Polycatenar pyrazole and pyrazolate ligands as building blocks of new columnar Pd(ii) metallomesogens

Article abstract of DOI:10.1039/c4dt00369a

Dicatenar pyridine-functionalised pyrazole ligands [Hpz^R(n,n)py] (R(n,n) = C₆H₃(OC_nH_2n+1) ₂, n = 4, 6, 8, 10, 12, 14, 16, 18) have been strategically synthesised to be used as new building blocks for designing discotic liquid crystalline materials. Their coordination to Pd(ii) fragments has allowed to achieve two novel families of metallomesogens, [Pd(pz^R(n,n)py) ₂] (I) and [PdCl₂(Hpz^R(n,n)py)] (II), in which the ligand is coordinated in the anionic form as pyrazolate or in the neutral form as pyrazole, respectively. Thermal studies showed that the ligands with n = 14 and 16 carbon atoms, as well as all the palladium complexes, display discotic mesophases in the temperature range of 68-141 °C. The results indicate that the coordination environment around the metal is a determining factor which allows control of the supramolecular arrangement of the mesophase. Disc-like molecules from complexes I pack themselves into cylindrical structures that result in hexagonal columnar phases (Col_h), while the half-disc shaped molecules from II self-assemble into a layer with an antiparallel dimeric disposition which generates lamellar columnar phases (Col_L). Schematic models based on X-ray powder diffraction (XRD) experiments are proposed to illustrate the molecular organisation of these Pd metallomesogens in the columnar mesophases.

Full text of DOI:10.1039/c4dt00369a

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Polycatenar pyrazole and pyrazolate ligands as
building blocks of new columnar Pd(II)
metallomesogens†
Cite this: Dalton Trans., 2014, 43,
8849
Cristián Cuerva,a José A. Campo,a Paloma Ovejero,a María R. Torresb and
Mercedes Cano*a
Dicatenar pyridine-functionalised pyrazole ligands [HpzR(n,n)py] (R(n,n) = C6H3(OCnH2n+1)2, n = 4, 6, 8, 10,
12, 14, 16, 18) have been strategically synthesised to be used as new building blocks for designing discotic
liquid crystalline materials. Their coordination to Pd(II) fragments has allowed to achieve two novel families
of metallomesogens, [Pd(pzR(n,n)py)2] (I) and [PdCl2(HpzR(n,n)py)] (II), in which the ligand is coordinated in
the anionic form as pyrazolate or in the neutral form as pyrazole, respectively. Thermal studies showed
that the ligands with n = 14 and 16 carbon atoms, as well as all the palladium complexes, display discotic
mesophases in the temperature range of 68–141 °C. The results indicate that the coordination environ-
ment around the metal is a determining factor which allows control of the supramolecular arrangement
of the mesophase. Disc-like molecules from complexes I pack themselves into cylindrical structures that
result in hexagonal columnar phases (Colh), while the half-disc shaped molecules from II self-assemble
into a layer with an antiparallel dimeric disposition which generates lamellar columnar phases (ColL).
Schematic models based on X-ray powder diffraction (XRD) experiments are proposed to illustrate the
molecular organisation of these Pd metallomesogens in the columnar mesophases.
Received 4th February 2014,
Accepted 11th April 2014
DOI: 10.1039/c4dt00369a
www.rsc.org/dalton
square-planar geometry are likely to achieve disc-like mole-
cules that allow to attain favourable columnar stacking
Introduction
In recent years, metallomesogens have been one of the major arrangements for inducing mesomorphism. So, molecular
areas of research1 and a lot of compounds exhibiting meso- systems containing Pd(II),14,15 Pt(II)16,17 or Ni(II)18 have been
morphic properties have been reported and their physical pro- found to exhibit columnar liquid crystal properties. However,
perties studied.2 In particular, discotic liquid crystals are of in 1986, for the first time a new series of disc-like copper com-
great interest due to their high charge-carrier mobility and plexes was reported which exhibited both columnar and
their one-dimensional aromatic π–π stacking,3,4 which can con- layered stacking in the mesophase.19 Since then, few metallo-
tribute to their potential applications such as field-effect tran- mesogens have been prepared and characterised with lamellar
sistors,5 photovoltaic solar cells,6 optical data storage devices,7 columnar mesophases (ColL).20–23
sensors8–10 and electroluminescent displays.11
On the other hand, pyrazole ligands have been proved to be
The formation of supramolecular structures favouring good candidates to induce mesomorphism in their coordi-
mesomorphic properties depends mainly on the combination nation to different metal centres. Pyrazole is an electron-rich
of the coordination geometry of metal ions and the nature ligand with weak π-accepting and strong σ-donating properties
of ligands.12,13 Tetracoordinated d8-transition metals with a as pyrazole derivatives are easily deprotonated to form anionic
species.24 A strategy used in the design of metallomesogens is
to incorporate functionalised bridging pyrazolates due to their
ability to attain an adequate geometry for achieving meso-
aDepartamento de Química Inorgánica I, Facultad de Ciencias Químicas,
Universidad Complutense, E-28040 Madrid, Spain. E-mail: mmcano@ucm.es;
morphic properties. In this context, pyrazole and pyrazolate
Fax: +34 91394 4352; Tel: +34 91394 4340
bLaboratorio de Difracción de Rayos-X, Facultad de Ciencias Químicas, Universidad
palladium,25,26 gold27–29 and silver10,30 complexes have been
described as liquid crystal materials with smectic and colum-
nar arrangements.
Complutense, E-28040 Madrid, Spain
†Electronic supplementary information (ESI) available: Full characterisation of
Recently, we have reported Ag(I)10 and Zn(II)31 metallomeso-
gens based on monocatenar pyridine-functionalised pyrazoles
which have been demonstrated to be excellent building blocks to
induce smectic behaviour. The presence of the pyridine moiety
the pyrazole ligands and their corresponding Pd(II) metallomesogens, selected
bond distances and angles for 1 and 12, PLUTO molecular drawing for 17 and
X-ray crystallographic data in CIF format for 1 and 12. CCDC 977934 and
977935. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c4dt00369a
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monocatenar ones.10 Reactions of 1–8 with palladium(II)
acetate or bis(benzonitrile)dichloridepalladium(II) in a 2 : 1 or
1 : 1 (ligand : metal) molar ratio yielded the new square-planar
complexes [Pd(pzR(n,n)py)2] 9–16 (type I) and [PdCl2(HpzR(n,n)py)]
17–24 (type II), respectively (Scheme 1). All compounds 1–24
were characterised by spectroscopic techniques (IR, 1H-NMR
and 13C-NMR in some representative cases) and CHN elemen-
tal analyses. Some ligands and complexes were obtained with
molecules of ethanol or dichloromethane of solvatation,
respectively (see the Experimental section and ESI†).
