Synthesis and liquid crystal properties of copper(II) and palladium(II) chelates with new ferrocene-containing enaminoketones

Article abstract of DOI:10.1016/j.poly.2009.01.045

Heterometallic liquid crystals are of special interest because of the possibility to combine optical, magnetic and electric properties of different metal ions in one mesogenic molecule. In order to investigate new heteropolynuclear mesogenic systems, a se

Full text of DOI:10.1016/j.poly.2009.01.045

Polyhedron 28 (2009) 1301–1307
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Polyhedron
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Synthesis and liquid crystal properties of copper(II) and palladium(II) chelates
with new ferrocene-containing enaminoketones
*
*
Oleg N. Kadkin , Eun Ho Kim, So Yeon Kim, Moon-Gun Choi
Department of Chemistry, Centre for Bioactive Molecular Hybrids, BK21, Yonsei University, 262 Seongsanno, Seodaemun-gu, Seoul 120-749, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Heterometallic liquid crystals are of special interest because of the possibility to combine optical, mag-
netic and electric properties of different metal ions in one mesogenic molecule. In order to investigate
new heteropolynuclear mesogenic systems, a series of b-aminovinylketone ligands derived from acetyl
ferrocene have been synthesized. Subsequently Cu(II) and Pd(II) ions were incorporated into the enami-
noketone chelate core. The obtained ligands and complexes were characterized by element analysis, 1H
NMR, IR and UV–Vis spectroscopies. According to thermal polarizing microscopy and DSC studies, the
ligands and Cu(II) complexes exhibit disordered soft crystal phases upon cooling from the isotropic liquid
state. The Pd(II) complexes showed monotropic smectic C mesomorphism. The metal centres in the syn-
thesized heteropolynuclear mesogens are in close vicinity to each other, which is of considerable interest
from the viewpoint of the potential electron-transfer interactions between a ferrocene core and the cen-
tral ions.
Received 9 December 2008
Accepted 30 January 2009
Available online 3 March 2009
Keywords:
Ferrocene
Liquid crystal
Metallomesogen
b-Aminovinylketone
Heteronuclear complex
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
theses of various liquid crystalline metallocomplexes [36–48]. In
comparison with the earlier reported ferrocene- and [3] ferroceno-
Metallomesogens attract considerable interest of many
researchers due to their special properties brought by metal atoms
in addition to liquid crystallinity [1–8]. Moreover, various new
molecular shapes can be realized in metal-containing liquid crys-
tals, such as square, folded square, lantern, pyramidal and octahe-
dral geometrical shapes, which are difficult to achieve in
conventional organic mesogens. Metallomesogen systems with
multiple metal centres are of special interest from the standpoint
of bringing various functional properties into liquid crystalline
materials, e.g. colour, luminescence, metamagnetism or electric
conductivity. This inspired many research groups to focus on
molecular design and the synthesis of new examples of hetero-
polynuclear metallomesogens [9–21]. Earlier we developed an ap-
proach which utilizes the advantages of a ferrocene unit, such as
chemical and thermal stability, three-dimensional structure, and
aromatic chemistry, for obtaining heteropolynuclear mesogenic
structures [15–21]. Ferrocene is an exceptional building block for
introducing metal atoms into liquid crystal molecules because of
its unique properties [22–35]. In this paper, we report promeso-
genic ferrocene derivatives containing a b-aminovinylketone che-
late core, which were used as versatile ligands for the syntheses
of heteronuclear metallomesogens. It is noteworthy that an enami-
noketone framework has been widely applied earlier for the syn-
phane-containing enaminoketone complexes, the metal centres in
the present compounds are positioned in a close proximity to each
other [17,21]. Indeed, it was interesting to compare the liquid crys-
tal properties of these structurally isomorphic heteronuclear sys-
tems. Potentially, the electronic exchange interactions between
the metal centres in the obtained complexes may lead to interest-
ing magnetic, optical and redox properties.
2. Experimental
2.1. General details
Reagent grade chemicals and solvents were purchased from Al-
drich, TCI and Fluka. Solvents were dried and freshly distilled just
before use. 1H NMR spectra were measured on a Bruker Avance/
DPX 250 using the internal TMS standard and CDCl3 as a solvent.
