Chemistry of Rh(I) complexes based on mesogenic 3,5-disubstituted pyrazole ligands. X-ray crystal structures of 3,5-di(4-n-butoxyphenyl)pyrazole (Hpzbp2) and [Rh(μ-pzR2)(CO)2]2 (R = C6H4OCnH2n+1, n = 10, 12) compounds. Part II

Article abstract of DOI:10.1016/S0022-328X(02)01400-6

Four new 3,5-disubstituted pyrazoles Hpz^R2 containing long-chain 4-n-alkyloxyphenyl substituents [R = C₆H₄OC_nH_2n+1; n=4 (1), 6 (2), 12 (5), 14 (6)] have been prepared and characterised. All of them showed mesomorphic behaviour,the stability and the range of the mesophases increasing with the length of the chain on the pyrazole. The X-ray structure of Hpz^bp2 (1) showed a highly linear molecular shape. Related results were deduced for the remained Hpz^R2 and the structural consequences agree with the observed mesomorphic properties. The mesogenic pyrazoles Hpz^R2 (1-6) were used as ligands towards [RhCl(CO)₂] and [Rh(CO)₂] fragments. [RhCl(CO)₂(Hpz^R2)] complexes (7-12) showed some physical properties dependant on the long-chained pyrazoles, and related to different molecular arrays in the solid state. In all cases these compounds evolved to [Rh(μ-pz^R2)(CO)₂]₂ in solution. The pyrazolate Rh(I) complexes [Rh(μ-pz^R2)(CO)₂]₂ (3-18) had the usual boat conformation, as deduced by the crystal structure of two of these derivatives [n =10 (16), 12 (17)]. The packing arrangement has both layer and columnar characteristics. No mesophases have been detected for any of the Rh(I) complexes.

Full text of DOI:10.1016/S0022-328X(02)01400-6

Journal of Organometallic Chemistry 654 (2002) 150ꢂ161
/
www.elsevier.com/locate/jorganchem
Chemistry of Rh(I) complexes based on mesogenic 3,5-disubstituted
pyrazole ligands. X-ray crystal structures of 3,5-di(4-n-
butoxyphenyl)pyrazole (Hpzbp2) and [Rh(m-pzR2)(CO)2]2 (Rꢀ
/
C6H4OCnH2nꢁ1, nꢀ
/
10, 12) compounds. Part IIꢀ
M.C. Torralba a, M. Cano a,*, J.A. Campo a, J.V. Heras a, E. Pinilla a,b, M.R. Torres b
a Departamento de Qu´ımica Inorga´nica I, Facultad de Ciencias Qu´ımicas, Universidad Complutense, E-28040 Madrid, Spain
b Laboratorio de Difraccio´n de Rayos-X, Facultad de Ciencias Qu´ımicas, Universidad Complutense, E-28040 Madrid, Spain
Received 22 January 2002; accepted 5 March 2002
Abstract
Four new 3,5-disubstituted pyrazoles HpzR2 containing long-chain 4-n-alkyloxyphenyl substituents [Rꢀ
/
C6H4OCnH2nꢁ1; nꢀ4
/
(1), 6 (2), 12 (5), 14 (6)] have been prepared and characterised. All of them showed mesomorphic behaviour, the stability and the
range of the mesophases increasing with the length of the chain on the pyrazole. The X-ray structure of Hpzbp2 (1) showed a highly
linear molecular shape. Related results were deduced for the remained HpzR2 and the structural consequences agree with the
observed mesomorphic properties. The mesogenic pyrazoles HpzR2 (1ꢂ
fragments. [RhCl(CO)2(HpzR2)] complexes (7ꢂ
related to different molecular arrays in the solid state. In all cases these compounds evolved to [Rh(m-pzR2)(CO)2]2 in solution. The
pyrazolate Rh(I) complexes [Rh(m-pzR2)(CO)2]2 (13ꢂ
18) had the usual boat conformation, as deduced by the crystal structure of two
of these derivatives [nꢀ10 (16), 12 (17)]. The packing arrangement has both layer and columnar characteristics. No mesophases
have been detected for any of the Rh(I) complexes. # 2002 Published by Elsevier Science B.V.
/6) were used as ligands towards [RhCl(CO)2] and [Rh(CO)2]
/12) showed some physical properties dependant on the long-chained pyrazoles, and
/
/
Keywords: Long-chain 3,5-disubstituted pyrazoles; Mesomorphic behaviour; Rhodiumꢂ
/
pyrazole complexes; Rhodiumꢂpyrazolate complexes; X-
/
ray structures
1. Introduction
have not been required to achieve the mesomorphic
behaviour [7,10ꢂ12].
In the first part of our work, we found two types of
interactions between square-planar
[RhCl(CO)2(HpzR)] complexes containing pyrazoles
with long-chained substituents at the 3 position [13].
As a continuation of our work in this field and following
our interest in liquid crystals based on pyrazole deriva-
tives, we are now investigating new rhodium complexes
of the type [RhCl(CO)2(HpzR2)] with related 3,5-disub-
/
Metallomesogens are an important current research
field owing to their potential applications. Conse-
quently, interest in the design of new metal complexes
Rhꢀ ꢀ ꢀRh
with improved properties has increased [1ꢂ3]. In this
/
context, in addition to an appropriate molecular shape,
other factors have been analysed in order to achieve
mesomorphic behaviour. Low molecular symmetry
appears to favour stable mesophases [1]. On the other
hand, some metallomesogenic complexes have been
stituted pyrazole ligands (Rꢀ
8, 10, 12, 14) (Scheme 1). Two of these pyrazoles with
nꢀ8 and 10 have previously been reported as mesogenic
/
C6H4OCnH2nꢁ1; nꢀ4, 6,
/
described containing mesogenic ligands or metalꢂ
interactions [1ꢂ9], although in other cases these features
/metal
/
/
compounds [14]. In this work, the mesomorphic beha-
viour of the other four pyrazoles is described. The
designed Rh-complexes [RhCl(CO)2(HpzR2)], in addi-
tion to containing mesogenic ligands, are rod-like
ꢀ Part I, see Ref. [13].
* Corresponding author. Fax: ꢁ
E-mail address: mmcano@quim.ucm.es (M. Cano).
