A novel series of heteropolynuclear metallomesogens: Organopalladium complexes with ferrocenophane-containing ligands

Article abstract of DOI:10.1002/ejic.200700750

Ferrocenophane-containing (Fcph) Schiff's bases p-C₁₂H ₂₅O-(C₆H₄)CH=N(C₆H₄)Fcph (L^AH) and p-C₁₂H₂₅O(C₆H ₄)COO-(C₆H₄)CH=N(C₆H ₄)Fcph (L^BH) react with palladium(II) acetate to form μ-acetato- and chloro-bridged dimeric organo-palladium complexes. By exchanging acetato-groups with the chloride anions, μ-chloro-bridged heteropolynuclear dimers are obtained that show thermotropic smectic A phases over a temperature range of 198 to 260°C. The complexes [PdClL ^A]₂ and [PdClL^B]₂ can be transformed into a variety of mixed-ligand Pd^II complexes by treatment with salicyl-aldimine p-C₁₂H₂₅O(C₆H ₄)COO(C₆H₃)(OH)CH=N(C₆H ₄)-Fcph (L^CH) and β-aminovinyl ketone p-C ₁₂H₂₅O(C₆H₄)-COCH=CHNH(C ₆H₄)Fcph (LDH). The obtained mixed-ligand heterometallic complexes [PdL^AL^C], [PdL^BL^C], [PdL^AL^D] and [PdL^BL^D] exhibit enantiotropic, thermotropic nematic phases over a broad temperature range from 71 to 205°C. The structures of the synthesized compounds were characterized by means of ¹H NMR, IR and UV spectroscopy, as well as elemental analysis. The liquid crystalline properties were studied by polarising optical microscopy and DSC. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200700750

FULL PAPER
DOI: 10.1002/ejic.200700750
A Novel Series of Heteropolynuclear Metallomesogens: Organopalladium
Complexes with Ferrocenophane-Containing Ligands
Oleg N. Kadkin,*[a] Jaein An,[a] Haksoo Han,[a] and Yuri G. Galyametdinov[b]
Keywords: Liquid crystals / Metallomesogens / Palladium / Ferrocene / Heterometallic complexes
Ferrocenophane-containing (Fcph) Schiff’s bases p-C12H25O-
(C6H4)CH=N(C6H4)Fcph (LAH) and p-C12H25O(C6H4)COO-
(C6H4)CH=N(C6H4)Fcph (LBH) react with palladium(II) ace-
tate to form µ-acetato- and chloro-bridged dimeric organo-
palladium complexes. By exchanging acetato-groups with
the chloride anions, µ-chloro-bridged heteropolynuclear di-
mers are obtained that show thermotropic smectic A phases
over a temperature range of 198 to 260 °C. The complexes
[PdClLA]2 and [PdClLB]2 can be transformed into a variety of
mixed-ligand PdII complexes by treatment with salicyl-
Fcph (LCH) and β-aminovinyl ketone p-C12H25O(C6H4)-
COCH=CHNH(C6H4)Fcph (LDH). The obtained mixed-li-
gand heterometallic complexes [PdLALC], [PdLBLC],
[PdLALD] and [PdLBLD] exhibit enantiotropic, thermotropic
nematic phases over a broad temperature range from 71 to
205 °C. The structures of the synthesized compounds were
characterized by means of 1H NMR, IR and UV spectroscopy,
as well as elemental analysis. The liquid crystalline proper-
ties were studied by polarising optical microscopy and DSC.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
aldimine
p-C12H25O(C6H4)COO(C6H3)(OH)CH=N(C6H4)-
With regard to heterometallic liquid crystalline systems
based on ferrocene-containing ligands the organopalladium
complexes showed rather low transition temperatures and
broad mesophases.[2d] Generally, cyclopalladated com-
pounds are one of the most fruitful and widely explored
areas of metallomesogens. Several research groups have suc-
cessfully employed azines,[5] azomethines[6] and pyrimid-
ines[7] in the preparation of liquid crystalline palladium(II)
complexes. The most remarkable examples of the com-
pounds discovered in this range are miscellaneous orthopal-
ladated mesogens with ferroelectric properties,[8] which were
pioneered by Espinet et al.[8a]
High transition temperatures and, frequently, instability
of the majority of the known metallomesogens interfere
with the demands of liquid crystalline technological appli-
cations. Organopalladium mesogens possess some unam-
biguous benefits from this point of view. Structural diver-
sity and the possibility of symmetry perturbations in organ-
opalladium complexes provide an additional powerful in-
strument for the controlled adjustments in their mesomor-
phic behaviour. The various mixed-bridged dinuclear and
mixed-ligand mononuclear palladium(II) coordination
compounds have exhibited the broad and relatively low-
temperature mesophases.[2d,5d,5f,6e,6g,6i,6j,8b,8d]
Introduction
Extensive research on metal-containing liquid crystals or
metallomesogens has led to the discovery of many interest-
ing kinds of liquid crystalline organometallic and coordina-
tion compounds.[1] The introduction of metal centres can
bring valuable physical properties to liquid crystalline mate-
rials (colour, polarisability, magnetism, nonlinear optical
behaviour, electric properties, etc.) and can potentially ex-
pand technological applications of liquid crystals. Metall-
omesogens with multiple metal centres are of special inter-
est because of the potential advantageous physicochemical
properties arising from a combination of dissimilar metals
in one molecule and interactions between the metal centres.
