room-temperature columnar mesophases of nickel-bis(dithiolene) metallomesogens

Room-temperature columnar mesophases of nickel-bis(dithiolene)metallomesogens{

Sisir Debnath,a Hassan F. Srour,a Bertrand Donnio,*b Marc Fourmiguea and Franck Camerel*a

Received 22nd February 2012, Accepted 22nd February 2012

DOI: 10.1039/c2ra20332d

Discotic nickel dithiolene complexes are prepared by sulfuration of original benzil proligands

appended with gallate fragments carrying long carbon chains (n = 8, 12, 16), separated from the

dithiolene core by ester or amide linkers. The electronic properties of these functional nickel

dithiolene complexes were studied by cyclic voltammetry and UV-vis spectroscopy. The thermotropic

properties were investigated by a combination of POM observations, DSC analysis and X-ray

diffraction experiments. The neutral dithiolene complexes, denoted CnesterNi and CnamideNi, all

exhibit columnar phases over large temperature ranges including room temperature. CnesterNi

complexes form columnar mesophases of rectangular (pseudo-hexagonal) and hexagonal symmetry

whereas the amide linkage in CnamideNi complexes strongly stabilizes hexagonal columnar

mesophases far below room temperature, as illustrated by C12amideNi which displays a Colhmesophase from 218 up to +177 uC. The role of hydrogen bonding between the amide functions in

the stabilisation of the mesophases in CnamideNi complexes and their benzil precursors was

confirmed by IR spectroscopy. Moreover, the C8amideNi compound exhibits a cubic phase, stable

over y50 uC, from 155 to 203 uC. Models for the arrangements within the different columnar

mesophases are proposed and discussed.

Introduction

Supramolecular chemistry,1 in which non-covalent interactions

drive the formation of elaborate and exotic superstructures, is an

elegant way to organize small molecules into highly functional

architectures of potential interest in life and material sciences.2

Among the diversity of materials able to self-assemble into

organized superstructures at the micro- and macroscopic scale,

liquid-crystalline materials (LCs) continuously emerge as attrac-

tive candidates to form active layers, especially in the fields of

optics and electronics.3 The family of discotic liquid crystals is a

particularly attractive class of materials since they possess the

ability to self-organize into various ordered columnar structures.

The intriguing large and anisotropic charge mobilities arising

from the self-assembly of aromatic molecules into stacked

structures make these systems attractive for their applications

in photonic and optoelectronic devices,4 such as field-effect

transistors (FETs),5 organic light emitting diodes (OLEDs),6

organic light emitting transistors (OLETs)7 and solar cells.8

Additional advantages of columnar discotic liquid crystals are

their ease of processing (via solution techniques), the possibility

of alignment by shear forces or by application of electrical or

magnetic fields, and their capacity for self-healing.

Besides, metallomesogens are also fascinating materials

combining the fluidity and the self-organisation properties of

liquid crystals with the unique magnetic and electronic properties

of metal ions, which expand the range of technological

applications. Such materials thus permit to organize and orient

the specific properties of metal complexes into matrix displaying

fast orientational response to external stimuli at the nanoscale.

In addition, metal ions offer multiple coordination modes, which

can allow the emergence of novel molecular architectures or

mesophases. In this respect, the design and synthesis of discotic

metallomesogens prepared from protomesogenic ligands having

oxygen or nitrogen atoms for metal complexation are legion and

have been widely explored.9 Strangely however, metal-com-

plexation of sulfur-based ligands still remains scarce and only a

few liquid crystalline disc-like materials have been obtained with

functional dithiooxamides,10 dithiocarboxylates11 and dithiolene

derivatives.12

Metal-bis(dithiolene) and their derivatives are strong near-IR

absorbers with unique electrochemical properties. In their

neutral state, they display high absorption coefficients (around

30 000 M21 cm21) in a wide range of NIR absorption maxima

aSciences Chimiques de Rennes, Universite de Rennes 1, UMR CNRS6226, Campus de Beaulieu, 35042, Rennes, France.E-mail: [email protected] de Physique et Chimie des Materiaux de Strasbourg (IPCMS),Universite De Strasbourg-CNRS (UMR 7504), 23 rue du Loess, BP 43,67034, Strasbourg Cedex 2, France. E-mail: [email protected]{ Electronic supplementary information (ESI) available: Full syntheticdetails and characterizations of the benzil compounds and theircorresponding metal complexes as well as DSC traces and XRD patternsof all the compounds, not presented in the main text. See DOI: 10.1039/c2ra20332d

RSC Advances Dynamic Article Links

Cite this: RSC Advances, 2012, 2, 4453–4462

www.rsc.org/advances PAPER

This journal is � The Royal Society of Chemistry 2012 RSC Adv., 2012, 2, 4453–4462 | 4453

Publ

ishe

d on

10

Apr

il 20

12. D

ownl

oade

d on

22/

10/2

014

04:2

3:56

. View Article Online / Journal Homepage / Table of Contents for this issue

http://dx.doi.org/10.1039/c2ra20332d



http://pubs.rsc.org/en/journals/journal/RA

http://pubs.rsc.org/en/journals/journal/RA?issueid=RA002010

that are tunable from 900 to 1600 nm by the judicious

combination of metal centre and dithiolene substituents.13 The

only known liquid crystalline columnar mesophases were

reported by Otha for octasubstituted dithiolene nickel complexes

(n = 1–12), monotropic for the short chain-length homologues

(n = 2–4), and enantiotropic for longer ones (n . 5) (molecules

A).12

The identity of the mesophase was unequivocally determined

by X-ray diffraction to be Colh while high electron mobilities

were reported for these mesomorphic Ni-bis(dithiolene) com-

plexes with p-stacked columnar structures.14 Recently, we also

described the analogous but paramagnetic octasubstituted gold

dithiolene complex and demonstrated that the extent of

intermolecular magnetic interactions could be finely controlled

at the crystal-to-mesophase transition to generate marked

magnetic hysteresis.15 Since the pioneered work of Ohta, a few

attempts to develop new dithiolene ligands able to generate

mesophases after metal-complexation have been made, but

remained unsuccessful.16 In addition, the only known columnar

mesophases observed with the octasubstituted dithiolene com-

plexes12,15 are stable between 70 and 110 uC which render these

liquid crystalline materials unsuitable for practical optoelectro-

nic applications at room temperature.

Room-temperature liquid crystals are materials with melting

points below 25 uC. To decrease the melting point of a mesogenic

material, one strategy is to increase the volume fraction of the

long flexible carbon chains around the rigid core.9b,17 We have

tried to introduce 12 carbon chains around the nickel-bis(dithio-

lene) core (B) by the synthetic route described by Ohta11,12 for

molecules A but the syntheses of the benzil precursors carrying

long carbon chains in the 3,4,5-positions were found to be

difficult. In fact, the yield of benzil formation strongly depends

on (i) the position, (ii) the nature and (iii) on the number of

substituents on the starting benzaldehyde. Thus, in order to

introduce 12 carbon chains around the nickel-bis(dithiolene)

core and to eventually obtain room-temperature liquid crystal-

line materials, another strategy was explored here and gallate

derivatives, carrying long carbon chains in the 3,4,5-positions,

were grafted on preformed benzil precursors through ester or

amide bonds.

