Functional isocyanide metal complexes as building blocks for supramolecular materials: Hydrogen-bonded liquid crystals

Article abstract of DOI:10.1039/b705478e

Gold, palladium and platinum complexes with an unusual isocyanide ligand containing a carboxylic acid function, [AuCl(CNC₆H₄COOH)], cis-[MI₂(CNC₆H₄COOH)₂] and trans-[MI₂(CNC

Full text of DOI:10.1039/b705478e

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/dalton | Dalton Transactions
Functional isocyanide metal complexes as building blocks for supramolecular
materials: hydrogen-bonded liquid crystals
Silverio Coco,* Elisa Espinet,† Pablo Espinet* and Ine´s Palape‡
Received 11th April 2007, Accepted 14th May 2007
First published as an Advance Article on the web 7th June 2007
DOI: 10.1039/b705478e
Gold, palladium and platinum complexes with an unusual isocyanide ligand containing a carboxylic
acid function, [AuCl(CNC6H4COOH)], cis-[MI2(CNC6H4COOH)2] and trans-[MI2(CNC6H4COOH)2]
(M = Pd, Pt) have been isolated. The carboxylic acid group of the coordinated isocyanide acts as a
hydrogen donor for hydrogen-bonding and three series of stable hydrogen-bonded liquid crystalline
metal complexes have been prepared with decyloxystilbazole. Although all the metal acid derivatives
used are not mesomorphic, and decyloxystilbazole only shows an ordered Smectic E phase, four out of
the five hydrogen-bonded decyloxystilbazole complexes studied display enantiotropic smectic A or
nematic mesophases. The single crystal X-ray diffraction structure of trans-[PdI2(CNC6H4COOH)2]·
C4H8O2 has been determined and confirms the formation of a supramolecular array in the solid state
supported by hydrogen-bonding.
ligand or in its isocyanide metal complexes, provided these can
be prepared, is its participation in hydrogen-bonds.
Introduction
Isocyanides (C≡NR) are interesting ligands in organometallic
Intermolecular hydrogen-bonding is a key attractive interaction
chemistry due to their coordination ability to give very stable
stabilizing condensed phases and promoting molecular self-
complexes with many metals.1,2 Isocyanide metal complexes are
assembly. It is present in many molecular systems ranging from
catalysts for polymerization,3 and for activation of Si–Si bonds,4
inorganic to biological structures. The lower strength of hydrogen-
or molecules used for one-dimensional electric conductors,5
bonds compared to covalent bonds provides some structural
and for liquid crystals.6 Moreover, the reaction of isocyanide
flexibility to hydrogen-bonded systems, which results in interesting
complexes with nucleophiles gives carbene complexes,7 which are
properties. In the field of liquid crystals it has been known
also catalytic systems.8,9 The chemical behavior of the organic
since the early years of the 20th century that 4-alkoxybenzoic
isocyanides depends on the steric and electronic features of
acids show liquid crystal behavior as a consequence of their self-
assembling by hydrogen-bonds into dimers.20,21 There are many
reports on the effects of intermolecular hydrogen-bonding in
the field of organic liquid crystals,22 but only a few cases in
the field of metal-containing liquid crystals (metallomesogens),6,23
namely some hydrogen-bonded ferrocene complexes,24,25 and a few
phenanthroline copper derivatives.26 This scarcity is probably due
to the usually high melting temperature of metallomesogens, which
is hardly compatible with the use of moderately weak hydrogen-
bonds as the force inducing self organization above the melting
point. In fact, the reported hydrogen-bonded organic liquid
crystals and metallomesogens usually have fairly low melting
temperatures.
