Mesogenic dinuclear cyclopalladated derivatives with mixed bridges - Crystal structure of cis-[Bis({4,4′-di-n-butoxy}benzylideneaniline-C 2,N)-(μ-n-butylthiolato)(μ-chloro)dipalladium(II)]

Article abstract of DOI:10.1002/(SICI)1099-0682(199809)1998:9<1235::AID-EJIC1235>3.0.CO;2-9

The dinuclear cyclopalladated compounds [Pd(μ-Cl)Ln]₂ (2) [HLn = p-C_nH_2n+1OC₆H₄CH=NC ₆H₄OC_nH_2n+1-p (n = 6, 8, and 10)] react with silver thiolates AgSRm (Rm = C_mH_2m+1, m = 6, 8, 10, and 18) to give dinuclear derivatives with mixed bridges [Pd₂(μ-Cl)(μ-SRm)Ln₂] (3). Treatment of derivatives 2 with silver acetate (Pd/AgOAc = 2:1) or treatment of [Pd(μ-OAc)Ln]₂ (1) with thiols HSRm (Pd/thiol = 2:1) affords acetato-thiolato bridged complexes [Pd₂(μ-OAc)(μ-SRm)Ln₂] (4). In addition to their mesogenic behavior, the most interesting feature of these complexes is the cis disposition of the palladium-imine moieties, that can be inferred from their ¹H-NMR spectra. The cis structure as well as the disposition of the bridges was confirmed by the X-ray diffraction study of 3 (n = m = 4).

Full text of DOI:10.1002/(SICI)1099-0682(199809)1998:9<1235::AID-EJIC1235>3.0.CO;2-9

FULL PAPER
Mesogenic Dinuclear Cyclopalladated Derivatives with Mixed Bridges ؊
Crystal Structure of cis-[Bis({4,4Ј-di-n-butoxy}benzylideneaniline-C2,N)-
(µ-n-butylthiolato)(µ-chloro)dipalladium(II)]
a
b
a
c
c
´
´
´
˜
Julio Buey , Gustavo A. Dıez , Pablo Espinet* , Santiago Garcıa-Granda , and Enrique Perez-Carreno
a
´
´
Departamento de Quımica Inorganica, Facultad de Ciencias, Universidad de Valladolid ,
E-47005 Valladolid, Spain
E-mail: espinet@cpd.uva.es
b
´
´
´
Laboratorio de Quımica Inorganica, Facultad de Quımicas, Universidad de Burgos ,
E-09002 Burgos, Spain
c
´
´
´
´
Departamento de Quımica Fısica y Analıtica, Facultad de Quımica, Universidad de Oviedo ,
E-33006 Oviedo, Spain
Received May 14, 1998
Keywords: Liquid crystals / Palladium / Metallomesogens / Orthometallated imine / Thiolate
The dinuclear cyclopalladated compounds [Pd(µ-Cl)Ln]2 (2)
[HLn = p-CnH2n+1OC6H4CH=NC6H4OCnH2n+1-p (n = 6, 8,
acetato-thiolato bridged complexes [Pd2(µ-OAc)(µ-SRm)Ln2]
(4). In addition to their mesogenic behavior, the most
interesting feature of these complexes is the cis disposition
of the palladium-imine moieties, that can be inferred from
their 1H-NMR spectra. The cis structure as well as the
disposition of the bridges was confirmed by the X-ray
diffraction study of 3 (n = m = 4).
and 10)] react with silver thiolates AgSRm (Rm = CmH2m+1
,
m = 6, 8, 10, and 18) to give dinuclear derivatives with mixed
bridges [Pd2(µ-Cl)(µ-SRm)Ln2] (3). Treatment of derivatives 2
with silver acetate (Pd/AgOAc = 2:1) or treatment of [Pd(µ-
OAc)Ln]2 (1) with thiols HSRm (Pd/thiol = 2:1) affords
The synthesis of metal-containing liquid crystals is an widest mesophase ranges (compared to other derivatives
area of research which has seen a fast development in the with azobenzene or azine as ligands)[5], although both the
last two decades[1]. Cyclometallated compounds of PdII melting and the clearing points are quite high, above 100
with imines and related groups have received much atten- and 200°C respectively. In both structures the separation
tion due to: i) their thermal stability; ii) the variety of li- between the two imine fragments leaves a wide empty space
gands useful for orthometallation leading either to calami- in the central part of the dimer, which could be filled using
tic or to discotic mesogens; and iii) the possibility of tuning bridges that contained long alkyl chains. This should have
the mesogenic properties not only by varying the nature or a noticeable effect on the thermal properties of the material.
the length of the chains, but also the nature of the bridges
Figure 1. Sketch of the different space-filling efficiencies for com-
in dinuclear complexes. The imine moiety provides the rigid
core and flexible chains needed for liquid-crystal behavior,
and two of these moieties are fused together upon orthome-
tallation to give a X-bridged dinuclear complex (Figure 1).