This consideration inspired us to pursue our research efforts
on the syntheses and investigation of heterometallic liquid
crystalline complexes.[2] Recently, heterometallic liquid crys-
talline complexes with rare earth elements and transition
metals have been synthesized by Binnemans et al.[3] Inter-
esting examples of ferrocenyl liquid crystals containing a
thiourea coordination core, which is suitable for obtaining
heterometallic mesogenic systems, were reported by
Seshadri et al.[4]
[a] Department of Chemistry, Yonsei University,
134 Shinchon-Dong, Seodaemoon-Gu, Seoul 120-749, South
Korea
The first liquid crystalline ferrocenophane derivatives by
Friedrichsen et al. exhibited broader mesophases as com-
pared with their unbridged counterparts.[9] Hence, we de-
cided to use ferrocenophane-containing ligand systems
for the syntheses of liquid crystalline heteropolynuclear or-
ganopalladates. Earlier we described the syntheses and
phase behaviour of some liquid crystalline [3]ferroceno-
Fax: +82-2-364-7050
E-mail: onk@yonsei.ac.kr
okadkin@hotmail.com
[b] Department of Physical and Colloid Chemistry, Kazan State
Technological University,
68 K. Marx St, 420015 Kazan, Russia
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
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A Novel Series of Heteropolynuclear Metallomesogens
phane-containing Schiff’s bases and β-enamino ketone, bridged dimers 1a and 1b. The acetato bridges were substi-
which represent superior organometallic ligands for ob- tuted with chloride anions by an exchange reaction, with
taining heteropolynuclear liquid crystalline systems.[10] Fur- a solution of HCl in methanol, yielding µ-chloro-bridged
ther utilization of the prepared ferrocenomesogens in cyclo- dimeric complexes 2a and 2b. The treatment of the latter
palladation and ligand exchange reactions gave rise to a compounds with ligands L3H and L4H in dichloromethane
novel series of heteropolynuclear metallomesogens: synthe- in the presence of anhydrous potassium carbonate led
ses, spectroscopic data and liquid crystalline properties of to the range of mixed-ligand complexes 3a, 3b, 4a and
some acetato- and chloro-bridged cyclopalladated dimers, 4b.
as well as several mixed-ligand palladium(II) complexes,
UV spectra of all the synthesized compounds 1–4 are
which contain a ferrocenophane unit, are reported in this represented by two absorption bands with maximums in the
article.
regions 320–330 and 390–400 nm, which are related to
metal-to-ligand charge-transfer n–π* electronic transitions
(see Table 1). The µ-acetato-bridged complexes 1a and 1b
show an additional absorption with a maximum at 342 nm,
which most likely arises from the n–π* charge-transfer tran-
Results and Discussion
Syntheses and Spectral Properties
The chemical structures of ferrocenophane-containing li- sitions between the palladium(II) ion and the ligands. In-
gands used in this work and the synthetic paths to the PdII tensive absorption in the region 260–280 nm, which is seen
complexes created with these ligands are illustrated in in all of the complexes 1–4, has been ascribed to spin-al-
Scheme 1. The syntheses of ligands L1H, L2H, L3H and lowed π–π* electronic transitions in the surrounding li-
L4H have been reported recently.[10] The cyclopalladation gands. In the UV spectra the ferrocene group in compounds
reaction with ligands L1H and L2H, which is carried out 1–4 shows characteristic nonintensive absorption bands at
using Pd(OAc)2 in glacial acetic acid as described earlier for 430–450 nm attributed to d–d transitions of the iron
some other azomethine ligands,[6a,6g,8d] afforded µ-acetato- atom.[11]
Scheme 1. Chemical structures of ferrocenophane-containing ligands and synthetic paths to the palladium(II) complexes.
Eur. J. Inorg. Chem. 2008, 1682–1688
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O. N. Kadkin, J. An, H. Han, Yu. G. Galyametdinov
FULL PAPER
Table 1. UV/Vis spectra of organopalladium complexes 1–4.
vibrations of the Pd–O, Pd–C and Pd–N bonds appear in
the region 510–760 cm–1 in all of the complexes 1–4.
