The effect of polyether terminal chains in the liquid crystalline behavior of ortho-palladated complexes

Article abstract of DOI:10.1016/j.jorganchem.2004.11.010

A series of benzylideneanilines bearing terminal polyether chains, HL (HL = R-C₆H₄-CHN-C₆H₄-R′: R = OC₈H₁₇, R′ = O(CH₂CH₂O) ₂C₂H₅; R = O(CH₂CH ₂O)₂C₂H₅, R′ = OC ₈H₁₇; R = R′ = O(CH₂CH₂O) ₂C₂H₅; R = OC₁₂H₂₅, R′ = O(CH₂CH₂O)₃C₂H ₅; R = O(CH₂CH₂O)₃C ₂H₅, R′ = OC₁₂H₂₅; R = R′ = O(CH₂CH₂O)₃C₂H ₅) have been prepared. Their dinuclear, [Pd(μ-X)L]₂ (X = OAc, Cl, Br, SC₈), [Pd₂(μ-SCn)(μ-X)L₂] (X = OAc, Cl; n = 8, 2) and mononuclear orthopalladated derivatives, Pd(acac)L, Pd(Ala)L, are reported and their mesogenic properties are compared with those of the analogous compounds with alkoxy chains. In general a great lowering in the melting points is produced for all the products. The free ligands and the alanine complexes are not liquid crystals. The chloro-bridged complexes bearing alkoxy and short polyether chains (O(CH₂CH₂O) ₂C₂H₅) show the larger improvement of mesogenic properties. Longer polyether chains (O(CH₂CH₂O) ₃C₂H₅) result usually in a destabilization of the mesophases. If only polyether chains are present, the destabilization is important regardless of the chain length. The ability of these molecules as ionic extractants and transporters was qualitatively evaluated for the more propitious cis-dinuclear complexes, which in fact showed some extracting ability, modest but improved compared to the free ligands.

Full text of DOI:10.1016/j.jorganchem.2004.11.010

Journal of Organometallic Chemistry 690 (2005) 998–1010
www.elsevier.com/locate/jorganchem
The effect of polyether terminal chains in the liquid
crystalline behavior of ortho-palladated complexes
a
M.J. Baena , J. Buey , P. Espinet , C.E. Garcıa-Prieto
b
b,
b
*
´
a
´ ´
Quımica Inorganica, E. T. S. de Ingenieros Industriales, Universidad de Valladolid, 47011 Valladolid, Spain
b
´ ´
Quımica Inorganica, Facultad de Ciencias, Universidad de Valladolid, 47005 Valladolid, Spain
Received 13 August 2004; accepted 8 November 2004
Abstract
A series of benzylideneanilines bearing terminal polyether chains, HL (HL = R-C6H4–CH@N–C6H4-R0: R = OC8H17,
R0 = O(CH2CH2O)2C2H5; R = O(CH2CH2O)2C2H5, R0 = OC8H17; R = R0 = O(CH2CH2O)2C2H5; R = OC12H25, R0 = O(CH2-
CH2O)3C2H5; R = O(CH2CH2O)3C2H5, R0 = OC12H25; R = R0 = O(CH2CH2O)3C2H5) have been prepared. Their dinuclear,
[Pd(l-X)L]2 (X = OAc, Cl, Br, SC8), [Pd2(l-SCn)(l-X)L2] (X = OAc, Cl; n = 8, 2) and mononuclear orthopalladated derivatives,
Pd(acac)L, Pd(Ala)L, are reported and their mesogenic properties are compared with those of the analogous compounds with alk-
oxy chains. In general a great lowering in the melting points is produced for all the products. The free ligands and the alanine com-
plexes are not liquid crystals. The chloro-bridged complexes bearing alkoxy and short polyether chains (O(CH2CH2O)2C2H5) show
the larger improvement of mesogenic properties. Longer polyether chains (O(CH2CH2O)3C2H5) result usually in a destabilization of
the mesophases. If only polyether chains are present, the destabilization is important regardless of the chain length. The ability of
these molecules as ionic extractants and transporters was qualitatively evaluated for the more propitious cis-dinuclear complexes,
which in fact showed some extracting ability, modest but improved compared to the free ligands.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Metallomesogens; Palladium; Orthometalated imine; Polyether; Substituent effect; Liquid crystals
1. Introduction
plexes and studied the structure-mesogenic activity rela-
tionships in these different molecular types [3], where we
have found the first cholesteric metallomesogens [4], as
well as properties of non-linear optics [5], ferroelectricity
[6] or lyotropism [7]. A few of these studies have been
carried out on orthopalladated azines [8].
Important issues for the potential application of met-
allomesogens in liquid crystal displays are the reduction
of transition temperatures, the expansion of mesogenic
ranges, the increase of thermal stability, and the
improvement of miscibility with other ingredients (such
as polar solvents) in mixtures. It is known that polyether
or polyethyleneglycol ligands can enhance the solubility
of the complexes in organic solvents and in water due to
the polarity introduced by the oxygen atoms [9]. It is
also likely that the introduction of polyether chains
Metallomesogens (metal-containing liquid crystals) is
an area of research with a fast development in the last
two decades. A great variety of such compounds have
been synthesized, and some reviews have appeared [1].
Since the first report by Ghedini et al. [2] of orthopalla-
dated mesogens other groups have developed these
interesting systems, as they form thermally stable com-
plexes, give rise to calamitic, discotic and lyotropic mes-
ophases, and offer different possibilities for tuning the
mesogenic properties. Our group has reported in the last
years a variety of cyclometallated (PdII, PtII) imine com-
*
Corresponding author. Tel.: +34983423231; fax: +34983423013.
E-mail address: espinet@qi.uva.es (P. Espinet).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.11.010