We have reported in the last years several types of cyclopal-
ladated imine complexes and studied the structure-meso-
genic activity relationships[2][3]. It seems from these studies
that the acetato-bridged derivatives [Pd(µ-OAc)Ln]2 (1) are
rigid non-planar dimers (“open book” or “butterfly”
shaped), both in the solid state and in solution. Because
of this unfavorable molecular shape the compounds do not
display mesogenic behavior (there are, however, a few excep-
tions: some chiral-carboxylate derivatives[3], as well as cer-
plexes having bridges without or with long alkyl chains
In this paper we report on the attempt of replacing the
tain carboxylate complexes using azine instead of imine as chloro or acetato groups by thiolates bearing long alkyl
ligand[4], are mesomorphic). Their NMR spectra show that chains. They were chosen taking advantage of the tendency
the acetato-bridged complexes are in fact a mixture of two of such ligands to form very stable PdII- or PtII-bridged
isomers, depending on the relative arrangement of the two complexes[6]. Furthermore, they could be expected to pro-
imine moieties (ca. 96% trans versus 4% cis). On the con- duce a basically planar dimer[7]. The results have shown
trary, planar (“H” shaped) chloro-bridged dimers [Pd(µ- that using silver thiolates only one of the chloro bridges is
Cl)Ln]2 (2) contain only the trans isomer, and show the displaced, leading to mixed-bridged derivatives.
Eur. J. Inorg. Chem. 1998, 1235Ϫ1241
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
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1235

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J. Buey, G. A. Dıez, P. Espinet, S. Garcia-Granda, E. Perez-Carren˜o
FULL PAPER
Scheme 1
chloro bridge yielding [Pd2(µ-OAc)(µ-SRm)Ln2] (4) was
achieved by treating derivatives 3 with silver acetate in
CH2Cl2 (Pd/acetate ϭ 2:1, method A). This kind of com-
plexes could also be obtained by displacement of one ace-
tato bridge in complexes 1 using the corresponding thiol
(Pd/thiol ϭ 2:1, method B). Yields were similar (64Ϫ86%)
in both cases.
All the complexes gave satisfactory elemental analyses,
1
and were characterized by IR and H-NMR spectroscopy.
The latter is very informative, because both the iminic pro-
ton and H3 are very sensitive to changes in the molecular
structure, and the reactions can be monitored using these
signals. These 1H-NMR parameters are summarized in
Table 2 only for complexes 3 and 4 with n ϭ m ϭ 6; the
rest of complexes show little variation, within ± 0.03 ppm
for the chemical shifts, and unnoticeable for the coupling
constants.
Characterization of Complexes 3
1
The H-NMR spectra of these complexes indicate that
there is only one thiolato group in the dinuclear molecule.
Three isomers are possible (Figure 2), but only one is
formed since only one set of signals is observed in the aro-
matic region.
