Liquid-crystalline zinc(II) and iron(II) alkyltriazoles one-dimensional coordination polymers

Article abstract of DOI:10.1021/ic300404r

Several series of unidimensional coordination polymers of formula [Zn(C_nH_2n+1trz)₃](Cl)₂?xH ₂O (n = 18, 16, 13, 11, 10, trz = 4-substituted-1,2,4-triazole), [Zn(C₁₈H₃₇trz)₃](ptol)₂?xH ₂O, [Fe(C_nH_2n+1trz)₃](X) ₂?xH₂O (n = 18, 16, 13, 10; X = Cl^- or ptol^-, where ptol^- = p-tolylsulfonate anion), and [Fe(C₁₈H₃₇trz)₃](X)₂?xH ₂O (X = C₈H₁₇PhSO₃^- and C₈H₁₇SO₃^-) are reported with their thermal, structural, and magnetic properties. Most of these materials exhibit thermotropic lamellar mesophases at temperatures as low as 410 K, as confirmed by textures observed by polarized optical microscopy. The corresponding phase diagrams deduced by differential scanning calorimetry are also reported. All iron-containing materials present a spin crossover phenomenon that occurs at temperatures ranging from 242 to 360 K, only slightly below the mesophase temperature domain, and remains complete and cooperative, even for the longer alkyl substituents. The use of stable diamagnetic Zn(II) analogues proves to be very useful to characterize the comparatively less stable and less crystalline Fe(II) analogues.

Full text of DOI:10.1021/ic300404r

Article
pubs.acs.org/IC
Liquid-Crystalline Zinc(II) and Iron(II) Alkyltriazoles One-Dimensional
Coordination Polymers
Pauline Grondin,†,‡ Diana Siretanu,†,‡ Olivier Roubeau,*,†,‡,§ Marie-France Achard,†,‡
and Rodolphe Clerac*,†,‡
́
†CNRS, CRPP, UPR 8641, F-33600 Pessac, France
‡Univ. of Bordeaux, CRPP, UPR 8641, F-33600 Pessac, France
§Instituto de Ciencia de Materiales de Aragon
́
(ICMA), CSIC−Universidad de Zaragoza, Departamento de Física de la Materia
Condensada, Facultad de Ciencias, Pedro Cerbuna 12, 50009 Zaragoza, Spain
S
* Supporting Information
ABSTRACT: Several series of unidimensional coordination polymers of formula
[Zn(CnH2n+1trz)3](Cl)2·xH2O (n = 18, 16, 13, 11, 10, trz = 4-substituted-1,2,4-
triazole), [Zn(C18H37trz)3](ptol)2·xH2O, [Fe(CnH2n+1trz)3](X)2·xH2O (n = 18, 16, 13,
10; X = Cl− or ptol−, where ptol− = p-tolylsulfonate anion), and [Fe(C18H37trz)3]-
−
−
(X)2·xH2O (X = C8H17PhSO3 and C8H17SO3 ) are reported with their thermal,
structural, and magnetic properties. Most of these materials exhibit thermotropic
lamellar mesophases at temperatures as low as 410 K, as confirmed by textures
observed by polarized optical microscopy. The corresponding phase diagrams deduced
by differential scanning calorimetry are also reported. All iron-containing materials
present a spin crossover phenomenon that occurs at temperatures ranging from 242 to
360 K, only slightly below the mesophase temperature domain, and remains complete
and cooperative, even for the longer alkyl substituents. The use of stable diamagnetic
Zn(II) analogues proves to be very useful to characterize the comparatively less stable
and less crystalline Fe(II) analogues.
the temperature range of the SC of this complex, no synergy
INTRODUCTION
■
between the two existing phenomena was observed. The same
conclusion holds for the first SC Fe(II) monomeric complexes
exhibiting a thermotropic mesophase.7 Therefore, researchers
orientated their projects toward complexes with higher spin
crossover temperatures and a more cooperative phenomenon.
In that sense, polymeric one-dimensional triazole-based Fe(II)
materials of general formula [Fe(Rtrz)3](A)2·xH2O (Rtrz =
4-substituted-1,2,4-triazole; A− = monovalent anion)8 are
particularly attractive as already illustrated by the elaboration
of SC nanoparticles,9 supramolecular gels,10 and thin films11
and development of optical devices prototypes.12 One of the
advantages of these materials is their flexibility. For the
[Fe(Rtrz)3](A)2 system, the SC temperature and cooperative
character can be easily tuned by the nature of the 4-substituent
on the triazole ligand and/or choice of the A− counteranion.13
Indeed, pro-mesogenic bis-alkyloxybenzylformylamino substitu-
ents could be introduced within these compounds, yielding a
synergic effect between a structural change and the spin
crossover, just above room temperature.14 Nevertheless, no
information on the nature of the high-temperature phase was
reported, while the observed SC was unfortunately very
incomplete. More recently, Gaspar et al. studied series of similar
In modern materials science, a large domain of research is
devoted to obtain a synergy between two or more physical
properties in materials1 through flexible synthesis of molecular
assemblies or formulation. The thermal spin crossover (SC)
phenomenon yields a synergetic effect between the magnetic
and the optical properties, in particular, in Fe(II) coordination
complexes.2 In certain so-called “cooperative systems”, large
thermal hysteresis cycles are observed, resulting from elastic
network interactions between SC complexes induced by either
direct bonding in coordination polymers or supramolecular
interactions like H-bonding networks and π−π stacking.3
Indeed, SC complexes have been used in a large number of
multifunctional materials.4 Implementing the magnetic and
optical bistabilities of SC systems within a liquid crystal (LC)
mesophase would, in addition to its intrinsic optical and
magnetic properties, allow a different control of the LC
orientation by external weak magnetic field depending on the
magnetic state of the SC unit (diamagnetic or paramagnetic).
This molecular control would bring great advantages within the
field of metallomesogens,5 in particular, for applications of
liquid crystals for which the color is necessary. The coexistence
of a SC phenomenon and thermotropic LC properties has been
demonstrated already a decade ago6 in a mononuclear Fe(III)
complex bearing dodecyloxybenzoyloxy arms. Nevertheless,
since the smectic mesophase (T > 391 K) occurred well above
Received: February 22, 2012
Published: April 9, 2012
© 2012 American Chemical Society
5417
dx.doi.org/10.1021/ic300404r | Inorg. Chem. 2012, 51, 5417−5426

Inorganic Chemistry
Article
compounds with different counteranions.15 Columnar or
columnar lamellar mesophases were observed for the longer
chains with 8, 10, and 12 carbons, but the SC remained gradual
and also incomplete, while mesophase textures were actually not
reported. Although the use of bulky pro-mesogenic substituents
on the triazole ligands is clearly a good strategy to produce
materials with coexisting SC and LC properties, maintaining a
cooperative and complete SC while favoring a fluid mesophase
remains a difficult task.16
using closed aluminum pans. Thermal equilibration was verified at the
starting and final temperatures of each scan using 1 min isotherms.
Temperature and enthalpy calibrations were made with a standard
sample of indium using its melting transition (156.6 °C, 3.296 kJ mol−1).
Excess enthalpies were deduced by subtracting a suitable baseline.
Elemental analyses were done either on a Perkin-Elmer 2400 analyzer at
Leiden University, The Netherlands, or by the CNRS Service Central
d’Analyze, Solaize, France. Thermogravimetric experiments were
performed with a Setaram TAG-1750. Measurements were done under
air with ramps of 3 °C min−1.
Materials. All solvents and reagents were obtained from commercial
sources as analytical grade and used without further purification.
