Interconversion between cyclodimer and cyclotrimer: Synthesis and characterization of cyclo-[Pd(II)Cl2(N-N)] complexes

Article abstract of DOI:10.1016/j.ica.2008.09.024

The reaction of (COD)PdCl₂ (COD = 1,5-cyclooctadiene) with (3-Py)₂SiR₁R₂ (3-Py = 3-pyridyl; R₁ = Ph, R₂ = Ph (m-pdps); R₁ = Ph, R₂ = Me (m-pmps)) in acetone affords si

Full text of DOI:10.1016/j.ica.2008.09.024

Inorganica Chimica Acta 362 (2009) 1963–1968
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Interconversion between cyclodimer and cyclotrimer: Synthesis
and characterization of cyclo-[Pd(II)Cl2(N–N)] complexes
Hyun Ji Kang a, Tae Hwan Noh a, Young Mee Na a, Kyung Ho Yoo b, Ok-Sang Jung a,
*
a Department of Chemistry, Pusan National University, Pusan 609-735, Republic of Korea
b Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 June 2008
Received in revised form 6 September 2008
Accepted 8 September 2008
Available online 20 September 2008
The reaction of (COD)PdCl2 (COD = 1,5-cyclooctadiene) with (3-Py)2SiR1R2 (3-Py = 3-pyridyl; R1 = Ph,
R2 = Ph (m-pdps); R1 = Ph, R2 = Me (m-pmps)) in acetone affords single crystals consisting of cyclodimers,
[PdCl2((3-Py)2SiR1R2)]2, whereas the same reaction in a mixture of dichloromethane and ethanol yields
amorphous spheres consisting of cyclotrimers, [PdCl2((3-Py)2SiR1R2)]3. In a boiling chloroform solution,
the cyclodimers are completely converted to cyclotrimers. These cyclotrimers, in the 10ꢀ60 °C range,
are partly returned to cyclodimers. By contrast, the reaction of (COD)PdCl2 with (3-Py)2SiR1R2 (R1 = Bu,
R2 = Me (m-pbms); R1 = dodecyl, R2 = Me (m-pddms)) yields amorphous spheres consisting of cyclotri-
mers irrespective of solvents. Both [PdCl2(m-pbms)]3 and [PdCl2(m-pddms)]3 are initially cyclotrimers
in chloroform, but they exist as a mixture of cyclodimers and cyclotrimers in solution in the 10ꢀ60 °C
range. The metallacycles tend to form cyclodimers in the order m-pdps > m-pmps > m-pbms > m-pddms.
The equilibrium between cyclodimers and the cyclotrimers is sensitive to solvent, temperature, and con-
centration as well as molecular structure.
Keywords:
Cyclodimers
Cyclotrimers
Interconversion
Microspheres
Palladium(II) complexes
Ó 2008 Published by Elsevier B.V.
1. Introduction
facile manipulation of well-defined micro-shapes remains an
important issue with regard to the development of advanced mate-
Among diverse dynamic systems, those that can control macro-
cyclic rings by means of chemical triggers are of importance in the
field of task-specific molecular materials. Thus, various metalla-
macrocycles have been synthesized as important building blocks
in the construction of functional supramolecular materials that
can be utilized for molecular machines, switches, recognition,
selective transformation, drug delivery systems, catalysts, storage,
and biomimics [1–10]. One of the facile synthetic systems is ring-
expansion [11–14], which includes cavity-control [15,16] by
means of labile metal–ligand coordination and thermodynamic
control. Some palladium(II) complexes of N-donor ligands have
been utilized in the development of coordination materials such
as catalysts [17], rectangular building blocks [18], submicrospheres
[19], desirable morphology [20], and ‘‘magic ring” with the associa-
tive/dissociative dual character PdꢀN bond [21]. Of the N-donor li-
gands, silicon-containing pyridyl ligands have been found to be
useful for the synthesis of targe-skeletal structures since they are
adjustable in bridging ability and length, possess flexible angles
around silicon, and are conformationally nonrigid [22–26]. Equilib-
ria of ionic palladium(II) metallacyclic compounds containing
NO3ꢀ, PF6ꢀ, or OTfꢀ have been observed [27,28], but ring-control
in neutral palladium(II) complexes is very rare. Nonetheless, the
rials. Intermolecular affinity is the key factor in the formation of a
particle-based morphology [29]. A comparative investigation of
single crystals versus amorphous morphology still remains a keen
challenge.