/
34-91-3944352.
unsymmetrical molecules with, potentially, metalꢂmetal
/
0022-328X/02/$ - see front matter # 2002 Published by Elsevier Science B.V.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 4 0 0 - 6

M.C. Torralba et al. / Journal of Organometallic Chemistry 654 (2002) 150ꢂ
/161
151
adequate crystals for X-ray studies from being obtained.
By contrast, the pyrazolate complexes could be crystal-
lised, and the X-ray structures of two of them, [Rh(m-
pzR2)(CO)2]2 (Rꢀ
dp, 16; ddp, 17), have been solved.
/
Both cases had the presence of the expected Rh(m-
pz)2Rh boat core, with four long linear alkyloxy chains
in an almost parallel disposition.
The mesomorphic behaviour of both pyrazole ligands
and Rh-complexes, [RhCl(CO)2(HpzR2)] and [Rh(m-
pzR2)(CO)2]2, was investigated by differential scanning
calorimetry (DSC) and polarising light microscopy.
Unfortunately non-mesomorphic behaviour was found
for both types of Rh-complexes, although [Rh(m-
pzR2)(CO)2]2 appear to have ordered phases close to
the melting point.
2. Experimental
2.1. Materials and physical measurements
All commercial reagents were used as supplied. The
starting Rh-complex [Rh(m-Cl)(CO)2]2 was purchased
from SigmaꢂAldrich and used as supplied.
/
The 4-n-alkyloxyacetophenone and ethyl 4-n-alkylox-
ybenzoate derivatives were synthesised by alkylation of
4-hydroxyacetophenone or ethyl 4-hydroxybenzoate,
respectively with the corresponding n-alkyliodide in
C3H6O solution of K2CO3 as previously described for
related compounds [13,18,19]. All these compounds
were characterised satisfactorily by analytical and spec-
troscopic techniques.
Scheme 1.
interactions. These characteristics make them interesting
for investigation of calamitic complexes.
On the other hand, the previously reported X-ray
structures of some [Rh(m-pzR)(L2)]2 complexes showed a
bowl-shape structure [15ꢂ17], which could also be
/
Elemental analyses for carbon, hydrogen and nitro-
gen were carried out by the Microanalytical Service of
the Complutense University. IR spectra were recorded
on a FTIR Nicolet Magna-550 spectrophotometer with
samples as KBr pellets or in CH2Cl2 solution in the
predicted for the related complexes studied in this
work. From these derivatives columnar mesophases by
stacking of the bowls on top each other could be
suggested.
In summary, the aim of this work was to widen the
knowledge of structure/mesomorphic properties rela-
tionship, firstly, with 3,5-alkyloxyphenyl substituted
pyrazole ligands (HpzR2) and, secondly, with their
Rh(I) complexes containing [RhCl(CO)2] or [Rh(CO)2]
fragments. In particular we have investigated the liquid
4000ꢂ
cmꢃ1 region were recorded on a Perkinꢂ
spectrometer using KBr pellets.
/
400 cmꢃ1 region. The IR spectra in the 400ꢂ
Elmer 1300
/
200
/
1H- and 13C{1H}-NMR spectra were performed on a
Varian VXR-300 or on a Bruker AM-300 spectro-
photometers of the NMR Service of the Complutense
University on CDCl3 solutions. Chemical shifts d are
listed in ppm relative to Me4Si using the signal of the
deuterated solvent as reference, and coupling constants
J are in hertz. Multiplicities are indicated as s (singlet), d
(doublet), t (triplet), qt (quintuplet), st (sextuplet), m
(multiplet) and br s (broad signal). The atomic number-
ing used in the assignment of the NMR signals is shown
in Scheme 1. The 1H and 13C chemical shifts are
accurate to 0.01 and 0.1 ppm, respectively, and coupling
crystal properties of four new pyrazoles HpzR2 [Rꢀ
/
C6H4OCnH2nꢁ1; nꢀ
4 (Hpzbp2, 1), 6 (Hpzhp2, 2), 12
/
(Hpzddp2, 5), 14 (Hpztdp2, 6) (Scheme 1a). These
compounds have either shorter and longer chains than
those of the related mesogenic pyrazoles with nꢀ8
/
(Hpzop2, 3) and 10 (Hpzdp2, 4) [14]. The structure of 1
has been solved and the molecular geometry and
packing
[RhCl(CO)2(HpzR2)] (Rꢀ
12) and [Rh(m-pzR2)(CO)2]2 (Rꢀ
tdp; 13ꢂ18) have also been prepared and characterised
established.
The
bp, hp, op, dp, ddp, tdp; 7ꢂ
bp, hp, op, dp, ddp,
Rh(I)
complexes
/
/
1
/
constants are accurate to 0.3 Hz for H-NMR spectra.
/
Phase studies were carried out by optical microscopy
using an Olympus BX50 microscope equipped with a
Linkam THMS 600 heating stage. The temperatures
(Scheme 1b and c, respectively). Evolution of
[RhCl(CO)2(HpzR2)] to [Rh(m-pzR2)(CO)2]2 prevented

152
M.C. Torralba et al. / Journal of Organometallic Chemistry 654 (2002) 150ꢂ161
/
were assigned on the basis of optic observations with
polarised light.
Measurements of the transition temperatures were
2.2.3. Preparation of [Rh(m-pzR2)(CO)2]2 (Rꢀ
op, dp, ddp, tdp) (13ꢂ18)
/bp, hp,
/
To a solution of [Rh(m-Cl)(CO2)]2 (0.15 mmol) in
MeOH (2 ml) was added a MeOH slurry (15 ml) of the
corresponding pyrazole HpzR2 (0.30 mmol). After few
minutes a solution of KOH in MeOH was slowly added
and a yellow solid started to precipitate. The mixture
was stirred for 1 h and the solid obtained was filtered
off, washed with MeOH and dried in vacuo. Yields are
given in Table 3.
made using a Perkinꢂ
calorimeter with the sample (2ꢂ
sealed in aluminium pans and with a heating or cooling
rate of 5ꢂ
108 minꢃ1
/Elmer Pyris 1 differential scanning
/6 mg) hermetically
/
.