Fe(ptol)2 and Zn(ptol)2 hydrates were obtained by stirring,
respectively, iron and zinc powder (0.5 mol per liter of solution) in
a 100 mL aqueous solution of p-toluenesulfonic acid (1.5 mol/L) at
80 °C for 4 h. After filtration of the remaining metal solid, the filtrate
was left cooling and standing at room temperature, allowing for cry-
stallization by slow evaporation of water of, respectively, Fe(ptol)2·
6H2O and Zn(ptol)2·6H2O crystals that were recovered by filtration
and washed with cold water. The water content of the hydrates was
determined by thermogravimetric analysis. Zn(ptol)2·6H2O: yield
29.57 g (57%). Anal. Calcd (Found) for ZnO12C14H26S2: C, 32.60
(32.7); H, 5.08 (5.0); S, 12.43 (12.3). Selected IR data (KBr pellet,
cm−1): 3389 (br), 1642 (m), 1176 (s), 1122 (s), 1037 (s), 1010 (s),
810 (m), 677 (m). Fe(ptol)2·6H2O: yield 27.40 g (54%). Anal. Calcd
(Found) for FeO12C14H26S2: C, 33.21 (33.25); H, 5.18 (5.24); S,
12.67 (12.58). Selected IR data (KBr pellet, cm−1): 3383 (br), 1644
(m), 1180 (s), 1122 (s), 1036 (s), 1009 (s), 812 (m), 675 (m).
Fe(C8H17SO3)2 and Fe(C8H17PhSO3)2 were obtained from FeCl2
by substitution of the anion with NaC8H17SO3 and NaC8H17PhSO3,
respectively. Both salts were stirred in water containing a small amount
of ascorbic acid. The resulting suspension was filtered. The white
compounds were isolated and dried over P2O5 under reduced pressure.
Yields were between 60% and 70%. Fe(C8H17SO3)2·6H2O: Anal.
Calcd (Found) for FeO12C16H46S2: C, 34.91 (34.95); H, 8.42 (8.50);
S, 11.65 (11.61). Selected IR data (KBr pellet, cm−1): 3369 (br), 2921
(m), 2849 (m), 1657 (m), 1470 (w), 1193 (s), 1139 (s), 1043 (s), 608
(s). Fe(C8H17PhSO3)2·6H2O: Anal. Calcd (Found) for
FeO12C28H54S2: C, 47.86 (47.91); H, 7.75 (7.79); S, 9.13 (9.10).
Selected IR data (KBr pellet, cm1): 3376 (br, w), 2917 (m), 2848
(m), 1623 (m), 1465 (s), 1219 (s), 1158 (s), 1133 (s), 1050 (s), 1014
(m), 696 (m), 608 (s).
In order to obtain SC gels and Langmuir−Blodgett films, our
research group has been interested in several series of such
M(II) triazole-based polymeric materials with long alkyl
substituents.10a,11a,17 These comparatively simpler substituents
may still represent a good alternative to tackle the remaining
drawbacks of these SC/LC systems. The first important
objective of our work is to maintain the typical cooperative
behavior of these materials even with pro-mesogenic
substitutents. This is not straightforward since even if the
one-dimensional structure may possess some intrinsic cooper-
ativity thanks to the direct N1,N2-triazole bridges, isolation of
the chains naturally tends toward a solution-like crossover
behavior. Moreover, too bulky substituents on the 4 position of
the triazoles result in strong shortening of the chain length and
thus in incomplete and gradual SC as shown by the bis-
alkyloxybenzylformylamino-substituted systems.14,15 The sec-
ond important aspect is related to the synchronism in tem-
perature or best to the possible synergetic effects between the spin
crossover and the crystal (Cr) to LC transition phenomena. In
order to design a material with a SC in the mesophase or a SC
simultaneous to or induced by the Cr to LC transition, the SC
characteristic temperature, TSC, must be above room temper-
ature. This can be achieved using the right anions such as
halides or sulfonates, known to induce SC at such temper-
atures.18 Nevertheless, although quite stable, these Fe(II)−
triazole compounds tend to undergo oxidation and decom-
position at temperatures above 180 °C (453 K). Then, lowering
the temperature domain of the mesophase is also an important
issue. In this respect, a long alkyl substituent may represent a
good compromise. Finally, use of similar systems with other
metal ions such as Zn(II) would allow one to perform thermal
studies free of potential oxidation/decomposition effects.
We report here on the thermal and structural behavior of the
compounds [Zn(CnH2n+1trz)3](Cl)2·xH2O (n = 18, 16, 13, 11,
10), [Zn(C18H37trz)3](ptol)2·xH2O, and [Fe(CnH2n+1trz)3]-
(X)2·xH2O (n = 18, 16, 13, 10, X = Cl−, ptol−, where ptol− =
p-tolylsulfonate anion), and [Fe(C18H37trz)3](X)2·xH2O
(X = C8H17SO3−, or C8H17PhSO3−) hereafter denoted as
MCnX. The presence of thermotropic lamellar mesophases is
evidenced in most of these materials, occurring in the Fe(II)
materials at temperatures just above the spin crossover, which
remains abrupt and complete.
4-n-Alkyl-1,2,4-triazole ligands were prepared as previously
described.20
Coordination polymers of formula [M(4-n-alkyl-1,2,4-triazole)3]-
A2·xH2O were synthesized following the same procedure: a hot
ethanolic solution (7 mmol, 40 mL) of the 4-n-alkyl-1,2,4-triazole was
added slowly to an aqueous solution of the iron(II) or zinc(II) salt
(2 mmol, 20 mL) containing in the iron(II) cases a small amount of
ascorbic acid to prevent oxidation to iron(III). A white precipitate
formed rapidly upon addition. After 30 min aging, the solution was
filtered and the solid washed with successively 2 × 40 mL of water,
20 mL of a 50:50 V/V water/ethanol mixture, and 2 × 50 mL ethanol.
After drying, the iron compounds turned purple, indicating the
presence of iron(II) ions in a low-spin state. The yields were between
75% and 86%. The formula, and in particular the water content x (that
was found to range from 1 to 4), of the coordination polymers were
determined by elemental and thermogravimetric analysis. Satisfactory
elemental analysis, IR bands, and thermogravimetric data were
obtained for all compounds.
[Zn(C10H21trz)3](Cl)2·2H2O. Anal. Calcd (Found) for ZnC36-
H73N9O2Cl2: C, 54.0 (54.4); H, 9.2 (9.2); N, 15.7 (15.9). Selected
IR data (KBr pellet, cm−1): 3404 (br), 3110 (m), 2954 (m), 2919 (s),
2851 (s), 1553 (m), 1468 8 m), 1397 (w), 1194 (m), 1078 (m), 1037
(m), 977 (w), 884 (br), 721 (m), 663 (w), 636 (m).
[Zn(C11H23trz)3](Cl)2·4H2O. Anal. Calcd (Found) for ZnC39H83-
N9O4Cl2: C, 53.3 (53.5); H, 9.5 (8.9); N, 14.4 (14.4). Selected IR data
(KBr pellet, cm−1): 3410 (br), 3110 (m), 2953 (m), 2918 (s), 2851
(s), 1553 (m), 1467 (m), 1397 (w), 1194 (m), 1078 (m), 1037 (m),
977 (w), 885 (br), 722 (m), 663 (w), 637 (m).
EXPERIMENTAL SECTION
■
Methods. Infrared spectra were performed on KBr pellets with a
FTIR 750 NICOLET (Magna-IR) spectrometer. Magnetization
measurements at variable temperature have been performed using a
Quantum Design MPMS-XL SQUID magnetometer, operating
between 1.8 and 400 K, in applied dc magnetic fields ranging from
−7 to 7 T. X-ray diffraction experiments at small angles (SAXS) were
performed on a homemade experimental setup equipped with an oven
working up to 150 °C.19 Measurements at higher angles were
performed on a Philips X’Pert powder diffractometer equipped with a
high-temperature chamber. Differential scanning calorimetry (DSC)
measurements were conducted on a Perkin-Elmer Pyris apparatus
5418
dx.doi.org/10.1021/ic300404r | Inorg. Chem. 2012, 51, 5417−5426

Inorganic Chemistry
Article
[Zn(C13H27trz)3](Cl)2·4H2O. Anal. Calcd (Found) for ZnC45H95-
N9O4Cl2: C, 56.2 (56.3); H, 10.0 (9.5); N, 13.1 (13.2). Selected IR
data (KBr pellet, cm−1): 3430 (br), 3110 (m), 2954 (m), 2917 (s),
2850 (s), 1552 (m), 1468 (m), 1394 (w), 1193 (m), 1077 (m), 1035
(m), 976 (w), 887 (br), 722 (m), 664 (w), 650 (m), 637 (m).
2851 (s), 1681 (m), 1558 (m), 1380 (w), 1217 (s), 1195 (s), 1124
(w), 1035 (m), 1012 (m), 694 (w).