In this context, a preliminary result in morphology-control via
the ring size of neutral metallamacrocyclic compounds has re-
cently been published [30]. In order to expand the systematic ten-
dency to form cyclodimers/cyclotrimers according to the organic
chains attached to silicon as well as the external conditions, we re-
port the formation and interconversion processes of metallacyc-
lodimers versus metallacyclotrimers.
2. Experimental
2.1. Materials and measurements
Palladium(II) chloride, 1,5-cyclooctadiene (COD), and various
dialkyldichlorosilanes were purchased from Aldrich, and used
without further purification. (COD)PdCl2 was prepared according
to the procedure described in the literature [31]. Bis(3-pyri-
dyl)dodecylmethylsilane (m-pddms) [32] and [PdCl2(m-pmps)]
(m-pmps = bis(3-pyridyl)methylphenylsilane) [30] were prepared
according to the previous studies. The 1H and 13C NMR spectra
were recorded on a Varian Gemini 300, the chemical shifts of
which were relative to the internal SiMe4. Infrared spectra were
* Corresponding author. Tel.: +82 51 510 2591; fax: +82 51 516 7421.
E-mail address: oksjung@pusan.ac.kr (O.-S. Jung).
0020-1693/$ - see front matter Ó 2008 Published by Elsevier B.V.
doi:10.1016/j.ica.2008.09.024

1964
H.J. Kang et al. / Inorganica Chimica Acta 362 (2009) 1963–1968
obtained on a Perkin Elmer 16F PC FTIR spectrophotometer with
samples prepared as KBr pellets. Elemental microanalyses (C, H,
N) were performed on solid samples in the Advanced Analytical
Division at KBSI, using a Perkin Elmer 2400 CHNS analyzer. Ther-
mal analyses were performed under a nitrogen atmosphere at a
scan rate of 10 °C/min with a Stanton Red Croft TG 100. Mass spec-
trometric analysis via a fast atom bombardment technique was
performed in chloroform using a KMS-700 Mstation mass spec-
trometer (Jeol, Japan) and an MS-MP9020D data system.
[MTꢀCl–HCl–Ph]+, 1173.9 [MTꢀCl–HCl]+, and 1138.5 [MTꢀL–Cl–
HCl]+.
2.6. Synthesis of [PdCl2(m-pbms)]3
An ethanol solution (7 ml) of m-pbms (2.56 mg, 0.01 mmol) was
slowly diffused into
a dichloromethane solution (5 ml) of
(COD)PdCl2 (2.85 mg, 0.01 mmol). Slow evaporation of the solvent
produced pale yellow spheres of [Pd(m-pbms)Cl2]3 in 70% yield
after 2 days. M.p. 195 °C (dec). Anal. Calc. for C45H60Cl6N6Pd3Si3:
C, 41.54; H, 4.65; N, 6.46. Found: C, 41.30; H, 4.55; N, 6.66%. 1H
NMR (CDCl3, SiMe4, ppm): 0.69 (s, 9H), 0.913 (m , 9H), 1.06–1.28
(m, 6H), 1.30–1.52 (m, 12H), 7.32 (t, J = 6.3 Hz, 6H), 7.77 (d,
J = 6.6 Hz, 6H), 8.85 (d, J = 6.3 Hz, 6H), 8.90 (s, 6H). 13C NMR (CDCl3,
SiMe4, ppm): ꢀ4.78, 12.97, 13.89, 25.60, 26.59, 125.18, 133.11,
144.88, 154.37, 157.90. Mass: m/e = 1187.7 [MTꢀ3HCl]+, 1079.0
[MTꢀ6HCl]+, 1009.2 [MTꢀL–HCl]+, 896 [MTꢀL–4HCl]+.
