Copper(II) and nickel(II) complexes of a tetradentate ligand containing an N,N'-bis(salicylidene)dodecane-1, 10-diamine core

Article abstract of DOI:10.1080/15421400802714098

The synthesis of mesomorphic Cu(II) and Ni(II) coordination compounds arising from a new series of tetradentate Schiff bases containing two salicylaldimine fragments connected by a very long spacer,-(CH2)12-, (H2Ln): L1=p-(C6H13O)-C6H4COO, L2=p-(C12H25O)-

Full text of DOI:10.1080/15421400802714098

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Copper(II) and Nickel(II)
Complexes of a Tetradentate
Ligand Containing an N,N′-
Bis(Salicylidene)Dodecane-1,
10-Diamine Core
Daniela Pucci a , Iolinda Aiello a , Anna Bellusci a ,
Giovanna Callipari a , Alessandra Crispini a & Mauro
Ghedini a
a Centro di Eccellenza CEMIF.CAL; LASCAMM, CR-
INSTM Unità della Calabria and LiCryl, CNR-INFM,
Dipartimento di Chimica , Università della Calabria ,
Italy
Published online: 18 Mar 2009.
To cite this article: Daniela Pucci , Iolinda Aiello , Anna Bellusci , Giovanna
Callipari , Alessandra Crispini & Mauro Ghedini (2009) Copper(II) and Nickel(II)
Complexes of a Tetradentate Ligand Containing an N,N′-Bis(Salicylidene)Dodecane-1,
10-Diamine Core, Molecular Crystals and Liquid Crystals, 500:1, 144-154, DOI:
10.1080/15421400802714098
To link to this article: http://dx.doi.org/10.1080/15421400802714098
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Mol. Cryst. Liq. Cryst., Vol. 500, pp. 144–154, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400802714098
Copper(II) and Nickel(II) Complexes of a Tetradentate
Ligand Containing an N,N0-Bis(Salicylidene)Dodecane-1,
10-Diamine Core
Daniela Pucci, Iolinda Aiello, Anna Bellusci,
Giovanna Callipari, Alessandra Crispini,
and Mauro Ghedini
`
Centro di Eccellenza CEMIF.CAL; LASCAMM, CR-INSTM Unita della
`
Calabria and LiCryl, CNR-INFM, Dipartimento di Chimica, Universita
della Calabria, Italy
The synthesis of mesomorphic Cu(II) and Ni(II) coordination compounds arising
from a new series of tetradentate Schiff bases containing two salicylaldimine
fragments connected by a very long spacer,-(CH2)12-, (H2Ln): L1 ¼ p-(C6H13O)-
C6H4COO, L2 ¼ p-(C12H25O)-C6H4COO, is described. The self-assembly and
liquid-crystalline properties of these complexes have been investigated by variable
temperature powder X-ray diffraction and the relationship between the global
molecular shape and the mesogenic performances is discussed. The reported Cu(II)
compounds are molecular materials which could be of interest for applications in
the field of magnetic molecule-based devices.
Keywords: Cu(II) and Ni(II) complexes; metallomesogens; salen-like Schiff bases
INTRODUCTION
Liquid crystals are intriguing functional materials, very important in
many applicative fields, including those requiring special electrooptic
devices [1]. The idea of introducing paramagnetic ions in liquid crystal-
line materials has been intensively pursued in the last two decades moti-
vated by several reasons: i) increase applications of one-dimensional
`
This work was partly supported by both the Ministero dell’Istruzione, dell’Universita
e della Ricerca through the Centro di Eccellenza CEMIF.CAL grant and by the Italian
PRIN founding n. 2006038447.
Address correspondence to Daniela Pucci, Centro di Eccellenza CEMIF.CAL; LASCAMM,
`
CR-INSTM Unita della Calabria and LiCryl, CNR-INFM, Dipartimento di Chimica,
`
Universita della Calabria, Arcavacata (CS) I-87036, Italy. E-mail: d.pucci@unical.it
144