FT-IR spectra were recorded on a Nicolet Abatar-360 FT-IR spec-
trometer in KBr pellets. DSC thermographs were obtained on a Per-
kin Elmer Diamond DSC with a scan rate of 10 °C/min. Thermo-
optical observations were carried out on a Nicon Eclipse E600 Pol
optical polarizing microscope equipped with a Mettler Toledo
FP82 HT hot stage system and a Mettler FP90 central processor.
Microphotographs were obtained with a Moticam 2300 digital
camera. UV and visible spectra in the region of 200–800 nm were
recorded on a Shimadzu UV-1650PC spectrophotometer using
CH2Cl2 as a solvent. Elemental analyses were performed on a Fisons
instrument 2A1108 at the Korea Institute of Science and
* Corresponding authors. Tel.: +82 2 2123 2645; fax: +82 2 364 7050.
E-mail addresses: okadkin@hotmail.com (O.N. Kadkin), choim@yonsei.ac.kr
(M.-G. Choi).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.01.045

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O.N. Kadkin et al. / Polyhedron 28 (2009) 1301–1307
Technology. Column chromatographic separations were carried out
on neutral Al2O3 from Aldrich. Alumina TLC plates D-5160 Duran
from Macherey–Nagel were used for selecting eluants and control-
ling the separation process. The literature procedure was used for
the syntheses of the 4-aminophenyl alkyloxybenzoates [49–54].
1014, 1009, 849, 815, 771, 578, 564, 549, 523, 490. Anal. Calc. for
76H88CuFe2N2O8: C, 68.49; H, 6.65,; N, 2.10. Found: C, 68.59; H,
6.58; N 2.26%.
C
2.1.5. Bis-{1-ferrocenyl-1-{[4-(4-hexadecyloxybenzoyloxy)
phenyl]amino}propen-2-onato} copper(II) (4b)
2.1.1. Ferrocenylketoacetaldehydate sodium (2)
This complex was synthesized in an analogous manner to the
previous reaction. Yield 97.0 mg (87%). FT-IR (cmÀ1): 2923 (C–H),
2848 (C–H), 1734 (C@O), 1599 (C@N), 1568 (C@C), 1513 (C@C
aryl), 1509 (C@C aryl), 1490 (C@C aryl), 1425, 1337, 1331, 1250,
1201, 1198, 1160, 1072, 1014, 1009, 847, 811, 770, 579, 564,
550, 524, 489. Anal. Calc. for C84H104CuFe2N2O8: C, 69.82; H, 7.25;
N, 1.94. Found: C, 69.58; H, 7.19; N, 2.04%.
Ethyl formate (1.2 mL, 14.9 mmol) and 1 (2.00 g, 8.77 mmol) in
absolute benzene (Caution: carcinogen! Consult MSDS) (15 mL)
were refluxed for 6 h in the presence of metallic sodium (Caution:
highly reactive material! Consult MSDS) (0.60 g, 26.1 mmol) [55].
A precipitate of sodium enolate was filtered off and recrystallized
from ethanol. Yield 2.44 g (86%), orange powder. Used without fur-
ther characterization.
2.1.6. Bis-{1-ferrocenyl-1-{[4-(4-dodecyloxybenzoyloxy)
2.1.2. 1-Ferrocenyl-1-{[4-(4-dodecyloxybenzoyloxy)
phenyl]amino}propen-2-onato} palladium(II) (5a)
phenyl]amino}propen-2-one (3a)
The ligand 3a (98.8 mg, 0.154 mmol) was dissolved completely
in freshly distilled 1,4-dioxane (2 mL) in a one-neck 25 mL round
flask. Pd(OAc)2 (20.4 mg, 0.091 mmol) was dissolved in 1,4-diox-
ane (1 mL) in a separate flask. The prepared solutions were mixed
and refluxed for 15 min. The product was precipitated by adding
ethanol (ꢀ4 mL). The precipitate was filtered off and recrystallized
from hot ethanol. Yield 48.2 mg (45.5%), brown powder. 1H NMR
(250 MHz): d 0.89 (t, 3H, CH3), 1.28 (br. s, 16H, CH2), 1.50 (m,
2H, OCH2CH2CH2), 1.83 (quintet, 2H, OCH2CH2), 3.96 (m, 2H,
C5H4), 4.07 (s overlapped with t, 7H, OCH2 and C5H5), 4.23 (t, 2H,
C5H4), 5.31 (d, JH,H = 7.5 Hz, 1H, H1), 6.91 (d, JH,H = 7.5 Hz, 1H,
H2), 7.01 (d, JH,H = 9 Hz, 2H, H6), 7.25 (d overlapped with CDCl3,
2H, H3), 7.44 (d, JH,H = 8 Hz, 2H, H4), 8.20 (d, JH,H = 9 Hz, 2H, H5).
