Diruthenium compounds of thiol capped oligo(phenyleneethynyl) ligand: Synthesis and characterization

Article abstract of DOI:10.1016/j.jorganchem.2006.06.005

Reactions between Ru₂(DMBA)₄(NO₃)₂ and OPEn-S-TMSE ligand under weak base conditions afford trans-Ru₂(DMBA)₄(OPEn-S-TMSE)₂ compounds, where DMBA is N,N′-dimethylbenzamidinate, TM

Full text of DOI:10.1016/j.jorganchem.2006.06.005

Journal of Organometallic Chemistry 691 (2006) 4021–4027
www.elsevier.com/locate/jorganchem
Diruthenium compounds of thiol capped
oligo(phenyleneethynyl) ligand: Synthesis and characterization
*
Jie-Wen Ying, Tong Ren
Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907, USA
Received 12 May 2006; received in revised form 3 June 2006; accepted 3 June 2006
Available online 15 June 2006
Abstract
Reactions between Ru2(DMBA)4(NO3)2 and OPEn-S-TMSE ligand under weak base conditions afford trans-Ru2(DMBA)4(OPEn-S-
TMSE)2 compounds, where DMBA is N,N0-dimethylbenzamidinate, TMSE is trimethylsilylethylene, and OPEn are –C„CC6H4– (1),
–C„C(2,5-(CH3O)2C6H2)–(C„CC6H4)– (2) and –(C„CC6H4)–C„C(2,5-(CH3O)2C6H2)–(C„CC6H4)– (3). Molecular structures of
compounds 1 and 2 were determined by X-ray diffraction, which revealed the extended rigid rod topology and coplanarity of phenylene-
ethynye units in 1 and 2. Electrochemical and optical energy gaps of compounds 1–3 were estimated to be 1.57 eV and ca. 1.43 eV, respec-
tively, from voltammetric and absorption spectral measurements.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Diruthenium; OPEs; Molecular wires
1. Introduction
include the a,x-ferrocenyl-OPEn-thioether series [9], an
Os3 cluster with a r-S–S(C6H4C„C)2Ph ligand [10], and
various Ru(II) and Au(I) complexes coordinated by OPEn
ligands in both r- and g2 modes [11]. Our laboratory is
interested in developing molecular wires based on linear
metal-alkynyl species with a focus on diruthenium com-
pounds supported by N,N0-bidentate ligands [12,13]. These
diruthenium alkynyl species exhibit small electrochemical
and optical energy gaps [14,15] and mediate efficient charge
transfer [16–18]. Corroborating results reported for other
metal-containing OPE molecules [19], recent STM study
of Ru2(ap)4(C„CC6H4)2S (ap is 2-anilinopyridinate)
embedded in the SAM of C11 alkane thiol revealed a mark-
edly improved molecular conductance over OPE molecule
of comparable length [12,20]. Also worthy of mentioning
is the recent demonstration of enhanced charge transfer
in trinuclear and pentanuclear metal complexes and single
molecule transistors based on this type compounds [21].
The promising result based on Ru2(ap)4(C„CC6H4)2S
inspires further study of Ru2 bis-alkynyl wires, for which
diruthenium compounds supported by symmetric DMBA
(N,N0-dimethylbenzamidinate) ligand is superior to
Ru2(ap)4 from both synthetic and structural perspectives.
Conjugated oligomers have drawn intense interest from
chemists and material scientists as the lead candidates to
replace silicon semiconductor in many (opto)electronic
applications [1], including photovoltaics [2], organic field
effect transistors [3], electrochemical and fluorescent sen-
sors [4], and molecular wires and devices [5]. Among many
established families of organic oligomers, both linear and
branched OPEs (OPE = oligo(phenyleneethynylene)) have
been heavily investigated due to their structural rigidity
and extensive p-conjugation [6], and the latter feature ren-
ders OPEs as efficient scaffolds for energy transfer over
long distances [7]. It has been noted that figures of merit
of materials may be improved over pure organic oligomers
when metal centers are incorporated into conjugated oligo-
mers either in the main chain or as the side chain pendants
[8]. Transition metal compounds with ligand containing
OPEn fragment (OPEn = (C„CC6H4)n, n P 2) have
become increasingly common in recent years, and examples
*
Corresponding author. Tel.: +1 765 494 5466; fax: +1 765 494 0239.
