was collected in the transmission mode underambient condition for ﬁnely powdered samples. The energy
at the zinc K-edge was referred to the value for Zn foil at
9660 eV. The sulfur K-edge EXAFS data were collectedby standard ﬂuorescence detection techniques using a Lytle
detector on ﬁnely powdered samples, which were spreadthin and as uniform as possible [63]. The sample was kept
under helium gas at room temperature during measurement. The ﬁrst intense pre-edge peak for Na2S2O3 Æ 5H2O
was referred to 2472.02 eV. The program of REX2000[64] was used to extract the EXAFS signal and to analyze
the data. Least-squares reﬁnements of the structuralparameters of the complexes were carried out against the
k3-weighted EXAFS signal to minimize the ﬁt index. The
cadmium K-edge is the borderline where this EXAFS
experiment is possible at KEK Photon Factory. The cadmium K-edge measurements for complexes 3, 4, and 6
are in progress at SPring-8 but they are not reported in thispaper.
4.4. Curve ﬁt analyses of zinc and sulfur K-edge EXAFS
Empirical back scattering and phase shifts of parameters
for the zinc K-edge EXAFS were extracted from 1 for Zn–
S and Zn–C bonds, and from 2 for Zn  Zn interaction.
Theoretical parameters were used based on McKale forZn  C interactions [65]. Debye–Waller factors for model
parameters were set to 0.06 Å. The crystallographic datafor 1 and 2 were based on Ref. [11]. For 1, the greatest peakin the range of 1.534–2.362 Å was deﬁned to Zn–S of
2.262 Å. Another peak in the range of 2.976–3.528 Å wasdeﬁned to Zn  C of 3.585 Å. For 2, the peak in the rangeof 2.700–3.160 Å was deﬁned to Zn  Zn of 3.312 Å andthat in the range of 3.160–3.559 Å was deﬁned to Zn  Cof 3.625 Å. The ﬁtting parameters in 5 were used basedon the back scattering and phase shifts of 2 for Zn–S andZn  Zn, and McKale for Zn  C [65].
The ﬁt parameter for S–C, S–Zn, S–Cd, S  Cfar, andS  S were extracted from the EXAFS data of complex 2
and 3 or theoretical parameters (McKale) [65]. The sulfur
K-edge energy is relatively low (2471 eV) compared withthat of metal, the obtained intensity is relatively low. Thus,
we only discussed short-range S  S distances. Debye–Waller factors for model parameters were set to 0.06 Å. The
corresponding bond distances of 2 and 3 are obtained fromeach crystal structure in the references [11,31]. For thecomplex 2, the peak in the range of 0.920–1.902 Å wasdeﬁned to S–C of 1.831 Å, and that in the range of
1.902–2.792 Å was deﬁned to S–Zn of 2.352 Å. The peaksin the range of 2.792–3.375 Å and in the range of 3.375–
3.958 Å were deﬁned to S  Cfar of 2.779 Å and S   S ofARTICLE IN PRESS
10Y. Matsunaga et al. / Journal of Inorganic Biochemistry xxx (2005) xxx–xxx

3.864 Å, respectively. The shells used for 3 were S–C of
1.848 Å in the range of 0.951–1.963 Å, S–Cd of 2.550 Å
in the range of 1.902–3.007 Å, S  Cfar of 2.75 Å in therange of 3.007–3.958 Å, and S  S of 4.136 Å in the rangeof 3.958–4.449 Å. The distances of S  Cfar and S  S wereused by crystallographic data [14]. For the curve ﬁtting of 5
in Fig. 9, the back scatterings and phase shifts of S–Zn, S–
C and S  S of 2 are used as experimental parameters and
McKale is used for S  Cfar interaction as theoreticalparameter. The curve ﬁtting of 6 in Fig. 10 was performedby using the back scatterings and phase shifts of S–Cd and
S–C of 3 as experimental parameters and of S  Cfar andS  S interaction as McKale [65]. In these data ﬁts, thethreshold energy shifts were found to between 7.7 and12.2 eV for the shells ﬁt with empirical parameters. The
shift values were between 9.1 and 14.5 eV for the shells
ﬁt with McKale parameters (Zn  C, S  Cfar, and S  S).