In the present work, we report the design and the successful

synthesis of new benzil protomesomorphic ligands substituted at

both ends by gallate derivatives through ester or amide linkers,

able to generate, after metal complexation, room-temperature

liquid crystalline metal-bis(dithiolene) complexes. Their electro-

nic properties have been determined by optical and electro-

chemical investigations. The thermotropic liquid crystalline

properties of the functional benzyl derivatives and their

corresponding nickel complexes have been investigated: all

nickel-bis(dithiolene) complexes are mesomorphic, forming

columnar mesophases over wide thermal ranges. An original

cubic mesophase was even observed for one of them. The

importance of the linker (ester, amide) on the thermal behavior

of both ligands and complexes will be discussed and packing

models in mesophases proposed.

Experimental

300.1 (1H) and 75.5 MHz (13C) NMR spectra were recorded on a

Bruker Avance 300 spectrometer at room temperature using

perdeuterated solvents as internal standards. FT-IR spectra were

recorded using a Varian-640 FT-IR spectrometer. UV-Vis-NIR

spectra were recorded using a Cary 5000 UV-Vis-NIR spectro-

photometer (Varian, Australia). Elemental analysis were per-

formed at the Centre Regional de Mesures Physiques de l9Ouest,

Rennes. Cyclic voltammetry were carried out on a 1023 M

solution of complex in CH2Cl2, containing 0.2 M nBu4NPF6 as

supporting electrolyte. Voltammograms were recorded using an

Autolab electrochemical analyser (PGSTAT 30, Ecochemie BV).

The reference electrode was SCE and the counter electrode was

graphite. Polarising optical microscopy images were taken with

a Nikon H600L polarising microscope. Differential scanning

calorimetry (DSC) was carried out by using a NETZSCH DSC

200 F3 instrument equipped with an intracooler. DSC traces

were measured at 10 uC min21 down to 230 uC. The XRD

patterns were obtained with a transmission Debye–Scherrer-like

geometry. A linear monochromatic Cu-Ka1 beam (l = 1.5405 A)

was obtained using a sealed-tube generator (900 W) equipped

with a bent quartz monochromator. The crude powder was filled

in Lindemann capillaries of 1 mm diameter and 10 mm wall-

thickness. In each case, exposure times were varied from 1 to 4 h.

The diffraction patterns were recorded with a curved Inel

CPS120 counter gas-filled detector linked to a data acquisition

computer (periodicities up to 60 A) and on image plates scanned

by STORM 820 from Molecular Dynamics with 50 mm

resolution (periodicities up to 100 A); the sample temperature

was controlled within ¡0.05 uC in the 20–200 uC temperature

range.

4-Methoxybenzaldehyde (99%) was purchased from Sigma

Aldrich and used as received. NiCl2 (99.9%), was purchased from

Alfa Aesar and used without further purification. DMI (99%),

P4S10 (98%) and hydrobromic acid (48%) were purchased from

Acros Organics. Anhydrous CH2Cl2 (Sigma-Aldrich) and

triethylamine (Alfa Aesar) were obtained by distillation over

P2O5 and KOH respectively. The reactions were followed using

thin layer chromatography (TLC) plates revealed by a UV-lamp

at 254 nm. All other reagents and materials from commercial

sources were used without further purification. Silica gel used in

chromatographic separations was obtained from Acros Organics

(Silica Gel, ultra pure, 40–60 mm). 4,49-Dihydroxybenzil,18

4,49-diaminobenzil19 and 3,4,5-trialkoxybenzoic acids20 were

prepared as previously described in the literature. Full synthetic

4454 | RSC Adv., 2012, 2, 4453–4462 This journal is � The Royal Society of Chemistry 2012

Publ

ishe

d on

10

Apr

il 20

12. D

ownl

oade

d on

22/

10/2

014

04:2

3:56

. View Article Online


details and characterizations of the Cnbenzilester and

Cnbenzilamide compounds (n = 8, 12, 16) and their correspond-

ing CnesterNi and CnamideNi nickel complexes are given in ESI{.

Results and discussion

Synthesis and characterisation

The synthetic route for the preparation of the CnesterNi and

CnamideNi complexes with n = 8, 12, 16 is shown in Scheme 1.

Starting 4,49-dihydroxybenzil18 and 4,49-diaminobenzil19 com-

pounds were synthesized according to reported procedures.

Cnbenzilester and Cnbenzilamide compounds with n = 8, 12 and

16 were readily obtained by reaction of the 4,49-dihydroxybenzil or

4,49-diaminobenzil with 3,4,5-trialkyloxybenzoic acid chloride

derivatives20 (n = 8, 12, 16) under anhydrous conditions using

triethylamine as base (Scheme 1). Purification of the compounds

was achieved by chromatography on silica gel followed by

recrystallization from CH2Cl2–MeOH. The ester and amide ligands

were isolated in good yield as light-yellow powders (C8benzilester,

55%; C12benzilester, 43%; C16benzilester, 60%; C8benzilamide, 51%;

C12benzilamide, 48%; C16benzilamide, 59%). 1H NMR spectra

obtained in CDCl3 of the Cnbenzilester compounds display a singlet

peak in the aromatic region (ca. 7.4 ppm), characteristic of the

aromatic protons on the gallate substituents and an AB system at

7.37–7.38 and 8.09–8.10 ppm which is attributed to the protons

localized on the benzil fragment. Formation of the ester bond is also

confirmed by the presence of a characteristic band at 1735 cm21 on

the infrared spectra. As for the amide compounds, in addition to

the singlet peak (7.04–7.06 ppm) and AB system (7.81–7.82 and

8.03–8.04 ppm) assigned to the gallate and benzil protons

respectively, another singlet was observed at 7.88–7.91 ppm,

corresponding to the NH proton. The formation of the amide

function was also confirmed by IR spectroscopy with the presence

of a characteristic CLO signal at 1640–1680 cm21.

The preparation of phenyl-substituted nickel dithiolene com-

plexes is most often based on sulfiding of the benzil moieties with

P4S10, followed by the hydrolysis of the intermediate phosphor-

ous thioester derivatives in the presence of a nickel salt such as

NiCl2?6H2O to directly afford the oxidized, neutral nickel

complex. This strategy was successfully used here for the

preparation of the CnesterNi and CnamideNi complexes with

n = 8, 12, 16, from the corresponding benzilester and benzilamide

ligands. 1,3-Dimethyl-2-imidazolidinone (DMI) was used as

solvent rather than dioxane, to improve the yield of the

syntheses.21 After purification by chromatography on silica gel

followed by crystallization from CH2Cl2–MeOH, the complexes

were isolated in good yields as dark-green powders (C8esterNi,

34%; C12esterNi, 58%; C16esterNi, 44%; C8amideNi, 44%;

C12amideNi, 46%; C16amideNi, 42%). The purity of the ester

complexes was unambiguously confirmed by 1H and 13C NMR

spectroscopy, IR spectroscopy and elemental analysis. After

sulfuration and metal complexation, the doublets from the AB

system, characteristic of the benzil fragment, shift upfield from

7.37–7.38 and 8.09–8.10 ppm to 7.17–7.20 and 7.50–7.52 ppm.

