Liquid crystals based on palladium orthometallated complexes with amido or dialkyldithiocarbamato ligands

Article abstract of DOI:10.1039/b101650o

The dinuclear cyclopalladated compounds [Pd₂(μ-OAc)₂(Lⁿ)₂] 2 derived from imines HLⁿ = p-C_nH_{2n + 1}OC₆H₄CH=NC₆H₄ OC_nH_{2n + 1}-p 1 (n = 2, 6 or 10) react with NaOH to give dinuclear derivatives [Pd₂(μ-OH)₂(Lⁿ)₂] 3. The reaction of 3 with amines (1 : 1 molar ratio) yields the corresponding hydroxo-amido complexes [Pd₂(μ-NHR)(μ-OH)(Lⁿ)₂] (R = C_mH_{2m + 1} (m = 1, 6, 10, 14 or 18) 4 or C₆H₄C₁₄H₂₉-p 5. With excess of amine [Pd₂(μ-NHR)₂(Lⁿ)₂] 6 (R = C_mH)_{2m + 1} are formed. Complexes 4 react with thiols or decanoic acid in 1 : 1 mole ratio to give the corresponding amido-thiolato or amido-carboxylato complexes [Pd₂(μ-SC_jH_{2j + 1})(μ-NHR)(Lⁿ)₂] 7 (j = 4, 10 or 18) or [Pd₂(μ-O₂CC₉H₁₉)(μ-NHR) (Lⁿ)₂] 8. The mononuclear complexes [Pd(S₂CNR′₂)(Lⁿ)] (R′ = C₂H₅ 9a or C₈H₁₇ 9b) are prepared when complexes 3 are treated with dialkylamines in the presence of carbon disulfide. Most of the complexes show liquid crystal behaviour and nematic, smectic A and smectic C phases are found.

Full text of DOI:10.1039/b101650o

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Liquid crystals based on palladium orthometallated complexes with
amido or dialkyldithiocarbamato ligands†
Laura Díez, Pablo Espinet* and Jesús A. Miguel
Departamento de Química Inorgánica, Facultad de Ciencias, Universidad de Valladolid,
47005 Valladolid, Spain. E-mail: espinet@qi.uva.es
Received 1st February 2001, Accepted 20th February 2001
First published as an Advance Article on the web 23rd March 2001
The dinuclear cyclopalladated compounds [Pd2(µ-OAc)2(Ln)2] 2 derived from imines HLn = p-CnH2n ϩ 1OC H CH᎐
᎐
6
4
NC6H4OCnH2n ϩ 1-p 1 (n = 2, 6 or 10) react with NaOH to give dinuclear derivatives [Pd2(µ-OH)2(Ln)2] 3. The
reaction of 3 with amines (1 : 1 molar ratio) yields the corresponding hydroxo–amido complexes [Pd2(µ-NHR)-
(µ-OH)(Ln)2] (R = CmH2m ϩ 1 (m = 1, 6, 10, 14 or 18) 4 or C6H4C14H29-p 5). With excess of amine [Pd2(µ-NHR)2(Ln)2]
6 (R = CmH2m ϩ 1) are formed. Complexes 4 react with thiols or decanoic acid in 1 : 1 mole ratio to give the
corresponding amido–thiolato or amido–carboxylato complexes [Pd2(µ-SCjH2j ϩ 1)(µ-NHR)(Ln)2] 7 ( j = 4, 10 or 18)
or [Pd2(µ-O2CC9H19)(µ-NHR)(Ln)2] 8. The mononuclear complexes [Pd(S2CNRЈ2)(Ln)] (RЈ = C2H5 9a or C8H17 9b)
are prepared when complexes 3 are treated with dialkylamines in the presence of carbon disulfide. Most of the
complexes show liquid crystal behaviour and nematic, smectic A and smectic C phases are found.
to new mesomorphic mononuclear orthometallated palladium
complexes containing N,N-dialkyldithiocarbamate.