E-mail address: tren@purdue.edu (T. Ren).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.06.005

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J.-W. Ying, T. Ren / Journal of Organometallic Chemistry 691 (2006) 4021–4027
[23,24], and OPE3-S-TMSE ligand was prepared from a
OPEn-S-TMSE
Sonogashira coupling reaction between trimethylsilyl 4-
ethynyliodobenzene and OPE2-S-TMSE. Trimethylsilyl-
ethylene (TMSE) was chosen as the thiol protection
group because of its superior chemical stability over ace-
tyl protection group, and methoxy phenyl substituents
were introduced in both OPE2 and OPE3 ligands to
improve the solubility of the resultant Ru2(DMBA)4 com-
pounds. Compounds 1–3 were prepared from reactions
between [Ru2(DMBA)4](NO3)2 and the appropriate
OPEn-S-TMSE ligand in the presence of Et3N, and puri-
fied on silica column. Compounds 1–3 are red, diamag-
netic crystalline materials, and soluble in common
organic solvents.
N
N
Ru
N
N
N
N
N
N
Ru
TMSE-S-nEPO
OPEn-S-TMSE
Compound
SiMe3
S
1
OMe
2.2. Molecular structures
SiMe3
S
2
3
Molecular structures of compounds 1 and 2 determined
via single crystal X-ray diffraction are shown in Figs. 1 and
2, respectively, and some selected bond lengths and angles
are collected in Table 1. In both cases, the asymmetric unit
contains one half of the diruthenium molecule, and a crys-
tallographic inversion center bisecting the Ru–Ru bond
relates one half of the molecule to the other half. It is clear
from Figs. 1 and 2 that the coordination sphere of Ru2 cen-
ter retains the paddlewheel motif of Ru2(DMBA)4(NO3)2
precursor. The Ru–Ru bond lengths determined,
MeO
OMe
SiMe3
S
MeO
Scheme 1. Wire-like Ru2(DMBA)4(OPEn)2 compounds.
We previously communicated the assembly of Au nanopar-
ticles with a series of Ru2(DMBA)4(OPEn-S-TMSE)2 com-
plexes [22], where OPEn is oligo(phenyleneethynylene) with
n indicating the degree of oligomerization and TMSE is
trimethylsilylethylene (Scheme 1). Reported herein are
detailed description of the synthesis, structural study and
voltammetric properties of these novel diruthenium
compounds.
˚
2.4597(8) (1) and 2.4626(8) A (2), are comparable with
those found for the related Ru2(DMBA)4(C„CAr)2 type
compounds [25,26], and consistent with the presence of a
Ru–Ru single bond [27]. Close examination of Table 2
revealed that the first coordination sphere of Ru2 core
exhibits significant distortion from the D4h symmetry
expected for an idealized paddlewheel motif: markedly
nonlinear Ru0–Ru–Ca angles and large variances in both
Ru–N bond lengths and Ru0–Ru–N angles. This type dis-
tortion is common among Ru2(III)-bisalkynyl species
[12,13,28], and has an origin of second-order Jahn–Teller
effect [29].
2. Results and discussion
2.1. Synthesis
Thiol capped OPE1-S-TMSE and OPE2-S-TMSE
ligands were prepared following the literature procedures
Fig. 1. ORTEP plot of compound 1 at 30% probability level. Hydrogen atoms were omitted for clarity.

J.-W. Ying, T. Ren / Journal of Organometallic Chemistry 691 (2006) 4021–4027
4023
Fig. 2. ORTEP plot of compound 2 at 30% probability level. Hydrogen atoms were omitted for clarity.
Table 1
Selected bond lengths (A) and angles (ꢁ) for compounds 1 and 2
about 10 structurally characterized metal-OPEn (n P 2)
compounds that are mostly mono-OPE species and metal
centers include Ru(II), Ni(II), Pd(II), Pt(II), Ag(I) and
Au(I) [30]. Examination of the deposited data in CSD
revealed that the twist between phenyleneethyne units is
prevalent. In the only related bis-OPEn example, trans-
Pt(PBu3)2(OPE2)2 [31], all phenyleneethyne units are close
to be coplanar. The near coplanarity observed in trans-
Pt(PBu3)2(OPE2)2, compounds 1 and 2 may indicate an
extended conjugation over the entire OPEn-M-OPEn frag-
ment, although the packing effect may also contribute to
the observed coplanarity. Last but not the least, the Sꢀ ꢀ ꢀS
distances in compounds 1–3 are critical for the assessment
of their molecular wire characteristics, and values deter-
˚
1
2
Ru–Ru0
Ru–C1
Ru–N1
Ru–N2
Ru–N3
Ru–N4
C1–C2
2.4597(8)
1.995(5)
2.4626(8)
1.968(5)
1.996(4)
1.977(4)
2.103(4)
2.101(4)
1.207(7)
1.907(14)
2.074(13)
2.181(12)
2.064(14)
1.204(7)
C1–Ru–Ru0
C2–C1–Ru
N1–Ru–Ru0
N2–Ru–Ru0
N3–Ru–Ru0
N4–Ru–Ru0
160.19(17)
172.6(5)
96.5(4)
96.3(4)
80.0(4)
161.38(17)
174.6(5)
95.73(11)
97.08(12)
80.09(11)
78.86(11)
79.4(4)