Here we report examples of stable gold, palladium and platinum
complexes with 4-isocyanobenzoic acid. The single crystal X-
ray diffraction structure of {trans-[PdI2(CNC6H4COOH)2].(l-
O,O-dioxane)}∞ was determined. These complexes are hydrogen
donors through the carboxylic acid group, giving mesomorphic
supramolecular complexes with decyloxystilbazole.
the R group, and this can be used to tune their properties. A
second functional group on R makes the molecule a bifunctional
ligand. The other possible groups in the molecule are limited by
the reactivity of the isocyanide group, but a number of func-
tionalized isocyanides and their corresponding metal complexes
have been reported.2,10 These include: hydroxyalkyl isocyanides;11
substituted-arylisocyanides such as 2-OH-C6H4NC,12 2,6-(OH)2-
+
C6H4NC,2 2-(CH2X)C6H4NC (X = PPh3 ,10 OSiMe3, OH,13 N3,14
or CpM(CO)3,15 with M = Cr, W); alkynylarylisocyanides;16
pyridylethynylarylisocyanides;17 and 4-isocyanobenzylidene-4-
alkoxyarylimines.18
Although organic isocyanides are hydrolysed by aqueous acids,
the synthesis of stable 4-isocyanobenzoic acid was achieved some
fifty years ago.19 In spite of the very interesting combination of
functions which make this molecule a promising building block,
further studies with this isocyanide, or its coordination to give
metal complexes, have not been reported. One behavior to be
expected for the carboxylic acid function, whether in the free
Results and discussion
IU CINQUIMA/Qu´ımica Inorga´nica, Facultad de Ciencias, Universidad
de Valladolid, E-47071, Valladolid, Spain. E-mail: espinet@qi.uva.es;
Tel: +34983423231
Synthesis and characterization
† Present address: Institut de Recerca Biome`dica, Parc Cient´ıfic de
Barcelona, Josep Samitier 1-5, E-08028, Barcelona, Spain
‡ Present address: Departamento de Qu´ımica, Universidad Arturo Prat,
Iquique, Chile
The originally reported synthesis of CNC6H4CO2H (1) uses
the carbylamine reaction on 4-aminobenzoic acid,19 but gives
poor yields and purification of the isocyanide requires successive
This journal is
The Royal Society of Chemistry 2007
Dalton Trans., 2007, 3267–3272 | 3267
©

View Article Online
crystallizations. We have improved this synthesis using a slight
modification of Ugi’s general method for the preparation of iso-
cyanides (Scheme 1):27 formylation of 4-amine-ethylbenzoate gives
4-N-formamido-ethylbenzoate. Dehydration with bis(trichloro-
methyl)carbonate (“triphosgene”) and triethylamine affords
4-isocyanoethylbenzoate. Finally, saponification with sodium
hydroxide and subsequent acidification to pH = 5 produces the
desired 4-isocyanobenzoic acid.
[MCl2(CNC6H4CO2H)2] + 2KI
→ trans-[MI2(CNC6H4CO2H)2] + 2KCl
M = Pd (5), Pt (6)
(3)
The IR spectra of 2–6 exhibit m(C≡N) absorptions for the
isocyanide group at higher wavenumbers than for the free ligand,
by about 100 cm−1 for Au(I) and 60–80 cm−1 for Pd(II) and Pt(II)
complexes. Linear 2 and trans-diiodopalladium and platinum
complexes (D2h symmetry) display one m(C≡N) IR absorption,
while cis-dichloropalladium and platinum complexes (C2v symme-
try) show two bands, as reported for similar metal aryl isocyanide
compounds.29,30 In addition, their m(C O) and m(O-H) bands
appear in the same region as the free isocyanide ligand.
=
The 1H NMR spectra of the complexes were recorded in THF-
d8, due to their low solubility in CDCl3 or in acetone-d6. This low
solubility suggests that the solvent needs to split the H-bonds in the
solid to get the compound dissolved. They spectra are all similar
to that of the free isocyanide ligand, showing two resonances
(AA‘XX’ spin system) for the aryl protons present in the molecule.
It is worth noting that coordination of the isocyanide produces a
deshieldingfor H1 (ca. 0.1 ppm) andH2 (ca. 0.3 ppm). This suggests
that the coordination of the isocyanide group reduces the electron
density on the aromatic ring, enhancing the acid character of the
carboxylic group. Consistently, the observation of the acidic H (in
complex (2)) required cooling down to 175 K in order to observe
a very broad signal at dOH 12,54.
Scheme 1
The IR spectrum of 1 shows a strong m(C≡N) absorption at
The molecular structure of trans-[PdI2(CNC6H4COOH)2] was
determined by single crystal X-ray diffraction methods. It crystal-
lizes with one hydrogen-bonded dioxane molecule per Pd atom.