M.J. Baena et al. / Journal of Organometallic Chemistry 690 (2005) 998–1010
999
may be beneficial for the mesogenic properties of ortho-
palladated derivatives [10]. The higher flexibility and the
preferred gauche conformation of the (OCH2CH2)n
units makes that these chains can adopt more easily a
helical conformation and occupy a significantly larger
mean lateral area per chain than comparable aliphatic
chains of the same length. Thus, it is expected that they
might lower the melting points and produce a significant
perturbation in the range of smectic mesophases.
Depending on the amphiphilicity of the molecule and
its ability to induce microsegregation, these mesophases
can result stabilized or destabilized [11].
lide complex of cobalt (III) with a hydrophobic octade-
cyl chain and two hydrophylic fragments, the cationic
cobalt centre and two oxyethylene chains. This com-
pound behaves as lyotropic liquid crystal [17].
In this paper, we report the preparation and meso-
genic properties of orthopalladated complexes contain-
ing polyether chains. In spite of the non-macrocyclic
nature of the polyether moieties in the complexes, some
of the compounds reported were checked towards
extraction of potassium ion.
Polyether chains have been utilized before in meso-
genic materials. For example, rod shaped organic esters
with a polyether terminal group show tilted and orthog-
onal smectic phases [12]. On the other hand, the addi-
tion of alkaline triflate to lamellar phases of mesogenic
polyethers induces the formation of columnar phases
[13]. By combining the ionophore activity of polyethers
with the peculiarities of the mesomorphic state (i.e., sen-
sitivity to small external influences and anisotropy) these
systems could play the function of a membrane. The
main advantages are the availability of low dimensional
ionic conductivities and an easy processability. In fact,
the investigation on liquid crystalline based membranes
is an area of growing interest [14]. Usually, organic LC
amphiphilic systems are used for this purpose and, to
our knowledge, no metallomesogens have been tested.
The cases of metal containing liquid crystals bearing
polyethers are very few. For example, orthopalladated
phenylpyrimidines [d,15] linked by oxyethylene units
to form macrocyclic molecular structures displaying
smectic and columnar mesophases have been reported.
Phthalocyanine metallomesogens derivatives have been
proposed as materials for the transport of either pho-
tons or electrons due to their stacking order, and they
are considered also suitable for ion transport. 15-
crown-5 ether copper phthalocyanine has been reported
to form mesophases in which channels are defined along
the columnar axis, but no data about their transport
properties are available [16]. A third example is an anne-
2. Results and discussion
In the text and Schemes to follow the chains
O(CH2CH2O)2C2H5 are abbreviated as O3C6H13O2,
while O4C8H17 stands for O(CH2CH2O)2C2H5.
2.1. Synthesis and structures
The imines 1.1 and 1.2 were readily prepared in good
yields by condensation of the corresponding aldehydes
and anilines. Imine 1.1a was already reported [3e]. The
method followed to introduce the polyether chains on
the p-hydroxybenzaldehyde or on the p-hydroxyacetan-
ilide is depicted in Scheme 1. As expected, the solubility
of the ligands depends on the nature and number of the
substituents. Ligands with two alkoxy chains precipitate
in ethanol, whereas ligands with a polyether chain are
more soluble. The double-chained derivative is com-
pletely soluble.
The cyclopalladated complexes were synthesized as
depicted in Scheme 2. The orthometallation of the imine
ligands was carried out as described elsewhere [3f], but
derivatives 2.2b and 2.2c could not be obtained suffi-
ciently pure. In these cases, the crude acetate-complexes
were treated with HCl, the chloro-complexes were puri-
fied by column chromatography and then reacted with
sodium acetate in order to get the pure acetate bridged
complexes. The trend of the solubility of the complexes
is the same as for the free ligands. Chloro bridged
Scheme 1.

1000
M.J. Baena et al. / Journal of Organometallic Chemistry 690 (2005) 998–1010
Scheme 2.
complexes 3.1 and 3.2 were obtained by treatment of the
acetate bridged complexes with HCl; these complexes
were precursors of the following complexes: (i) bromo
bridged derivatives 4.2 by reaction with KBr, (ii) chloro-
and thiolate-mixed bridged derivatives 6.1 and 7.1 by
reaction with one equivalent of the appropriate silver
thiolate, (iii) mononuclear derivatives 8.1 and 8.2 by
reaction with thallium acetylacetonate. Complexes 5.1
have two thiolate bridges and this is the first time that
this molecular type is reported as mesogen. Reaction
of 2.1 with two equivalents of alkylthiol affords these
new complexes. Mononuclear derivatives 9.2 were ob-

M.J. Baena et al. / Journal of Organometallic Chemistry 690 (2005) 998–1010
1001
Scheme 3.
tained by reaction of the acetate bridged complex with
two equivalents of alanine.
Some syntheses were carried out with a p-polyether
disubstituted azine. A tetranuclear orthopalladated
complex 10 was obtained by reaction of the azine with
two equivalents of palladium acetate (Scheme 3).
n = 8 and 1:1.3 for n = 8*. An exchange between isomers
was observed in solution for the last one, producing a
small excess of the cis form in two days. For complex
10 only one isomer was found in the resonance spectrum
which is assigned to the structure depicted in Scheme 3,
consistent with the spectral features observed.
All the compounds gave satisfactory CHN analyses,
IR and 1H NMR spectra. Except for the new double-thi-
olate bridged complexes 5, the main structural features
for complexes 2–4 and 6–9 have been reported in detail
in previous papers dealing with their analogs with alkyl
chains [3e–3g]. The acetate-bridged complexes 2 are but-
terfly-shaped and are obtained mainly as a cis:trans mix-
ture 1:24. The chloro- and bromo-bridged complexes 3
and 4 are planar and only the trans isomer is formed.
Mixed-bridged compounds 6 and 7 are cis isomers with
the thiolate bridge cis to the orthometallated carbons.
The thiolate–acetate bridged complexes are non-planar
in the solid state [18], but their NMR spectra in solution
indicate that a fast inversion at the sulfur atom occurs
[19]. The different size of the two bridges leads to a
non-parallel arrangement of the imine ligands, which
converge towards the thiolate moiety. Thiolate–chloro
bridged complexes are planar with the long axes of the
imines parallel to each other and the thiolate chain
pointing backwards the Pd–Pd plane. Only one isomer
is possible for the acac complexes 8. For the alanine
derivatives 9 the reaction affords only the isomer with
the two nitrogen atoms mutually trans [20]. For com-
plexes 5, cis and trans isomers are seen in their 1H
NMR spectra, which show two signals for the iminic
proton. The cis:trans ratios of these isomers are 1:6 for
2.2. Mesogenic properties
Optical, thermal and thermodynamic data of the
complexes studied are collected in Tables 1–8 and com-
pared in Figs. 1–3. When mesogenic behavior appeared,
the mesophases were identified by their characteristic
textures [21].
2.2.1. Imines
Out of the eight ligands prepared, six are non-meso-
genic and only the two with two alkoxy chains exhibit
a short range of mesophase (Table 1). In general, the
melting points of the compounds with polyether chains
are about 30 ꢁC lower than the analogous derivatives
with alkoxy chains, and the more polyether chains, the
lower the melting point.
2.2.2. Dinuclear complexes
[Pd(l-OAc)L]2. Due to its unfavorable molecular
geometry, the acetate bridged complexes do not show li-
quid crystal behavior (Table 2). Nevertheless, the pres-
ence of polyether chains causes the melting points to
decrease over 80 ꢁC in compounds 2.1b–d and 100 ꢁC
in compounds 2.2b–d compared to their homologous
with alkoxy chains 2.1a and 2.2a. For the same chain

