Bis(benzonitrile)palladium(II) dihalides: Structures and cocrystallization of the cubic cluster Pd6Cl12 with (E)-stilbene and with bis(benzonitrile)palladium(II) dichloride

Article abstract of DOI:10.1021/ic0000597

Crystals of the planar, trans complexes, bis(benzonitrile)palladium(II) dichloride and bis(benzonitrile)palladium(II) dibromide, suitable for single-crystal X-ray diffraction studies are obtained by growth from solutions in benzonitrile and their structures determined. While bis(benzonitrile)palladium(II) dichloride readily loses benzonitrile to form the cubic cluster Pd₆Cl₁₂, which cocrystallizes with a variety of planar aromatic hydrocarbon molecules, the much less soluble complex bis(benzonitrile)palladium(II) dibromide does not act as a source of the so far unknown cluster Pd₆Br₁₂. Attempts to prepare the hypothetical bis(benzonitrile)palladium(II) diiodide by reaction of PdI₂ with benzonitrile were not successful. A solution of bis(benzonitrile)palladium(II) dichloride in p-xylene on standing produces crystals of Pd₆Cl₁₂·(PhCN)₂PdCl₂·p-xylene, which contain columns of alternating Pd₆Cl₁₂. and (PhCN)₂PdCl₂ molecules in face-to-face orientations along with similar columns in which Pd₆Cl₁₂ and p-xylene molecules are interleaved in face-to-face arrays. A solution of bis(benzonitrile)palladium(II) dichloride and (E)stilbene in benzene solution leads, not to coordination of palladium to the olefin, but to deposition of crystals of the ternary molecular compound, Pd₆Cl₁₂·0.5((E)-stilbene)·2(benzene). In this solid, two Pcl₆Cl₁₂ clusters make face-to-face contact with phenyl rings on opposite sides of the (E)-stilbene molecule, but the olefinic portion is far from the palladium cluster. Additionally, one of the two benzene rings abuts the Pd₆Cl₁₂ cluster in a face-to-face fashion.

Full text of DOI:10.1021/ic0000597

Inorg. Chem. 2000, 39, 4555-4559
4555
Bis(benzonitrile)palladium(II) Dihalides: Structures and Cocrystallization of the Cubic
Cluster Pd6Cl12 with (E)-Stilbene and with Bis(benzonitrile)palladium(II) Dichloride
Marilyn M. Olmstead,* Pin-pin Wei, Arwa S. Ginwalla, and Alan L. Balch*
Department of Chemistry, University of California, Davis, California 95616
ReceiVed January 18, 2000
Crystals of the planar, trans complexes, bis(benzonitrile)palladium(II) dichloride and bis(benzonitrile)palladium-
(II) dibromide, suitable for single-crystal X-ray diffraction studies are obtained by growth from solutions in
benzonitrile and their structures determined. While bis(benzonitrile)palladium(II) dichloride readily loses benzonitrile
to form the cubic cluster Pd6Cl12, which cocrystallizes with a variety of planar aromatic hydrocarbon molecules,
the much less soluble complex bis(benzonitrile)palladium(II) dibromide does not act as a source of the so far
unknown cluster Pd6Br12. Attempts to prepare the hypothetical bis(benzonitrile)palladium(II) diiodide by reaction
of PdI2 with benzonitrile were not successful. A solution of bis(benzonitrile)palladium(II) dichloride in p-xylene
on standing produces crystals of Pd6Cl12‚(PhCN)2PdCl2‚p-xylene, which contain columns of alternating Pd6Cl12
and (PhCN)2PdCl2 molecules in face-to-face orientations along with similar columns in which Pd6Cl12 and p-xylene
molecules are interleaved in face-to-face arrays. A solution of bis(benzonitrile)palladium(II) dichloride and (E)-
stilbene in benzene solution leads, not to coordination of palladium to the olefin, but to deposition of crystals of
the ternary molecular compound, Pd6Cl12‚0.5((E)-stilbene)‚2(benzene). In this solid, two Pd6Cl12 clusters make
face-to-face contact with phenyl rings on opposite sides of the (E)-stilbene molecule, but the olefinic portion is
far from the palladium cluster. Additionally, one of the two benzene rings abuts the Pd6Cl12 cluster in a face-
to-face fashion.