λmax [nm] (log ε [Lcm–1 –1])
The roof-shaped structure of the µ-acetato-bridged com-
plex 1a can be concluded from its 1H NMR spectrum, since
the two distinct multiplets at δ = 3.52 and 3.72 ppm for
two diastereotopic CH2O protons of the alkoxy chains were
observed (see Figure 1). The stereochemistry of the µ-acet-
ato-bridged ortho-palladated azomethine complexes, in
terms of their folded structure, has already been described
earlier in detail and with convincing proofs.[6c] In contrast
to the latter compounds, PdII complexes 1a and 1b have
additional elements of asymmetry connected with the
planar chirality of their ferrocenophane fragments. Never-
theless, the possible diastereomeric pairs caused by the pres-
[b]
1a 276 (4.688)
–
342 (4.497) 400 (4.321)
460[a] (4.054)
474[a] (4.173)
466 (4.018)
1b 269 (5.071) 330 (4.714) 342 (4.680) 400 (4.367)
2a 272 (4.779) 334 (4.605)
2b 263 (4.872) 327 (4.486)
3a 267 (5.024) 321 (4.619)
3b 267 (5.057) 320 (4.600)
–
–
–
–
–
–
382 (4.359)
382[a] (4.076) 475 (3.775)
[b]
401 (4.453)
400 (4.358)
396 (4.475)
391 (4.493)
–
[b]
–
[b]
4a 281 (4.654) 321 (4.407)
–
[b]
[b]
4b 279 (4.845)
–
–
[a] Shoulder. [b] The band is evidently not revealed.
Characteristic absorptions in the IR spectra of complexes
1–4 are represented by stretching vibrations of the CH=N
group of the ligands in the region of about 1605 cm–1. The
low frequency shift of the CH=N stretch, in comparison
with the free ligands,[10] is consistent with N-coordination
1
ence of several stereogenic units are not exposed in the H
NMR spectrum of 1a.
Dramatic changes occurred in the1H NMR spectrum of
of palladium(II) ions to the azomethine ligand. Fur- 1b as compared with a spectrum of 1a (see the details in
themore, additional absorption peaks from the stretching the Supporting Information). For complex 1b there are four
Figure 1. One of the possible enanthiomeric pairs in a roof-shaped structure of µ-acetato-bridged complexes 1a and 1b, which are
conditionally designated here as LDL | DLD.
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A Novel Series of Heteropolynuclear Metallomesogens
distinct NMR signals of the methyl groups in the acetato of compounds 2a and 2b. The observed transition tempera-
bridges, four distinct signals of the azomethine groups and tures for the µ-chloro-bridged dimer 2a, with two benzene
four pairs of doublets for the aromatic AB system of a ter- rings in a ferrocenophane-containing ligand rigid core, are
minal 4-(dodecyloxy)benzoyl substituent. The appearance comparable with those for analogous µ-chloro-bridged or-
1
of the H NMR signals described above is in accordance ganopalladium complexes with convenient organic azome-
with four possible diastereomeric pairs (2n/2, where n = the thines.[6d,6e,6g] The thermal behaviour of the µ-chloro-
number of elements of chirality in a molecule) in 1b. Con- bridged complexes 2a and 2b is consistent with their planar
trary to 1a, the influence of planar chirality of ferroceno- structure, when effective low-energy molecular packing can
phane substituents comes into effect in addition to the assy- be realized in the solid state. In addition the presence of
1
metry of a roof-shaped structure in the H NMR spectrum chloride ions contributes to further stabilization of the solid
of 1b. Adding a bulky and polar phenyl carboxylic group state by orthogonal interactions with palladium atoms of
significantly increases the overall asymmetry of a roof- neighbouring molecules. Presumably the latter interactions
shaped molecule, since the ferrocenophane-containing azo- also play a significant role in the packing of the µ-chloro-
methine ligands obtain a more elongated structure. At the bridged dimer into smectic layers causing their smectic A
same time diastereotopic protons of the alkoxy chains (Ha mesomorphism. The ferrocenophane fragment undoubtedly
and Hb, see Figure 1) become more distant from the ele- has the effect of lowering the phase transition temperatures
ments of asymmetry so no splitting of the NMR signals for as could be seen for compounds 1a and 1b, which were
these protons was observed in 1b.
compared with the analogous complexes containing the un-
According to their 1H NMR spectra the µ-chloro- bridged ferrocene.[2d]
bridged palladium(II) complexes 2a and 2b have a planar
structure with increased symmetry. There are no signal
splittings for the methylene protons in the alkoxy chains of
compound 2a as compared with 1a, and no such complex
1H NMR patterns in 2b as we observed in 1b.
Table 2. Thermooptical and thermodynamic data of phase transi-
tions in palladium(II) complexes 1–4. The dots symbolize tempera-
ture areas which are beyond phase-transition points.
Crystal T (∆H)
Mesophase T (∆H)
[°C] ([kJ/mol])
Isotropic
liquid
[°C] ([kJ/mol]) type
Two different chelates in mixed-ligand complexes from
1
series 3 and 4 show a separate set of H NMR signals for
1a
1b
2a
2b
3a
3b
4a
4b
•
•
•
•
•
•
•
•
–
–
–
–
174 (40.0)
•
•
•
•
•
•
•
•
205 (25.9)
each ligand, which is in full agreement with the proposed
structures. It is remarkable that in the case of complex 3b
the two ligands have only minimal differences. The palla-
dium atom in one of the ligands is attached to an aromatic
ring by a direct covalent bond with a carbon atom, and
there is an oxygen atom between the palladium atom and a
benzene ring in another ligand. Despite this distinction be-
ing rather small, two separate ligands are revealed in the 1H
NMR spectrum of compound 3b.