An ORTEP view of the compound is given in Fig. 1(a), while
Fig. 1(b) shows the crystalline arrangement of molecules in the
solid. Table 1 gives the data collection and refinement parameters.
2128 cm−1. In addition, not reported before, the IR spectrum in
=
KBr shows a strong m(C O) stretching band at 1694 and a broad
m(O-H) band at 2986 cm−1, supporting the existence of a hydrogen-
1
bonded dimer in the solid state.28 The H NMR spectrum of 1
has not been reported before. In THF-d8 at 300 MHz it shows
for the aryl hydrogen atoms two distorted “doublets” (d1 8.08, d2
7.54); this is a deceptively simple pattern arising from the strictly
speaking AA‘XX’ spin system. Moreover, at 250 K a broad singlet
(dOH 11.95) is observed for the acidic H. In CDCl3 (a less good
¯
The compound crystallizes in the triclinic space group P1, with one
formula unit in the unit cell. With the palladium atom being on an
inversion centre, the palladium coordination environment must
be exactly planar, the cis C-Pd-I angles of 89.8(6) and 90.2(6)◦
are not significantly different from 90◦ so the palladium has
an essentially perfect square-planar environment. Pd-C and Pd-
I distances are within the ranges found in similar complexes.31
The carboxylic acid function is practically coplanar with the aryl
ring. Each dioxane oxygen is hydrogen-bonded to one of the
hydrogen acceptor than THF) the AA‘XX’ signals appear at d1
5
8.15, d2 7.49 (3J3,4 + J3,4 = 8.3 Hz), but the acidic H is not seen at
ꢀ
243 K.
As a ligand, [CNC6H4CO2H] appears to be less strongly
coordinating than other isocyanides; yet it forms easily metal
complexes according to eqn 1–3. The reaction of 1 with
[AuCl(tht)] (tht = tetrahydrothiophene) in THF gave the white
complex [AuCl(CNC6H4CO2H)] (2). Similarly, reactions of 4-
isocyanobenzoic acid with [MCl2(tht)2] (M = Pd, Pt) in THF
afforded the pale yellow complexes cis-[MCl2(CNR)2] [M = Pd
(3), Pt (4)], very little soluble in the usual organic solvents.
Taking advantage of our previous experience that isocyanide
iodo-complexes stabilize the trans isomer,29 exchange reactions in
acetone with KI afforded the corresponding trans-[MI2(CNR)2]
complexes [M = Pd (5), Pt (6)]. C, H, N analyses for the
complexes, yields, and relevant IR and NMR data are given in
the experimental section.
[AuCl(tht)] + CNC6H4CO2H (1)
→ [AuCl(CNC6H4CO2H)] (2) + tht
(1)
[MCl2(tht)2] + CNC6H4CO2H
Fig. 1 (a) Crystal structure of 5 with the atom-numbering scheme.
Displacement ellipsoids at the 50% probability level. (b) Extended network
formed by intermolecular hydrogen-bonding.
→ cis-[MCl2(CNC6H4CO2H)2] + 2tht
M = Pd (3), Pt (4)
(2)
3268 | Dalton Trans., 2007, 3267–3272
This journal is
The Royal Society of Chemistry 2007
©

View Article Online
Table 1 X-Ray data and data collection and refinement parameters for
trans-[PdI2(CNC6H4COOH)2]·C4H8O2
carboxylic groups of the adjacent trans-[PdCl2(CNC6H4COOH)2]
molecules, giving rise to the polymeric chains shown in Fig. 1(b).
None of the OH hydrogens was located in a difference Fourier
map, so their positions were calculated with a riding model. The
Empirical formula
C20H18 I2 N2 O6 Pd
˚
distance O · · · O is 2.69(2) A. After correction for a plausible O-H
Formula weight
Crystal system
Space group
742.56
Triclinic
¯
P1
32
˚
bond length (0.97 A based on neutron diffraction results), the
estimated H · · · O distance is 1.74 A and the O-H · · · O angle 164 .
