Supramolecular aggregation of Pd6Cl12, a cluster of comparable size to a fullerene, with aromatic donors and with C60

Article abstract of DOI:10.1021/ja960939d

Molecular solids comprised of octahedra, hexagonal plates, and truncated icosahedra result from the co-crystallization of Pd₆Cl₁₂, benzene and its methylated derivatives, and C₆₀. Solutions of bis(benzonitrile)palladium(II) dichloride in benzene deposit deep red crystals of solvate-free Pd₆Cl₁₂, 1, while solutions of bis(benzonitrile)palladium(II) dichloride in the following solvents or solutions produce binary or ternary compounds as follows: from mesitylene, Pd₆Cl₁₂·(CH₃)₃C₆H₃ (2); from mesitylene/benzene, Pd₆Cl₁₂·(CH₃)₃C₆H₃·0.5C₆H₆ (3); from durene/benzene, Pd₆Cl_{1 2}·(CH₃)₄C₆H₂ (4); from benzene/hexamethylbenzene, Pd₆Cl₁₂· l.5(CH₃)₆C₆ (5); from benzene/biphenyl, Pd₆Cl₁₂·(C₆H₅)₂ (6); and from benzene/fullerene C₆₀, Pd₆Cl₁₂·0.5C₆₀·1.5C₆H₆ (7). The geometric structures of each of these seven compounds have been determined by X-ray crystallography, and the electronic structure of Pd₆Cl₁₂ has been probed with SCF-Xα-SW calculations. In each crystalline compound the structure of the Pd₆Cl₁₂ unit is virtually invariant. It consists of an octahedral array of six palladium atoms that are surrounded by twelve equivalent chlorine atoms in edge-bridging sites. The long face-to-face Pd···Pd separations (4.675 A? in 1) indicate that there is no direct Pd-Pd bonding in the cluster. In 1 these octahedra interact with one another through pairwise Pd···Cl contacts. In 2, 3, 4, and 6, layer-like structures are found in which each Pd₆Cl₁₂ cluster makes face-to-face contact with an arene moiety on opposite PdCl₄ faces and each arene makes contact with two Pd₆Cl₁₂ clusters. In these four compounds, the clusters also make contact with each other through pairwise Pd···Cl contacts that are like those found in 1. The structure of Pd₆Cl₁₂·1.5(CH₃)₆C₆ (5) is unique in that three hexamethylbenzene molecules make face-to-face contact with orthogonal faces of the Pd₆Cl₁₂ cluster and the cluster-cluster separations are larger than those in 1-4 and 6. The structure of Pd₆Cl₁₂·0.5C₆₀·1.5C₆H₆ (7) consists of a complex array of molecular components with face-to-face contacts between the benzene molecules and both C₆₀ and Pd₆Cl₁₂. Pd₆Cl₁₂ itself dissolves in aromatic solvents. The electronic spectra of the resulting solutions show variations that are indicative of a degree of charge transfer between the Pd₆Cl₁₂ cluster as an electron acceptor and the arene as an electron donor.

Full text of DOI:10.1021/ja960939d

J. Am. Chem. Soc. 1996, 118, 7737-7745
7737
Supramolecular Aggregation of Pd6Cl12, a Cluster of
Comparable Size to a Fullerene, with Aromatic Donors and
with C60
Marilyn M. Olmstead,* Arwa S. Ginwalla, Bruce C. Noll, Dino S. Tinti, and
Alan L. Balch*
Contribution from the Department of Chemistry, UniVersity of California,
DaVis, California 95616
ReceiVed March 22, 1996X
Abstract: Molecular solids comprised of octahedra, hexagonal plates, and truncated icosahedra result from the co-
crystallization of Pd6Cl12, benzene and its methylated derivatives, and C60. Solutions of bis(benzonitrile)palladium(II)
dichloride in benzene deposit deep red crystals of solvate-free Pd6Cl12, 1, while solutions of bis(benzonitrile)-
palladium(II) dichloride in the following solvents or solutions produce binary or ternary compounds as follows:
from mesitylene, Pd6Cl12‚(CH3)3C6H3 (2); from mesitylene/benzene, Pd6Cl12‚(CH3)3C6H3‚0.5C6H6 (3); from durene/
benzene, Pd6Cl12‚(CH3)4C6H2 (4); from benzene/hexamethylbenzene, Pd6Cl12‚1.5(CH3)6C6 (5); from benzene/biphenyl,
Pd6Cl12‚(C6H5)2 (6); and from benzene/fullerene C60, Pd6Cl12‚0.5C60‚1.5C6H6 (7). The geometric structures of each
of these seven compounds have been determined by X-ray crystallography, and the electronic structure of Pd6Cl12
has been probed with SCF-XR-SW calculations. In each crystalline compound the structure of the Pd6Cl12 unit is
virtually invariant. It consists of an octahedral array of six palladium atoms that are surrounded by twelve equivalent
chlorine atoms in edge-bridging sites. The long face-to-face Pd‚‚‚Pd separations (4.675 Å in 1) indicate that there
is no direct Pd-Pd bonding in the cluster. In 1 these octahedra interact with one another through pairwise Pd‚‚‚Cl
contacts. In 2, 3, 4, and 6, layer-like structures are found in which each Pd6Cl12 cluster makes face-to-face contact
with an arene moiety on opposite PdCl4 faces and each arene makes contact with two Pd6Cl12 clusters. In these four
compounds, the clusters also make contact with each other through pairwise Pd‚‚‚Cl contacts that are like those
found in 1. The structure of Pd6Cl12‚1.5(CH3)6C6 (5) is unique in that three hexamethylbenzene molecules make
face-to-face contact with orthogonal faces of the Pd6Cl12 cluster and the cluster-cluster separations are larger than
those in 1-4 and 6. The structure of Pd6Cl12‚0.5C60‚1.5C6H6 (7) consists of a complex array of molecular components
with face-to-face contacts between the benzene molecules and both C60 and Pd6Cl12. Pd6Cl12 itself dissolves in
aromatic solvents. The electronic spectra of the resulting solutions show variations that are indicative of a degree
of charge transfer between the Pd6Cl12 cluster as an electron acceptor and the arene as an electron donor.