198 (47.5)
• SmA[a]
• SmA
• N[e]
• N
230 (–423.0[b]
)
255[c]
239[d] (–1395)
148 (2.2)
205 (0.9)
148[f]
71 (9.6)
74 (11.1)
140 (32.0)
148 (16.0)
• N
• N
201 (2.1)
[a] Liquid crystalline phase of a smectic A type. [b] An exothermic
peak revealed on the DSC curve from the decomposition of the
compound. [c] Smectic A mesophase was observed with a polarisa-
tion optical microscope on the background of a decomposition
process. [d] A complex exothermic peak on the DSC curve between
235 and 260 °C with a maximum at 239 °C. [e] Liquid crystalline
phase of a nematic type. [f] The DSC peak of the isotropic transi-
tion is masked by the crystal–nematic transition peak.
Liquid Crystalline Properties
Complexes 1a and 1b did not exhibit mesomorphism,
which is in agreement with the fact that liquid crystalline
All the compounds in both series 3 and 4 of the mixed-
µ-acetato-bridged cyclopalladated complexes with azome- ligand palladium(II) complexes showed an enantiotropic
thine ligands are thus far unknown. However, azine ligands nematic phase. Marbled and nematic schlieren optical tex-
do form mesogenic µ-acetato-bridged organopalladium di- tures were observed under a microscope between crossed
mers.[5c,5d] When the acetate anions were replaced by chlo- polarizers. It is remarkable, that mesophase transition tem-
ride ions the smectic A phase was observed in both com- peratures in this case were relatively low whereas most of
pounds 2a and 2b. The mesophase was identified by charac- the other known heteronuclear systems with ferrocene-con-
teristic focal-conic optical textures observed under a micro- taining ligands show high temperatures of the phase transi-
scope between crossed polarisers. The phase transition tem- tions.[2] Two factors undoubtedly play a significant role in
peratures were rather high in both compounds (see Table 2), lowering mesophase transition temperatures in the palladi-
especially in the case of the µ-chloro-bridged dimer 2b with um(II) complexes 3 and 4: (1) the presence of an alkylene
three benzene rings in a ligand rigid core, which is addition- bridge at the end of the ferrocenophane fragment of li-
ally extended by a cyclopentadienyl ring of a ferroceno- gands; (2) and lowering of symmetry in the coordinational
phane fragment. In the latter case the mesophase was ob- surroundings of the palladium atom. The significance of the
served by placing a sample of the compound on a heating latter is particularly noticeable when taking into account
plate right before the mesophase transition to avoid longer that the nematic transition temperature in compound 3b,
exposure to high temperatures. The transition to the iso- with minimal symmetry disturbance, is more than 100 °C
tropic liquid state was accompanied by the decomposition lower than could be expected in comparison with the sym-
Eur. J. Inorg. Chem. 2008, 1682–1688
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O. N. Kadkin, J. An, H. Han, Yu. G. Galyametdinov
FULL PAPER
(m, 1 H, C5H3Fe), 4.18 (m, 2 H, C5H4Fe), 4.49 (m, 2 H, C5H4Fe),
6.03 (m, 1 H, C6H3Pd), 6.58 (m, 1 H, C6H3Pd), 6.66 (m, 2 H,
C6H4), 7.13 (m, 1 H, C6H3Pd), 7.18 (m, 2 H, C6H4), 7.52 (s, 1 H,
metric square-planar palladium chelates with a very similar
shape and structural elements.[2c]
It is interesting to note that crystal-to-nematic transition
temperatures, when 3a is compared with 3b, and 4a with 4b,
have only small distinctions. At the same time their clearing
points are substantially different (see Table 2). These com-
plexes are differerent from each other by the length of a
rigid core in only one of the ferrocenophane-containing
azomethine ligands. Thus, greater anisotropy of polarizab-
ilty when adding a phenylenecarboxyl unit into one of the
azomethine ligands in complexes 3b and 4b causes a signifi-
CH=N) ppm. IR (KBr): ν = 2922 (C–H), 2850 (C–H), 1605 (C=N),
˜
1569, 1534, 1410, 1263, 1224, 1202, 1032, 840, 810, 685, 611,
513 cm–1. C80H98Fe2N2O6Pd2 (1508.18): calcd. C 63.71, H 6.55, N
1.86; found C 63.56, H 6.58, N 1.82.
Complex 1b: Organopalladium complex 1b was obtained in the
same manner as complex 1a from Schiff’s base L2H (0.6734 g,
0.95 mmol) and palladium(II) acetate (0.2132 g, 0.95 mmol) in gla-
cial acetic acid (20 mL). Yield 0.6677 g (80%) of brown powder.