Figure 2. Sketch of the three possible isomers in mixed-bridged
complexes 3 and 4
Results and Discussion
Synthesis of the Complexes
Mixed-bridged chloro-thiolate or acetato-thiolate com-
plexes were prepared as shown in Scheme 1. The syntheses
of the precursors 1 and 2 have been recently described by
our group[3]. Treatment of [Pd(µ-Cl)Ln]2 (2) with the appro-
The trans-I structure can be discounted since the different
priate silver thiolate (AgSRm) in CH2Cl2 (Pd/thiolate ϭ environment of the two imines should give rise to two sets
2:1.1) afforded [Pd2(µ-Cl)(µ-SRm)Ln2] (3) in good yields of signals. Thus, the disposition of the palladium-imine
(73Ϫ91%). It should be noted that, regardless of the reac- moieties must be cis. The cis-II structure is favored because
tion conditions or the ratio Pd/AgSRm used, only mono- the antisymbiotic behavior of the palladium atom should
substitution was obtained. The replacement of the second place the thiolate group cis to the metallated carbon
1
Table 1. H-NMR parameters for complexes 3 and 4[a]
[c]
X
H
H3
H5
H6
H2Ј,6Ј[b]
H3Ј,5Ј[b]
OϪCH2/OϪCHЈ2
S-CH2ЈЈ[c] OTHERS[d]
Cl
7.93 s 7.39 d [2.3] 6.58 dd [8.2, 2.4] 7.28 d [8.3] 7.21 [8.9] 6.80 [8.9] 4.04 t/3.94 t
2.96 t
2.46 t
Ϫ
Ϫ
OAc 7.89 s 7.49 d [2.3] 6.48 dd [8.3, 2.3] 7.21 d [8.3] 7.19 [8.9] 6.81 [8.9] 4.00 m/3.88 t
1.62 s MeCO2
[b]
[a] In CDCl3 at 300.13 MHz; δ values and [J in Hz]; key: s, singlet; d, doublet; t, triplet; dd, doublet of doublets; m, multiplet. Ϫ
[c]
[d]
Apparent AB system. Ϫ Broad signals. Ϫ Aliphatic proton signals (R, RЈ, and RЈЈ) appear in the range δ ϭ 2.0Ϫ0.8.
1236 Eur. J. Inorg. Chem. 1998, 1235Ϫ1241

Mesogenic Dinuclear Cyclopalladated Derivatives with Mixed Bridges
FULL PAPER
atom[8]. In fact, this structure has been observed in com- Table 2. Selected bond lengths [A] and angles [°] for complex 3
˚
plexes [M2(µ-Cl)(µ-SR)Cl2(PR3)2] (M ϭ Pd or Pt)[9]: for
(n ϭ m ϭ 4)
M ϭ Pd only the cis isomer was obtained, whereas for M ϭ
M1
M2
Pt a mixture of cis and trans isomers was found. On the
contrary, cycloplatinated complexes similar to 3 lead only
to the cis isomer[10]. Complexes 3 are expected to be basi-
cally planar both in solution and in the solid state and the
comparable sizes of the chloro- and sulfur-bridging atoms
Pd(1)ϪC(16)
Pd(1)ϪN(1)
Pd(1)ϪS(1)
Pd(1)ϪCl(1)
Pd(2)ϪC(37)
2.03(2)
2.11(2)
2.300(6)
2.483(5)
1.99(2)
Pd(4)ϪC(62)
Pd(4)ϪN(3)
Pd(4)ϪS(2)
Pd(4)ϪCl(2)
Pd(3)ϪC(83)
1.98(2)
2.065(13)
2.307(5)
2.464(6)
1.93(2)
should lead to an approximately parallel arrangement of Pd(2)ϪN(2)
the two imines.
2.142(14) Pd(3)ϪN(4)
2.13(2)
Pd(2)ϪS(1)
2.261(6)
2.444(6)
1.73(2)
Pd(3)ϪS(2)
Pd(3)ϪCl(2)
S(2)ϪC(47)
2.266(5)
2.444(5)
1.90(2)
Pd(2)ϪCl(1)
Bridged dimers with orthopalladated ligands either have
trans structure, or are mixtures of cis/trans isomers (cis be-
ing the minor isomer). Thus, these complexes are interesting
for they afford isomerically pure cis-cyclopalladated deriva-
tives in high yields. The cis arrangement is particularly
interesting in view of possible application where a net di-
S(1)ϪC(1)
C(16)ϪPd(1)ϪN(1) 84.2(6)
C(16)ϪPd(1)ϪS(1) 90.3(5)
C(16)ϪPd(1)ϪCl(1) 172.9(5)
N(1)ϪPd(1)ϪS(1)
N(1)ϪPd(1)ϪCl(1)
S(1)ϪPd(1)ϪCl(1)
C(62)ϪPd(4)ϪN(3) 83.1(6)
C(62)ϪPd(4)ϪS(2) 92.4(5)
C(62)ϪPd(4)ϪCl(2) 174.8(5)
N(3)ϪPd(4)ϪS(2)
N(3)ϪPd(4)ϪCl(2)
S(2)ϪPd(4)ϪCl(2)
C(83)ϪPd(3)ϪN(4) 77.8(7)
C(83)ϪPd(3)ϪS(2) 96.2(5)
C(83)ϪPd(3)ϪCl(2) 177.3(6)
N(4)ϪPd(3)ϪS(2)
N(4)ϪPd(3)ϪCl(2)
S(2)ϪPd(3)ϪCl(2)
Pd(3)ϪS(2)ϪPd(4)
174.1(4)
102.4(4)
83.0(2)
175.4(4)
100.6(4)
83.8(2)
polar moment on the material is required. The proposed C(37)ϪPd(2)ϪN(2) 79.3(8)
C(37)ϪPd(2)ϪS(1)
C(37)ϪPd(2)ϪCl(1) 173.2(6)
N(2)ϪPd(2)ϪS(1)
N(2)ϪPd(2)ϪCl(1)
S(1)ϪPd(2)ϪCl(1)
Pd(1)ϪS(1)ϪPd(2)
95.2(6)
structure was confirmed by the X-ray crystal analysis of the
complex with n ϭ m ϭ 4. This is one of the few X-ray
crystal structures of a cyclopalladated mesogen[11], prob-
ably due to the difficulty to obtain crystals suitable for X-
ray analysis when long aliphatic chains are present. This
complex displays an SA mesophase between 175 and 235°C
on heating.