Table 1 Numbering of the compounds described in this work
Compounda
[HpzR(n,n)py
Type
n
Number
]
4
6
8
1
2
3
4
5
6
7
8
10
12
14
16
18
4
[Pd(pzR(n,n)py)2]
I
9
6
8
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
The IR spectra of palladium complexes 9–24 in the solid
state show the characteristic absorption bands from the
ligands, which are slightly shifted in relation to free pyrazoles.
Among them, the overlapped ν(CvN) and ν(CvC) bands of
the pyridine and pyrazole heterocycles around 1595 cm−1 and
the γ(CH) band corresponding to the deformation of the pyri-
dine group at ca. 766 cm−1 were remarkable. In addition,
bands to ca. 3190 cm−1 from the NH-pyrazole group were also
observed for 17–24, confirming the neutral nature of the
ligand in these compounds. By contrast, their absence in 9–16
agrees with their coordinative form as a pyrazolate group.
The 1H-NMR spectra of all ligands and compounds in
CDCl3 solution at room temperature, as well as the 13C-NMR
spectra of the ligands 1–8 and derivatives 10, 13 and 18, 21 as
representative examples of complexes I and II, display the
expected resonances.
10
12
14
16
18
4
6
8
10
12
14
16
18
[PdCl2(HpzR(n,n)py)]
II
a R(n,n) = C6H3(OCnH2n+1)2.
in the rigid core enables modification of the molecular geometry
and polarisation, thus influencing the mesomorphic behaviour.
In the present work, we describe the synthesis and charac-
terisation of a novel series of dicatenar pyridine-functionalised
pyrazole ligands, 3-(3,5-bis(alkyloxy)phenyl)-(5-pyridin-2-yl)pyra-
zole [HpzR(n,n)py] (R(n,n) = C6H3(OCnH2n+1)2, n = 4, 6, 8, 10, 12,
14, 16, 18), and their corresponding palladium metallomeso-
gens [Pd(pzR(n,n)py)2] and [PdCl2(HpzR(n,n)py)]. The square-
planar environment around the metal centre as well as the use
of the above-mentioned ligands are useful for obtaining disc-
like molecules, which are properly organised to form columnar
mesophases. The introduction of two alkyloxy chains in each
pyrazole ligand has contributed to the formation of these self-
assemblies. On the other hand, the results show that the
ordering of the disc-like molecules in the mesophases signifi-
cantly depends on the coordination environment around the
metal. So, the palladium complexes prepared with a 2 : 1
(ligand : metal) molar ratio show hexagonal columnar phases
(Colh), while those with a 1 : 1 relation exhibit lamellar colum-
nar mesophases (ColL). In addition, the length of the terminal
chains constitutes a very important factor to achieve stable
mesophases in a wide range of temperatures.
1
Particularly, in the H-NMR spectra of the complexes I the
6-H signal (ca. 10.40 ppm) is down-field shifted with respect to
that observed in the free pyrazoles (ca. 8.64 ppm). This shift is
attributed not only to the coordination of the pyridine group
to the Pd(II) metal centre, but also to the formation of intra-
molecular hydrogen bonds (C–H⋯N) as was observed in the
crystal structure of [Pd(pzR(10,10)py)2] 12, which is described
later. Moreover, the presence of unique signals for each type of
protons or carbons in the 1H and 13C spectra indicates the
equivalence of the two pyridylpyrazole ligands.
All the new compounds described in this work (1–24) are
schematically presented in Table 1, including the numbering
used to identify them.
Results and discussion
Synthesis and characterisation
Dicatenar pyridylpyrazole ligands [HpzR(n,n)py] 1–8 were syn-
Scheme 1 Synthesis of the ligands and complexes. The atom number-
thesised by a procedure similar to that described for related ing is used in the NMR assignments.
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In addition, for compounds II the characteristic NH signal
of the pyrazole ligands is observed in the 1H-NMR at ca.
11.20 ppm according to the neutral nature of the coordinated
ligand.
It is also interesting to note that the chemical shift of the
4′-H proton of the pyrazole ring is slightly modified in com-
pounds II, but is up-field shifted for I, which is also associated
with the anionic aromatic nature of the ligand in these
compounds.
Fig. 2 Packing of [HpzR(4,4)py)] 1 through the a-axis.
The dimeric units are arranged in a layered structure, exhi-
biting an extensive interdigitation of the alkyl chains (Fig. 2).
Crystal structure of [HpzR(4,4)py] 1
Single crystals suitable for X-ray diffraction experiments were
obtained by vapour diffusion of hexane into a solution of the
ligand in dicholoromethane. The molecular structure of 1 is
depicted in Fig. 1 and selected bond distances and angles are
given in Table S1 in the ESI.† The compound crystallises in the
monoclinic system, space group P21/n, with four formula units
per unit cell.
Crystal structure of [Pd(pzR(10,10)py)2] 12
Suitable crystals of 12 were obtained by slow vapour diffusion
of acetone into a chloroform solution of the complex. The
compound crystallises in the triclinic system, space group P1,
with the Pd atom located in the centre of inversion. The mole-
cular structure is depicted in Fig. 3, and Table S2 (see the
ESI†) lists selected bond distances and angles.
ˉ
The bond distances in the pyrazole, pyridine and benzene
rings evidence a delocalised π system. The benzene group is
practically coplanar with the pyrazole ring (dihedral angle of
5.1(1)°), while the pyridine group is slightly rotated with
respect to the pyrazole ring (dihedral angle of 11.2(1)°). The
N1 and N3-donor atoms are cis-located, unlike the trans posi-
tions that they occupy in related 1-pyridylpyrazoles.32 The alkyl
chains located at the 3- and 5-positions of the benzene ring
show the characteristic C–C distances corresponding to single
bonds. The two terminal chains are practically situated on the
plane of the own benzene ring (torsion angles of ca. 180°).
One remarkable characteristic is the presence of intermole-
cular N–H⋯N hydrogen bonds between the NH group at the
pyrazole ring and the N-pyrazolic atom of the neighbouring
molecule (N1⋯N2, 2.899(3) Å; <(N1–H1⋯N2), 142.8°; sym-
metry operation: −x + 2, −y, −z + 1), giving rise to the for-
mation of dimers (see the inset in Fig. 1). The two molecules
of the dimer adopt a head-to-tail conformation which is
responsible for the disc-like molecular shape of this com-
pound, in contrast with the elongated shape of monocatenar
pyrazoles [HpzR(n)py] described previously by us.10
The palladium atom adopts a tetracoordination defined by
four nitrogen atoms of the two pyrazolate ligands, giving rise
to an almost square-planar environment. The Pd–N1 and Pd–
N3 distances of 1.929(7) and 2.041(7) Å, respectively, are con-
sistent with those observed in related compounds.33 The
major deviation from the ideal geometry is imposed by the
bite N1–Pd–N3 angle of 78.5(4)°. The bidentate coordination
of the ligand generates an almost planar five-membered metal-
locycle PdN1C5C6N3 (maximum deviation of 0.019(1) Å for
N1), which is coplanar to the coordination plane PdN1N3N1′
N3′ defined by the metal centre and the four nitrogen atoms of
the two bidentate ligands (dihedral angle of 1.3(4)°).