˚
mined from structure refinements are 20.8 and 34.4 A for
1 and 2, respectively, and the estimated value for 3 is about
˚
48 A.
In the structure of 1, two phenyleneethyne units are
related by an inversion center and hence rigorously copla-
nar. While similar coplanarities between phenyleneethyne
units related by inversion are expected in molecule 2, it is
interesting to note that two phenyleneethyne units within
the same OPE2 are nearly coplanar as well. There are
2.3. Electrochemical and spectroscopic properties
The ability of conjugated species to function as molec-
ular wires is intimately related to their redox characteris-
tics, and those of compounds 1–3 were examined via
cyclic voltammetric technique. As shown in Fig. 3, com-
pounds 1–3 display nearly identical cyclic voltammograms
Table 2
that consist of
a reversible oxidation (A) and a
Crystallographic parameters for compounds 1 Æ C6H14 and 2 Æ C6H14
(quasi)reversible reduction (B). As the OPEn ligand elon-
gates, the reduction couple (B) becomes less reversible,
and an additional anodic wave at more positive potential
(C) is noticeable in the CV of 3, indicating partial disso-
ciation of OPE3 ligand on reduction [15]. On the other
hand, features of the oxidation couple (A) remain invari-
ant across the series. Based on the electrode potentials,
the HOMO–LUMO gaps of the solvated Ru2-OPEn were
estimated to be ca. 1.57 V from the relationship of
Eg = E1/2(A) ꢁ E1/2(B) [32].
1 Æ C6H14
2 Æ C6H14
Formula
Fw
C68H92N8Ru2S2Si2
1343.9
C2
11.219(2)
18.897(3)
16.872(3)
C88H108N8O4Ru2S2Si2
1664.3
ꢀ
Space group
P1
˚
a (A)
12.976(1)
13.840(1)
14.245(1)
106.950(2)
104.661(2)
107.477(2)
2165.2(3)
1
1.276
0.477
Mo Ka
300(2)
0.060, 0.12
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
106.173(3)
3
˚
Volume (A )
3435.6(9)
2
1.299
As shown in Fig. 4, compound 1 exhibits an intense
band at 506 nm and an NIR band at 893 nm with moderate
intensity, and the combination of both results in the dark
red appearance of the compound. The previously studied
Ru2(DMBA)4(C„CAr)2 type compounds display similar
Vis–NIR spectra of absorptions at 500–510 nm and 850–
Z
Dcalc (g cmꢁ3
)
l (mmꢁ1
)
0.580
Radiation
T (K)
R1, wR2 (I > 2r(I))
Mo Ka
300(2)
0.041, 0.095

4024
J.-W. Ying, T. Ren / Journal of Organometallic Chemistry 691 (2006) 4021–4027
that the red-shift of p ! p* band due to metallation grad-
B
B
ually diminishes upon the extension of OPEn ligand. As
shown by the inset in Fig. 4, the lowest energy band at
893 nm (1.39 eV) in 1 has been blue-shifted to 867 nm
(1.43 eV) in 2 and 846 nm (1.47 eV) in 3, while the intensity
remains the same.
1
2
A
A
A
3. Conclusion
A series of soluble and thiol-capped diruthenium-OPEn
compounds was prepared and characterized with X-ray
and voltammetric techniques. These novel compounds bear
strong similarity in both the structural and voltammetric
characteristics to the series of Ru2(DMBA)4(C2nFc)2 com-
pounds, where highly efficient hole transfer was demon-
strated through bulk solution spectroelectrochemistry
studies [17,18]. Hence, compounds 1–3 may exhibit
enhanced molecular conductance over pure OPEs of com-
parable lengths, and the measurements of single molecule
conductance are being pursued with a variety of nano-junc-
tion techniques.