The complex formation is also ascertained by the complete

disappearance of the characteristic vibration band of the benzil

function (Ph–CO–CO–Ph) localized at 1672 cm21 on the IR

spectra of the Cnbenzilester compounds. In contrast, no clear

NMR spectra were obtained for the amide complexes, likely due

to a strong tendency of the complexes to aggregate in solution

and in the solid state through hydrogen bonding between the

amide fragments.22 Nevertheless, the appearance of a character-

istic dark green colour of the nickel-bis(dithiolene) complexes,

the disappearance of the peak characteristic of the benzil

function (Ph–CO–CO–Ph) located at 1654 cm21 in the IR

spectrum and the elemental analysis confirmed the formation of

the CnamideNi complexes with n = 8, 12, 16.

Electronic properties

Optical and electrochemical data for the CnesterNi and CnamideNi

complexes (n = 8, 12, 16) determined in solution are given in

Table 1. The absorption spectra of CnesterNi complexes (n = 8, 12,

Scheme 1 Syntheses of the Cnbenzilester and Cnbenzilamide ligands and corresponding nickel-bis(dithiolene) complexes (R = OCnH2n+1 with n = 8, 12

and 16).


Publ

ishe

d on

10

Apr

il 20

12. D

ownl

oade

d on

22/

10/2

014

04:2

3:56



16) show a main absorption band peak at 284 nm with a shoulder

at 308 nm (Fig. 1 and Table 1) in the UV region. These absorption

bands are assigned to p–p* transitions localized on the dithiolene

ligands. Another strong absorption band centred at 866 nm,

extending from 700 nm up to 1100 nm with high extinction

coefficients (e # 30 000 M21 cm21), is also observed in the near-

IR region and is characteristic of the neutral Ni-bis(dithiolene)

complexes. This low-energy absorption band is attributed to an

electronic transition from the HOMO (Lp) of b1u symmetry to the

LUMO (Lp*–adxy) with a metallic character of b2g symmetry.12b

Similarly, CnamideNi complexes (n = 8, 12, 16) display a strong

absorption band in the near-IR region centred at 920 nm,

extending from 750 nm up to 1100 nm. By comparison with

complexes A described by Ohta,12 the near-IR absorption band is

centred at even lower energy, 933 nm (Table 1).21b The observed

hypsochromic shift in the CnesterNi and CnamideNi complexes

(n = 8, 12, 16) can be understood by the electron-withdrawing

ability of the various connecting functions used here, that

increases on going from the ether (molecules A) to amide linkage

and from amide to ester linkage. It is noted that there is no

influence of the length of the carbon chains on the electronic

properties of the Ni complexes.

Electrochemical properties of nickel complexes were investi-

gated by cyclic voltammetry in CH2Cl2. The CnesterNi com-

plexes (n = 8, 12, 16) exhibit two reversible reduction processes

centred at 0.1 and 20.7 V (vs. SCE), corresponding to the

formation of the monoanionic and the dianionic species,

respectively (Fig. 2 and Table 1). The redox potentials are

weakly affected by the variation of the length of the hydrocarbon

chain. Comparison with molecule A reveals an anodic shift of the

redox potentials which, again, is due to the electron-withdrawing

ability of the ester linkage. Introduction of four electron-

withdrawing ester linkages renders the reduction of the complex

more facile than that of complex A with ether linkages. Cyclic

voltammograms of CnamideNi complexes (n = 8, 12, 16) also

display two reversible reduction processes centred at 0.0 V

(0 A 21) and 20.8 V (21 A 22) (vs. SCE). The reduction

potentials are slightly more cathodic than for the corresponding

CnesterNi complexes, a behaviour in line with a stronger

electron-withdrawing ability of the ester linkage. As for the

ester complexes, there is no real influence of the carbon chain

length.

Table 1 Optical and electrochemical properties of the CnesterNi and CnamideNi complexes (n = 8, 12, 16)

Complex la/nm ea/M21 cm21 E1/2(21/22)b/V E1/2(0/21)b/V E1/2(+1/0)b/V

C8esterNi 282 99 300 20.70 0.16 —867 32 200

C12esterNi 283 98 700 20.68 0.17 —867 38 700

C16esterNi 282 91 400 20.74c 0.07c —867 29 600

C8amideNi 313 85 600 20.78 0.02 —917 36 500

C12amideNi 311 117 800 20.79 0.0 —919 44 500

C16amideNi 312 98 900 20.8c 20.01c —919 27 300

Molecule A (n = 12)21b 933 31 300 21.33 20.10 0.915a Determined in dichloromethane solution (c y 1025 M). b In 0.1 M nBu4NPF6–dichloromethane at room temperature; scan rate, 100 mV s21;E1/2 = (Epa + Epc)/2; Epa and Epc are the anodic peak and the cathodic peak potentials, respectively. c Measured at 50 uC.

Fig. 1 (a) UV-vis-NIR spectra of CnesterNi and CnamideNi complexes

(n = 8, 12, 16) in dichloromethane (c y 1025 mol l21).

Fig. 2 Cyclic voltammograms of C16esterNi and C16amideNi in

dichloromethane (vs. SCE, v = 100 mV s21, electrolyte 0.2 M nBu4NPF6).


Publ

ishe

d on

10

Apr

il 20

12. D

ownl

oade

d on

22/

10/2

014

04:2

3:56



Thermal studies

The thermal behavior of the Cnbenzilester and Cnbenzilamide

proligands (n = 8, 12 and 16) and of their corresponding nickel

complexes was investigated by a combination of polarizing

optical microscopy (POM), differential scanning calorimetry

(DSC) and small-angle X-ray diffraction (SA-XRD). The

measured transition temperatures, enthalpy values and meso-

phase parameters are given in Table S1 in ESI{.

Cnbenzilester (n = 8, 12, 16). None of the Cnbenzilester

compounds are mesomorphic and reveal instead a classical

melting behaviour. All display a single reversible transition

associated with high enthalpies (y90 kJ mol21) and strong

supercooling effects (Fig. S1–S3, ESI{).