Introduction
of infinite linear chains in which each palladium atom is
coordinated by four chlorine atoms in a square, while each
Recently, this laboratory reported that a number of supramo-
lecular aggregates of the cubic cluster Pd6Cl12 with methylated
benzenes (i.e., durene and mesitylene), the fullerene C60, and
polynuclear aromatic hydrocarbons (i.e., naphthalene and 1,2:
5,6-dibenzanthracene) can be isolated in crystalline form.1,2
Compounds of this type, which include Pd6Cl12‚(durene), Pd6-
Cl12‚1.5(naphthalene), Pd6Cl12‚0.5C60‚1.5(benzene), and Pd6Cl12‚
0.5(1,2:5,6-dibenzanthracene)‚0.5(benzene), consist of individual
molecules of Pd6Cl12 and the flat aromatic molecules arranged
in close, face-to-face proximity. These molecules are formed
by simply mixing the appropriate hydrocarbon or fullerene (as
a solution in benzene if it is not a liquid) with the labile complex,
bis(benzonitrile)palladium(II) dichloride, and allowing the mix-
ture to stand over a prolonged period. Eventually, deep red,
air-stable crystals of the aggregates crystallize from solution.
The Pd6Cl12 cluster itself is soluble in aromatic solvents.
Spectroscopic studies on solutions of Pd6Cl12 in various me-
thylated benzenes (i.e., mesitylene, xylene, and toluene) are
consistent with charge-transfer interactions between the aromatic
donors and the palladium cluster.
chlorine atom bridges two palladium atoms.3 The â-form
consists of discrete molecules of Pd6Cl12.4-6 This cluster has
an octahedral array of palladium atoms that are surrounded by
four equivalent chlorine atoms.6 Each chlorine atom bridges an
edge of the cube that can be inscribed about the octahedron of
palladium atoms. The cluster-containing â-form of palladium-
(II) dichloride can be prepared in several ways. Treatment of
Pd3(acetate)6 with carbon monoxide in glacial acetic acid with
some perchloric acid yields polycrystalline Pd6Cl12.5 Larger,
single, crystals of Pd6Cl12 may be prepared by gradual precipita-
tion of Pd6Cl12 from a benzene/chloroform solution of bis-
(benzonitrile)palladium(II) dichloride or by the slow decarbo-
nylation of Pd2(µ-Cl)2Cl2(CO)2 in thionyl chloride.6 Commercial
PdCl2 is not soluble in aromatic solvents and has been reported
to consist of another polymorph of currently unknown structure.7
The solid-state structure of palladium(II) dibromide has been
shown to consist of infinite linear chains, ‚‚‚PdBr2PdBr2‚‚‚, that
are similar to the chains seen in R-PdCl2.8 Several polymorphs
of PdI2 are known; the â-phase has a complex structure
consisting of planar Pd2I6 units.9 However, solid phases contain-
ing the discrete clusters Pd6Br12 and Pd6I12 are, to our
Here we report studies designed to form the unknown clusters
Pd6Br12 and Pd6I12 from the corresponding bis(benzonitrile)-
palladium(II) dihalides. Additionally, two new compounds that
contain the Pd6Cl12 cluster cocrystallized with its precursor, bis-
(benzonitrile)palladium(II) dichloride, and with a potential
ligand, (E)-stilbene, are described.
(3) Wells, A. F. Z. Kristallogr., Mineralog. Petrogr., Abt. A 1938, No.
1940, 189.
(4) Scha¨fer, H.; Wiese, U.; Rincke, K.; Brendel, K. Angew. Chem., Int.
Ed. Engl. 1967, 6, 253.