Cu(II) and Ni(II) Complexes
145
magnets in order to repair defects in their structure, ii) realize alignment
or re alignment with a very small field, iii) obtain magneto-optic data
storage devices. The most of magnetic liquid crystals reported are based
on rare-heart ions which offer a large magnetic anisotropy [2], but a
number of paramagnetic mesogens have been synthesized also including
in the molecular skeleton a d metal as spin source which, coordinated to a
diamagnetic ligand, gives rise to a cylindrical, discotic or sphaero
symmetrical whole molecular shape depending on the position, nature
and number of substituents on the molecular core [3].
In particular, bidentate or tetradentate ligands derived from
salicylaldehyde and properly substituted anilines (Schiff bases), are
ligands which have been widely used in the synthesis of magnetic
metallomesogens. The first calamitic bis-N-(4-substituted)salicylaldi-
minato Cu(II) and Ni(II) complexes based on bidentate Schiff bases
of molecular structure I (Chart 1) described by Galyametdinov and
co-workers in 1984 [4], were followed by only few examples of Cu(II)
and VO(II) mesogens [5–7]. They all show a lamellar smectic meso-
morphism, whose investigations by EPR and magnetic susceptibility
measurements, enabled some relevant correlations between magnetic
properties and molecular structure, regarding, for example, the align-
ment of the molecules along an external magnetic field.
Though M(salen)-type complexes (salen) ¼ N,N0- ethylenebis(salicy-
lideneiminato) form a class of coordination compounds which are
strategic in material chemistry, due to their photophysical pro-
perties and their versatility in the structure and in the co-
ordination modes [8], there are very few examples of paramagnetic
CHART 1 Basic chemical structures of mesomorphic metal complexes of
Schiff bases.

146
D. Pucci et al.
metallomesogens based on this kind of tetradentate ligand. Starting
from 2-hydroxybenzaldehydes judiciously substituted in 5 position with
substituents bearing terminal chains of suitable length, it was possible
to synthesize Cu(II) and Ni(II) complexes with the alkylene spacer of
2 or 3 C atoms (salen and salpen respectively), for which the N,N-cis
metal coordination mode affords to a roughly square planar or square
pyramidal coordination geometry, depending on the nature of the metal
centre. These metallomesogens show a rod-like molecular shape II
(Chart 1) promoting calamitic mesomorphism (nematic and smectic
phases) but they have very high transition temperatures (higher than
200ꢀC) which prevented any possible applications [9–11].
Since molecular symmetry, packing and mesogenic properties are
dramatically influenced by the nature and=or the geometry of periph-
eral substituents, the effect of the introduction of lateral or unsym-
metrical terminal groups has been tested, but they did not find to be
relevant in affecting the melting behaviour [12].
On the contrary, the presence of very long Cn (n> 14) alkoxy chains at
the 4 position of the aromatic rings of salen or salpen-based Cu(II) and
VO(IV) complexes gives rise to the molecular shape III (Chart 1) which
promoted an intriguing (a bilayer mesophase or a lamello-columnar
phase) and relatively low melting mesomorphism, driven by the position
of the ring substitution as well as by the metal centres [13]. In order to
prepare new functional liquid crystals useful for molecule-based mag-
netic devices, we are interested in studying paramagnetic complexes
arising from tetradentate Schiff bases whose thermal, mesomorphic
and magnetic properties can be strongly modulated by little changes of
single tectons able to deeply influence the molecular geometry, the inter-
molecular-assembly and ultimately their performances as molecular
materials. In particular we have focused our investigations on the
modification of some structural elements of the prototypal M(salen-like)
molecular structure II in Chart 1: i) the length of the central diamine
spacer (A) by replacing the short central bridge for a flexible backbone
consisting of 12 carbon atoms and ii) the length and the position of the
peripheral flexible chains (B). In the present paper we report on the syn-
thesis, characterization and mesogenic properties of two tetradentate
Schiff bases, H2Ln and of their corresponding Cu(II) complexes. The
H2Ln like ligands featuring a short central bridge (e.g., 2–4 carbon
atoms) display a O,N,N,O cavity which can accomodate metal ions
requiring either a tetrahedral (i.e., Cu(II)) or a square planar (i.e., Ni(II))
coordination geometry. In order to test the influence of the metal centre
on the thermotropic properties induced by these H2Ln ligands on metal
ions demanding a different coordination environment the synthesis has
been worked up to the homologous Ni(II) compounds.