B
3
C
1
0
-1
E/V, vs Ag/AgCl
-2
Fig. 3. Cyclic voltammograms of compounds 1–3 recorded in THF at a
scan rate of 0.10 V/s.
80000
2000
4. Experimental
1500
60000
Pd(PPh3)2Cl2 was purchased from Aldrich, 1-bromo-
thiophenol, diisopropylamine, triethylamine, iodine,
1,4-dimethoxybenzene, vinyltrimethylsilane, tert-butyl per-
oxide and copper iodide from ACROS, trimethylsilylacety-
lene and trimethylsilyl ethynyliodobenzene from GFS, and
silica gel from Merck. Ru2(DMBA)4(NO3)2 [33] and
OPE1-S-TMSE [23] were prepared according to the litera-
ture. THF was distilled over Na/benzophenone under an
N2 atmosphere prior to use. 1H NMR spectra were
recorded on a Bruker AVANCE300 NMR spectrometer,
with chemical shifts (d) referenced to the residual CHCl3.
Infrared spectra were recorded on a Perkin–Elmer 2000
FT-IR spectrometer using KBr disks. UV–Vis–NIR
spectra were obtained with either a Perkin–Elmer Lambda-
900 UV–Vis–NIR spectrophotometer or a Cary300 UV–
Vis spectrometer. Cyclic voltammograms were recorded
in 0.2 M (n-Bu)4NPF6solution (THF, N2-degassed) on a
CHI620A voltammetric analyzer with a glassy carbon
working electrode (diameter = 2 mm), a Pt-wire auxiliary
electrode and a Ag/AgCl reference electrode. Typical CV
was recorded from 0 V to more negative potential during
the cathodic scan, and from 0 V to more positive potential
during the anodic scan. The concentration of diruthenium
species is always 1.0 mM. The ferrocenium/ferrocene cou-
ple was observed at 0.586 V (vs. Ag/AgCl) under experi-
mental conditions.
1000
500
ε
40000
20000
0
0
600
800
1000
Comp01
Comp02
Comp03
400
600
800
1000
λ
Fig. 4. Vis–NIR spectra of compounds 1–3 recorded in THF solution.
870 nm [25]. According to the TD-DFT (B3LYP) analysis
of Ru2(DMBA)4(C„CFc)2 [18], the lowest energy absorp-
tion is attributed to the p*(Ru2) ! d*(Ru2) transition,
where the axial alkynyl ligand contributes through the anti-
bonding overlap between p(C„C) and p*(Ru2). The
absorption around 510 nm is likely a mixture of both
the L(N) ! d*(Ru2) and d(Ru2) ! d*(Ru2) transitions. The
free ligand TMS-OPE1-S-TMSE displays a p ! p* transi-
tion at 294 nm (4.22 eV) (see Section 4). The corresponding
transition in compound 1 occurs around 338 nm (3.67 eV),
implying a 0.55 eV red-shift upon metallation. Compounds
2 and 3 exhibit very intense p ! p* bands at 403 nm
(3.08 eV) and 382 nm (3.25 eV), respectively, while the free
ligands TMS-OPE2-S-TMSE and TMS-OPE3-S-TMSE
display lowest p ! p* bands at 373 nm (3.32 eV) and
377 nm (3.29 eV), respectively. These data seem to indicate
4.1. Synthesis of TMSOPE2-S-TMSE
A solution of 0.500 g (1.4 mmol) of 2-iodo-5-(trimeth-
ylsilyl)ethynyl-1,4-dimethoxybenzene, which was prepared
using the literature procedure with slight modification
[23], and 0.325 g (1.39 mmol) of OPE1-S-TMSE, 0.139 g

J.-W. Ying, T. Ren / Journal of Organometallic Chemistry 691 (2006) 4021–4027
4025
(0.2 mmol) of Pd(PPh3)2Cl2, 0.139 g (0.70 mmol) of CuI,