Introduction
molecules have been designed.5 Less attention has been given
to the formation of crystalline compounds that consist of
components drawn from both the inorganic and organic realms
without the formation of classical coordination bonding between
the components. However, in this area charge transfer interac-
tions are a likely source of energetic stabilization. A number
of examples of charge transfer complexes of aromatic hydro-
carbons with simple inorganic compounds such as osmium(VIII)
tetroxide,6 titanium(IV) tetrachloride,7 and tin(IV) tetrachloride8
have been characterized spectroscopically, but these complexes
have resisted attempts to crystallize them. This article is
concerned with crystal organization in a range of new solids
that consist of combinations of an inorganic halide cluster, Pd6-
Cl12, with an array of aromatic hydrocarbons.
Considerable recent attention has been given to aspects of
supramolecular chemistry1 that lead to the formation of orga-
nized arrays of numbers of different molecules within a single
crystal. Identification of the specific factors that can orient one
molecule with respect to another may eventually lead to the
preparation of crystals by designsi.e. crystal engineering.2
However, for the present it is necessary to uncover the range
of specific intermolecular interactions that can be expected to
contribute to crystal organization. For crystals comprised of
wholly organic molecules, considerable progress has been made
toward identifying specific interactions that now range from an
array of different types of hydrogen bonds3 through the iodo-
nitro interaction and halogen‚‚‚halogen interactions. Examples
of the use of many of these interactions to obtain new organic
phases in which two or more molecular components are
combined are now known. In inorganic chemistry labile
coordination to metal ions has facilitated the preparation of an
array of complex networked and layered systems.4 Inorganic
solids with network structures that are able to encapsulate small
Several polymorphic forms of PdCl2 are known. The R-form
consists of infinite, linear chains of PdCl2 units in which each
palladium atom is coordinated by four chlorine atoms and each
chlorine atom is doubly bridging.9 The â-form,10 which is
isomorphic with the crystallographically characterized â-PtCl2,11
(4) Hoskins, B. F.; Robson, R.; Scarlett, N. V. Y. J. Chem. Soc., Chem.
Commun. 1994, 2025. Abrahams, B. F.; Hoskins, B. F.; Liu, J. P.; Robson,
R. J. Am. Chem. Soc. 1991, 113, 3045.
(5) Mu¨ller, A.; Reuter, H.; Dillinger, S. Angew. Chem., Int. Ed. Engl.
1995, 34, 2328.
X Abstract published in AdVance ACS Abstracts, August 1, 1996.
(1) Votgle, F. Supramolecular Chemistry: an Introduction; Wiley: New
York, 1991.
(2) Desiraju, G. R. Angew. Chem., Int. Ed. Engl. 1995, 34, 2311.
(3) Rebek, J. Angew. Chem., Int. Ed. Engl. 1990, 29, 245. Whitesides,
G. M.; Simanek, E. E.; Mathias, J. P.; Seto, C. T.; Chin, D. N.; Mammen,
M.; Gordon, D. M. Acc. Chem. Res. 1995, 28, 37.
(6) Wallis, J. M.; Kochi, J. K. J. Am. Chem. Soc. 1988, 110, 8207.
(7) Bru¨ggerman, K.; Czernuszewicz, R. S.; Kochi, J. K. J. Phys. Chem.
1992, 96, 4405.
(8) Bru¨ggerman, K.; Kochi, J. K. J. Org. Chem. 1992, 57, 2956.
S0002-7863(96)00939-0 CCC: $12.00 © 1996 American Chemical Society

7738 J. Am. Chem. Soc., Vol. 118, No. 33, 1996
Olmstead et al.
Table 1. Comparative Distances (Å) for Compounds 1-7
Pd6Cl12‚
Pd6Cl12‚(CH3)3C6H3‚
Pd6Cl12‚
(CH3)4C6H2
(4)
Pd6Cl12‚
1.5(CH3)6C6
(5)
Pd6Cl12‚
C12H10
(6)
Pd6Cl12‚0.5C60‚
1.5C6H6
(7)
Pd6Cl12
(CH3)3C6H3
0.5C6H6
(1)
(2)
(3)
Pd-Cl (ave)a
2.307(3)
3.306(23)
4.675(2)
3.714(2)
2.308(4)
3.310(12)
4.682(26)
3.598(2)
3.836(2)
3.290(2)
3.243(3)
3.249(3)
2.308(5)
3.313(7)
4.685(21)
3.701(2)
2.310(5)
3.315(17)
4.688(27)
3.519(2)
2.307(2)
3.313(8)
4.685(2)
5.534(2)
2.305(3)
2.309(6)
4.679(13)
3.308(2)
3.520(2)
3.488(2)
3.245(2)
2.312(6)
3.311(18)
4.683(13)
3.404(5)
Pd‚‚‚Pd (bridged)a
Pd‚‚‚Pd (face to face)b
Pd‚‚‚Pd (intermolecular)
Pd‚‚‚Cl (intermolecular)
3.364(3)
3.278(2)
3.298(2)
3.342(3)
3.343(3)
3.219
3.407
3.248
3.260(2)
3.362(2)
4.053(2)
3.465(7)
3.651(7)
3.647(7)
Pd‚‚‚C-C (centroid)
3.240
3.334
3.251
3.365
3.264
3.252
3.346
3.319
3.330
3.398
3.254
3.376
3.338
3.341
PdCl4(plane)‚‚‚C6(plane)
3.385
a
b
Average values; average deviations in parentheses. Values for 2, 3, 4, 6, and 7 are averages; average deviations in parentheses.
spectra show a prominent feature at 350-365 nm with a tail at
lower energy. This tail becomes a distinct peak at 450 nm in
the spectrum obtained from the mesitylene solution. The
absorption spectrum obtained from a mull of Pd6Cl12 dispersed
in mineral oil also shows a prominent band at ca. 370 nm.