(5) Yatsimirski, A.; Ugo, R. Inorg. Chem. 1983, 22, 1395.
(6) Belli Dell’Amico, D.; Calderazzo, F.; Marchetti, F.; Ramello, S.
Angew. Chem., Int. Ed. Engl. 1996, 35, 1331.
(7) Soulen, J. R.; Chappel, W. H., Jr. J. Phys. Chem. 1965, 69, 3669.
(8) Brodersen, K.; Thiele, G.; Gaedcke, H. Z. Anorg. Allg. Chem. 1966,
348, 162.
In the context of this work, it should be noted that palladium-
(II) dichloride forms several polymorphs. The R-form consists
(1) Olmstead, M. M.; Ginwalla, A. S.; Noll, B. C.; Tinti, D. S.; Balch, A.
L. J. Am. Chem. Soc. 1996, 118, 7737.
(2) Olmstead, M. M.; Wei, P.; Balch, A. L. Chem.sEur. J. 1999, 5, 3136.
(9) Thiele, G.; Brodersen, K.; Kruse, E.; Holle, B. Chem. Ber. 1968, 101,
2771.
10.1021/ic0000597 CCC: $19.00 © 2000 American Chemical Society
Published on Web 08/31/2000

4556 Inorganic Chemistry, Vol. 39, No. 20, 2000
Olmstead et al.
Table 1. Selected Interatomic Distances and Angles for (PhCN)2PdX2 Complexes
(PhCN)2PdBr2
(PhCN)2PdCl2
1.974(2)
molecule 1
Bond Lengths (Å)
1.99(2)
1.94(2)
2.427(2)
1.16(3)
1.12(3)
molecule 2
Pd6Cl12‚(PhCN)2PdCl2‚p-xylene
Pd-N
1.955(14)
1.976(6)
Pd-X
N-C
2.2857(8)
1.141(3)
2.407(2)
1.13(2)
2.296(2)
1.137(8)
Bond Angles (deg)
N-Pd-N
X-Pd-X
N-Pd-X
180
180
90.52(7)
89.48(7)
177.9(2)
180
180
180
90.3(4)
89.7(4)
175.6(15)
180
180
90.4(2)
89.6(2)
172.9(6)
179.5(1)
89.8(1)
90.2(1)
180
C-N-Pd
180
Table 2. Crystallographic Data
(PhCN)2PdCl2
(PhCN)2PdBr2
Pd6Cl12‚(PhCN)2PdCl2‚p-xylene
Pd6Cl12‚0.5(stilbene)‚2(benzene)
empirical formula
fw
a, Å
b, Å
C14H10Cl2N2Pd
383.54
C14H10Br2N2Pd
472.5
8.272(3)
20.529(9)
18.102(7)
90
97.43(2)
90
3048(2)
8
C22H20Cl14N2Pd7
1553.50
16.550(5)
15.489(4)
15.850(4)
90
109.91(2)
90
3820(2)
4
C19H18Cl12Pd6
1310.13
11.383(2)
12.155(2)
12.803(2)
78.050(14)
67.70(2)
80.16(2)
1595.0(5)
2
5.715(2)
8.277(2)
8.576(2)
116.05(2)
95.09(2)
93.31(2)
360.9(2)
1
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
crystal system
space group
color
triclinic
P1h
pale red
0.710 73
1.765
1.641
0.93-0.69
0.026
monoclinic
C2/c
yellow orange
0.710 73
2.059
monoclinic
C2/c
dark red
0.710 73
2.701
4.221
0.87-0.64
0.042
triclinic
P1h
dark red
0.710 73
2.728
4.329
0.70-0.57
0.047
λ(Mo KR), Å
F, g/cm3
µ, mm-1
6.447
max-min transm
R1a (obsd data)
wR2b (all data, F2 refinement)
0.78-0.42
0.068
0.063
0.068c
0.105
0.129
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑w(Fo - Fo )2/∑w(Fo )2]1/2
.
c Rw ) ∑||Fo| - |Fc||w1/2/∑|Fo|w1/2
.