RESULTS AND DISCUSSION
■
Synthesis and Spectroscopic Observations. The
chloride and organosulfonate anions were selected for this
study. One-dimensional triazole Fe(II) coordination polymers
with these anions are expected to display SC phenomenon
around or above room temperature.13,18 Bromide or iodide ions
were discarded despite their potential high SC temperatures
due to the observation of decomposition at low temperatures
for some triazole derivatives.21 Zn(II) analogues were also syn-
thesized to allow comparison with a more stable and diamagnetic
system. In addition to the different response of the diamagnetic or
paramagnetic mesophase under an applied dc magnetic field, these
Zn analogues allow one to study a structurally similar system
without facing oxidation issues known in the Fe(II) compounds.
Indeed, liquid-crystal phases have been described in the Fe(II)/
triazole system, but no characteristic optical texture was reported
in any of the few reports so far.14,15 In thermotropic LC,
characteristic textures are usually observed by polarized optical
microscopy cooling the systems from their isotropic liquid to the
LC phase. In the case of Fe(II) systems, this technique becomes
problematic as it faces their partial oxidization/decomposition at
temperatures required to achieve the isotropic phase.
[Zn(C16H33trz)3](Cl)2·2H2O. Anal. Calcd (Found) for ZnC54H109
-
N9O2Cl2: C, 61.6 (61.8); H, 10.4 (10.2); N, 12.0 (12.1). Selected IR
data (KBr pellet, cm−1): 3440 (br), 3110 (m), 2953 (m), 2918 (s),
2850 (s), 1553 (m), 1469 (m), 1397 (w), 1194 (m), 1078 (m), 1037
(m), 978 (w), 887 (br), 720 (w), 663 (w), 638 (m).
[Zn(C18H37trz)3](Cl)2·2H2O. Anal. Calcd (Found) for ZnC60H121
-
N9O2Cl2: C, 63.4 (63.7); H, 10.7 (10.6); N, 11.1 (11.2). Selected IR
data (KBr pellet, cm−1): 3437 (br), 3110 (m), 2954 (m), 2918 (s),
2850 (s), 1553 (m), 1469 (m), 1397 (w), 1194 (m), 1079 (m), 1037
(m), 978 (w), 887 (br), 721 (m), 663 (w), 639 (m).
[Zn(C18H37trz)3](ptol)2·2H2O. Anal. Calcd (Found) for ZnC74H135
-
N9O8S2: C, 63.1 (63.5); H, 9.7 (9.6); N, 8.9 (9.0); S, 4.5 (4.3).
Selected IR data (KBr pellet, cm−1): 3095 (br), 3023 (w), 2955 (m),
2920 (s), 2850 (s), 1568 (m), 1458 (m), 1402 (w), 1214 (s), 1196 (s),
1124 (s), 1036 (s), 1012, (s) 815 (m), 721 (w), 682 (m), 646 (w),
568 (m).
[Fe(C10H21trz)3](Cl)2·3H2O. Anal. Calcd (Found) for FeC36H75N9-
O3Cl2: C, 53.5 (53.3); H, 9.4 (9.4); N, 15.6 (16.0). Selected IR data
(KBr pellet, cm−1): 3370 (br), 3058 (w), 2957 (m), 2925 (s), 2855
(s), 1555 (m), 1465 (m), 1415 (w), 1209 (m), 722 (w), 640 (m).
[Fe(C13H27trz)3](Cl)2·3H2O. Anal. Calcd (Found) for FeC45H93N9-
O3Cl2: C, 57.8 (58.1); H, 10.0 (10.0); N, 13.5 (13.4). Selected IR data
(KBr pellet, cm−1): 3380 (br), 3054 (w), 2957 (m), 2922 (s), 2853
(s), 1554 (m), 1466 (m), 1415 (w), 1210 (m), 722 (w), 641 (w).
[Fe(C16H33trz)3](Cl)2·4H2O. Anal. Calcd (Found) for FeC54H111N9-
O4Cl2: C, 60.1 (59.3); H, 10.5 (10.4); N, 11.7 (11.4). Selected IR data
(KBr pellet, cm−1): 3390 (br), 3055 (w), 2956 (m), 2921 (s), 2852
(s), 1554 (m), 1468 (m), 1415 (w), 1207 (m), 721 (w), 642 (w).
[Fe(C18H37trz)3](Cl)2·H2O. Anal. Calcd (Found) for FeC60H119N9-
OCl2: C, 65.0 (65.4); H, 10.8 (11.1); N, 11.4 (11.4). Selected IR data
(KBr pellet, cm−1): 3391 (br), 3053 (w), 2956 (m), 2919 (s), 2850
(s), 1553 (m), 1468 (m), 1414 (w), 1211 (m), 721 (w), 642 (w).
[Fe(C10H21trz)3](ptol)2·2H2O. Anal. Calcd (Found) for FeC50H87N9-
O8S2: C, 56.5 (56.6); H, 8.3 (8.2); N, 11.9 (12.1) ; S 6.0 (5.7).
Selected IR data (KBr pellet, cm−1): 3480 (br), 3088 (m), 3018 (w),
3055 (m), 2925 (s), 2854 (s), 1558 (m), 1467 (m), 1401 (w), 1215
(s), 1193 (s), 1124 (s), 1035 (s), 1012 (s), 814 (m), 720 (w), 683 (s),
646 (w), 568 (m).
Coordination polymers were synthesized as previously
reported by reacting an aqueous solution of the Zn(II) or
Fe(II) salt with an excess of the alkyl-triazole dissolved in hot
ethanol. Upon addition of the ethanol solution of triazole, a
white precipitate forms immediately for the longer alkyl sub-
stituents and within minutes for the decyl one. It is worth
mentioning that it is important to keep the precipitate in
contact with the solution for at least 20 min before recovering
the solid material. Below this aging time, the SC phenomenon
observed for the Fe(II) compounds is systematically more
gradual and less complete. These “truncated” properties are due
to the presence of shorter oligomers for which the terminal
Fe(II) ions does not exhibit a SC as observed for the trinuclear
Fe(II)/triazole systems.22 As a consequence, the intrinsic
cooperativeness arising from triple N1,N2-triazole bridges
along the chain is thus significantly reduced.
[Fe(C13H27trz)3](ptol)2·2H2O. Anal. Calcd (Found) for FeC59H105
-
N9O8S2: C, 59.6 (60.1); H, 8.9 (9.3); N, 10.6 (10.6); S, 5.4 (5.0).
Selected IR data (KBr pellet, cm−1): 3487 (br), 3090 (m), 3018 (w),
2956 (m), 2927 (s), 2855 (s), 1556 (m), 1466 (m), 1401 (w), 1215
(s), 1194 (s), 1126 (s), 1036 (s), 1012 (s), 815 (m), 721 (w), 685 (s),
646 (w), 569 (m).
The 1,2-coordination mode of the triazole rings is confirmed
by IR spectroscopy (Figure S1, Supporting Information). In all
cases including for the Zn(II) compounds, a shift of the
aromatic νC−H vibrations and of the ring bands in the range
̃
[Fe(C16H33trz)3](ptol)2·H2O. Anal. Calcd (Found) for FeC68H121
-
1300−1500 cm−1 (depending on the nature of the metal center
and the counteranion) is systematically observed. Moreover,
the intensities of the ring torsion vibration modes of the
triazoles around 670 cm−1 are very weak as expected when the
local triazole ring symmetry is C2v.23 UV−vis absorption spectra
for the Fe(II) compounds with Cl− and ptol− anions at room
N9O7S2: C, 63.0 (63.3); H, 9.4 (9.9); N, 9.7 (9.5); S, 5.0 (4.7).
Selected IR data (KBr pellet, cm−1): 3510 (br), 3087 (m), 3020 (w),
2956 (m), 2923 (s), 2853 (s), 1560 (m), 1469 (m), 1400 (w), 1217
(s), 1190 (s), 1124 (s), 1035 (s), 1013 (s), 815 (m), 722 (w), 683 (s),
646 (w), 565 (m).
Fe(C18H37trz)3](ptol)2·2H2O. Anal. Calcd (Found) for FeC74H135
-
1
1
N9O8S2: C, 63.5 (63.3); H, 9.7 (9.8); N, 9.0 (9.0); S, 4.6 (4.7).
