Synthesis, mesomorphism, and spectroscopic characterization of bis[4-(n- alkoxy)-5-(p-n-tetradecylphenylazo)]-substituted (N,N'- salicylidenediaminato)nickel(II) complexes

Article abstract of DOI:10.1002/(sici)1099-0682(199908)1999:8<1367::aid-ejic1367>3.0.co;2-m

The bis[4-(n-C(m)H(2m+1)O)-5-(p-C(14)H(29)C₆H₄N=N)]-substituted N,N'- salicylidenediamines H₂[L(N)(m,14)] (N = 1: 1,2-diaminoethane; N = 2: 1,3- diaminopropane; N = 3: 1,3-diamino-2,2-dimethylpropane; m = 6 or 18) have been synthesized. Both the N = 2 and 3 series of compounds display a smectic C (SmC) mesophase, with clearing points well below 100 °C. By treating the H₂[L(N)(m,14)] ligands with an Ni(II) salt, liquid crystalline mononuclear complexes with 'unconventional' (lateral-tailed) molecular shape form. These Ni[L(N)(m, 14)] complexes, showing nematic and smectic disordered phases, are stable over a quite large temperature range and have been characterized by different spectroscopic techniques. The newly synthesized mesogens exhibit lower transition temperatures and higher thermal stability than homologous complexes Ni[L(N)(14)] with a 'conventional' rod-like molecular geometry.

Full text of DOI:10.1002/(sici)1099-0682(199908)1999:8<1367::aid-ejic1367>3.0.co;2-m

FULL PAPER
Synthesis, Mesomorphism, and Spectroscopic Characterization
of Bis[4-(n-alkoxy)-5-(p-n-tetradecylphenylazo)]-Substituted
(N,NЈ-Salicylidenediaminato)nickel(II) Complexes
Iolinda Aiello,[a] Mauro Ghedini,*[b] Massimo La Deda,[a] Daniela Pucci,[a]
and Oriano Francescangeli[c]
Keywords: Metallomesogens / Nickel / Salicylidenediamines / Azo compounds / (E)/(Z) photoisomerization /
Isomerizations
The bis[4-(n-CmH2m+1O)-5-(p-C14H29C6H4N=N)]-substituted
N,NЈ-salicylidenediamines H2[LN(m,14)] (N 1: 1,2-
diaminoethane; N = 2: 1,3-diaminopropane; N = 3: 1,3-
“unconventional” (lateral-tailed) molecular shape form.
These Ni[LN(m,14)] complexes, showing nematic and smectic
disordered phases, are stable over a quite large temperature
=
diamino-2,2-dimethylpropane; m = 6 or 18) have been range and have been characterized by different
synthesized. Both the N = 2 and 3 series of compounds spectroscopic techniques. The newly synthesized mesogens
display a smectic C (SmC) mesophase, with clearing points
well below 100 °C. By treating the H2[LN(m,14)] ligands with
an NiII salt, liquid crystalline mononuclear complexes with
exhibit lower transition temperatures and higher thermal
stability than homologous complexes Ni[LN(14)] with
“conventional” rod-like molecular geometry.
a
gands bearing the n-C14H29 alkyl chains. However, all these
mesogens display poor thermal stability, and strong de-
Introduction
The photoisomerization of liquid crystals containing an composition is observed when, at about 300°C, the meso-
azobenzene core has been envisaged as useful tool in de- phase to isotropic liquid transition occurs. This drawback
signing optical switching materials based on light-induced severely limits any practical applications; therefore, in order
isothermal phase transitions.[1,4] In an endeavour to im- to preserve chemical stability, the melting transition tem-
prove or explore possible new applications of mesomorphic peratures of these materials must decrease Ϫ i.e. a different
species, metal atoms have been incorporated into mesogenic molecular structure has to be considered.
molecular structures and a further class of materials (metal-
lomesogens), for which some physical properties (e.g. op-
tical, electrical, or magnetic) depend on the nature of the
metal centre, is now available.[5] In principle, new materials
can be obtained from compounds whose molecular struc-
tures combine different features; thus, in particular, photo-
isomerizable metal-based liquid crystals could be relevant
for applications in electrooptic devices.
We are currently concerned with the design and synthesis
of metallomesogens[6,7] and with reference to the above-
mentioned uses have recently reported[8] rod-like thermo-
tropic complexes of NiII, CuII, or VO2ϩ with a series of
bis[5-(p-n-alkylphenylazo)]-substituted N,NЈ-salicylidenedi-
amines (see Scheme 1). The results of such a comparative
investigation indicate that: i) the mesomorphism appears
for NʝN ϭ 1,2-diaminoethane or 1,3-diaminopropane
only; ii) the lowest clearing temperatures are shown by the
NiII species and iii) the better mesomorphic properties (na-
mely larger mesomorphic range) are obtained for the li-
Scheme 1. General formula of the M[LN(n)] complexes (ref.[8]
)
The relationship between chemical structure and meso-
genic properties is an extensively investigated area in the
field of liquid crystal chemistry and, although the greater
part of the available data concerns organic species,[9] some
rules could also be of use for the metallomesogens. In par-
ticular, it has been proven that lateral addition of long alkyl
chains to a rod-like molecular structure gives rise to a class
of “nonconventional” liquid crystals, whose mesophase-iso-
tropic transition temperatures are significantly lower than
those of the corresponding rod-like compounds.[10] Thus,
speculating on this trend, low-temperature phase transitions
could be predicted for metallomesogens with similar struc-
tural features.