2
2
2
knowledge, unknown, whereas the series of clusters Pd6Cl12-nBrn
where n ) 1-12 has been detected in the gas phase from
vaporization of mixtures of PdCl2 and AgBr.10 The analogous
cubic platinum clusters, Pt6Cl12 and Pt6Br12, have been iso-
lated,11,12 but their ability to cocrystallize with organic molecules
has not been explored.
tion of bis(benzonitrile)palladium(II) dibromide at its boiling
point for 14 h produced only R-PdBr2 with an X-ray powder
pattern identical to that obtained previously.8 Additionally,
attempts to prepare the unknown complex bis(benzonitrile)-
palladium(II) diiodide by treatment of solid palladium(II) iodide
with hot benzonitrile did not produce the expected product;
indeed, the palladium(II) iodide does not dissolve in neat, hot
benzonitrile. We presume that the Pd-I bonds in solid palla-
dium(II) iodide are simply too strong to undergo displacement
by benzonitrile, which is generally a weakly bound ligand.
Results
Bis(benzonitrile)palladium(II) dichloride is a labile complex
which readily loses benzonitrile to form complexes with
coordinated PdCl2 groups or Pd6Cl12 in the absence of strongly
ligating molecules.13,14 To obtain crystals of bis(benzonitrile)-
palladium(II) dichloride itself, it was necessary to use benzoni-
trile as the solvent to prevent loss of this ligand from the
complex. Crystals of bis(benzonitrile)palladium(II) dibromide
were grown similarly from benzonitrile solution. However, bis-
(benzonitrile)palladium(II) dibromide is much less soluble than
bis(benzonitrile)palladium(II) dichloride, and despite numerous
attempts, we have been unable to find conditions under which
the hypothetical cluster Pd6Br12 can be formed from bis-
(benzonitrile)palladium(II) dibromide. Heating a benzene solu-
Upon standing, the dark red solution formed by dissolving
bis(benzonitrile)palladium(II) dichloride in p-xylene gradually
produced crystals of the ternary compound Pd6Cl12‚(PhCN)2-
PdCl2‚p-xylene that were suitable for X-ray diffraction. Simi-
larly, dissolution of bis(benzonitrile)palladium(II) dichloride in
benzene in the presence of (E)-stilbene produced deep red
crystals of Pd6Cl12‚0.5((E)-stilbene)‚2(benzene). The structures
of each of these compounds were determined by single-crystal
X-ray diffraction. Relevant data for these crystal structures and
their determinations are summarized in Tables 1 and 2.
Structures of Bis(benzonitrile)palladium(II) Dichloride
and Bis(benzonitrile)palladium(II) Dibromide. Figure 1
shows perspective drawings of trans-(PhCN)2PdCl2 and trans-
(PhCN)2PdBr2. Selected bond distances and angles are given
in Table 1. Figures 2 and 3 compare the solid-state packings
within the two compounds.
(10) Scha¨fer, H. Z. Anorg. Allg. Chem. 1975, 415, 217.
(11) Scha¨fer, H.; Weise, U.; Rinke, K.; Brendel, K. Angew. Chem. 1967,
79, 244.
(12) Brodersen, K.; Thiele, G.; von Schnering, H. G. Z. Anorg. Allg. Chem.
1965, 337, 210.
(13) Kharasch, M. S.; Ashford, T. A. J. Am. Chem. Soc. 1936, 58, 1733.
(14) Balch, A. L.; Petridis, D. Inorg. Chem. 1969, 8, 2247.
Bis(benzonitrile)palladium(II) dichloride crystallizes with half

Bis(benzonitrile)palladium(II) Dihalides
Inorganic Chemistry, Vol. 39, No. 20, 2000 4557
Figure 3. Stereoview of the solid-state packing in trans-(PhCN)2PdBr2.