2.2. Synthetic methods
2.2.1. Preparation of HpzR2 (Rꢀ
6)
/
bp 1, hp 2, ddp 5, tdp
2.3. X-ray structure determination
Colourless prismatic single crystals of Hpzbp2 (1) were
obtained by layering a CH2Cl2 solution with Et2O.
To a mixture of 4-n-alkyloxyacetophenone (20 mmol)
and ethyl 4-n-alkyloxybenzoate (30 mmol) in dimethox-
yethane (80 ml) was carefully added 60% NaH (50
mmol), and then the mixture refluxed for 3 h. The
mixture was cooled at room temperature (r.t.), poured in
water (150 ml) and acidified with dilute HCl. The
product was extracted several times with Et2O, and the
combined extracts dried over Na2SO4 and then filtered.
Evaporation of the solvent gave the corresponding 1,3-
bis(4-n-alkyloxyphenyl)propane-1,3-dione which were
fully characterised (Yield: ca. 75%).
To a suspension of the b-diketone (2 mmol) in EtOH
(50 ml) was added an excess of hydrazine hydrate (2.2
mmol), and the mixture refluxed for 3 h. Then, the
solution was allowed to cool at r.t. and kept overnight at
4 8C. The precipitated product was filtered and dried in
vacuo, giving rise to the desired pyrazole. Yields are
given in Table 1.
Yellow crystals of [Rh(m-pzR2)(CO)2]2 (Rꢀ
/
dp 16, ddp
17) were obtained by layering CH2Cl2 solutions with
C6H14. The data were collected on a EnrafꢂNonius
/
CAD4, on a Nonius-Kappa CCD and on a Smart
Bruker CCD diffractometers for 1, 16 and 17, respec-
tively. A summary of the fundamental crystal data for
the three compounds is given in Table 4.
The molecular structures were solved by direct
methods and conventional Fourier techniques and
refined by full-matrix least-squares on F2 [20]. Final
mixed refinements were performed for the three com-
pounds with the following differences. For 1, all non-
hydrogen atoms have been refined anisotropically
except the carbon atoms in the butoxy chains which
were refined isotropically with geometrical restraints.
The hydrogen atoms were calculated and refined as
riding on the carbon bonded atom with a common
isotropic displacement parameter, except H1 bonded to
N1 which has been found as the first peak in a Fourier
difference, included and its coordinates fixed.
2.2.2. Preparation of [RhCl(CO)2(HpzR2)] (Rꢀ
hp, op, dp, ddp, tdp) (7ꢂ12)
/bp,
/
To a solution of [Rh(m-Cl)(CO)2]2 (0.15 mmol) in
CH2Cl2 (2 ml) was added a CH2Cl2 solution (8 ml) of
the corresponding pyrazole HpzR2 (0.30 mmol). The
yellow solution was stirred for 1 h under dinitrogen, and
then the volume was reduced in vacuo to ca. 2 ml.
Addition of C6H14 precipitated a yellow solid. This was
filtered off, washed with C6H14 and dried in vacuo.
Yields are given in Table 2.
Because no resolvable thermal and positional disorder
has been found for 16 and 17, some carbon atoms in the
decyloxy and dodecyloxy chains, respectively, were
refined only two cycles anisotropically and in the last
cycles the thermal factors have been fixed. These carbon
atoms were refined with geometrical restraints and a
variable common carbonꢀ
/
carbon distance. The rest of
the non-hydrogen atoms were refined anisotropically.
Table 1
IR data, isolated yield and elemental analyses of HpzR2 (Rꢀbp 1, hp 2, ddp 5, tdp 6)
a
b
Compound
IR (cmꢃ1
)
Yield (%)
Molecular formula
Calculated (%)
Found (%)
n(NH)
n(CN)
C
H
N
C
H
N
1
2
5
6
3229
3219
3430
3431
1617
1615
1614
1615
85
54
52
76
C
23H28N2O2
C27H36N2O2
39H60N2O2
C43H68N2O2
75.8
77.2
79.6
80.1
7.7
7.7
6.7
4.8
4.4
75.6
76.9
79.3
79.3
8.1
7.7
6.4
4.7
4.2
8.6
10.2
10.6
8.9
10.2
10.6
C
a
Compounds 3 (Rꢀop) and 4 (Rꢀdp) have previously been described [14].
In KBr discs.
b

M.C. Torralba et al. / Journal of Organometallic Chemistry 654 (2002) 150ꢂ
/161
153
Table 2
IR data, colour, isolated yield and elemental analyses of [RhCl(CO)2(HpzR2)] (Rꢀbp, hp, op, dp, ddp, tdp) (7ꢂ
/
12)
a
Compound IR (cmꢃ1
)
Colour
Yield (%) Molecular formula
Calculated (%) Found (%)
n(NH)
n(CN) n(CO)
C
H
N
C
H
N
7
8
3216, 3147 1613
3172, 3141 1611
2081br, 2014br
2086, 2072, 2015, 2009
2081, 2003
Deep-yellow 62
Deep-yellow 73
Light-yellow 88
Light-yellow 64
Light-yellow 67
Light-yellow 92
C
25H28ClN2O4Rh
53.7 5.1 5.0 53.7 5.0 5.0
56.6 5.9 4.6 56.4 5.9 4.5
59.1 6.6 4.2 58.7 6.6 4.1
61.1 7.2 3.9 60.8 7.2 3.8
62.9 7.7 3.6 62.8 7.7 3.6
64.4 8.2 3.3 64.2 8.1 3.3
C29H36ClN2O4Rh
C33H44ClN2O4Rh
C37H52ClN2O4Rh
9
3273
3277
3275
3275
1613
1616
1615
1614
10
11
12
2082, 2004
2082, 2004
2083, 2004
C41H60ClN2O4Rh
C45H68ClN2O4Rh
a
In KBr discs.
The hydrogen atoms were calculated and refined as
riding on the carbon bonded atom with a common
isotropic displacement parameters.
are shown in Table 7. All the pyrazoles except 1 showed
more than one mesophase. DSC thermograms of 1 and 5
are depicted in Fig. 1 as representative examples.
Textures of the mesophases observed with a polarising
light microscope for the same derivatives are shown in
Fig. 2. The two most interesting results deal with: (a) the
mesophase range; and (b) the melting and clearing
points, being wider and lower, respectively with increas-
ing carbon chain length (22.3, 184 and 206.38 for 1 and
60, 116.1 and 160.68 for 6; see Table 7).
