Rhodium(I) and iridium(I) complexes containing β-diketonate or pyrazole ligands. liquid crystal and nonlinear optical properties

Article abstract of DOI:10.1021/ic9814017

Square-planar rhodium or iridium "n-decyloxy-β-diketonate" complexes of the general formula [M(β-diketonate)-(CO)₂] (M = Rh (1-3) or Ir (4-6)) and pyrazole-rhodium derivatives of the type [RhCl(CO)₂(pyrazole)] (7-9) have been prepare

Full text of DOI:10.1021/ic9814017

Inorg. Chem. 1999, 38, 3085-3092
3085
Rhodium(I) and Iridium(I) Complexes Containing â-Diketonate or Pyrazole Ligands. Liquid
Crystal and Nonlinear Optical Properties
Joaqu´ın Barbera´,† Anabel Elduque,‡ Raquel Gime´nez,† Fernando J. Lahoz,‡ Jose´ A. Lo´pez,‡
Luis A. Oro,*,‡ Jose´ Luis Serrano,*,† Bele´n Villacampa,§ and Julio Villalba§
Departamento de Qu´ımica Orga´nica, Departamento de Qu´ımica Inorga´nica, and Departamento
de F´ısica de la Materia Condensada, Instituto de Ciencia de Materiales de Arago´n, Universidad
de Zaragoza-Consejo Superior de Investigaciones Cient´ıficas, 50009 Zaragoza, Spain
ReceiVed December 8, 1998
Square-planar rhodium or iridium “n-decyloxy-â-diketonate” complexes of the general formula [M(â-diketonate)-
(CO)2] (M ) Rh (1-3) or Ir (4-6)) and pyrazole-rhodium derivatives of the type [RhCl(CO)2(pyrazole)] (7-9)
have been prepared and their liquid-crystalline properties studied. Compounds 1 and 4 show monotropic smectic
A phases, and complex 7 shows a monotropic nematic phase. The behavior of the melting points seems to be
related to the X group directly bonded at the 3-position of the â-diketonate ligand (1-6) or at the 4-position of
the pyrazole ring (7-9). When X ) OOC higher melting points are obtained. Two different polymorphs, red (M
) Rh) or blue (M ) Ir) and yellow (M ) Rh, Ir), have been obtained for complexes 1, 4, and 6. The yellow form
for compound 4 (C31H35IrO9‚CH3OH, monoclinic system, space group P21/c (No. 14) with a ) 26.991(6) Å, b
) 4.0093(8) Å, c ) 31.169(6) Å, â ) 104.950(13)°, and Z ) 4) has also been characterized by an X-ray single-
crystal diffraction experiment in order to explain the influence of the packing arrangement in the formation of
different polymorphs. Additionally, measurements of the first-order optical hyperpolarizability (â) of the rhodium
compounds and some of the precursor ligands using the EFISH technique have also been performed.
Introduction
) nitrogen-donor promesogenic ligand).5 Taking advantage of
the mesogenicity of certain â-diketone and pyrazole ligands pre-
viously reported by our group (Scheme 1, ligands HL1-HL3,
HL′1-HL′3)1c and their ability to coordinate metal atoms, we
decided to prepare and investigate the liquid crystal properties
of new rhodium and iridium complexes containing these rodlike
â-diketonate and pyrazole ligands. The resulting compounds can
exhibit conjugated structures in which the metal environments,
[M(CO)2] or [RhCl(CO)2], act as a terminal polar group and
the decyloxy group, at the other end of the molecule, could
play the role of an electron-donor group. These compounds
therefore fulfill a priori the requirements for second harmonic
generation and thus are potentially interesting for nonlinear optic
studies.
In pursuance of our research on liquid crystals based on
â-diketone, pyrazole, and isoxazole derivatives,1 we became
interested in the design of new structures exhibiting improved
properties by the incorporation of metal atoms into organic
molecules.2 Specific properties such as color, paramagnetism,
electric conductivity, etc., can be obtained more easily in metal-
organic complexes than in purely organic compounds.3 Fur-
thermore, other molecular properties such as polarizability or
hyperpolarizability can be enhanced by the presence of metals.3
Few examples of calamitic (rodlike) liquid crystals containing
rhodium or iridium have been described in the literature,3c,4-6
and they have a cis-[MCl(CO)2L] structure (M ) Rh or Ir; L
We report new rhodium- and iridium-â-diketonate com-
plexes as well as the first organometallic pyrazole derivative
presenting a liquid crystal behavior. Part of this work has been
preliminarily communicated.7 We have also performed measure-
ments of the first-order optical hyperpolarizability (â) of the
† Departamento de Qu´ımica Orga´nica.
‡ Departamento de Qu´ımica Inorga´nica.
§ Departamento de F´ısica de la Materia Condensada.
(1) (a) Barbera´, J.; Cativiela, C.; Serrano, J. L.; Zurbano, M. M. Liq. Cryst.
1992, 11, 887. (b) Barbera´, J.; Gime´nez, R.; Serrano, J. L. AdV. Mater.
1994, 6, 470. (c) Cativiela, C.; Serrano, J. L.; Zurbano, M. M. J. Org.
Chem. 1995, 60, 3074. (d) Iglesias, R.; Serrano, J. L.; Sierra, T. Liq.
Cryst. 1997, 22, 37.
(2) (a) Barbera´, J.; Cativiela, C.; Serrano, J. L.; Zurbano, M. M. AdV.
Mater. 1991, 3, 602. (b) Atencio, R.; Barbera´, J.; Cativiela, C.; Lahoz,
F. J.; Serrano, J. L.; Zurbano, M. M. J. Am. Chem. Soc. 1994, 116,
11558. (c) Barbera´, J.; Elduque, A.; Gime´nez, R.; Oro, L. A.; Serrano,
J. L. Angew. Chem., Int. Ed. Engl. 1996, 35, 2832. (d) Barbera´, J.;
Elduque, A.; Gime´nez, R.; Lahoz, F. J.; Lo´pez, J. A.; Oro, L. A.;
Serrano, J. L. Inorg. Chem. 1998, 37, 2961.
(3) (a) Ros, M. B. In Metallomesogens. Synthesis, Properties and
Applications; Serrano, J. L., Ed.; VCH: Weinheim, Germany, 1996,
Chapter 11. (b) Bruce, D. W. J. Chem. Soc., Dalton Trans. 1993, 2984.