Pyridine and benzene rings are also coplanar with the pyra-
zolate one (dihedral angles of 0.6(1) and 3.9(1)°, respectively).
The lower value of these angles with respect to those observed
in the corresponding free ligand may be associated with an
increased conjugation and delocalisation of the π electronic
charge as a result of their coordination to the metal centre in
Fig. 1 ORTEP plot for [HpzR(4,4)py)] 1 with 20% probability. Hydrogen
atoms, except H1, have been omitted for clarity. The inset shows the
dimeric units defined by hydrogen bonds.
Fig. 3 ORTEP plot for [Pd(pzR(10,10)py)2] 12 with 40% probability. Hydro-
gen atoms have been omitted for clarity.
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the pyrazolate form. The C5–C6 and C3–C11 distances of
1.46(2) Å are slightly shorter than in the free pyrazole, in agree-
ment with the above proposal.
The substituent alkyl chains show the characteristic C–C
distances associated with single bonds. They are almost co-
planar with the benzene ring, as deduced from the angle of
ca. 85° between the normal to the benzene plane and the line
that connects the extremes of each chain.
An important feature was the establishment of intramolecu-
lar hydrogen bonds (C–H⋯N) between the free nitrogen atom
at the pyrazolate ring and the nearest carbon atom from the
pyridine group of the other ligand (C10⋯N2, 3.047(1) Å;
<(C10–H10⋯N2), 143.5°; symmetry operation: −x + 1, −y + 1,
−z + 1) (Fig. 4). These bonds appear to be maintained in solu-
tion as is deduced from the chemical shift observed for the
6-H proton in the 1H-NMR spectra. The pyrazolate ligands
adopt a trans-arrangement with their terminal alkyl chains
pointed in opposite directions and located all parallel to each
other. In summary, the molecular structure contains an
almost planar rigid core surrounded by four peripheral chains,
thus defining a suitable molecular shape to achieve the supra-
molecular ordering of the observed mesophases.
In addition, each molecular unit is related with their neigh-
bours by weak π⋯π interactions of ca. 3.4 Å involving the pyri-
dine group and benzene rings of neighbouring molecules,
thus generating columns along the a-axis (Fig. 5). Molecules
are displaced from each other, so that the palladium centres
are located at 6.79(1) Å. In this situation, the core is rotated
40.3(1)° with respect to the axis defined by the palladium
atoms.
Fig. 6 Packing of [Pd(pzR(10,10)py)2] 12 through the a-axis.
packing may be related to the mesomorphic behaviour
observed in these derivatives (see Thermal behaviour) and con-
stitutes a support to propose the existence of a structural
relationship between the mesophase and the solid state.
Thermal behaviour
Thermal properties of the compounds were studied by
polarised optical microscopy (POM), differential scanning
calorimetry (DSC) and X-ray diffraction at variable temperature
(XRD), the latter one used only in representative complexes.
Tables 2 and 3 list the phase transition temperatures and their
associated enthalpy data established by DSC.
Ligands 6 and 7 displayed enantiotropic liquid crystal pro-
perties showing a fibrous texture (Fig. 7), which was similar to
that previously reported for the ColL mesophase of meso-tetra
(4-alkylamidophenyl)porphyrin liquid crystals.34 The remain-
Molecular packing can be described as a columnar stacking
of molecules, in such a way that the terminal chains of neigh-
bouring columns exhibit extensive interdigitation (Fig. 6). This
Table 2 Phase behaviour of ligands 1–8 determined by POM and DSC
n
Transitiona
Tb/°C
ΔH/kJ mol−1
29.3
1
2
3
4
5
6
4
6
8
Cr→I
I→Cr
Cr→I
I→Cr
Cr→I
I→Cr
Cr→I
I→Cr
100
63c
105
38c
88
46.5
36.5
35c
89
10
12
14
54.4
34c
67
Cr→I
I→Cr
50.5
38c
81c
83
Fig. 4 Disc-like core showing the hydrogen bonds.
Cr→ColL
ColL→I
I→ColL
ColL→Cr
Cr→ColL
ColL→I
I→ColL
ColL→Cr
Cr→I
76.5d
32c
27c
84c
86
7
8
16
18
92.6d
48.2
35c
30c
85
I→Cr
40c
a Cr = crystalline phase, ColL = lamellar columnar mesophase, I =
isotropic liquid. b DSC onset peaks. c Detected by POM. d Overlapped
processes.
Fig. 5 Column formed by π⋯π interactions along a-axis.
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Table 3 Phase behaviour of Pd(II) complexes determined by POM and DSC
[Pd(pzR(n,n)py)2]
[PdCl2(HpzR(n,n)py)]
Compounds II
17
n
Compounds I
Transitiona
Tb/°C
ΔH/kJ mol−1
Transitiona
Tb/°C
ΔH/kJ mol−1
4
9
Cr→Cr′→Colh
Colh→I
I→Colh
Colh→Cr
Cr→Colh
Colh→I
I→Colh
Colh→Cr
Cr→Cr′
Cr′→Colh
Colh→I
I→Colh
Colh→Cr
Cr→Colh
Colh→I
I→Colh
Colh→Cr
141c
285
284
112
99
269
269
99
64
90
246
246
82
117.4
2.8
−2.0
13.6
53.8
2.5
−2.3
−7.5
19.6
16.7
3.5
−1.9
−1.4
80.6
2.2
Cr→ColL
ColL→I
I→ColL
ColL→Cr
Cr→ColL
ColL→I
134
262e
226
111d
120
248
232
106d
103
228
199
92d
22.0
20.8
−15.5
6
8
10
11
18
19
17.6
23.0
−20.6
I→ColL
ColL→Cr
Cr→ColL
ColL→I
I→ColL
ColL→Cr
56.1
22.9
−12.1
10
12
14
16
18
12
13
14
15
16
80
20
21
22
23
24
Cr→Cr′
Cr′→ColL
ColL→I
I→ColL
ColL→Cr
Cr→Cr′
Cr′→ColL
ColL→I
I→ColL
ColL→Cr
Cr→Cr′→ColL
ColL→I
61
68
199
187
58d
70
2.9
10.9
13.7
234
230
65d
−1.3
−14.7
Cr→Cr′→Colh
Colh→I
I→Colh
88c
204
204
60d
98.6
1.1
−0.9
17.2
22.0
9.0
−4.3
−21.6
55.8
13.2
−13.6
−29.5
82
190
164
74
Colh→Cr
Cr→Cr′
Cr′→Colh
Colh→I
83
95
206
205
60d
76
2.5
121.4
2.4
90c
188
159
78
I→ColL
ColL→Cr
I→Colh
−1.9
Colh→Cr
Cr→Cr′
Cr′→Colh
Colh→I
56.2
142.4
1.2
−1.5
−59.6
30.3
147.0
1.3
−1.3
Cr→Cr′
Cr′→ColL
ColL→I
75
93
0.7
13.9
0.6
96
187
186
73
157e
135d
89d
78
I→Colh
I→ColL
Colh→Cr
Cr→Cr′
Cr′→Colh
Colh→I
I→Colh
Colh→Cr
ColL→Cr
Cr→Cr′
Cr′→ColL
ColL→I
I→ColL
ColL→Cr
74
1.6
20.1
1.0
102
177
176
60d
97
160e
138d
90d
a Cr, Cr′ = crystalline phases, Colh = hexagonal columnar mesophase, ColL = lamellar columnar mesophase, I = isotropic liquid. b DSC onset
peaks. c Overlapped processes. d Detected by POM. e Partial decomposition.