The aromatic molecules benzene, mesitylene, durene, and
hexamethylbenzene as well as Buckminsterfullerene (C60) form
crystalline compounds with Pd6Cl12. These solids are readily
prepared from the appropriate aromatic molecule and bis-
(benzonitrile)palladium(II) dichloride, a labile complex which
is a good source of PdCl2 units.14a The products all crystallize
as dark red solids. Thus an orange solution of bis(benzonitrile)-
palladium(II) dichloride in mesitylene produces 2, Pd6Cl12‚(CH3)3-
C6H3, upon standing for 48 h. Benzene solutions of bis-
(benzonitrile)palladium(II) dichloride in the presence of mesi-
tylene, durene, hexamethylbenzene, and biphenyl produce 3,
(Pd6Cl12‚(CH3)3C6H3‚0.5C6H6), 4 (Pd6Cl12‚1,2,4,5-(CH3)4C6H2),
Figure 1. Electronic absorption spectra for solutions of Pd6Cl12 in
5 (Pd6Cl12‚(CH3)6C6), and 6 (Pd6Cl12‚C12H10), respectively.
aromatic solvents.
Treatment of C60 with bis(benzonitrile)palladium(II) dichloride
in benzene, which was expected to yield a palladium adduct of
the fullerene, produced the crystalline compound 7 (Pd6-
Cl12‚0.5C60‚1.5C6H6). Treatment of benzene solutions of Pd6-
Cl12 with stronger donors, triphenylphosphine or pyridine, results
consists of discrete molecules of Pd6Cl12. These molecules have
an octahedral array of metal atoms. Each metal atom is
surrounded by four equivalent chlorine atoms that bridge edges
of the octahedron. The â-form has been prepared in polycrys-
in disruption of the cluster and the formation of the conventional
talline form by treatment of Pd3(acetate)6 with carbon monoxide
compounds bis(triphenylphosphine)palladium(II) dichloride and
in glacial acetic acid that contains some perchloric acid.12 This
bis(pyridine)palladium(II) dichloride, respectively.
phase is soluble in aromatic solvents, and it has been speculated
that the donor properties of the solvent are responsible for
altering the electronic spectrum of the cluster. Commercial
Structural Studies. The structures of each of the compounds
1-7 have been determined by single-crystal X-ray diffraction.
Relevant data from these crystal structures are summarized in
PdCl2, which is not soluble in aromatic solvents, is reported to
Tables 1 and 2. Views of the individual structures are presented
consist of another polymorph whose structure is currently
in Figures 2-10.
unknown.13
The Structure of 1, Pd6Cl12.14b Solvate-free 1 crystallizes
with the Pd6Cl12 cluster at a site of 3h point symmetry with the
three-fold axis passing through the center of a Cl3 triangle. Part
A of Figure 2 shows a drawing of the highly regular cluster.
The four independent Pd-Cl bonds have an average length of
2.307 Å with an average deviation of 0.003 Å. Similarly, all
bond angles are very close to 90 or 180°. Within the cluster
the closest Pd‚‚‚Pd contact, which involves two palladium
centers that are bridged by chloride ligands, is 3.306(23) Å.
This distance is longer than those found where Pd-Pd bonds
are present. The palladium atom is displaced 0.031 Å to the
outside of the least-squares plane of the four adjacent chlorine
Results
Synthetic Studies. Dark red 1, which consists of discrete
molecules of Pd6Cl12, is readily obtained as X-ray quality single
crystals by allowing solutions of bis(benzonitrile)palladium(II)
dichloride in a benzene/chloroform mixture to stand. The dark
red prisms of the product redissolve in aromatic solvents
(benzene, toluene) but do not dissolve in dichloromethane or
chloroform. Electronic absorption spectra of Pd6Cl12 in benzene,
toluene, p-xylene, and mesitylene are shown in Figure 1. The
(9) Wells, A. F. Z. Kristallogr., Mineralog. Petrogr. Abt. A 1938, 100,
189.
(10) Scha¨fer, H.; Wiese, U.; Rincke, K.; Brendel, K. Angew. Chem., Int.
Ed. Engl. 1967, 6, 253.
(11) Brodersen, K.; Thiele, G.; Schnering, H. G. Z. Anorg. Allg. Chem.
1965, 337 120.
(12) Yatsimirski, A.; Ugo, R. Inorg. Chem. 1983, 22, 1395.
(13) Soulen, J. R.; Chappel, W. H., Jr. J. Phys. Chem. 1965, 69, 3669.
(14) (a) Kharasch, M. S.; Ashford, T. A. J. Am. Chem. Soc. 1936, 58,
1733. Balch, A. L.; Petridis, D. Inorg. Chem. 1969, 8, 2247. (b) Note added
in proof: The formation of solvate-free Pd6Cl12 from Pd2Cl4(CO)2 in thionyl
chloride and crystallographic characterization of the cluster have been
recently reported. Belli Dell’Amico, D.; Calderazzo, F.; Marchetti, F.;
Ramello, S. Angew. Chem. Int. Ed. Engl. 1996, 35, 1331.