174.2(5)
100.6(4)
84.7(2)
98.1(2)
173.8(5)
100.8(5)
85.1(2)
97.5(2)
lengths in the two molecules are slightly different: 2.03(2)
˚
˚
The crystal structure consists of four molecules per unit and 1.99(2) A in M1 and 1.93(2) and 1.98(2) A in M2. They
cell, grouped in pairs. There are two different molecules in are in good agreement with those described for [Pd2(µ-
each pair (labelled as M1 and M2) in a disposition perpen- Cl)2(imine)2] 1.97 A[11]. The distances PdϪCl and PdϪS are
˚
dicular to one another, and parallel to the molecules of the also quite similar to those found in complexes of the type
other pair. A perspective ORTEP view of these independent [Pd2(µ-Cl)(µ-SR)Cl2(PRЈ3)2] (R ϭ alkyl or aryl; RЈ ϭ Me,
molecules is given in Figure 3. Selected bond lengths and Et, Ph)[12]. The small bite of the bidentate imine ligands
angles are listed in Table 2.
produces the deviation of the angles around the palladium
atoms from the ideal square disposition, 84.2(6) and
79.3(8)° in M1, and 77.8(7) and 83.1(6)° in M2. The angle
between the two palladium-imine moieties is small, 16.5(2)°
in M1 and 9.1(2)° in M2. The non-bonding PdϪPd dis-
Figure 3. ORTEP view of the two independent molecules, M1 and
M2, of complex 3 (n ϭ m ϭ 4) showing the atom-labelling scheme
˚
tances within each molecule are 3.443 A in M1 and 3.437
˚
A in M2. Due to the tetrahedral coordination of the sulfur
atom the first methylene of the thiolate group lies out of
the mean PdϪSϪPd plane. The CH2ϪS bond makes an
angle with this PdϪSϪPd plane of 106° in M1 and 105.2°
in M2. However, in both molecules the thiolato chains align
themselves in the direction of the long molecular axis.
Figure 4a shows the crystal packing viewed perpendicu-
lar to the long molecular axis. A layer structure can be
easily recognized where the molecular long axis is tilted re-
spect to the layer plane, reminiscent of the SC packing. The
molecular arrangement within the layers is better seen in
Figure 4b, which shows a view approximately along the mo-
lecular axis. It consists in arrays of pairs of molecules in
alternate (zig-zag) directions. The minimun PdϪPd distance
between the antiparallel molecules making a pair is
˚
Pd(2)ϪPd(4) ϭ 4.024 A. Some other non-bonding distances
between the palladium atom and the carbon atoms of the
other antiparallel molecule are quite short [e.g.
˚
The coordination at each palladium atom is approxi- Pd(2)ϪC(62) ϭ 3.34 A]. One of the rings linked to the ni-
mately square planar, with maximum deviations from the trogen atom lies close to the empty space between the cyclo-
˚
mean plane of 0.019 (Pd1) and 0.053 (Pd2) A on M1 and palladated moieties (Figure 4c), thus filling this space. The
˚
0.017 (Pd3) and 0.028 (Pd4) A on M2. The PdϪC bond angles between the free-to-rotate phenyl ring linked to the
Eur. J. Inorg. Chem. 1998, 1235Ϫ1241
1237

´
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J. Buey, G. A. Dıez, P. Espinet, S. Garcia-Granda, E. Perez-Carren˜o
FULL PAPER
nitrogen atom and the cyclometallated ring are quite differ- expected for a planar complex, due to a fast inversion at
ent 38.7(4)° and 47.2(5)° in M1 and 21.5(4)° and 57.6(5)° the sulfur atom[17]. Furthermore, the different size of the
in M2, indicating poor conjugation along the imine ligands. two bridges leads to a non-parallel arrangement of the long
axes of the imine ligands.