◦
˚
˚
a/A
5.085(4)
9.923(8)
13.415(11)
79.378(15)
618.0(9)
1
1.995
3.284
˚
b/A
Hydrogen-bonded decyloxystilbazole complexes
˚
c/A
b/deg
The hydrogen-bonded decyloxystilbazole complexes were pre-
pared by dissolving together equimolar proportions of the corre-
sponding compound 1–6 and decyloxystilbazole in THF at room
temperature, followed by evaporation of the solvent in vacuum
to obtain compounds 1a–6a (Scheme 2). All the metal complexes
prepared were orange or yellow solids.
The formation of the supramolecular hydrogen-bonded decy-
loxystilbazole complexes (1a, 2a, 4a, 5a and 6a) was confirmed by
IR spectroscopy. Their infrared spectra in the solid state do not
show the m(O-H) absorption of the precursors, and the carbonyl
stretching absorption bands appear shifted from their positions in
the parent complexes. This change supports that self-association
of the precursors through the carboxylic acid group is replaced
by hydrogen-bonding to the decyloxystilbazole, as reported for
organic compounds of benzoic acid with decyloxystilbazole.22a
3
˚
V/A
Z
D
calc/g cm−3
Abs. coeff./mm−1
F(000)
352
Crystal size/mm
Temp./K
0.21 × 0.10 × 0.07
298(2)
h range for data collection/deg
1.65–23.39
0.71073
˚
Wavelength/A
Index ranges
−4 ≤ h ≤5, −10 ≤ k ≤10,
−13 ≤ l ≤ 14
2725
1763 [Rint = 0.0323]
23.39 (97.8%)
SADABS
1.000000 and 0.472756
1763/0/142
1.167
R1 = 0.0783, wR2 = 0.2123
R1 = 0.0934, wR2 = 0.2187
1.372 and −1.005
Reflections collected
Independent reflections
Completeness to h
Abs. corr.
Max. and min. transmittance
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2s(I)]
R indices (all data)
−3
˚
Mesogenic behavior
Largest diff. peak and hole/e A
Compounds 1–6 are not mesogenic and decompose above 200 ◦C
without melting. The decyloxystilbazole used in this work displays
Scheme 2
This journal is
The Royal Society of Chemistry 2007
Dalton Trans., 2007, 3267–3272 | 3269
©

View Article Online
Table 2 Optical, thermal and thermodynamic data for decyloxystilbazole
complexes
Compound
Transitiona
Temperatureb/◦C
DHb/KJ mol−1
1a
2a
C → SmA
SmA → I
C → Cꢀ
74.1c
146d
30.4
118.9
160.9
187d
3.6
24.81
Cꢀ → SmA
SmA → I
C → dec
C → N
4a
5a
182.0d
152.0
210d
49.2
31.2
N → I
6a
C → Sm
Sm → N
N → I
132.7
182d
210d
a C, crystal, Sm, smectic, N, nematic, I, isotropic liquid. b Data referred
to the first DSC cycle starting from the crystal. c Combined enthalpies.
d Microscopic data.
Fig. 3 Polarized optical microscopic texture (×100) observed for 6a. The
picture shows the marbled texture of the N phase, at 210 ◦C on heating
from the crystal.
a smectic E phase.33 The supramolecular compounds 1a–6a
were investigated by DSC and by hot-stage polarized optical
microscopy. Their optical, thermal and thermodynamic data are
collected in Table 2.
the corresponding compound 1–6. Probably for this reason the
clearing points, and the smectic to nematic transition of compound
6a are not observed by DSC.
All complexes that give rise to mesophases have a rod-like
structure. Consequently it is not unexpected that they display
calamitic mesophases. More interestingly, the symmetric trans-
palladium (5a) and trans-platinum (5b) supramolecular complexes
favor the formation of a nematic phase, as found for other
symmetric metallomesogens.35
In summary, we have prepared examples of gold, palladium and
platinum complexes with an unusual isocyanide ligand containing
a carboxylic acid function. They are the first examples of metal
complexes of the bifunctional 4-isocyanobenzoic acid, and have
a promising structure as metalla-ligands, as metalla-acids, and
as amphiphilic metal complexes. In fact these complexes act as
hydrogen donors to decyloxystilbazole through the carboxylic
acid group, and are building blocks to prepare supramolecular
complexes that display liquid crystalline properties. These initial
results demonstrate the utility of this bifunctional ligand.