Cnbenzilamide (n = 8, 12, 16). In contrast to the above

Cnbenzilester compounds, all the benzilamide compounds

possess mesomorphic properties, evidencing the strong influence

of the linker nature on the thermal behaviour. DSC reveals the

presence of one endothermic peak with moderate enthalpy values

at 103, 112 and 103 uC, for the three compounds with n = 8, 12

and 16, respectively (Fig. 3a and Fig. S4 and S7 in ESI{), above

which the samples are isotropic (POM). On cooling from the

isotropic state, a homogeneous and fluid texture develops

between crossed-polarizers (developable cylindrical domains)

characteristic of a columnar phase (Fig. 4a).23 XRD confirmed

the occurrence of a single columnar mesophase below 103 uC

down to room temperature for the C8 derivative: the diffracto-

grams recorded displays two small-angle, not too intense

reflections, one relatively sharp corresponding to the funda-

mental reflection of a rectangular lattice (attributed to the (11)

and (20) reflections), and another slightly broadened peak, which

could be indexed as the (12) second-order reflection (Fig. S5,

ESI{).24 In addition, an intense and diffuse halo in the wide-

angle range is also observed, associated to the mean distance

between the aliphatic chains in their molten state (hch = 4.5–

4.6 A). The formation of a 2D columnar hexagonal mesophase

(Colh) is suggested for the other two benzilamide derivatives

between 90 and 112 uC (C12benzilamide, a = 36.1 A, at T =

100 uC, Table S1, ESI{ and Fig. 3a) and 40 and 100 uC(C16benzilamide, a = 41.2 A at 80 uC, Table S1 and Fig. S7,

ESI{), by combining both XRD measurements (Fig. S6 and S8,

ESI{) and POM observations (Fig. 4a, homeotropic areas), as

only one single and sharp small-angle peak, associated to the

fundamental reflection, and the broad wide-angle scattering were

observed. Below 40 uC, partial crystallization of C16benzilamide

was evidenced by the appearance of birefringence in the

homeotropic domains and striations of the pseudo-fan shapes

(see Fig. S7, ESI{).Fig. 3 DSC traces of (a) C12benzilamide and (b) C16esterNi (top: second

heating curve; bottom: first cooling curve).

Fig. 4 (a) C12benzilamide and (b) C12esterNi complex observed by

optical microscopy between crossed-polarizers at 105 and 115 uC,

respectively (crossed-polarizers symbolized by the white cross in the

corner of the picture).


Publ

ishe

d on

10

Apr

il 20

12. D

ownl

oade

d on

22/

10/2

014

04:2

3:56



Finally for the C12benzilamide compound, no clear texture

change was observed at 90 uC, and XRD confirmed the existence

of a low-temperature Colr phase down to room temperature (no

phase transition down to 0 uC) (Fig. 5a). The pattern exhibits a

series of four sharp, small-angle peaks that can either be indexed

as (11), (20), (22), (42) or as the (20), (11), (40), (60) reflections of

a rectangular lattice with c2mm plane group (both solutions are

equiprobable and compatible with the centred lattice, Table S1,

ESI{).24 These peaks are also associated with a broad signal at

4.6 A (hch) confirming the molten state of the alkyl chains as

found for the high-temperature Colh.

CnesterNi (n = 8, 12, 16). The C8 complex, C8esterNi, displays

two reversible transitions on the DSC curves at 89 and 142 uC(Fig. S9, ESI{). On cooling from the isotropic liquid, the

formation of a texture characteristic of columnar mesophases

with homeotropic domains and pseudo-fan shapes is clearly

observed between 142 and 89 uC. Below 89 uC, no clear textural

change could be observed but the compound remained fluid, an

indication of another mesomorphic state. XRD confirmed the

existence of two mesophases, namely a high-temperature Colhphase and a Colr (with a pseudo-hexagonal symmetry) at lower

temperature (Table S1, ESI{). The three sharp reflections

observed at 120 uC, in square spacing ratio 1 : !7 : 3, were

respectively indexed as the (10), (21) and (30) reflections of a

hexagonal lattice, with a parameter of 38.8 A (Fig. S10 and

Table S1, ESI{). The large number of small-angle reflections

observed in the lower temperature mesophase (Fig. S11 and

Table S1, ESI{), consistent with a substantial symmetry breaking

(e.g. reflections h + k = 2n + 1), is typical for a pseudo-hexagonal

mesophase with non-centered rectangular p2gg lattice.25 In the

wide angle region, a broad halo centred at 4.5 A (hch) confirms

the liquid crystalline nature of the phases. Two additional signals

(thereafter labelled hM and h0) centred at 4.05 and 3.55 A,

respectively were also observed in the wide-angle region. The low

intensity broad peak at 3.55 A, which is classically observed in

the few reported metal-bis(dithiolene) mesophases,11,12 is attrib-

uted to the stacking distance between the NiS4 cores (h0). The

small peak at 4.05 A (hM) is likely attributed to some residual

interactions between the benzyl-ester arms, which are also

probably slightly rotated from the Ni-S4 mean plane for steric

constraints.

The DSC traces of the C12esterNi complex displays three

reversible transitions located at 210, 90 and 125 uC (Fig. S12,

ESI{). The broad transition observed at 210 uC is attributed to

the crystallization, whereas above 125 uC, the compound is

isotropic. Between 210 and 125 uC, texture characteristic of

columnar mesophases were observed (Fig. 4b). No clear texture

change was observed around 90 uC. XRD confirmed the

existence of two mesophases, unambiguously characterized as

Colh and Colr phases; the hexagonal symmetry was deduced for

the upper phase from the presence of five sharp small-angle

reflections in the expected ratio (Fig. 5b), and the rectangular

symmetry p2gg (Fig. S13, ESI{) was evidenced by the presence of

additional peaks, consistent with the re-organization of the local

packing of the columns, as C8esterNi.

Finally, the C16esterNi complex displays a broad and energetic

thermal transition at 46 uC and a second weak and broad

transition centered at 82 uC (Fig. 3b). The low-temperature

transition is attributed to a crystal-to-mesophase transition

whereas the high-temperature transition corresponds to the

mesophase-to-isotropic liquid transition. In this temperature

interval, a fluid texture characteristic of columnar phase is

observed, the hexagonal nature of which was confirmed by XRD

(Table S1 and Fig. S14, ESI{).

These results highlight that complexation of a metal center by

two non-mesogenic ester ligands leads to the formation of a

mesogenic molecules that can form one (n = 16), and even two

(n = 8, 12) stable columnar mesophases. Mesophase stability is

increased as the pendant aliphatic chain-lengths are decreased

and, interestingly, room-temperature columnar mesophases

Fig. 5 XRD Patterns of C12benzilamide at 60 uC in the Colr phase,

C12esterNi at 100 uC in the Colh phase and C8amideNi at 160 uC in the

cubic phase respectively.


Publ

ishe

d on

10

Apr

il 20

12. D

ownl

oade

d on

22/

10/2

014

04:2

3:56



containing redox-active metal-bisdithiolene cores are isolated

here for the first time. Now, one can wonder what will be the

effect of the introduction of an amide linker on the thermotropic

properties of the nickel-bisdithiolene complexes obtained after

metal complexation by the mesogenic benzil Cnbenzilamide

proligands?