(c) Espinet, P.; Esteruelas, M. A.; Oro, L. A.; Serrano, J. L.; Sola, E.
Coord. Chem. ReV. 1992, 117, 215.
(4) Serrano, J. L.; Sierra, T. In Metallomesogens. Synthesis, Properties
and Applications; Serrano, J. L., Ed.; VCH: Weinheim, Germany,
1996; Chapter 3.
(5) (a) Bruce, D. W.; Lalinde, E.; Styring, P.; Dunmur, D. A.; Maitlis, P.
M. J. Chem. Soc., Chem. Commun. 1986, 581. (b) Esteruelas, M. A.;
Sola, E.; Oro, L. A.; Ros, M. B.; Serrano, J. L. J. Chem. Soc., Chem.
Commun. 1989, 55. (c) Esteruelas; M. A.; Sola, E.; Oro, L. A.; Ros,
M. B.; Marcos, M.; Serrano, J. L. J. Organomet. Chem. 1990, 387,
103. (d) Bruce, D. W.; Dunmur, D. A.; Esteruelas, M. A.; Hunt, S.
E.; Le Lagadec, R.; Maitlis, P. M.; Marsden, J. R.; Sola, E.; Stacey,
J. M. J. Mater. Chem. 1991, 1, 251. (e) Adams, H.; Bailey, N. A.;
Bruce, D. W.; Hudson, S. A.; Marsden, J. R. Liq. Cryst. 1994, 16,
643.
(6) (a) Berdague´, P.; Courtieu, J.; Maitlis, P. M. J. Chem. Soc., Chem.
Commun. 1994, 1313. (b) Bruce, D. W.; Hall, M. D. Mol. Cryst. Liq.
Cryst. 1994, 250, 373.
(7) Gime´nez, R.; Barbera´, J.; Serrano, J. L.; Oro, L. A.; Elduque, A.
International Symposium on Metallomesogens, 4th, Universita` della
Calabria, Cetraro, Italy; 1995.
10.1021/ic9814017 CCC: $18.00 © 1999 American Chemical Society
Published on Web 05/29/1999

3086 Inorganic Chemistry, Vol. 38, No. 13, 1999
Barbera´ et al.
Scheme 1
Table 1. Thermal Behavior (Transition Temperatures and
rhodium complexes and some of the precursor ligands using
the EFISH technique.8 The aim of this study is to evaluate the
effect of the presence of the metal on the nonlinear response of
the molecule as well as to check the influence of the different
groups X (see Scheme 1) in the conjugation path.
Enthalpies, Determined by OM and DSC) and IR νC≡O Absorptions
(Nujol Suspension) of Complexes 1, 4, and 6a
OM-DSC
compd
[°C (KJ mol-1)]
IR νCtO (cm-1
2088, 2027
)
1 (yellow form)
C, 80 (6.1); C′,
101 (48.5); I
C′, 100 (51.5); I
C, 78 (19.4); C′,
128 (39.9); I
C′, 123 (27.9); I
C, 112 C′, 118 I
C′, 116 (28.9); I
Results and Discussion
1 (red form)
4 (yellow form)
2081, 2027sh, 2005, 1978sh
2079, 1997br
Preparation of Rhodium and Iridium â-Diketonate Com-
plexes. Complexes of general formula [M(â-diketonate)(CO)2]
(M ) Rh, Ir) (1-6), have been prepared in accordance with
Scheme 1, i. Compounds 1-3 have also been obtained by direct
reaction of sodium diketonate salts and the tetracarbonyl
rhodium complex [Rh2(µ-Cl)2(CO)4] (Scheme 1, ii).
4 (blue form)
6 (yellow form)
6 (blue form)
2067, 2022br, 1983
2044, 1988, 1977
2054, 2006br, 1979, 1970
a C, C′, crystal phases; I, isotropic liquid; sh, shoulder; br, broad
signal.
The 1H NMR spectra of complexes 1-6 in CDCl3 solutions
confirm the coordination of the â-diketonate groups to the metal
centers.
in solution. The existence of two polymorphic forms for related
complexes has previously been reported.10d-e
We have also studied the thermochromism of complexes 1,
4, and 6 by optical microscopy. Heating the yellow-colored
solids causes them to change to the dark colored forms (red M
) Rh or blue M ) Ir). Finally, yellow isotropic liquids were
obtained. In parallel, a thermal study has been performed by
differential scanning calorimetry (DSC), and the results are
shown in Table 1. The yellow samples exhibit one crystal-
crystal transition (C-C′), corresponding to the transformation
to the dark polymorphs observed under the optical microscope,
and a crystal-liquid (C′-I) transition. The dark forms only show
a crystal-isotropic liquid transition.
Preparation of Rhodium Pyrazole Complexes. Yellow
complexes of general formula cis-[RhCl(CO)2(pyrazole)] (pyra-
zole ) HL′1 (7), HL′2 (8), HL′3 (9)) were prepared by reaction
of [Rh2(µ-Cl)2(CO)4] with the corresponding pyrazole ligand
(Scheme 1, iii). These complexes were characterized by analyti-
cal and spectroscopic methods. In particular, the 1H NMR
spectra of these compounds show a singlet at δ ) 11.5 ppm
corresponding to the NH proton and two singlets in the range
2.15-2.57 ppm, indicating the inequivalence of the methyl
groups of the pyrazole ligands.
Complexes 2 and 5 are yellow, while compound 3 was
isolated as a red solid. However, two different polymorphs were
obtained for complexes 1, 4, and 6 depending on the solid
formation conditions: a red (M ) Rh) or dark blue (M ) Ir)
polymorph and the other yellow (M ) Rh, Ir). The more colored
forms (red or blue), obtained at higher temperatures, show, in
the solid state, complex IR spectra probably due to metal
2
stacking as a consequence of the dz orbital interactions, as
previously observed for related complexes.9 The yellow color
of the second polymorph, together with a simpler IR spectrum
(see Table 1) suggest a packing arrangement without interme-
tallic interactions,10 as has been observed for complex 4 by an
X-ray crystallographic study (see below). The red (M ) Rh) or
blue (M ) Ir) solid polymorphs transform to the yellow form,
(8) (a) Levine, B. F.; Bethea, C. G. J. Chem. Phys. 1975, 63, 2666. (b)
Oudar, J. L. Chem. Phys. 1977, 67, 446.