Four out of the five hydrogen-bonded decyloxystilbazole com-
pounds studied display enantiotropic mesophases. Only 4a, which
does not have a rod-like structure, does not show liquid crystal
behavior (because of this, the corresponding Pd complex was not
made). Complexes 1a and 2a display a SmA mesophase, with
typical oil steles and homeotropic textures reorganizing to the fan-
shaped texture at temperatures close to the clearing point, and the
focal-conic texture on cooling from the isotropic liquid (Fig. 2).
Compounds 5a and 6a give rise to a N mesophase with typical
marbled and schlieren textures (Fig. 3).34 Compound 5a shows
additionally a second viscous mesophase at lower temperatures,
displaying lancets and regions with a mosaic texture on cooling
from the nematic mesophase. These observations are consistent
with a smectic G mesophase.34 At the clearing transitions to
the isotropic liquid formation of some crystals is observed. This
suggests that decomposition, most likely due to the thermal lability
of the hydrogen-bond, is generating free decyloxystilbazole and
Experimental
Experimental conditions for the analytical, spectroscopic and
diffraction studies were as reported elsewhere.35 Literature
methods were used to prepare [AuCl(tht)],36 [PdCl2(tht)2] and
[PtCl2(tht)2],37 (tht = tetrahydrothiophene).
The isocyanide [CN-C6H4-COOH] that has been described
starting directly from the amine [H2N-C6H4-COOH],19 was syn-
thesized by an improved method from 4-isocyanoetylbenzoate.
Model preparation procedures of the new compounds are given
below.
Preparation of 4-isocyanoethylbenzoate
The procedure described by Ugi et al. for other isocyanides was
used,27 using triphosgene instead of phosgene as a dehydrating
agent. To a solution of 4-N-formamido-ethylbenzoate (6.70 g,
34.69 mmol), (prepared by reaction of the amine with formic
acid) and triethylamine (9.8 mL, 69.38 mmol) in 350 ml of
Fig. 2 Polarized optical microscopic texture (×100) observed for 2a. The
picture shows the focal-conic texture of the SmA phase, on cooling from
the isotropic liquid at 175 ◦C.
3270 | Dalton Trans., 2007, 3267–3272
This journal is
The Royal Society of Chemistry 2007
©

View Article Online
dichloromethane, was added dropwise a solution of trichloro-
methylcarbonate (triphosgene) (3.50 g, 11.56 mmol) in 30 mL of
CH2Cl2. The mixture was stirred for 30 min and then the solvent
was removed on a rotary evaporator. The resulting residue was
chromatographed (silica gel, CH2Cl2/hexane, 2 : 1 as eluent) and
the solvent was evaporated to obtain the product as a greenish
liquid. (84% yield). IR/(CH2Cl2, cm−1): m(C≡N): 2128; m(CO):
a rotary evaporator and the solid obtained was recrystallized from
tetrahydrofurane–hexane at −15 ◦C to give an orange solid. M =
−1
=
palladium (5): yield 32%. IR (cm /KBr): m(C≡N): 2193, m(C O):
1698. 1H NMR (THF-d8): d1 8.18, d2 7.79 (AA‘XX’ spin system,
3
ꢀ
J1,2 + J1,2 = 8.6 Hz). Anal. calcd for C16H10PdI2N2O4: C, 29.34;
H, 1.52; N, 4.28. Found: C, 29.19; H, 1.54; N, 4.30. M = platinum
−1
1
=
(6): yield 23%. IR (cm /KBr): m(C≡N): 2186, m(C O): 1697. H
1
3
1718. H NMR (CDCl3): d1 8.09, d2 7.45 (C6H4, AAꢀXXꢀ spin
NMR (THF-d8): d1 8.18, d2 7.78 (AA‘XX’ spin system, J1,2
+
system, 3JAX + 5JAX = 8.5 Hz), 4.40 (q, OCH2, J = 7.1 Hz, 1.40
J1,2 = 8.6 Hz). Anal. calcd for C16H10PtI2N2O4: C, 25.86; H, 1.36;
5
ꢀ
ꢀ
(t, OCH2CH3, J = 7.1 Hz).
N, 3.77. Found: C, 25.60; H, 1.55; N, 3.56.