FT-IR (cmÀ1): 2920 (C–H), 2850 (C–H), 1731 (C@O), 1605 (C@N),
1575 (C@C), 1506 (C@C aryl), 1500 (C@C aryl), 1411, 1350, 1251,
1191, 1165, 1074, 1014, 1010, 845, 811, 759, 564, 560, 500, 490.
Anal. Calc. for C76H88Fe2N2O8Pd: C, 66.36; H, 6.45; N, 2.04. Found:
C, 65.70; H, 6.43; N, 2.26%.
The p-aminophenyl ester of p-dodecyloxy benzoic acid (1.165 g,
2.93 mmol) and 2 (0.815 g, 2.93 mmol) were dissolved separately
in hot ethanol, and then mixed together. Concentrated aqueous
HCl (26 lL, 0.30 mmol) was added dropwise to the mixture by a
syringe, and then the mixture was refluxed for 30 min. An orange
precipitate was filtered out after the mixture cooled down. The
precipitate was dissolved in CH2Cl2 and filtered through Celite
545. The solvent was evaporated using a rotary evaporator. Recrys-
tallization from n-butanol gave 0.472 g (25%) of an orange powder.
1H NMR (250 MHz): d 0.89 (t, 3H, CH3), 1.27 (br. s, 16H, CH2), 1.48
(m, 2H, OCH2CH2CH2), 1.82 (quintet, 2H, OCH2CH2), 4.04 (t, 2H,
OCH2), 4.19 (s, 5H, C5H5), 4.47 (t, 2H, C5H4), 4.80 (t, 2H, C5H4),
5.61 (d, JH,H = 7.5 Hz, 1H, H1), 6.98 (d, JH,H = 10 Hz, 2H, H6), 7.09
(d, JH,H = 8 Hz, 2H, H3), 7.17 (d, JH,H = 8 Hz, 2H, H4), 7.30 (dd,
JH,H(1) = 7.5 Hz, JH,H(2) = 12.5 Hz, 1H, H2), 8.13 (d, JH,H = 10 Hz, 2H,
H5), 11.84 (d, JH,H = 12.5 Hz, 1H, NH). FT-IR (cmÀ1): 2915 (C–H),
2846 (C–H), 1727 (C@O), 1627 (C@O), 1602 (COC@C), 1515 (C@C
aryl), 1508 (C@C aryl), 1489 (C@C aryl), 1256, 1199, 1165, 1083,
1072, 1029, 1010, 823, 788, 759, 525, 504, 486. Anal. Calc. for
C38H45FeNO4: C, 71.81; H, 7.13; N, 2.20. Found: C, 71.81,; H, 7.22;
N, 2.45%.