(9) Aullo´n, G.; Alvarez, S. Chem. Eur. J. 1997, 3, 655, and references
cited therein.
(10) (a) Gordon, G. C.; Dehaven, P. W.; Weiss, M. C.; Goedken, V. L. J.
Am. Chem. Soc. 1978, 100, 1003. (b) Elduque, A.; Finestra, C.; Lo´pez,
J. A.; Lahoz, F. J.; Mercha´n, F.; Oro, L. A.; Pinillos, M. T. Inorg.
Chem. 1998, 37, 824. (c) Kolel-Veetil, M. K.; Rheingold, A. L.;
Ahmed, K. J. Organometallics 1993, 12, 3439. (d) Pannetier, G.;
Bonnaire, R.; Fougeroux, P.; Davignon, L.; Platzer, N. J. Organomet.
Chem. 1973, 54, 313. (e) Davignon, L.; Manoli, J. M.; Dereigne, A.
J. Less-Common Met. 1976, 44, 201.
Mesomorphic Properties. Complexes 1-9 have been studied
by optical microscopy with polarized light and a heating-
cooling stage and by DSC. The results obtained are summarized
in Table 2.

Rh and Ir Metallomesogen Complexes
Inorganic Chemistry, Vol. 38, No. 13, 1999 3087
Table 2. Optical, Thermal, and Thermodynamical Properties of
Ligands HL1-HL3 and Their Complexes 1-6 and of Ligands
HL′1-HL′3 and Their Complexes 7-9
this fact should benefit, in a first approximation, the mesomor-
phic state. However, we observed that there is not only a
noninduction of mesomorphism but a disappearance of the
monotropic mesophases N and SA when X ) OOC, and N when
X ) COO. This observation, in addition to the higher melting
points of the complexes, leads us to the conclusion that the
global effect of the introduction of the [M(CO)2] unit is a
stabilization of the crystalline phase to the detriment of the
mesomorphic phases.
compd
HL1
X
transition
T (°C)
∆H (kJ mol-1)
COO
C1-C2
C2-I
27.7
65.9
50.7
45.2
25.1
46.4
79.4
27.5
24.9
49.8
55.8
80.2
100.8
93.8
144.6
111.3
78.0
127.6
96.0
128.1
116.1
68.6
3.8
37.5
-0.4
-0.4
1.0
18.3
15.6
-0.9
-0.6
42.7b
I-Na
N-SA
a
HL2
OOC
C1-C2
C2-C3
C3-I
Pyrazole Derivatives (7-9) (Table 2). Only complex 7 (X
) COO) is mesomorphic and shows a monotropic nematic
phase. The texture observed under the microscope is shown in
Figure 1b (nematic drops with Schlieren texture). The pyrazole
ligands HL′1 and HL′2 show monotropic nematic mesophases.
Comparing these ligands with the complexes 7 and 8, the
addition of the [RhCl(CO)2] unit to the ligand structure maintains
or even reduces the melting points. This behavior can be
explained assuming that the metal unit restricts the interaction
between the pyrazole rings through hydrogen bonds. As already
mentioned for the â-diketonate metal derivatives, the introduc-
tion of the [RhCl(CO)2] unit in the pyrazole chain leads to a
noninduction or worsening of the mesomorphic properties.
Single-Crystal X-ray Analysis of [IrL1(CO)2]‚CH3OH
(4‚CH3OH). An X-ray diffraction analysis of a tiny plate of
the yellow polymorph of compound 4 was carried out. A
molecular drawing of this molecule is shown in Figure 2.
Selected bond distances and angles are listed in Table 3.
The â-diketonate ligand (L1) is bonded in a chelate fashion
to the metal center through the two oxygen atoms, O(3) and
O(4); additionally, two carbonyl groups complete a slightly
distorted square-planar environment at the iridium atom. The
six-membered metallacycle formed is almost planar, with a
maximum deviation from the mean plane of 0.026(8) Å for O(3).
The Ir-O distances (2.038 and 2.027(7) Å) are very similar to
those reported for the closely related compounds [M(acac)(cod)]
(M ) Ir, 2.039 and 2.045(3) Å,12 or M ) Rh, 2.040 and 2.044-
(4) Å 13).
I-Na
N-SA
a
HL3
CH2
C1-I
C2-I
C1-C2
C2-I
1
COO
6.1
48.5
-3.7
36.9
32.9
19.4
39.9
c
18.2
28.9
2.3
4.4
31.6
-
21.4
-0.9
0.6
2.2
1.1
25.0
26.9
-0.6
23.4
29.1
21.6
a
I-SA
2
3
4
OOC
CH2
COO
C-I
C-I
C1-C2
C2-I
a
I-SA
5
6
HL1′
OOC
CH2
COO
C-I
C-I
C1-C2
C2-C3
C3-I
I-Na
C-I
94.3
156.0
146d
125.3
78.9
49.7
75.8
101.3
136.7
139.7
123.5
126.2
73.6
HL2′
HL3′
OOC
CH2
I-Na
C1-C2
C2-C3
C3-C4
C4-I
C-I
7
COO
I-Na
C-I
8
9
OOC
CH2
C1-C2
C2-I
87.4
a Monotropic transition. b Includes both transitions. c No enthalpy
value could be obtained due to partial overlapping with the crystal-
d
lization peak. Optical microscopy data.
The whole molecule adopts an extended rodlike shape, with
an all-trans conformation of the decyloxy chain. The orientation
of ester group C1 (see Figure 2) with respect to the adjacent
phenyl (B1) and metallacycle (acac) rings are described by the
dihedral angles C1/B1 60.5(7)° and C1/acac 55.1(7)°, in such
a way that these two rings are nearly parallel (9.9(3)°). In the
case of the other carboxyl group, C2, the orientation with respect
to the O- and C-bonded phenyl rings are 60.1 and 1.9(8)°. As
expected, the relative orientations between carboxyl and phenyl
groups are almost coplanar for the C-bonded and significantly
rotated (60° approximately) for the O-bonded.14 Interestingly,
the principal molecular axis of the rodlike molecule is ap-
proximately parallel to the crystallographic a axis (Figure 3a).