Selected IR data (KBr pellet, cm−1): 3490 (br), 3086 (m), 3018 (w),
2959 (m), 2925 (s), 2855 (s), 1560 (m), 1470 (m), 1400 (w), 1215
(s), 1193 (s), 1125 (s), 1038 (s), 1011 (s), 814 (m), 721 (w), 683 (s),
646 (w), 569 (m).
[Fe(C18H37trz)3](C8H17SO3)2·H2O. Anal. Calcd (Found) for FeC76-
H153N9O7S2: C, 64.1 (64.0); H, 10.8 (10.9); N, 8.8 (8.9); S, 4.5 (4.6).
Selected IR data (KBr pellet, cm−1): 3344 (br), 2918 (s), 2846 (m),
1658 (m), 1468 (w), 1379 (w), 1212 (s), 1175 (s), 1141 (s), 712 (w),
603 (w).
temperature are dominated by the A1 to T1 band around
550 nm, thus confirming the LS state of the materials. The
presence of a very weak and broad band around 800 nm is
revealing traces of HS Fe(II) ions ascribed to the Fe(II) ions
located at the polymeric chain ends. In air, the iron compounds
were found to decompose just before or during the melting in
the 170−210 °C temperature range, turning to a typical brown
color. This was not the case for the zinc compounds in
agreement with an oxidation process of the iron ones.
Magnetic and Thermal Signatures of the Spin
Crossover. The thermal spin crossover of most of the Fe(II)
compounds reported here has been previously described.18a,b,20
[Fe(C18H37trz)3](C8H17PhSO3)2·H2O. Anal. Calcd (Found) for FeC88-
H161N9O7S2: C, 67.8 (67.8); H, 10.3 (10.4); N, 8.0 (8.2); S, 4.1 (4.0).
Selected IR data (KBr pellet, cm−1): 3444 (br), 3092 (m), 2921 (s),
5419
dx.doi.org/10.1021/ic300404r | Inorg. Chem. 2012, 51, 5417−5426

Inorganic Chemistry
Article
The reproducibility of their properties was checked, and the
typical thermal variation of the χT product (where χ is the
molar magnetic susceptibility) is given in Figure 1 and Figures S2
Although the χT product at low temperatures does reach
very small values, it is not zero, as would be expected for a pure
diamagnetic state. This residual paramagnetism is due to the
Fe(II) ions situated at the coordination polymer chain ends
that possess a HS ground state as also detected by absorption
spectroscopy (vide supra). As observed for trinuclear com-
plexes,22 the HS Fe(II) sites are stabilized by different coor-
dination spheres, including either water or monocoordinated
triazole ligands. Thus, the amount of residual paramagnetism is
an indirect probe of the average length of the polymeric chains.
The very high residual paramagnetism observed in previous
studies14,15 therefore corresponds to small oligomeric chains, as
−
indeed expected with the counteranions like ClO4 or long
substituents on the triazole ring.20 On the other hand, the
results obtained here with Cl− and ptol− anions indicate and
confirm the almost complete SC and thus long polymeric
Fe(II) chains.
The spin crossover of these materials is also detected by DSC
technique (see below and Table 1), with a broad peak centered
at temperatures that are in good agreement with the magnetic
properties. The associated enthalpies are relatively high, ranging
from 3.0 to above 20.0 kJ/mol, as usually observed in the presence
of a marked cooperative character of the spin crossover. Therefore,
these values are expected for these polymeric materials as recently
studied in detail.24
Solid-State Structure. Selected powder diffraction patterns
of the reported materials are shown in Figure 2. As previously
observed, the 1D triazole-based Fe(II) materials are poorly
crystalline. Indeed, the one-dimensional linear structure of this
type of materials, shown in Scheme 1, was initially
demonstrated by EXAFS, XANES, and WAXS studies25 by
comparison with trinuclear complexes for which the crystallo-
graphic structure is known.22 Only very recently in 2011 the
structure of [Fe(Htrz)2(trz)](BF4) and [Fe(NH2trz)3]-
(NO3)2·nH2O could be determined respectively by modulation
enhanced X-ray powder diffraction26 and single-crystal X-ray
diffraction.8 On the other hand, the Zn(II) compounds present
well-defined powder X-ray patterns (see Figure 2). This is also
the case of Cu(II) derivatives for which the structure could be
solved from single-crystal diffraction.27 Overall, all previous
Figure 1. Temperature dependence of the product χT on cooling
(empty symbols) and heating (full symbols) modes for FeC18ptol
(circles) and FeC18Cl (rhombs) at about 1 K/min under 1000 Oe.
and S3, Supporting Information, for [Fe(C18H37trz)3](X)2
(X = Cl−, ptol−, C8H17PhSO3 , and C8H17SO3 ; the respective
compounds are noted thereafter FeC18Cl, FeC18ptol,
FeC18(C8H17PhSO3), and FeC18(C8H17SO3)). Table 1 gathers
SC parameters for all studied compounds. In the case of Cl−
and ptol− compounds, the SC occurs above room temperature
and is abrupt, as evidenced by the sharp decrease of χT upon
lowering the temperature from about 3.0 (value typical for an
S = 2 HS configuration) to roughly 0.1 cm3 K mol−1. These spin
crossover phenomena are reversible and present a small thermal
hysteresis at a temperature sweeping rate of around 1 K/min.
For complexes FeC18(C8H17PhSO3) and FeC18(C8H17SO3)
containing long alkyl chain counterions, the χT values decrease
very gradually when lowering the temperature, achieving 0.18
and 1.2 cm3 K mol−1 at 60 K for FeC18(C8H17PhSO3) and
FeC18(C8H17SO3) respectively.
−
−
Table 1. Parameters Describing the Structural Arrangement and the SC Properties of MCnX Compounds
a
b
c
c
compound
ZnC18Cl
dRT/dLC (Å) TSC/ΔT (K, from χT vs T)
TSC (K, from DSC)
Tm (K)
ΔHm (kJ mol−1
)
Tclear (K)
ΔHclear (kJ mol−1
)
26.8/32.5
23.7/29.6
20.1/25.8
−/23.0
N/A
N/A
N/A
N/A
N/A
N/A
357/3
358/6
N/A
N/A
N/A
N/A
N/A
N/A
363
409
410
417
431
424
430
419
421
426
422
451
455
455
469
78.6
65.5
71.3
68.7
61.6
15
485
481
462
[427]
[384]
506
476
477
480
460
543
543
546
4.3
4.1
4.8
2.9
1.4
35
ZnC16Cl
ZnC13Cl
ZnC11Cl
ZnC10Cl
ZnC18ptol
FeC18Cl
48/33
11.9
7.0
1.3
1.0
1.8
1.0
1.7
1.5
2.4
FeC16Cl
362
FeC13Cl
364
2.5
FeC10Cl
338/4
328/6
328/5
295/10
335/2
244
362
4.7
FeC18ptol
FeC16ptol
FeC13ptol
FeC10ptol
FeC18(C8H17PhSO3)
FeC18(C8H17SO3)
38.2/26.6
33.2/25.1
30.3/23.4
310
19.3
19.4
14.1
4.4
327
330
326
242
278
294
450
3.0
a
b
TSC are those upon warming, ΔT being the hysteresis width at a 1 K/min sweeping rate. Temperature of the peak maximum upon warming, since
c
in some cases determination of a correct baseline is difficult, making the onset of the peak poorly defined. Tm and Tclear are derived from the DSC
peak maxima; values in brackets indicate the clearing temperature from the monotropic phase.
5420
dx.doi.org/10.1021/ic300404r | Inorg. Chem. 2012, 51, 5417−5426

Inorganic Chemistry
Article
N1,N2 triazole bridges that are disposed in an eclipsed alter-
nating propeller disposition along the polymeric chains.
The alkyl substituents in the present systems are thus
approximately pointing perpendicular to the chain direction in
(at least) six directions. In agreement with this schematic view
(see Scheme 1), the room temperature small angle XRD
diffractograms of all Zn(II) and Fe(II) compounds studied here
are dominated by an intense peak at low q. Diffraction peaks
with q ratios of 1:2:3:4 are observed as the signature of a
lamellar organization. This strong diffraction can clearly be
ascribed to interchain metal−metal separation as the position of
the main peak is influenced by the length of the alkyl chains.