Supramolecular Aggregation of Pd6Cl12
J. Am. Chem. Soc., Vol. 118, No. 33, 1996 7739
Table 2. Crystallographic Data for Compounds 1-7
Pd6Cl12‚
Pd6Cl12‚(CH3)3C6H3‚
Pd6Cl12‚
(CH3)4C6H2
(4)
Pd6Cl12‚
1.5(CH3)6C
(5)
Pd6Cl12‚
C12H10
(6)
Pd6Cl12‚0.5C60‚
1.5C6H6
(7)
Pd6Cl12
(CH3)3C6H3
0.5C6H6
(1)
(2)
(3)
formula
fw
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Cl12Pd6
1063.80
12.971(3) 8.118(2)
12.971(3) 11.437(2)
8.552(2) 14.314(3)
90
90
C9H12Cl12Pd6
1184.0
C12H15Cl12Pd6
1223.0
8.169(3)
11.378(4)
15.160(4)
84.06(2)
78.40(2)
80.71(3)
1358.5(7)
2
C10H14C12Pd6 C18H27Cl12Pd6 C12H10Cl12Pd6 C39H9Cl12Pd6
1198.01
7.954(2)
8.804(2)
11.199(2)
99.23(2)
106.90(2)
109.17(2)
624.2(2)
1
1307.20
15.326(5)
15.326(5)
23.465(7)
90
90
120
1218.00
31.505(6)
7.953(2)
15.806(3)
90
111.17(2)
90
1541.26
12.544(3)
50.655(10)
24.669(5)
90
90
90
71.85(2)
87.48(2)
79.42(2)
120
1246.1(5) 1241.3(4)
3
4773(3)
6
2520.9(11)
4
15675(8)
16
Z
2
crystal system
space group
T, °C
trigonal
R3h
-143
0.71073
4.253
8.26
triclinic
P1h
-143
0.71073
3.168
5.54
triclinic
P1h
triclinic
P1h
trigonal
R3h
-143
0.71073
2.729
4.34
monoclinic
C2/c
-143
0.71073
3.209
5.46
0.056
0.140
orthorhombic
Cmcm
-143
-75
-143
λ, Å
0.71073
2.990
5.07
0.073
0.223
0.71073
3.187
5.51
0.034
0.085
0.71073
2.612
F, g/cm3
µ, cm-1
R1 (obsd data)a
3.55
0.093
0.286
0.057
0.059
0.164
0.033
0.083
wR2 (all data F2 refinement)b 0.120
R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) ∑[w(F -F 2)2]/∑[w(F )2].
a
b
2
2
x
o
c
o
Each of the compounds, 2, 3, 4, and 6, forms a layered-like
solid in which the octahedral clusters and the flat aromatic
molecules are interleaved. In each case the clusters make face-
to-face contact with arene molecules on two opposite sides of
the cluster. A view of a typical example of the arene-cluster-
arene sandwich is shown in part A of Figure 11. Additionally,
the two faces of the aromatic molecules make contact with
different Pd6Cl12 clusters. Relatively close, pairwise Pd‚‚‚Cl
contacts between clusters result in the formation of stepped
chains in 2, 4, and 6. In each of the Figures 4-6 and 8, the
chains produced by these pairwise Pd‚‚‚Cl contacts run parallel
to the figure plane. These chains are generally similar to those
found in solvate-free 1. In 3, however, these same pairwise
contacts result in the formation of slightly different, zigzag
chains as seen in Figure 5.
The Structure of 5, Pd6Cl12‚1.5(CH3)6C6. The binary
compound, 5, has a nonlayered structure that differs in important
respects from those of 2, 3, 4, and 6. The cluster has
crystallographic 3-fold symmetry while the aromatic molecule
has inversion symmetry. In 5, as in 2, 3, 4, and 6, the
hexamethylbenzene molecules are sandwiched between two Pd6-
Cl12 clusters. As shown in Figure 7 and in part B of Figure 11,
three adjacent, orthogonal sides of the cluster make face-to-
face contacts with hexamethylbenzene molecules. The other
three sides of the cluster lack the close pairwise Pd‚‚‚Cl contacts
that are a significant characteristic of compounds 1-4 and 6.
In 5 the shortest Pd‚‚‚Cl separation is 4.053 Å.
The Structure of 7, Pd6Cl12‚0.5C60‚1.5C6H6 (6). A view
of this complex structure is shown in Figure 9. The formula
and asymmetric unit for this compound belies its overall
complexity. There are eight individual components, and each
possesses some degree of crystallographic symmetry. These
components include the following: (1) a Pd6Cl12 cluster with
mm symmetry that involves atoms Pd(1)-Pd(3) and Cl(1)-
Cl(5); (2) a Pd6Cl12 cluster with 2/m symmetry that involves
atoms Pd(4) and Pd(5) and Cl(6)-Cl(9); (3) a Pd6Cl12 cluster
with m symmetry that is comprised of atoms Pd(6)-Pd(9) and
Cl(10)-Cl(16); (4) a benzene molecule with m symmetry that
utilizes atoms C(1)-C(4) with these atoms lying within the
mirror plane; (5) a benzene molecule with m symmetry that
consists of atoms C(5)-C(7) with the mirror plane bisecting
an edge of the six-membered ring; (6) a benzene molecule with
m symmetry that consists of atoms C(8)-C(10); (7) one quarter
Figure 2. (A) Structure of solvate-free Pd6Cl12, 1, showing anisotropic
thermal ellipsoids at the 50% probability level. (B) A perspective
drawing showing the pairwise Cl‚‚‚Pd intermolecular contacts between
two Pd6Cl12 units in 1.
atoms. The two parallel planes of four chlorine atoms in a single
cluster are separated by 4.613 Å. The corresponding Pd‚‚‚Pd
separation is slightly longer, 4.675 Å.
As shown in part B of Figure 2, the intermolecular interactions
are dominated by pairwise Pd‚‚‚Cl contacts at 3.364 Å that are
21.8° from the normal to the PdCl4 plane. The clusters are offset
to allow these two complementary interactions on each face of
the cluster. This produces stepped chains of the clusters. Figure
3 shows a stereoscopic view of the packing of individual Pd6-
Cl12 molecules within the solid.