[a]
`
Dipartimento di Chimica, Universita della Calabria,
I-87030 Arcavacata (CS), Italy
[b]
[c]
`
Dipartimento di Chimica, Universita della Calabria,
I-87030 Arcavacata (CS), Italy
Fax: (internat.) ϩ 39-0984/492062
E-mail: m.ghedini@unical.it
Dipartimento di Scienze dei Materiali e della Terra and Istituto
Nazionale per la Fisica della Materia, Universita di Ancona,
The target of the research work we are presently involved
in is to obtain thermally stable photoactive metal-contain-
`
Via Brecce Bianche, I-60131 Ancona, Italy
Eur. J. Inorg. Chem. 1999, 1367Ϫ1372
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
1434Ϫ1948/99/0808Ϫ1367 $ 17.50ϩ.50/0
1367

I. Aiello, M. Ghedini, M. La Deda, D. Pucci, O. Francescangeli
FULL PAPER
Scheme 2. Synthetic route to Ni[LN(m,14)] complexes 1؊6; reagents and conditions: i) KOH, n-CmH2mϩ1Br, ethanol; ii) 4-(n-tetradecyl)-
aniline, HCl, NaNO2, NaOH, water; iii) N ϭ 1,2-diaminoethane or 1,3-diaminopropane or 1,3-diamino-2,2-dimethylpropane, ethanol;
iv) Ni(CH3COO)2 · 4 H2O, ethanol
ing liquid crystals. As an extension of the previous study,[8] propriate alkyl bromide n-CmH2mϩ1Br [intermediates I(6)
this paper reports on the synthesis, mesomorphic behaviour, for m ϭ 6 and I(18) for m ϭ 18], and then coupled with the
and spectroscopic properties of the complexes that the NiII diazonium chloride obtained from the 4-n-tetradecylaniline.
ion forms with a series of salicylidenediamino ligands ob- Finally, the new formed intermediates II(6,14) and II(18,14)
tained by the symmetric addition of two aliphatic tails to were condensed with the selected diamines (namely 1,2-di-
the bis[5-(p-n-tetradecylphenylazo)]-substituted N,NЈ-sal- aminoethane, N ϭ 1; 1,3-diaminopropane, N ϭ 2; and 1,3-
icylidenediamine skeleton (see Scheme 2).
diamino-2,2-dimethylpropane, N ϭ 3). The H2[LN(m,14)]
compounds are orange solids which, by treatment with
nickel(II) acetate tetrahydrate, give the corresponding
Ni[LN(m,14)] complexes 1؊6 (Scheme 2) as brown to red
solids.
Results and Discussion
Synthesis
The ligands and complexes were characterized by IR and
The H2[LN(m,14)] ligands were synthesized in satisfac- 1H-NMR spectroscopies and their purity confirmed by
tory yields as outlined in Scheme 2. The starting material, elemental analysis (see Experimental Section). These data
2,4-dihydroxybenzaldehyde, was treated first with the ap- as a whole account for the general formula shown in
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Eur. J. Inorg. Chem. 1999, 1367Ϫ1372

Bis[4-(n-alkoxy)-5-(p-n-tetradecylphenylazo)]-Substituted (N,NЈ-Salicylidenediaminato)nickel(II) Complexes
FULL PAPER
1
Scheme 2. Moreover, both the IR and H-NMR spectra, Ligands
except for the signal attributable to the n-CmH2mϩ1O chain,
None of the H2[L1(m,14)] ligands displays mesomorphic
behaviour, melting directly to an isotropic liquid at about
100°C; a crystal-to-crystal transition at 86°C (DSC, XRD)
appears only for the m ϭ 18 homologues.
compare well with those of the previously described
H2[LN(n)] and Ni[LN(n)] compounds (see Scheme 1).[8]
Thus, for complexes 1؊6, an [LN(m,14)] bonding mode, like
that which the [LN(n)] groups exhibit in Ni[LN(n)] and ex-
pected for ligands containing the salicylidenediaminato
core, is proposed (see Scheme 2).
Increasing the bridge size promotes liquid crystalline be-
haviour (N ϭ 2 and 3 series). The smectic C (SmC) meso-
phase is the only one observed in these compounds, irres-
pective of the bridging diamine or the length of the lateral
n-CmH2mϩ1OϪ group. In particular, an enantiotropic (m ϭ
6) or monotropic (m ϭ 18) SmC phase, featuring the typical
schlieren texture, is exhibited by the H2[L2(m,14)] couple,
showing clearing temperatures ranging from 66°C (m ϭ 18)
to 83°C (m ϭ 6). Worthy of note is an exothermic peak
detected at 65°C (DSC) for the H2[L2(6,14)] sample just
after the formation of the SmC phase, indicating a tran-
sition to a thermodynamically more stable form before re-
aching the isotropic liquid. In contrast, in the H2[L2(18,14)]
compound, a crystal-to-crystal transition is observed at
52°C (DSC, XRD). For both the H2[L2(m,14)] species, an
SmC mesophase first appears on cooling from the isotropic
liquid but, on further cooling, crystallization does not occur
and the samples solidify into a glassy state retaining the
structure of the SmC phase.