Figure 4. Crystal packing viewed (a) perpendicular to, and (b) ap-
proximately along the major molecular axis, (c) Chem3D view of
the closest perpendicular molecules; hydrogen atoms are omitted
Mesogenic Behavior
for clarity
All the complexes display liquid-crystal behavior. Their
mesophases, nematic (N) and smectic A (SA), and/or smec-
tic C (SC) have been identified by their characteristic tex-
tures, noticeably more viscous than in organic mesogens[18]
.
The transition temperatures, as well as the corresponding
enthalpies were determined by differential scanning calo-
rimetry and are given in Tables 3 and 4 (in a few cases the
transitions could not be detected by DSC and microscope
data are given). Figure 5 shows this mesogenic behavior
compared to that of the parent dinuclear complexes 2 (for
complexes 3) or 1 (for complexes 4).
Table 3. Optical, thermal, and thermodynamic data for the com-
plexes 3[a]
n/m
transition
C-SC
T [°C]
∆H [kJ molϪ1
]
6/6
129.0
164.0
210.1[c]
126.6
136.0
189.4[c]
102.9
132.0
196.5[c]
103.5
108.0
192.7[c]
115.7
129.0
193.1[c]
101.9
126.2
192.4[c]
66.5
8.0
Ϫ
7.3
26.8
Ϫ
3.2
24.3
Ϫ
1.5
32.0
Ϫ
6.1
17.7
Ϫ
1.9
8.9
Ϫ
4.9
Ϫ12.7
2.9
[b]
SC-SA
SA-I
6/8
C-SC
[b]
SC-SA
SA-I
6/10
6/18
8/6
C-SC
[b]
SC-SA
SA-I
C-SC
[b]
SC-SA
SA-I
C-SC
[b]
SC-SA
SA-I
8/8
C-SC
[b]
SC-SA
SA-I
8/10
C-CЈ
CЈ-SC[b]
SC-SA
SA-I
94.5
129.0
192.4[c]
111.8
187.2[c]
115.8
196.2[c]
118.4
179.8[c]
108.2
112.0
184.2[c]
114.7
117.0
181.8[c]
Characterization of Complexes 4
4.2
35.5
6.2
8/18
10/6
10/8
C-SA
SA-I
As for 3, there is only one set of signals in the aromatic
1
region of the H-NMR spectra of complexes 4, indicating
C-SA
SA-I
18.7
7.0
the presence of only one isomer. It is assigned the structure
cis-II (Figure 2) for the same reasons discussed for com-
C-SA
SA-I
19.9
8.8
plexes 3, and for the previously reported mixed-bridged 10/10
C-SC
20.5
[b]
thiolate-chiral carboxylate derivatives[13]. Both the signal of
SC-SA
Ϫ
-I
SA
8.6
39.8
the first methylene group of the thiolate (δ ϭ 2.47) and the
methyl group of the acetato bridge (δ ϭ 1.60) appear up-
field with respect to their parent complexes 3 and 1, respec-
tively. The proposed disposition of the ligands is in agree-
ment with the X-ray structures of similar orthopalladated
complexes [Pd2(µ-OAc)(µ-SR)(imine)2][14] or [Pd2(µ-
CF3CO2)(µ-tBuS)(C-N)2][15], (C-N ϭ cyclopalladated 8-
10/18
C-SC
SC-SA
[b]
SA-I
[a] C, CЈ ϭ crystal; N ϭ nematic; SA ϭ smectic A; SC ϭ smectic C.
[b]
[c]
Ϫ
Optical microscopy data. Ϫ Decomposition.