CnamideNi (n = 8, 12, 16). As for the aforedescribed ester

series, all the discotic CnamideNi complexes exhibit liquid-

crystalline properties, which are stable over broad temperature

ranges. POM observations reveal that C8amideNi complex

remains in highly viscous birefringent state from room tempera-

ture up to the decomposition temperature around 230 uC. DSC

traces display a broad and reversible transition around 150 uC(Fig. S15, ESI{) but, since the isotropisation point can not be

reached, no clear texture was developed and no clear textural

changes could be detected between the two mesomorphic states.

The low-temperature phase was unambiguously assigned to a

Colh phase, as deduced by the presence of eight sharp small-

angle reflections in the XRD pattern, easily indexed within the

hexagonal symmetry (Fig. S16, Table S1, ESI{). Unexpectedly,

the high-temperature mesophase was assigned as a cubic phase,

not yet observed to date with metal-bis(dithiolene) complexes.

The XRD pattern measured at 160 uC indeed displays a series of

nine sharp peaks in the low-angle regions in perfect accordance

with a cubic lattice symmetry with the Im3-m space group.26

Along with these reflections, an intense halo corresponding to

the molten state of the chains (hch = 4.5 A) and a weak halo

(more or less visible) around 3.5 A (h0) corresponding to short-

range p–p stacking interactions (Fig. 5c, Table S1, ESI{) were

also observed.

Finally, both higher homologs C12amideNi and C16amideNi

display a broad and reversible transition at 218 and 30 uC,

respectively, attributed to the melting of a crystalline phase (Fig.

S17 and S19, ESI{) and a second weak and reversible transition

at 177 and 115 uC, respectively, corresponding to the isotropisa-

tion of the compounds. Between these temperature intervals,

XRD patterns confirm the formation of a columnar hexagonal

phase. For C12amideNi, the five sharp peaks in the low-angle

region can be indexed in a 2D hexagonal lattice (a = 42.7 A,

Table S1, Fig. S18, ESI{). For C16amideNi, only one peak has

been detected in the small-angle region on the XRD patterns

measured between 30 and 115 uC (Fig. S20, ESI{) but on the

basis of the POM observations, and thanks to optical textures

reminiscent of hexagonal phase, the mesophase can nevertheless

be safely assigned as Colh.

The thermal behaviours of the CnesterNi and CnamideNi

complexes with n = 8, 12, 16 are summarized in Table 2 and in

Fig. 6 (see ESI{ for full details). All the complexes remain in

liquid-crystalline states over wide thermal ranges, especially at

room temperature (except C16 complexes), with a constant

decrease of the clearing temperature as the chain length is

increased.27 Such room-temperature columnar mesophases,

containing metal-bisdithiolene cores, potentially able to effi-

ciently carry charges when stacked into columnar structures, can

be of great interest for applications in electronic devices using

room-temperature liquid crystalline properties. It can also be

noticed that the introduction of amide functions leads to a

stronger stabilization of the hexagonal columnar phase with a

decrease of the melting points and an increase of the isotropiza-

tion points, when compared to the CnesterNi ester compounds,

likely due to the formation of additional hydrogen bonding

networks (vide infra). At room temperature, CnesterNi com-

pounds allow isolation of rectangular columnar phases whereas

CnamideNi compounds form hexagonal columnar phases. It is

interesting to note that C12amideNi compound is in a hexagonal

columnar mesophase over a temperature range of 195 uC from

218 up to 177 uC. In the series of CnamideNi complexes, a

original cubic phase is observed at high temperature above the

Colh phase.

Infrared spectra of the mesophases

The strong stabilization of the columnar phases observed with

the amide compounds, when compared with the ester ones, is

certainly induced by the formation of an intermolecular

hydrogen bonding network. To address this point, the amide

functions were studied by FT-IR spectroscopy, a powerful tool

to probe hydrogen bonding and ordering of hydrocarbon chains.

FTIR measurements performed in the room-temperature Colh or

Colr mesophases of the precursor Cnbenzilamide (n = 8, 12)

compounds as well as on the CnamideNi (n = 8, 12) complexes at

25 uC, after heating at 118, 120, 160 and 180 uC respectively,

confirm that the molecular organization is stabilized by

hydrogen-bonding interactions, as clearly evidenced by the nNH

and nCO stretching vibrations that lie respectively at 3282–3300

and 1652–1653 cm21. Note that corresponding values for the free

amides are at 3400 cm21 for nNH and around 1680 cm21 for

nCO.28 The presence of single nCO and nNH stretching vibrations

on the FTIR spectra also indicate the formation of a hydrogen-

bonded network involving all amide functions. The frequencies

of the bands due to CH2 antisymmetric and symmetric modes

[na(CH2) and ns(CH2)] of the alkyl chains appear at ca. 2920–

2924 and ca. 2851–2853 cm21 in the mesophase and also indicate

that the hydrocarbon chains are all in trans conformation.29

These trans peaks shift indeed to #2926 and 2855 cm21

respectively, if the population of gauche form in the alkyl chains

increases.30

Packing study of the liquid crystalline phases

The mesomorphism of all the mesogens described here is

essentially characterized by the formation of columnar meso-

phases, and therefore the molecules are likely to stack on top of

each other in order to generate columns with circular cross-

sections (as in Colh phase) or non-circular cross-sections

(reduced symmetry as in Colr phase).24 The columnar packing

is characterized by the columnar cross-section, Scol, and the

stacking periodicity h along the columnar axis, both parameters

being analytically linked through the relation h 6 Scol = Z 6VM, where Z is the number of molecules within a columnar

stratum (disc) h-thick and VM the molecular volume. With the

Cnbenzilamide precursors, the formation of columns requires the

association of at least two mesogenic molecules, likely in a side-

by-side type as classical hexacatenar materials,24 to generate a

‘‘supramolecular’’ discotic slice h-thick that stacks into columns

(Fig. 7, left). Note here that benzil molecules can adopt either a

transoid or cisoid conformation: in solution, the transoid form


Publ

ishe

d on

10

Apr

il 20

12. D

ownl

oade

d on

22/

10/2

014

04:2

3:56



must be the predominant one in order to minimize dipolar

interactions, whereas in columnar mesophases, pairing of the

cisoid forms will allow a better space filling of the discs and the

introduction of stabilizing dipolar interactions. The absence of

short-range periodicities on the XRD patterns of the benzilamide

precursors, except the carbon chain interactions, indicates indeed

that there is no interaction between the benzil cores and that the

columns are generated by a continuum of molecules in a fluid

state, and consequently the average thickness of such a

supramolecular aggregate is given by hch. In fact, aggregation

may take place in such a way that the molecules contained in a

‘‘slice’’ are not in the same plane, but just point their tips towards

the column core without the need to form discrete discs. On the

other hand, in the case of the nickel complexes, due to their disc-

like shape, only one mesogen is necessary to form a columnar

slice (Fig. 7, right). The reduction of the phase symmetry of the

planar arrangements (from hexagonal to pseudo-hexagonal) of

the columns results from the combination of a more or less

pronounced tilt of the molecular plane with respect to the lattice

plane. The tilt, which increases with temperature decrease,

concomitantly hinders rotation about the columnar axis, and

freezes the different orientations (random orientations) of the

elliptical projection of the columnar cross sections onto the

lattice plane. The presence of a stacking distance h0 with the Ni

Table 2 Thermal behaviour and X-ray characterization of the liquid-crystalline phasesa