The largest residual peak in the final difference map
˚
was 0.266, 2.95 (at 1.1 A of the C67 atom) and 0.45 e
ꢃ3
˚
A
for 1, 16 and 17, respectively.
3. Results and discussion
3.1. Ligands HpzR2 (Rꢀ
/
bp 1, hp 2, ddp 5, tdp 6)
The 3,5-di(4-n-octyloxyphenyl)pyrazole (3) and 3,5-
di(4-n-decyloxyphenyl)pyrazole (4) derivatives have pre-
viously been reported as mesogenic compounds [14]. In
this work, we have extended this study to new deriva-
tives with either shorter or longer chains. We have
synthesised and characterised four new derivatives with
3.2. X-ray structure of 3,5-di(4-n-
butoxyphenyl)pyrazole Hpzbp2 (1)
The most favourable geometry for calamitic (rodlike)
mesophases is the linear one, and in agreement with this
feature we have observed these mesophases in all the
pyrazoles investigated.
As structural diffraction data have not been reported
for pyrazoles of this type, we were interested in solving
the crystal structure of some of these compounds. Then
the X-ray structure of Hpzbp2 (1) has been solved (Fig.
3). This compound crystallises in the P21/n space group
with four molecules per unity cell. Some representative
bond distances and angles are listed in Table 8.
OCnH2nꢁ1 chains [nꢀ
4 (Hpzbp2, 1), 6 (Hpzhp2, 2), 12
/
(Hpzddp2, 5), 14 (Hpztdp2, 6)] (Scheme 1a) and their
mesomorphic behaviour has been studied.
The ligands were prepared by an analogous procedure
to that reported for related pyrazoles [13,16,21], and
fully characterised by spectroscopic and analytical
techniques (Tables 1, 5 and 6). Assignment of the
NMR signals was made following the literature pre-
cedents [13,16,22,23].
All four derivatives showed enantiotropic mesophases
when they were analysed by DSC and polarising light
microscopy. The transition temperatures and enthalpies
The most interesting feature was the presence of a
strong NHꢀ ꢀ ꢀN intermolecular hydrogen bond between
the NH group and the N atom of neighbouring
molecules (Fig. 4). It suggests a dimeric structure which
Table 3
IR data, colour, isolated yield and elemental analyses of [Rh(m-pzR2)(CO)2]2 (Rꢀbp, hp, op, dp, ddp, tdp) (13ꢂ
/18)
a
Compound
IR (cmꢃ1
)
Colour
Yield (%)
Molecular formula
Calculated (%)
Found (%)
n(CN)
n(CO)
C
H
N
C
H
N
13
14
15
16
17
18
1613
1613
1613
1613
1613
1613
2087, 2069, 2015
2087, 2067, 2015
2086, 2068, 2014
2086, 2068, 2014
2086, 2068, 2014
2086, 2068, 2013
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
81
71
79
51
76
55
C
50H54N4O8Rh2
58H70N4O8Rh2
57.5
60.2
62.4
64.3
65.9
67.3
5.2
6.1
6.8
7.4
8.0
8.4
5.4
4.8
4.4
4.1
3.8
3.5
57.6 4.8 5.4
59.8 6.2 4.8
60.0 6.4 4.4
64.3 7.5 3.9
65.1 7.6 3.8
66.9 8.1 3.6
C
C66H86N4O8Rh2
74H102N4O8Rh2
C
C82H118N4O8Rh2
C90H134N4O8Rh2
a
In KBr discs.

154
M.C. Torralba et al. / Journal of Organometallic Chemistry 654 (2002) 150ꢂ161
/
Table 4
Crystal and refinement data for Hpzbp2 (1) and [Rh(m-pzR2)(CO)2]2 (Rꢀdp 16, ddp 17)
1
16
17
Empirical formula
Formula weight
T (K)
C
364.47
23H28N2O2
C74H102N4O8Rh2
1381.42
293(2)
C82H118N4O8Rh2
1493.62
296(2)
293(2)
Monoclinic
P21/n
Crystal system
Space group
Triclinic
¯
Triclinic
¯
/
P1/
/
P1/
˚
a (A)
15.842(3)
5.732(2)
23.976(3)
14.972(1)
15.491(1)
15.106(1)
16.401(1)
˚
b (A)
˚
c (A)
17.512(1)
79.86(1)
17.759(1)
80.997(2)
a (8)
b (8)
g (8)
106.66(3)
74.31(1)
67.24(1)
3594.0(4)
73.357(2)
74.508(2)
4052.6(6)
3
˚
V (A )
Z
2085.9(9)
4
784
2
1456
2
1584
F(000)
rcalc (g cmꢃ3
m (mmꢃ1
)
1.161
0.074
1.277
0.514
1.224
0.461
)
Crystal dimensions (mm)
Scan technique
Data collected
0.40ꢄ0.15ꢄ0.12
v/2u
0.20ꢄ0.20ꢄ0.15
f and v
0.20ꢄ0.17ꢄ0.12
f and v
(ꢃ18, 0, 0) to (18, 6, 28)
(0, ꢃ18, ꢃ22) to (19, 20, 23)
(ꢃ17, ꢃ19, ꢃ21) to (9, 18, 20)
u range (8)
1.81ꢂ/24.97
1.51ꢂ/28.32
1.20ꢂ25.00
/
Reflections collected
Independent reflections
Data/restraints/parameters
Observed reflections
[I ꢀ2s(I)]
3590
17 781
17 781
21 440
3502 [Rintꢀ0.017]
3502/6/206
935
14 073 [Rintꢀ0.079]
14 073/44/541
3838
17 781/44/683
13 253
a
R
0.073
0.289
0.066
0.179
0.066
0.185
b
RwF
a
a [jFojꢃjFcj]/ a jFoj.
(a
/
[w(Fo2 ꢃFo2)2]=a [w(Fo2)2])1=2
:/
b
certainly should favour the molecular ordering in the
fluid phases [14].
prepared by reaction of the corresponding pyrazole and
[Rh(m-Cl)(CO)2]2 (Scheme 2i) in an analogous procedure
to that described with the related 3-substituted pyrazoles
[13].