Improved method for the preparation of 4-isocyanobenzoic acid (1)
Preparation of hydrogen-bonded supramolecular complexes 1a–6a
To a solution of 4-isocyanoetylbenzoate (3 g, 17.13 mmol) in
500 mL ethanol was added NaOH (2.74 g, 68.50 mmol) dissolved
in 15 mL of water. After refluxing for 2 h, the solvent was removed
on a rotary evaporator. Water (100 mL) and ether (50 mL) were
added to the solid residue obtained and the stirred mixture was
treated with 3% hydrochloric acid until pH = 5. The organic
phase was collected and the water solution extracted again with
ether (3 × 25 mL). The ether extracts were dried over anhydrous
magnesium sulfate and filtrated. The solvent was removed on a
rotary evaporator to obtain the product as a cream solid, which
was dried under vacuum (70% yield). IR (cm−1/CH2Cl2): m(C≡N):
2128; m(CO): 1702. IR (cm−1/KBr): m(O-H): 2986; m(C≡N): 2128;
The supramolecular complexes were all prepared from pure
components. Exact stoichiometric molar amounts of the two
compounds were dissolved in dry tetrahydrofurane at ambient
temperature, and the solvent was eliminated under vacuum.
Experimental procedure for X-ray crystallography
Crystals of trans-[PdI2(CNC6H4COOH)2]·C4H8O2 (5) were ob-
tained by direct diffusion of hexane into a solution of the complex
in 1,4-dioxane. Crystallographic data (excluding structure factors)
for the structure reported in this paper have been deposited with
the Cambridge Crystallographic Centre and as supplementary ma-
terial: CCDC reference number 643465. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/b705478e.
1
m(CO): 1694. H NMR (THF-d8): d1 8.08, d2 7.54 (AA‘XX’ spin
system, 3J1,2 + 5J1,2 = 8.4 Hz); dOH 11.95 (broad singlet at 250 K).
ꢀ
Preparation of [AuCl(CNC6H4COOH)] (2)
Acknowledgements
To
a solution of [AuCl(tht)] (0.500 g, 1.560 mmole) in
70 ml of tetrahydrofurane was added [CNC6H4COOH] (0.27 g,
1.81 mmole). After stirring for 30 min the solvent was reduced to
15 mL under reduced pressure and hexane (10 mL) was added to
This work was sponsored by the D. G. I. (Project CTQ2005-
08729/BQU) and the Junta de Castilla
y Leo´n (Project
VA099A05). I. P. thanks the Universidad Arturo Prat for leave
of absence and for a grant.
obtain the product as a white solid. (61.87% yield). IR (cm−1/KBr):
1
=
m(C≡N): 2208; m(C O): 1696. H NMR (THF-d8): d1 8.16, d2 7.84
3
5
ꢀ
(AA‘XX’ spin system, J1,2 + J1,2 = 8.5 Hz). Anal. calcd for
C8H5AuClNO2: C, 25.32; H, 1.33; N, 3.69. Found: C, 25.37; H,
1.36; N, 3.63.
References
1 (a) L. Malatesta and F. Bonati, Isocyanide Complexes of Metals, John
Wiley, London, 1969; (b) D. Lentz, Angew. Chem., Int. Ed. Engl., 1994,
33, 1315.
2 M. Tamm and F. E. Hahn, Coord. Chem. Rev., 1999, 182, 175.
3 M. Tanabiki, K. Tsuchiya, Y. Kumanomido, K. Matsubara, Y. Mo-
toyama and H. Nagashima, Organometallics, 2004, 23, 3976.
4 Y. Ito, M. Sugimone and M. Murakami, J. Am. Chem. Soc., 1991, 56,
1948.
Preparation of cis-[MCl2(CNC6H4COOH)2]
To a solution of [MCl2(tht)2] (M = Pd, Pt) (0.21 mmol) in 20 mL
of tetrahydrofurane was added [CNC6H4COOH] (0.47 mmol).
The mixture was left stirring for 30 min at room temperature,
and then hexane (10 mL) was added to obtain the product as
5 Y. Sun, K. Ye, H. Zhang, J. Zhang, L. Zhao, B. Li, G. Yang, B. Yang,
Y. Wang, S.-W. Lai and C.-M. Che, Angew. Chem., Int. Ed., 2006, 45,
5610.
a yellow solid. M = palladium (3): yield 42%. IR (cm−1/KBr):
−1
=
6 (a) Metallomesogens, ed. J. L. Serrano, VCH, Weinheim, 1996; (b) B.