The Structures of 2, 3, 4, and 6. The structures of the binary
compounds formed from Pd6Cl12 and mesitylene, durene, and
biphenyl (2, 4, and 6) and the ternary compound 3,
Pd6Cl12‚(CH3)3C6H3‚0.5C6H6, have a number of features in
common. Stereoviews of these structures are shown in Figures
4-6 and 8. As can be seen from Table 1, the Pd6Cl12 clusters
in these four compounds have similar geometries and dimen-
sions to those of the parent cluster in solvate-free Pd6Cl12, 1.

7740 J. Am. Chem. Soc., Vol. 118, No. 33, 1996
Olmstead et al.
Figure 3. A stereoscopic view of the structure of solvate-free Pd6Cl12, 1.
Figure 4. A stereoscopic view of the structure of Pd6Cl12‚(CH3)3C6H3, 2.
Figure 5. A stereoscopic view of the structure of Pd6Cl12‚(CH3)3C6H3‚0.5C6H6, 3.
Figure 6. A stereoscopic view of the structure of Pd6Cl12‚(CH3)4C6H2, 4.
Figure 7. A stereoscopic view of the structure of Pd6Cl12‚1.5(CH3)6C6, 5.
of a disordered molecule of C60 with 2/m symmetry that involves
atoms C(11)-C(31); and (8) a second, disordered quarter of a
molecule of C60 with 2/m symmetry that involves atoms C(32)-
C(50).
molecules is dictated by donor-acceptor interactions or simply
by the efficient packing of similar-sized molecules. For example
(see Figure 9), two of the benzene molecules are the middle
layer in a stack of C60/benzene/Pd6Cl12. The contacts are typical
for π-stacking of these molecules, suggesting that benzene is
acting as a bi-directional donor. However, the structure has
other instances of C60 and Pd6Cl12 in close proximity with no
interleaving benzene molecules. In fact, the nearest neighbors
for one of the C60 molecules consist of two face-on and four
edge-on benzene molecules, two molecules of C60 and six Pd6-
Cl12 clusters; the other C60 is surrounded by four face-on and
two edge-on benzene molecules in addition to two C60 molecules
and six Pd6Cl12 clusters. The C60 molecules stack along the a
direction in side-by-side columns. The separation between their
Few molecular solids can boast the collection of geometric
shapes, truncated icosahedra, octahedra, and hexagons, that are
found in this one. These figures have considerable similarity
in their sizes. The C60 diameter of 7.1 Å is only slightly larger
than the Pd6Cl12 body diagonal of 6.6 Å, and in terms of van
der Waals radii they are roughly the same size. Since the H‚‚‚H
span of benzene is ca. 4.8 Å, it is easily sandwiched between
palladium clusters or C60. In an examination of the packing in
this unusual structure it is therefore not entirely clear what
intermolecular forces come into play, whether the proximity of

Supramolecular Aggregation of Pd6Cl12
J. Am. Chem. Soc., Vol. 118, No. 33, 1996 7741
Figure 8. A stereoscopic view of the structure of Pd6Cl12‚(C6H5)2, 6.
Figure 9. A view of the structure of Pd6Cl12‚0.5C60‚1.5C6H6, 7. The
C60 molecules are disordered at sites of 2/m symmetry. In this view,
ideal C60 molecules have been drawn at the appropriate locations.
Figure 11. (A) A view of the contact between two mesitylene
molecules and the Pd6Cl12 cluster in Pd6Cl12‚(CH3)3C6H3, 2. This is a
common motif in the structures of 2, 3, 4, and 6. (B) A view of the
contact between three hexamethylbenzene molecules and the Pd6Cl12
cluster in Pd6Cl12‚1.5(CH3)6C6, 5.
can be viewed as components of the third system. For example,
the Pd6Cl12 cluster is formally a collection of six interacting
PdCl2 units, each with a 90° bond angle and C2V symmetry.
Each PdCl2 unit interacts directly with four other units: the
two Cl atoms bond on the same side of the PdCl2 plane to the
Pd atoms of two other units and the Pd atom bonds within the
PdCl2 plane to a Cl atom of two additional units. The result is
a cubic arrangement of six, square-planar PdCl4 faces wherein
each of the Cl atoms is shared between two faces. The bonding
2-
within a face should resemble the well-known PdCl4 com-
plex.15 The highest order rotation axis is chosen as the z axis
in all cases. The other axes are chosen such that the molecule
2-
is in the yz plane for PdCl2 and in the xy plane for PdCl4
.
The x and y axes are parallel to the Pd-Cl bond axes in both
2-
PdCl4 and Pd6Cl12. Accordingly, the correlations for PdCl2
involve a change of axes; for example, dyz in PdCl2 correlates
Figure 10. A portion of the structure of Pd6Cl12‚0.5C60‚1.5C6H6, 7.
This view emphasizes the group of eight clusters that surround C60
molecules.
to dx -y in Pd6Cl12 and PdCl42-. The Pd-d orbitals in Pd6Cl12
2
2
2
2
are labeled in terms of the PdCl4 faces, so that dx -y in Pd6Cl12
refers to orbitals that are predominantly in the PdCl4 planes and
directed along the Pd-Cl axes of all of the PdCl4 faces.