The packing arrangement in the ac plane situates contiguous
molecules antiparallel, with adjacent molecules disposed in
opposite senses. The solid-state molecular organization could
be described as a layered structure (along the bc plane), each
layer being formed by almost perpendicular molecules with
alternate orientations. There exists some degree of interdigitation
between two consecutive layers through the long hydrocarbon-
ated chains (along the a axis approximately). As a result of this
packing arrangement there is a stacking of the molecules along
the short b axis (4.0093(8) Å), but with the metal coordination
plane not perpendicular to this crystallographic axis (the angle
Diketonate Derivatives (1-6) (Table 2). Complexes 1 and
4 show a monotropic smectic A phase. Under the optical micro-
scope with polarized light the textures are fan-shaped with ho-
meotropic regions. Figure 1a corresponds to the mesophase of
1. The thermograms show that, on cooling the isotropic liquid
at 10 °C min-1, the mesophase of compound 1 appears at 93.8°
and remains over 20 °C. In the case of the iridium complex 4
the mesophase appearance and the crystallization are almost si-
multaneous, showing a DSC thermogram with these two transi-
tions partially overlapped. This fact prevented us from calculat-
ing the enthalpy for the isotropic liquid-mesophase transition.
Complexes 2, 3, 5, and 6 did not show liquid crystal properties.
Melting points are, in general, between 111 and 145 °C.
The â-diketone ligands HL1 (X ) COO) and HL2 (X ) OOC)
show monotropic nematic and smectic A mesophases1c char-
acterized by their typical textures (Schlieren and fan-shaped,
respectively), and their melting points are always lower than
those of the related complexes. [These data present some
disagreement with those reported in a recent publication where
a nonmesogenic behavior for the â-diketonate ligand HL2 (X
) OOC) is described.11] Comparing the complexes with their
respective ligands, the group [M(CO)2] makes the molecule
longer without varying significantly the molecular width, and
(12) Tucker, P. A. Acta Crystallogr. 1981, B37, 1113.
(13) Huq, F.; Skapski, A. C. J. Cryst. Mol. Struct. 1974, 4, 411.
(14) Schweizer, W. B.; Dunitz, J. D. HelV. Chim. Acta 1982, 65, 1547.
(11) Wan, W.; Guang, W.-J.; Zhao, K.-Q.; Zheng, W.-Z.; Zhang, L.-F. J.
Organomet. Chem. 1998, 557, 157.

3088 Inorganic Chemistry, Vol. 38, No. 13, 1999
Barbera´ et al.
Figure 1. (a) Microphotograph of the texture of the smectic A mesophase of compound 1. (b) Microphotograph of the texture of the nematic
mesophase of compound 7. Crossed polarizers.
Figure 2. Molecular representation of 4 with numbering scheme used. An indication of the labeling used for calculated least-squares planes is also
included.
between the b axis and the normal to the coordination plane is
24.5(2)°) (Figure 3b). This particular intermetallic disposition
together with the long Ir‚‚‚Ir separation seems to exclude a direct
metal-metal interaction in this yellow polymorph.9 However,

Rh and Ir Metallomesogen Complexes
Inorganic Chemistry, Vol. 38, No. 13, 1999 3089
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
[IrL1(CO)2] (4)a
Ir‚‚‚Ir′
4.0093(12)
1.856(13)
2.038(7)
Ir-C(1)
Ir-C(2)
Ir-O(4)
1.860(11)
2.027(7)
Ir-O(3)
O(1)-C(1)
O(3)-C(3)
C(3)-C(4)
O(5)-C(8)
O(5)-C(9)
O(6)-C(8)
1.130(15)
1.293(12)
1.389(15)
1.368(13)
1.426(11)
1.192(12)
O(2)-C(2)
O(4)-C(5)
C(4)-C(5)
O(7)-C(15)
O(7)-C(12)
O(8)-C(15)
1.122(13)
1.287(12)
1.421(13)
1.373(13)
1.422(11)
1.210(12)
Figure 4. Charge transfer for molecules with X ) OOC (a) and for
molecules with X ) COO (b). A is the acceptor group, and D is the
donor group.
C(1)-Ir-C(2)
C(1)-Ir-O(3)
C(1)-Ir-O(4)
Ir-C(1)-O(1)
Ir-O(3)-C(3)
O(3)-C(3)-C(4)
C(3)-C(4)-C(5)
88.6(5)
91.4(4)
178.2(5)
178.5(11)
128.1(7)
125.9(9)
124.6(9)
O(3)-Ir-O(4)
C(2)-Ir-O(4)
C(2)-Ir-O(3)
Ir-C(2)-O(2)
Ir-O(4)-C(5)
O(4)-C(5)-C(4)
87.5(3)
92.6(4)
177.7(5)
179.0(11)
130.0(7)
123.8(9)
Table 4. Experimental µ0â Values Measured at 1380 nm and µ0â0
Values Deduced from a Two-Level Model (10-48 Esu) and
Absorption Bands Maxima (nm) of â-Diketone and Pyrazole
Derivatives
a Primed atom is related to the unprimed one by the symmetry
transformation x, 1 + y, z.
compd
X
λmax
267
268, 328
270, 323
323
263
274
265, 339
270, 337
265, 338
(µ0â)1,38
(µ0â0)
HL1
1
2
3
HL′1
HL′2
7
8
9
COO
COO
OOC
CH2
COO
OOC
COO
OOC
CH2
32
≈20
46
26
≈15
34
≈20
≈15
18
15
31
26
53
23
25
18
38
16
orbitals of the metal centers into alignment, and most likely
the intermetallic interaction proposed for the high-temperature
polymorph could take place generating a darker color for this
alternative crystalline form.
Nonlinear Optical Properties. The experimental µ0â and
the µ0â0 values deduced from a simple two-level model15 are
shown in Table 4.
If we compare the ligands HL1 and HL′1, the higher µ0â value
of the former qualitatively agrees with the results obtained in
other â-diketone and pyrazole derivatives.16 The origin of this
difference can be found in the stronger acceptor character of
the â-diketone group as compared with the pyrazole.