Introduction
Many metal-containing liquid crystals (metallomesogens) have
been reported in the last years. Recent reviews show that the
field is dominated by coordination compounds and there are
fewer liquid crystals of the organometallic type.1 Among the
latter, a large family is constituted by dinuclear and mono-
nuclear orthometallated complexes. It was using variations of
this versatile family of molecules that our group reported: (i)
the first examples of ferroelectric metallomesogens,2 and the
improvement of their properties;3 (ii) ways to reach an import-
ant decrease in melting points and viscosity of these materials;4
and (iii) the first cholesteric metal-containing liquid crystal.5
Within this family of complexes, the dinuclear [Pd(µ-X)Ln]2
permit one to induce thermotropic changes not only by modify-
ing terminal alkyl or alkoxy chains in Ln (which we have studied
for X = halide),3,6,7 but also by modifying the bridging system
(X = others). In this respect we have reported mesomorphic
materials containing one or two bridging thiolates.5,8
Results and discussion
1 Syntheses and structures
The imines 1 and the acetato-bridged dimeric palladium
precursors 2 were prepared and characterized according to the
literature procedures.23,24 Reaction of 2 with NaOH in acetone–
water solution led to exchange of the bridging acetato ligands
by hydroxo groups, giving 3 in very good yield (ca. 95%)
(Scheme 1). Their analytical data are consistent with the
proposed formulae, and the presence of the µ-OH ligands is
supported by a weak IR band at 3606 cmϪ1. The H NMR
1
spectra reveal that the complexes exist in solution as a 4 : 1
mixture of trans and cis isomers, depending on the arrangement
of the two imine moieties. Similar mixtures of isomers have
been found for the complexes [Pd2R2(PRЈ3)2(µ-OH)2] (R = Ph
i
or Me; RЈ = Ph, Cy or Pr).25–27 The trans isomers show only
The reactivity of dinuclear compounds [Pd(µ-OH)Ln]2
towards protic substrates like amines, thiols, and carboxylic
acids bearing alkyl chains can provide a fairly general entry to
other dinuclear complexes with double and mixed bridges.
We report here the synthesis, structural characterization and
thermotropic properties of uncommonly air stable amido–
hydroxo, anilido–hydroxo, bis-amido, amido–thiolato, and
amido–carboxylato complexes that extend the number of amido
complexes and mixed bridges, which are the first examples of
metallomesogens with these ligands. Specially remarkable is
the thermal stability of those with amido ligands containing
β-hydrogens: the number of known dinuclear amido-bridged
palladium complexes is limited9–21 and even fewer possess
β-hydrogens,18,19 because there is a strong tendency for the late
transition metal amido complexes to undergo β-hydrogen
elimination, usually followed by decomposition.22
one singlet at δ Ϫ2.07 for the bridging hydroxo groups, while
those of the cis isomers have different chemical environments
and, consequently, appear as two singlets at δ Ϫ0.99 and Ϫ2.80.
Aminolysis reactions of late transition metal hydroxo com-
plexes have been reported for Rh and Ir28 and Pt,29 as well as for
Pd. As reported for the latter,11–15,18,19 the basic character of our
hydroxo bridged palladium complexes allows for the prepar-
ation of new dinuclear amido complexes. Thus, the reaction of
3 with RNH2 (R = alkyl or p-substituted aryl) in dichloro-
methane (molar ratio 1 : 1 when R = alkyl and 1 : 2 when
R = aryl) gave the corresponding µ-hydroxo–µ-amido com-
plexes 4 and 5, resulting in a facile and fast method for the
synthesis of monoamido-bridged derivatives. The observation
of only one set of 1H NMR resonances of the orthopalladated
imine ligands suggests the isomeric purity of 4 and 5 as far as
cis (syn) or trans (anti) arrangement of the orthometallated
imines is concerned, and supports cis (or syn) for them. The
main different feature between 4 and 5 is the appearance of the
iminic OCH2 protons, which appear as diastereotopic for 5 and
as equivalent for 4. Since the amido group defines two different
situations at each side of the square planes of the Pd atoms,
In addition, based on the reaction of the [Pd(µ-OH)Ln]2 with
an amine in the presence of carbon disulfide, we describe a way
† Electronic supplementary information (ESI) avaiable: analytical data
for complexes 3–9. See http://www.rsc.org/suppdata/dt/b1/b101650o/
DOI: 10.1039/b101650o
J. Chem. Soc., Dalton Trans., 2001, 1189–1195
This journal is © The Royal Society of Chemistry 2001
1189

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Scheme 1
diastereotopic iminic OCH2 protons should be expected both
Treatment of 4 with HSCjH2j ϩ 1 ( j = 4, 10 or 18, molar ratio
for 4 and 5.