Figure 11 shows the energy ordering of the higher valence
orbitals. These are numbered with neglect of the core levels
and labeled in terms of their symmetry and major Pd-d or Cl-p
character. The predominantly Cl-p orbitals are identified further
as to σ or π type, with the π type differentiated by the symmetry
centers is 12.54 and 12.49 Å between like molecules and 9.99
Å between the two different molecules of C60. Furthermore,
the Pd6Cl12 clusters have adopted an interesting arrangement
to accommodate the spherical shape of the C60. Figure 10 shows
how a group of eight Pd6Cl12 clusters form a pocket into which
a C60 molecule can fit. Several intermolecular contacts between
Pd6Cl12 clusters allow this to form: a pairwise interaction
between Pd7 and Cl11 of 3.465 Å and a longer one between
Pd7 and Cl12 of 3.615 Å. There is also a triangular arrangement
of Pd6Cl12 clusters that form equal bifurcated contacts between
Cl4 and Pd8 and Pd8′ of 3.647 Å.
with respect to the molecular plane (h ) horizontal or in-plane,
2-
v ) vertical or out-of-plane) in PdCl2 and PdCl4
. The
differentiation of π type is not made for Pd6Cl12, since πv
becomes σ and only πh (parallel to an edge of the cube) remains
π-type. The πh and σ types also both include the t1u representa-
tion. The orbitals of Pd6Cl12 in Figure 12 not explicitly noted
as Cl-p by the σ or π label are predominantly Pd-d. The orbitals
The Electronic Structure of Pd6Cl12. In order to probe the
binding within the cluster, a series of SCF-XR-SW calcula-
2-
tions were performed on PdCl2 (C2V symmetry), PdCl4 (D4h
symmetry), and Pd6Cl12 (Oh symmetry). The first two systems
(15) Gray, H. B.; Ballhausen, C. J. J. Am. Chem. Soc. 1963, 85, 260.

7742 J. Am. Chem. Soc., Vol. 118, No. 33, 1996
Olmstead et al.
the spectra of Pd2X62-, where X ) Br and I.16 The intense
absorptions are expected to involve the allowed chlorine-to-
palladium charge transfer (LMCT) excited states. These LMCT
excitation energies are given in Table 3.
The calculations can be compared with experiment most
readily for PdCl42-, wherein the assignments and energies are
well-known. The singlet states associated with the d-d
1
transitions are observed at 2.73, 2.98, and 3.72 eV for A2g,
1
1Eg, and B1g, respectively.16 The order agrees with the
calculations, but the calculated energies are too small by 0.2-
0.8 eV. The lowest energy LMCT absorption is seen at 4.46
eV and assigned to the 1A2u state.16 The lowest energy singlet
1
LMCT state from the calculations is Eu at 3.79 eV, with the
1A2u state at 3.96 eV. The calculated energies are again too
small. Such errors are not unexpected, in part because the
calculations at best refer to the mean of the singlet and triplet
states resulting from a given excitation.
The low-energy onset of the d-d transitions in Pd6Cl12 is
calculated to occur at 2.19 eV (570 nm), while the lowest energy
allowed LMCT transitions are calculated at 3.33, 3.66, and 3.79
eV. Hence, we predict that the absorption spectrum will be
dominated by LMCT transitions somewhat above 3.3 eV (375
nm). This is in surprising agreement with the observed intense
absorption band seen at ≈3.3 eV in mulls of neat Pd6Cl12 and
at 3.4 eV in solutions of Pd6Cl12 in aromatic solvents. The
2-
enhanced agreement relative to the PdCl4 case may be
fortuitous, but it also could reflect the better results anticipated
for more spherical systems from SCF-XR-SW calculations.
The onset of absorption in benzene solution (≈2.3 eV) also
agrees with the calculated energy for the onset of d-d
transitions.
Figure 12. A molecular orbital energy diagram for the higher valence
orbitals in the Pd6Cl12 cluster.
have their correct relative energies within each system, but the
systems have been displaced in energy to place the gap between
the filled and virtual orbitals at similar energies.
The energy order of the Pd-d orbitals in PdCl2 is dyz (4b2,
Discussion
2
2
2
LUMO) > dx -y , z (5a1, HOMO) > dxy (2a2) > dxz (2b1) >
2
2
2
dz , x -y (4a1), but the 1a2 and 2a2 orbitals have nearly equal
Pd-dxy and Cl-pπv character. The highest energy, filled ligand
orbital in PdCl2 is 3b2 (Cl-pπh). Each of the orbitals in PdCl2
correlates to six orbitals in Pd6Cl12. For example, the 3b2 Cl-
pπh orbital in PdCl2 correlates to the 2t1g and 5t1u Cl-pπ orbitals
in Pd6Cl12. The Cl-pπv orbitals in PdCl2 become Cl-pσ orbitals
in Pd6Cl12. Similarly, the dyz (4b2) LUMO in PdCl2 correlates
As Table 1 shows, the Pd6Cl12 cluster retains an invariant
structure throughout the series of compounds, 1-7. Since the
palladium atoms protrude slightly to the outside of the plane of
the four adjacent chlorine atoms, there is no evidence of direct
Pd-Pd bonding. The face-to-face Pd‚‚‚Pd separation of 4.675
Å in 1 is considerably longer than the distance (2.5310(9) Å)
found for the unsupported Pd-Pd single bond in [Pd2-
(CNCH3)6]2+ 17
The Pd6Cl12 cluster is geometrically related to
.
2
2
to the six dx -y (5t2u, 5eg, and 2a2g) lowest lying virtual orbitals
in Pd6Cl12. The correlations for the filled Pd-d orbitals are more
complicated, since the resulting groups of orbitals in Pd6Cl12
overlap in energy and mixing occurs among orbitals of the same
symmetry. However, the HOMO in Pd6Cl12 (2a2u, dxy) derives
Pt6Cl12 and to a number of early transition metal clusters which
all have an octahedral array of metal atoms and twelve edge-
bridging halogen atoms. However, in the early transition metal
clusters with [M6X12]n+ cores (where M ) Nb or Ta, X )
halogen, and n ) 2, 3, or 4) there is significant metal-metal
bonding, and the metal centers are drawn inward toward one
another.18,19
from the HOMO in PdCl2 (5a1, dx -y , z ). In PdCl42-, the Pd-d
2
2
2
2
2
orbitals have the expected order dx -y (3b1g, LUMO) > dxy (2b2g,
2
HOMO) > dxz, dyz (2eg) > dz (3a1g). The correlations between
2-
Pd6Cl12 and PdCl4 are also as expected. The HOMO in
The formation of the array of adducts 2-7, in which an
aromatic component is crystallized along with the Pd6Cl12
cluster, is a direct consequence of the donor/acceptor interaction
between these components. It is clear that the aromatic
component is not merely occupying what would otherwise be
a void in the structure, since the cluster is able to crystallize in
the solvate-free form, 1. The solubility of Pd6Cl12 in aromatic
solvents is also a consequence of these interactions. The empty
2-
PdCl4 (2b2g, dxy) correlates to the HOMO (2a2u) and other
high-energy filled Pd-d orbitals (2eu and 5t2g) in Pd6Cl12,
although the 1eu and 2eu orbitals in Pd6Cl12 have roughly equal
Pd and Cl character. The ligand orbitals 1a2g and 3eu (Cl-pπh)
in PdCl42- correlate to the ligand orbitals 2t1g and 5t1u (Cl-pπ)
in Pd6Cl12.