The diffraction at higher q, corresponding to organization at
shorter distances and thus within the coordination chains, is
very poor for the Fe compounds, although a more intense peak
or massif is detected in all Zn and Fe compounds in the range
1.4−1.6 Å1. Overall, the MCnX compounds studied here can
be pictured as packed rod-like polymers separated by alkyl arms
and organized in layers, as indirectly confirmed by the obser-
vation of textures in optical microscopy typical of a liquid-
crystalline lamellar phase (vide infra).
The interlamellar distances d, gathered in Table 1, are
derived from the position of the main peaks using d = 2π/q.
Assuming fully stretched alkyl chains, the diameter of the
cylinder formed by one coordination Fe(II)/triazole chain
could reach at most 32 Å for n = 10 to 47 Å for n = 18. The
determined interlamellar distances for the ZnCnCl compounds
(Table 1), in other words the interchain metal−metal distances,
are all much smaller, indicating that the alkyl chains are
interdigitated and/or folded. The variation of the interlamellar
distance d with the length of the alkyl chain n is shown in
Figure 3 for the ZnCnCl system. d is a linear function of n,
Figure 2. X-ray powder diffraction patterns in the (crystalline) solid
state for ZnC18Cl (top), FeC18Cl (middle), and FeC18ptol (bottom).
Exact temperatures are indicated in each graph. Insets show the log−
log plot of the low angle area. Data are taken from two separate
measurements on two experimental set ups for small-angle and wide-
angle ranges (see Experimental Section).
Scheme 1. Representation of (a) 4-n-Alkyl-1,2,4-triazole
ligands, (b) the 1D Chain Formed through Triple N1−N2
Bridges upon Coordination to Fe(II) or Zn(II) Ions (shown
as orange balls, nitrogen and carbon are, respectively,
depicted as blue and gray), and (c) the Space Fill Idealized
Conformation of One of These Bridges with Fully-Stretched
Decyl Substituent on the Triazole Ring
Figure 3. Interlamellar distance d as a function of n, the length of the
4-n-alkyl substituent on the triazole ligand, for the series ZnCnCl in the
solid crystalline state (empty circles) and in the mesophase at 430−
440 K (full circles).
suggesting a similar structural organization in all compounds of
the series. The slope of the linear regression is 1.33 Å. This
value is slightly higher than one C−C bond (ca. 1.25 Å in trans
conformation), confirming the strong interdigitation of the
alkyl arms, which is certainly reinforcing the good cohesion
between the coordination M(II)/triazole chains (note that in
the absence of interdigitation, the slope should be equal to two
C−C bonds). On the other hand, the interlamellar distance in
FeC18Cl amounts to 48 Å, indicating the absence or at best the
weak alkyl chain interdigitation in this material. The data for
the FeCnptol series in the solid state show a less pronounced
decrease of d with decreasing n and no clear linear trend
(Figure S4, Supporting Information). These observations agree
with the much poorer crystallinity of the Fe-containing solids
structural information available on these triazole-based mat-
erials agree with the presence of M(II) chains linked by triple
5421
dx.doi.org/10.1021/ic300404r | Inorg. Chem. 2012, 51, 5417−5426

Inorganic Chemistry
Article
(Figure 2) and likely indicate amorphous folding of the alkyl
chains in the latter case.
Indeed, between simple glass slides and under a crossed polarizer
and analyzer some birefringence is observed fugaciously (Figure S5,
Supporting Information) and rapidly disappears, leaving a black
texture, thus indicating the perpendicular orientation of
molecules with respect to the substrate. Special glass cells treated
to favor a flat organization have thus been used, allowing
observation of stable focal conic textures over large areas. For the
shorter alkyl chain compounds, even under these conditions, the
homeotropic tendency subsists and textures can only be observed
in small domains, as shown in Figure 4b for ZnC13Cl.
Mesomorphic Behavior. Such rod-shaped molecules with
peripheral divergent alkyl chains may self-organize as columnar
or lamellar phases as observed in polycatenars or neat soaps.28
Indeed, most compounds studied here possess thermotropic
liquid crystal properties. The mesophases have been studied by
polarized optical microscopy (POM), differential scanning
calorimetry (DSC), and X-ray scattering. The structural,
thermal, and thermodynamic data are collected in Table 1. It
is well known that the liquid-crystal phases are very dependent
on the purity of the mesogenic molecules or complexes;
therefore, the tendency of the Fe compounds to partially
oxidize at temperatures as low as 180 °C (453 K) makes their
study more complicated. For this reason, we first investigated in
great detail the more stable zinc analogues.
X-ray diffraction measurements (Figure 5) in the adequate
temperature range confirm the appearance of a lamellar phase.
Zn(II)/Triazole Systems. Polarized optical microscopy of
ZnC18Cl reveals a phase transition from a crystalline phase to a
birefringent one at ca. 409 K with a clearing point to the isotropic
liquid state at ca. 485 K. The observed focal conic textures
are typical for a lamellar phase, as shown in Figure 4a. These
Figure 5. X-ray powder diffraction patterns in the mesophase for
ZnC18Cl (top), FeC18Cl (middle), and FeC18ptol (bottom). Exact
temperatures are indicated in each graph. Data are taken from two
separate measurements on two experimental set ups for small-angle
and wide-angle ranges (see Experimental Section).
For ZnC18Cl, the wide-angle diffraction in this temperature
range shows only a very broad peak at q = 1.3 Å that can be
ascribed to the average separation between alkyl chains within a
partially organized fluid mesophase.
At small angles, intense peaks with a q ratio of 1:2:3 are still
observed, in agreement with a lamellar mesophase, as revealed
by POM. All thermally induced modifications are perfectly
reversible in all the Zn-containing compounds studied. As expected,
the interlamellar distance is systematically higher in the mesophase
than in the crystal state, although a linear dependence (Figure 3)
on the alkyl chain length n remains with almost the same slope
(1.34 Å). Hence, the alkyl arms remain interdigitated even in the
liquid crystal phase. Extrapolation to n = 0 gives a value of 8.5 Å,
which is in reasonable agreement with the diameter of a cylinder
made of a [Zn(trz)3]n core, estimated at 7 Å. The schematized
structural organization of the mesophase in layers of coordination
polymers is depicted in Scheme 2.
Figure 4. Polarized optical microscopic textures observed for ZnC18Cl
(a) and ZnC13Cl (b) at 481 and 440 K, respectively, upon cooling
from the isotropic liquid and FeC18ptol (c) at 480 K upon warming
from room temperature.
observations are perfectly reversible, and textures are indeed better
observed after cooling from the isotropic liquid (I).
The compounds with a smaller alkyl substituent on the
triazole ring show a similar behavior down to C13, only differing
in the Cr → lamellar transition and the clearing temperatures
(Table 1). For ZnC10Cl and ZnC11Cl, textures corresponding
to the lamellar mesophase could only be observed upon cooling
from the isotropic liquid, thus indicating a monotropic phase,
which was confirmed by DSC experiments (vide infra). These
compounds present a tendency toward homeotropic anchoring.
Differential scanning calorimetry (DSC) data for ZnC18Cl
and ZnC10Cl are shown in Figure 6 as representative for the
5422
dx.doi.org/10.1021/ic300404r | Inorg. Chem. 2012, 51, 5417−5426

Inorganic Chemistry
Article
Scheme 2. Schematic Representation of (a) a Hexacatenar
Moiety That Would Form Repetitive Triple 4-Octadecyl-
1,2,4-triazole Bridges with Fully-Stretched Alkyl Arms in
Eclipsed Conformation and (b and c) Lamellar Packing of
the Resulting Rods with Interdigitation, Respectively,
Perpendicular and Parallel to the Average Rod Axis
rest of the compounds (whose data are given in the Supporting
Information, Figure S6). These measurements are in good
agreement with POM observations and the existence of
mesophases. Indeed, DSC traces of ZnCnCl (n = 18, 16, 13)
reproducibly show two endothermic peaks upon warming,
clearly associated by pairs with two exothermic ones upon
cooling. These two characteristic anomalies occur at temper-
atures similar to those observed by POM, corresponding to the
Cr → lamellar phase transition and the clearing point.