1002
M.J. Baena et al. / Journal of Organometallic Chemistry 690 (2005) 998–1010
Table 1
Optical, thermal and thermodynamic data for the imine ligands, HL
(1.1f and 1.2)
Table 3
Optical, thermal and thermodynamic data for complexes 3.1 and 3.2
Complex
Transitiona
T (ꢁC)
DH (kJ molꢀ1
)
Ligand
Transitiona
T (ꢁC)
DH (kJ molꢀ1
)
3.1a
C–SC
SC–SA
SA–I
175.3
205.0
270.0c
15.4
b
1.1a
C–SC [3e]
SC–N
N–I
100.6
109.7
112.5
36.8
8.0b
–
3.1b
3.1c
3.1d
3.2a
3.2b
C–SC
SC–SA
SA–I
108.9
170.0
260.0c
4.8
b
1.1b
1.1c
1.1d
C–I
C–I
C–I
71.8
76.3
74.7
41.1
43.1
43.1
–
C–SC
SC–SA
SA–I
122.5
160.0
260.0c
17.5
80.4b
b
1.2a
C–SC
SC–I
101.1
106.7
–
1.2b
1.2c
1.2d
a
C–I
C–I
C–I
78.5
75.2
68.4
58.8
58.8
76.3
C–SC
SC–SA
SA–I
111.7
120.0
220.0c
13.7
b
–
C = crystal; SC = smectic C; I = isotropic liquid.
Combined enthalpies.
C–SC
SC–SA
SA–I
120.2
213.0
254.8c
59.1
b
b
11.0
C–C0
86.0
95.8
17.0
6.7
length, a decrease in the melting point is observed when
more polyether chains are involved.
C0–SC
SC–SA
SA–I
b
138.0
215.0c
[Pd(l-Cl)L]2. All the new chloro-bridged complexes
synthesized are liquid crystals (Table 3), exhibiting Sc
and SA mesophases as expected for species with long
chain substituents. Fig. 1 displays graphically their ther-
mal behavior. Again large differences in melting point
are observed between the complexes with four alkoxy
goups and those with four polyether groups: DT = 60
ꢁC (3.1a versus 3.1d) and DT = 140 ꢁC (3.2a versus
3.2d). In addition, the ranges of mesophase are 20–50
ꢁC broader for the polyether derivatives. The range of
mesophase in 3.2d is much smaller than in 3.1d (35 ꢁC
versus 110 ꢁC). Again this suggests that the more disor-
dered conformation of the longer chains for the polye-
ther prevents efficient intermolecular interactions and
facilitates a lower clearing temperature. The compounds
with two polyether chains and two alkoxy chains (3.1b,
3.1c and 3.2b, 3.2c) have more or less intermediate prop-
6.5
3.2c
C–SC
SC–SA
SA–I
96.0
137.4
220.5
13.6
b
8.6
3.2d
C–SC
SC–SA
SA–I
79.6
105.0
115.1
15.9
b
1.0
a
C = crystal; SC = smectic C; SA = smectic A; I = isotropic liquid.
Optical microscopy data.
Decomposition.
b
c
Table 4
Optical, thermal and thermodynamic data for the complexes 4.2
Complex
Transitiona
T (ꢁC)
DH (kJ molꢀ1
)
4.2a
C–C0
94.3
160.8
194.7
248.5c
27.6
30.6
–
C0–SC
SC–SA
SA–I
b
Table 2
Optical, thermal and thermodynamic data for the complexes 2.1 and
2.2
9.5
4.2b
4.2c
C–SA
SA–I
I–SA
118.7
203.7
187.7
116.0
87.8
19.5
7.6
Complex
2.1a
Transitiona
C–Ib
T (ꢁC)
DH (kJ molꢀ1
)
206.6
57.7
ꢀ1.0
–
b
SA–SC
SC–C
2.1b
C–C0
C0–I
80.2
150.4
3.3
32.9
ꢀ10.7
C–SA
SA–I
I–SA
105.2
203.5
200.7
100.8
75.7
22.8
8.51
ꢀ8.9
–
2.1c
C–C0
C0–I
46.6
161.5
10.8
36.4
b
2.1d
2.2a
2.2b
2.2c
C–I
C–I
127.7
185.0
127.7
139.4
29.9
Sa–SC
SC–C
b
ꢀ9.3
68.6
–
2.3
C–I
C–I
33.2
39.5
4.2d
C–SC
SC–SA
SA–I
58.7
82.7
84.9
b
2.2d
C–C0
C0–C00
C00–I
48.4
58.7
88.6
4.7
0.5
a
C, C0 = crystal; SC = smectic C; SA = smectic A; I = isotropic
21.6
liquid.
b
a
C, C0, C00 = crystal; I = isotropic liquid.
Decomposition.
Optical microscopy data.
Decomposition.
b
c