Donnio and D. W. Bruce, Struct. Bonding, 1999, 95, 193; (c) P. Espinet,
Gold Bull., 1999, 32, 127.
m(C≡N): 2214, m(C O): 1696; IR(cm /THF): m(C≡N): 2214,
2235 (sh). Anal. calcd for C16H10PdCl2N2O4: C, 40.75; H, 2.14;
N, 5.94. Found: C, 40.61; H, 3.01; N, 5.72. M = platinum (4):
7 C. Bartolome´, M. Carrasco-Rando, S. Coco, C. Cordovilla, P. Espinet
−1
=
yield 59%. IR (cm /KBr): m(C≡N): 2205, m(C O): 1696; IR
´
and J. Mart´ın-Alvarez, Organometallics, 2006, 25, 2700.
−1
=
8 D. McGuinness and K. J. Cavell, Organometallics, 2000, 19, 741.
9 W. A. Herrmann, Angew. Chem., Int. Ed., 2002, 41, 1290.
10 (a) R. A. Michelin, M. F. C. Guedes da Silva and A. J. L. Pombeiro,
Coord. Chem. Rev., 2001, 218, 75; (b) W. P. Fehlhammer and M. Fritz,
Chem. Rev., 1993, 93, 1243.
(cm /(THF): m(C≡N): 2204, 2235 (sh), m(C O): 1720. Anal.
calcd for C16H10PtCl2N2O4: C, 34.30; H, 1.80; N, 5.00. Found:
C, 34.54; H, 2.05; N, 4.82.
11 U. Plaia, H. Stolzenberger and W. P. Fehlhammer, J. Am. Chem. Soc.,
1985, 118, 235.
Preparation of trans-[MI2(CNC6H4COOH)2]
12 K. Bartel and W. P. Fehlhammer, Angew. Chem., Int. Ed. Engl., 1974,
13, 599.
13 G. Facchin, R. A. Michelin, M. Mozzon and A. Tassan, J. Organomet.
Chem., 2002, 662, 70.
KI (0.390 mmol) was added to [MCl2(CNC6H4COOH)2] (M = Pd,
Pt) (0.15 mmol) in 40 mL of acetone. The mixture was stirred for
3 h and the KCl formed was filtered. The solvent was removed on
This journal is
The Royal Society of Chemistry 2007
Dalton Trans., 2007, 3267–3272 | 3271
©

View Article Online
14 M. Basato, F. Benetollo, G. Facchin, R. A. Michelin, M. Mozzon, S.
Pugliese, P. Sgarbossa, S. M. Sbovata and A. Tassan, J. Organomet.
Chem., 2004, 689, 454.
P. Romero, J. L. Serrano and T. Sierra, J. Am. Chem. Soc., 2006, 128,
12403.
23 D. W. Bruce, in Inorganic Materials, ed. D. W. Bruce and D. O’Hare,
15 G. Facchin, P. Uguagliati and R. A. Michelin, Organometallics, 1984,
3, 1818.
Wiley, Chichester, 2nd edn, 1996, ch. 8.
24 R. Deschenaux, F. Monnet, E. Serrano, F. Turpin and A.-M. Levelut,
Helv. Chim. Acta, 1998, 81, 2072.
25 P. Massiot, M. Impero´r-Clerc, M. Veber and R. Deschenaux, Chem.
Mater., 2005, 17, 1946.
16 Z.-L. Lu, A. Mayr and K.-K. Cheung, Inorg. Chim. Acta, 1999, 284,
205.
17 A. Mayr and J. Guo, Inorg. Chem., 1999, 328, 921.
18 S. Wang, A. Mayr and K.-K. Cheung, J. Mater. Chem., 1998, 8, 1561.
19 D. Samuel, B. Weinraub and D. Ginsburg, J. Org. Chem., 1956, 21,
376.
26 R. Ziessel, G. Pickaert, F. Camerel, B. Donnio, D. Guillon, M. Cesario
and T. Prange´, J. Am. Chem. Soc., 2004, 12403.