Complexes 3 show lower melting and clearing tempera-
methylquinoline). According to these structures complexes tures than the chloro complexes 2. In all cases there is some
4 are not planar in the solid state, showing a folded struc- decomposition at the clearing point. In complexes 4 the im-
ture with an average angle of 98° between the two moieties provement of the mesogenic properties is clear, since the
of the molecule in the acetate-thiolate complex above men- acetato complexes 1 are not mesogenic. Furthermore, com-
tioned. In solution the NMR spectra observed are those pared to 1 these complexes display nematic phases for short
1238
Eur. J. Inorg. Chem. 1998, 1235Ϫ1241

Mesogenic Dinuclear Cyclopalladated Derivatives with Mixed Bridges
FULL PAPER
Table 4. Optical, thermal, and thermodynamic data for the com- pears clearly. Planar complexes 3 display quite high tran-
plexes 4[a]
sition temperatures as a consequence of the strong intermo-
lecular interactions as well as a good packing of molecules
n/m
transition
T [°C]
∆H [kJ molϪ1
]
leading to ordered smectic mesophases (SA, SC). Changing
to the folded structure in complexes 4, a less efficient pack-
ing of molecules leads to lower molecular interactions, less
ordered mesophases (appearance of nematic phases), and
lower transition temperatures. The stronger molecular inter-
actions in complexes 3 can be also verified looking at the
enthalpy figures of the same transition in both families: The
crystal to smectic A mesophase gives a value of 21.4 and
18.7 kJ molϪ1 for the complexes 3 and 4 (n ϭ 10, m ϭ
6), respectively.
6/6
C-SA
SA-N
N-I
C-SA
SA-N
N-I
C-SA
SA-I
C-SA
SA-N
N-I
C-SA
SA-I
C-SA
SA-I
C-SA
SA-I
C-SA
SA-I
C-SA
SA-I
C-SA
SA-I
C-SA
SA-I
C-SA
SA-I
154.4
168.9
173.2
130.8
158.0
161.8
120.0
161.3
96.7
144.6
146.4
126.4
172.1
124.0
156.9
112.7
146.9
81.0
13.7
2.5[b]
6/8
16.5
2.8[b]
6/10
6/18
19.5
3.2
13.8
2.8[b]
8/6
11.4
3.8
8/8
28.5
3.3
Conclusions
8/10
8/18
10/6
10/8
10/10
10/18
23.5
3.0
i) Isomerically pure dinuclear complexes with mixed
bridges leading to a cis structure can be easily prepared. ii)
These complexes improve the mesogenic properties of the
starting materials, either by decreasing the transition tem-
peratures or by generating new mesophases . iii) The meso-
genic properties of this kind of compounds can be doubly
tuned, either by varying the nature of the thiolato bridge, or
by replacing the second bridge with other bridging groups.
6.4
145.6
106.9
163.4
114.1
149.2
116.3
141.7
67.0
3.6
21.4
4.2
28.2
3.6
33.7
3.5
19.1
3.7
136.9
´
´
We thank the Comision Interministerial de Ciencia y Tecnologıa
[a]
C ϭ crystal; N ϭ nematic; SA ϭ smectic A. Ϫ [b] Combined en-
´
˜
(project MAT96-0708), the Direccion General de Ensenanza Su-
perior (project PB96-0556), and the Junta de Castilla y Leon (pro-
thalpies.
´
ject VA41/96) for financial support.
chains in the imines and the thiolate. This phase is not usual
in dinuclear cyclopalladated imine mesogens. It is also re-
markable that complexes 4 are able to display lyotropic be-
havior on mixing with linear alkanes or chiral solvents. The
derivatives with n ϭ m ϭ 6 display broad ranges of nematic
(or chiral nematic) lyomesophases, which are maintained
Experimental Section
General Procedures and Measurements:. 1H-NMR spectra:
Bruker AC-80 or AC-300 MHz spectrometers using CDCl3. Ϫ El-
emental analyses: Perkin-Elmer 2400 microanalyzer. Ϫ IR spectra:
Perkin-Elmer 843 spectrophotometer using KBr pellets, unless
otherwise noted. Ϫ The textures of the mesophases were studied
with a Leitz Laborlux-D polarizing microscope, equipped with a
Leitz 350 hot stage. Ϫ Transition temperatures and enthalpies were
measured by differential scanning calorimetry, with a Perkin-Elmer
DSC-7 operated at a scanning rate of 5°C minϪ1 on heating, using
aluminium crucibles and N2 as inert gas. The apparatus was cali-
brated with indium (156.6°C, 28.5 J gϪ1) as standard.
until room temperature[16]
.