Figure 4. Molecular components present in Pd6Cl12‚trans-(PhCN)2PdCl2‚
p-xylene.
generated by inversion through the crystallographic center of
symmetry. The coordination environments of both molecules
of (PhCN)2PdBr2 are similar to each other and to that of
(PhCN)2PdCl2. The two molecules of (PhCN)2PdBr2 differ
owing to rotations of the planes of the phenyl rings about the
NC-Ph axes.
Figure 1. Molecular structures of (A) trans-(PhCN)2PdCl2 and (B)
the two independent molecules of trans-(PhCN)2PdBr2.
As seen in Figures 2 and 3, the molecular packings of
(PhCN)2PdCl2 and (PhCN)2PdBr2 in the solid state differ. In
the structure of (PhCN)2PdCl2, the phenyl rings are in parallel
planes but do not make face-to-face contact. However, there
are close contacts (2.68 Å for H(7) and 2.82 Å for H(5)) between
aromatic hydrogen atoms of one molecule and the chloride
ligands on adjacent molecules. The molecular packing in
(PhCN)2PdBr2 shows regions of face-to-face contacts between
the phenyl rings of adjacent molecules as seen in Figure 3. The
separation of the parallel phenyl rings is 3.37 Å, which is
consistent with typical π-π contact between aromatic rings.15
There are also a close contact of an aromatic hydrogen atom
with the bromide ligand of an adjacent molecule (distance to
H(17) 2.94 Å) and a short Br(2)-Br(2′) separation of 3.532 Å.
Pd6Cl12‚(PhCN)2PdCl2‚p-xylene. Figure 4 shows a drawing
of the three different molecules that are present. There are
crystallographic centers of symmetry located within each of
these three molecules. No unusual geometric distortions are
observed in any of the molecular structures in this solid. For
example, as seen in Table 1, the (PhCN)2PdCl2 molecule in Pd6-
Cl12‚(PhCN)2PdCl2‚p-xylene has geometric parameters that are
very close to those found in crystalline (PhCN)2PdCl2 itself.
The molecular packing of these components within crystalline
Pd6Cl12‚(PhCN)2PdCl2‚p-xylene is shown in Figure 5. As seen
Figure 2. Stereoview of the solid-state packing in trans-(PhCN)2PdCl2.
of the molecule in the asymmetric unit and with the other half
generated by inversion through a center of symmetry. The bond
distances and angles in the complex fall within normal ranges.
Bis(benzonitrile)palladium(II) dibromide crystallizes with two
half-molecules in the asymmetric unit. For the molecule
containing Pd(1), the other half of the molecule is generated
by reflection through a mirror plane which passes through the
palladium atoms and the coordinated nitrile moiety. For the
molecule containing Pd(2), the remainder of the molecule is
(15) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornell
University Press: Ithaca, NY, 1960; p 260.

4558 Inorganic Chemistry, Vol. 39, No. 20, 2000
Olmstead et al.
Figure 7. Stereoview of the solid-state molecular packing in Pd6Cl12‚
0.5((E)-stilbene)‚2(benzene).
from Pd(3) to the nearest carbon atoms are as follows: to C(12),
3.38 Å; to C(7), 3.50 Å; and to C(13), 3.46 Å. Notice that the
olefinic portion is not coordinated to palladium but that the
phenyl rings of the (E)-stilbene molecule make face-to-face
contacts with the Pd6Cl12 cluster. Additionally, Pd6Cl12 clusters
make face-to-face contacts with one another as is also seen in
pristine Pd6Cl12 itself and many of its cocrystals.
Figure 5. Stereoview of the solid-state molecular packing in Pd6Cl12‚
trans-(PhCN)2PdCl2‚p-xylene.
The molecular structures and internal motions of (E)-stilbenes
in crystalline environments have been the subject of considerable
interest.16-18 In crystals of (E)-stilbene itself, there are two
independent half-molecules (R and â) in the asymmetric unit.