Thus, the ﬁts using MaKale parameters were rationalized.
Debye–Waller factors in 3 and 6 were very small. One possible reason for these strange factors is pinhole eﬀects,
which was sometimes observed in the same experimental
conditions.
Acknowledgments
We thank Professor K. Tanaka of Institute of Molecular
Science for FT-Raman measurements. This research was inpart supported by Grant-in-Aid for Scientiﬁc Research(Nos. 11640555, 13555257, and 14540510) from Japan Society for the Promotion of Science, and the 21st Century COE(Center of Excellence) program (Promotion of Creative
Interdisciplinary Materials Science for Novel Functions)from Ministry of Education, Culture, Sports, Science andTechnology. Finally, we appreciate the kind editing of thismanuscript by Dr. Peng Chen of Harvard University.
Appendix A. Supplementary data
Crystallographic data have been deposited at the
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK andcopies can be obtained on request, free of charge, by quoting the publication citation and the deposition numbers
260804. Supplementary data associated with this article(zinc K-edge EXAFS data with each ﬁtting data (Figs.
S1–S3) and the obtained radial distances, Debye–Waller
factors and coordination numbers (Table S1)) can befound, in the online version at doi:10.1016/
j.jinorgbio.2005.11.004.
References[1] G. Henkel, B. Krebs, Chem. Rev. 104 (2004) 801–824.
[2] I.G. Dance, Polyhedron 5 (1986) 1037–1104.
[3] P.J. Blower, J.R. Dilworth, Coord. Chem. Rev. 76 (1987) 121–185.
[4] Y. Zhang, S. Mukherjee, E. Oldﬁeld, J. Am. Chem. Soc. 127 (2005)
2370–2371.
[5] S. Lipton, C. Bergquist, G. Parkin, P.D. Ellis, J. Am. Chem. Soc. 125(2003) 3768–3772.

[6] M.F. Summers, Coord. Chem. Rev. 86 (1988) 43–134.
[7] L.M. Utschig, J.W. Bryson, T.V. O’Halloran, Science 268 (1995) 380–
385.
[8] G. Fleissner, P.M. Kozlowski, M. Vargek, J.W. Bryson, T.V.
O’Halloran, T.G. Spiro, Inorg. Chem. 38 (1999) 3523–3528.
[9] Y. Matsunaga, K. Fujisawa, N. Amir, Y. Miyashita, K. Okamoto, J.
Coord. Chem. 58 (2005) 1047–1061.
[10] Y. Matsunaga, K. Fujisawa, N. Amir, Y. Miyashita, K. Okamoto,Appl. Organomet. Chem. 19 (2005) 778–789.
[11] Y. Matsunaga, K. Fujisawa, N. Ibi, N. Amir, Y. Miyashita, K.
Okamoto, Bull. Chem. Soc. Jpn. 78 (2005) 1285–1287.
[12] E.I. Solomon, B. Hedman, K.O. Hodgson, A. Dey, R.K. Szilagyi,
Coord. Chem. Rev. 249 (2005) 97–129.
[13] T. Glaser, B. Hedman, K.O. Hodgson, E.I. Solomon, Acc. Chem.
Res. 33 (2000) 859–868.
[14] J.E. Penner-Hahn, Coord. Chem. Rev. 249 (2005) 161–177.
[15] A. Vogel, O. Schilling, W. Meyer-Klaucke, Biochemistry 43 (2004)
10379–10386.
[16] D.A. Tobin, J.S. Pickett, H.L. Hartman, C.A. Fierke, J.E. PennerHahn, J. Am. Chem. Soc. 125 (2003) 9962–9969.
[17] S. Priggemeyer, P. Eggers-Borkenstein, F. Ahlers, G. Henkel, M.