Compound State T/uC (DH/kJ mol21) Mesophase parameters

C8esterNi Heating: Colr 88.5b Colh 142 (10.0) Iso Colh-p6mm (T = 120 uC)Cooling: Iso 139 (29.7) Colh 87b Colr a = 38.8 A, Sh = 1305 A2, Z y 1

Colr-p2gg (T = 80 uC)a = 68.42 A, b = 39.54 ASr = 1351 A2, Z y 1.1

C12esterNi Heating: Cr 210b Colr 90 (10.3) Colh 125 (9.7) Iso Colh-p6mm (T = 100 uC)Cooling: Iso 120 (28.4) Colh 86.5 (211.0) Colr 215b Cr a = 42.67 A, Sh = 1577 A2, Z y 1

Colr-p2gg (T = 40 uC)a = 74.8 A, b = 43.2 ASh = 1615 A2, Z y 1.05

C16esterNi Heating: Cr 46 (132.5) Colh 82 (6.6) Iso Colh-p6mm (T = 60 uC)Cooling: Iso 79 (24.3) Colh 37 (2138.4) Cr a = 46.36 A, Sh = 1861 A2, Z y 1

C8amideNi Heating: Colh 156 (10.0) Cub 230 (decomp.) Colh-p6mm (T = 100 uC)Cooling: Cub 140 (28.2) Colh a = 38.7 A, Sh = 1295.8 A2, Z y 1

Cub-Im3-m (T = 160 uC)

a = 47.3 A, Vcub y 106 A3, Nagg y 20–24C12amideNi Heating: Cr 218b Colh 177 (4.5) Iso Colh-p6mm (T = 100 uC)

Cooling: Iso 155 (24.8) Colh 220b Cr a = 42.7 A, Sh = 1580.8 A2, Z y 1C16amideNi Heating: Cr 30 (155.4) Colh 115 (3.1) Iso Colh-p6mm (T = 50 uC)

Cooling: Iso 82 (22.3) Colh 23 (2149.2) Cr a = 48.0 A, Sh = 1998.5 A2, Z y 1a Cr, crystalline phase; Iso, isotropic liquid; Colh, hexagonal columnar mesophase; Colr, rectangular columnar mesophase; Cub, cubic phase;decomp. = decomposition temperature (evaluated by POM observations); a and b are the lattice parameters of the mesophases; Sh and Sr are thecolumnar cross-section area of hexagonal and rectangular phases, and Vcub, the volume of the cubic lattice, respectively; Z is the number ofcomplexes per columnar slice of thickness h (h = h0); Nagg is the number of complexes within the cubic lattice. See ESI for full details. b Broadtransition.

Fig. 6 Thermal behaviour of CnesterNi and CnamideNi complexes as a

function of chain length (n = 8, 12, 16) (room temperature (RT) = 25 uC).Fig. 7 Suggested molecular organisation of the Cnbenzilamide (n = 8,

12, 16) precursors (two molecules per plateau) (left) and of the nickel

complexes CnesterNi or CnamideNi (one molecule per plateau) (right).


Publ

ishe

d on

10

Apr

il 20

12. D

ownl

oade

d on

22/

10/2

014

04:2

3:56



complexes, although very weak and partially hidden by the

strong scattering of the alkyl chains, clearly indicates some short-

range stacking of the extended cores. The columns are generated

by the stacking of the discs and the mutual organisation of these

columns into a hexagonal or rectangular lattice leads to the

formation of the mesophase. An alternated p/2 stacking along

the columnar axis likely occurs between two consecutive slices to

optimize molecular packing within the mesophase (Fig. 7), but

obviously is not correlated over too long distances.

Thermotropic cubic phases, as ordered three-dimensional

supramolecular edifices, with body-centered space groups are

not so common in thermotropic liquid crystals,17,31 and their

structure is not well understood yet. It may consist, either of

bicontinuous, interwoven rod-networks32 or alternatively, of a

discontinuous three-dimensional arrangement of pseudo-spheri-

cal micelles located at the nodes of the cubic lattice.33 The

formation of a bicontinuous cubic structure seems more reason-

able since it appears difficult to arrange such discoid complexes

into micelles. The generation of a bicontinuous cubic structure

would thus result from the perturbation at short range of the

stacking, consequent to substantial molecular conformational

changes, forcing the molecules to develop interactions in the

three spatial directions.

Conclusion

Following the original dialkoxy derivatives described more than

twenty years ago, we have identified here two new families of

protomesogenic ligands with added ester or amide functionalities.

After sulfuration and metal complexation of these rationally

designed benzil proligands, original functional metallomesogens

with a nickel bis(dithiolene) core have been isolated. They all

exhibit columnar phases over large temperature ranges especially

around room temperature. CnesterNi complexes form columnar

mesophases of rectangular and hexagonal symmetry whereas the

amide linkage in CnamideNi complexes strongly stabilize hexago-

nal columnar mesophases down to room temperature, as

illustrated by C12amideNi which display a Colh mesophase from

218 up to + 177 uC. The role of hydrogen bonding between the

amide functions in the stabilisation of the mesophases was

confirmed by IR spectroscopy. Furthermore, with the

C8amideNi compound, a cubic phase, stable over y50 uC, from

155 to 203 uC, and never observed up to now with metal-

bis(dithiolene), was clearly identified. The most probable model

suggests that the short-range molecular stacks would perturb the

long-range 2D supramolecular arrangement, and generate instead

the formation of two distinct, interdigitated cylindrical 3D

networks.

The strategy adopted here has allowed for the formation of

columnar mesophases of hexagonal or rectangular symmetry at

room temperature. Such materials, also strongly absorbing in the

NIR region, can be of potential interest, as active layers, in

optoelectronic applications. Future work will be first devoted to

the measurements of charge motilities in these new systems.

Acknowledgements

Financial support from the Region Bretagne (Post doctoral

grant to S. D.) and from the University Rennes 1 (Incitative

Action 2010) is gratefully acknowledged. BD thanks the CNRS-

Universite de Strasbourg for support and Dr Benoıt Heinrich for

fruitful discussions.

References

1 J.-M. Lehn, Supramolecular Chemistry, Wiley-VCH, New-York 1995.2 (a) G. K. Such, A. P. R. Johnston and F. Caruso, Chem. Soc. Rev.,

2011, 40, 19–29; (b) S. Yamamichi, Y. Jinno, N. Haraya, T. Oyoshi,H. Tomitori, K. Kashiwagi and M. Yamanaka, Chem. Commun.,2011, 47, 10344–10-346; (c) F. J. M. Hoeben, P. Jonkheijm, E. W.Meijer and A. P. H. J. Schenning, Chem. Rev., 2005, 105, 1491–1546;(d) T. Kato, Science, 2002, 295, 2414–2418; (e) I. W. Hamley, Angew.Chem., Int. Ed., 2003, 42, 1692–1712.