Mesomorphism
The thermal behaviour of all the newly synthesized com-
pounds belonging to the three homologous series N ϭ 1Ϫ3,
was investigated by combining polarized optical microscopy
(POM), miscibility tests with reference compounds,
differential scanning calorimetry (DSC) and variable-tem-
perature low-angle X-ray diffraction (XRD) measurements.
The transition temperatures and associated enthalpies for
both the ligands H2[LN(m,14)] and their related NiII com-
plexes are reported in Tables 1 and 2, respectively.
Table 1. Transition temperatures, phase assignments[a] and enthalpy
changes for the H2[LN(m,14)] ligands
Finally, both the N ϭ 3 compounds give an SmC phase
showing a sanded texture. On cooling down from the iso-
tropic liquid, the SmC phase is not restored for H2[L3(6,14)]
and the sample becomes an amorphous solid (POM,
DSC, XRD).
At room temperature, the compound with the longest lat-
eral chain, H2[L3(18,14)], is a viscous material, slightly bire-
fringent when sheared, whose XRD patterns reveals a sem-
icrystalline structure with a hexagonal smectic-like struc-
ture. As the temperature is increased, the material becomes
more fluid and an SmC phase is observed at 48°C, before
reaching the clearing point at 52°C. Upon cooling, the SmC
phase reappears at 41°C and the SmC texture remains until
solidification (without crystallization) occurs.
As expected, the results obtained for the N ϭ 2 and 3
series demonstrate that longer lateral tails or bulkier bridges
gradually decrease the transition temperatures, whereas the
thermal stability of the mesophase progressively reduces.
Moreover, since liquid crystalline properties were not ob-
served for any of the [LN(14)] series,[8] the H2[LN(m,14)]
thermal behaviour is a further example of the role the lat-
eral n-CmH2mϩ1OϪ chains could play in mesomorphism.[9]
Ligand
Transition
T [°C]
∆H
[kJmolϪ1
]
H2[L1(6,14)]
H2[L1(18,14)]
CrϪI
CrϪCrЈ
CrЈϪI
94.5
85.6
106.4
61.8
83.4
52.5
65.9
61.7
42.5
49.7
62.9
48.1
51.9
69.1
28.4
72.7
83.3
39.5
47.9
2.7
H2[L2(6,14)]
H2[L2(18,14)]
CrϪSmC
SmCϪI
CrϪCrЈ
CrЈϪI
IϪSmC[b]
SmCϪCr
CrϪSmC
SmCϪI
CrϪSmC
SmCϪI
2.5
44.6
27.5
18.0
4.1
H2[L3(6,14)]
H2[L3(18,14)]
24.1
[a]
[b]
Cr: crystal; Sm: smectic; I: isotropic liquid. Ϫ
Monotropic
transition.
Table 2. Transition temperatures, phase assignments[a] and enthalpy
changes for the Ni[LN(m,14)] complexes 1؊6
Compound
Transition
T [°C]
∆H
[kJmolϪ1
]
1 {Ni[L1(6,14)]}
2 {Ni[L1(18,14)]}
CrϪI
213.7
65.5
101.2
127.3
226.0[b]
89.5
102.2
180.0[b]
128.1
293.0[b]
117.8
190.1
46.7
46.0
2.5
CrϪSmC
SmCϪI
CrϪN
3 {Ni[L2(6,14)]}
4 {Ni[L2(18,14)]}
49.6
Complexes
NϪI
CrϪSmC
SmCϪSmA
SmAϪI
CrϪSmA
SmAϪI
CrϪSmA
SmAϪI
29.9
1.0
All the Ni[LN(m,14)] complexes (except for 1) are liquid
crystals which exhibit higher clearing points and larger me-
somorphic ranges than those of the corresponding ligands.
Of the N ϭ 1 species, 1 (m ϭ 6) melts directly to the
isotropic liquid at 214°C but the lengthening of the lateral
aliphatic chain to m ϭ 18 (complex 2), induces mesomorph-
ism. Indeed 2 shows an enantiotropic SmC phase, stable in
5 {Ni[L3(6,14)]}
6 {Ni[L3(18,14)]}
61.8
31.1
5.0
[a]
Cr: crystal; Sm: smectic; N: nematic; I: isotropic liquid. Ϫ
From optical microscopy.
[b]
Eur. J. Inorg. Chem. 1999, 1367Ϫ1372
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I. Aiello, M. Ghedini, M. La Deda, D. Pucci, O. Francescangeli
FULL PAPER
the range 65Ϫ101°C. Upon cooling, this mesophase re- pseudo stilbenes, the latter class containing the azobenzenes
appears at 88°C and is supercooled to room temperature. substituted with electron-donating and -accepting groups.