30 mL of diisopropylamine and 30 mL of THF was stir-
red under argon at 70 ꢁC overnight. The solvents were
removed and the residue was purified by column chroma-
tography with CH2Cl2/hexanes (1/5, v/v) to yield 0.57 g
(88%) of pure product. Data for TMS-OPE2-S-TMSE:
1H NMR: 7.47 (d, 2H, aromatic), 7.25 (m, 2H, aromatic),
6.98 (d, 2H, aromatic), 3.88 (d, 6H, CH3O–), 3.02–2.98
(m, 2H, TMSCH2CH2S–), 0.98–0.95 (m, 2H,
TMSCH2CH2S–), 0.29 (s, 9H, –Si(CH3)3), 0.09 (s, 9H, –
Si(CH3)3). UV–Vis (THF), kmax (nm, e (Mꢁ1 cmꢁ1)):
323(14900), 362(19200), 373(17100). UV–Vis (THF) of
reaction mixture was stirred at room temperature for
2 h. Upon the solvent removal, the residue was purified
by column chromatography, and eluted with THF/hex-
anes (1/5, v/v) to afford 0.108 g (38%) title compound
as red crystalline solid. Data for Ru2(DMBA)4(OPE2-S-
TMSE)2: 1H NMR: 7.48–7.41 (m, 16H, aromatic), 7.21
(d, 4H, aromatic), 7.05 (d, 8H, 6.90 aromatic), 6.89 (s,
2H, aromatic), 6.63 (s, 2H, aromatic), 3.80 (s, 6H,
CH3O–), 3.70 (s, 6H, CH3O–), 3.35 (s, 24H, MeN–),
2.99–2.94 (m, 4H, TMSCH2CH2S-), 0.95–0.83 (m, 4H,
TMSCH2CH2S–), 0.04 (s, 9H, –Si(CH3)3), 0.01 (s, 9H,
–Si(CH3)3); MS-FAB (m/e, based on 101Ru): 1581 [M+];
TMS-OPE1-S-TMSE,
k
max(nm,
e
(Mꢁ1 cmꢁ1)):
Vis–NIR,
k
max(nm,
e
(Mꢁ1 cmꢁ1)): 867(1740), 502
294(27300).
(15730), 403(54300); IR (cmꢁ1), t(C„C): 2069(s); electro-
chemistry, E1/2/V, DEp/V, ibackward/iforward: A, 0.478,
0.061, 0.99; B, ꢁ1.056, 0.061, 0.89.
4.2. Synthesis of TMS-OPE3-S-TMSE
A mixture of 0.500 g (1.27 mmol) of OPE2-S-TMSE
(prepared from desilylation of TMS-OPE2-S-TMSE with
excess of K2CO3 in THF/CH3OH (1/1, v/v)), and 0.38 g
(1.27 mmol) of trimethylsilyl ethynyliodobenzene, 0.150 g
(0.21 mmol) of Pd(PPh3)2Cl2, 0.150 g (0.8 mmol) of CuI,
40 mL of diisopropylamine and 40 mL of THF was stirred
under argon at 70 ꢁC overnight. Solvents were removed
and the residue was purified by column chromatography
with CH2Cl2/hexanes (1/5, v/v) to yield 0.550 g (76%) of
4.5. Synthesis of compound 3
To a suspension of 0.200 g (0.22 mmol) of Ru2(DM-
BA)4(NO3)2 in 50 mL THF was added 0.680 g (1.38 mmol)
of OPE3-S-TMSE, prepared from desilylation of TMS-
OPE3-S-TMSE with excess of K2CO3 in THF/CH3OH
(1/1, v/v), and 20 mL Et3N. The reaction mixture was stir-
red at room temperature for 2 h. Upon the solvent
removal, the residue was purified by column chromatogra-
phy, and eluted with THF/hexanes (1/5, v/v) to afford
0.130 g title compound (33%). Data for Ru2(DM-
BA)4(OPE3)2: 1H NMR: 7.49–7.39 (m, 20H, aromatic),
7.28–7.26 (m, 4H, aromatic), 6.93–7.05 (m, 16H, 6.90 aro-
matic), 3.90 (s, 12H, CH3O–), 3.32 (s, 24H, MeN–), 3.03–
2.97 (m, 4H, TMSCH2CH2S–), 0.99–0.86 (m, 4H,
TMSCH2CH2S–), 0.07 (s, 9H, –Si(CH3)3), 0.02 (s, 9H,
–Si(CH3)3); MS-FAB (m/e, based on 101Ru): 1283
[M+ ꢁ OPE3]; Vis–NIR, kmax(nm, e (Mꢁ1 cmꢁ1)): 846
(2024), 505(sh), 381(74320); IR (cmꢁ1), t(C„C): 2069
(s); electrochemistry, E1/2/V, DEp/V, ibackward/iforward: A,
0.530, 0.073, 0.99; B, ꢁ1.047, 0.075, 0.89.