3 (a) M. Grell and D. D. C. Bradley, Adv. Mater., 1999, 11, 895–905;(b) Y. Shimizu, K. Oikawa, K.-I. Nakayama and D. Guillon,J. Mater. Chem., 2007, 17, 4223–4229; (c) T. Kato, N. Mizoshita andK. Kishimoto, Angew. Chem., Int. Ed., 2006, 45, 38–68.

4 (a) S. Laschat, A. Baro, N. Steinke, F. Giesselmann, C. Hagele, G.Scalia, R. Judele, E. Kapatsina, S. Sauer, A. Schreivogel and M.Tosoni, Angew. Chem., Int. Ed., 2007, 46, 4832–4887; (b) S. Sergeyev,W. Pisula and Y. H. Geerts, Chem. Soc. Rev., 2007, 36, 1902–1929;(c) S. Kumar, Chem. Soc. Rev., 2006, 35, 83–109; (d) W. Pisula, M.Zorn, J. Young, C. K. Mullen and R. Zentel, Macromol. RapidCommun., 2009, 30, 1179–1202; (e) B. R. Kaafarani, Chem. Mater.,2011, 23, 378–396; (f) S. Kumar, Liq. Cryst., 2009, 36, 607–638.

5 (a) A. M. van de Craats, N. Stutzmann, O. Bunk, N. N. Nielsen, M.Watson, K. Mullen, H. D. Chanzy, H. Sirringhaus and R. H. Friend,Adv. Mater., 2003, 15, 495–499; (b) W. Pisula, A. Menon, M.Stepputat, I. Lieberwirth, U. Kolb, A. Tracz, H. Sirringhaus, T.Pakula and K. Mullen, Adv. Mater., 2005, 17, 684–689; (c) T.Kitamura, S. Nakaso, N. Mizoshita, Y. Tochigi, T. Shimomura, M.Moriyama, K. Ito and T. Kato, J. Am. Chem. Soc., 2005, 127,14769–14775; (d) J.-P. Hong, M.-C. Um, S.-R. Nam, J.-I. Hong andS. Lee, Chem. Commun., 2009, 310–312.

6 (a) U. Mitschke and P. Bauerle, J. Mater. Chem., 2000, 10,1471–1507; (b) T. Hassheider, S. A. Benning, H.-S. Kitzerow,M.-F. Achard and H. Bock, Angew. Chem., Int. Ed., 2001, 40,2060–2063.

7 (a) M. A. Loi, E. Da Como, R. Zamboni and M. Muccini, Synth.Met., 2003, 139, 687–690; (b) M. A. Loi, E. Da Como, F. Dinelli, M.Murgia, R. Zamboni, F. Biscarini and M. Muccini, Nat. Mater.,2004, 4, 81–85.

8 (a) B. A. Greeg, M. A. Fox and A. J. Bard, J. Phys. Chem., 1990, 94,1586; (b) A. M. Fox, J. V. Grant, D. Melamed, T. Torimoto, C.-Y.Liu and A. J. Bard, Chem. Mater., 1998, 10, 1771; (c) L. Schmidt-Mende, A. Fechtenkotter, K. Mullen, E. Moons, R. H. Friend andJ. D. MacKenzie, Science, 2001, 293, 1119–1122; (d) W. Kubo, S.Kambe, S. Nakade, T. Kitamura, K. Hanabusa, Y. Wada and S.Yanagida, J. Phys. Chem. B, 2003, 107, 4374–4381.

9 (a) B. Donnio, D. Guillon, D. W. Bruce and R. Deschenaux,Metallomesogens, in Comprehensive Coordination Chemistry II: FromBiology to Nanotechnology, ed. J. A. McCleverty and T. J. Meyer,Elsevier, Oxford, UK 2003, vol. 7 (ed. M. Fujita and A. Powell), ch.7.9, pp. 357–627; (b) R. W. Date, E. Fernandez Iglesias, K. E. Rowe,J. M. Elliott and D. W. Bruce, Dalton Trans., 2003, 1914–1931.

10 (a) M. C. Aversa, P. Bonaccorsi, D. W. Bruce, F. Caruso, P.Giannetto, S. Lanza and S. Morrone, Inorg. Chim. Acta, 1997, 256,235–2415; (b) M. C. Aversa, P. Bonaccorsi, D. W. Bruce, F. Caruso,B. Donnio, P. Giannetto, D. Guillon, S. Lanza and S. Morrone, Mol.Cryst. Liq. Cryst. Sci. Technol., Sect. A, 2000, 348, 53–64.

11 (a) K. Ohta, H. Ema, I. Yamamoto and K. Matsuzaki, Liq. Cryst.,1988, 3, 1671–1687; (b) K. Ohta, Y. Morizumi, H. Ema, T. Fujimotoand I. Yamamoto, Mol. Cryst. Liq. Cryst., 1991, 208, 55–63.

12 (a) K. Ohta, H. Hasebe, H. Ema, T. Fujimoto and I. Yamamoto,J. Chem. Soc., Chem. Commun., 1989, 1610–1611; (b) K. Ohta, H.Hasebe, H. Ema, M. Moriya, T. Fujimoto and I. Yamamoto, Mol.Cryst. Liq. Cryst., 1991, 208, 21–32; (c) K. Ohta, H. Hasebe, M.Moriya, T. Fujimoto and I. Yamamoto, Mol. Cryst. Liq. Cryst.,1991, 208, 33–41; (d) K. Ohta, Y. Inagaki-Oka, H. Hasebe and I.Yamamoto, Polyhedron, 2000, 19, 267–274.

13 R. Perochon, C. Poriel, O. Jeannin, L. Piekara-Sady and M.Fourmigue, Eur. J. Inorg. Chem., 2009, 5413–5421.


Publ

ishe

d on

10

Apr

il 20

12. D

ownl

oade

d on

22/

10/2

014

04:2

3:56



14 J.-Y. Cho, B. Domercq, S. C. Jones, J. Yu, X. Zhang, Z. An, M.Bishop, S. Barlow, S. R. Marder and B. Kippelen, J. Mater. Chem.,2007, 17, 2642–2647.

15 R. Perochon, P. Davidson, S. Rouziere, F. Camerel, L. Piekara-Sady,T. Guizouarn and M. Fourmigue, J. Mater. Chem., 2011, 21,1416–1422.

16 T.-T. Bui, O. Thiebaut, E. Grelet, M.-F. Achard, B. Garreau-deBonneval and K. I. Moineau-Chane Ching, Eur. J. Inorg. Chem.,2011, 2663–2676.

17 A. Escande, L. Guenee, H. Nozary, G. Bernardinelli, F. Gumy, A.Aebischer, G. Bunzli J.-C, B. Donnio, D. Guillon and C. Piguet,Chem.–Eur. J., 2007, 13, 8696–8713.