In our previous work on [RhCl(CO)2(HpzR)] chem-
istry, two crystalline polymorphs (red and yellow) were
isolated depending on the substituents [13]. The yellow
form, which consisted in dimeric unities through Cl
bridges, was favoured with the longer-chained substitu-
ents. By contrast, the red one defined by the stacking of
individual square-planar molecules with considerable
In addition the molecule presents an almost linear
geometry which can be deduced from the a angle, as
defined in Fig. 5 (Table 9). The a value of 154.18 found
for 1 agrees with that obtained for 3,5-diphenylpyrazole
from AM1 and CNDO/2 calculations [14]. Unfortu-
nately no adequate crystals from the other pyrazoles
could be obtained for X-ray purposes. However, some
of their a angles could be deduced by extrapolation
from the X-ray structures of some of their correspond-
ing complexes, as will be discussed in Section 3.5 (Table
9). As expected, longer chains at the 3 and 5 positions of
the pyrazole give rise to high a values increasing the
linearity of these compounds. This fact agrees with the
stability range found for the mesophases.
metalꢂ
isolated for the shorter chains.
In this work, the
[RhCl(CO)2(HpzR2)] (Rꢀ
bp, hp, op, dp, ddp, tdp; 7ꢂ
/
metal interactions, was the unique polymorph
new
compounds
/
/
12) were isolated as yellow solids and characterised by
spectroscopic (IR and NMR) and analytical techniques
(Tables 2 and 5). All of them were air-stable. However, 7
rapidly evolves to [Rh(m-pzbp2)(CO)2]2 (13), even when it
is stored under dinitrogen. This made its isolation and
the study of its thermal behaviour difficult.
3.3. Compounds [RhCl(CO)2(HpzR2)] (Rꢀ
dp, ddp, tdp) (7ꢂ12)
/bp, hp, op,
/
Following our previous results on [RhCl(CO)2(HpzR)]
(RꢀC6H4OCnH2nꢁ1 substituent at the 3 position of the
From the NMR spectra, well-defined signals for all
protons were observed in all cases (Table 5), in agree-
ment with the absence of metallotropic equilibrium. The
IR spectra in dichloromethane solution showed the two
/
pyrazole) [13], we are now investigating related com-
pounds containing the mesogenic 3,5-disubstituted pyr-
azoles HpzR2. These complexes [RhCl(CO)2(HpzR2)]
(Rꢀ
/
bp, hp, op, dp, ddp, tdp; 7ꢂ
/
12) (Scheme 1b) were
expected n(CO) bands at ca. 2085 and 2015 cmꢃ1
,

M.C. Torralba et al. / Journal of Organometallic Chemistry 654 (2002) 150ꢂ
/161
155
Table 5
1H-NMR data (CDCl3, 298 K) of the compounds studied in this work
a
Compound
Pyrazole
ꢀC6H4ꢀ
Ho
ꢀOR
b
NH
H4
Hm
1
n.o.
6.68s
7.63d
Jomꢀ8.5
6.93d
CH2-1?: 4.00t
CH2-2?: 1.80qt
CH2-3?: 1.51st
CH3-4?: 0.99t
J1?2?ꢀ6.3
J2?3?ꢀ7.0
J3?4?ꢀ7.1
6
n.o.
6.68s
7.63d
Jomꢀ8.7
6.95d
CH2-1?: 3.99t
CH2-2?: 1.80qt
J
1?2?ꢀ6.6
2?3?ꢀ7.1
J
CH2-3?ꢂ
CH3-14?: 0.88t
/
13?: 1.5ꢂ
/
1.1m
1.2m
1.0m
J13?14?ꢀ6.8
7
11.65br s
11.64br s
6.60s
6.60s
7.67d
7.51d
7.02d
6.99d
CH2-1?: 4.03m
CH2-2?: 1.80qt
CH2-3?: 1.53st
CH3-4?: 0.99t
J
1?2?ꢀ6.2
2?3?ꢀ7.2
J
Jomꢀ8.4
J3?4?ꢀ7.2
12
7.66d
7.51d
7.02d
6.98d
CH2-1?: 4.01m
CH2-2?: 1.81qt
J
1?2?ꢀ5.9
2?3?ꢀ6.8
J
Jomꢀ8.4
CH2-3?ꢂ
/
13?: 1.6ꢂ
/
CH3-14?: 0.88t
J13?14?ꢀ6.7
13
6.58s
6.57s
7.99d
Jomꢀ8.4
7.05d
7.05d
CH2-1?: 4.08t
CH2-2?: 1.85qt
CH2-3?: 1.57st
CH3-4?: 1.03t
J
1?2?ꢀ6.4
2?3?ꢀ7.5
J
J3?4?ꢀ7.2
18
7.99d
Jomꢀ8.6
CH2-1?: 4.07t
CH2-2?: 1.86qt
J
1?2?ꢀ6.4
2?3?ꢀ7.2
J
CH2-3?ꢂ
/
13?: 1.5ꢂ
/
CH3-14?: 0.88t
J13?14?ꢀ6.6
a
As expected, the NMR data of each type of compounds are similar. Therefore, only those of the first and last compounds of each serie are given
as representative examples.
b
n.o., not observed.
typical of mononuclear Rh(I) compounds [16,24]. How-
ever, in the solid state the pattern of the n(CO) bands
was different for 7 and 8 with respect to those containing
[RhCl(CO)2(HpzR)]2 dimers by Rhꢀ
tions between monomers was ascribed to the steric
consequences of the chain length [14]. In this context
/
Clꢀ ꢀ ꢀRh interac-
longer chains (9ꢂ
/
12). The former one was consistent
the new derivatives [RhCl(CO)2(HpzR2)] (7ꢂ
12) could
be suggested to have structures in the solid state with
/
with the presence of four bands or two very broad bands
for 8 and 7, respectively, while the later only exhibited
two sharp bands (Table 2). These features could be
different molecular arrays, varying from those with a
molecular stacking in which the metalꢂ
tions, if there are, are very weak (for 7 and 8, deep
yellow) to those with potential dimeric nature (for 9ꢂ12,
pale yellow).