dium complexes I and II, which have been unequivocally
characterised in this work (see below), was carried out. So,
POM observations revealed that the mesophase of 6 was not
miscible with the Colh phase of 12 but it was with the ColL
phase of 20, thus confirming the columnar lamellar nature of
the mesophase of the pyrazole ligands.
The mesomorphic behaviour of the new ligands [HpzR(n,n)py
]
contrasts with that observed in the related monocatenar pyra-
zoles of the type [HpzR(n)py], which exhibited smectic meso-
phases.10 The increase of the number of terminal chains has
been used as a strategy to produce a disc-like molecular shape
and to reduce melting points.
Fig. 7 Microphotograph of [HpzR(16,16)py] 7 at 85.4 °C on heating.
In general, the palladium complexes show crystalline poly-
morphism and enantiotropic liquid crystal behaviour, exhibit-
ing the characteristic optical textures of discotic phases. The
melting point was easily detected on heating by the appear-
ance of a phase with intense birefringence and high mobility.
For complexes I, the formation of the mesophase from the
ing ligands were not liquid crystals, showing the melting point
at temperatures below 105 °C.
In order to establish the nature of this mesophase, a
contact preparation study of 6 with the phases of the palla-
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Fig. 8 Microphotographs of (a) [Pd(pzR(12,12)py)2] 13 at 192 °C, (b) [Pd(pzR(12,12)py)2] 13 at 183 °C, (c) [Pd(pzR(14,14)py)2] 14 at 164 °C and (d) [Pd(pzR(14,14)py)2]
14 at 127 °C, on cooling (type I).
isotropic liquid gave rise to a dendritic texture with linear bi- sition temperatures is consistent with the viscous nature
refringent defects, which slowly grew at lower temperatures to observed in the mesophase.
form a pseudo-focal conic texture typical of Colh mesophases
In general terms, the DSC traces of complexes I show on
(Fig. 8).35 By contrast, a broken fan-like texture was observed heating three endothermic peaks corresponding to solid–solid,
for complexes II, suggesting lamellar columnar structures solid–mesophase and mesophase–isotrope phase transitions,
(Fig. 9). Similar textures were also found in ColL mesophases respectively. In particular, complexes 9 and 13 melt immedi-
of Ni(II)21 and Pt(II)23 complexes previously reported in the ately after the solid–solid transformation, so that the two first
literature.
DSC studies support the above results. So, the thermograms
peaks are overlapped.
Also, the exothermic peak after the solid–solid process was
of 6 and 7 show a single broad endothermic peak at ca. 87 °C remarkable, which can be perfectly observed in the thermo-
in the first heating cycle, which involves overlapped solid– grams of complexes 14 and 16 (ΔH = −11.3 and −32.9 kJ
mesophase and mesophase–isotropic liquid transitions in mol−1, respectively). This fact suggests that this transformation
agreement with the POM observations (Fig. S1†). On the other occurs to give rise to a more stable solid phase through Pd–Pd
hand, the pronounced hysteresis determined from the tran- interactions, achieving a supramolecular organisation suitable
for the development of hexagonal columnar mesophases. On
cooling, the peak corresponding to the isotrope–mesophase
process was detected at temperatures close to the clearing.
However, the peak from the mesophase–solid transition was
not registered in the thermograms of complexes with long
alkyl chains (except for 15), probably due to the slow solidifica-
tion process as observed by POM.
The DSC thermograms of complexes II with long alkyl
chains (20–24) show on heating three endothermic peaks
corresponding to the solid–solid, solid–mesophase and meso-
phase–isotrope phase transitions. By contrast, only two peaks
consistent with the melting and clearing points were observed
in complexes 17–19. On cooling, the formation of mesophase
Fig. 9 Microphotograph of [PdCl2(HpzR(14,14)py)] 22 at 153 °C on cooling
(type II).
is established in most cases from the exothermic peak regis-
tered at the highest temperatures. Mesophase–solid phase
8854 | Dalton Trans., 2014, 43, 8849–8860
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transition could not be observed probably due to the involve- by increasing the length of the alkyl chains, giving rise to the
ment of a slow transition to a more organised phase. In widest mesophase stability ranges when the alkyl chains are
addition, the hysteresis observed in these complexes suggests the shortest, complexes 10 and 20 exhibiting the highest stabi-
the presence of severe restrictions, which makes difficult the lity interval.
molecular mobility and, consequently, the formation of the
Variable-temperature powder X-ray diffraction studies
mesophase on cooling.
In order to discuss the thermal behaviour of both types of
compounds, two effects were taken into account, the coordi-
nation environment and the alkyl chain length. According to
the first one, the melting points of the pyrazolate complexes I
are only slightly higher than those of the dichloride com-
pounds II (except when n = 6 and 8), while the clearing temp-
eratures are significantly higher. This fact suggests a greater
packing efficacy in the hexagonal columnar phases of I, prob-
ably due to greater electronic delocalisation on the molecular
core and to stronger intermolecular core–core interactions,
which provide greater molecular stability in the Colh phases.
As a consequence of these variations on the melting and clear-
ing temperatures, the mesophase stability ranges of I are
higher than those obtained in the compounds II for any chain
length (Fig. 10).