2.1.7. Bis-{1-ferrocenyl-1-{[4-(4-hexadecyloxybenzoyloxy)
phenyl]amino}propen-2-onato} palladium(II) (5b)
This complex was synthesized in an analogous manner to the
previous reaction. Yield 44.0 mg (37%). 1H NMR (250 MHz): d
0.88 (t, 3H, CH3), 1.27 (br. s, 24H, CH2), 1.50 (m, 2H, OCH2CH2CH2),
1.84 (quintet, 2H, OCH2CH2), 3.96 (m, 2H, C5H4), 4.07 (s overlapped
with t, 7H, OCH2 and C5H5), 4.23 (t, 2H, C5H4), 5.31 (d, JH,H = 7.5 Hz,
1H, H1), 6.91 (d, JH,H = 7.5 Hz, 1H, H2), 7.01 (d, JH,H = 9 Hz, 2H, H6),
7.25 (d overlapped with CDCl3, 2H, H3), 7.44 (d, JH,H = 8 Hz, 2H, H4),
8.19 (d, JH,H = 9 Hz, 2H, H5). FT-IR (cmÀ1): 2924 (C–H), 2849 (C–H),
1732 (C@O), 1604 (C@N), 1576 (C@C), 1504 (C@C aryl), 1502 (C@C
aryl), 1410, 1350, 1250, 1192, 1164, 1074, 1013, 1011, 847, 810,
760, 563, 561, 503, 489. Anal. Calc. for C84H104Fe2N2O8Pd: C,
67.81; H, 7.05; N, 1.88. Found: C, 67.99; H, 7.01; N, 1.96%.
2.1.3. 1-Ferrocenyl-1-{[4-(4-hexadecyloxybenzoyloxy)
phenyl]amino}propen-2-one (3b)
This compound was prepared in an analogous manner to the
previous reaction from 3.295 mmol of the appropriate reagents.
Yield 0.64 g (28%). 1H NMR (250 MHz): d 0.88 (t, 3H, CH3), 1.26
(br. s, 24H, CH2), 1.48 (m, 2H, OCH2CH2CH2), 1.82 (quintet, 2H,
OCH2CH2), 4.04 (t, 2H, OCH2), 4.20 (s, 5H, C5H5), 4.47 (t, 2H,
C5H4), 4.80 (t, 2H, C5H4), 5.61 (d, JH,H = 7.5 Hz, 1H, H1), 6.97 (d,
JH,H = 10 Hz, 2H, H6), 7.09 (d, JH,H = 9 Hz, 2H, H3), 7.18 (d,
JH,H = 9 Hz, 2H, H4), 7.31 (dd, JH,H(1) = 7.5 Hz, JH,H(2) = 12.5 Hz, 1H,
H2), 8.13 (d, JH,H = 10 Hz, 2H, H5), 11.84 (d, JH,H = 12.5 Hz, 1H,
NH). FT-IR (cmÀ1): 2917 (
1626 ( , C@O), 1603 ( , COC@C), 1514 (
C@C aryl), 1490 ( , C@C aryl), 1257, 1201, 1164, 1082, 1072,
m, C–H), 2849 (
m
m
, C–H), 1727 (
, C@C aryl), 1509 (
m, C@O),
3. Results and discussion
m
m
m,
m
3.1. Synthesis and characterization
1030, 1008, 824, 790, 757, 524, 509, 489. Anal. Calc. for C42H53Fe-
NO4: C, 72.93; H, 7.72; N, 2.02. Found: C, 72.85; H, 7.69; N, 1.98%.
The syntheses of the compounds reported in this paper were
performed according to Scheme 1. Acetyl ferrocene 1 can be pre-
pared using a Friedel-Crafts acylation procedure, as was estab-
lished in the early classical works on ferrocene [55–58]. The
addition of AlCl3 catalyst in small portions to equimolar amounts
of ferrocene and acetyl chloride allowed the yield of the mono-
acylated product to increase to over 70%. Compound 1 was sepa-
rated by column chromatography on Al2O3 from the mixture of
products.
2.1.4. Bis-{1-ferrocenyl-1-{[4-(4-dodecyloxybenzoyloxy)
phenyl]amino}propen-2-onato} copper(II) (4a)
The ligand 3a (104.3 mg, 0.1641 mmol) and Cu(OAc)2ÁH2O
(17.1 mg, 0.0856 mmol) were dissolved separately in hot ethanol.