Systematically, the lower temperature peaks have a much
higher associated enthalpy (65−79 kJ mol−1) than the peaks at
higher temperatures (between 4.1 and 4.8 kJ mol−1). This
observation confirms the POM conclusions that ascribed the
first peak to the melting of the crystalline solid to a liquid-
crystalline phase existing over a large range of temperature up
to the second peak corresponding to the clearing point and
transition to the isotropic liquid. For ZnC10Cl and ZnC11Cl,
DSC traces exhibit only one melting peak from the crystalline
phase to the isotropic liquid upon warming at, respectively, 424
and 431 K, indicating the mesophase does not form from the
crystalline state. Upon cooling, a first poorly energetic peak (1.4
and 2.9 kJ mol−1) appears, corresponding to the I → lamellar
phase transition followed by a second peak with much larger
associated enthalpies (61 and 69 kJ mol−1) corresponding to
crystallization from the lamellar phase at 353 and 350 K,
respectively. When warming again from the lamellar phase, only a
poorly energetic peak attributed to the transition toward the iso-
tropic liquid is detected at 384 and 427 K, respectively (see inset in
Figures 6 and S6, Supporting Information). In the case of ZnC11Cl,
this clearing point almost coincides with the normal melting
temperature. These observations are typical of a mono-
tropic liquid crystal phase, observed here in the cooling mode.
Gathering the data from POM, DSC, and PXRD measure-
ments for the ZnCnX compounds, the transition temperatures
as a function of n, the alkyl chain length, have been plotted in a
phase diagram shown in Figure 7. The clearing temperature in
the series ZnCnCl regularly increases with increasing n, from
384 K for n = 10 to 485 K for n = 18. On the other hand, the
melting temperature decreases with increasing n, from 431 K
for n = 10 to 409 K for n = 18. Thus, for n < 12, a monotropic
mesophase is observed with Tm > Tclear, while for n > 12,
the lamellar mesophase exists over a wide temperature
range, reaching 76 K for n = 18. From the trend observed for
Figure 6. DSC traces of ZnC18Cl (top), ZnC10Cl (middle), and
ZnC18ptol (bottom) at 10 K/min, exhibiting heat flow humps
associated with the transitions among the solid state (Cr), lamellar
mesophase (LC), and isotropic liquid state (I). Arrows indicate the
warming or cooling modes; endotherms are up. Inset of the figure
middle shows experimental evidence of the monotropic mesophase
[LC], occurring only in the cooling mode in the case of ZnC10Cl
(see text).
Figure 7. Phase diagram showing the temperature domains for the
solid state (Cr), lamellar mesophase (LC, Lα is used to indicate a
lamellar arrangement), and isotropic liquid state (I) for ZnCnX and
X = Cl (circles) and ptol (squares). Melting and clearing temperatures
are represented by full and empty symbols, respectively. Lines are only
guides for the eye.
n = 10−18 it is unlikely that longer alkyl substituents would result
in a much larger clearing temperature or more importantly a lower
melting temperature that would be necessary to observe the SC
phenomenon within the mesophase. These transition temper-
atures are even found to be about 20 K higher in ZnC18ptol,
5423
dx.doi.org/10.1021/ic300404r | Inorg. Chem. 2012, 51, 5417−5426

Inorganic Chemistry
Article
Figure 8. DSC traces of FeC18Cl (top) and FeC16ptol (bottom) at
10 K/min, exhibiting heat flow humps associated with the SC
phenomenon and transitions among the solid state (Cr), lamellar
mesophase (LC), and isotropic liquid state (I). Arrows indicate the
warming or cooling mode; endotherms are up.
which is the reason why the full series was not studied with the
ptol− anion.
Figure 9. Phase diagrams showing the temperature domains for the solid
state (CrLS and CrHS), pseudolamellar mesophase (LC, Lα is used to
indicate a lamellar arrangement), and isotropic liquid state (I) for FeCnCl
(top) and FeCnptol (bottom). SC, melting, and clearing temperatures are
represented by square, full, and empty symbols, respectively, and all taken
from DSC data. Lines are only guides for the eye.
Fe(II)/Triazole Systems. Besides the peak associated with the
SC phenomenon in the 360−365 K range, the DSC traces of
the FeCnCl compounds upon warming (Figures 8 and S7,
Supporting Information) are similar to those observed for the
Zn compounds with a strong peak around 420 K followed by a
much weaker peak in the 460−480 K range. By analogy to the
Zn systems (vide supra), these peaks can be associated with a
crystal to liquid crystal transition and the transition to isotropic
phase, although the energies associated are about 4 times
smaller with respect to the Zn analogues. Unfortunately, the
compounds show signs of decomposition/oxidation, even at
temperatures close to the melting and up to the clearing point.
The FeCnptol compounds (Figures 8 and S8, Supporting
Information) exhibit a very similar behavior upon warming,
with DSC traces showing peaks associated with the SC in the
310−330 K range, the melting to an intermediate lamellar
phase in the 450−470 K range and a transition to an isotropic
phase coupled to an evident partial decomposition around
545 K. For both Cl− and ptol− compounds, the SC peak is
observed upon cooling in a reproducible manner over several
cycles, indicating the decomposition is only very partial since a
large part of the material maintains its original magnetic
properties. For all the Fe compounds, the poorly energetic peak
(expected for the transition from the isotropic liquid to the
mesophase) is absent of the DSC trace upon cooling from the
isotropic liquid. Only a strong exothermic peak or a smooth
step is observed for the Cl− and ptol− compounds, probably
due to crystallization/solidification. In the case of the
FeC18(C8H17PhSO3) and FeC18(C8H17SO3) compounds with
long alkyl chain counteranion, DSC traces show a broad peak at
242 and 294 K that corresponds to CrHS → CrLS spin crossover
and a sharp peak at 364 and 341 K, respectively, on heating
mode. As no melting was observed by POM measurements at
364 and 341 K, the endothermic peak can only be attributed to
a CrHS → Cr′HS structural transition. It is worth mentioning that
these phase transitions are reversible on cooling (Figure S9,
Supporting Information). At higher temperature, only
FeC18(C8H17SO3) exhibits an weak endothermic peak at 450 K,
which could be attributed to a Cr′HS → LC phase transition
based on POM observations. Unfortunately for both
compounds, no isotropic peak is observed up to 530 K and
above this temperature the compound decomposes very fast.
The existence of a lamellar liquid-crystalline phase is further
supported by POM observations of birefringence at 480 K for
the FeC18(ptol) in its liquid crystal phase (Figure 4c), although
no clear texture could be observed. For the other Fe compounds
(except FeC18(C8H17PhSO3)), birefringence in POM was
observed at best in a transitory manner upon heating. Due to
the decomposition of the Fe(II) compounds at temperatures
lower than the clearing point, the POM textures of these systems
are unfortunately extremely difficult to observe.
Powder X-ray diffractograms performed in the temperature
range of existence of the mesophase show in all cases only one
very broad peak at high angles centered at ca. 1.3 Å. This
diffraction peak that corresponds to the alkyl “halo” as for the
Zn compounds and the disappearance of the (poor) diffractions
at high angles indicates formation of liquid-crystalline phase. In
the small angle region, mostly one strong peak is observed to be
very similar to that observed for the Zn analogues and thus
5424
dx.doi.org/10.1021/ic300404r | Inorg. Chem. 2012, 51, 5417−5426

Inorganic Chemistry
Article
shifted toward larger q with respect to the low-temperature
phase (see Figures 2 and 5). The higher order peaks associated
with the lamellar phase are not observed in any of the Fe(II)
materials. These X-ray diffraction results together with the
difficulty to observe stable textures seem to indicate that the Fe
compounds likely only exhibit a short-range preorganization
without developing a real lamellar phase. This absence of long-
range lamellar phase is probably the result of the poor crystallinity
of the solid phase that may arise from shorter one-dimensional
coordination chains and/or a broader distribution of their lengths.
The presence of impurities arising from the oxidation/
decomposition of a fraction of the material may also contribute
to the weak stability of the thermotropic mesophase in the Fe
compounds. Unfortunately, the decomposition/oxidation ob-
served from temperatures just above the melting (ptol− com-
pounds) or close to the clearing temperature (Cl− and C8H17SO3−
compounds) impedes a deeper study of these phases.