1H NMR (main product is the trans isomer; minor amount of cis
cant increase in the thermal stability of the nematic phase. isomer occurs) (300 MHz, CDCl3, 25 °C): δ = 0.89 (t, 6 H, CH3),
1.25–1.30 (m, 36 H, CH2), 1.45–1.65 (m, 4 H, CH2), 1.74 (s, 3 H,
CH3COO), 1.76 (s, 3 H, CH3COO), 1.80–2.00 (m, 12 H, C3H6
bridge), 3.28 (m, 2 H, C5H3Fe), 3.80 (m, 4 H, C5H4Fe), 4.02 (m, 4
H, CH2O), 4.09 (m, 6 H, overlapped signals of C5H3Fe and
C5H4Fe), 4.25 (m, 2 H, C5H3Fe), 6.03 (m, 1 H, C6H3Pd), 6.49 (d,
1 H, C6H3Pd), 6.90 (m, 4 H, C6H4), 7.00–7.10 (m, 6 H, overlapped
signals of C6H4 and C6H3Pd), 7.10–7.20 (m, 4 H, C6H4), 7.28 (m,
2 H, C6H3Pd), 7.69 (s, 1 H, CH=N), 7.68 (s, 1 H, CH=N), 8.28
The combination of the relatively low melting point with
the higher clearing point in compound 3b leads to a broad
mesophase of 130 °C by width, which is outstanding for
heteropolynuclear metallomesogens considering the pres-
ence of bulky ferrocene fragments in the molecule of the
complex.
(m, 4 H, C H ) ppm. IR (KBr): ν = 2922 (C–H), 2850 (C–H), 1728
˜
6
4
Conclusions
(C=O), 1605 (C=N), 1567, 1509, 1413, 1256, 1233, 1162, 1067, 842,
763, 690, 648, 582, 511 cm–1. C94H106Fe2N2O10Pd2 (1748.40): calcd.
C 64.57, H 6.11, N 1.60; found C 64.81, H 6.08, N 1.56.
A new series of mesogenic heteropolynuclear organopal-
ladium complexes has been synthesized using ferroceno-
phane-containing Schiff’s bases and β-aminovinyl ketone as
ligands. Smectic A and nematic mesophases were observed
in the obtained compounds. It was demonstrated that using
heteroannularly bridged ferrocene, and introducing sym-
metry disturbances into the palladium(II) coordinational
surroundings, enables heteropolynuclear metallomesogens
with enhanced liquid crystalline properties to be obtained.
Complex 2a: A solution (1.3 ) of HCl in MeOH (0.35 mL,
0.45 mmol) was added dropwise to a stirred solution of the µ-acet-
ato-bridged dimer 1a (0.6054 g, 0.40 mmol) in CH2Cl2 (15 mL).
The reaction mixture was stirred for 12 h at room temperature and
then carefully evaporated with a rotary vacuum evaporator from
the solvents and small amounts of acetic acid generated from the
reaction. The obtained residue was eluted by CH2Cl2 through a
silica gel column. The eluate was concentrated and the µ-chloro-
bridged complex 2a was precipitated from a dichloromethane solu-
tion by adding ethanol, and then underwent further removal of the
1
more volatile CH2Cl2. Yield 0.4210 g (75%) of orange powder. H
Experimental Section
NMR (300 MHz, CDCl3, 25 °C): δ = 0.89 (t, 3 H, CH3), 1.23–1.28,
(m, 18 H, CH2), 1.60–1.65 (m, 2 H, CH2), 1.85–2.10 (m, 6 H, C3H6
bridge), 3.43 (m, 1 H, C5H3Fe), 3.89 (m, 3 H, overlapped signals
of CH2O and C5H3Fe), 4.14 (m, 1 H, C5H3Fe), 4.23 (m, 2 H,
C5H4Fe), 4.51 (m, 2 H, C5H4Fe), 6.54 (m, 1 H, C6H3Pd), 6.80 (m,
1 H, C6H3Pd), 7.13–7.25 (m, 3 H, overlapped signals of C6H4 and
C6H3Pd), 7.39 (m, 2 H, C6H4), 7.82 (s, 1 H, CH=N) ppm. IR
Materials and Instrumental Methods: Melting points were deter-
mined by the capillary method where applicable. Liquid crystalline
properties were studied using the polarising optical microscope
“Olympus BH-2” equipped with a heating stage HS1 (INSTEC)
and remote temperature controller RTC1 (INSTEC). DSC analyses
of the phase transitions were performed on the differential scanning
calorimeter (TA instruments Q-10) at the scanning rate 5 °C/min.
The temperatures of the phase transitions are given on the base of
the DSC curves. IR spectra were recorded using a Perkin–Elmer
Paragon 1000 instrument. UV and visible spectra in the region of
250–600 nm were recorded with the Lambda-14 (Perkin–Elmer)
spectrophotometer in CH2Cl2. 1H NMR spectra were measured
with the ARX 300 (Bruker) spectrometer with TMS as internal
standard. Dried and distilled solvents were used in all cases. Cyclo-
palladated complexes were synthesized by adapting the procedures
developed by Baena et al. for azomethine ligands.[8d]
(KBr): ν = 2920 (C–H), 2849 (C–H), 1605 (C=N), 1579, 1540,
˜
1451, 1310, 1263, 1202, 1025, 840, 796, 585, 511 cm–1.
C76H92Cl2Fe2N2O2Pd2 (1461.00): calcd. C 62.48, H 6.35, N 1.92;
found C 62.55, H 6.31, N 1.89.
Complex 2b: The µ-chloro-bridged complex 2b was prepared in the
same manner as complex 2a from complex 1b (0.51 g, 0.29 mmol).