On the other hand, the influence of the alkyl chain length
on the liquid crystal properties is the same for the two families
of compounds I and II. When the number of the carbon atoms
is small, the melting temperatures decrease by increasing the
chain length. However, in compounds with n > 10 the van der
Waals interactions among the hydrophobic tails are greater by
increasing the chain length, thus making the melting tempera-
tures increase. In contrast, the clearing points always decrease
Selected mesomorphic derivatives of families I and II were sub-
jected to variable-temperature powder XRD experiments to
confirm the hexagonal and lamellar columnar nature of the
mesophases observed by POM. Calculated values of Bragg’s
spacing (dcalc.) were obtained from the reciprocal spacing ratio
characteristic for hexagonal and lamellar symmetry consider-
ing the first peak observed as the (100) and (001) reflection,
respectively. Lattice constants were calculated in order to study
the supramolecular organisation in the columnar phases.36
The results are summarised in Table 4.
Diffractograms of compound 16, selected as a representa-
tive example of the type I complexes were registered in the first
heating cycle (Fig. 11). As can be seen, the XRD pattern shows
the existence of the phases that were established from POM
and DSC studies. So, the diffractograms obtained at tempera-
tures at which the liquid crystal state is reached (blue colour in
Fig. 11) display a strong fundamental reflection in the low-
angle region assigned to (100) with a Bragg’s spacing (d) of
26.54 Å, followed by a set of weak reflections (d = 15.44, 13.38,
10.25 Å) with a d-spacing ratio of 1 : 1/√3 : 1/√4 : 1/√7 corres-
ponding to (110), (200) and (210) reflections of a hexagonal
columnar phase.
The intracolumnar distance generated by the π⋯π stacking
between mesogenic units of each column is evident from the
(001) reflection which appears in the high-angle region with a
d-spacing of 3.4 Å. The relationship between the molecular
Table 4 X-Ray diffraction data
Phase 2θ (°) dmeas a (Å) [hkl]b dcalc a (Å) Parametersc
16 Colh
3.3
5.7
6.6
8.6
26.2
20.0
26.5
15.4
13.4
10.2
3.4
100
110
200
210
001
—
26.5
15.3
13.3
10.0
—
T = 105 °C
a = 31 Å
Vmol = 2691 Å3
Scol = 829 Å2
4.5
—
17 ColL
22 ColL
5.5
11.0
16.1
8.0
001
002
16.1
8.0
T = 160 °C
d = 16.1 Å
Vmol = 929 Å3
Amol = 115 Å2
2.9
5.8
8.7
30.0
15.2
10.1
4.5
001
002
003
—
30.0
15.0
10.0
—
T = 110 °C
d = 30.3 Å
Vmol = 1367 Å3
Amol = 90 Å2
20.0
a dmeas and dcalc are the measured and calculated diffraction spacings.
b [hkl] are the Miller indices of the reflections. c Molecular volume: Vmol
= Mw/(NAρ), where Mw is the molecular weight, NA is Avogadro’s
number and ρ is the density (∼1 g cm−3). For hexagonal columnar
phases: lattice constant a = ∑dhk√(h2 + k2 + hk)/√(3Nhk), where Nhk is
the number of hk0 reflections; columnar cross-section area Scol
=
(√3)a2/2. For lamellar columnar phases: lamellar periodicity d =
(∑ld00l)/N00l, where N00l is the number of 00l reflections; molecular
cross-section area Amol = 2Vmol/d.
Fig. 10 Bar diagram showing the range of the phases present in the
complexes of each family.
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Fig. 11 Powder 2D XRD diffraction pattern for the compound [Pd(pzR(18,18)py)2] 16 showing solid (black), liquid crystalline (blue) and liquid (green)
phases. A detail of indexed reflections at 105 °C can be observed in the inset.
volume (Vm) and the columnar cross-section area (Scol) is con- the core (Lcore) was significantly lower, of ca. 13 Å. The com-
sistent with the stacking distance observed above; this value parison of both values suggests that the terminal chains
suggests the existence of a long-range order along the columns present high interdigitation or non-linear conformations in
and, consequently, a highly ordered mesophase (Fig. 12a).
the Colh phases.37
In addition, a broad diffuse peak centred at 20.0 Å corres-
On the other hand, the ColL mesophases observed by POM
ponds to the liquid-like order of the molten terminal chains. It in complexes II was confirmed from the diffractogram of 22,
is interesting to note that they can adopt different confor- which display at 110 °C the (001), (002) and (003) reflections of
mations around the rigid core due to their high mobility in the a lamellar columnar phase with a d-spacing ratio of 1 : 1/2 : 1/3,
liquid crystalline phases. The length of the alkyl chains (Ln) respectively. In addition, a diffuse band was localised in the
was estimated from the distances measured in the molecular wide-angle region around 20°, indicating the liquid-like order
structure, and is ca. 21.1 Å. However, the difference established of the molten chains. However, for complex 17 only two reflec-
between the intercolumnar distance (a) and the diameter of tions with a Bragg’s spacing of 16.10 and 8.01 Å indexed to the
(001) and (002) reflections from the ColL mesophase could be
observed.
The lamellar periodicity (d) measured for the ColL phases
in 17 and 22 were 16.1 and 30.3 Å, respectively. Again in both
cases, the values of molecular volume (Vmol) and cross-section
area (Amol) are in perfect agreement with a lamellar structure
(see Table 4).
On this basis, we propose that the half-disc shaped mole-
cules of compounds II should be arranged into layers but with
an antiparallel disposition driven by Pd–Pd interactions,
which should account for their columnar packing (Fig. 12b).
Conclusions
A new series of dicatenar pyridylpyrazole ligands [HpzR(n,n)py
]
and their corresponding palladium(II) derivatives [Pd(pzR(n,n)py)2]
and [PdCl2(HpzR(n,n)py)] were prepared and characterised.
Thermal studies revealed that those ligands having long alkyl
chains at the C6H3(OCnH2n+1)2 substituents (n = 14 and 16)
Fig. 12 Proposed schematic model representing the (a) columnar
hexagonal and (b) columnar lamellar packing in the mesophase for
compounds I and II, respectively. Chloride atoms have been omitted for
clarity.
display enantiotropic discotic mesomorphism to temperatures
of ca. 80 °C in contrast with the monotropic smectic behaviour
observed for the related monocatenar pyrazoles [HpzR(n)py] in
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agreement with their elongated shape. The ionic nature of the Elmer Pyris 1 differential scanning calorimeter with the
ligands in [Pd(pzR(n,n)py)2] favours the formation of non-con- sample (1–4 mg) sealed hermetically in aluminium pans and
ventional intramolecular hydrogen bonds (C–H⋯N), stabiliz- with a heating or cooling rate of 10 K min−1. The X-ray diffrac-
ing a head-to-tail disposition of the coordinated ligands and tograms at variable temperature were recorded on a Panalytical
generating a rigid metallocyclic core with a disc-like shape.