Like for the Zn compounds, the melting and clearing
temperatures have been gathered to build a pseudophase
diagram, also including the transition from the LS to the HS
state (Figure 9). In contrast to the ZnCnCl series, these transition
temperatures stay roughly constant with n for both for FeCnCl and
FeCnptol systems, although the observed temperatures for n = 18
and thus the corresponding domains of existence of the
mesophase are close to those determined for the Zn analogue
(see Table 1). The absence of a significant influence of the alkyl
arms length on the melting and clearing temperatures is likely to
be related to the structural organization of the coordination Fe(II)
polymer. In line with the variation of the interlamellar distance
along the FeCnptol series (vide infra, Figure S4), these results
suggest an amorphous folding and noninterdigitation of the alkyl
chains in the Fe(II) materials.
currently being employed with branched substituents on the
triazole ligands.
ASSOCIATED CONTENT
* Supporting Information
■
S
FT-IR spectra, additional magnetic properties, and DSC
measurements. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: roubeau@unizar.es; clerac@crpp-bordeaux.cnrs.fr.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
This work was supported by the Centre National de la
Recherche Scientifique (CNRS), the University of Bordeaux,
■
́
the Conseil Regional d’Aquitaine, GIS Advanced Materials in
Aquitaine (COMET Project), the ANR (NT09_469563, AC-
MAGnets project), the Erasmus Mundus External Cooperation
Window of the European Community Mobility Programme for
the Ph.D. fellowship of Dr. D. Siretanu, and the Spanish
National Council of Sciences CSIC (PIE to O.R.).
REFERENCES
(1) (a) Coronado, E.; Galan
■
́
-Mascaros
́
, J. R.; Gom
́
ez-García, C. J.;
Laukhin, V. Nature 2000, 408, 447−449. (b) Miller, J. S. Angew. Chem.,
Int. Ed. 2003, 42, 27−29.
(2) (a) Gutlich, P.; Goodwin, H. A., Eds. Topics in Current Chemistry;
̈
2004; Vols. 233, 234, 235. (b) Gutlich, P. Struct. Bonding (Berlin)
̈
1981, 44, 83−195. (c) Gutlich, P.; Garcia, Y.; Goodwin, H. A. Chem.
̈
Soc. Rev. 2000, 29, 419−427. (d) Gutlich, P.; Hauser, A.; Spiering, H.
̈
CONCLUSIONS
Angew. Chem., Int. Ed. Engl. 1994, 33, 2024−2054.
■
(3) (a) Vreugdenhil, W.; van Diemen, J. H.; de Graff, R. A. G.;
Haasnoot, J. G.; Reedijk, J.; van der Kraan, A. M.; Kahn, O.;
Zn(II) one-dimensional coordination polymers formed through
triple N1,N2-4-n-alkyl-1,2,4-triazole (with n = 10−18) bridges
and obtained with chloride and sulfonate anions display a
thermotropic lamellar liquid-crystalline phase stable over
a wide temperature range, for example, 409 to 485 K for
[Zn(C18H37trz)3](Cl)2. For the shorter alkyl substituent (decyl,
undecyl), the mesophase is monotropic and occurs only in the
cooling mode. The Fe(II) analogues, besides presenting a
cooperative spin crossover and its associated magnetic and
optical signatures, maintain a similar thermotropic behavior,
although only reaching a preorganization, probably as a consequence
of poor size homogeneity/crystallinity and/or impurity formed
through partial oxidation/decomposition at high temperatures.
The SC phenomenon in these materials occurs above room
temperature but still below the liquid-crystal temperature
domains in such a way that the two phenomena do not
influence each other. The derived phase diagrams indicate that
the use of longer alkyl substituents (n > 18) on the triazole
ligands would probably not allow lowering sufficiently the
temperature domain of the mesophase. On the other hand, as
shown by the FeC18(C8H17PhSO3) and FeC18(C8H17SO3)
compounds, functionalization of the counteranions by a long
alkyl chain is also not a good strategy to improve the meso-
morphic behavior. These conclusions highlight the necessity to
adopt branched alkyl substituents on triazole ligands or anions
to bring both phenomena to a common temperature range. On
the other hand, the use of stable diamagnetic Zn(II) analogues
has proven to be very useful to study the comparatively less
stable and less crystalline Fe(II) analogues. This strategy is
Zarembowitch, J. Polyhedron 1990, 9, 2971−2979. (b) Krober, J.;
̈
Audier
̀
e, J.-P.; Claude, R.; Codjovi, E.; Kahn, O.; Haasnoot, J. G.;
e, F.; Jay, C.; Bousseksou, A.; Linares, J.; Varret, F.; Gonthier-
ard, J.-F.;
Grolier
̀
̀
Vassal, A. Chem. Mater. 1994, 6, 1404−1412. (c) Let
́
Guionneau, P.; Codjovi, E.; Lavastre, O.; Bravic, G.; Chasseau, D.;
Kahn, O. J. Am. Chem. Soc. 1997, 119, 10861−10862. (d) Niel, V.;
Martinez-Agudo, J. M.; Munoz, M. C.; Gaspar, A. B.; Real, J. A. Inorg.
̃
Chem. 2001, 40, 3838−3839. (e) Weber, B.; Bauer, W.; Obel, J. Angew.
Chem., Int. Ed. 2008, 47, 10098−10101. (f) Craig, G. A.; Costa, J. S.;
Roubeau, O.; Teat, S. J.; Aromí, G. Chem.Eur. J. 2011, 17, 3120−
3127.
(4) Gaspar, A. B.; Ksenofontov, V.; Seredyuk, M.; Gutlich, P. Coord.
̈
Chem. Rev. 2005, 249, 2661−2676.
(5) (a) Donnio, B.; Bruce, D. W. Struct. Bonding (Berlin) 1999, 95,
193−247. (b) Binnemans, K.; Gorller-Walrand, C. Chem. Rev. 2002,
̈
102, 2303−2346. (c) Serrano, J. L.; Sierra, T. Coord. Chem. Rev. 2003,
242, 73−85. (d) Piguet, C.; Bunzli, J. C. G.; Donnio, B.; Guillon, D.
̈
Chem. Commun. 2006, 36, 3755−3768. (e) Donnio, D.; Guillon, D.;
Deschenaux, R.; Bruce, D. W. Compr. Coord. Chem. II 2003, 7, 357−
627. (f) Gaspar, A. B.; Seredyuk, M.; Gutlich, P. Coord. Chem. Rev.
̈
2009, 253, 2399−2413.
(6) Galyametdinov, Y.; Ksenofontov, V.; Prosvirin, A.; Ovchinnikov,
I.; Ivanova, G.; Gutlich, P.; Haase, W. Angew. Chem., Int. Ed. 2001, 40,
̈
4269−4271.
(7) (a) Hayami, S.; Danjobara, K.; Inoue, K.; Ogawa, Y.; Matsumoto,
N.; Maeda, Y. Adv. Mater. 2004, 16, 869−872. (b) Hayami, S.;
Motokawa, N.; Shuto, A.; Masuhara, N.; Someya, T.; Ogawa, Y.;
Inoue, K.; Maeda, Y. Inorg. Chem. 2007, 46, 1789−1794.
(8) The first single-crystal structure of an Fe(II) triazole-based chain
compound was only recently reported, see: Grosjean, A.; Daro, N.;
5425
dx.doi.org/10.1021/ic300404r | Inorg. Chem. 2012, 51, 5417−5426

Inorganic Chemistry
Article
Kauffmann, B.; Kaiba, A.; Let
2011, 47, 12382−12384.
(9) (a) Coronado, E.; Galan
́
ard, J. F.; Guionneau, G. Chem. Commun.
Reedijk, J. J. Am. Chem. Soc. 1983, 105, 1682−1683. (c) Kolnaar, J. J.
A.; van Dijk, G.; Kooijman, H.; Spek, A. L.; Ksenofontov, V.; Gutlich,
̈
-Mascaros
́
, J. R.; Monrabal-Capilla, M.;
P.; Haasnoot, J. G.; Reedijk, J. Inorg. Chem. 1997, 36, 2433−2440.
(23) Haasnoot, J. G.; Groeneveld, W. L. Z. Naturforsch. 1977, 32b,
533.