Cu(II) and Ni(II) Complexes
147
EXPERIMENTAL SECTION
Measurements
The infrared spectra in KBr were recorded on a Perkin-Elmer Spec-
trum One FT-IR spectrometer equipped for reflectance measurements.
The 1H NMR spectra were recorded on a Bruker WH-300 spectrometer
in CDCl3 solutions, with TMS as internal standard. Elemental analy-
ses were performed with a Perkin-Elmer 2400 analyzer.
The textures of the mesophases were studied with a Zeuss Axioscope
polarizing microscope equipped with a Linkam C0 600 heating stage.
The transition temperatures and enthalpies were measured on a Per-
kin-Elmer Pyris 1 Differential Scanning Calorimeter with a heating
and cooling rate of 10ꢀC=min. The apparatus was calibrated with indium.
Two or more heating=cooling cycles were performed on each sample.
The powder X-ray diffraction patterns were obtained using a
Bruker AXS General Area Detector Diffraction System (D8 Discover
with GADDS) with Cu Ka radiation; the high sensitive area detector
was placed at a distance from the sample of 20 cm and equipped with
a CalCTec (Italy) heating stage. The sampes were heated at a rate of
5.0ꢀC minꢁ1 to the appropriate temperature. Measuements were per-
formed by charging samples in Lindemann capillary tubes with inner
diameter of 0.5 mm.
Preparation
The preparation of 4-alkoxy-benzoic acid 4-formyl-3-hydroxy-phenyl
esters (I1 and I2) was accomplished following the synthesis reported
in literature [14]. Colours, yields, melting points, IR and 1H NMR data
and elemental analyses are as follows.
Synthesis of the Intermediates, In
4-hexyloxy-benzoic acid 4-formyl-3-hydroxy-phenyl ester (I1). White
solid. Yield: 0.87 g (38%). Mp: 92ꢀC. IR (KBr): n 2939–2868 (stretching
=
aliphatic CH), 1738 (ester stretching C O), 1656 (aldehydic stretching
1
C O), 1606, 1246 cmꢁ1. H NMR (CDCl3): d 11.25 (s, 1H, OH), 9.88 (s,
=
0
0
1H, CH O), 8.12 (d, 2H, J ¼ 8.64 Hz, H2 ,6 ), 7.61 (d, 1H, J ¼ 7.20 Hz,
=
0
0
H6), 6.98 (d, 2H, J ¼ 8.64 Hz, H3 ,5 ), 6.93 (d, 1H, J ¼ 1.92 Hz, H3),
6.89 (dd, 1H, J3,5 ¼ 1.92 Hz=J5,6 ¼ 7.20 Hz, H5), 4.05 (t, 2H, J ¼ 6.72 Hz,
OCH2), 1.87–0.89 (m, 11H, aliphatic protons) ppm. Anal. Calcd. for
C20H22O5: C, 70.16; H, 6.48%. Found: C, 70.01; H, 6.49.
4-dodecyloxy-benzoicacid 4-formyl-3-hydroxy-phenyl ester (I2). White
solid. Yield: 0.65 g (25%). Mp: 78ꢀC. IR (KBr): n 2956–2851 (stretching
=
aliphatic CH), 1735 (ester stretching C O), 1681 (aldehydic stretching