Yield 0.3097 g (62%) of orange powder. 1H NMR (300 MHz,
CDCl3, 25 °C): δ = 0.90 (t, 3 H, CH3), 1.25–1.35 (m, 16 H, CH2),
1.40–1.52 (m, 2 H, CH2), 1.81 (m, 2 H, CH2CH2O), 1.96 (m, 6 H,
C3H6 bridge), 3.36 (m, 1 H, C5H3Fe), 3.77 (m, 1 H, C5H3Fe), 3.98
(m, 2 H, CH2O), 4.08 (m, 3 H, overlapped signals of C5H3Fe and
C5H4Fe), 4.44 (m, 2 H, C5H4Fe), 6.83 (d, 2 H, C6H4), 6.96 (m, 1
H, C6H3Pd), 7.09 (m, 1 H, C6H3Pd), 7.25 (m, 2 H, C6H4), 7.33 (m,
1 H, C6H3Pd), 7.39 (d, 2 H, C6H4), 7.95 (s, 1 H, CH=N), 7.98 (m,
Complex 1a: Schiff’s base L1H (0.7067 g, 1.20 mmol) and palladi-
um(II) acetate (0.2690 g, 1.20 mmol) in glacial acetic acid (15 mL)
were stirred at 55 °C for 24 h. The precipitate of organopalladium
complex 1a was filtered, washed several times with cold acetone
and dried. Yield 0.7296 g (81%) of brown powder. 1H NMR (main
product is the trans isomer; minor amount of cis isomer occurs)
(300 MHz, CDCl3, 25 °C): δ = 0.89 (t, 3 H, CH3), 1.25–1.30, (m,
16 H, CH2), 1.55–1.75 (m, 4 H, CH2), 1.85 (s, 3 H, CH3COO),
1.90–2.10 (m, 6 H, C3H6 bridge), 3.36 (m, 1 H, C5H3Fe), 3.52 (m,
2 H, C H ) ppm. IR (KBr): ν = 2920 (C–H), 2850 (C–H), 1729
˜
6
4
(C=O), 1606 (C=N), 1508, 1466, 1263, 1237, 1162, 1061, 839, 760,
580, 516 cm–1. C90H100Cl2Fe2N2O6Pd2 (1701.21): calcd. C 63.54, H
5.92, N 1.65; found C 63.78, H 5.87, N 1.59.
Complex 3a: Complex 2a (0.0773 g, 0.053 mmol), Schiff’s base L3H
1 H, CH2O), 3.72 (m, 1 H, CH2O), 3.89 (m, 1 H, C5H3Fe), 4.13 (0.0768 g, 0.106 mmol) and potassium carbonate (≈0.2 g) were
1686 Eur. J. Inorg. Chem. 2008, 1682–1688
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A Novel Series of Heteropolynuclear Metallomesogens
stirred at room temperature for 24 h in dichloromethane (10 mL).
The resulting mixture was filtered through Celite and the filtrate
was concentrated with a rotary evaporator. The product was pre-
cipitated by adding ethanol to a concentrated solution, and dichlo-
romethane was removed. Yield 0.1423 g (94.71%) of orange pow-
7.05 Hz, 1 H, CH=CH), 6.42 [dd, JH,H (1) = 2.37 Hz, JH,H (2) =
8.35 Hz, 1 H, C6H3Pd], 6.69 (d, JH,H = 9.01 Hz, 2 H, C6H4), 7.18
(d, JH,H = 8.35 Hz, 1 H, C6H3Pd), 7.28 (d, JH,H = 9.01 Hz, 2 H,
C6H4), 7.29 (d, JH,H = 8.63 Hz, 2 H, C6H4), 7.33 (d, JH,H
=
8.69 Hz, 2 H, C6H4), 7.36 (d, JH,H = 8.69 Hz, 2 H, C6H4), 7.46 (d,
JH,H = 7.05 Hz, 1 H, CH=CH), 7.47 (d, JH,H = 8.63 Hz, 2 H,
1
der. H NMR (300 MHz, CDCl3, 25 °C): δ = 0.89 (t, 3 H, CH3),
0.89 (t, 3 H, CH3), 1.23–1.33, 1.33–1.56 (m, 36 H, CH2), 1.75–2.10
(m, 16 H, overlapped signals of C3H6 bridge and CH2CH2O), 3.32
C H ), 8.01 (s, 1 H, CH=N) ppm. IR (KBr): ν = 2922 (C–H), 2850
˜
6 4
(C–H), 1603 (C=N), 1578, 1559, 1542, 1519, 1492, 1466, 1438,
(m, 2 H, CH2O), 3.39 (m, 1 H, C5H3Fe), 3.48 (m, 1 H, C5H3Fe), 1402, 1345, 1247, 1194, 1171, 840, 810, 764, 514 cm–1. C78H94Fe2N-
3.84 (m, 1 H, C5H3Fe), 3.90 (m, 1 H, C5H3Fe), 4.02 (t, 2 H, CH2O),
2O3Pd (1325.71): calcd. C 70.67, H 7.15, N 2.11; found C 70.74, H
4.11 (m, 1 H, C5H3Fe), 4.14 (m, 1 H, C5H3Fe), 4.17 (m, 2 H, 7.19, N 2.09.