M.J. Baena et al. / Journal of Organometallic Chemistry 690 (2005) 998–1010
1003
Table 5
Optical, thermal and thermodynamic data for the complexes 5.1d
Table 7
Optical, thermal and thermodynamic data for the complexes 8.1 and
8.2
Complex
Transitiona
T (ꢁC)
DH (kJ molꢀ1
)
Complex
Transitiona
T (ꢁC)
DH (kJ molꢀ1
)
5.1d (n = 8)
C–I
C0–I
58.9
73.9
35.0b
8.1a
C–SA
C0–SA
SA–N
N–I
63.2
84.6
35.8
1.9
3.7b
5.1d (n = 8*)
C–I
69.2
83.5
64.1
7.4
5.9
123.7
124.6
C0–I
I–SꢁC
ꢀ1.7
8.1b
8.1c
C–SA–N
N–I
78.3
84.9
76.0
47.7
0.6
a
C, C0 = crystal; SꢁC = chiral smectic C; I = isotropic liquid.
Combined enthalpies.
b
SA–Nc
1.2
C–SA
SA–N
N–I
73.0
78.0
81.5
36.9
0.5
erties. A handicap of these compounds is that, even
when the transition temperatures decrease by introduc-
tion of polyether substituents, nearly all of them under-
go some decomposition at the clearing point, which
prevents their use in repeated heating-cooling cycles.
[Pd(l-Br)L]2. Bromo-bridged derivatives were syn-
thesized in order to evaluate the influence of a small
structural change on the mesogenic properties. The long
chain series 4.2 was chosen for this study. All of them
are liquid crystals with the same kind of mesophases
(SC and SA) as their chloro-bridged parents (Table 4
and Fig. 1). Changing four alkoxy chains by four polye-
ther chains results in a dramatic decrease of the melting
(DT = 100 ꢁC) and clearing temperatures (DT = 160 ꢁC).
At the same time the range of mesophase is severely re-
duced. The location of the polyether chain (either in the
orthometallated or in the anilinic ring) seems not to af-
fect largely the mesogenic properties, neither for the bro-
mo- nor for the chloro-complexes. The change of
halogen atom often causes a stabilization of the less or-
dered mesophases [3f]. In the present study the range of
smectic A mesophase for 4.2 broadens respect to com-
1.5
8.1d
8.2a
8.2b
C–I
I–N
52.9
21.4
20.2
-0.5
C–C0–SA
SA–I
91.7
124.4
34.1
7.2
C–SA
SA–I
58.5
65.6
27.6
2.9
8.2c
8.2d
a
SA–I
I
66.0
–
3.6
–
C, C0 = Crystal; SA = smectic A; N = nematic; I=isotropic liquid.
Combined enthalpies.
Second heating.
b
c
plexes 3.2, except for complex 4.2d. Comparing 3.2d
and 4.2d the transition temperatures are lower for the
latter and the mesophase range is shorter. Derivatives
4.2b and 4.2c display higher melting points than the
chloro-complexes analogous, and the smectic C meso-
phase is monotropic.
[Pd(l-SCn)L]2. It is known that thiolates form very
stable and planar PdII- or PtII-bridged complexes
[22,19]. If this bridging ligands bears long alkyl chains,
the empty space between the iminic chains in the dimer
could be filled and this should produce an important ef-
fect on the thermal properties. Double long chain thio-
late-bridged complexes, not described so far, looked
promising but the results reported here show that they
do not fulfill the expectations. As we can see from Table
5, compound 5.1d (n = 8) is not mesogenic, while 5.1d
(n = 8*) only develops a monotropic chiral smectic C
phase. The compounds were obtained as a mixture of
cis- and trans-isomers. Thus, the two melting points ob-
served can be attributed to the different melting point of
Table 6
Optical, thermal and thermodynamic data for complexes 6.1 and 7.1
Complex
(l-X)
Transitiona
T (ꢁC)
DH (kJ molꢀ1
)
6.1a (n = 8)
(l-OAc)
C–SA [3g]
SA–I
124.0
156.9
28.5
3.3
6.1d (n = 8)
(l-OAc)
C–I
51.9
76.1
47.0
56.2
19.9
C0–I
I–SC
b
ꢀ4.3
25.6
6.1d (n = 8*)
7.1a (n = 8)
(l-OAc)
(l-Cl)
C–I
70.5
C–SC [3g]
SC–SA
SA–I
101.9
126.2
192.4
8.9
–
4.9
Table 8
Optical, thermal and thermodynamic data for the complexes 9.2
7.1d (n = 8)
(l-Cl)
(l-Cl)
(l-Cl)
C–I
I–SC
106.7
101.5
22.9
ꢀ2.8
21.0
1.8
Complex
Transitiona
C–C0
T (ꢁC)
DH (kJ molꢀ1
)
7.1d (n = 8*)
C–SꢁC–I
SꢁC–Ib
81.4
64.6
9.2a
47.3
175.3
9.3
15.7
7.1d (n = 2)
C–SA
SA–I
91.7
142.8
11.4
4.5
9.2b
9.2c
9.2d
a
C–I
C–I
C–I
155.9
149.9
124.0
17.7
19.3
14.8
a
C, C0 = crystal; SA = smectic A; SC = smectic C; SꢁC = chiral
smectic C; I = isotropic liquid.
b
Data from the second heating.
C = crystal, I = isotropic liquid.

1004
M.J. Baena et al. / Journal of Organometallic Chemistry 690 (2005) 998–1010
Fig. 1. Thermal behavior of compounds 3.1, 3.2 and 4.2 (h: phases present on heating; c: phases present on cooling).
each isomer. The introduction of a chiral centre in the
alkyl thiolate chain is deemed responsible for the meso-
genic behavior of 5.1d (n = 8*), as it carries also a small
dipolar moment which increases the intermolecular
forces.
Dinuclear complexes with mixed bridges. In general,
the complexes were not isolated as microcrystalline sol-
ids, but as plastic–like materials. Most of them do not
crystallize on cooling and the mesophase (sometimes
fairly fluid) is maintained at room temperature. Only
one, 7.1d (n = 8) devitrifies on heating and its analogue
7.1d (n = 8*) apparently shows a glass transition (Tg).
Table 6 and Fig. 2 gather the mesogenic properties ob-
served. As expected, the polyether derivatives have low-
er transition temperatures than the alkoxy derivatives,
but the thermal stability of the mesophases also de-
creases. With polyether chains the thiolate-acetate com-
plex 6.1d (n = 8) shows a monotropic SC mesophase. Its
chiral analog 6.1d (n = 8*) is not liquid crystal in this
case.
The chloro-thiolate complexes are liquid crystals, dis-
playing enantiotropic smectic C and smectic A phases
for the alkoxy derivatives, but only smectic A and
monotropic smectic C for the complexes with polyether.
The introduction of a chiral center affords a chiral mes-
ophase (7.1d, n = 8*).
2.2.3. Mononuclear derivatives
A usual strategy to improve the mesogenic proper-
ties from dinuclear complexes is to reduce the symme-
try of the molecular shape by converting them into
mononuclear acetylacetonato derivatives [3e]. The
Fig. 2. Thermal behavior of compounds 6.1 and 7.1 (c: mesophase observed on cooling; 2nd h: mesophase observed on the 2nd heating).