2.2. Synthesis of bis(3-pyridyl)diphenylsilane (m-pdps)
n-Butyllithium (14.4 mmol, 2.5 M solution in hexane) was
added dropwise to a solution of 3-bromopyridine (14 mmol) in
dry ethyl ether (40 ml) under nitrogen gas at ꢀ78 °C, at which tem-
perature the resulting mixture was stirred for 1 h. At 0 °C, dichlo-
rodiphenylsilane (6.5 mmol) was slowly added to the yellow
suspension over 2 h. Distilled water (20 ml) was added into the
reaction solution, and the organic solution layer was separated.
The organic solution was washed with water (2 ꢁ 10 ml), and then
was dried over MgSO4. The crude product was purified by column
chromatography on silica gel with ethyl acetate. The solvent was
evaporated to obtain a pale yellow solid in 60% yield. 1H NMR
(CDCl3, SiMe4, ppm): 7.27 (t, J = 6.3 Hz, 2H), 7.36–7.44 (m, 10H),
7.76 (dt, J = 7.5 Hz, J = 1.6 Hz, 2H), 8.70 (dd, J = 6.3 Hz, J = 1.4 Hz,
2H), 8.75 (s, 2H). 13C NMR (CDCl3, SiMe4, ppm): 123.66, 128.58,
128.92, 130.64, 131.94, 136.42, 143.98, 151.20, 156.57.
2.7. Synthesis of [PdCl2(m-pddms)]3
An ethanol solution (7 ml) of m-pddms (3.68 mg, 0.01 mmol)
was slowly diffused into a dichloromethane solution (5 ml) of
(COD)PdCl2 (2.85 mg, 0.01 mmol). Slow evaporation of the solvent
afforded thin yellow powders of [PdCl2(m-pddms)]3 in 70% yield
after 2 days. M.p. 168 °C. Anal. Calc. for C69H108Cl6N6Pd3Si3: C,
50.60; H, 6.65; N, 5.13. Found: C, 51.40; H, 6.55; N, 5.08%. 1H
NMR (CDCl3, SiMe4, ppm): 0.68–1.58 (m, 84H), 7.34 (t, J = 6.6 Hz,
6H), 7.77 (d, J = 7.5 Hz, 6H), 8.86(d, J = 6.6 Hz, 6H), 8.91 (s, 6H).
13C NMR (CDCl3, SiMe4, ppm): ꢀ4.82, 13.27, 14.38, 22.92, 23.54,
29.40, 29.58, 29.78, 29.88, 32.14, 33.64, 125.16, 133.15, 144.87,
154.38, 157.88. Mass: m/e = 1608 [MTꢀCl]+, 1233.8 [MTꢀL–HCl]+,
and 1198.8 [MTꢀL–Cl–HCl]+.
2.3. Synthesis of bis(3-pyridyl)butylmethylsilane (m-pbms)
A similar reaction was carried out using n-butylmethyldichlo-
rosilane instead of dichlorodiphenylsilane. The solvent was evapo-
rated to obtain a viscous liquid in 58% yield. 1H NMR (CDCl3, SiMe4,
ppm): 0.55 (s, 3H), 0.78–0.83 (t, J = 6.7 Hz, 3H), 1.03–1.08 (m, 2H),
1.27–1.32 (m, 4H), 7.21 (t, J = 6.2 Hz, 2H), 7.69 (dt, J = 7.4 Hz,
J = 1.0 Hz, 2H), 8.54 (dd, J = 6.1 Hz, J = 1.0 Hz, 2H), 8.62 (s, 2H). 13C
NMR (CDCl3, SiMe4, ppm): ꢀ4.95, 13.20, 13.66, 25.68, 26.40,
123.38, 131.32, 142.02, 150.40, 154.52.