1 : 1) led to displacement of the bridging hydroxo ligand by
thiolato, giving the corresponding dinuclear complexes 7, with
mixed amido–thiolato bridges. The 1H NMR resonances of the
orthopalladated imine ligand indicate a planar structure, iso-
meric purity of the complexes, and a cis arrangement of the
two imine moieties in these complexes. An arrangement with
the thiolato group cis to the iminic nitrogen atoms is pro-
posed consistent with the upfield shift of the methylene
groups of the SR chain, because in this position they lie in
the region of anisotropic shielding by the close phenyl group,
in accordance with the values found for SR chains in similar
environments.31 The assignments of resonances for 7 given in
Table 1 were made with the help of COSY. The arrangement
proposed is in discrepancy with the usual antisymbiotic
behaviour of the soft palladium atom.32 Attempts at intro-
ducing first the thiol and then the amine in order to get the
isomer with the thiolato group trans to the iminic nitrogen
were unsuccessful, because the reaction of 3 with 1 equivalent
of alkanethiol converted half of 3 to [Pd(µ-SR)Ln]2. Unfor-
tunately, despite repeated attempts under different conditions,
we have been unable to obtain crystals of 7 suitable for an X-ray
analysis.
n-Decanoic acid was also deprotonated by complexes 4 to
give 8, containing mixed µ-amido–µ-carboxylato bridges. The
1H NMR resonances of the orthopalladated imine ligand
indicate a non-planar structure and an isomerically pure cis
arrangement of the two imine moieties in these complexes. A
similar arrangement has been reported in the cyclometallated
complex cis-[{Pd(CH2C9H6N)}2(µ-O2CCH3)(µ-NHR)] (R =
aryl) obtained by reaction of cis-[{Pd(CH2C9H6N)}2(µ-O2-
CCH3)(µ-OH)] with H2NR.12
However any dynamic process producing fast inversion of
the amido group can bring about chemical equivalence of these
methylenic protons, as observed for 4. Inversions of bridging
amido groups have been reported for related complexes,9,16,18,30
and possible mechanisms have been proposed.9 The NMR
pattern observed for the aromatic proton signals of the anilido
group indicates that rotation about the C–N bond in 5 is rapid
on the 1H NMR timescale. An arrangement of the amido group
cis to the metallated carbon atoms is supported by NOE
experiments for the complexes [Pd2(µ-NHCH3)(µ-OH)(L2)2]
and [Pd2(µ-NHC6H4C14H29-p)(µ-OH)(L6)2], and is in accord
with the structure observed by X-ray diffraction in the related
mixed amido–hydroxo bridged complex [Pd2Ph2(PPh3)2-
(µ-OH)(µ-NHtBu)].18 The IR spectra of 4 and 5 show two weak
bands near 3615 and 3280 cmϪ1, assigned to ν-OH and ν-NH
respectively. The presence of the hydroxo ligand is also estab-
lished by the observation of a high-field resonance at ca. δ Ϫ3.0,
whereas the amido NH resonance is detected in the proton
NMR spectra at ca. δ 1.1 and 2.9 for complexes 4 and 5
respectively. Attempts to prepare analogous complexes with
other primary amines, such as the p-substituted benzylamines
H2NCH2C6H4OC10H21-p, or with dialkylamines (HNEt2, HN-
(C8H17)2) resulted in the decomposition of 3. This result is in
agreement with observations reported recently about reactivity
for other dimeric palladium hydroxides with dialkylamines.18
A large excess of alkylamine was needed to achieve dinuclear
species 6 involving bis(µ-amido) bridges (otherwise there is
a persistent problem of impurities in the corresponding
µ-hydroxo, µ-amido complexes). The complexes 6 turned out to
be highly soluble, even in non-polar hydrocarbon solvents such
as hexane, and we were unable to isolate significant amounts
of pure 6. The NMR spectrum of [Pd2(µ-NHC18H37)2(L10)2]
showed the presence of one single isomer with diastereotopic
OCH2 protons. On the other hand the NCH2 protons were
diastereotopic but did not show cross peaks in a COSY experi-
ment. These data suggest a non-planar cis (or syn) complex. On
the other hand, with p-substituted anilines and despite their
higher acidity, the bis(µ-anilido) complexes were not even
detected. A similar behaviour has been reported for other
neutral palladium complexes, where kinetic inhibition, presum-
ably as a result of steric crowding, was postulated.11,14,18,19
The hydroxo complexes allow also for the preparation of new
mononuclear N,N-dialkyldithiocarbamate complexes 9, by
reaction with the corresponding dialkylamines in the presence
of carbon disulfide, a well known reactivity of hydroxo com-
plexes.33 As reported in other cases,33,34 the rotation around the
C–N bond of the dithiocarbamate group is hindered, and
the alkyl groups on the dithiocarbamate are inequivalent
and give two separate sets of resonances for NR2 protons. The
most relevant absorption bands expected in the IR spectra for
Ϫ
R2NCS2 ligands bonded in a bidentate coordination mode35
are overlapped with the imine ligand absorptions.