X’Pert PRO MPD diffractometer with Cu-Kα (1.54 Å) radiation
θ–θ configuration equipped with an Anton Paar
The existence of π⋯π lateral interactions of 3.4 Å between in
a
the pyridine and benzene rings of neighbouring molecules HTK1200 heating stage (X-Ray Diffraction Service of Complu-
gives rise to columns that run along the a crystallographic axis, tense University).
as was established from the crystalline structure of 12. In
agreement with the above results, all Pd(II)-bispyrazolate com-
Synthesis of the compounds
plexes exhibit hexagonal columnar mesophases (Colh) in wide
temperature ranges. On the other hand, the half-disc shape of
[PdCl2(HpzR(n,n)py)] also allows to achieve the supramolecular
organisation of the liquid crystal state through the inverted
arrangement of molecules in layers, leading to lamellar colum-
nar mesophases (ColL).
In summary, the liquid crystal behaviour of the studied
compounds significantly depends on both factors, the coordi-
nation environment and the alkyl chains length. Results show
that the increase of the core–core and van der Waals inter-
actions are determining factors for attaining adequate order-
ing in the mesophase.
Ligands 3-(3,5-bis(alkyloxy)phenyl)-(5-pyridin-2-yl)pyrazole
[HpzR(n,n)py] (1–8). To a solution of the corresponding 3,5-n-
dialkyloxyacetophenone (3.72 mmol) in dry THF (100 mL) was
carefully added 60% NaH (7.81 mmol, 0.31 g). The reaction
mixture was stirred for 1 h at room temperature. Then, ethyl
picolinate (3.72 mmol, 0.56 g) was added and the solution was
refluxed for 24 h. The mixture was cooled at room temperature
and then 10 mL of methanol were incorporated to quench the
excess of NaH. Evaporation of the solvent afforded a residue
which was dissolved in ethyl acetate (100 mL), and acidified to
pH = 4–5 with dilute HCl 0.2 M. The mixture was washed with
water (3 × 50 mL) and dried upon anhydrous magnesium sul-
phate. After taking the reaction mixture to dryness, a brown
residue corresponding to β-diketone was obtained.
Without further purification, to a solution of the corres-
ponding β-diketone (1.12 mmol) in 100 mL of ethanol, hydra-
zine monohydrate (1.12 mmol, 56 mg) was slowly added. The
mixture was stirred for 24 h at 80 °C and then cooled at 4 °C.
The white precipitate obtained was filtered off and dried
in vacuo.
Experimental section
Materials and physical measurements
All commercial reagents were used as supplied. The starting
Pd(II) compounds were purchased from Sigma-Aldrich. The
new 3,5-n-dialkyloxyacetophenone compounds were syn-
thesised by alkylation of 3,5-dihydroxyacetophenone with the
corresponding derivative CnH2n+1Br in acetone solution as pre-
viously described for related compounds.38 These compounds
were characterised by analytical and spectroscopic techniques.
Elemental analyses for carbon, hydrogen and nitrogen were
carried out by the Microanalytical Service of Complutense Uni-
versity (validated range: %C 0.5–94.7, %H 0.5–7.6, %N
0.5–23.0). IR spectra were recorded on a Perkin Elmer Spec-
trum 100 FTIR spectrophotometer with a universal ATR acces-
sory in the 4000–650 cm−1 region: w (weak), m (medium) and s
(strong). 1H- and 13C-NMR spectra were performed at room
temperature on a Bruker DPX-300 spectrophotometer (NMR
Service of Complutense University) from solutions in CDCl3.
Chemical shifts δ are listed relative to Me4Si using the signal
of the deuterated solvent as a reference (7.26 and 77.0 ppm for
1H and 13C, respectively) and coupling constants J are in hertz.
Multiplicities are indicated as s (singlet), d (doublet), t
1
All compounds were characterised by IR, H and 13C-NMR
spectroscopies and elemental analyses (deposited as ESI†).
Specific examples of the characterisation are given below.
[HpzR(6,6)py] (2). Colourless solid (74%). Found: C, 73.3; H,
8.5; N, 9.6. C26N3H35O2·0.3EtOH requires C, 73.1; H, 8.1; N,
9.7%. νmax/cm−1 3207w ν(N–H), 1589s ν(CvC + CvN), 789m
γ(C–H)py. δH (300 MHz; CDCl3; Me4Si): 0.90 (6H, t, 3J 7.0, CH3),
1.24 (t, 3J 7.0, EtOH), 1.34 (8H, m, CH2), 1.45 (4H, m, CH2),
3
3
3
1.79 (4H, qt, J 6.7, CH2), 3.74 (q, J 7.0, EtOH), 4.00 (4H, t, J
6.6, OCH2), 6.45 (1H, t, 4J 2.2, Hp), 6.97 (2H, d, 4J 2.2, Ho), 7.06
(1H, s, 4′-H), 7.26 (1H, m, 5-H), 7.79 (1H, m, 3-H), 7.79 (1H, m,
3
4-H), 8.63 (1H, d, J 4.7, 6-H). δC (75.48 MHz; CDCl3; Me4Si):
14.0 (CH3), 22.5 (CH2), 25.6 (CH2), 29.2 (CH2), 31.5 (CH2), 68.0
(OCH2), 100.7 (C-4′), 101.4 (Cp), 104.0 (Co), 120.1 (C-3), 122.7
(C-5), 134.1 (Ci), 136.9 (C-4), 144.9 (C-3′), 148.8 (C-2), 149.3
(C-6), 151.1 (C-5′), 160.5 (Cm).
[HpzR(12,12)py] (5). Colourless solid (74%). Found: C, 77.0; H,
(triplet), q (quartet), qt (quintet), ddd (doublet of doublets of 10.1; N, 7.0. C38N3H59O2·0.2EtOH requires C, 76.8 H, 9.6; N,
doublets), m (multiplet). The 1H and 13C chemical shifts are 7.1%. νmax/cm−1 3159, 3148, 3104w ν(N–H), 1592s ν(CvC +
accurate to 0.01 and 0.1 ppm, respectively, and coupling CvN), 778m γ(C–H)py. δH (300 MHz; CDCl3; Me4Si): 0.88 (6H,
3
3
constants to 0.3 Hz.
t, J 6.9, CH3), 1.24 (t, J 7.0, EtOH), 1.26 (36H, m, CH2), 1.79
3
3
3
Phase studies were carried out by optical microscopy using (4H, qt, J 6.6, CH2), 3.72 (q, J 7.0, EtOH), 4.00 (4H, t, J 6.4,
an Olympus BX50 microscope equipped with a Linkam THMS OCH2), 6.46 (1H, t, 4J 2.2, Hp), 6.97 (2H, d, 4J 2.1, Ho), 7.08 (1H,
600 heating stage. The temperatures were assigned on the s, 4′-H), 7.27 (1H, m, 5-H), 7.77 (1H, m, 3-H), 7.77 (1H, m,
3
basis of optic observations with polarised light. Measurements 4-H), 8.64 (1H, d, J 4.8, 6-H). δC (75.48 MHz; CDCl3; Me4Si):
of the transition temperatures were made using a Perkin 14.1 (CH3), 22.7–31.9 (CH2), 68.1 (OCH2), 100.6 (C-4′), 101.4
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(Cp), 104.2 (Co), 120.0 (C-3), 122.7 (C-5), 134.1 (Ci), 137.0 (C-4), 50.7; H, 5.9; N, 7.0%. νmax/cm−1 3184w ν(N–H), 1600s ν(CvC +
144.6 (C-3′), 148.6 (C-2), 149.4 (C-6), 151.6 (C-5′), 160.6 (Cm).