Excitation energies, obtained simply from the ground state
orbital energies, are given in Table 3 for the lower-lying
palladium d-d and some of the chlorine-to-palladium charge
transfer excitations. The d-d excitations are predicted to be
lowest lying in all of the systems. The states that result from
the d-d excitations are formally symmetry forbidden in
absorption from the ground state only in PdCl42-, but the
transitions are expected to remain weak in Pd6Cl12 based on
the local site symmetry of the Pd. Similar arguments, based
on the effect of the local symmetry, have been used in explaining
2
2
2a2g dx -y orbital of Pd6Cl12 should not be important in this
(16) Day, P.; Smith, M. J.; Williams, R. P. J. J. Chem. Soc. A 1968,
668.
(17) Doonan, D. J.; Balch, A. L.; Goldbery, S. Z.; Eisenberg, R.; Miller,
J. S. J. Am. Chem. Soc. 1975, 97, 1962.
(18) Hubert-Pfalzgraf, L. G.; Postel, M.; Reiss, J. G. In ComprehensiVe
Coordination Chemistry; Wilkinson, G., Gillard, R. D., McCleverty, J. A.,
Eds.; Pergamon Press: New York, 1987; Vol. 3, p 585.
(19) Koknat, F. W.; McCarley, R. E. Inorg. Chem. 1974, 13, 295. Koknat,
F. W.; McCarley, R. E. Inorg. Chem. 1972, 11, 812.

Supramolecular Aggregation of Pd6Cl12
J. Am. Chem. Soc., Vol. 118, No. 33, 1996 7743
Table 3. Calculated Energies of Some Palladium d-d and Chlorine-to-Palladium Charge Transfer (LMCT) Excitations in PdCl2, Pd6Cl12. and
2-
PdCl4
2-
PdCl2
excitation (states)
Pd6Cl12
excitation (states)
PdCl4
∆E/eV
∆E/eV
excitation (states)
∆E/eV
1,3
1,3
d-d
5a1-4b2 (1,3B2)
2a2-4b2 (1,3B1)
2b1-4b2 (1,3A2)
4a1-4b2 (1,3B2)
3b2-4b2 (1,3A1)
1a2-4b2 (1,3B1)
1.37
1.49
1.61
1.66
2.17
3.04
2a2u-2a2g
(
A )
2.19
2b2g-3b1g
(
A )
2.58
2.70
2.92
1u
2g
2eg-3b1g
(
1,3Eg)
1,3
3a1g-3b1g
(
B )
1g
1,3
LMCT
2t1g-5t2u
(
T )
3.33
3.66
3.79
3eu-3b1g
(
1,3Eu)
3.79
3.96
1u
5t1u-5eg (1,3T1u)
1b2u-3b1g ( A )
1,3
2u
1,3
3t2u-2a2g
( T )
1u
regard since the orbital is concentrated in the PdCl4 planes and
narrow range, 3.247-3.385 Å. However, the interplanar
separations and Pd‚‚‚C contacts are well beyond the conven-
tional bonding range. In typical palladium olefin complexes
such as (norbornadiene)palladium(II) dichloride the Pd-C
distances are 2.159(4) and 2.166(4) Å,22 in η3-alkyl complexes
like (η3-2-methallyl)palladium(II) chloride dimer the Pd-Cl
distances are 2.082(19), 2.102(16), and 2.062(18) Å,23 and in
cases where two palladium atoms are sandwiched between two
arene rings, as in (C6H6)2Pd2(Al2Cl7)2, the shortest Pd-C
distances range from 2.26 to 2.63 Å.24 The Pd‚‚‚C contacts
are also longer than the metal-carbon contact observed in the
weak hexamethylbenzene/mercury(II) bis(trifluoroacetate) dimer,
where the Hg-C distances are 2.56 and 2.58 Å.25 Perhaps the
closest analogs to the interactions between the cluster and the
aromatic molecules seen here are found in the adducts of
aromatic molecules and tetrakis(triphenylacetato)dichromium(II).26
In these crystalline materials, chains of alternating molecules
of tetrakis(triphenylacetato)dichromium(II) and the aromatic
molecule are formed with the aromatic component situated
perpendicular to the Cr-Cr axis and centered between the two
adjacent chromium atoms. The resulting Cr‚‚‚ring centroid
distances are in the range 3.310-3.388 Å. Although the
individual Pd-C contacts are long in solids 2-7, there is
sufficient attraction between the clusters and the arenes to
produce this remarkable array of binary and ternary solids.
The nature of the arene/cluster interactions in binary complex
2, Pd6Cl12‚(CH3)3C6H3, and ternary compound 3, Pd6Cl12‚(CH3)3-
C6H3‚0.5C6H6, is similar as can be seen by comparison of
drawings A and B with C and D in Figure 13. In ternary
compound 3, Pd6Cl12‚(CH3)3C6H3‚0.5C6H6, it is the mesitylene
molecules, which are the better π donors, rather than the benzene
molecules that make the face-to-face contact with the Pd6Cl12
cluster. In 3, the benzene molecules are positioned within the
layers of mesitylene molecules and are oriented with their planes
roughly perpendicular to the direction of the mesitylene
molecules as seen in Figure 5.
very poor overlap will occur with any aromatic π-orbital.