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J. Chem. Soc., Dalton Trans., 2001, 1189–1195
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imine (L2) and a smectic A phase for the rest, a similar
behaviour to the complexes with the alkylamido longest chains
(m = 14 or 18), although with higher transition temperatures
and narrower ranges of mesophase.
The replacement of the hydroxo bridge in complexes 4 by
thiolates bearing alkyl chains (SCjH2j ϩ 1, j = 4, 10 or 18) to give
complexes 7 could provide a better filling of the space between
the two imine moieties and have an important influence on the
thermal properties of the materials. However, the compounds
turned out not to have good thermal stability. Most (except
those with long chains in the amine, thiolate, and amido
groups) decomposed at clearing (Table 2), even in cases when
this was at reasonably low temperatures (about 130 ЊC). Overall,
the results are disappointing since only for quite long chains the
compounds display mesophases, usually SA. The melting points
are always above 100 ЊC leading to mesophase ranges lower
than for the parent compounds 4. Even so, for the combin-
ations of highest chains in the amido and thiolato groups
(m = 10, 14 or 18, k = 10 or 18), the compounds clear without
decomposition and give rise to monotropic SA or SC phases
upon cooling, which eventually solidify in a glassy state. This is
not uncommon in compounds with low crystallization temper-
atures, high molecular weight and high viscosity, and is interest-
ing in view of the possible use of the materials for optical
storage.31,37 It is remarkable and surprising that the compounds
7 with the imine L6 show liquid crystal behaviour only when the
amido group is very short (m = 1) or very large (m = 10).
The replacement of µ-OH in 4 by µ-carboxylato to give 8
produces better results. Comparing the properties of com-
pounds 7 and 8, both bearing an alkyl chain in the amido group
of six carbons, there is a noticeable lowering of both the
melting and clearing temperatures. Moreover, the compounds
can be taken into the isotropic state without showing signs of
decomposition.
Finally, the change from dinuclear complexes to the mono-
nuclear complexes 9 involves a dramatic change in the mol-
ecular shape. The complexes with diethyldithiocarbamate
show liquid crystalline properties only when the imine bears the
longest chain, L10. The effect of increasing the chain length of
the dithiocarbamato (to R = C8H17) is to decrease the transition
temperatures noticeably, and the complexes are liquid crystals,
monotropic for the imines L2 and L6, and enantiotropic for L10.
All of them retain mesophase ordering on cooling to give glassy
solids.
Fig. 1 Thermal behaviour of compounds (a) 4, 5, 8, 9a and 9b, (b) 7.
For 4, m represents the number of carbon atoms in the amide. For 7, m
and j represent the number of carbon atoms in the amide and thiolate
respectively; in each pair, the left bar corresponds to the L6 derivative
and the right bar to the L10 derivative. C = Crystal; SC = smectic C;
SA = smectic A; N = nematic; * = monotropic transition.
2 Mesogenic behaviour
The mesogenic behaviour of complexes 3–9 is summarized in
Table 2 and in Fig. 1. The hydroxo complexes 3 are not liquid
crystals in contrast with the long ranges of mesogenic
behaviour displayed by analogous complexes containing (µ-Cl)2
or (µ-Br)2 bridges and medium or long chains. This difference
can be attributed to the probable non-planar structure of 3,
which hinders good molecular packing; in fact the crystal struc-
ture of [Pd2Ph2(PPh3)2(µ-OH)2] reveals a butterfly structure
with an O–Pd–O–Pd torsion angle of ca. 36Њ.27 Thus 3 should
be structurally quite similar to the acetato-bridged complexes,
also with butterfly structures,36 which are non-mesomorphic as
well.24
Conclusion
We have established a new route for the preparation of
organometallic liquid crystals using the highly reactive
dinuclear hydroxo-bridged species [Pd2(µ-OH)2(Ln)2] 3. This
seems to be a versatile entry into other dinuclear complexes
with double or mixed bridges: amido–hydroxo, anilido–
hydroxo, bis-amido, amido–thiolato, and amido–carboxylato.