The solutions were mixed and refluxed for 15 min. A brown precip-
itate was formed after cooling, which was centrifuged and washed
3 times with ethanol using the centrifugation method. Yield
90.0 mg (82%). FT-IR (cmÀ1): 2924 (C–H), 2850 (C–H), 1735
(C@O), 1597 (C@N), 1567 (C@C), 1515 (C@C aryl), 1508 (C@C aryl),
1489 (C@C aryl), 1424, 1338, 1333, 1247, 1201, 1199, 1161, 1070,
The crossed Claisen condensation of the acetyl ferrocene 1 with
ethyl formate gave the sodium salt of the appropriate ketoalde-

O.N. Kadkin et al. / Polyhedron 28 (2009) 1301–1307
1303
Na+
O
O
CH3
O
O
Fe
Fe
+
+
Na
H
H
OC2H5
2
1
O
O
OCnH2n+1
H2N
2 + HCl (aq. conc); EtOH
H5
H6
O
O
H1
H2
N
H3
H4
OCnH2n+1
H5'
H6'
O
H
Fe
H3'
H4'
3a (n=12)
3b (n=16)
M(OAc)2
O
Fe
OCnH2n+1
N
O
O
M
O
O
N
CnH2n+1
O
Fe
O
4a (M=Cu2+, n=12)
4b (M=Cu2+, n=16)
5a (M=Pd2+, n=12)
5b (M=Pd2+, n=16)
Scheme 1. Syntheses of ligands 3a–b and heteronuclear complexes 4a–b and 5a–b.
hyde 2. The reaction of compound 2 with p-alkoxybenzoyloxy ani-
line in ethanol in the presence of an equimolar amount of concen-
trated HCl (aq) led to the b-aminovinyl ketones 3a–b. The
copper(II) complexes 4a–b and palladium(II) complexes 5a–b were
obtained by treatment of 3a–b with the corresponding acetate
salts in ethanol and 1,4-dioxane, respectively.
The chemical compositions of the synthesized compounds are
in good agreement with the data of elemental analyses. The FT-
IR spectra of 3a–b are distinguished by characteristic stretching
bands of the ester carbonyl near 1726 cmÀ1, and ketone carbonyl
at 1627 cmÀ1. In addition, the CÀ@1C bond stretching of the ethenyl
group is exposed near 1603 cm . There is a group of absorption
peaks in the area 1480–1515 cmÀ1 which are connected with the
deformations of the aromatic rings. Metal-ring vibrations of the
ferrocene moiety are displayed in the long-wave area, at 485–
525 cmÀ1. The C@O stretches of the ester group are shifted in the
complexes 4a–b and 5a–b to a higher frequency region by 8 and
4 cmÀ1, respectively. The valence vibration of the ketone carbonyl
near 1627 cmÀ1 disappears upon complex formation and addi-
tional peaks connected with the C@N and C@C bonds in the region
1570–1600 cmÀ1 are generated. In addition vibration modes of the
M–O and M–N bonds in the area 560–600 cmÀ1 are displayed in
the IR spectra of the metallochelates. Thus, considerable changes
occur in the infrared spectra of 4a–b and 5a–b in comparison with
the free ligands 3a–b, undoubtedly indicating the successful com-
plex formation.
The UV–Vis spectra of the ligands 3a–b are represented by three
absorption bands (see Table 1). The first band with a maxima near
260 nm is associated with
p–
p* electronic transitions of the aro-
matics rings. The next band is related to the carbonyl chromo-
phore, which is shifted bathochromically to 366 nm due to the
conjugational effect of the adjacent ethenyl and cyclopentadienyl
groups [59]. The less intensive band at ꢀ465 nm belongs to d–d
type transitions of the electrons of the iron atoms [60–62].
An additional shoulder appears near 292–298 nm upon com-
plex formation, which is connected to a ligand-to-metal charge
transfer transition in the case of the copper(II) complexes 4a–b
[63], and a metal-to-ligand charge transfer transition in the case

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O.N. Kadkin et al. / Polyhedron 28 (2009) 1301–1307
Table 1
of the palladium(II) complexes 5a–b [64]. It is noteworthy, that in
UV–Vis spectral data for 3a–b, 4a–b and 5a–b.
the metal complexes an absorption band associated with the car-
bonyl group is bathochromically shifted in comparison with the
free ligand. The shift can be explained by the added electronic con-
jugational effect due to involving this group into the metalloche-
late cycle. The ferrocenyl group in the complexes 4a–b and 5a–b
reveals d–d electronic transitions in the same area, 465 nm, as
the free ligands 3a–b.