148
=
D. Pucci et al.
C O), 1608, 1254 cmꢁ1. 1H NMR (CDCl3):d 11.25 (s, 1H, OH), 9.88 (s, 1H,
0
0
CH O), 8.12 (d, 2H, J ¼ 8.54 Hz, H2 ,6 ), 7.61 (d, 1H, J ¼ 8.54 Hz, H6), 6.98
=
0
0
(d, 2H, J ¼ 8.54 Hz, H3 ,5 ), 6.91 (dd, 1H, J3,5 ¼ 2.44 Hz=
J5,6 ¼ 8.54 Hz, H5), 6.88 (d, 1H, J ¼ 2.44 Hz, H3), 4.05 (t, 2H, J ¼ 6.10 Hz,
OCH2), 1.82-0.88 (m, 23H, aliphatic protons) ppm. Anal. Calcd. for
C26H34O5: C, 73.21; H, 8.03%. Found: C, 71.93; H, 7.57.
Synthesis of H2Ln
N,N0-bis[(40-hexyloxy)benzoyloxy benzylidene]-1,12-diaminodode-
cane, H2L1. 1,12-Diaminododecane (0.12 g, 0.59 mmol) was added to a
hot solution of I1 (0.5 g, 1.17 mmol) in methanol (15 mL). The precipi-
tate, which immediately formed, was stirred under reflux for 4 h, then
filtered and washed with ethanol. The crude product was purified by
recrystallization from acetone and then dried in vacuo. Yellow solid.
Yield: 0.52 g (83%). IR (KBr): n 2921-2848 (stretching aliphatic CH),
ꢁ1
.
1H
=
=
1726 (stretching C O), 1637 (stretching C N), 1606, 1253 cm
=
NMR (CDCl3): d 14.13 (s, 2H, OH), 8.30 (s, 2H, CH N), 8.12 (d, 4H,
0
0
J ¼ 7.32 Hz, H20 ,6 ), 7.25 (d, 2H, J ¼ 7.20 Hz, H6), 6.96 (d, 4H,
0
J ¼ 7.32 Hz, H3 ,5 ), 6.79 (br s, 2H, H3), 6.71 (d, 2H, J ¼ 7.20 Hz, H5),
=
4.03 (t, 4H, J ¼ 7.32 Hz, OCH2), 3.585-3.55 (m, 4H, C NCH2), 1.84-
0.91 (m, 42H, aliphatic protons) ppm. Anal. Calcd. for C52H68N2O8:
C, 73.56; H, 8.07; N, 3.30%. Found: C, 73.45; H, 7.84; N, 3.66%.
N,N0-bis[(40-dodecyloxy)benzoyloxy benzylidene]-1,12-diaminodo-
decane, H2L2. The H2L2 ligand was prepared following the procedure
1
described for H2L1. Colour, yield, IR and H NMR data and elemental
analyses are as follows. Yellow solid. Yield: 0.52 g (88%). IR (KBr): n
=
2919–2849 (stretching aliphatic CH), 1727 (stretching C O), 1638
ꢁ1
(stretching C N), 1606, 1509, 1467, 1253 cm
.
1H NMR (CDCl3):
=
=
d 14.13 (s, 2H, OH), 8.31 (s, 2H, CH N), 8.12 (d, 4H, J ¼ 8.850Hz,
0
0
0
H2 ,6 ), 7.26 (d, 2H, J ¼ 7.89 Hz, H6), 6.96 (d, 4H, J ¼ 8.85Hz, H3 ,5 ),
6.79 (d, 2H, J ¼ 1.98Hz, H3), 6.71 (dd, 2H, J3,5 ¼ 1.98 Hz=J5,6 ¼ 7.89 Hz,
5
=
H ), 4.04 (t, 4H, J ¼ 6.87 Hz, OCH2), 3.58 (t, 4H, J ¼ 6.90 Hz, C NCH2),
1.85-0.85 (m, 66H, aliphatic protons) ppm. Anal. Calcd. for C64H92N2O8:
C, 75.55; H, 9.11; N, 2.75%. Found: C, 75.59; H, 9.08; N, 2.84%.
Synthesis of Complexes
NiL1. Nickel acetato tetrahydrate (0.044 g, 0.18 mmol) was added to
a hot solution of H2L1 (0.15 g, 0.18 mmol) in ethanol (15 mL). The
reaction mixture was stirred at reflux for 5 h and then cooled to room
temperature. The solid, collected by filtration, was washed with water,
ethanol and chloroform and then dried in vacuo. Green solid. Yield:
0.12 g (77%). IR (KBr): n 2924-2853 (stretching aliphatic CH), 1731

Cu(II) and Ni(II) Complexes
149
(stretching C O), 1608 (stretching C N), 1435, 1257 cmꢁ1. Anal. Calcd.
for C52H66N2O8Ni: C, 68.95; H, 7.34; N, 3.09%. Found: C, 69.26;
H, 7.14; N, 3.33%.
=
=
NiL2. The NiL2 complex was prepared following the procedure
1
described for NiL1. Colour, yield, IR and H NMR data and elemental
analyses are as follows. Green solid. Yield: 0.12 g (77%). IR (KBr): n
=
2922–2852 (stretching aliphatic CH), 1728 (stretching C O), 1618
(stretching C N), 1606, 1540, 1255 cmꢁ1. Anal. Calcd. for C64H90N2O8Ni:
=
C, 71.57; H, 8.44; N, 2.61%. Found: C, 71.89; H, 8.44; N, 2.91%.
CuL1. Copper(II) acetate monohydrate (0.029 g, 0.15 mmol) was
added to a hot solution of H2L1 (0.150 g, 0.15 mmol) in ethanol
(15 mL). The reaction mixture was stirred at reflux for 5 h and then
cooled to room temperature. The solid, collected by filtration, was
washed with water, ethanol and chloroform and then dried in vacuo.
Green solid. Yield: 0.12 g (76%). IR (KBr): n 2924-2853 (stretching
=
=
aliphatic CH), 1730 (stretching C O), 1606 (stretching C N), 1542,
1256 cmꢁ1. Anal. Calcd. for C52H66N2O8Cu: C, 68.58; H, 7.30; N,
3.08%. Found: C, 68.59; H, 7.12; N, 3.28%.
CuL2. The CuL2 complex was prepared following the procedure
1
described for CuL1. Colour, yield, IR and H NMR data and elemental
analyses are as follows Green solid. Yield: 0.12 g (78%). IR (KBr):
=
n 2923-2852 (stretching aliphatic CH), 1722 (stretching C O), 1624
(stretching C Ncmꢁ1), 1604, 1538, 1257. Anal. Calcd. for C64H90N2O8Cu:
=
C, 71.24; H, 8.41; N, 2.60%. Found: C, 71.51; H, 8.24; N, 2.91%.
RESULTS AND DISCUSSION
Synthesis
The synthetic protocol envisaged the use the 2,4-dihydroxybenzalde-
hyde as starting reactant, which was treated with the appropriate
n-alkoxy-benzoic acid and then condensed with 1,12-diaminododecane
in a 2:1 molar ratio to give the target compounds H2Ln in good yields
as summarized in Scheme 1.
1
The identity of all compounds was confirmed by H NMR and IR
spectroscopies and elemental analysis. In particular, in the IR spectra
ꢁ1
of H2Ln the C O band appeared at 1726 cm , the C N band is
detected at 1638 cmꢁ1 as well as a broad band is observed in the region
of the OH stretching. In 1H NMR spectra, recorded in CDCl3 solution,
is noticeable the signal attributable to the imminic hydrogen at
8.30 ppm and the phenolic hydrogen signal at 14.13 ppm. Reactions
=
=