The R sites display orientational disorder, and the ethylene bond
lengths at both sites are shorter (by 0.05 and 0.02 Å) than
expected (1.337 Å) for a normal ethylene bond. In Pd6Cl12‚
0.5((E)-stilbene) ‚2(benzene), scattering is dominated by the
heavy Pd6Cl12 cluster. Consequently, the precision of the
geometric parameters for the (E)-stilbene molecule in this
cocrystal are lower than those obtained for simple crystalline
stilbenes. However, in Pd6Cl12‚0.5((E)-stilbene)‚2(benzene),
there is no sign of disorder of the (E)-stilbene molecule and
the olefinic link has a length (1.36(2) Å) that is somewhat long.
Figure 6. Molecular components present in Pd6Cl12‚0.5((E)-stilbene)‚
2(benzene).
in other compounds where Pd6Cl12 crystallizes with aromatic
molecules, the solid consists of columns of alternating Pd6Cl12
and p-xylene molecules which make parallel, face-to-face
contacts. Additionally, there are columns of alternating Pd6Cl12
and (PhCN)2PdCl2 molecules in which the PdCl2N2 units are
parallel to PdCl4 faces of the cluster. In both cases, the surfaces
are offset from one another. For the Pd6Cl12/p-xylene interaction,
the closest Pd‚‚‚C contacts involve C(9), which is 3.402 Å from
Pd(2), and C(8), which is 3.484 Å from Pd(2). For the Pd6Cl12/
(PhCN)2PdCl2 interaction, the Pd(3)-Pd(4) distance is 3.358
Å, while the Pd(3)-Cl(7′) distance is 3.434 Å and the Pd(4)-
Cl(4) distance is 3.544 Å. The phenyl rings of the (PhCN)2PdCl2
portion do not make face-to-face contact with the Pd6Cl12
clusters.
Pd6Cl12‚0.5((E)-stilbene)‚2(benzene). Figure 6 shows a view
of the four different molecules that are present in the solid and
gives some idea of their relative orientations. The (E)-stilbene
molecule resides on a crystallographic center of symmetry, while
the other three molecules do not have any crystallographically
imposed symmetry. Both the (E)-stilbene molecule and one of
the benzene molecules (benzene-1) make parallel, face-to-face
contacts with the Pd6Cl12 cluster. On the other hand, benzene-
2, which shows evidence of libration about its center, does not
make any such contact with the Pd6Cl12 cluster. Figure 7 shows
a stereoview of the overall organization of these units in the
solid state. There are columns of alternating benzene molecules
and Pd6Cl12 clusters that run roughly along the a axis. The Pd6-
Cl12 cluster is offset toward one corner of the benzene molecule.
The shortest contacts between atoms of these units are Pd(5)‚
‚‚C(2) at 3.27 Å and Pd(5)‚‚‚C(3) at 3.46 Å. Two Pd6Cl12
clusters interact with each (E)-stilbene molecule and are located
on opposite faces of the (E)-stilbene molecule. The distances
Discussion
The results reported here demonstrate the difficulties in
extending the synthesis of the cubic cluster Pd6Cl12 from the
complex bis(benzonitrile)palladium(II) dichloride to other ha-
lides. Although bis(benzonitrile)palladium(II) dibromide has
been prepared and structurally characterized, it has very limited
solubility and has not been found to yield Pd6Br12 in any form.
PdI2 is insoluble in benzonitrile and does not form bis-
(benzonitrile)palladium(II) diiodide. The hypothetical cluster
Pd6I12 also remains unknown.
Solutions of bis(benzonitrile)palladium(II) dichloride continue
to deposit new crystalline phases that contain the cluster Pd6-
Cl12. Thus, a solution of bis(benzonitrile)palladium(II) dichloride
in p-xylene results not only in cocrystallization of Pd6Cl12 with
molecules of the solvent but also in cocrystallization with the
precursor complex, bis(benzonitrile)palladium(II) dichloride, to
form the ternary material, Pd6Cl12‚(PhCN)2PdCl2‚p-xylene.