27 I. Ugi, U. Fetzer, H. Knupfer and K. Offermann, Angew. Chem., Int.
Ed. Engl., 1965, 4, 472.
20 G. W. Gray, Molecular Structure and Liquid Crystals, Academic Press,
London, 1967, p. 161, and references therein.
28 (a) E. T. J. Nibbering and T. Elsaesser, Chem. Rev., 2004, 104, 1887;
(b) T. Steiner, Angew. Chem., Int. Ed., 2002, 41, 48.
29 S. Coco, F. D´ıez-Expo´sito, P. Espinet, C. Ferna´ndez-Mayordomo, J. M.
21 Handbook of Liquid Crystals, ed. D. Demus, J. Goodby, G. W. Gray,
H. W. Spiess and D. V. Vill, Wiley-VCH, Weinheim, 1998.
22 (a) T. Kato and J. M. J. Fre´chet, J. Am. Chem. Soc., 1989, 8533; (b) M.-J.
Brienne, J. Gabard, J.-M. Lehn and I. Stibor, J. Chem. Soc., Chem.
Commun., 1989, 1868; (c) K. Willis, D. J. Price, H. Adams, G. Ungar
and D. W. Bruce, J. Mater. Chem., 1995, 5, 2195; (d) C. M. Paleos and
D. Tsiourvas, Liq. Cryst., 2001, 28, 1127; (e) D. W. Bruce, Adv. Inorg.
Chem., 2001, 52, 151; (f) M. Grunet, R. A. Howie, A. Kaeding and C. T.
Imrie, J. Mater. Chem., 1997, 7, 211; (g) J.-F. Eckert, U. Maciejezuk,
D. Guillon and J.-F. Nierengarten, Chem. Commun., 2001, 14, 1278;
(h) F. Wu¨rthner, S. Yao, B. Heise and C. Tschierske, Chem. Commun.,
2001, 14, 2260; (i) N. Mizoshita, H. Monobe, M. Inoue, M. Ukon, T.
Watanabe, Y. Shimizu, K. Hanabusa and T. Kato, Chem. Commun.,
2002, 15, 428; (j) G. Pickaert, L. Douce, R. Ziessel and D. Guillon,
Chem. Commun., 2002, 15, 1584; (k) S. Jin, Y. Ma, S. C. Zimmerman
and S. Z. D. Cheng, Chem. Mater., 2004, 16, 2975; (l) T. Kajitana,
S. Kohmoto, M. Yamamoto and K. Kishikawa, Chem. Mater., 2004,
16, 2329; (m) J. A. McCubbin, X. Tong, Y. Zhao, V. Snieckus and
R. P. Lemieux, Chem. Mater., 2005, 17, 2574; (n) J. Barbera´, L. Puig,
´
Mart´ın-Alvarez and A. M. Levelut, Chem. Mater., 1998, 10, 3666.
30 R. Bayo´n, S. Coco and P. Espinet, Chem.–Eur. J., 2005, 11, 1079.
31 M. E. Squires and A. Mayr, Inorg. Chim. Acta, 1997, 264, 161.
32 R. Taylor and O. Kennard, Acc. Chem. Res., 1984, 17, 320.
33 D. W. Bruce, D. A. Dummur, E. Lalinde, P. M. Maitlis and P. Styring,
Liq. Cryst., 1988, 3, 385.
34 (a) D. Demus and L. Richter, in Textures of Liquid Crystals, VEB,
Leipzig, 2nd edn, 1980; (b) G. W. Gray and J. W. Goodby, Smectic
Liquid Crystals: Textures and Structures, Hill, Glasgow, London, 1984;
(c) I. Dierking, in Textures of Liquid Crystals, Wiley-VCH, Weinheim,
2003.
´
35 S. Coco, C. Cordovilla, P. Espinet, J. Mart´ın-Alvarez and P. Mun˜oz,
Inorg. Chem., 2006, 45, 10180.
36 R. Uso´n, A. Laguna and J. Vicente, J. Organomet. Chem., 1977, 131,
471.
37 R. Uso´n, J. Fornie´s, F. Mart´ınez and M. Tomas, J. Chem. Soc., Dalton
Trans., 1980, 888.
3272 | Dalton Trans., 2007, 3267–3272
This journal is
The Royal Society of Chemistry 2007
©