CvN), 770m γ(C–H)py. δH (300 MHz; CDCl3; Me4Si): 0.92 (6H,
3
Complexes [Pd(pzR(n,n)py)2] (9–16). To a solution of the t, J 6.6, CH3), 1.38 (8H, m, CH2), 1.48 (4H, m, CH2), 1.84 (4H,
corresponding pyrazole [HpzR(n,n)py] (0.44 mmol) in 40 mL of qt, 3J 6.7, CH2), 4.00 (4H, t, 3J 6.3, OCH2), 5.30 (s, CH2Cl2), 6.55
CH2Cl2 was added 60% NaH (0.88 mmol, 35.2 mg). After (1H, t, 4J 2.1, Hp), 6.66 (2H, d, 4J 2.1, Ho), 7.04 (1H, s, 4′-H),
3
4
3
30 min of stirring at room temperature, a solution of 7.43 (1H, ddd, J 7.7, 5.7, J 1.2, 5-H), 7.85 (1H, d, J 7.6, 3-H),
3
4
3
[Pd(OOCCH3)2] (0.22 mmol, 49.37 mg) in 3 mL of CH2Cl2 was 8.07 (1H, ddd, J 7.7, 7.6, J 1.4, 4-H), 9.09 (1H, d, J 5.7, 6-H),
added under a nitrogen atmosphere. The reaction was refluxed 11.26 (1H, s, NH). δC (75.48 MHz; CDCl3; Me4Si): 14.0 (CH3),
for 24 h and then cooled at room temperature to yield a pre- 22.5 (CH2), 25.6 (CH2), 29.1 (CH2), 31.5 (CH2), 68.5 (OCH2),
cipitate which dissolved in CHCl3 (20 mL). The solution was 102.0 (C-4′), 103.5 (Cp), 104.3 (Co), 122.5 (C-3), 124.8 (C-5),
filtered over celite and concentrated until a solid begins to pre- 127.4 (Ci), 140.5 (C-4), 146.0 (C-3′), 150.4 (C-6), 150.6 (C-2),
cipitate. The yellow compound obtained was filtered off, 151.9 (C-5′), 161.0 (Cm).
[PdCl2(HpzR(12,12)py)] (21). Pale orange solid (63%). Found: C,
washed with acetone and dried in vacuo.
1
59.5; H, 7.7; N, 5.5. PdC38N3H59O2Cl2 requires C, 59.5; H, 7.5;
N, 5.6%. νmax/cm−1 3187w ν(N–H), 1598s ν(CvC + CvN),
771m γ(C–H)py. δH (300 MHz; CDCl3; Me4Si): 0.88 (6H, t, 3J 6.6,
CH3), 1.27 (32H, m, CH2), 1.46 (4H, m, CH2), 1.78 (4H, m,
All compounds were characterised by IR, H spectroscopies
and elemental analyses (deposited as ESI†). In addition, com-
plexes 10 and 13 were also characterised by 13C-NMR as rep-
resentative examples of this family.
[Pd(pzR(6,6)py)2] (10). Yellow solid (68%). Found: C, 65.9; H, CH2), 3.96 (4H, t, 3J 6.6, OCH2), 6.51 (1H, t, 4J 2.2, Hp), 6.65
4
3
7.2; N, 8.9. PdC52N6H68O4 requires C, 65.7; H, 7.0; N, 9.0%. (2H, d, J 2.2, Ho), 7.07 (1H, s, 4′-H), 7.41 (1H, ddd, J 7.8, 5.5,
νmax/cm−1 1593s ν(CvC + CvN), 761m γ(C–H)py. δH (300 MHz; 4J 1.3, 5-H), 7.90 (1H, d, J 7.8, 3-H), 8.08 (1H, ddd, J 7.8, 7.7,
3
3
CDCl3; Me4Si): 0.94 (12H, t, J 6.8, CH3), 1.39 (16H, m, CH2), 4J 1.3, 4-H), 9.01 (1H, d, 3J 5.5, 6-H), 11.32 (1H, s, NH). δC
3
1.52 (8H, m, CH2), 1.85 (8H, qt, J 6.8, CH2), 4.09 (8H, t, 3J 6.9, (75.48 MHz; CDCl3; Me4Si): 14.0 (CH3), 22.6–31.8 (CH2), 68.5
3
OCH2), 6.42 (2H, t, 4J 2.1, Hp), 6.79 (2H, s, 4′-H), 7.04 (4H, d, 4J (OCH2), 102.1 (C-4′), 103.6 (Cp), 104.2 (Co), 122.6 (C-3), 124.9
3
4
3
2.1, Ho), 7.11 (2H, ddd, J 7.5, 5.4, J 1.3, 5-H), 7.43 (2H, d, J (C-5), 127.4 (Ci), 140.5 (C-4), 145.9 (C-3′), 150.3 (C-6), 150.6
7.8, 3-H), 7.67 (2H, ddd, 3J 7.5, 7.8, 4J 1.3, 4-H), 10.24 (2H, d, 3J (C-2), 151.9 (C-5′), 161.0 (Cm).
5.4, 6-H). δC (75.48 MHz; CDCl3; Me4Si): 14.1 (CH3), 22.7 (CH2),
25.8 (CH2), 29.4 (CH2), 31.7 (CH2), 68.0 (OCH2), 99.5 (C-4′),
100.0 (Cp), 103.7 (Co), 118.0 (C-3), 120.0 (C-5), 136.9 (Ci), 138.3
X-ray crystal structure determination
(C-4), 149.4 (C-3′), 149.9 (C-2), 150.6 (C-6), 153.2 (C-5′), 160.2
(Cm).
Data collection for all compounds was carried out at room
temperature on a Bruker Smart CCD diffractometer using
graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å)
operating at 50 kV and 20 mA for 1 and 50 kV and 35 mA for
12. In both cases, data were collected over a hemisphere of the
reciprocal space by combination of three exposure sets. Each
exposure was of 20 s covered 0.3° in ω. The cell parameters
were determined and refined by a least-squares fit of all
reflections.