Figure 5. Thermotropic behavior of complexes 3 and 4; n and m
represent the number of carbon atoms in the imine and thiolate,
respectively; the left bar on each group corresponds to the chloro-
brigded derivative in complexes 3, and to the acetato-brigded deri-
vative in complexes 4
Materials: CH2Cl2 was distilled from CaH2. Literature pro-
cedures were used to synthesize the silver thiolates (AgSRm)[19]
,
[Pd(µ-OAc)Ln]2 (1) and [Pd(µ-Cl)Ln]2 (2)[3]. AgOAc and aliphatic
thiols (HSRm) were obtained from commercial sources and were
used without further purification.
Preparation of [Pd2(µ-Cl)(µ-SRm)Ln2] (3): A solution of 2 (0.2
mmol) in 25 ml of CH2Cl2 was treated with a slight excess of the
correspondig silver thiolate (Pd/AgSRm ϭ 1:1.1), and the mixture
was stirred in the dark for 5 h. The AgCl formed, as well as the
excess thiolate, were filtered off and ethanol was added to the solu-
tion. Evaporation of the CH2Cl2 gave complexes 3 as yellow crys-
talline solids, which were filtered, washed with ethanol and air-
dried. Yields were in the range 75Ϫ92%. Ϫ IR (KBr): ν˜ ϭ 1603 s
(CϭN), 1247 s 1028 m (CϪOϪC), 1574 s 829 m (Ar) cmϪ1. Ϫ
Analysis (%) for each n/m compound: 6/6: calcd. C, 59.70; H, 7.24;
N, 2.49; found C, 59.64; H, 7.10; N, 2.53. 6/8: calcd. C, 60.33; H,
Comparing the properties of compounds 3 and 4, the in-
fluence of the structure on the liquid crystal behavior ap- 7.42; N, 2.43; found: C 60.07, H 7.28, N 2.64. 6/10: calcd. C 60.93,
Eur. J. Inorg. Chem. 1998, 1235Ϫ1241 1239

´
´
J. Buey, G. A. Dıez, P. Espinet, S. Garcia-Granda, E. Perez-Carren˜o
FULL PAPER
H 7.58, N 2.37; found C 61.34, H 7.50, N 2.38. 6/18: calcd. C 63.07,
H 8.17, N 2.16; found C 63.13, H 8.11, N 2.09. 8/6: calcd. C 62.05,
H 7.89, N 2.26; found C 62.44, H 7.71, N 2.30. 8/8: calcd. C 62.57,
H 8.03, N 2.21; found C 62.35, H 7.55, N 2.41. 8/10: calcd. C 63.07,
H 8.17, N 2.16; found C 62.86, H 8.11, N 2.12. 8/18: calcd. C 64.87,
H 8.66, N 1.99; found C 64.66, H 8.37, N 1.92. 10/6: calcd. C 64.01,
H 8.43, N 2.07; found: C 64.11, H 8.19, N 2.09. 10/8: calcd. C
64.41, H 8.55, N 2.03; found C 64.58, H 8.35, N 1.92. 10/10: calcd.
C 64.87, H 8.66, N 1.99; found C 64.89, H 8.53, N 1.79. 10/18:
calcd. C 66.40, H 9.08, N 1.84; found C 65.97, H 8.79, N 1.94.
Table 5. Crystal data and structure refinement for complex 3
(n ϭ m ϭ 4)
crystal data
formula
C46H61ClN2O4Pd2S
986.28
mol weight
crystal system
space group
monoclinic
P21
˚
a [A]
10.275(5)
23.713(7)
18.780(13)
93.52(5)
4566(4)
˚
b [A]
˚
c [A]
Preparation of [Pd2(µ-OAc)(µ-SRm)Ln2] (4). Ϫ Method A:
AgOAc (0.1 mmol) was added to a solution of 3 (0.1 mmol) in 25
ml of CH2Cl2 (Pd/AgOAc ϭ 2:1), and the mixture was stirred in
the dark for 1 h. After removal of the AgCl formed, ethanol was
added to the solution and the CH2Cl2 was removed in vacuo, yield-
ing complexes 4 as yellow crystalline solids, which were filtered,
washed with ethanol and air-dried. Ϫ Method B: To a red solution
of 1 (0.1mmol) in 25 ml of CH2Cl2 was added the corresponding
amount of thiol (0.1 mmol, Pd/HSRm ϭ 2:1). The solution became
orange-yellow, and was stirred for 2 h. After addition of ethanol,
the solution was worked up as in method A. Ϫ Yields were in the
range 65Ϫ86%. Ϫ IR (KBr): ν˜ ϭ 1605 s (CϭN), 1245 s 1028 m
(CϪOϪC), 1574 s 829 m (Ar) cmϪ1. Ϫ Analysis (%) for each n/m
compound: 6/6: calcd. C 60.57, H 7.36, N 2.43; found C 60.51, H
7.22, N 2.48. 6/8: calcd. C 61.16, H 7.52, N 2.37; found C 60.99,