The µ0â values seem to reflect the global charge transfer in
the whole molecule which can be modified in different ways
by the local charge transfer in the COO and OOC ester groups.
In the molecule as a whole, the charge moves from the
n-decyloxy group to the â-diketone or pyrazole group, the same
direction as in the X ) OOC group, because the oxygen atom
placed in the molecular axis is a π donor and could give charge
to the main acceptor (Figure 4a). On the other hand, for X )
COO, the π acceptor carbon atom of the ester group is directly
linked to the main acceptor group and the charge transfer is
partially interrupted. (Figure 4b). The relatively low µ0â values
of complexes 3 and 9 can also be explained in terms of charge
transfer, as the CH2 group disrupts the molecular conjugation.
The absorption spectra of rhodium-pyrazole complexes show
a main band centered around 265-270 nm similar to that of
the corresponding ligand (see Table 4). This band is assigned
to a π f π* intraligand transition. It also shows one smaller
band at higher wavelength (around 338 nm) associated with a
transition involving metal orbitals. As can be seen in Table 4,
the rhodium-pyrazole complexes show slightly higher µ0â
values than their ligands. A similar behavior, with a more
Figure 3. Drawing of the packing of molecules in 4: (a) in the ac
plane and (b) along the b axis.
it seems reasonable that under thermal stress a minor reorga-
nization of the crystal could take place by a small rotation of
the metal coordination planes to make them perpendicular to
(15) Oudar, J. L.; Chemla, D. S. J. Chem. Phys. 1977, 66, 2664.
(16) Barbera´, J.; Gime´nez, R.; Serrano, J. L.; Alcala´, R.; Villacampa, B.;
Villalba, J.; Ledoux, I.; Zyss, J. Liq. Cryst. 1997, 22, 265.
2
the crystallographic b axis. This situation will bring the dz
(17) Bruce, D. W.; Thornton, A. Mol. Cryst. Liq. Cryst. 1993, 231, 253.

3090 Inorganic Chemistry, Vol. 38, No. 13, 1999
Barbera´ et al.
Table 5. Crystallographic Data for [IrL1(CO)2]‚CH3OH (4‚CH3OH)
chem formula
cryst color and habit
fw
C32H39IrO10
yellow, prismatic block
775.83
F(calcd), g cm-3
µ, mm-1
1.581
4.151
2.3-25.0
-1 e h e +30, -1 e k e +4,
-37 e l e +36
7831
5625 (Rint ) 0.0629)
ψ-scan
0.273, 0.422
5625/107/394
0.0583
0.1566
1.040
θ range data collecn, deg
index ranges
temp, K
173(2)
cryst syst
space group
a, Å
b, Å
c, Å
â, deg
V, Å3
Z
monoclinic
P21/c (No. 14)
26.991(6)
4.0093(8)
31.169(6)
104.950(13)
3258.8(12)
4
collecd reflcns
unique reflcns
abs corr method
min, max transm factors
data/restraints/params
R(F) [F 2 > 2σ(F 2)]a
Rw(F 2) [all data]b
S [all data]c
a R(F) ) ∑||Fo| - |Fc||/∑|Fo|, for 3794 observed reflections. b Rw(F2) ) (∑[w(Fo2 - Fc2)2]/∑[w(Fo )2])1/2
.
c S ) [∑[w(Fo2 - Fc2)2]/(n - p)]1/2; n
2
) number of reflections, p ) number of parameters.
Solvents were purified by standard procedures and distilled under argon
prior to use. All other reagents were purchased from Aldrich and used
as received.
important enhancement of the nonlinear response, has been
previously observed in stilbazole derivative rhodium com-
plexes.11 The reported µ0â value of the [RhCl(CO)2(4-stilba-
zole)] complex is 149 × 10-48 esu bigger than that of the ligand
(60 × 10-48 esu). Kanis et al.18 explain similar results in other
stilbazole complexes as resulting from the increase of the
electron acceptor character of the pyridine cycle induced by the
metal group. This also could explain the effect of the metal
group [RhCl(CO)2] in the pyrazole ligand.
The experimental µ0â values obtained for the â-diketone
ligand HL1 and its complex show that the presence of the metal
decreases the nonlinear response. To explain the difference
between pyrazole and â-diketone derivatives, it is necessary to
note that the metal environment is different in the two series of
compounds ([RhCl(CO)2] and [Rh(CO)2], respectively), and the
presence of a chlorine atom in the pyrazole complexes, acting
as a charge acceptor, could be related to the enhancement of
the nonlinear response.
1
Experimental Measurements. Infrared spectra, H and 13C NMR
spectra, elemental analyses, optical textures of the mesophases, dif-
ferential scanning calorimetries, absorption spectra, and EFISH mea-
surements were recorded as previously described.2d,8,16
X-ray Structural Analysis of [IrL1(CO)2]‚CH3OH (4‚CH3OH).
A summary of crystal data and refinement parameters is given in Table
5. Yellow crystals of 4 were obtained by slow diffusion of methanol
in a concentrated solution of 4 in dichloromethane. A yellow plate of
approximate dimensions 0.09 × 0.25 × 0.30 mm was selected and
used for data collection; diffraction data were measured with a Siemens
P4 diffractometer using graphite-monochromated Mo KR radiation (λ
) 0.710 73 Å). Cell constants were obtained from the least-squares fit
on the setting angles of 60 reflections in the range 20 e 2θ e 35°. A
set of 7831 reflections with 2θ in the range 4-50° was measured using
the ω scan technique and corrected for Lorentz and polarization effects;
a semiempirical absorption correction, based on azimuthal ψ-scans from
20 reflections, was also applied.22 Three standard reflections were
measured every 97 reflections as a check of crystal and instrument
stability; no important variation was observed.