The mesomorphic behaviour of the Ni[L2(m,14)] series Each of these classes behave differently as far as the (Z)/(E)
proves to be quite sensitive to changes in the lateral alkoxy isomerization is concerned and, in particular, the donor-
tail length and confirms the general trend that longer chains acceptor azobenzenes isomerize on a millisecond time scale
promote more ordered phases. Thus, compound 3 (m ϭ 6) at room temperature.[11] The lack of spectral evidence for
displays a nematic (N) phase showing a homeotropic tex- the (E)/(Z) isomerization of Ni[L2(18,14)], Ni[L2(14)],
ture over its entire temperature range, whereas the upper H2[L2(18,14)], or H2[L2(14)] could therefore be ascribed to
homologues 4 (m ϭ 18) exhibits an SmC (blurred a very fast (Z)/(E) thermal isomerization process which
“schlieren” texture) followed by an SmA phase. This latter takes place in the time required to move the sample from
mesophase becomes more and more fluid and displays ho- the irradiating lamp to the spectrometer (see Experimental
meotropic zones as the temperature is increased. However, Section). These results suggest that in the compounds
both complexes exhibit mesogenic behaviour over a tem- examined each molecular half (see Scheme 2) behaves as a
perature range of about 100°C; the corresponding clearing pseudo stilbene. Moreover, since the n-C14H19 chain is a
peaks, only detected by POM observations, were not ob- common feature of these species, an investigation compar-
served in the DSC scans. When cooled from the isotropic ing the ligands with the corresponding NiII complexes and
liquid to room temperature, both compounds 3 and 4 trans- the rod-like molecules with the lateral alkoxy-substituted
formed into an amorphous solid (XRD).
ones indicates that neither complexation to an NiII ion nor
Finally, of the N ϭ 3 derivatives, the Ni[L3(m,14)] com- the addition of a lateral alkoxy chain to the aromatic ring
plexes 5 and 6 exhibit an SmA phase, identified from the A (Scheme 2) changes the photophysical properties of these
ˆ
appearance, via batonnetes, of the focal conic fan texture at NϭN-containing molecules significantly.
128°C (5) and 118°C (6). On cooling from the isotropic
liquid, in compound 5 the SmA phase develops at 280°C
and remains stable until, at 103°C, crystallization takes
place (POM, XRD). In contrast, for compound 6 no crys-
Conclusions
tallization or glass transition was observed until Ϫ20°C.
However, for these three series of Ni[LN(m,14)] com-
plexes it is possible to conclude that the clearing points de-
The present investigation was planned in order to explore
crease by about 50°C (for N ϭ 2) or 100°C (for N ϭ 1,3) a convenient synthetic route to prepare thermally stable
as the lateral chain changes from C6H13O to C18H37O, photoisomerizable metallomesogens. All the members of
while they rise only slightly as the number of the carbon the Ni[LN(m,14)] series display thermotropic mesomorph-
atoms of the bridging diamine increases (from 2, N ϭ 1, to ism except for the complex Ni[L1(6,14)]. In no case was de-
3, N ϭ 2, 3). A similar trend is not observed for the melting composition observed, the mesophases are stable over a
transitions and, consequently, for the stability range of the rather large temperature range, and the clearing tempera-
different mesophases.
tures decrease as the lateral chains increase in length.
These results prove that the addition of two lateral n-
alkoxy tails to bis[5-(p-n-alkylphenylazo)]-substituted N,NЈ-
salicylidenediaminato species produces the correct molecu-
lar geometry for nematic and smectic metal-containing
liquid crystalline compounds with good thermal stability.
Azobenzene (E)/(Z) Photoisomerization
Measurements
Experiments concerning the (E)/(Z) photoisomerization Indeed, a comparison of the newly synthesized mesogens
were performed at room temperature in dichloromethane with the corresponding rod-like complexes[8] (Scheme 1)
solutions on Ni[L2(18,14)] and, for the sake of comparison, shows that the lateral chains i) lower both the melting and
on its rod-like homologues Ni[L2(14)] and on both of the clearing temperatures by some 100°C (N ϭ 2) or 200°C
uncomplexed ligands H2[L2(18,14)] and H2[L2(14)].
(N ϭ 1), ii) promote mesomorphism in the N ϭ 3 deriva-
The absorption spectra of azobenzenes in their thermally tives, and iii) cause more disordered mesophases (N and
stable (E) configuration exhibit absorption maxima at SA) to appear in the N ϭ 1 and 2 series. Thus, as far as
about 350 and 450 nm, and it was observed that irradiation the thermal behaviour is concerned, the addition of lateral
at about 360 nm induces (E)/(Z)-NϭN isomerization.[11] groups to metallomesogens with a rod-like structure in-
Absorptions at similar wavelengths were also recognized in duces effects similar to those observed for organic liquid
the spectra of the azo compounds considered; nevertheless crystals.[10]
under the experimental conditions used, no spectral
Practical applications which require metal-based meso-
changes attributable to (Z) isomers were detected after ir- genic optical switching materials can now be considered.
radiation.