́
García-Martínez, J.; Pardo-Iban
́
ez, P. Adv. Mater. 2007, 19, 1359−
̃
1361. (b) Forestier, T.; Mornet, S.; Daro, N.; Nishihara, T.; Mouri,
S.-I.; Tanaka, K.; Fouche, O.; Freysz, E.; Letard, J.-F. Chem. Commun.
2008, 4327−4329. (c) Forestier, T.; Kaiba, A.; Pechev, S.; Denux, D.;
Guionneau, P.; Etrillard, C.; Daro, N.; Freysz, E.; Let
(24) Roubeau, O.; Castro, M.; Burriel, R.; Haasnoot, J. G.; Reedijk, J.
́
́
J. Phys. Chem. B 2011, 115, 3003−3012.
(25) (a) Michalowicz, A.; Moscovici, J.; Kahn, O. J. Phys. IV Fr. 1997,
C2−633. (b) Verelst, M.; Sommier, L.; Lecante, P.; Mosset, A.; Kahn,
O. Chem. Mater. 1998, 10, 980−985.
́
ard, J.-F. Chem.
Eur. J. 2009, 15, 6122−6130. (d) Tokarev, A.; Salmon, L.; Guari, Y.;
Nicolazzi, W.; Molnar, G.; Bousseksou, A. Chem. Commun. 2010, 46,
8011−8013. (e) Tokarev, A.; Salmon, L.; Guari, Y.; Molnar, G.;
Bousseksou, A. New J. Chem. 2011, 35, 2081−2088. (f) Etrillard, C.;
́
(26) Urakawa, A.; van Beek, W.; Monrabal-Capilla, M.; Galan-
Mascaros
1323−1329.
́
, J. R.; Palin, L.; Milanesio, M. J. Phys. Chem. C 2011, 115,
́
Faramarzi, V.; Dayen, J. F.; Letard, J. F.; Doudin, B. Chem. Commun.
(27) (a) Garcia, Y.; van Koningsbruggen, P. J.; Bravic, G.; Guionneau,
P.; Chasseau, D.; Cascarano, G. L.; Moscovici, J.; Lambert, K.;
Michalowicz, A.; Kahn, O. Inorg. Chem. 1997, 36, 6357−6365.
(b) Drabent, K.; Ciunik, Z. Chem. Commun. 2001, 1254−1255.
(c) Garcia, Y.; van Koningsbruggen, P. J.; Bravic, G.; Chasseau, D.;
Kahn, O. Eur. J. Inorg. Chem. 2003, 356−362.
2011, 47, 9663−9665. (g) Prins, F.; Monrabal-Capilla, M.; Osorio,
E. A.; Coronado, E.; van der Zant, H. S. J. Adv. Mater. 2011, 23, 1545−
1549.
́
(10) (a) Roubeau, O.; Colin, A.; Schmitt, V.; Clerac, R. Angew.
Chem., Int. Ed. 2004, 43, 3283−3286. (b) Fujigaya, T.; Jiang, D.-L.;
Aida, T. Chem. Asian J. 2007, 2, 106−113. (c) Rubio, M.; Lop
́
ez, D.
̀
(28) (a) Nguyen, H. T.; Destrade, C.; Malthtete, J. In Handbook of
Eur. Polym. J. 2009, 45, 3339−3346.
Liquid Crystals; Demus, D., Goodby, J. W., Gray, G. W., Spiess, H. W.,
Vill, V., Eds.; Wiley VCH: Weinheim, 1998; Vol. 2B, pp 865−885;
(b) Giroud-Godquin, A. M.; Maitlis, P. M. Angew. Chem., Int. Ed. Engl.
1991, 30, 375−402 and references therein.
(11) (a) Roubeau, O.; Agricole, B.; Cler
́
ac, R.; Ravaine, S. J. Phys.
́
Chem. B 2004, 108, 15110−15116. (b) Thibault, C.; Molnar, G.;
Salmon, L.; Bousseksou, A.; Vieu, C. Langmuir 2009, 26, 1557−1560.
(c) Faulmann, C.; Chahine, J.; Malfant, I.; de Caro, D.; Cormary, B.;
Valade, L. Dalton Trans. 2011, 40, 2480−2485. (d) Chen, C.; Ma,
J.-G.; Zhang, J.-J.; Shi, W.; Cheng, P.; Liao, D.-Z.; Yan, S.-P. Chem.
Commun. 2010, 46, 5073−5075.
(12) (a) Kahn, O.; Jay Martinez, C. Science 1998, 279, 44−48.
́
(b) Letard, J.-F.; Guionneau, P.; Goux-Capes, L. Top. Curr. Chem.
2004, 235, 221−249.
(13) (a) Kahn, O; Codjovi, E. Philos. Trans. R. Soc. London A 1996,
354, 359−379. (b) Aromí, G.; Barrios, L. A.; Roubeau, O.; Gamez, P.
Coord. Chem. Rev. 2011, 255, 485−546.
(14) Fujigaya, T.; Jiang, D.-L.; Aida, T. J. Am. Chem. Soc. 2003, 125,
14690−14691.
(15) (a) Seredyuk, M.; Gaspar, A. B.; Ksenofontov, V.; Reiman, S.;
Galyametdinov, Y.; Haase, W.; Rentschler, E.; Gutlich, P. Chem. Mater.
̈
2006, 18, 2513−2519. (b) Seredyuk, M.; Gaspar, A. B.; Ksenofontov,
V.; Galyametdinov, Y.; Verdaguer, M.; Villain, F.; Gutlich, P. Inorg.
̈
Chem. 2008, 47, 10232−10245.
(16) Lee, Y. H.; Komatsu, Y.; Yamamoto, Y.; Kato, K.; Shimizu, T.;
Ohta, A.; Matsui, T.; Hayami, S. Inorg. Chem. Commun. 2011, 14,
1498−1500.
(17) (a) Roubeau, O.; Natividad, E.; Agricole, B.; Ravaine, S.
Langmuir 2007, 23, 3110−3117. (b) Grondin, P.; Roubeau, O.;
Castro, M.; Saadaoui, H.; Colin, A.; Cler
5184−5195.
́
ac, R. Langmuir 2010, 26,
(18) (a) Haasnoot, J. G. In Magnetism: a supramolecular function;
Kahn, O., Ed.; NATO Advanced Study Institute Series; Kluwer
Academic Publishers: Dordrecht, 1996; Vol. C 484, p 299.
(b) Haasnoot, J. G. Coord. Chem. Rev. 2000, 200−202, 131−185.
(c) Berezovskii, G. A.; Bessergenev, Y. G.; Lavrenova, L. G.; Ikorskii,
V. N. Russ. J. Phys. Chem. 2002, 76, 1246−1250. (d) Codjovi, E.;
Sommier, L.; Kahn, O.; Jay, C. New J. Chem. 1996, 20, 2075.
(e) Garcia, Y.; van Konningsbruggen, P. J.; Lapouyade, R.; Fournes
̀
, L.;
Rabardel, L.; Kahn, O.; Ksenovontov, V.; Levchenko, G.; Gutlich, P.
̈
Chem. Mater. 1998, 10, 2426−2433. (f) Toyazaki, S.; Nakanishi, M.;
Komatsu, T.; Kojima, N.; Matsumura, D.; Yokoyama, T. Synth. Met.
2001, 121, 1794−1795.
(19) Nguyen, H. T.; Bouchta, A.; Navailles, L.; Barois, P.; Isaert, N.;
Twieg, R. J.; Maaroufi, A.; Destrade, C. J. Phys. II Fr. 1992, 2, 1889−
1906.
(20) Roubeau, O.; Alcazar Gomez, J. M.; Blaskus, E.; Kolnaar, J. J. A.;
Haasnoot, J. G.; Reedijk, J. New J. Chem. 2001, 25, 144−150.
(21) Haasnoot, J. G. Private communication.
(22) (a) Garcia, Y.; van Koningsbruggen, P. J.; Bravic, G.; Guionneau,
P.; Chasseau, D.; Cascarano, G. L.; Moscovici, J.; Lambert, K.;
Michalowicz, A.; Kahn, O. Inorg. Chem. 1997, 36, 6357−6365.
̂
(b) Vos, G.; Le Febre, R. A.; de Graaf, R. A. G.; Haasnoot, J. G.;
5426
dx.doi.org/10.1021/ic300404r | Inorg. Chem. 2012, 51, 5417−5426