C5H4Fe), 4.21 (m, 2 H, C5H4Fe), 4.47 (m, 2 H, C5H4Fe), 4.54 (m,
Complex 4b: The reaction of µ-chloro-bridged complex 2b
2 H, C5H4Fe), 5.49 (d, JH,H = 2.36 Hz, 1 H, C6H3Pd), 6.41 (m, 3
H, overlapped signals of C6H3OPd and C6H3Pd), 6.91 (d, JH,H
9.00 Hz, 2 H, C6H4), 7.18 (d, JH,H = 8.37 Hz, 1 H, C6H3Pd), 7.23
(m, 1 H, C6H3OPd), 7.28 (d, JH,H = 8.65 Hz, 2 H, C6H4), 7.39 (d,
JH,H = 8.66 Hz, 2 H, C6H4), 7.48 (2 overlapped d, JH,H = 8.66 Hz,
JH,H = 8.65 Hz, 4 H, C6H4), 7.97 (s, 1 H, CH=N), 8.05 (s, 1 H,
(0.1200 g, 0.070 mmol) and β-aminovinyl ketone L4H (0.0890 g,
0.141 mmol), carried out in the same manner as that for complex
4a, afforded the mixed-ligand complex 4b. Yield 0.1775 g (87%) of
light-orange powder. 1H NMR (300 MHz, CDCl3, 25 °C): δ = 0.89
(2 overlapped t, 6 H, CH3), 1.25–1.36 (m, 34 H, CH2), 1.70–1.78
(m, 2 H, CH2CH2O), 1.78–1.87 (m, 2 H, CH2CH2O), 1.88–2.12 (m,
12 H, C3H6 bridge), 3.37 (m, 1 H, C5H3Fe), 3.49 (m, 1 H, C5H3Fe),
3.84 (m, 1 H, C5H3Fe), 3.88 (t, 2 H, CH2O), 3.94 (m, 1 H, C5H3Fe),
4.00 (t, 2 H, CH2O), 4.01 (m, 1 H, C5H3Fe), 4.14 (m, 2 H, C5H4Fe),
4.18 (m, 1 H, C5H4Fe), 4.28 (m, 2 H, C5H4Fe), 4.32 (m, 1 H,
C5H4Fe), 4.36 (m, 1 H, C5H4Fe), 4.56 (m, 2 H, C5H4Fe), 5.45 (d,
JH,H = 2.18 Hz, 1 H, C6H3Pd), 5.70 (d, JH,H = 6.98 Hz, 1 H,
=
CH=N), 8.10 (d, JH,H = 9.00 Hz, 2 H, C H ) ppm. IR (KBr): ν =
˜
6
4
2920 (C–H), 2849 (C–H), 1731 (C=O), 1605 (C=N), 1577, 1517,
1433, 1312, 1251, 1199, 1166, 1149, 1118, 1059, 982, 840, 809, 764,
611, 512 cm–1. C83H96Fe2N2O5Pd (1419.78): calcd. C 70.21, H 6.81,
N 1.97; found C 69.95, H 6.76, N 2.01.
Complex 3b: Complex 3b was prepared in the same manner as com-
plex 3a from the µ-chloro-bridged complex 2b (0.0307 g,
0.018 mmol) and Schiff’s base L3H (0.0262 g, 0.036 mmol). Yield
0.0495 g (89%) of orange powder. 1H NMR (300 MHz, CDCl3,
25 °C): δ = 0.89 (2 overlapped t, 6 H, CH3), 1.25–1.43 (m, 32 H,
CH2), 1.43–1.54 (m, 4 H, CH2), 1.78–1.87 (m, 4 H, CH2CH2O),
1.91–2.08 (m, 12 H, C3H6 bridge), 3.37 (m, 1 H, C5H3Fe), 3.48 (m,
1 H, C5H3Fe), 3.83 (m, 1 H, C5H3Fe), 3.86 (m, 1 H, C5H3Fe), 4.01
(2 overlapped t, 4 H, CH2O), 4.05 (m, 1 H, C5H3Fe), 4.12 (m, 1
H, C5H3Fe), 4.14 (m, 1 H, C5H4Fe), 4.15 (m, 1 H, C5H4Fe), 4.17
(m, 2 H, C5H4Fe), 4.34 (m, 1 H, C5H4Fe), 4.38 (m, 1 H, C5H4Fe),
4.56 (m, 2 H, C5H4Fe), 5.43 (d, JH,H = 2.19 Hz, 1 H, C6H3Pd),
6.39 (d, JH,H = 2.30 Hz, 1 H, C6H3OPd), 6.42 [dd, JH,H (1) =
CH=CH), 6.69 (d, JH,H = 8.99 Hz, 2 H, C6H4), 6.77 (d, JH,H
=
9.01 Hz, 2 H, C6H4), 6.83 [dd, JH,H (1) = 2.18 Hz, JH,H (2) =
8.11 Hz, 1 H, C6H3Pd], 7.28–7.32 (overlapped m, 8 H, C6H4), 7.32
(d, JH,H = 8.11 Hz, 1 H, C6H3Pd), 7.29 (d, JH,H = 8.63 Hz, 2 H,
C6H4), 7.33 (d, JH,H = 8.69 Hz, 2 H, C6H4), 7.36 (d, JH,H
=
8.69 Hz, 2 H, C6H4), 7.45 (d, JH,H = 6.98 Hz, 1 H, CH=CH), 7.49
(d, JH,H = 8.63 Hz, 2 H, C6H4), 7.80 (d, JH,H = 9.01 Hz, 2 H,
C H ), 8.13 (s, 1 H, CH=N) ppm. IR (KBr): ν = 2922 (C–H), 2850
˜
6
4
(C–H), 1733 (C=O), 1604 (C=N), 1586, 1559, 1517, 1492, 1466,
1436, 1401, 1345, 1247, 1163, 1069, 841, 812, 763, 514 cm–1.