Moreover, it has been recently reported that some com-
Based on the spectral features, Rau[11] classified the sub- plexes containing the (salicylidenediaminato)nickel(II) core
stituted azobenzenes into three different classes depending display second-order nonlinear optical properties,[12] and
on the electronic effects the different substituents exert: na- this makes coordination compounds such as those reported
mely, the azobenzene type, the aminobenzene type, and the herein even more attractive materials.
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Bis[4-(n-alkoxy)-5-(p-n-tetradecylphenylazo)]-Substituted (N,NЈ-Salicylidenediaminato)nickel(II) Complexes
FULL PAPER
cording to the procedure decribed for II(6,14). Yellow. Yield 0.70 g
(40%). M.p. 79°C. Ϫ IR (KBr): ν˜ ϭ 1653 cmϪ1 (CHO). Ϫ 1H
NMR (CDCl3): δ ϭ 11.63 (s, 1 H, H2), 9.82 (s, 1 H, H1), 7.95 (s,
1 H, H6), 7.82 (d, 2 H, Hb,c), 7.31 (d, 2 H, Ha,d), 6.59 (s, 1 H, H3),
4.22 (t, 2 H, OCH2), 2.68 (t, 2 H, CH2). Ϫ C45H74N2O3 (691.09):
calcd. C 78.21, H 10.19, N 4.05; found C 78.31, H 10.15, N 4.34.
Experimental Section
1
General: IR: PerkinϪElmer F.T.2000; as KBr pellets. Ϫ H NMR:
Bruker WH-300 spectrometer; in CDCl3 solutions, with TMS as
internal standard. Ϫ Elemental analyses: PerkinϪElmer 2400 ana-
lyzer. Ϫ Phase transitions and optical textures: Zeiss Axioscope
polarizing microscope equipped with a Linkam C0 600 heating
stage. Ϫ Transition temperatures and enthalpies: PerkinϪElmer
DSC-7 differential scanning calorimeter (DSC) operating at a scan-
ning rate of 10.0°C/min; the apparatus was calibrated with indium
(156.6°C, 3.3 kJ mol ). Ϫ X-ray diffraction: INEL CPS-120 powder
diffractometer using a monochromatized Cu-Kα radiation (λ ϭ
N,NЈ-Bis[4-(n-hexyloxy)-2-hydroxy-5-{[p-(n-tetradecyl)phenyl]azo}-
benzylidene]ethylenediamine {H2[L1(6,14)]}: A mixture of II(6,14)
(0.25 g, 0.47 mmol) and 1,2-diaminoethane (0.016 mL, 0.23 mmol)
in ethanol (15 mL) was refluxed for 4 h. The precipitate was then
filtered off and purified by recrystallization from chloroform/etha-
1
˚
nol to yield 0.21 g (82%) of a red solid. Ϫ H NMR (CDCl3): δ ϭ
1.54 A). Ϫ Room-temperature absorption spectra of aerated di-
14.07 (br. s, 2 H, H2), 8.31 (s, 2 H, H1), 7.78 (d, 4 H, Hb,c), 7.69 (s,
2 H, H6), 7.28 (d, 4 H, Ha,d), 6.54 (s, 2 H, H3), 4.16 (t, 4 H, OCH2),
3.90 (s, 4 H, NCH2), 2.67 (t, 4 H, CH2). Ϫ C68H102N6O4 (1069.61):
calcd. C 76.36, H 9.80, N 7.86; found C 76.39, H 9.83, N, 7.24.
chloromethane solutions: PerkinϪElmer Lambda 5 spectrometer.
Ϫ Irradiation experiments: At selected wavelengths by using the
150-W xenon lamp of a Spex Fluorolog II Spectrofluorimeter. Ϫ
All the commercially available chemicals were used without further
purification. The reference compounds H2[L2(14)] and Ni[L2(14)]
were prepared as previously reported.[8]
H2[L1(18,14)]: Prepared according to the procedure described for
H2[L1(6,14)] with the appropriate diamine. Yellow orange. Yield
0.230 g (75%). Ϫ 1H NMR (CDCl3): δ ϭ 14.10 (br. s, 2 H, H2),
8.31 (s, 2 H, H1), 7.77 (d, 4 H, Hb,c), 7.68 (s, 2 H, H6), 7.27 (d, 4
H, Ha,d), 6.53 (s, 2 H, H3), 4.17 (t, 4 H, OCH2), 3.69 (s, 4 H,
NCH2), 2.66 (t, 4 H, CH2). Ϫ C92H152N6O4 (1404.26): calcd. C
78.58, H 10.89, N 5.98; found C 78.88, H 11.24, N 5.80.