M.J. Baena et al. / Journal of Organometallic Chemistry 690 (2005) 998–1010
1005
Fig. 3. Thermal behavior of compounds 8.1 and 8.2. (c: mesophase observed on cooling).
new polyether complexes studied here might combine
2.3. Experiments of ionic extraction and transport
the reduction in symmetry with the presence of more
disordered chains to give rise to complexes with very
low transition temperatures. Acetylacetonato 8.1 and
8.2 and alanine 9.2 orthopalladated imines were syn-
thesized with this aim.
Pd(acac)L. Both series of acetylacetonate complexes
have lower melting and clearing points than the halo-
bridged complexes and exhibit more disordered meso-
phases. Table 7 and Fig. 3 show the behavior of these
compounds. SA and N for 8.1b and 8.1c, only SA for
8.2b and 8.2c. This last complex is liquid crystal at room
temperature. Also complex 8.1d is a monotropic nematic
liquid crystal at room temperature, while 8.2d is ob-
tained as an isotropic liquid, which shows no mesopha-
ses at lower temperature.
The ranges of mesophase are very narrow and almost
all the acetylacetonato complexes with polyether chains
retain the mesophase texture on cooling. For derivatives
8.1b and 8.2b the enthalpy of the melting point is larger
than for 8.1c and 8.2c. This is in agreement with the pre-
viously observed feature [3f] that when the more disor-
dered chains (polyether chains) are on the free ring,
the packing is less efficient leading to lower melting
points and transition enthalpies.
[Pd(Ala)L]. The alanine derivatives 9.2 were synthe-
sized with aiming at producing chiral mesophases, since
the aminoacid bears a chiral centre. This strategy failed
due to the high melting points exhibited by the com-
pounds (Table 8). Despite this, a cholesteric mesophase
could be observed at rapid cooling rates (faster than 10
ꢁC/min).
Representative complexes were chosen for extraction
experiments. These included the dinuclear mixed
bridged complexes because the cis-disposition of the ter-
minal chains is a good preconditioning and might de-
crease the unfavorable entropic effect in a cooperative
complexation of cations by two chains of the dimer,
compared to complexation of two chains of different
molecules in other molecular types [23]. The acetate–thi-
olate complexes were chosen because the convergence in
the space of the chains could be a further structural fac-
tor to enhance the ion capture. Extraction and transport
experiments were as well carried out with the tetranu-
clear specie 10 which, due to its folded structure, brings
the chains closer than the chloro-bridged compounds.
The experiments were carried out as described in the
Experimental Section.
Qualitative results for transport experiments show
that the complexes are only modest transporters. The
acetate–thiolate bridges are better than the chloro-thio-
late or the tetranuclear complex but none of them can be
considered useful as ionic transporter.
More accurate measurements were carried out on
extraction efficiency, comparing the complexes with
the free ligands. (Table 9). For all the cases, the extrac-
tion, although poor, improved significantly with the
complexes compared to the ligands. Again the mixed
acetate–thiolate bridge combined with a long alkyl chain
at the thiolate produced the highest complexation of K+.
3. Conclusions
2.2.4. Tetranuclear derivative 10
In spite of the beneficial effects of polyether chains
on the melting points, neither the azine ligand nor
the acetate-bridged complex are liquid crystals (see
Scheme 3).
In summary, the substitution of alkoxy terminal
chains by polyether chains in complexes derived of
orthopalladated imines leads to a marked lowering
of the melting points. The presence of four polyether

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M.J. Baena et al. / Journal of Organometallic Chemistry 690 (2005) 998–1010
Table 9
Efficiency as extractant (e) [24] of representative complexes and ligands (npc = number of polyether chains)
Compound
mol Lꢀ1
npc
mmol KPic extracted
e
10
6.1d (n = 8*)
2 · 10ꢀ3
2 · 10ꢀ3
2 · 10ꢀ3
2 · 10ꢀ3
1.8 · 10ꢀ3
2 · 10ꢀ3
4 · 10ꢀ3
4
4
2
4
2
2
2
1.91 · 10ꢀ4
4.61 · 10ꢀ4
2.68 · 10ꢀ4
3.05 · 10ꢀ4
2.19 · 10ꢀ4
0.0
0.96
2.3
[Pd2(l-OAc)(l-SC2)(L)2], L = Im O4C8/OC4
7.1d (n = 2)
1.3
1.5
[Pd2(l-Cl)(l-SC2)(L)2], L = Im O4C8/OC12
H2Az, O3C6/O3C6
1.1d
1.2
0.0
2 · 10ꢀ5
0.03
chains affords the lowest transition temperatures, but
the change from O3C6 to O4C8 produces the disap-
pearing of mesogenic stability for all types of
complexes.
The complexes with cis conformation of the polyether
chains in orthometallated-imine dimeric complexes are
very modest ionic transporters. The best transporters
are the acetate–thiolate bridged complexes.
Milli-Q quality water was used for the extraction and
transport experiments.
4-Dodecyloxianiline [26] and 4-dodecyloxibenzalde-
hyde [27] were synthesized by conventional methods.
Similar methods were used to attach the polyether chains,
but using tosylate precursors instead of bromides.
Note. Since it is known that polyethers tend to inter-
act with water, the complexes were checked and con-
firmed to be water free prior to any thermal studies.
Watering on purpose, followed by air drying, showed
considerable uptake of water by the samples, although
the influence on the LC behavior and the transition tem-
peratures was very small (variations of about 3 ꢁC were
observed in the cases tested).
4. Experimental
4.1. General procedures
1H NMR spectra were recorded in Bruker AC-300
or ARX-300 MHz spectrometers, in CDCl3. Elemental
analyses were made in a Perkin–Elmer 2400 microana-
lyzer. IR spectra were recorded with a FT 1720X Per-
kin–Elmer spectrophotometer (4000–400 cmꢀ1) using
KBr pellets, or a Perkin–Elmer 883 spectrophotometer
(4000–200 cmꢀ1) using a Nujol emulsion supported be-
tween two polyethylene films. The textures of the mes-
4.2. O3C6H13Tos and O4C8H17Tos
100 mL of triethylamine and 25 mL (143.07 mmol) of
the corresponding polyethylenglycol were mixed and
introduced in an ice bath. 30 g (157.38 mmol) of TosCl
(10% of excess) were added and the mixture was stirred
for 6 h. Then, 150 mL of HCl and 200 g of ice were
added and the product was extracted with diethylether,
washed with water to neutral pH, and dried over
MgSO4. Further filtration and solvent evaporation gave
the product as a viscous liquid.
ophases were studied with
a
Leica polarizing
microscope mod. DMRB, equipped with a Mettler
FP-82HT hot stage and a temperature controller Met-
tler FP-90. Transition temperatures and enthalpies
were measured by differential scanning calorimetry,
with a Perkin–Elmer DSC-7, using aluminum crucibles.
The apparatus was calibrated with indium (156.6 ꢁC,
28.45 J gꢀ1) as standard. Concentrations of KPic were
determined colorimetrically with a Shimadzu UV–visi-
ble spectrophotometer UV-1603.
4.3. p-(1,4,7-Trioxanonanyl)aniline and
p-(1,4,7,10-tetra- oxadodecanyl)aniline
The tosylate (35.32 mmol) was added over an ethan-
olic solution (50 mL) of 4-hydroxyacetanilide (2.9 g,
32.11 mmol) and KOH (2.2 g, 40.14 mmol) dissolved
in the minimum amount of water. The mixture was re-
fluxed for 4 h. Then, water was added, ethanol was
evaporated and the product was extracted with chloro-
form. The organic phase was separated and dried over
MgSO4. After filtration, the solvent was removed and
the compound was vacuum-dried. A viscous liquid
was obtained which corresponds to the polyether
substituted acetanilide. To a solution of the described
acetanilide (10 g, 32.11 mmol) in 40 mL of ethanol, a
solution of KOH (11.19 g, 199.43 mmol) in 10 mL of
water was added. The red solution was refluxed for
Solvents were dried and distilled before use. Station-
ary phase used for column chromatography was silica-
gel (230–400 mesh ASTM). Literature procedures were
used to synthesize the silver thiolates (AgSCnH2n + 1
)
[25], and the compounds 1.1a [3e], 2.1a [3e], 3.1a [3e],
8.1a [3e], 6.1a [3g], and 7.1a [3g]. The compounds
4-hydroxybenzaldehyde, 4–hidroxyacetanilide, poly-
ethylenglycols O3C6H14 and O4C8H18, p-toluenesulfo-
nyl chloride (TosCl), AgOAc, and aliphatic thiols
were obtained from commercial sources and used with-
out further purification. KPic was obtained by reaction
of picric acid with sodium carbonate and recrystallized.