150
D. Pucci et al.
SCHEME 1 Synthetic route to H2Ln ligands.
of the H2Ln ligands with an equimolar nickel(II) acetate tetrahydrate
or copper(II) acetate monohydrate were carried out in EtOH at reflux,
giving rise to the corresponding complexes in good yields. In the IR
spectra of the complexes the CN band, with respect to the organic
ligand, is shifted to the lower wave numbers upon coordination. On
the other hand, the disappearance of the OH absorption confirmed
the coordination in an analogous manner such as proposed for similar
tetradentate Schiff base ligands with alkyl backbones of eight carbon
atoms [15].
Liquid Crystalline Properties
The thermal behaviour of all synthesized species was characterized
using both polarized optical microscopy (POM) and differential
scanning calorimetry (DSC), while the nature of the mesophase was
confirmed using temperature-dependent powder X-ray diffraction
(XRD). All thermal data are summarized in Tables 1 and 2.
For both the H2Ln ligands, in spite of their transoid N,N confor-
mation (Scheme 1), the presence of a very long, flexible alkylene
spacer in the core structure, allows the appearance of liquid crystal-
line character, whatever the length of the terminal substituents
grafted on the aromatic rings connected to the salicylaldimine moiety
via an ester link. Both ligands, after crystal to crystal transitions,

Cu(II) and Ni(II) Complexes
151
TABLE 1 Thermal Behaviour of H2Ln Ligands
Compound
Transitiona
T=ꢀCb
DH=KJ molꢁ1
H2L1
Cr-Cr0
Cr0-N
N-I
I-N
N-Cr
Cr0-Cr0
Cr -Cr00
Cr00-SmC
SmC-N
N-I
I-N
N-SmC
SmC-Cr
64.7
113.1
133.7
133.1
77.8
17.4
43.0
7.7
9.0
28.9
18.5
38.0
15.7
1.7
8.3
9.0
1.9
65.2
H2L2
87.2
92.3
100.4
113.6
121.2
120.9
113.8
80.8
aCr: crystal; Sm: smectic; N: nematic, I: isotropic liquid.
bTemperature data as onset peak.
TABLE 2 Thermal Behaviour of MLn Complexes
Compound
Transitiona
T=ꢀCb
DH=KJ molꢁ1
NiL1
Cr-r0
60.8
239.7
264.1
98.4
4.8
42.3
20.7
13.3
30.0
0.7
2.8
4.8
31.5
12.6
Cr0-N
N-Idec
Cr-Cr0
Cr0-SmC
SmC-N
N- I
NiL2
175.7
186.6
195.2
198.3
139.1
104.4
79.4
I-N
N-SmC þ Cr
Cr-Cr0
Cr-Cr0
Cr0-SmC
SmC-N
N-I dec
Cr-Cr0
Cr0-N
N-I
I-N
N-Cr
Cr-Cr
CuL1
CuL2
200c
2.7
219c
232c
92.3
12.7
37.9
1.9
4.2
31.5
12.0
175.5
182.9
176.2
144.3
90.4
aCr: crystal; Sm: smectic; N: nematic, I: isotropic liquid.
c
bTemperature data as onset peak. Microscopic data.