The strategy could be applied to other protic bridging ligands,
and to related complexes.
Many of the complexes 4 are mesomorphic. We have studied
the influence of the alkoxy chain in the imines (n = 2, 6 or 10)
and the effect of changing the alkyl length of the bridging alkyl-
amido ligand (m = 1, 6, 10, 14 or 18). These µ-hydroxo–µ-amido
complexes decompose upon clearing, around 175 ЊC. With the
shortest chain in the imine, L2, only the compounds with longer
chains in the amido group (m = 14 or 18) are liquid crystals,
exhibiting short ranges of nematic mesophase. With longer
imines, L6 and L10, the materials are enantiotropic showing
wide ranges of SA mesophase. On increasing the chain length of
the imine from six to ten, the melting and clearing points
decrease, and for the shortest chain in the amido group (m = 1)
a mesophase is induced for L10.
Each moiety in the system can be varied easily and influences
the thermal properties of the materials. Although the complex
shape of the molecules does not permit one to establish simple
relationships to the properties observed, it is clear that meso-
phases can be obtained from varied molecules, showing the
great potential of the basic unit in the structure, the orthometal-
lated moiety, to induce mesomorphism.
Experimental
Literature methods were used to prepare the imines HLn 1,23
[Pd2(µ-OAc)2(Ln)2] 2.24 H2NC6H4C14H29-p, aliphatic amines
H2NCmH2m ϩ 1, aliphatic thiols HSCjH2j ϩ 1, and dialkylamines
HN(R)2 were obtained from commercial sources and used
without further purification. C, H, N analyses were carried out
The µ-hydroxo–µ-anilido complexes 5 are liquid crystals
showing a nematic phase with the shortest chain length of the
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Table 2 Phase transition temperatures (ЊC) and enthalpies (kJ molϪ1) (in parentheses) for the compounds 3–9a
Compound
n
m
j
Heating scan
3
3
3
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
5
5
5
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
2
6
10
2
2
2
2
2
6
6
Cr 191 Ib,c
Cr 202 Ib,c
Cr 167 Ib,c
1
Cr 150 Ib,c
6
10
14
18
1
Cr 180 Ib,c
Cr 193.5 (68.1) Ib
Cr 173.7 (37.7) N 181.6 (0.6) Ib
Cr 147.6 (28.4) N 165.1 (0.3) Ib
Cr 174.7 (16.7) Ib
6
Cr 128.6 (31.5) SA 179.2 (4.2) Ib
Cr 104.6 (35.0) SA 180 Ib,c
Cr 74.2 (46.5) SA 180.5 (5.5) Ib
Cr 79.1 (39.8) SA 168.7 (2.3) Ib
Cr 135.6 (21.1) SA 163 Ib,c
Cr 120.8 (29.5) SA 176.5 (7.6) Ib
Cr 106.7 (26.7) SA 175.3 (5.9) Ib
Cr 76.5 (22.5) SA 167.8 (5.8) Ib
Cr 57.4 (18.2) SA 164 Ib,c
6
6
6
10
14
18
1
10
10
10
10
10
2
6
10
2
2
2
2
2
2
2
2
2
6
6
6
6
6
10