Conclusions
The structure was solved by direct methods (SIR92)23 and difference
Fourier techniques and refined by full-matrix least squares on F2
(SHELXL97),24 first with isotropic and then with anisotropic displace-
ment parameters for all non-hydrogen atoms. The hydrogen atoms were
introduced in calculated positions and refined riding on the correspond-
ing carbon atoms. At this stage, a difference Fourier map showed a
heavily disordered solvent with peaks up to 2.61 e Å-3. The Squeeze
procedure25 implemented in PLATON26 was used to calculate the
potential solvent volume (332.5 Å3/unit cell) and the electron count
missing in the model (64 e-/unit cell approximately). With these data
we decided to include one methanol solvent molecule per asymmetric
unit (4 × 18 e-) modeled as two carbon atoms disordered in five
positions. The largest peak remaining in this solvent zone was 1.28 e
Å-3. The refinement converged at Rw(F2) ) 0.1566 for 394 parameters,
107 restraints, and 5625 unique reflections. The calculated weighting
New liquid crystal pyrazole or â-diketonate-rhodium or
-iridium derivatives have been prepared. Two different poly-
morphs, for some of the â-diketonate compounds, have been
obtained at the solid state. The color, as well as the infrared
spectra displayed for the solids forms, seems to be related to a
2
different intermetallic-packing arrangement suggesting a dz
orbital interaction for the metal centers in the dark solid
polymorphs, as indicated by the X-ray crystallographic study
made for compound 4.
On the other hand, the presence of the metal in the rhodium-
pyrazole derivatives leads to an enhancement of the nonlinear
response, probably due to the presence of a chlorine atom
bonded to the metal center acting as a charge acceptor. However,
the â-diketonate derivatives, presenting a different metal
environment, show the opposite trend.
2
2
scheme is 1/[σ2(Fo ) + (0.0732P)2 + 14.15P], where P ) (max(Fo ,0)
+ 2Fc2)/3. Scattering factors were used as implemented in the
refinement program.24 The largest peak and hole in the final difference
Experimental Section
map were 1.67 (close to iridium atom) and -0.97 e Å-3
.
All reactions were carried out under argon using standard Schlenk
techniques. The â-diketone ligands1c (HL1, 3-[(4′-((4′′-n-decyloxyben-
zoyl)oxy)phenoxy)carbonyl]-2,4-pentanedione; HL2, 3-[(4′-((4′′-n-de-
cyloxybenzoyl)oxy)benzoyl)oxy]-2,4-pentanedione; HL3, 3-[(4′-(4′′-n-
decyloxybenzoyl)oxy)benzyl]-2,4-pentanedione), the pyrazole ligands1c;
(HL′1, 4-[(4′-((4′′-n-decyloxybenzoyl)oxy)phenoxy)carbonyl]-3,5-di-
methylpyrazole; HL′2, 4-[(4′-((4′′-n-decyloxybenzoyl)oxy)benzoyl)oxy]-
3,5-dimethylpyrazole; HL′3, 4-[4′-((4′′-n-decyloxybenzoyl)oxy)benzyl]-
3,5-dimethylpyrazole)), [Rh2(µ-Cl)2(COD)2],19 [Rh2(µ-Cl)2(CO)4],20 and
[Ir2(µ-Cl)2(COD)2]21 were prepared according to literature methods.
Synthesis of the Complexes [RhL(CO)2] (L ) L1 (1), L2 (2), L3
(3). These compounds were prepared by two general methods:
(19) Giordano, G.; Crabtree, R. H. Inorg. Synth. 1979, 19, 218.
(20) Hieber, W.; Lagally, H. Z. Anorg. Allg. Chem. 1943, 251, 96.
(21) Herde, J. L.; Lambert, J. C.; Seneff, C. V. Inorg. Synth. 1974, 15, 18.
(22) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.
1968, A24, 351.
(23) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. J. Appl.
Crystallogr. 1994, 27, 435.
(24) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
(18) Kanis, D. R.; Lacroix, P. G.; Ratner, M. A. J. Am. Chem. Soc. 1994,
116, 10089.
(25) Van der Sluis, P.; Spek, A. L. Acta Crystallogr. 1990, A46, 194.
(26) Spek, A. L. Acta Crystallogr. 1990, A46, C34.

Rh and Ir Metallomesogen Complexes
Inorganic Chemistry, Vol. 38, No. 13, 1999 3091
complexes 1-3 starting from â-diketone (0.236 mmol), KOH in
methanol (0.8 mL, 0.294 M), and [Ir2(µ-Cl)2(COD)2] (79.2 mg, 0.118
mmol).
Chart 1
[Ir(L1)(CO)2] (4). Compound 4 was isolated as two crystalline forms,
dark blue and yellow. The blue form was obtained by precipitating the
solid by evaporation of the solvent at high temperatures. The yellow
form was precipitated at room temperature. Yield: 68-72%. IR (Nujol,
NaCl, cm-1): Blue solid: 2067, 2022(b), 1983 (CtO), 1731 (b) (Cd
O), 1605 (ar C-C), 1574 (CdO), 1510 (ar C-C), 1258 (C-O). Yellow
solid: 2079, 1997 (CtO), 1728 (CdO), 1607 (ar C-C), 1574 (Cd
O), 1511,1505 (ar C-C), 1259 (C-O). IR (CH2Cl2): 2077, 2000 (Ct
O). 1H NMR (CDCl3): δ 0.87 (t, J ) 6.5 Hz, 3H, Ha), 1.19-1.46 (m,
14H, Hb), 1.78-1.83 (m, 2H, Hc), 2.39 (s, 6H, Hj), 4.03 (t, J ) 6.4 Hz,
2H, Hd), 6.96 (d, J ) 8.8 Hz, 2H, He), 7.19 (d, J ) 9.0 Hz, 2H, Hg),
7.25 (d, J ) 9.0 Hz, 2H, Hf), 8.12 (d, J ) 8.8 Hz, 2H, Hh). 13C NMR
(CDCl3): δ 187.7. Anal. Calcd for C31H35IrO9: C, 50.06; H, 4.74.
Found: C, 50.12; H, 4.94.
[Ir(L2)(CO)2] (5). Compound 5 was isolated as a yellow micro-
crystalline solid. Yield: 72%. IR (Nujol, NaCl, cm-1): 2067, 1988
(CtO), 1737 (CdO), 1603 (ar C-C), 1577 (CdO), 1510 (ar C-C),
1259 (C-O). IR (CH2Cl2): 2070, 1995 (CtO). 1H NMR (CDCl3): δ
0.87 (t, J ) 6.7 Hz, 3H, Ha), 1.26-1.46 (m, 14H, Hb), 1.78-1.81 (m,
2H, Hc), 2.11 (s, 6H, Hj), 4.03 (t, J ) 6.5 Hz, 2H, Hd), 6.97 (d, J ) 8.9
Hz, 2H, He), 7.36 (d, J ) 8.7 Hz, 2H, Hg) 8.13 (d, J ) 8.9 Hz, 2H,
Hf), 8.24 (d, J ) 8.7 Hz, 2H, Hh). 13C NMR (CDCl3): δ 182.0. Anal.