2.8. Crystal structure determination
X-ray data were collected on a Bruker SMART automatic diffrac-
tometer with graphite-monochromated Mo
K
a
radiation
(k = 0.71073 Å) and a CCD detector at ambient temperature. Forty
five frames of two-dimensional diffraction images were collected
and processed to obtain the cell parameters and orientation ma-
trix. The data were corrected for the Lorentz and polarization ef-
fects. The absorption effects were corrected using the empirical
2.4. Synthesis of [PdCl2(m-pdps)]2
An acetone solution (5 ml) of m-pdps (3.38 mg, 0.01 mmol) was
slowly diffused into an acetone solution (5 ml) of (COD)PdCl2
(2.85 mg, 0.01 mmol). The solvent of the reaction mixture was
slowly evaporated to obtain pale yellow crystals suitable for X-
ray single crystallography. M.p. 201 °C (dec). Anal. Calc. for
C44H36Cl4N4Pd2Si2: C, 51.23; H, 3.52; N, 5.43. Found: C, 51.10; H,
3.55; N, 5.33%. 1H NMR (CDCl3, SiMe4, ppm): 7.27 (t, J = 6.0 Hz,
4H), 7.41–7.56 (m, 20H), 7.73 (d, J = 7.5 Hz, 4H), 8.86 (d,
J = 6.0 Hz, 4H), 9.70 (s, 4H). 13C NMR (CDCl3, SiMe4, ppm):
124.86, 129.02, 129.57, 130.56, 131.40, 136.48, 145.90, 154.33,
160.35. Mass: m/e = 997.1 [MDꢀCl]+ and 960.9 [MDꢀCl–HCl]+.
w
-scan method. The structures were solved using the direct meth-
od (SHELXS 97) and refined by full-matrix least squares techniques
SHELXL 97) [33]. The non-hydrogen atoms were refined anisotropi-
(
cally, and the hydrogen atoms were placed in calculated positions
and refined only for the isotropic thermal factors. The crystal
parameters and procedural information corresponding to the data
collection and structure refinement are listed in Table 1.
Table 1
Crystal data and structure refinement for [PdCl2(m-pdps)]2
Formula
Mw
C22H18Cl2N2PdSi
515.77
2.5. Synthesis of [PdCl2(m-pdps)]3
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Monoclinic
C2/c
An ethanol solution (7 ml) of m-pdps (3.38 mg, 0.01 mmol) was
slowly diffused into
a dichloromethane solution (5 ml) of
17.9540(9)
13.9431(7)
19.0212(9)
114.8390(10)
4321.2(4)
(COD)PdCl2 (2.85 mg 0.01 mmol). Evaporation of the solvent affor-
ded pale yellow spheres of [Pd(m-pdps)Cl2]3 in 70% yield after
1 day. M.p. 278 °C (dec). Anal. Calc. for C66H54Cl6N6Pd3Si3: C,
51.23; H, 3.52; N, 5.43. Found: C, 51.20; H, 3.48; N, 5.38%. 1H
NMR (CDCl3, SiMe4, ppm): 7.3 (t, J = 5.7 Hz, 6H), 7.44–7.53 (m,
30H), 7.86 (d, J = 7.5 Hz, 6H), 8.87 (d, J = 5.7 Hz, 6H), 8.90 (s, 6H).
13C NMR (CDCl3, SiMe4, ppm): 124.88, 125.16, 129.03, 129.08,
129.55, 130.57, 130.68, 131.46, 136.50, 145.91, 146.44, 154.33,
154.76, 159.56, 160.34. Mass: m/e = 1513.1 [MTꢀCl]+, 1317.0
b (°)
V (Å3)
Z
8
l
(mmꢀ1
)
1.172
1.070
GOF on F2
Final R indices [I > 2
r
(I)]
R1 = 0.0238, wR2 = 0.0641
R1 = 0.0299, wR2 = 0.0667
R indices (all data)a
P
P
P
P
2
1=2
a
R1
¼
kFoj ꢀ jFck= jFoj:wR2
¼
wðF2o ꢀ F2c Þ = wF2oÞ
.