14
18
Cr 185.7 (24.8) N 198.0 (1.5) Ib
Cr 139.3 (17.6) SA 184.8 (3.2) Ib
Cr 82.1 (19.7) CrЈ 123.9 (14.9) SA 180.2 (5.4) Ib
Cr 192.8 (30.4) Ib
1
6
4
4
4
4
4
10
10
18
18
4
4
4
4
4
10
10
10
10
10
18
18
18
Cr 179.8 (33.2) Ib
10
14
18
10
18
10
18
1
Cr 135.9 (3.5) CrЈ 148.6 (32.3) Ib
Cr 102.4 (1.5) CrЈ 135.8 (35.2) Ib
Cr 85.2 (3.4) CrЈ 101.9 (12.2) CrЉ 139.1 (31.2) Ib
Cr 97.9 (1.5) CrЈ 104.5 (12.9) CrЉ 143 Ib,c
Cr 64.7 (9.6) CrЈ 86.7 (8.7) CrЉ 138.1 (43.0) Ib
Cr 76.4 (3.1) CrЈ 82.6 (3.9) CrЉ 126.8 (29.0) I
Cr 66.3 (14.0) CrЈ 109.5 (29.8) I
Cr 113.7 (4.4) CrЈ 185.3 SA 189.1 (51.4)d Ib
Cr 141.4 (59.0) Ib
6
10
14
18
1
Cr 135 Ib,c
b
Cr 65.3 (2.7) CrЈ 107.7 (20.9) CrЉ 127.2 (39.7) SA
b
6
6
6
6
6
6
6
6
Cr 102.2 (12.9) CrЈ 128.9 (43.2) SA
Cr 114.5 (7.9) CrЈ 158.3 CrЉ 163.4 (49.2)d SA 180 Ib,c
Cr 149.3 (62.2) Ib
6
10
14
18
1
6
10
Cr 101.0 (25.4) CrЈ 132.3 (45.6) Ib
Cr 106.5 (25.4) CrЈ 119.9 (33.9) SA 130.1 (7.8) Ib
Cr 95.4 (35.7) CrЈ 116.7 (34.4) SA 125.3 (5.9) Ib
Cr 144.8 CrЈ 150.0 (59.2)d SA 169.6 (12.6) Ib
Cr 89.9 (37.1) CrЈ 135.5 (44.9) Ib
6
Cr 75.5 (25.1) CrЈ 122.4 (44.7) I
I 111.0 (Ϫ4.9) SA
e,f
7
7
6
6
14
18
18
18
Cr 90.3 (36.9) CrЈ 129.1 (51.3) I
I 115.5 (Ϫ6.2) SA
e,f
Cr 132.5 (49.3) I
I 119.7 (Ϫ5.9) SA
e,f
7
7
7
7
7
7
7
7
10
10
10
10
10
10
10
10
1
6
10
14
18
1
4
4
4
4
4
10
10
10
Cr 126.5 (2.8) CrЈ 160.0 (23.3) SA 174.4 (8.2) Ib
Cr 103.0 (15.8) CrЈ 124.7 (24.7) SA 143.5 (8.4) Ib
Cr 90.0 (4.5) CrЈ 115.7 (17.2) CrЉ 131.1 (34.0) SA 135.7 (6.6) Ib
Cr 106.4 (11.6) CrЈ 125.8 (41.5) SA 134.0 (8.4) Ib
Cr 86.7 (3.6) CrЈ 99.5 (20.2) CrЉ 117.3 (34.5) SA 130.7 (8.2) Ib
Cr 135.5 (25.5) SA 167.3 (6.7) Ib
6
10
Cr 94.6 (9.7) CrЈ 134.6 CrЉ 135.9 (44.1)d SA 138.2 (7.1) I
Cr 89.4 (23.6) CrЈ 116.5 (2.4) CrЉ 133.8 (55.1) I
I 128.9 (Ϫ8.1) SA 113.3 (Ϫ24.3) Cr e
7
7
10
10
14
18
10
10
Cr 86.4 (18.0) CrЈ 127.4 (58.5) I
I 122.9 (Ϫ7.4) SA 84.8 (Ϫ0.5) SC
Cr 102.3 (2.4) CrЈ 127.1 (60.2) I
I 122.4 (Ϫ8.2) SA 86.5 (Ϫ1.0) SC
e,f
e,f
7
7
7
10
10
10
1
6
10
18
18
18
Cr 119.8 (12.5) CrЈ 134.8 (14.2) SA 160.2 (6.3) Ib
Cr 54.6 (Ϫ4.8) CrЈ 101.5 (13.6) SA 122.7 (6.8) Ib
Cr 83.6 (38.6) CrЈ 130.3 (74.2) I
I 122.6 (Ϫ7.9) SA 84.7 (Ϫ20.3) Cr e
Cr 67.0 (30.1) CrЈ 127.2 (70.8) I
I 124.3 (Ϫ8.2) SA 110.5 (Ϫ36.4) Cr e
Cr 68.1 (30.1) CrЈ 124.4 (63.6) I
I 122.3 (Ϫ8.1) SA 105.0 (Ϫ33.1) Cr e
Cr 149.3 (31.7) I
7
7
10
10
14
18
18
18
8
8
2
6
Cr 133.9 (38.1) I
I 130.0 (Ϫ1.0) N 124.2 (Ϫ0.4) SA 85.8 (0.9) g e
Cr 75.8 (13.7) SA 107.5 (1.9) I
Cr 170.8 (41.1) I
8
10
2
6
9a
9a
9a
Cr 97.1 (17.3) I
Cr 83.8 (11.5) SA 99.5 (6.4) I
10
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Table 2 (Contd.)