Compound
Absorption max, nm (log
e
, L Â cmÀ1 Â molÀ1
)
I band
II band (shoulder)
III band
IV band
3a
4a
5a
3b
4b
5b
260 (4.40)
263 (4.94)
259 (4.75)
260 (4.50)
262 (4.64)
263 (4.74)
366 (4.36)
383 (4.47)
374 (4.60)
367 (4.51)
382 (4.47)
388 (4.28)
465 (3.43)
454 (3.82)
462 (4.08)
466 (3.50)
450 (3.77)
457 (3.68)
278 (4.39)
295 (4.45)
290 (4.36)
298 (4.25)
The ligands 3a–b and complexes 5a–b are also characterized by
1H NMR. It is interesting to note that the proton signals of the
Table 2
Data of thermo-optical and DSC studies of 3a–b, 4a–b and 5a–b.
Compound
Phase transitions,a °C (
Heating process
DH, kJ/mol)
Cooling process
3a
1st cycle: Cr1 68(1.5) Cr2 139(34.3) I
I [99.5(À20.0)]b X 87(À0.9) Cr2
67(À1.9) Cr
2nd cycle: Cr 88(1.9) Cr1 01(À9.1)
Cr2 138(28.7) I
I [96(À12.0)] X 87(À1.0) Cr2
67(À2.3) Cr
4a
5a
3b
Cr1 150.5(À7.0) Cr2 164.5(50.7) I
Cr1 183.5(24.5) Cr2 221(58.0) I
1st cycle: Cr1 109(18.4) Cr2 132(39.5) I
2nd cycle: Cr 100(13.8) Cr1 119(À16.1)
Cr2 132(38.7) I
I [107]c
X
I [140] SmCd
I [114(À21.5)] X 89(À11.0) Cr
I [114(À21.4)] X 88(À13.8) Cr
4b
5b
Cr 145(65.8) I
Cr1 201(64.1) I
I [120]c
I [136] SmCd
X
a
b
c
Cr: crystal; X: soft crystal; SmC: smectic C; I: isotropic liquid phases.
Monotropic mesophase transitions are shown in square brackets.
No peaks were observed on the DSC cooling course in the point where star-like domains were observed under POM.
The mesophase was observed upon rapid cooling in a polarizing microscope, while the corresponding DSC peaks were not resolved.
d
Fig. 1. DSC thermograms of 3a–b: (a) the first heating and cooling cycle, 3a; (b) the second heating and cooling cycle, 3a; (c) the first heating and cooling cycle, 3b; (d) the
second heating and cooling cycle, 3b.

O.N. Kadkin et al. / Polyhedron 28 (2009) 1301–1307
1305
Fig. 2. Optical textures of 3a under a polarizing microscope: (a) two spherical soft crystal domains growing from the isotropic liquid; (b) the spherical domains mixed with
each other; (c and d) development of the spherulitic crystalline structure.
Fig. 3. DSC thermograms of heteronuclear complexes: (a) 4a; (b) 5a; (c) 4b and (d) 5b.

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O.N. Kadkin et al. / Polyhedron 28 (2009) 1301–1307
substituted cyclopentadiene ring of the ferrocene moiety in 5a–b
are high-field shifted by 0.6 ppm in relation to comparable signals
in the free ligands 3a–b. Such a significant shift is due to the fact
that the ferrocene unit in these complexes is situated very close
to the central chelate core, and there is a considerable electron-do-
nor effect from the Pd(II) ion on it. As for the protons of the ethenyl
link, a similar high-field shift is also observed, though the effect is
weaker in this case.
sition from the isotropic liquid to a highly disordered soft crystal
phase. Two other smaller peaks in the cooling cycle can be assigned
to crystal polymorphic phase transitions. A series of microphoto-
graphs in Fig. 2 illustrates the development of spherical domains
on cooling from the isotropic liquid state in a sample of 3a under
a polarizing microscope. The spherical shape of the domains re-
veals a possible organization into supramolecular assemblies. The
last assumption is founded on the presence of C@O and polar NH
groups in 3a–b, which are capable of forming intermolecular
hydrogen bonds. Upon further cooling these spherical formations
are transformed into big spherulitic crystals, similar to those ob-
served frequently during crystallization from smectic mesophases.