1
pure product. Data for TMS-OPE3-S-TMSE H NMR:
7.50–7.42 (m, 7H, aromatic), 7.25–7.22 (m, 1H, aromatic),
7.01 (d, 2H, aromatic), 3.89 (d, 6H, CH3O–), 3.01–2.95 (m,
2H, TMSCH2CH2S–), 0.97–0.91 (m, 2H, TMSCH2CH2S–),
0.25 (s, 9H, –Si(CH3)3), 0.05 (s, 9H, –Si(CH3)3). UV–Vis
(THF),
k
max(nm,
e
(Mꢁ1 cmꢁ1)): 322(42900) and
377(52900).
4.3. Synthesis of compound 1
To a suspension of 0.200 g (0.22 mmol) of Ru2(DM-
BA)4(NO3)2 in 50 mL THF was added 0.500 g (2.14 mmol)
of OPE1-S-TMSE and 20 mL of Et3N. The reaction mix-
ture was stirred at room temperature for 2 h. Upon the sol-
vent removal, the residue was triturated with methanol and
filtered to afford a red powder 0.180 g (73%). Data for
4.6. Structure determination
Single crystals were obtained by slow diffusion of hex-
anes into THF solution (1) or benzene solution (2). X-ray
intensity data were measured at 300 K on a Bruker
SMART 1000 CCD-based X-ray diffractometer system
1
Ru2(DMBA)4(OPE1-S-TMSE)2: H NMR: 7.42–7.36 (m,
12H, aromatic), 7.14 (d, 4H, aromatic), 6.99 (t, 12H, aro-
matic), 3.26 (s, 24H, MeN–), 2.85–2.79 (m, 4H,
TMSCH2CH2S–), 0.87–0.80 (m, 4H, TMSCH2CH2S–),
0.03 (s, 18H, –Si(CH3)3); MS-FAB (m/e, based on 101Ru):
1262 [M+]; Vis–NIR, kmax(nm, e(Mꢁ1 cmꢁ1)): 893(1780),
506(13750), 338(41670); IR (cmꢁ1), t(C„C) 2078(s); elec-
trochemistry, E1/2/V, DEp/V, ibackward/iforward: A, 0.517,
0.057, 0.96; B, ꢁ1.060, 0.057, 0.94.
˚
using Mo Ka (k = 0.71073 A). For data collection, a red
plate of 1 with approximate dimensions 0.28 · 0.13 ·
0.04 mm3 was sealed in a 0.2 mm capillary with mother
liquor, while a red plate of 2 with approximate dimensions
0.19 · 0.13 · 0.03 mm3 cemented to a quartz fiber with
epoxy glue. Data were measured using omega scans of
0.3ꢁ per frame for 30 s for 1 and 40 s for 2 so that a hemi-
sphere (1271 frames) was collected. The frames were inte-
4.4. Synthesis of compound 2
ꢀ
grated with the Bruker SAINT software package [34]
To a suspension of 0.160 g (0.18 mmol) of Ru2(DM-
BA)4(NO3)2 in 50 mL THF was added 0.496 g
(1.06 mmol) of OPE2-S-TMSE and 20 mL Et3N. The
using a narrow-frame integration algorithm, which also
corrects for the Lorentz and polarization effects. Absorp-
tion corrections were applied using SADABS.

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J.-W. Ying, T. Ren / Journal of Organometallic Chemistry 691 (2006) 4021–4027
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Cluster Sci. 17 (2006) 65.
Structures were solved and refined using the Bruker
ꢀ
SHELXTL (Version 5.1) software package [35] in space
ꢀ
groups of C2 (1) and P1 (2). Positions of all non-hydrogen
atoms were revealed by direct method. All non-hydrogen
atoms are anisotropic and the hydrogen atoms were put
in calculated positions and riding mode. Each structure
was refined to convergence by least squares method on
F2, SHELXL-93, incorporated in SHELXTL.PC V 5.03. Crystal-
lographic data are given in Table 2.
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Acknowledgements
Financial support from the National Science Foundation
(CHE0242623/0553564) and Purdue University is gratefully
acknowledged. We thank Drs. Wei-Zhong Chen and Guo-
Lin Xu for experimental assistance and discussion.
S.A. Getty, C. Engtrakul, L. Wang, R. Liu, S.-H. Ke, H.U.
Baranger, W. Yang, M.S. Fuhrer, L.R. Sita, Phys. Rev. B 71
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Appendix A. Supporting information
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic Data
Center, CCDC 246907 and 246908 for compounds 1 and 2,
respectively. Copies of this information may be obtained
free of charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK, fax: +44-1233-336033; email:
deposit@ccdc.cam.ac.uk or www:http://ccdc.cam.ac.uk.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.
2006.06.005.
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