Compound
n
m
j
Heating scan
9b
9b
9b
2
6
Cr 43.0 (4.1) I
I 41.1 (Ϫ2.8) SA
Cr 79.7 (25.8) I
I 71.3 (Ϫ4.4) SA
e,f
e,f
10
Cr 56.1 (19.1) SA 73.4 (4.3) I
a Cr, CrЈ = Crystal; SA = smectic A; SC = smectic C; I = isotropic liquid; N = nematic; g = glass transition. b Decomposition. c Observed by means
of polarized light microscopy only. d Combined enthalpies. e Monotropic transition (data for the cooling cycle). f A glassy mesophase is obtained on
cooling.
on a Perkin-Elmer 2400 microanalyser. All the new compounds
gave satisfactory elemental analyses (Table S1, ESI Supplemen-
tary Materials†). IR spectra were recorded on a Perkin-Elmer
FT-1720X spectrometer using Nujol mulls between poly-
ethylene plates, 1H NMR spectra on a Bruker AC-300 or
ARX-300 MHz spectrophotometer. The textures of the meso-
phases were studied with a Leitz microscope equipped with a
Mettler FP82HT hot stage and a Mettler FP90 central proces-
sor and polarizers at a heating rate of approximately 10 ЊC
minϪ1. Transition temperatures and enthalpies were measured
by differential scanning calorimetry, with a Perkin-Elmer
DSC-7 instrument operated at a scanning rate of 10 ЊC minϪ1
on heating. The apparatus was calibrated with indium (156.6 ЊC,
28.5 J gϪ1) as standard, the samples were sealed in aluminium
capsules in air, and the holder atmosphere was dry nitrogen.
[Pd2(ꢀ-O2CC9H19)(ꢀ-HNC6H13)(L6)2] 8. n-Decanoic acid
(14 mg, 0.08 mmol) was added to a solution of 4 (0.075 g, 0.069
mmol) in dichloromethane (20 mL) and stirred for 30 min. The
orange solution was evaporated to a small volume. Addition of
methanol afforded 8 as a yellow solid, which was filtered off,
washed with 2 × 3 mL of methanol and vacuum dried. Yield:
65%. IR (Nujol, cmϪ1): ν(C᎐N) 1609; ν(C᎐O) 1554.
᎐
᎐
[Pd2(S2CNEt2)(L6)2] 9. To a suspension of [Pd2(µ-OH)2(L6)2]
3 (0.100 g, 0.098 mmol) in dichloromethane (20 mL) was added
HNEt2 (21 µL, 0.198 mmol) and CS2 (18 µL, 0.30 mmol) and
the mixture stirred for 4 h at room temperature. Acetonitrile (10
mL) was added and the resulting solution concentrated to a
small volume. A yellow solid appeared which was filtered off,
washed with acetonitrile (2 × 3 mL) and vacuum dried. Yield:
65%. IR (Nujol, cmϪ1): ν(C᎐N) 1605.
᎐
Synthesis of the complexes
Acknowledgements
Only examples are described as the syntheses were similar for
the rest of the complexes.
We gratefully acknowledge financial support by the Spanish
Comisión Interministerial de Ciencia y Tecnología (Project
MAT99-0971), and the Junta de Castilla y León (Project VA16/
99). L. D. thanks the Spanish Ministerio de Educación for a
studentship.
[Pd2(ꢀ-OH)2(L6)2] 3. To a suspension of 2 (0.500 g, 0.47
mmol) in acetone (40 mL) was added a solution of NaOH
(0.11 g, 2.75 mmol) in water (30 mL). The mixture was
stirred for 24 h at room temperature. The yellow precipitate
was filtered off, washed with water (3 × 5 mL) and acetone
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᎐
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᎐
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᎐
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1194
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