Körner, H. Witzel, H.-F. Nolting, C. Hermes, B. Krebs, Inorg. Chem.
34 (1995) 1445–1454.
[18] J.L. Thorvaldsen, A.K. Sewell, A.M. Tanner, J.M. Peltier, I.J.
Pickering, G.N. George, D.R. Winge, Biochemistry 33 (1994) 9566–
9577.
[19] R.A.D. Pattrick, J.F.W. Mosselmans, J.M. Charnock, Eur. J.
Mineral. 10 (1998) 239–249.
[20] H. Hosokawa, K. Murakoshi, Y. Wada, S. Yanagida, M. Satoh,Langmuir 12 (1996) 3598–3603.
[21] Q. Zhou, T.W. Hambley, B.J. Kennedy, P.A. Lay, Inorg. Chem. 42(2003) 8557–8566.
[22] J.-S. Kim, M. Ree, T.J. Shin, O.H. Han, S.J. Cho, Y.-T. Hwang, J.Y.
Bae, J.M. Lee, R. Ryoo, H. Kim, J. Catal. 218 (2003) 209–219.
[23] J.M. Corker, J. Evans, J. Chem. Soc., Chem. Commun. (1994) 1027–
1029.
[24] C.E. Hayter, J. Evans, J.M. Corker, R.J. Oldman, B.P. Williams, J.
Mater. Chem. 12 (2002) 3172–3177.
[25] S.J. Hibble, R.I. Walton, M.R. Feaviour, A.D. Smith, J. Chem. Soc.,
Dalton Trans. (1999) 2877–2883.
[26] P. Roubin, S. Varin, C. Crépin, B. Gauthier-Roy, A.-M. Flank, R.
Delaunay, M. Pompa, B. Tremblay, J. Chem. Phys. 109 (1998) 7945–
7948.
[27] J. Evans, J.M. Corker, C.E. Hayter, R.J. Oldman, B.P. Williams,
Chem. Commun. (1996) 1431–1432.
[28] S.J. Hibble, R.I. Walton, D.M. Pickup, J. Chem. Soc., Dalton Trans.
(1996) 2245–2251.
[29] S. Maeyama, M. Sugiyama, S. Huen, M. Oshima, J. Cryst. Growth
150 (1995) 1122–1125.
[30] Z. Gui, A.R. Green, M. Kasrai, G.M. Bancroft, M.J. Stillman, Inorg.
Chem. 35 (1996) 6520–6529.
[31] J. Sola, P. Gonzáles-Duarte, J. Sanz, I. Casals, T. Alsina, I. Sobrados,
A. Alvarez-Larena, J.-F. Piniella, X. Solans, J. Am. Chem. Soc. 115(1993) 10018–10028.
[32] T. Costa, J.R. Dorfman, K.S. Hagen, R.H. Holm, Inorg. Chem. 22(1983) 4091–4099.
[33] K.S. Hagen, J.G. Reynolds, R.H. Holm, J. Am. Chem. Soc. 103(1981) 4045–4063.
[34] K.S. Hagen, J.M. Berg, R.H. Holm, Inorg. Chim. Acta 45 (1980)
L17–L18.
[35] I.G. Dance, J. Am. Chem. Soc. 101 (1979) 6264–6273.
[36] I.G. Dance, J.C. Calabrese, J. Chem. Soc., Chem. Commun. (1975)
762–763.
[37] Z.-X. Huang, H.-Y. Hu, W.-Q. Gu, G. Wu, J. Inorg. Biochem. 54(1994) 147–155.
[38] J.L. Hencher, M.A. Khan, F.F. Said, D.G. Tuck, Polyhedron 4(1985) 1263–1267.
[39] K.S. Hagen, R.H. Holm, Inorg. Chem. 22 (1983) 3171–3174.

ARTICLE IN PRESS
Y. Matsunaga et al. / Journal of Inorganic Biochemistry xxx (2005) xxx–xxx[40] S.L. Guo, E. Ding, S.M. Liu, Y.Q. Yin, J. Inorg. Biochem. 70 (1998)
7–10.