H.J. Kang et al. / Inorganica Chimica Acta 362 (2009) 1963–1968
1965
analogues. [PdCl2(m-pbms or m-pddms)]2 and [PdCl2(m-pbms or
m-pddms)]3 products existed in equilibrium in the solution. The
equilibrium is sensitive to concentration and temperature. The
reactions were originally conducted in the 1:1 mole ratio of Pd(II)
to ligands, but the products were not significantly affected by the
mole ratio. The present products are remarkable in that there
was no evidence for polymerization, not even under high concen-
trations. All of the compounds are soluble in dichloromethane,
chloroform, N,N-dimethylformamide, and dimethylsulfoxide, but
are insoluble in water, hexane, ethanol, and nitromethane. The ele-
mental analyses and NMR spectra of the products were consistent
with desirable structures.
3. Results and discussion
3.1. Synthesis
The reaction of (COD)PdCl2 with the present ligands at room
temperature yielded discrete cyclic compounds, as shown in
Scheme 1. The reaction of (COD)PdCl2 with m-pdps or m-pmps
[30] in acetone yielded single crystals suitable for X-ray single
crystallography, whereas the reaction in a mixture of dichloro-
methane and ethanol produced amorphous microspheres. When
the single crystals were treated in a mixture of dichloromethane
and ethanol, the same microspheres formed. Furthermore, recrys-
tallization of the microspheres in acetone yielded single crystals.
The single crystal consisted of cyclodimers whereas the amorphous
microsphere consisted of cyclotrimers, as will be discussed in de-
tail. Thus, the cyclodimers and the cyclotrimers could be smoothly
isolated and interconverted. However, for the m-pbms and m-
ddmps analogues, single crystals consisting of cyclodimers could
not be isolated, instead amorphous microspheres were produced
irrespective of solvents in contrast to above m-pdps or m-pmps
3.2. Crystal structure of [PdCl2(m-pdps)]2
The crystal structure of [PdCl2(m-pdps)]2 is illustrated in Fig. 1,
and the relevant bond lengths and angles are listed in Table 2. The
ORTEP shows that the single crystal consists of cyclodimers,
[PdCl2(m-pdps)]2. The local geometry around the palladium(II)
ion approximates to a typical square planar arrangement with
two chlorides in trans position (ClꢀPdꢀCl = 174.67(2)°;
NꢀPdꢀN = 177.72(7)°; PdꢀCl = 2.2984(6) Å, 2.2874(6) Å; Pd–
N = 2.045(2) Å, 2.007(2) Å). The m-pdps ligand connects two palla-
dium(II) ions to form a 16-membered cyclodimer. The ligand acts
as an unusual horse-shoe tectonic, which is useful for the construc-
tion of molecular rectangles [24]. The structure of [PdCl2(m-pdps)]2
is a centrosymmetric molecule, in contrast to that of [PdCl2(m-
pmps)]2 [30]. The crystal consists of discrete cyclodimeric mole-
cules with no close intermolecular contacts. No other exceptional
features, including those of either bond lengths or angles, were
observed.
R1 = Phenyl, R2= Phenyl
2
m
R1 = Phenyl, R2= Methyl
R2
Cl
Pd
Cl
R1
Cl
Si
N
N
Pd
N
N
Pd
Si
R1
R2
Pd
Cl
Cl
Pd
Cl
R2
R1
R1
Si
R2
N
N
N
N
Cl
Cl
Si
N
N
Cl
Cl
Si
R2
R1
3.3. NMR behavior and related properties
The 1H NMR spectra of both the single crystal, [PdCl2(m-pdps)]2,
and the amorphous microsphere, [PdCl2(m-pdps)]3, were mea-
sured in chloroform at room temperature (Fig. 2). The two spectra
show a similar pattern, except for the chemical shifts of 2H-Py. The
2H-Py of [PdCl2(m-pdps)]3 relative to that of [PdCl2(m-pdps)]2 was
significantly upfield-shifted, from 9.70 to 8.90 ppm. The cyclodi-
meric structure seems to be unusually rigid even in solution, and
thus 2H-Py is strongly affected by the anisotropy effect. The weak
interaction (C–Hꢂ ꢂ ꢂCl = 2.59 Å) can partly be ascribed to the down-
field shift of 2H-Py in the cyclodimer. In contrast, for the cyclotri-
mer, the upfield shift of 2H-Py can be explained by the more
fluxional motion of the pyridyl group. The FAB mass data for
[PdCl2(m-pdps)]2 and [PdCl2(m-pdps)]3 (matrix: nitrobenzylalco-
hol) (Fig. 3) were obtained in order to characterize their chemical
structures. The mass peaks of the amorphous microsphere (m/
Slow eva. of
CH2Cl2/EtOH Soln.