M.J. Baena et al. / Journal of Organometallic Chemistry 690 (2005) 998–1010
1007
5 h. Then, ethanol was evaporated and the product was
extracted in chloroform. The organic layers were col-
lected, dried over MgSO4 and, after vacuum evapora-
tion of the solvent, the amine was obtained as a dark
red liquid.
carried out transforming into their chloro-bridge deriv-
atives as reported below. From these, pure acetate
complexes were recovered as follows: sodium acetate
(Pd:OAc = 1:2) was added to 30 mL of an acetone-
dichloromethane solution of 0.07 mmol of [Pd(l-
Cl)L]2 and was stirred for 14 h. The resulting suspen-
sion was evaporated to dryness and the complex was
extracted in CH2Cl2 and filtered through a pad of
Kiesselgur. By addition of n-hexane and further evap-
oration of the CH2Cl2, a yellow solid was obtained
which was filtered off, washed with cold n-hexane and
dried in vacuum (yields: 85–90%). All these com-
pounds, except 2.2a, acquire pasty textures. IR
(KBr): 2.2a: 1610 s (C@N), 1252 vs, 1029 s (C–O–C),
1542 s, 836 m (Ar), 1573 vs (C@O); 2.1b–d, 2.2b–d:
1608 s m(C@N), 1251 vs, 1062 m, 1119 s m(C–O–C),
1543 s, 834 m m(Ar), 1573 vs m(C@O). Analysis (%):
2.1b: calc.: C, 53.16; H, 6.11; N, 2.30; found: C,
54.94; H, 5.95; N, 2.30; 2.1c: calc.: C, 57.47; H, 6.82;
N, 2.31; found: C, 57.12; H, 6.62; N, 2.72; 2.1d: calc.:
C, 57.47; H, 6.82; N, 2.31; found: C, 57.07; H, 6.58; N,
2.88; 2.2a: calc.: C, 65.57; H, 8.70; N, 1.96; found: C,
65.68; H, 8.78; N, 1.99; 2.2b: calc.: C, 59.52; H, 7.56;
N, 1.98; found: C, 59.51; H, 7.37; N, 1.98; 2.2c: calc.:
C, 59.52; H, 7.56; N, 1.98; found: C, 59.50; H, 7.41;
N, 1.88; 2.2d: calc.: C, 53.33; H, 6.49; N, 2.00; found:
C, 53.02; H, 6.20; N, 2.24.
4.4. p-(1,4,7-Trioxanonanyl)benzaldehyde and
p-(1,4,7,10-tetraoxadodecanyl) benzaldehyde
To a solution of 4-hydroxybenzaldehyde (35.42
mmol) in 100 mL of acetone, was added 38.96 mmol
of the corresponding tosylate, and 70.8 mmol of
K2CO3. The mixture was then refluxed for 48 h. and
the yellow suspension was filtered to remove the excess
of K2CO3 and KCl formed. The filtrate was taken to
dryness and the residue was chromatographied on a sil-
ica column using a mixture of n-hexane/ethyl acetate 2:3
as eluent.
4.5. Imines (HL) (1.1b–d, 1.2a–d)
All the imines were synthesized by condensation of
their respective aldehydes and anilines in absolute etha-
nol with acetic acid as catalyst [28]. Yields were in the
range 60–70%. IR (KBr): 1.2a: 1623 s (C@N), 1253 vs,
1025 s (C–O–C), 1680 s, 842 m (Ar) cmꢀ1; 1.1b–d,
1.2b–d: 1623 s m(C@N), 1254 vs, 1025 m, 1141 s m(C–
O–C), 1609 s, 842 m m(Ar) cmꢀ1. Analysis (%): 1.1b:
calc.: C, 67.39; H, 7.92; N, 3.14; found: C, 67.50; H,
7.74; N, 3.06. 1.1c: calc.: C, 73.43; H, 8.90; N, 3.17;
found: C, 73.23; H, 8.68; N, 3.47; 1.1d: calc.: C, 73.43;
H, 8.40; N, 3.17; found: C, 73.33; H, 8.66; N, 3.66;
1.2a: calc.: C, 80.82; H, 10.82; N, 2.55; found: C,
81.15; H, 11.11; N, 2.57; 1.2b: calc.: C, 73.16; H, 9.50;
N, 2.58; found: C, 73.01; H, 9.49; N, 2.34; 1.2c: calc.:
C, 73.16; H, 9.50; N, 2.58; found: C, 73.36; H, 9.69;
N, 2.68; 1.2d: calc.: C, 65.27; H, 8.12; N, 2.64; found:
C, 65.59; H, 8.35; N, 2.33.
4.7. [Pd(l-Cl)L]2 derivatives (3.1b–d, 3.2a–d)
To a stirred solution of [Pd(l-OAc)L]2 (1.75 mmol) in
20 mL of dichloromethane was added dropwise the stoi-
chiometric amount of a solution of HCl in methanol
(Pd:HCl = 1:1). After 1 h stirring the solvent was evap-
orated and the product was chromatographied through
a silica column using different eluents: CH2Cl2 for 3.2a;
a 98.5:1.5 CH2Cl2/methanol mixture for 3.1d and 3.2d,
and a 99.9:0.1 CH2Cl2/methanol mixture for 3.1b, 3.1c,
3.2b and 3.2c. The solutions obtained were taken to dry-
ness and dissolved in dichloromethane. 3.2a precipitates
by adding acetone. The other complexes precipitate by
adding n-hexane. The solids were filtered off, washed
with the appropriate solvent and vacuum dried. All of
them are yellow solids with different grades of pasty tex-
ture. Yields: 60–95%. IR (KBr): 3.2a: 1610 s (C@N),
1250 vs, 1029 s (C–O–C),1582 s, 832 m (Ar), 250 Pd-
Cl (Nujol) cmꢀ1; 3.1b–d, 3.2b–d: 1607 s (C@N), 1251
vs, 1031 m, 1114 s (C–O–C), 1580 vs, 831 m (Ar), 248
Pd-Cl (Nujol); Analysis (%): 3.1b: calc.: C, 51.20; H,
5.84; N, 2.39; found: C, 50.88; H, 5.59; N, 2.30; 3.1c:
calc.: C, 55.68; H, 6.57; N, 2.40; found: C, 55.32; H,
6.44; N, 2.66; 3.1d: calc.: C, 55.68; H, 6.57; N, 2.40;
found: C, 55.41; H, 6.36; N, 2.42; 3.2a: calc.: C, 64.33;
H, 8.46; N, 2.02; found: C, 64.13; H, 8.09; N, 2.05;
3.2b: calc.: C, 58.06; H, 7.38; N, 2.06; found: C, 57.34;
H, 6.95; N, 2.05; 3.2c: calc.: C, 58.06; H, 7.38; N, 2.06;
4.6. [Pd(l-OAc)L]2 derivatives (2.1b–d, 2.2a–d)
A mixture of 1.29 mmol of paladium acetate [29]
and the stoichiometric amount of the corresponding
imine (3.86 mmol) in 15 mL of glacial acetic acid
was stirred at 50 ꢁC for 14 h. The compounds were iso-
lated in different ways depending on their nature. 2.2a
was filtered off from the resulting suspension, washed
with cold acetone and dried in vacuum, obtaining a
yellow solid (yield: 91%). To obtain 2.1d and 2.2d,
the acetic acid was evaporated, the reddish solid was
dissolved in CH2Cl2 and then filtered through a pad
of Kiesselgur. N-hexane was added and CH2Cl2 was
evaporated to obtain a yellow solid which was filtered
off, washed with cold n-hexane, and vacuum dried.
Yields: 85–99%. Complexes 2.1b, 2.1c, 2.2b and 2.2c
were not obtained pure in this way. Purification was