Additionally, Pd6Cl12 has been found to cocrystallize rather than
coordinate with (E)-stilbene to form another ternary material,
Pd6Cl12‚0.5((E)-stilbene)‚2(benzene).
The following set of rules have been suggested for the
analysis of structures that involve cocrystallization of Pd6Cl12
and molecules with conjugated π-systems:2 (1) The planar
π-conjugated molecules are sandwiched between Pd6Cl12 clus-
ters and make face-to-face contacts with these clusters on both
(16) Galli, S.; Mercandelli, P.; Sironi, A. J. Am. Chem. Soc. 1999, 121,
3767.
(17) Ogawa, K.; Sano, T.; Yoshimura, S.; Takeuchi, Y.; Toriumi, K. J.
Am. Chem. Soc. 1992, 114, 1041.
(18) Bernstein, J.; Mirsky, K. Acta Crystallogr. 1978, A34, 161.

Bis(benzonitrile)palladium(II) Dihalides
Inorganic Chemistry, Vol. 39, No. 20, 2000 4559
the tubes and collecting the solid by filtration, followed by rapid
washings with p-xylene and then ether. Yield: 25.7 mg (0.0165 mmol,
25.4%).
sides. (2) In cases where two different π-conjugated molecules
are present within the solid, the molecule with the lower
ionization potential preferentially makes face-to-face contact
with the Pd6Cl12 cluster. (3) Individual Pd6Cl12 clusters interact
with pairs of planar π-conjugated molecules in a face-to-face
arrangement on two opposite faces of the cluster. (4) Pd6Cl12
clusters interact with one another through nearly parallel, face-
to-face contacts, with the closest contacts generally between a
palladium atom of one cluster and a chlorine atom of another.
The structure of Pd6Cl12‚(PhCN)2PdCl2‚p-xylene conforms
to the above rules without exception, whereas the structure of
Pd6Cl12‚0.5((E)-stilbene)‚2(benzene) obeys these rules with one
exception. Although the benzene/Pd6Cl12 arrangement in Pd6-
Cl12‚0.5((E)-stilbene)‚2(benzene) conforms to rule 3 so that
columns of alternating molecules of benzene and Pd6Cl12 are
found, the (E)-stilbene/Pd6Cl12 interaction is different, as seen
in Figure 7. While there is a face-to-face arrangement of an
(E)-stilbene molecule on one side of the cluster, there is no (E)-
stilbene molecule aligned parallel to the opposite face of the
cluster. Rather there is a face-to-face cluster/cluster contact in
its place.
Pd6Cl12‚0.5((E)-stilbene)‚2(benzene). Samples of 314.4 mg (1.744
mmol) of (E)-stilbene and 96.4 mg (0.251 mmol) of bis(benzonitrile)-
palladium(II) dichloride were dissolved in 3 mL of benzene. The
resulting dark red solution was filtered, and the filtrate was placed in
5 mm od glass tubes, which were then set aside for 3 weeks. The
crystals were harvested by cracking the tubes and collecting the solid
by filtration, followed by a rapid washing with benzene. Yield: 43.4
mg (0.033 mmol, 79.2%).
X-ray Crystallography. The crystals together with small amounts
of the mother liquor were removed from the glass tube in which they
had been prepared and immediately coated with a hydrocarbon oil on
a microscope slide.20 Suitable crystals were mounted on glass fibers
with silicone grease and placed in the cold stream of a Siemens R3m/V
diffractometer equipped with an Enraf-Nonius low-temperature ap-
paratus. The diffractometer utilized a sealed Mo tube that operated at
2 kW and a graphite monochromator. All the data sets were collected
at 130(2) K. Only random fluctuations of less than 2% were observed
in the check reflections for all data sets. Scattering factors and
corrections for anomalous dispersion were taken from a standard
source.21 The structures were solved by Patterson or direct methods
using the software of SHELXTL 5 and were refined on the basis of
F2, except in the case of bis(benzonitrile)palladium(II) dibromide, where
SHELXTL PLUS, VMS version, was used and the structure was refined
with the program SHELXTL-93 (based on F). Absorption corrections
were applied to the structures with the program XABS2, which
calculates 24 coefficients from a least-squares fit of 1/A vs sin2(θ) to
a cubic equation in sin2(θ) by minimization of Fo2 and Fc2 differences.22
Hydrogen atoms were added geometrically and refined with a riding
model. All non-hydrogen atoms were refined with anisotropic thermal
parameters, except in the case of bis(benzonitrile)palladium(II) dibro-
mide, where only palladium and bromine atoms were treated aniso-
tropically.