4-(n-Hexyloxy)-2-hydroxybenzaldehyde [I(6)]: KOH (0.81 g,
14.5 mmol) and subsequently an ethanolic solution (10 mL) of 1-
bromohexane (3.5 mL, 21.7 mmol) was added to a solution of 2,4-
dihydroxybenzaldehyde (2.0 g, 14.5 mmol) in ethanol (30 mL). The
resulting mixture was heated at reflux for 24 h, allowed to cool to
room temp. and 15 mL of H2O was added. The brownish solid
formed was filtered and washed with diethyl ether. The organic
layer was dried with Na2SO4 and the solvent removed under re-
duced pressure to afford a yellow oil, which was purified by column
chromatography on silica gel (diethyl ether/petroleum ether, 1:1
v:v). Yield 1.82 g (55%). Ϫ IR (KBr): ν˜ ϭ 1677 cmϪ1 (CHO). Ϫ
1H NMR (CDCl3): δ ϭ 11.49 (s, 1 H, H2), 9.70 (s, 1 H, H1), 7.42
(d, 1 H, H6), 6.53 (dd, 1 H, H5), 6.41 (d, 1 H, H3), 4.03 (t, 2
H, OCH2).
H2[L2(6,14)]: Prepared as described for H2[L1(6,14)] with the ap-
propriate diamine. Orange, yield 0.21 g (81%). Ϫ 1H NMR
(CDCl3): δ ϭ 14.30 (br. s, 2 H, H2), 8.28 (s, 2 H, H1), 7.77 (d, 4
H, Hb,c), 7.68 (s, 2 H, H6), 7.27 (d, 4 H, Ha,d), 6.52 (s, 2 H, H3),
4.17 (t, 4 H, OCH2), 3.69 (t, 4 H, NCH2), 2.66 (t, 4 H, CH2), 2.12
(m, 2 H, NCH2CH2). Ϫ C69H104N6O4 (1081.62): calcd. C 76.62, H
9.69, N 7.77; found C 76.70, H 9.70, N 7.75.
H2[L2(18,14)]: Prepared according to the procedure decribed for
H2[L1(6,14)] with the appropriate diamine. Yellow orange, yield
0.28 g (90%). Ϫ 1H NMR (CDCl3): δ ϭ 14.26 (br. s, 2 H, H2), 8.29
(s, 2 H, H1), 7.78 (d, 4 H, Hb,c), 7.69 (s, 2 H, H6), 7.27 (d, 4 H,
Ha,d), 6.53 (s, 2 H, H3), 4.17 (t, 4 H, OCH2), 3.69 (t, 4 H, NCH2),
2.66 (t, 4 H, CH2), 2.13 (m, 2 H, NCH2CH2). Ϫ C93H154N6O4
(1420.28): calcd. C 78.65, H 10.93, N 5.92; found C 78.60, H 10.70,
N 5.99.
2-Hydroxy-4-(n-octadecyloxy)benzaldehyde [I(18)]: Compound
I(18) was prepared according to the procedure decribed for I(6).
The white solid afforded was purified by recrystallization from
ethanol. Yield 2.86 g (50)%. M.p. 60°C. Ϫ IR (KBr): ν˜ ϭ 1676
1
cmϪ1 (CHO). Ϫ H NMR (CDCl3): δ ϭ 11.50 (s, 1 H, H2), 9.70
(s, 1 H, H1), 7.41 (d, 1 H, H6), 6.52 (dd, 1 H, H5), 6.41 (d, 1 H,
H3), 4.00 (t, 2 H, OCH2). Ϫ C25H42O3 (390.6): calcd. C 76.87, H
10.84; found C 76.67, H 10.84.
H2[L3(6,14)]: Prepared according to the procedure decribed for
H2[L1(6,14)] with the appropriate diamine. Dark red, yield 0.21 g
4-(n-Hexyloxy)-2-hydroxy-5-{[p-(n-tetradecyl)phenyl]azo}benzal-
dehyde [II(6,14)]: 4-(n-Tetradecylyl)aniline (1.3 g, 45.0 mmol) was
dissolved in water (15 mL) and HCl (1.12 mL, 13.49 mmol). The
solution was cooled to 0°C and an aqueous solution (8 mL) of
NaNO2 (0.3 g, 48.6 mmol) was added dropwise. I(6) (1 g,
45.0 mmol), dissolved in NaOH (5.17 mL, 2 ⁾ and ethanol (3 mL),
was added to the solution of the diazonium salt. The reaction mix-
ture was stirred for 1 h at 0°C and then allowed to warm slowly to
room temp. The brown solid formed was filtered, washed several
times with H2O and dissolved in dichloromethane. The organic
layer was dried with anhydrous Na2SO4, the solvent removed and
the crude product purified by column chromatography on silica
gel (diethyl ether/petroleum ether, 1:4 v:v). Further purification by
recrystallization from methanol afforded the pure product as a yel-
low solid. Yield 0.70 g (30%). M.p. 81°C. Ϫ IR (KBr): ν˜ ϭ 1653
1
(70%). Ϫ H NMR (CDCl3): δ ϭ 14.48 (br. s, 2 H, H2), 8.25 (s, 2
H, H1), 7.78 (d, 4 H, Hb,c), 7.70 (s, 2 H, H6), 7.27 (d, 4 H, Ha,d),
6.53 (s, 2 H, H3), 4.18 (t, 4 H, CH2), 3.46 (s, 4 H, NCH2), 2.66 (t,
4 H, OCH2), 1.32 [s, 6 H, C(CH3)2]. Ϫ C71H108N6O4 (1109.68):
calcd. C 76.85, H 9.81, N 7.50; found C 76.81, H 9.79, N 7.55.