Recrystallization
in Acetone
R1
R2
N
Si
(COD)PdCl2
+
N
e = 1513.1[MTꢀCl]+,
1317.0
[MTꢀCl–HCl–Ph]+,
1173.9
[MTꢀLꢀHCl]+, 1138.5 [MTꢀL–Cl–HCl]+; MT = cyclotrimer) indicate
Cl
Pd
Cl
Cl
Pd
Cl
R2
Si
Cl
Pd
Cl
R1
N
N
Pd
N
N
Pd
Si
R2
R1
R1
R2
R1
R2
N
N
N
Si
Si
Cl
Cl
N
CDCl3
N
N
Cl
Cl
Si
R2
R1
R1 = Butyl, R2= Methyl
R1 = Dodecyl, R2= Methyl
Scheme 1.
Fig. 1. X-ray structure of [PdCl2(m-pdps)]2.

1966
H.J. Kang et al. / Inorganica Chimica Acta 362 (2009) 1963–1968
Table 2
that it consists of cyclotrimers; the mass data for the single crystal
show that it consists of cyclodimers (m/e = 997.1 [MDꢀCl]+, 960.9
[MDꢀCl–HCl]+; MD = cyclodimer). Of course, conducting similar
elemental analyses of the two compounds (C, H, N) was satisfac-
tory. Furthermore, the cyclotrimers in chloroform at the 60 °C
transformed them into cyclodimers (Fig. 4). Another interesting
feature is that in the 10ꢀ60 °C range, the cyclotrimer partly returns
to the cyclodimer in solution. Both the cyclodimer and the cyclotri-
mer are locked in the solution below 10 °C. The equilibria in the
10ꢀ60 °C range are dependent on temperature and concentration.
High concentration favors the cyclotrimer. For [PdCl2(m-pbms)]3
and [PdCl2(m-pddms)]3, the 1H NMR data show that they are ini-
tially cyclotrimers in chloroform (see the mass data for [PdCl2(m-
pbms)]3 and [PdCl2(m-pddms)]3: Supplementary material S7).
The two peaks of 2H-Py arose from the unsymmetricity via the
presence of two significantly different organic groups. As time
passes, these groups exist as a mixture of cyclodimers and cyclotri-
mers in the 10ꢀ60 °C range (Fig. 5). However, complete intercon-
version from cyclotrimers to cyclodimers does not occur, in
contrast to [PdCl2(m-pdps)] and [PdCl2(m-pmps)].
Bond lengths (Å) and angles (°) for [PdCl2(m-pdps)]2
Pd(1)–N(2)#1
Pd(1)–N(1)
Pd(1)–Cl(2)
Pd(1)–Cl(1)
N(2)–Pd(1)#1
2.0073(18)
2.0452(17)
2.2874(6)
2.2984(6)
2.0073(18)
N(2)#1–Pd(1)–N(1)
N(2)#1–Pd(1)–Cl(2)
N(1)–Pd(1)–Cl(2)
N(2)#1–Pd(1)–Cl(1)
N(1)–Pd(1)–Cl(1)
Cl(2)–Pd(1)–Cl(1)
177.72(7)
87.76(6)
91.27(5)
88.13(6)
92.71(5)
174.67(2)
C(1)–N(1)–Pd(1)
C(5)–N(1)–Pd(1)
C(21)–N(2)–Pd(1)#1
C(22)–N(2)–Pd(1)#1
121.83(14)
120.39(14)
124.08(15)
117.46(15)
Symmetry transformations used to generate equivalent atoms: #1 ꢀx, ꢀy + 1, ꢀz.