/metal interac-
related
with
the
previous
observations
of
[RhCl(CO)2(HpzR)] complexes [13], for which the uni-
dimensional molecular stacking of the red form was
disrupt by the longer-chain substituent giving rise to a
favourable approach between the molecules of neigh-
bouring columns, and consequently dimeric unities were
obtained (yellow form) [13]. Intense colours (red, blue,
/
The n(NH) band at ca. 3200 cmꢃ1 was shifted in all
cases at lower frequencies compared to the free ligands,
and it appeared at about the same values observed for
related [RhCl(CO)2(HpzR)] compounds which had in-
tramolecular NHꢀ ꢀ ꢀCl hydrogen bonding interactions
[13]. These features support the potential presence of
related interactions in the complexes described in this
work. In agreement with the carbonyl behaviour,
compounds 7 and 8 show the lower n(NH) values
violet) are characteristic of unidimensional metalꢂ
interactions [4,13,16,24ꢂ26], but by contrast discrete
molecular structures are found with light colours
[4,13,27ꢂ29]. The adoption of either a unidimensional
molecular stacking with metalꢂmetal interactions be-
tween molecules or
[RhCl(CO)2(HpzR)]
/metal
/
/
/
compared with those of 9ꢂ12.
/

156
M.C. Torralba et al. / Journal of Organometallic Chemistry 654 (2002) 150ꢂ161
/
Table 6
13C{1H}-NMR data (CDCl3, 298 K) of the pyrazoles HpzR2 and [Rh(m-pzR2)(CO)2]2
a
Compound
CO
Pyrazole carbons
C3 C4 C5
ꢀC6H4ꢀ
Ca
ꢀOR
Co
Cm
Cp
1
148.6 98.9
148.6 124.2 126.9 114.9 159.3 C1?: 67.9
C2?,3?: 31.4, 19.3
C4?: 13.9
6
148.2 98.6
148.2 123.9 126.8 114.8 159.3 C1?: 68.1
C2?ꢂ/11?: 31.9, 29.7, 29.5, 29.4, 29.3, 26.0, 22.7
C14?: 14.1
13
184.5
JRhꢀ66.5
155.6 103.4 155.6 126.2 129.4 114.2 159.2 C1?: 67.7
C2?,13?: 31.3, 19.2
C4?: 13.8
18
184.5
JRhꢀ67.0
155.7 103.5 155.7 126.3 129.5 114.3 159.3 C1?: 68.1
C2?ꢂ
/
13?: 31.9, 29.7, 29.5, 29.4, 26.1, 22.7
C14?: 14.1
a
As expected, the NMR data of each type of compounds are similar. Therefore, only those of the first and last compounds of each serie are given
as representative examples.
In the low frequency region, the n(Rhꢀ
/
Cl) band at ca.
300 cmꢃ1 had same value as those observed in the red or
yellow forms of [RhCl(CO)2(HpzR)] derivatives, so that
these results could not been used as guide to define the
presence of metalꢂ/metal interactions or dimeric struc-
tures.
Unfortunately, the evolution observed in solution of
[RhCl(CO)2(HpzR2)] to [Rh(m-pzR2)(CO)2]2 prevented
us obtaining crystals of 7ꢂ12 for the X-ray structural
/
characterisation.
Table 7
Phase properties of the pyrazoles HpzR2 (Rꢀbp 1, hp 2, ddp 5, tdp 6)
determined by DSC
a
Compound
Transition
T (8)
DH (kJ molꢃ1
)
1
Cr10Cr2
Cr20SmA
SmA0I
Cr10Cr2
Cr20SmC
SmC0I
Cr10Cr2
Cr20SmC
SmC0I
Cr10Cr2
Cr20SmX
93.2
184.0
206.3
47.4
5.0
20.2
4.9
b
2
19.5
14.7
5.0
158.5
198.0
93.4
c
5
51.6
14.1
8.0
124.8
174.9
85.8
6
1.4
d
100.6
116.1
160.6
60.9
14.0
8.3
SmX0SmC
SmC0I
a
The phase properties of 3 (Rꢀop) and 4 (Rꢀdp) have previously
been described [14].
b
A new mesophase is only observed by polarising light microscopy
at ca. 200 8C corresponding to SmA.
A new mesophase is only observed by polarising light microscopy
Fig. 1. DSC thermograms of: (a) Hpzbp2 (1); and (b) Hpzddp2 (5).
c
at ca. 174 8C corresponding to N.
Unknown ordered mesophase.
d

M.C. Torralba et al. / Journal of Organometallic Chemistry 654 (2002) 150ꢂ
/161
157
3.4. Compounds [Rh(m-pzR2)(CO)2]2 (Rꢀ
dp, ddp, tdp) (13ꢂ18)
/bp, hp, op,
/
In order to obtain adequate crystals of
[RhCl(CO)2(HpzR2)] for X-ray purposes, new products
were isolated and determined to be [Rh(m-pzR2)(CO)2]2
(Scheme 2iii) whose identities were confirmed by com-
parison with IR and NMR spectra of authentic samples
(Tables 3, 5 and 6). These complexes were alternatively
prepared by reaction of [Rh(m-Cl)(CO)2]2 and the
pyrazolate ligand (Scheme 2ii) in a similar way to that
used for the related well-known class of pyrazolate-
bridged dimers [15ꢂ
/17].
Complexes 13ꢂ18 (Scheme 1c) were isolated as deep
/
yellow solids which were air-stable in the solid state and
in solution of various organic solvents. The IR spectra
in solid state and in dichloromethane solution have the
three expected n(CO) bands at ca. 2086, 2067 and 2015
cmꢃ1 (Table 3). The 1H- and 13C-NMR show the
resonances of the pyrazolate groups in the relation
corresponding with the proposed formula (Tables 5 and
6). Therefore, only signals due to the equivalence of the
four substituents as well as one type for the H(4) and
C(4) nuclei were observed.
The formation of [Rh(m-pzR2)(CO)2]2 (13ꢂ
through their related monomeric compounds
[RhCl(CO)2(HpzR2)] (7ꢂ
12) is a representative example
of the non-requirement of a deprotonating medium (i.e.
in apparently neutral conditions) to produce the pyr-
azolate-bridged coordination. This behaviour has pre-
viously been found for other metal-derivatives [30].