H2[L3(18,14)]: Prepared according to the procedure decribed for
H2[L1(6,14)] with the appropriate diamine. Dark orange, yield
0.23 g (73%). Ϫ 1H NMR (CDCl3): δ ϭ 14.51 (br. s, 2 H, H2), 8.25
(s, 2 H, H1), 7.77 (d, 4 H, Hb,c), 7.70 (s, 2 H, H6), 7.27 (d, 4 H,
Ha,d), 6.53 (s, 2 H, H3), 4.17 (t, 4 H, OCH2), 3.46 (s, 4 H, NCH2),
2.66 (t, 4 H, CH2), 1.25 [s, 6 H, C(CH3)2]. Ϫ C95H158N6O4
(1448.34): calcd. C 78.78, H 5.80, N 11.00; found C 78.72, H 5.90,
N 11.50.
Ni[L1(6,14)] (1): A mixture of nickel(II) acetate tetrahydrate (0.02 g,
0.09 mmol) and an equimolar amount of H2[L1(6,14)] (0.1 g) in
ethanol (15 mL) was refluxed for 4 h. The dark red solid formed
was filtered off and the pure product was obtained by recrystalliza-
tion from chloroform/ethanol. Yield 0.09 g (86%). Ϫ 1H NMR
(CDCl3): δ ϭ 7.70 (d, 4 H, Hb,c), 7.55 (s, 2 H, H6), 7.32 (br. s, 2
H, H1), 7.19 (d, 4 H, Ha,d), 6.60 (s, 2 H, H3), 4.09 (t, 4 H, OCH2),
3.33 (s, 4 H, NCH2), 2.61 (t, 4 H, CH2). Ϫ C68H102N6NiO4
1
cmϪ1 (CHO). Ϫ H NMR (CDCl3): δ ϭ 14.62 (s, 1 H, H2), 9.81
(s, 1 H, H1), 7.93 (s, 1 H, H6), 7.81 (d, 2 H, Hb,c), 7.30 (d, 2 H,
Ha,d), 6.58 (s, 1 H, H3), 4.21 (t, 2 H, OCH2), 2.67 (t, 2 H, CH2). Ϫ
C33H50N2O3 (522.77): calcd. C 75.82, H 9.64, N 5.36; found C
75.78, H 9.60, N 5.15.
2-Hydroxy-4-(n-octadecyloxy)-5-{[4-(n-tetradecyl)phenyl]azo}-
benzaldehyde [II(18,14)]: Compound II(18,14) was prepared ac-
Eur. J. Inorg. Chem. 1999, 1367Ϫ1372
1371

I. Aiello, M. Ghedini, M. La Deda, D. Pucci, O. Francescangeli
FULL PAPER
(1126.29): calcd. C 72.52, H 9.13, N 7.46; found C 72.62, H 9.12,
N 7.46.
Acknowledgments
Ni[L1(18,14)] (2): Prepared according to the procedure decribed for
Ni[L1(6,14)] with the appropriate ligand. Brick red, yield 0.073 g
This work was partially supported by the Italian Ministero
1
(70%). Ϫ H NMR (CDCl3): δ ϭ 7.72 (d, 4 H, Hb,c), 7.57 (s, 2 H,
`
dellЈUniversita e della Ricerca Scientifica e Tecnologica
H6), 7.39 (d, 2 H, H1), 7.22 (d, 4 H, Ha,d), 6.62 (s, 2 H, H3), 4.09
(t, 4 H, OCH2), 3.37 (s, 4 H, NCH2), 2.63 (t, 4 H, CH2). Ϫ
C92H150N6NiO4 (1462.93): calcd. C 75.53, H 10.33, N 5.74; found
C 75.60, H 10.59, N 5.88.
(MURST), Consiglio Nazionale delle Ricerche (CNR) and
Regione Calabria (POP 94/99). We thank Dr. Francesco Ba-
rigelletti (Istituto FRAE-CNR, Bologna) for his help dur-
ing the (E)/(Z) photoisomerization experiments.
Ni[L2(6,14)] (3): Prepared according to the procedure decribed for
Ni[L1(6,14)] with the appropriate ligand. Brown, yield 0.057 g
(53%). Ϫ H NMR (CDCl3): δ ϭ 7.73 (d, 4 H, Hb,c), 7.57 (s, 2 H,
1
[1]
S. Xie, A. Natansohn, P. Rochon, Chem. Mater. 1993, 5,
H6), 7.25 (d, 6 H, Ha,d and H1), 6.60 (s, 2 H, H3), 4.10 (t, 4 H,
OCH2), 3.50 (t, 4 H, NCH2), 2.64 (t, 4 H, CH2), 1.89 (m, 2 H,
NCH2CH2). Ϫ C69H102N6NiO4 (1138.30): calcd. C 72.81, H 9.03,
N 7.38; found C 72.80, H 9.10, N 7.40.