[41] P.A.W. Dean, J.J. Vittal, Inorg. Chem. 26 (1987) 278–283.
[42] I.G. Dance, A. Choy, M.L. Scudder, J. Am. Chem. Soc. 106 (1984)6285–6295.
[43] A. Choy, D. Craig, I. Dance, M. Scudder, J. Chem. Soc., Chem.
Commun. (1982) 1246–1247.
[44] P.A.W. Dean, N.C. Payne, J. Wranich, J.J. Vittal, Polyhedron 17(1998) 2411–2416.
[45] I.G. Dance, Inorg. Chem. 20 (1981) 2155–2160.
[46] P.A.W. Dean, J.J. Vittal, Y. Wu, Can. J. Chem. 70 (1992) 779–791.
[47] P.A.W. Dean, J.J. Vittal, N.C. Payne, Inorg. Chem. 26 (1987) 1683–
1689.
[48] P.A.W. Dean, N.C. Payne, J.J. Vittal, Y. Wu, Inorg. Chem. 32 (1993)
4632–4639.
[49] I.G. Dance, J. Am. Chem. Soc. 102 (1980) 3445–3451.
[50] T. Løver, G.A. Bowmaker, J.M. Seakins, R.P. Cooney, Chem. Mater.
9 (1997) 967–975.
[51] I.L. Abraham, C.D. Garner, W. Clegg, J. Chem. Soc., Dalton Trans.
(1987) 1577–1579.
[52] A.D. Watson, C.P. Rao, J.R. Dorfman, R.H. Holm, Inorg. Chem. 24(1985) 2820–2826.
[53] W.L.F. Armarego, D.D. Perrin, Puriﬁcation of Laboratory Chemicals, fourth ed., Butterworth-Heinemann, Oxford, 1997.
[54] K.K. Khullar, L. Bauer, J. Org. Chem. 36 (1971) 3038–3040.
[55] J.M. Kokosa, L. Bauer, R.S. Egan, J. Org. Chem. 40 (1975) 3196–
3199.

11

[56] CrystalClear Ver. 1.3., J.W. Pﬂugrath, Acta Crystallogr. D55 (1999)
1718.
[57] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M. Burla,
G. Polidori, M. Camalli, J. Appl. Crystallogr. 27 (1994) 435.
[58] P.T. Beurskens, G. Admiraal, G. Beurskens, W.P. Bosman, R. de
Gelder, R. Israel, J.M.M. Smits, The DIRDIF-99 program system,
Technical Report of the Crystallography Laboratory, University of
Nijmegen, The Netherlands, 1999.
[59] CrystalStructure 3.51: Crystal Structure Analysis Package, Rigaku
and Rigaku/MSC, 2003.
[60] Crystal Issue 10: D.J. Watkin, C.K. Prout, J.R. Carruthers, P.W.
Betteridge, Chemical Crystallography Laboratory, Oxford, UK,
1996.
[61] M. Nomura, A. Koyama, M. Sakurai, KEK Report 91 (1) (1991) 1–
21.
[62] M. Nomura, A. Koyama, J. Synchrotron Rad. 6 (1999) 182–
184.
[63] Y. Izumi, T. Minato, K. Aika, A. Ishiguro, T. Nakajima, Y.
Wakatsuki, Studies in Surface Science and Catalysis, in: E.
Gaigneaux, D.E. De Vos, P. Grange, P.A. Jacobs, J.A. Martens,
P. Ruiz, G. Poncelet (Eds.), Scientiﬁc Bases for the Preparationof Heterogeneous Catalysts, vol. 143, Elsevier, Amsterdam, 2002,
pp. 361–368.
[64] XAFS analysis software ver. 2.04: REX2000 for Windows, Rigaku(2000).
[65] A.G. McKale, B.W. Veal, A.P. Paulikas, S.-K. Chan, G.S. Knapp, J.
Am. Chem. Soc. 110 (1988) 3763–3768.