Exactly the same textures were observed under a polarizing micro-
scope in the case of 3b.
Two DSC peaks corresponding to the crystal-to-crystal and crys-
tal-to-isotropic liquid transitions were observed in the first heating
cycle of 4a, and only one peak from the isotropic liquid phase tran-
sition was observed in the case of 4b (Fig. 3). In the cooling cycle
any phase transition peaks were not resolved. The main informa-
tion about the phase transition behaviour of 4a–b in the cooling
path was obtained from POM observations. Typical optical textures
developed from the isotropic liquid state of 4a–b under a polariz-
ing microscope are presented in Fig. 4. Most likely the observed
star-like and flower-like formations are associated with a disor-
dered soft crystal phase. Samples in this state had limited flowabil-
ity when subjected to stress.
3.2. Mesomorphism
Liquid crystal properties of the new synthesized metallomeso-
gens have been investigated by thermal polarizing optical micros-
copy (POM) and differential scanning calorimetry (DSC). The
obtained data on the thermal behaviour of the ligands 3a–b and
two series of heteronuclear complexes 4a–b and 5a–b are pre-
sented in Table 2.
In the first heating cycle of the DSC measurements, crystal-to-
crystal phase transition peaks were observed for the ligands 3a–
b (Fig. 1), although it was small in the case of n = 12. In the cooling
course, there are several broad responses in the DSC thermogram
of 3a and two sharp peaks in a case of 3b. During the second heat-
ing cycle exothermic peaks appeared in both cases between the
first crystal-to-crystal and crystal-to-isotropic liquid phase transi-
tions. This can be explained by partial vitrification of the samples
in the first cooling cycle, accomplishing a low energy crystal pack-
ing at higher temperatures when increased mobility of molecules
allows it to be completed. Enthalpy values of the first DSC peaks
after cooling from the isotropic liquid state are relatively high in
both 3a and 3b. Presumably, these peaks are the result of the tran-
Similar DSC thermograms were obtained for 5a–b in the heating
cycle: two peaks corresponding to the crystal-to-crystal and crys-
tal-to-isotropic liquid transitions in the case of 5a, and only one
peak due to an isotropic liquid transition in the case of 5b
Fig. 4. Emergence of star-like and flower-like domains from the isotropic liquid
state in: (a) 4a and (b) 4b.
Fig. 5. Optical textures of 5a under a polarizing microscope: (a) sand-like optical
texture and (b) schlieren texture of smectic C.

O.N. Kadkin et al. / Polyhedron 28 (2009) 1301–1307
1307
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(Fig. 3). DSC peaks were not revealed on cooling. Monotropic smec-
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5b by polarizing optical microscopy. The typical sand-like and
schlieren textures of smectic C were observed upon cooling from
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Thus, in comparison with the earlier synthesized heteronuclear
mesogens with ferrocene- [17] and ferrocenophane-containing
[21] b-aminovinylketones, the present compounds exhibited
rather poor mesomorphism. In fact the bulky ferrocene moieties
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4. Conclusions
Novel ferrocene-containing b-aminovinylketone derivatives
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been synthesized and fully characterized by elemental analyses, 1H
NMR, FT-IR and UV–Vis spectroscopies. The synthesized ligands
exhibited disordered soft crystal phases. New heteropolynuclear
metallomesogen systems were generated from these ligands by
incorporating Cu(II) and Pd(II) ions into the enaminoketone chelat-
ing site. The synthesized heteronuclear complexes of copper(II),
like the free ligands, showed a soft crystal phase. The Pd(II) com-
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Acknowledgements
This work has been supported by a grant from the Korea Science
and Engineering Foundation (KOSEF) through the Center for Bioac-
tive Molecular Hybrids (CBMH), and the program Brain Korea 21
(BK-21).
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