H 7.22, N 2.06. 6/10: calcd. C 61.73, H 7.68, N 2.32; found C 61.66,
H 7.53, N 2.25. 6/18: calcd. C 63.76, H 8.25, N 2.12; found C 63.70,
H 8.00, N 2.05. 8/6: calcd. C 62.79, H 7.98, N 2.22; found C 62.73,
H 7.83, N 2.63. 8/8: calcd. C 63.29, H 8.12, N 2.17; found C 63.25,
H 7.91, N 2.25. 8/10: calcd. C 63.76, H 8.25, N 2.12; found C 63.07,
H 8.00, N 1.91. 8/18: calcd. C 65.48, H 8.73, N 1.95; found C 65.71,
H 8.54, N 1.81. 10/6: calcd. C 64.66, H 8.50, N 2.09; found C 64.61,
H 8.01, N 2.37. 10/8: calcd. C 65.08, H 8.62, N 2.00; found C 65.32,
H 8.50, N 1.85. 10/10: calcd. C 65.48, H 8.73, N 1.96; found C
65.53, H 8.55, N 1.61. 10/18: calcd. C 66.95, H 9.14, N 1.81; found
C 67.04, H 8.94, N 1.55.
β [°]
V [A]3
˚
Z
4
Dcalcd. [g cmϪ3
F(000)
]
1.435
2032
µ [Ϫ1
]
0.934
crystal size [mm]
0.36 ϫ 0.25 ϫ 0.20
data collection and refinement
T [K]
293
θmax [°]
25
˚
radiation, λ [A]
Mo-Kα ֊ft parenthesis-
graphite), 0.71073
scan type
data set
ω-2θ
h Ϫ12:12, k Ϫ28:0, l Ϫ22:0
total no. of data
obsd. data [I > 2σ(I)]
no. of refined parameters
weighting scheme
8915
8230
775
2
w ϭ 1/[σ2 (Fo ) ϩ
(0.0868·P)2]
0.042, 0.115
final R, wR2
min and max residual density [e AϪ3] Ϫ0.57, 0.71
˚
a common thermal parameter. The final conventional agreement
factors were R ϭ 0.042 and wR2 ϭ 0.115 for the 8230 “observed”
reflections and 775 variables. The function minimized was Σw(Fo
Ϫ Fc)2, w ϭ 1/[σ2(Fo2) ϩ 0.0868·P)2] with σ(Fo) from counting
2
statistics and P ϭ [max(Fo2,0) ϩ 2·Fc ]/3. The maximum shift/e.s.d.
Crystal-Structure Determination of 3 (n ϭ m ϭ 4)[20]: Details ratio in the last full-matrix least-squares cycle was 0.019. Atomic
of the crystal and refinement data for the structure are given in
Table 5.
scattering factors were taken from International Tables for X-ray
Crystallography[26]
Geometrical calculations were made with
PARST[27]. The figure showing the coordination and the atomic
.
Suitable yellow single crystals were grown by slow diffusion of a
CHCl3 solution of the complex into ethanol at room temperature. numbering scheme was drawn by EUCLID package[28]. All calcu-
All diffraction measurements were made with an Enraf-Nonius
lations were made with VAX computers at the Scientific Computer
CAD-4 single-crystal diffractometer. The unit-cell dimensions were Center of the University of Oviedo.
determined from the angular settings of 25 reflections in the range
15° < θ < 22°. The intensity data of 8915 reflections were measured,
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three standard reflections every 60 min. The final drift correction
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sis was performed[21][22]. 8230 reflections were “observed” with I >
2σ(I). Lorentz and polarization corrections were applied and the
data were reduced to Fo values. The structure was solved by Pat-
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least-squares refinement, using SHELXL93[24], an empirical ab-
sorption correction was applied using DIFABS[25]. The maximum
and minimum absorption correction factors were 0.48 and 0.41,
respectively. During the final stages of the refinement on F2, the
positional parameters and the anisotropic thermal parameters of
the non-H atoms were refined, except the carbon atoms of the n-
butoxy groups, which were refined isotropically as a rigid group
with a common thermal parameter for each group. Hydrogen
atoms were isotropically refined riding on their parent atoms with
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