N
H
H
N
N
H
H
N
Ph
Si
Ph
Ph
Ph
Si
a
3.4. Formation of spheres
Slow evaporation of (COD)PdCl2 (0.01 mmol in 5 ml of CH2Cl2)
with each ligand (0.01 mmol in 7 ml of EtOH) yielded micro-
spheres, as shown in Fig. 6. Preliminary results on the formation
and control of microspheres were published in our previous papers
Ph
Si Ph
N
N
N
H
H
H
N
Ph
Ph
Si
H
N
N
H H
b
Si Ph
Ph
0 h
12 h
ppm
9.50
9.00
8.50
8.00
7.50
10.00
Fig. 2. 1H NMR spectra of [PdCl2(m-pdps)]2 (a) and [PdCl2(m-pdps)]3 (b).
indicates PdCl2.
24 h
100
a
80
60
ppm
9.50
9.00
8.50
8.00
7.50
Fig. 4. 1H NMR spectra for process of conversion from [PdCl2(m-pdps)]3 to
[PdCl2(m-pdps)]2 in CDCl3 at 60 °C.
40
20
0
0 h
m/z
1500
900
1000 1100 1200 1300 1400
100
b
12 h
80
60
24 h
40
20
0
ppm
9.50
9.00
8.50
8.00
7.50
Fig. 5. Time-dependent 1H NMR spectra for a process of conversion of [PdCl2(m-
pddms)]3 to [PdCl2(m-pddms)]2 in CDCl3 at 60 °C. (d: peaks from cyclotrimer; .:
peaks from cyclodimer).
m/z
1500
900
1000 1100 1200 1300 1400
Fig. 3. FAB mass data for [PdCl2(m-pdps)]2 (a) and [PdCl2(m-pdps)]3 (b).

H.J. Kang et al. / Inorganica Chimica Acta 362 (2009) 1963–1968
1967
[30,34]. The SEM images show that the sphere-size is dependent on
the organic groups attached to Si. The sphere-size of [PdCl2(m-
trol the nucleation, growth, and alignment of inorganic morphol-
ogy [35,36].
pdps)]3 (500 nm–1
However, the spheres of [PdCl2(m-pbms)]3 and [PdCl2(m-pddms)]3
m), with long aliphatic chains, are larger than [PdCl2(m-
pdps)]3 under the same external conditions. The formation of dif-
ferent sizes can be explained by the solubility in the organic sol-
vents. That is, long chain compounds are the more soluble in
organic solvents, and thus a small number of seeds form, resulting
in the formation of larger spheres. By contrast, for less soluble
compounds, a large number of seeds form, resulting in the forma-
lm) is very similar to that of [PdCl2(m-pmps)]3.