C85H98Fe2N2O5Pd (1445.82): calcd. C 70.61, H 6.83, N 1.94; found
C 70.83, H 6.77, N 1.92.
8.72 Hz, JH,H (2) = 2.30 Hz, 1 H, C6H3OPd], 6.79 (d, JH,H
=
Supporting Information (see also the footnote on the first page of
this article): DSC curves of compounds 1–4 are shown in Fig-
ures S1–S8. Examples of liquid crystalline textures observed under
a polarization microscope are represented by Figures S9 and S11.
1H NMR patterns of 1–4 are shown in Figures S12–S18. Explana-
tions are given for the appearance of H NMR signals for the dia-
stereotopic protons in 1a, and for the signals of four different dia-
stereomeric pairs in 1b.
8.97 Hz, 2 H, C6H4), 6.81 [dd, JH,H (1) = 8.05 Hz, JH,H (2) =
2.19 Hz, 1 H, C6H3Pd] 6.91 (d, JH,H = 9.02 Hz, 2 H, C6H4), 7.23
(d, JH,H = 8.72 Hz, 1 H, C6H3OPd), 7.29 (d, JH,H = 8.62 Hz, 2 H,
C6H4), 7.31 (d, JH,H = 8.05 Hz, 1 H, C6H3Pd), 7.35 (q of AB sys-
tem, JH,H = 8.95 Hz, 4 H, C6H4), 7.49 (d, JH,H = 8.62 Hz, 2 H,
C6H4), 7.80 (d, JH,H = 8.93 Hz, 2 H, C6H4), 8.04 (s, 1 H, CH=N),
8.09 (s, 1 H, CH=N), 8.09 (d, JH,H = 8.95 Hz, 2 H, C6H4) ppm. IR
1
(KBr): ν = 2921 (C–H), 2850 (C–H), 1731 (C=O), 1605 (C=N),
˜
1577, 1548, 1517, 1467, 1437, 1314, 1250, 1164, 1122, 1063, 1008,
983, 895, 842, 811, 762, 692, 632, 562, 513 cm–1. C90H100Fe2N2-
O7Pd (1539.89): calcd. C 70.20, H 6.55, N 1.82; found C 70.43, H
6.52, N 1.80.
Acknowledgments
O. N. K. gratefully acknowledges the Deutscher Akademischer
Austauschdienst (DAAD) for a stipend. Special thanks go to Prof.
Dr. Willy Friedrichsen for encouraging this work. Financial sup-
port from BK-21 (Brain Korea) is also gratefully acknowledged.
Complex 4a: µ-Chloro-bridged complex 2a (0.0662 g, 0.045 mmol)
and β-aminovinyl ketone L4H (0.0572 g, 0.091 mmol) in CH2Cl2
(15 mL) were stirred for 24 h at room temperature in the presence
of potassium carbonate (≈0.2 g). The resulting mixture was treated
as described in the previous syntheses. Yield 0.1012 g (89%) of yel-
low powder. 1H NMR (300 MHz, CDCl3, 25 °C): δ = 0.89 (t, 3 H,
CH3), 0.90 (t, 3 H, CH3), 1.20–1.34 (m, 34 H, CH2), 1.38–1.45 (m,
2 H, CH2), 1.46–1.54 (m, 2 H, CH2), 1.71–1.77 (m, 2 H,
CH2CH2O), 1.86–2.13 (m, 12 H, C3H6 bridge), 3.29 (t, 2 H,
CH2O), 3.41 (m, 1 H, C5H3Fe), 3.49 (m, 1 H, C5H3Fe), 3.88 (t, 2
H, CH2O), 3.89 (m, 1 H, C5H3Fe), 3.94 (m, 1 H, C5H3Fe), 4.10
(m, 1 H, C5H3Fe), 4.17 (m, 1 H, C5H3Fe), 4.20 (m, 2 H, C5H4Fe),
4.28 (m, 2 H, C5H4Fe), 4.44 (m, 2 H, C5H4Fe), 4.55 (m, 2 H,
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Eur. J. Inorg. Chem. 2008, 1682–1688
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Received: July 16, 2007
Published Online: February 11, 2008
1688
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Eur. J. Inorg. Chem. 2008, 1682–1688