Calcd for C31H35IrO9: C, 50.06; H, 4.74. Found: C, 49.98; H, 4.53.
[Ir(L3)(CO)2] (6). Compound 6 was isolated as two crystalline forms,
dark blue and yellow. The blue form was obtained by precipitating the
solid by evaporation of the solvent at high temperatures. The yellow
form was precipitated at room temperature. Yield: 70-75%. IR (Nujol,
NaCl, cm-1). Blue solid: 2054, 2006(b), 1979, 1970 (CtO), 1733 (Cd
O), 1605 (ar C-C), 1564 (CdO), 1510 (ar C-C), 1255 (C-O). Yellow
solid: 2044, 1988, 1977 (CtO), 1736, 1725 (CdO), 1603 (ar C-C),
1559 (CdO), 1509 (ar C-C), 1259 (C-O). IR (CH2Cl2): 2060, 1990
(CtO). 1H NMR (CDCl3): δ 0.84 (t, J ) 6.3 Hz, 3H, Ha), 1.26-1.48
(m, 14H, Hb), 1.77-1.82 (m, 2H, Hc), 2.14 (s, 6H, Hj), 3.79 (s, 2H,
Hi), 4.02 (t, J ) 6.5 Hz, 2H, Hd), 6.94 (d, J ) 8.9 Hz, 2H, He), 7.11
(s, 4H, Hg, Hh), 8.11 (d, J ) 8.9 Hz, 2H, Hf). 13C NMR (CDCl3): δ
186.6. Anal. Calcd for C31H37IrO7: C, 52.16; H, 5.22. Found: C, 52.02;
H, 5.51.
(a) Method 1. To a suspension of sodium diketonate (prepared in
situ by reaction of â-diketone (HL1-HL3) (0.536 mmol) and sodium
acetate (44 mg, 0.536 mmol), in methanol (15 mL), [Rh2(µ-Cl)2(CO)4]
(104 mg, 0.268 mmol) was added. The reaction mixture was stirred at
room temperature for 1 h. Then, the resulting precipitate was separated
by filtration, washed with methanol, and vacuum-dried.
(b) Method 2. Carbon monoxide was bubbled through a solution
of [Rh(L)(COD)] (0.506 mmol) [prepared by reaction of potassium
diketonate (KOH in methanol/â-diketone: 1.7 mL, 0.294 M/0.506
mmol) and [Rh2(µ-Cl)2(COD)2] (124 mg, 0.252 mmol)] in diethyl ether
(15 mL) for 30 min. The concentration of the solvent to 2 mL and
addition of methanol (10 mL) afforded a solid which was separated by
filtration and dried in a vacuum.
[Rh(L1)(CO)2] (1). Compound 1 (see Chart 1) was isolated as two
crystalline forms, red and yellow. The red form was obtained by
precipitating the solid by evaporation of the solvent at high temperatures.
The yellow form was precipitated at room temperature. Yield: 78-
82% (method 1). IR (Nujol, NaCl, cm-1). Red solid: 2081, 2027, 2005,
1978 (CtO), 1742, 1731 (CdO), 1605 (ar C-C), 1580 (CdO), 1508
(ar C-C), 1254 (C-O). Yellow solid: 2088, 2027 (CtO), 1735 (Cd
O), 1607 (ar C-C), 1586 (CdO), 1504 (ar C-C), 1254 (C-O). IR
1
Synthesis of the Complexes cis-[RhCl(CO)2(HL′)] (L′ ) L′1 (7),
L′2 (8), L′3 (9)). The appropriate pyrazole ligand (0.305 mmol) was
added to a solution of [Rh2(µ-Cl)2(CO)4] (59.3 mg, 0.152 mmol) in
dichloromethane (10 mL). The reaction mixture was stirred for 30 min,
and the solvent was concentrated to 0.5 mL. Addition of hexane (5
mL) led to the precipitation of a solid which was separated by filtration
and recrystallized from dichloromethane/hexane.
(CH2Cl2): 2089, 2017 (CtO). H NMR (CDCl3): δ 0.87 (t, J ) 6.6
Hz, 3H, Ha), 1.26-1.46 (m, 14H, Hb), 1.78-1.83 (m, 2H, Hc), 2.35 (s,
6H, Hj), 4.02 (t, J ) 6.4 Hz, 2H, Hd), 6.95 (d, J ) 8.8 Hz, 2H, He),
7.18 (d, J ) 9.0 Hz, 2H, Hg) 7.24 (d, J ) 9.0 Hz, 2H, Hf), 8.11 (d, J
) 8.8 Hz, 2H, Hh). 13C NMR (CDCl3): δ 14.1, 22.6, 25.9, 27.5, 29.0,
29.3, 29.3, 29.5, 31.8, 68.3, 111.4, 114.3, 121.2, 122.8, 132.3, 147.8,
148.5, 163.6, 164.8, 167.9, 183.0 (d, JRhC ) 73 Hz), 188.6 (b). Anal.
Calcd for C31H35O9Rh: C, 56.89; H, 5.39. Found: C, 56.86; H, 5.25.
cis-[RhCl(CO)2(HL′1)] (7). Compound 7 was isolated as a yellow
solid. Yield: 78%. IR (Nujol, NaCl, cm-1): 2086, 2078, 2020, 2009
(CtO), 1731 (CdO), 1605, 1505 (ar C-C), 1258 (C-O). IR
[Rh(L2)(CO)2] (2). Compound 2 was isolated as a yellow micro-
crystalline solid. Yield: 79% (method 1). IR (Nujol, NaCl, cm-1): 2080,
2008 (CtO), 1736 (CdO), 1604 (ar C-C), 1585 (CdO), 1510 (ar
C-C), 1254 (C-O). IR (CH2Cl2): 2080, 2010 (CtO). 1H NMR
(CDCl3): δ 0.87 (t, J ) 6.7 Hz, 3H, Ha), 1.26-1.48 (m, 14H, Hb),
1.79-1.83 (m, 2H, Hc), 2.10 (s, 6H, Hj), 4.03 (t, J ) 6.5 Hz, 2H, Hd),
6.97 (d, J ) 8.9 Hz, 2H, He), 7.34 (d, J ) 8.8 Hz, 2H, Hg) 8.13 (d, J
) 8.9 Hz, 2H, Hf), 8.23 (d, J ) 8.8 Hz, 2H, Hh). 13C NMR (CDCl3):
δ 182.4 (b), 183.4 (d, JRhC ) 73 Hz). Anal. Calcd for C31H35O9Rh: C,
56.89; H, 5.39. Found: C, 56.92; H, 5.18.