/18)
Fig. 2. Textures of the mesophases for: (a) Hpzbp2 (1) at 204 8C; and
(b) Hpzddp2 (5) at 170 8C.
/
Table 8
bp2
˚
Selected bond distances (A) and angles (8) for Hpz
(1)
Bond distances
3.5. X-ray crystal structures of [Rh(m-pzR2)(CO)2]2
N1ꢀN2
N1ꢀC5
N2ꢀC3
C3ꢀC4
C4ꢀC5
1.343(6)
1.358(7)
1.354(7)
1.390(8)
1.355(7)
C3ꢀC6
1.448(8)
1.446(8)
0.8639
2.19
(Rꢀdp, 16; ddp, 17)
/
C5ꢀC12
N1ꢀH1
N2?ꢀ ꢀ ꢀH1
N1ꢀ ꢀ ꢀN2?
¯
Both complexes are isostructural (space group P1:
The molecular structure of 16 and 17 are illustrated in
Figs. 6 and 7 respectively. Selected bond distances and
angles with estimated standard deviations are given in
Table 10.
Two pyrazolate groups are bonded in an exo-biden-
tate fashion to the two rhodium atoms of the dimer, and
two CO groups in each rhodium complete the distorted
2.883(6)
Bond angles
N2ꢀN1ꢀC5
N1ꢀN2ꢀC3
C3ꢀC4ꢀC5
112.7(6)
105.9(6)
109.3(6)
N2ꢀN1ꢀH1
C5ꢀN1ꢀH1
N1ꢀH1ꢀ ꢀ ꢀN2?
119.0
128.2
136.9
Symmetry operation (’): ꢃxꢁ2, ꢃyꢁ1, ꢃzꢁ2.
Fig. 3. Perspective ORTEP plot of 1. Hydrogen atoms, except H1, have been omitted for clarity, and thermal ellipsoids are at 35% probability level.

158
M.C. Torralba et al. / Journal of Organometallic Chemistry 654 (2002) 150ꢂ161
/
Fig. 4. Molecular packing of 1 through the b axis, showing the intermolecular hydrogen bond.
(by
considering
the
clockwise
direction
Table 9
Values of the a angle for the pyrazoles HpzR2 (Rꢀbp 1, dp 4, ddp 5)
a
Rh1N1N2Rh2N4N3) are twisted with respect to their
own pyrazolate planes at angles of 36.4(2), 32.9(2)8 and
37.6(4), 36.8(4)8 for 16 and 17, respectively, while the
other two at the 3 position are more coplanar with their
corresponding pyrazolate groups (the corresponding
angles are 18.0(2), 24.9(2)8 and 18.8(4), 23.0(4)8 for 16
and 17, respectively). The principal molecular axis
(which contains both Rh-atoms) could be defined as
approximately parallel to the a crystallographic axis
(angle of 35.13(1) and 35.27(2)8 for 16 and 17 respec-
tively).
Compound
a angle (8)
1
154.1
Â162.3
Â164.5
b
4
b
5
a
a angle as defined in Fig. 5.
The packing arrangement can be described as layer-
like (Fig. 8). Each layer is formed by the stacking of two
sheets of dimers. Each sheet in turn arises from dimers
having the same orientation of molecular cores, but
opposite between contiguous sheets (i.e. the boats are
inverted). Interdigitation between neighbouring mole-
cules of the layer through the long-chained substituents
is observed. The layers could be described along a plane
(defined by the four nitrogen atoms of the two
pyrazolate groups) which forms a dihedral angle of
36.2(2) and 35.7(1)8 for 16 and 17 respectively with the
plane ac.
In addition, by considering the crystallographically
imposed molecular disposition, a columnar stacking
along the a axis could also be defined with interdigita-
tion between substituents of neighbouring columns.
However, neither the intermolecular distances in the
Scheme 2.
square-planar environment. The molecule in both cases
comprises a Rh2(m-pz)2 core in which the metallocycle
Rh(NN)2Rh has the usual boat conformation, with the
˚
Rhꢀ ꢀ ꢀRh distance being 3.1633(6) and 3.144(1) A for 16
and 17, respectively. Each of the pyrazolate groups carry
two terminal alkyloxyphenyl chains in the 3 and 5
positions, and all the aromatic rings in the chains are
almost planar. Those phenyl rings at the 5 position
Fig. 5. Schematic representation of the a angle, defined as the angle between the lines connecting the middle of the pyrazole ring and the last carbon
of the substituent-chain.

M.C. Torralba et al. / Journal of Organometallic Chemistry 654 (2002) 150ꢂ
/161
159
Fig. 6. Perspective ORTEP plot of 16. Hydrogen atoms have been omitted for clarity, and thermal ellipsoids are at 30% probability level.
column nor the direction of dz2 orbitals of the Rh atoms
of the stacked dimers were adequate to render inter-
molecular interactions.
Table 10
Selected bond distances (A) and angles (8) for [Rh(m-pzR2)(CO)2]2
(Rꢀdp 16, ddp 17)
˚
It is possible that these structural results are related to
the lack of a molecular orientation in the fluid phases.
16
17
Bond distances
Rh1ꢀ ꢀ ꢀRh2
Rh1ꢀN1
Rh1ꢀN3
Rh1ꢀC33
Rh1ꢀC34
Rh2ꢀN2
Rh2ꢀN4
Rh2ꢀC35
Rh2ꢀC36
N1ꢀN2
3.1633(6)
2.081(3)
2.072(3)
1.855(5)
1.859(5)
2.073(3)
2.083(3)
1.858(5)
1.848(5)
1.377(4)
1.369(4)
3.144(1)
2.061(8)
2.071(7)
1.76(1)
3.6. Thermal studies of compounds 7ꢂ
/
18
Complexes 7ꢂ18 have been studied by polarising light
/
1.79(1)
microscopy and DSC. The results obtained are sum-
marised in Table 11. No mesophases have been detected
for these complexes. However, it is interesting to note
2.060(7)
2.068(8)
1.78(1)
that for the pyrazolate Rh-complexes 13ꢂ18, some
/
1.79(1)
1.374(8)
1.382(4)
ordering close to the melting point could be proposed
from microscopic observations, but unfortunately these
transformations could not be detected in the corre-
sponding DSC thermograms. The significant structural
changes upon coordination of the mesogenic organic
ligands appear to be responsible of the absence of liquid
crystal properties on the Rh-complexes. Further efforts
should be made to achieve organised liquid phases.