3.5. Mechanistic aspect of interconversion
(5 ꢃ 7
l
This system is an effective means of clearly showing the differ-
ence between the cyclodimer and the cyclotrimer. Indeed, the most
significant difference between the two species, as established by
the 1H NMR spectra, is the molecular rigidity. The rigid cyclodimer
produces single crystals, but the relatively fluxional cyclotrimer af-
fords amorphous spheres. Furthermore, [PdCl2(m-pbms)]3 and
[PdCl2(m-pddms)]3 with a long aliphatic chain cannot be obtained
as single crystals in the solid state. That is, the complexes of the li-
gands containing the long aliphatic chains favor the cyclotrimers
whereas the complexes of the ligands containing phenyl groups fa-
vor the cyclodimers in solution. Thus, the cyclodimer tends to form
in the order m-pdps > m-pmps > m-pbms > m-pddms. The growth
kinetics of solid products is determined by the interplay between
the internal lattice structure and the external environment. Forma-
tion of spheres seems to be determined by a combination of sur-
face tension, molecular flexibility, and solvent effects. Of course,
the equilibrium between the cyclodimer and the cyclotrimer is
sensitive to molecular structure, solvent, temperature, and concen-
tration. Cyclodimer/cyclotrimer interconversion via temperature
can be explained by the entropy difference between the two
tion of smaller spheres. Moreover, the sphere-size (300 nm–7 lm)
can be controlled by the evaporation rate of the solvent. Fast evap-
oration of solvent for 1 min using a rotary evaporator affords
ꢃ300 nm diameter submicrospheres. The part around Pd(II)Cl2
seems to be hydrophilic, and the ligand moiety with a long ali-
phatic chain seems to be hydrophobic. These amphiphilic proper-
ties apparently form, without any additive, amorphous
microspheres. Generally, monomodal submicrospheres of metal
oxides are formed with organic additives and/or templates to con-
(3D ¢ 2T;
D
Gs
=
D
Hs ꢀ T
D
Ss). If H and S favor opposite processes,
spontaneity will depend on temperature [37]. The formation of
cyclotrimers is predominant above the chloroform reflux tempera-
tures, meaning that the entropy of two cyclotrimer molecules is
remarkably higher than that of three cyclodimer molecules in solu-
tion at high temperatures
(D TD
Hs = positive; Ss = positive;
D
Hs < T
D
Ss;
D
Gs = negative). However, in the 10ꢀ60 °C tempera-
ture range,
D
Gs is positive because the Hs term is larger than the
D
T
D
Ss term. Thus, the reverse reaction is
a
D
spontaneous
(D
Hs = negative; T Ss = negative; Hs > T Ss;
D
D
D
Gs = positive)
one below the reflux temperatures. The high entropy of the cyclo-
trimer is closely related both to the flexible NMR spectra and the
formation of amorphous spheres. The cyclotrimer in chloroform
below 0 °C is locked, indicating that the interconversion process re-
quires somewhat higher activation energy. Thus, the conversion
rate is slow.
4. Conclusions
The palladium(II) complexes of bidentate bis(3-pyridyl)dialk-
ylsilane ligands are an effective system for explaining the relation-
ship between molecular structure and physicochemical properties
such as NMR behavior, morphology, temperature, and solvent.
Such a control of morphology via the molecular ring size yields
interesting results. Certainly, the structural rigidity of metal com-
plexes will contribute to the development of molecular materials.
Acknowledgment
This work was supported financially by KOSEF R01-2007-000-
20245-0 in Korea.
Appendix A. Supplementary material
CCDC 692358 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. IR spectra of m-pdps (a), [PdCl2(m-pdps)]2 (b),
and [PdCl2(m-pdps)]3 (c) (Fig. S1), IR spectra of m-pbms (a) and
[PdCl2(m-pbms)]3 (b) (Fig. S2), IR spectra of m-pddms (a) and
Fig. 6. SEM images of [PdCl2(m-pdps)]3 (a), [PdCl2(m-pbms)]3 (b) , and [PdCl2(m-
pddms)]3 (c).

1968
H.J. Kang et al. / Inorganica Chimica Acta 362 (2009) 1963–1968
[PdCl2(m-pddms)]3 (b) (Fig. S3), 13C NMR spectra of m-pdps (a),
[PdCl2(m-pdps)]2 (b), and [PdCl2(m-pdps)]3 (c) (Fig. S4), 13C NMR
spectra of m-pbms (a) and [PdCl2(m-pbms)]3 (b) (Fig. S5), 13C
NMR spectrum of [PdCl2(m-pddms)]3 (a) (Fig. S6), FAB mass data
for [PdCl2(m-pbms)]3 (a) and [PdCl2(m-pddms)]3 (b) (Fig. S7), 1H
NMR spectra on a conversion process of [PdCl2(m-pbms)]3 to
[PdCl2(m-pbms)]2 in CDCl3 at 60 °C (Fig. S8). Supplementary data
associated with this article can be found, in the online version, at
doi:10.1016/j.ica.2008.09.024.
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