18 H. Horie, A. Takagi, H. Hasebe, T. Ozawa and K. Otha, J. Mater.Chem., 2001, 11, 1063–1071.

19 H. L. Gee and J. Harley-Mason, J. Chem. Soc., 1947, 251.20 F. Camerel, G. Ulrich and R. Ziessel, Org. Lett., 2004, 6, 4171–4174,

and references therein.21 (a) K. Takuma, Y. Irizato and K. Katho, PCT Int. Appl., 1990, 22,

WO9012019; (b) R. Perochon, L. Piekara-Sady, W. Jurga, R. Cleracand M. Fourmigue, Dalton Trans., 2009, 3052–3061.

22 F. Camerel, B. Donnio, C. Bourgogne, M. Schmutz, D. Guillon, P.Davidson and R. Ziessel, Chem.–Eur. J., 2006, 12, 4261–4274.

23 (a) J. Malthete, H. T. Nguyen and C. Destrade, Liq. Cryst., 1993, 13,171–187; (b) H. T. Nguyen, C. Destrade and J. Malthete, Adv.Mater., 1997, 9, 375–388; (c) D. Fazio, C. Mongin, B. Donnio, Y.Galerne, D. Guillon and D. W. Bruce, J. Mater. Chem., 2001, 11,2852–2863.

24 (a) B. Donnio, B. Heinrich, H. Allouchi, J. Kain, S. Diele, D. Guillonand D. W. Bruce, J. Am. Chem. Soc., 2004, 126, 15258–15268; (b) F.Morale, R. W. Date, D. Guillon, D. W. Bruce, R. L. Finn, C. Wilson,A. J. Blake, M. Schroder and B. Donnio, Chem.–Eur. J., 2003, 9,2484–2501; (c) J. Matraszek, J. Mieczkowski, D. Pociecha, E.Gorecka, B. Donnio and D. Guillon, Chem.–Eur. J., 2007, 13,3377–3385.

25 The rectangular lattice is primitive (for example p2gg), as shown bythe (12) which excludes centered groups according the extinction ruleh + k = 2n + 1. Actually, the phase structure likely results from asymmetry breaking of the local hexagonal packing of columns,leading to a doubling of the lattice periodicities with parameters a andb of 57.92 and 33.44 A, respectively (a/b = !3). The symmetry breakcan result from a shift between the columns of intercalated row fromthe lattice center.

26 The reflections, in the ratio !2 : !8 : !12 : !14 : !16 : !18 :!20 : !24 : !26, are all theoretically compatible with the reflectionconditions of cubic space groups with simple (cs) or body-centred (bcc)symmetry, but totally excludes the cfc system (F) [reflectionconditions, 0kl: k, l = 2n (and k + l = 4n), hhl: h + l = 2n or h, l =

2n, h00: h = 2n or 4n]. The absence of numerous low-angle reflections,not only explained by the groups’ extinction conditions, also exclude thecs groups with symmetry Pm3

-, Pn3

-, Pm3

-m, Pm3

-n, Pn3

-n and Pn3

-m.

The reflections were thus indexed as (110), (220), (222), (321), (400),(330/411), (420), (422), and (431/510) of the (bcc) groups Im3

-and Im3

-m

[reflection conditions, 0kl: k + l = 2n, hhl: l = 2n, h00: h = 2n](C. Hammond in The Basics of Crystallography and Diffraction, IUCr,Oxford Science Publications, Oxford, 2nd edn, 2001; International Tablesfor Crystallography Vol. A, ed. T. Hahn, The International Union ofCrystallography, Kluwer Academic, Dordrecht, 4th edn, 1995.Aggregation into the highest symmetry is generally admitted for liquidcrystalline materials. The symmetry of the observed liquid-crystallinecubic phase can thus characterized by a body-centered cubic networkwith the Im3m space group (no. 229) and a lattice parameter a = 47.3 A(a = ghkl(h

2 + k2 + l2)0.5 6 dhkl/Nhkl]). As deduced from the calculatedmolecular volume (4660 A3), the unit cell of the cubic lattice contains#20–24 C8amideNi mesogens.

27 A. Escande, L. Guenee, E. Terazzi, T. B. Jensen, H. Nozary and C.Piguet, Eur. J. Inorg. Chem., 2010, 2746–2759.

28 F. Camerel, L. Bonardi, G. Ulrich, L. Charbonniere, B. Donnio, C.Bourgogne, D. Guillon, P. Retailleau and R. Ziessel, Chem. Mater.,2006, 18, 5009–5021.

29 M. J. Hostetler, J. J. Stokes and R. W. Murray, Langmuir, 1996, 12,3604–3612.

30 S.-H. Park and C. E. Lee, Chem. Mater., 2006, 18, 981–987.31 (a) D. J. P. Yeardley, G. Ungar, V. Percec, M. N. Holerca and G.

Johansson, J. Am. Chem. Soc., 2000, 122, 1684–1689; (b) H. Duan,S. D. Hudson, G. Ungar, M. N. Holerca and V. Percec, Chem.–Eur.J., 2001, 7, 4134–4141; (c) I. Bury, B. Heinrich, C. Bourgogne, D.Guillon and B. Donnio, Chem.–Eur. J., 2006, 12, 8396–8413; (d) X.Zeng, G. Ungar and M. Imperor-Clerc, Nat. Mater., 2005, 4,562–567; (e) E. Terazzi, S. Torelli, G. Bernardinelli, J.-P. Rivera,J.-M. Benech, C. Bourgogne, B. Donnio, D. Guillon, D. Imbert, J.-C.G. Bunzli, A. Pinto, D. Jeannerat and C. Piguet, J. Am. Chem. Soc.,2005, 127, 888–903; (f) J.-K. Kim, M.-K. Hong, J.-H. Ahn and M.Lee, Angew. Chem., Int. Ed., 2005, 44, 328–332; (g) T. Cardinaels, J.Ramaekers, P. Nockemann, K. Driesen, K. Van Hecke, L. VanMeervelt, G. Wang, S. De Feyter, E. Fernandez Iglesias, D. Guillon,B. Donnio, K. Binnemans and D. W. Bruce, Soft Matter, 2008, 4,2172–2185; (h) S. Coco, C. Cordovilla, B. Donnio, P. Espinet, M. J.Garcia-Casas and D. Guillon, Chem.–Eur. J., 2008, 14, 3544–3552.

32 (a) A. M. Levelut and M. Clerc, Liq. Cryst., 1998, 24, 105–115; (b) X.Zeng, G. Ungar and M. Imperor-Clerc, Nat. Mater., 2005, 4,562–567.

33 (a) S. Diele, Curr. Opin. Solid State Mater. Sci., 2002, 6, 333–342; (b)S. Kutsumizu, Curr. Opin. Solid State Mater. Sci., 2002, 6, 537–543;(c) M. Imperor-Clerc, Curr. Opin. Chem. Biol., 2005, 9, 370–376.


Publ

ishe

d on

10

Apr

il 20

12. D

ownl

oade

d on

22/

10/2

014

04:2

3:56



room-temperature columnar mesophases of nickel-bis(dithiolene) metallomesogens

Documents