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M.J. Baena et al. / Journal of Organometallic Chemistry 690 (2005) 998–1010
found: C, 57.78; H, 7.17; N, 2.08; 3.2d: calc.: C, 51.64;
H, 6.27; N, 2.07; found: C, 51.11; H, 6.05; N, 2.14.
4.11. [Pd(l-SCn)(l-Cl)L]2 derivatives
(7.1d (n = 2, 8, 8*))
4.8. [Pd(l-Br)L]2derivatives (4.2a–d)
Complex 3.1d (0.827 mmol) was disolved in 20 mL of
CH2Cl2. To this solution was added the respective
AgSCnH2n + 1 (0.827 mmol) and the mixture was stirred
for 2 h protected from the light. After filtration through
a pad of Kiesselgur, the solution vas evaporated to dry-
ness. The residue was treated with acetone and a gelati-
nous solid was obtained, filtered off, washed with
acetone and vacuum dried. Yields: 75–95%. IR (KBr):
1607 s (C@N), 1265 s, 1061 m, 1117 vs (C–O–C), 1577
s, 831 m (Ar) (cmꢀ1). Analysis (%): 7.1d (n = 2): calc.:
C, 52.11; H, 5.89; N, 2.34; found: C, 51.65; H, 5.93;
N, 2.34; 7.1d (n = 8): calc.: C, 54.31; H, 6.68; N, 2.18;
found: C, 54.21; H, 6.16; N, 2.24; 7.1d (n = 8*): calc.:
C, 54.31; H, 6.68; N, 2.18; found: C, 54.01; H, 6.35;
N, 1.98.
To a suspension of 0.068 mmol of [Pd(l-Cl)L]2ꢀ in 40
mL chloroform/acetone (2:1) was added an excess of
KBr (2.08 mmol; Pd:Br 1:15), and the solution was re-
fluxed for 5 h. After this time, the reaction was evapo-
rated to dryness, dissolved in dichloromethane and
filtered through Kiesselgur in order to eliminate the
potassium salts formed. EtOH was poured on the solu-
tion in 4.2a and n-hexane was added in the other cases.
After that, dichloromethane was evaporated. The solids
obtained were filtered, washed with the adequate cold
solvent and dried in vacuum. Yields: 73–95%. IR
(KBr): 4.2a: 1609 s (C@N), 1250 vs, 1028 s (C–O–C),
1580 s, 831 m (Ar) cmꢀ1; 4.2b–d: 1607 s (C@N), 1250
vs, 1029 m, 1114 s (C–O–C), 1580 s, 832 m (Ar). Anal-
ysis (%): 4.2a: calc.: C, 60.45; H, 7.95; N, 1.90; found:
C, 60.46; H, 7.68; N, 1.92; 4.2b: calc.: C, 54.51; H,
6.93; N, 1.93; found: C, 55.2; H, 6.84; N, 2.14; 4.2c:
calc.: C, 54.51; H, 6.93; N, 1.93; found: C, 54.58; H,
6.64; N, 2.10; 4.2d: calc.: C, 48.45; H, 5.89; N, 1.95;
found: C, 48.69; H, 5.73; N, 2.07.
4.12. Pd(acac)L derivatives (8.1b–d, 8.2a–d)
To a stirred solution of [Pd(l-Cl)L]2 (0.07 mmol) in
20 mL of CH2Cl2 was added 0.14 mmol of thallium(I)
acetylacetonate (Pd:acac = 1:1). The solution was pro-
tected from the light and stirred for half an hour. Then
it was filtered through a pad of Kiesselgur in order to re-
move the TlCl. n-Hexane was added to the filtrate and
the dichloromethane was evaporated. The solid formed
was filtered off, washed with n-hexane, and dried in vac-
uum, except the derivative 8.2d which was obtained as a
liquid at room temperature. Yields: 60–90%. IR (KBr):
8.2a: 1609 s (C@N), 1253 vs, 1039 s (C–O–C), 1535 s,
833 m (Ar), 1573 vs (C@O) cmꢀ1. 8.1b–d, 8.2b–d: 1609
s (C@N), 1252 vs, 1034 m, 1115 s (C–O–C), 1536 s,
829 m (Ar), 1578 vs (C@O). Analysis (%): 8.1b: calc.:
C, 5.93; H, 6.36; N, 2.15; found: C, 54.68; H, 5.93; N,
2.32; 8.1c: calc.: C, 59.49; H, 7.02; N, 2.17; found: C,
59.36; H, 6.87; N, 2.49; 8.1d: calc.: C, 59.49; H, 7.02;
N, 2.17; found: C, 58.86; H, 6.71; N, 2.09; 8.2a: calc.:
C, 66.87; H, 8.68; N, 1.85; found: C, 66.56; H, 8.61;
N, 1.64; 8.2b: calc.: C, 61.16; H, 7.69; N, 1.87; found:
C, 60.74; H, 7.54; N, 2.32; 8.2c: calc.: C, 61.16; H,
7.69; N, 1.87; found: C, 60.96; H, 7.35; N, 1.87.
4.9. [Pd(l-SCn)L]2 derivatives (5.1d (n = 8, 8*))
The n-alkyl-thiol (n = 8, 8*) (26.2 lL, 0.15 mmol) was
added to the yellow solution of 2.1d (87.6 mg, 0.072
mmol) in 20 mL of CH2Cl2. Immediately the color got
lighter. After 1 h the solvent was evaporated and the
product was crystallized in cold CH2Cl2/EtOH. The yel-
low solid was filtered off and washed with cold EtOH.
Yields: 53, 75%. IR (KBr): One isomer: 1604 s (C@N),
1263 s, 1062 m, 1109 s (C–O–C), 1539 s, 829 m (Ar).
The other isomer: 1576 s (C@N), 1247 s, (C–O–C),
1504 s, 829 m (Ar) (cmꢀ1). Analysis (%): 5.1d (n = 8):
calc.: C, 56.93; H, 7.38; N, 2.01; found: C, 56.51; H,
7.13; N, 1.71; 5.1d (n = 8*): calc.: C, 56.93; H, 7.38; N,
2.01; found: C, 52.49; H, 6.28; N, 2.31.
4.10. [Pd(l-SCn)(l-OAc)L]2 derivatives
(6.1d (n = 8, 8*))
4.13. Pd(Ala)L derivatives (9.2a–d)
A solution of 2.1d (0.038 mmol) and 5.1d (n = 8, 8*)
(0.038 mmol) in 20 mL of CH2Cl2 was stirred for 2 h.
After removal of the solvent, the residue was treated
with n-hexane, filtered off and washed with cold n-hex-
ane. The yellow solid obtained had a pasty texture.
Yields: 80, 85%. IR (KBr): 1607 m, 1580 vs (C@N),
1251 vs, 1056 m, 1113 vs (C–O–C), 1556, 1541 vs, 833
m m(Ar) (cmꢀ1). Analysis (%): 6.1d (n = 8): calc.: C,
55.17; H, 6.79; N, 2.14; found: C, 54.98; H, 6.48; N,
2.15; 6.1d (n = 8*): calc.: C, 55.17; H, 6.79; N, 2.14;
found: C, 54.79; H, 6.26; N, 2.14.
To a stirred suspension of [Pd(l-OAc)L]2 (0.068
mmol) in 20 mL of methanol was added the stoichiom-
etric amount of alanine and the mixture was refluxed for
1 h. The solvent was evaporated to dryness and the
product was extracted in CH2Cl2 and filtered through
a pad of Kiesselgur in order to eliminate the remaining
alanine. The compounds were column chromatogra-
phied using dichloromethane–methanol (97:3) as eluent.
The resultant solution was evaporated to dryness and
dissolved in dichloromethane. 9.2a was precipitated by