403Ϫ411.
[2]
J. Newton, H. Walton, H. Coles, P. Hodge, Mol. Cryst. Liq.
Cryst. 1995, 260, 107Ϫ113.
[3]
O. Tsutsumi, T. Shiono, T. Ikeda, G. Galli, J. Phys. Chem. B
1997, 101, 1332Ϫ1337 and references therein.
Ni[L2(18,14)] (4): Prepared according to the procedure decribed for
[4]
S. Furumi, H. Akiyama, S. Morino, K. Ichimura, J. Mater.
Ni[L1(6,14)] with the appropriate ligand. Ochre yellow, yield
Chem. 1998, 8, 65Ϫ70.
[5] [5a]
1
0.095 g (92%). Ϫ H NMR (CDCl3): δ ϭ 7.73 (d, 4 H, Hb,c), 7.57
D. W. Bruce in: Inorganic Materials (Eds.: D.W. Bruce, D.
OЈHare), Wiley, Chichester, 1992. Ϫ [5b] J. L. Serrano, Metallo-
mesogens, VCH, Weinheim, 1996. Ϫ [5c] A. M. Giroud-Godquin
in Handbook of Liquid Crystals, vol. 2B (Eds.: D. Demus, J.
Goodby, G. W. Gray, H. W. Spiess, V. Vill), Wiley-WCH,
Weinheim, 1998.
(s, 2 H, H6), 7.25 (d, 6 H, Ha,d and H1), 6.60 (s, 2 H, H3), 4.10 (t,
4 H, OCH2), 3.50 (t, 4 H, NCH2), 2.64 (t, 4 H, CH2), 1.89 (m, 2
H, NCH2CH2). Ϫ C93H152N6NiO4 (1476.96): calcd. C 75.63, H
10.37, N 5.69; found C 75.73, H 10.46, N 5.70.
[6]
F. Neve, M. Ghedini, O. Francescangeli, S. Campagna, Liq.
Ni[L3(6,14)] (5): Prepared according to the procedure decribed for
Cryst. 1998, 24, 673Ϫ680.
[7]
Ni[L1(6,14)] with the appropriate ligand. Brown, yield 0.060 g
M. Ghedini, F. Neve, D. Pucci, Eur. J. Inorg. Chem. 1998,
1
(57%). Ϫ H NMR (CDCl3): δ ϭ 7.74 (d, 4 H, Hb,c), 7.59 (s, 2 H,
501Ϫ504.
[8]
H6), 7.26 (d, 4 H, Ha,d), 7.13 (s, 2 H, H1), 6.62 (s, 2 H, H3), 4.11
(t, 4 H, CH2), 3.26 (s, 4 H, NCH2), 2.65 (t, 4 H, OCH2), 1.48 (s, 6
H, C(CH3)2). Ϫ C71H106N6NiO4 (1166.37): calcd. C 73.11, H 9.16,
N 7.21; found C 73.40, H 9.25, N 7.32.
I. Aiello, M. Ghedini, F. Neve, D. Pucci, Chem. Mater. 1997,
9, 2107Ϫ2112.
[9]
D. Demus in Handbook of Liquid Crystals, vol. 1 (Eds.: D. De-
mus, J. Goodby, G. W. Gray, H. W. Spiess, V. Vill), Wiley-WCH,
Weinheim, 1998.
[10]
W. Weissflog in Handbook of Liquid Crystals, vol. 2B (Eds.: D.
Ni[L3(18,14)] (6): Prepared according to the procedure decribed for
Demus, J. Goodby, G. W. Gray, H. W. Spiess, V. Vill), Wiley-
Ni[L1(6,14)] with the appropriate ligand. Red, yield 0.097 g (94%).
WCH, Weinheim, 1998.
[11]
1H NMR (CDCl3): δ ϭ 7.74 (d, 4 H, Hb,c), 7.59 (s, 2 H, H6),
H. Rau in Photochromism (Eds.: H. Durr, H. Bouas-Laurent),
Ϫ
7.26 (d, 4 H, Ha,d), 7.12 (s, 2 H, H1), 6.62 (s, 2 H, H3), 4.10 (t, 4
H, CH2), 3.25 (s, 4 H, NCH2), 2.65 (t, 4 H, OCH2), 1.26 [s, 6 H,
C(CH3)2). Ϫ C95H156N6NiO4 (1505.01): calcd. C 75.82, H 10.45,
N 5.58; found C 75.73, H 10.75, N 5.83.
Elsevier, Amsterdam, 1990, chapter 4.
[12]
`
S. Di Bella, I. Fragala, I. Ledoux, M. A. Diaz-Garcia, T. J.
Marks, J. Am. Chem. Soc. 1997, 119, 9550Ϫ9957.
Received December 21, 1998
[I98445]
1372
Eur. J. Inorg. Chem. 1999, 1367Ϫ1372