152
D. Pucci et al.
showed mesomorphism typical of a calamitic material: a nematic
phase, with a typical schlieren texture for the lower homologue and
a smectic C phase followed by the nematic one, both identified with
a schlieren texture, for the higher homologue. As expected, the
melting and clearing points as well the temperature range decreased
with the elongation of the terminal chains.
After complexation, for all the resulting MLn derivatives, the
length-to-breadth ratio does not hamper the molecules to retain a
global rod shape and to preserve the calamitic mesomorphism of the
corresponding organic precursors, but the mesomorphism has been
found to be very sensitive to the metal atom. In particular, the Ni(II)
complexes retain the same mesophase sequence of the corresponding
organic precursor but the transition temperatures were increased
upon complexation. Moreover, comparing the mesomorphic behaviour
of H2L1 and the corresponding Ni(II) derivative NiL1, the metal com-
plexation broadens the mesomorphic range even if the relatively high
clearing was accompanied by partial decomposition preventing the
reproducibility and XRD measurements. With respect to the corres-
ponding ligands, the mesomorphic behaviour is reversed when the
Cu(II) replace the Ni(II) centre: indeed the Cu ion promote the appear-
ance and the disappareance of the smectic C phase for the lowest and
higher homologues, respectively while the clearing temperatures
slightly decrease with respect to the Ni(II) compounds.
The effect of the different metal atoms directly influenced also the
thermal stability which, in each series, decreased with increasing
the terminal aliphatic chains, but for the highest Cu(II) homologues
CuL2, becomes very narrow.
CONCLUSIONS
The aim of the work was to synthesize new paramagnetic metallo-
mesogens for molecule-based devices. Since for this kind of materi-
als the performances strongly depends on the molecular-assembly
structures, we have investigated the effect of the variation of single
tectons of metal complexes derived from salicylaldimine-based
ligands, the most widely used compounds for the synthesis of
paramagnetic metallomesogens, on the properties of the overall
molecular material.
In particular, a new series of tetradentate Schiff bases with an
extended central core has been designed and synthetized by introdu-
cing as alkyl spacer a backbone of 12 carbon atoms. Moreover, the
influence of the length and position of the peripheral chains has been
investigated by introducing two alkoxy substituents (6 or 12 carbon

Cu(II) and Ni(II) Complexes
153
atoms) in the unusual 4 position of the an aromatic rings connected to
the salicylaldimine moiety via an ester link.
For both ligands, according to a rod-like overall molecular shape,
calamitic mesomorphism is observed, as in similar dimeric salicylaldi-
mine-based mesogens [16] though the alkylene spacer is considerably
longer. As usual, increasing the length of the terminal chains, the
nematic phase is joined by a smetic C one.
After complexation, even if the archetypal structure of the M(Salen)
framework has been deformed and a further variation has been
induced through the different nature of the metal ion, the mesomorph-
ism has been retained in the MLn derivatives. The introduction of a
very long spacer in the central core of the Schiff bases, due to its
intrinsic flexibility, did not influence the rod like molecular architec-
ture of the metal complexes, allowing them to retain the global rod-
shape of the organic precursors. Moreover, the mutual orientation of
the terminal substituents plays an important role in the shape, the
molecular assembly and in the induction of liquid crystalline proper-
ties. Indeed, nevertheless the length to breath ratio has been modified
through complexation, the ribbon-like architecture drives the forma-
tion of mesomorphism and, together with the change of the nature
of the metal centre, influences only the kind of calamitic phase.
As a whole the mesomorphic properties of the described mesogens
evidence that the H2Ln ligands, with reference to the corresponding
M(II) complexes, reacting with Cu(II) form mesophases at tempera-
ture lower that with Ni(II), so suggesting that similar H2Ln species
featuring a large salicylaldimine spacer can tolerate M(II) ions
requiring either a tetrahedral or square planar coordination sphere
being, in particular, very useful for the preparation of Cu(II) meso-
gens. The synthesis of these Cu(II) containing materials with double
properties of liquid crystallinity and magnetism allow us to measure
their thermomagnetic properties and to find for them proper applica-
tions, for example as optically switchable molecular compounds or as
dopant in liquid crystalline mixture to improve their orientation
properties.
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