1
(CH2Cl2): 2100, 2020 (CtO). H NMR (CDCl3): δ 0.86 (t, J ) 6.8
Hz, 3H, Ha), 1.20-1.52 (m, 14H, Hb), 1.77-1.81 (m, 2H, Hc), 2.60 (s,
6H, Hj), 2.72 (s, 3H, Hk) 4.03 (t, J ) 6.6 Hz, 2H, Hd), 6.95 (d, J ) 8.8
Hz, 2H, He), 7.18-7.27 (m, 4H, Hf, Hg) 8.12 (d, J ) 8.8 Hz, 2H, Hh),
11.57 (b, 1H, Hl). 13C NMR (CDCl3): δ 12.9, 14.2, 15.8, 22.6, 25.9,
29.0, 29.3, 29.3, 29.5, 31.9, 68.3, 110.3, 114.3, 121.2, 122.5, 122.8,
132.3, 147.2, 147.8, 148.7, 155.3, 161.0, 163.6, 164.8, 180.0 (b). Anal.
Calcd for C31H36N2ClO7Rh: C, 54.20; H, 5.28; N, 4.08. Found: C,
53.80; H, 5.21; N, 4.09.
[Rh(L3)(CO)2] (3). Compound 3 was isolated as a red solid. Yield:
85% (method 1). IR (Nujol, NaCl, cm-1). Red solid: 2068, 1999, 1988
(CtO), 1744, 1735 (CdO), 1605 (ar C-C), 1573 (CdO), 1511 (ar
C-C), 1254 (C-O). IR (CH2Cl2): 2080, 2010 (CtO). 1H NMR
(CDCl3): δ 0.84 (t, J ) 6.7 Hz, 3H, Ha), 1.26-1.45 (m, 14H, Hb),
1.77-1.82 (m, 2H, Hc), 2.10 (s, 6H, Hj), 3.73 (s, 2H, Hi), 4.02 (t, J )
6.5 Hz, 2H, Hd), 6.94 (d, J ) 8.7 Hz, 2H, He), 7.10 (s, 4H, Hg, Hh),
cis-[RhCl(CO)2(HL′2)] (8). Compound 8 was isolated as a yellow
solid. Yield: 80%. IR (Nujol, NaCl, cm-1): 2096, 2022 (CtO), 1731
(CdO), 1604, 1510 (ar C-C), 1264 (C-O). IR (CH2Cl2): 2100, 2020
(CtO). 1H NMR (CDCl3): δ 0.87 (t, J ) 6.6, 3H, Ha), 1.26-1.52 (m,
14H, Hb), 1.77-1.82 (m, 2H, Hc), 2.23 (s, 6H, Hj), 2.31 (s, 3H, Hk)
4.04 (t, J ) 6.6, 2H, Hd), 6.97 (d, J ) 8.8, 2H, He), 7.37(d, J ) 8.8,
2H, Hg), 8.13 (d, J ) 8.8, 2H, Hf), 8.24 (d, J ) 8.8, 2H, Hh), 11.30 (b,
1H, Hl). 13C NMR (CDCl3): δ 180.0 (b). Anal. Calcd for C31H36N2-
ClO7Rh: C, 54.20; H, 5.28; N, 4.08. Found: C, 54.17; H, 5.22; N,
3.98.
8.10 (d, J ) 8.7 Hz, 2H, Hf). 13C NMR (CDCl3): δ 183.9 (d, JRhC
)
73 Hz), 187.4 (b). Anal. Calcd for C31H37O7Rh: C, 59.62; H, 5.97.
Found: C, 59.58; H, 5.76.
Synthesis of the Complexes [IrL(CO)2] (L ) L1 (4), L2 (5), L3
(6). Complexes 4-6 were prepared by method 2 described for
cis-[RhCl(CO)2(HL′3)] (9). Compound 9 was isolated as a yellow
solid. Yield: 75%. IR (Nujol, NaCl, cm-1): 2069, 2009 (CtO), 1736

3092 Inorganic Chemistry, Vol. 38, No. 13, 1999
Barbera´ et al.
(CdO), 1606, 1511 (ar C-C), 1251 (C-O). IR (CH2Cl2): 2080, 2010
(CtO). 1H NMR (CDCl3): δ 0.86 (t, J ) 6.8 Hz, 3H, Ha), 1.26-1.52
(m, 14H, Hb), 1.77-1.82 (m, 2H, Hc), 2.19 (s, 6H, Hj), 2.29 (s, 3H,
Hk) 3.75(s, 2H, Hi), 4.02 (t, J ) 6.6 Hz, 2H, Hd), 6.94 (d, J ) 8.8 Hz,
2H, He), 7.09 (s, 4H, Hg, Hh), 8.10 (d, J ) 8.8 Hz, 2H, Hf), 11.09 (b,
1H, Hl). 13C NMR (CDCl3): δ 180.2(d, JRhC ) 62 Hz), 183.1(d, JRhC
) 62 Hz). Anal. Calcd for C31H38N2ClO5Rh: C, 56.67; H, 5.83; N,
4.26. Found: C, 56.68; H, 5.91; N, 4.27.
CICYT (Project MAT96-1073) for Financial Support and the
Diputacio´n General De Arago´n for a Research Studentship to
R. G.
Supporting Information Available: Crystallographic data, frac-
tional atomic coordinates, anisotropic displacement parameters, hydro-
gen coordinates, bond distances and angles, and some least-squares
planes, in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
Acknowledgment. We thank the DGICYT (Project PB94-
1186; Programa De Promocio´n General Del Conocimiento) and
IC9814017