M.J. Baena et al. / Journal of Organometallic Chemistry 690 (2005) 998–1010
1009
addition of EtOH; 9.2b–d were precipitated with n-hex-
ane. The solid was filtered off, washed with the appropri-
ate cold solvent and dried by suction in vacuum. Yields:
50–80%. IR (KBr): 9.2a: 1611 s (C@N), 1253 vs, 1051 s
(C–O–C), 1579 s, 832 m m(Ar), 3218 (NH2) cmꢀ1. 9.2b–
d: 1609 s (C@N), (C@O), 1252 vs, 1061 m, 1115 s (C–O–
C), 1500 s, 834 m (Ar), 3242 (NH2). Analysis (%): 9.2a:
calc.: C, 64.63; H, 8.68; N, 3.77; found: C, 62.59; H,
8.41; N, 3.53; 9.2b: calc.: C, 58.81; H, 7.68; N, 3.81;
found: C, 58.37; H, 7.38; N, 3.88; 9.2c: calc.: C, 58.81;
H, 7.68; N, 3.81; found: C, 58.72; H, 7.10; N, 3.86;
9.2d: calc.: C, 52.86; H, 6.65; N, 3.85; found: C, 52.64;
H, 6.46; N, 3.77.
The source phase was 10 mL of 10ꢀ2 M KPic and the
receiving phase was 10 mL of H2O. A second identical
U tube with 15 mL of dichloromethane as liquid mem-
brane and equal source and receiving phases was used
as reference. After moderate stirring for 77 h, [KPic]
at the receiving phase was determineded by UV–Vis
spectrophotometry (k = 357 nm).
Acknowledgements
We acknowledge financial support by the Spanish
´
Comision Interministerial de Ciencia y Tecnologıa (Pro-
ject MAT2002–00562), and the Junta de Castilla y Leon
´
´
(Project VA050/02), and thank valuable assistance in the
transport and extraction experiments by Dr. Gloria
Alcaide.
4.14. Azine ligand (H2Az)
To a stirred solution of H13C6O3–C6H4–CHO (2 g,
8.40 mmol) in absolute ethanol was added H2N-
NH2.H2O (0.210 g, 4.20 mmol) and a few drops of acetic
acid. A yellowish solid was formed which was filtered
and washed with cold ethanol. Yield: 82%. IR (KBr):
1630 m m(C@N), 1251 s, 1065 m, 1103 vs m(C–O–C),
1604 s, 841 m m(Ar) cmꢀ1. Analysis (%): calc.: C,
66.08; H, 7.68; N, 5.93; found: C, 66.21; H, 7.73; N,
6.04.
Appendix A. Supplementary material
1
Tables of relevant H NMR data for compounds 1–
10. Supplementary data associated with this article can
be found, in the online version at doi:10.1016/
j.jorganchem.2004.11.010.
4.15. [Pd2(l-OAc)Az]2 (10)
References
Palladiun acetate (1g, 1.48 mmol) and the azine
(1.052g, 2.23 mmol) were mixed in 10 mL of acetic acid
and heated at 50 ꢁC for 36 h. The acetic acid was evap-
orated and the residue was treated with CH2Cl2 and fil-
tered through a pad of Kiesselgur. Evaporation of the
solvent gave an orange solid which was washed with
cold EtOH. Yield: 89% IR (KBr): 1566vs (C@N), 1266
s, 1053 m, 1131 s (C–O–C), 1577 vs (Ar). Analysis
(%): calc.: C, 44.96; H, 5.53; N, 3.50; found: C, 44.61;
H, 4.89; N, 3.47.
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