N3ꢀN4
Bond angles
C33ꢀRh1ꢀC34
C33ꢀRh1ꢀN1
C34ꢀRh1ꢀN1
C33ꢀRh1ꢀN3
C34ꢀRh1ꢀN3
N1ꢀRh1ꢀN3
C35ꢀRh2ꢀC36
C35ꢀRh2ꢀN2
C36ꢀRh2ꢀN2
C35ꢀRh2ꢀN4
C36ꢀRh2ꢀN4
N2ꢀRh2ꢀN4
90.4(2)
90.6(2)
176.8(2)
177.8(2)
88.4(2)
88.5(1)
90.5(2)
88.1(2)
178.5(2)
176.6(2)
92.6(2)
88.7(1)
90.7(5)
91.8(4)
177.1(4)
176.2(4)
88.2(4)
89.2(3)
90.2(4)
88.8(4)
177.7(4)
177.1(4)
92.6(4)
88.4(3)
4. Supplementary material
Tables of the NMR data of all compounds have been
deposited as supplementary material. Crystallographic
Fig. 7. Perspective ORTEP plot of 17. Hydrogen atoms have been omitted for clarity, and thermal ellipsoids are at 35% probability level.

160
M.C. Torralba et al. / Journal of Organometallic Chemistry 654 (2002) 150ꢂ161
/
Fig. 8. Molecular arrangement of 17, showing the layer like distribution. The same distribution is also observed for 16.
[4] J. Barbera´, A. Elduque, R. Gime´nez, F.J. Lahoz, J.A. Lo´pez, L.A.
Table 11
a
Oro, J.L. Serrano, B. Villacampa, J. Villalba, Inorg. Chem. 38
Phase properties of compounds 7ꢂ18 determined by DSC
/
(1999) 3085.
[5] D.W. Bruce, E. Lalinde, P. Styring, D.A. Dunmur, P.M. Maitlis,
J. Chem. Soc. Chem. Commun. (1986) 581.
Compound
Transition
T (8)
DH (kJ molꢃ1
)
8
9
Cr0I
Cr0I
Cr0I
Cr0I
Cr0I
Cr0I
Cr0I
Cr0I
Cr0I
Cr0I
Cr0I
68.3
65.0
32.1
47.0
65.1
68.1
90.8
60.6
59.6
63.6
79.2
88.1
74.6
[6] D.W. Bruce, D.A. Dunmur, M.A. Esteruelas, S.E. Hunt, R. Le
Lagadec, P.M. Maitlis, J.R. Marsden, E. Sola, J.M. Stacey, J.
Mater. Chem. 1 (1991) 251.
10
11
12
13
14
15
16
17
18
75.5
78.8
[7] W. Wan, W.J. Guang, K.Q. Zhao, W.Z. Zheng, L.F. Zhang, J.
Organomet. Chem. 557 (1998) 157.
86.9
231.7
194.2
159.5
143.8
133.4
126.0
[8] P. Berdague´, J. Courtieu, P.M. Maitlis, J. Chem. Soc. Chem.
Commun. (1994) 1313.
[9] H. Adams, N.A. Bailey, D.W. Bruce, D.A. Dunmur, E. Lalinde,
M. Marcos, C. Ridway, P. Styring, P.M. Maitlis, Liq. Cryst. 2
(1987) 381.
[10] M.A. Esteruelas, E. Sola, L.A. Oro, M.B. Ros, M. Marcos, J.L.
Serrano, J. Organomet. Chem. 387 (1990) 103.
a
The unstability of 7 has precluded to study its thermal behaviour.
[11] H. Adams, N.A. Bailey, D.W. Bruce, S.A. Hudson, J.R. Marsden,
Liq. Cryst. 16 (1994) 643.
data for the structural analysis have been deposited with
the Cambridge Crystallographic Data Centre, CCDC
[12] M.A. Esteruelas, E. Sola, L.A. Oro, M.B. Ros, J.L. Serrano, J.
Chem. Soc. Chem. Commun. (1989) 55.
[13] M.C. Torralba, M. Cano, J.A. Campo, J.V. Heras, E. Pinilla,
M.R. Torres, J. Organomet. Chem. 633 (2001) 91.
[14] J. Barbera, C. Cativiela, J.L. Serrano, M.M. Zurbano, Liq. Cryst.
11 (1992) 887.
deposition numbers 176606ꢂ176608 for compounds 1,
16 and 17. Copies of this information may obtained free
of charge from The Director, CCDC, 12 Union Road
/
Cambridge CB2 1EZ, UK (Fax: ꢁ44-1223-336033; e-
/
[15] C. Lo´pez, J.A. Jime´nez, R.M. Claramunt, M. Cano, J.V. Heras,
J.A. Campo, E. Pinilla, A. Monge, J. Organomet. Chem. 511
(1996) 115.
mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk)
[16] M. Cano, J.V. Heras, M. Maeso, M. Alvaro, R. Ferna´ndez, E.
Pinilla, J.A. Campo, A. Monge, J. Organomet. Chem. 534 (1997)
159.
Acknowledgements
[17] J.A. Campo, M. Cano, J.V. Heras, E. Pinilla, M. Ruiz-Bermejo,
R. Torres, J. Organomet. Chem. 582 (1999) 173.
[18] K. Ohta, H. Muroki, K.I. Hatada, I. Yamamoto, K. Matsuzaki,
Mol. Cryst. Liq. Cryst. 130 (1985) 249.
Financial support from the DGES of Spain is grate-
fully acknowledged (Project no. PB98-0766). We are
grateful to Dr A. Coetzee of Nonius (The Netherlands)
for the collection of X-ray data of compound 16.
[19] J.A. Campo, M. Cano, J.V. Heras, M.C. Lagunas, J. Perles, E.
Pinilla, M.R. Torres, Helv. Chim. Acta 84 (2001) 2316.
[20] G.M. Sheldrick, SHELXL97, Program for Refinement of Crystal
Structure, University of Gottingen, Gottingen, Germany, 1997.
¨ ¨
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