Experimental Section
Preparations. Bis(benzonitrile)palladium(II) Dichloride. This
compound was prepared as described in the literature.19
For crystal growth, 100 mg (0.261 mmol) of bis(benzonitrile)-
palladium(II) dichloride was dissolved in 2 mL of benzonitrile. The
resulting dark orange solution was transferred to a 10 mL beaker and
heated for 60 min at 100 °C. Dark red crystals formed as the solution
partially evaporated and then cooled. The crystals were collected by
filtration and washed with diethyl ether. Yield: 21.5 mg (0.0561 mmol,
21.5%).
Bis(benzonitrile)palladium(II) Dibromide. Palladium(II) dibromide
(0.5386 g, 2.02 mmol) was added to 15 mL (147 mmol) of benzonitrile.
The mixture was heated to 140 °C for 1 h. The resulting dark red
solution was quickly filtered while hot to remove any unreacted
palladium(II) dibromide. A 70 mL portion of diethyl ether was added,
and the solution was chilled to 0 °C for 5 min. The powdery orange
solid that formed was collected by filtration on a glass frit and washed
with diethyl ether. Yield: 0.594 g (1.26 mmol, 62.4%).
Acknowledgment. We thank the National Science Founda-
tion (Grant CHE 9610507) for financial support, Johnson
Matthey, Inc., for a loan of palladium chloride, and D. Lane
for experimental assistance. P.W. was the recipient of a
Presidential Undergraduate Fellowship from the University of
California, Davis.
For crystal growth, 100 mg (0.211 mmol) of bis(benzonitrile)-
palladium(II) dibromide was dissolved in 2 mL of benzonitrile. The
resulting dark red solution was transferred to a 10 mL beaker and heated
for 60 min at 100 °C. Dark red crystals formed as the solution
evaporated and then cooled. The crystals were collected by filtration
and washed with diethyl ether. Yield: 15 mg (0.032 mmol, 15%).
Pd6Cl12‚(PhCN)2PdCl2‚p-xylene. A 150 mg (0.391 mmol) sample
of bis(benzonitrile)palladium(II) dichloride was dissolved in 10 mL
(81.6 mmol) of p-xylene. The resulting dark red solution was shaken
and filtered. The filtrate was placed in 5 mm od glass tubes, which
were then set aside for 1 week. The crystals were harvested by cracking
Supporting Information Available: Listings of X-ray experimental
details, atomic coordinates, thermal parameters, bond lengths, and bond
angles for bis(benzonitrile)palladium(II) dichloride, bis(benzonitrile)-
palladium(II) dibromide, Pd6Cl12‚(PhCN)2PdCl2‚p-xylene, and Pd6Cl12‚
0.5((E)-stilbene)‚2(benzene). This material is available free of charge
via the Internet at http://pubs.acs.org.
IC0000597
(20) Hope, H. ACS Symp. Ser. 1987, 357, 257.
(21) International Tables for X-ray Crystallography; D. Reidel Publishing
Co.: Boston, MA, 1992; Vol. C.
(22) Parkin, S. R.; Moezzi, B.; Hope, H. XABS2: An empirical absorption
correction program. J. Appl. Crystallogr. 1995, 28, 53.
(19) Anderson, G. K.; Minren, L. Inorg. Synth. 1990, 28, 61.