The first 100 frames were recollected at the end of the data
collection to monitor crystal decay, and no appreciable decay
was observed. A summary of the fundamental crystal and
refinement data is given in Table 5.
The structures were solved by direct methods and refined
by full-matrix least-square procedures on F2.39 All non-hydro-
gen atoms were refined anisotropically. Despite the high
quality of the crystals obtained by different crystallisation
methods, the structure of 12 could not be refined further
because of its poor diffraction, as indicated by the Rint value.
The hydrogen H1 linked to N1 for 1 was located in a
Fourier synthesis and refined riding on its N-bonded atom.
The remaining hydrogen atoms were included in their calcu-
lated positions and refined as riding on the respective carbon
atoms. For 12 some of the C-atoms from the chains were
refined using geometric restraints and variable common C–C
distances.
[Pd(pzR(12,12)py)2] (13). Yellow solid (78%). Found: C, 71.1; H,
9.1; N, 6.5. PdC76N6H116O4 requires C, 71.0; H, 8.8; N, 6.6%.
νmax/cm−1 1598s ν(CvC + CvN), 766m γ(C–H)py. δH (300 MHz;
3
CDCl3; Me4Si): 0.88 (12H, t, J 6.9, CH3), 1.27 (72H, m, CH2),
1.84 (8H, qt, 3J 6.7, CH2), 4.05 (8H, t, 3J 6.6, OCH2), 6.43 (2H, t,
4
4J 2.2, Hp), 6.89 (2H, s, 4′-H), 7.07 (4H, d, J 2.2, Ho), 7.23 (2H,
3
4
3
ddd, J 7.8, 5.3, J 1.3, 5-H), 7.58 (2H, d, J 7.5, 3-H), 7.79 (2H,
ddd, 3J 7.8, 7.5, 4J 1.3, 4-H), 10.38 (2H, d, 3J 5.3, 6-H). δC
(75.48 MHz; CDCl3; Me4Si): 14.2 (CH3), 22.7–32.0 (CH2), 68.0
(OCH2), 99.6 (C-4′), 100.1 (Cp), 103.7 (Co), 118.2 (C-3), 120.3
(C-5), 136.8 (Ci), 138.6 (C-4), 149.8 (C-3′), 150.0 (C-2), 150.8
(C-6), 153.3 (C-5′), 160.3 (Cm).
Complexes [PdCl2(HpzR(n,n)py)] (17–24). A solution of the
corresponding pyrazole [HpzR(n,n)py] (0.26 mmol) in CH2Cl2
(20 mL) was added over a solution of [PdCl2(C6H5CN)2]
(0.26 mmol, 99.72 mg) in 10 mL of CH2Cl2. The reaction
mixture was stirred for 24 h at reflux temperature and then fil-
tered over celite. A pale orange solid was precipitated by
the addition of acetonitrile, which was filtered off and dried
in vacuo.
1
All compounds were characterised by IR, H spectroscopies
and elemental analyses (deposited as ESI†). In addition, com-
plexes 18 and 21 were also characterised by 13C-NMR as rep-
resentative examples.
[PdCl2(HpzR(6,6)py)] (18). Pale orange solid (57%). Found: C,
51.1; H, 5.8; N, 6.8. PdC26N3H35O2Cl2·0.2CH2Cl2 requires C,
Further crystallographic details for the structure reported in
this paper may be obtained from the Cambridge Crystallo-
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Table 5 Crystal and refinement data for [HpzR(4,4)py)]
(pzR(10,10)py)2] 12
1 and [Pd-
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42, 2107.
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Chem., Int. Ed., 1998, 37, 121.
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13, 1588.
1
12
Empirical formula
Formula weight
[C22H27N3O2]
365.47
[C68H100N6O4Pd]
1171.94
Crystal system
Space group
Monoclinic
P21/n
Triclinic
P1
ˉ
Space group number
a/Å
b/Å
c/Å
α (°)
β (°)
11
2
8.771(1)
21.741(2)
11.139(1)
90
103.364(2)
90
6.785(2)
14.665(5)
18.048(5)
67.868(6)
83.627(7)
82.800(7)
1646.3(9)
1
γ (°)
V/Å3
2066.6(3)
4
Z
T/K
293(2)
784
1.175
0.076
ω and φ
(−10, −25, −14) to
(11, 27, 14)
1.87 to 27.00
18 199
296(2)
628
1.182
0.331
ω and φ
(−8, −17, −21) to
(7, 16, 21)
1.22 to 25.00
11 266
F(000)
ρc/g cm−3
μ/mm−1
Scan technique
Data collected
θ Range (°)
Reflections collected
Independent reflections
4507
5635
(Rint = 0.0493)
100
(Rint = 0.1462)
97.3
Completeness
to maximum θ (%)
Data/restraints/parameters
Observed reflections
[I > 2σ(I)]
4507/0/244
1497
5635/13/346
1597
Ra
0.0470
0.1532
0.0717
0.1394
b
RwF
16 H.-C. Chang, K. Komasaka, K. Kishida, T. Shiozaki,
T. Ohmori, T. Matsumoto, A. Kobayashi, M. Kato and
S. Kitagawa, Inorg. Chem., 2001, 50, 4279.
17 C.-T. Liao, H.-H. Chen, H.-F. Hsu, A. Poloek, H.-H. Yeh,
Y. Chi, K.-W. Wang, C.-H. Lai, G.-H. Lee, C.-W. Shih and
P.-T. Chou, Chem. Eur. J., 2011, 17, 546.
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8, 1355.
19 K. Ohta, H. Muroki, A. Takagi, K. Hatada, H. Ema,
I. Yamamoto and K. Matsuzaki, Mol. Cryst. Liq. Cryst., 1986,
140, 131.
a ∑[|Fo| − |Fc|]/∑[|Fo|. b {∑[w(Fo2 − Fc2)2]/∑[w(Fo2)2]}1/2
.
graphic Data Centre, on quoting the depository number CCDC
977934 (1) and 977935 (12).
A preliminary study of 17 shows the square-planar environ-
ment around the metal centre of the complexes II (Fig. S2 in
the ESI†).
20 K. Usha, K. Vijayani and S. Chandrasekhar, Liq. Cryst.,
1993, 15, 575.
21 Y. Abe, H. Akao, Y. Yoshida, H. Takashima, T. Tanase,
H. Mukai and K. Ohta, Inorg. Chim. Acta, 2006, 359,
3147.
Acknowledgements
The authors are grateful to the Ministerio de Economía y Com-
petitividad (Spain), project CTQ2011-25172.
22 M.
Seredyuk,
A.
B.
Gaspar,
V.
Ksenofontov,
Y. Galyametdinov, M. Verdaguer, F. Villain and P. Gütlich,
Inorg. Chem., 2008, 47, 10232.
Notes and references
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