2
2
However, the empty 5eg and 5t2u dx -y orbitals of Pd6Cl12 are
2
contaminated with dz and dxz, dyz character, respectively, which
have large amplitudes normal to the PdCl4 planes. Presumably,
these orbitals are involved in the face-to-face interaction with
an arene whose plane is parallel to the PdCl4 face.
The absorption spectrum of Pd6Cl12 in solutions of methylated
benzenes shows an additional absorption band at ≈2.75 eV (450
nm). Based on the shift of this band that occurs with variation
in the number of methyl substituents, the band must involve
the arene moiety. One possibility is that the band represents
the nominally spin-forbidden transition between the ground and
3
lowest excited ππ* states of the aromatic solvent, since this
transition is expected to gain intensity from the external heavy-
atom effect caused by the Pd6Cl12 cluster. However, this
assignment can be discounted on energy grounds since the band
maxima in absorption would occur much further to the blue
(electronic origins at e360 nm).20 The assignment which we
propose for the excited state of the band involves a charge-
2
2
transfer transition from a π-orbital of the aromatic to a dx -y
virtual orbital of Pd6Cl12. This assignment is prompted by the
apparent red shift of the band that occurs with increasing number
of methyl substituents among toluene, p-xylene, and mesitylene,
which parallels the expected direction of their decreasing
ionization energies. In order to check the viability of this
assignment, the ionization energy and electron affinity of Pd6-
Cl12 were estimated from transition state and total energy
calculations. The calculated ionization energy is ≈12 eV,
significantly greater than the ionization energies of methylated
benzenes (8.8 eV in toluene and 8.4 eV in mesitylene),21 so
that the aromatic is expected to function as the donor in any
charge-transfer state. The calculated electron affinity is ≈6.0
eV. Hence, a very crude estimate of the energy of the charge-
transfer excited state is ≈2.6 eV (≈500 nm).
The face-to-face contacts between the square PdCl4 portions
of the clusters and the aromatic molecules are a major feature
of the series of compounds 2-7. Figure 13 shows views of
these contacts which emphasize the relative positioning of the
aromatic hexagon above the PdCl4 square. In each drawing
the view is made perpendicular to the PdCl4 plane. Generally
the aromatic groups are arranged so the palladium atom lies
within the aromatic hexagon and generally near one of the
carbon atoms. The exception is found in one of the benzene/
Pd6Cl12 contacts in 7, where the palladium atoms lie beneath
the center of the benzene ring (see H in Figure 13). The Pd‚‚‚C
distances in these compounds range from 3.171 to 3.410 Å.
The PdCl4 plane and the plane of the aromatic molecule that
are involved in the face-to-face contact are nearly parallel. The
separations between these (see Table 1) fall in a relatively
It is interesting to note that hexamethylbenzene, which is the
best donor, forms a greater number of face-to-face contacts with
the cluster than do the other aromatic donors utilized in this
study. Hexamethylbenzene is also the largest of the donors,
but as depicted in Figure 8 the dimensions of the aromatic
molecule are large enough to allow the methyl groups to extend
beyond the edges of the cluster face. Therefore, somewhat
surprisingly, favorable donor-acceptor interactions between
faces of the aromatic molecules and the Pd6Cl12 cluster occur
even in the presence of six methyl groups.
(22) Baenziger, N. C.; Richards, G. F.; Doyle, J. R. Acta Crystallogr.
1965, 18, 924.
(23) Mason, R.; Wheeler, A. G. J. Chem. Soc. A 1968, 2549.
(24) Allegra, G.; Immirzi, A.; Porri, L. J. Am. Chem. Soc. 1965, 87,
1394.
(20) McGlynn, S. P.; Azumi, T.; Kinoshita, M. Molecular Spectroscopy
of the Triplet State, Prentice-Hall: Englewood Cliffs, NJ, 1969.
(21) Briegleb, G. Electronen-Donator-Acceptor-Komplexe; Springer-
Verlag: Berlin, 1961.
(25) Lau, W.; Kochi, J. K. J. Org. Chem. 1986, 51, 1801.
(26) Cotton, F. A.; Feng, X.; Kibala, P. A.; Matusz, M. J. Am. Chem.
Soc. 1988, 110, 2807. Cotton, F. A.; Daniels, L. M.: Kibala, P. A. Inorg.
Chem. 1992, 31, 1865.

7744 J. Am. Chem. Soc., Vol. 118, No. 33, 1996
Olmstead et al.
Figure 13. Views of the projection of the aromatic components of 2-7 onto the plane of the adjacent PdCl4 face of the Pd6Cl12 cluster: (A and
B) Pd6Cl12‚(CH3)3C6H3, 2; (C and D) Pd6Cl12‚(CH3)3C6H3‚0.5C6H6, 3; (E) Pd6Cl12‚(CH3)4C6H2, 4; (F) Pd6Cl12‚1.5(CH3)6C6, 5; (G) Pd6Cl12‚(C6H5)2,
6; (H and I) Pd6Cl12‚0.5C60‚1.5C6H6, 7. The closest Pd‚‚‚C contacts are as follows: (A) 3.171 Å; (B) 3.410 Å; (C) 3.231 Å; (D) 3.395 Å; (E) 3.311
Å; (F) 3.389 Å; (G) 3.334 Å; (H) 3.328 Å; and (I) 3.474 Å.
The fullerene, C60, shows a marked propensity to form both
intercalation compounds with considerable electron transfer27
and solids in which a range of other molecules are simply co-
crystallized. The latter include examples such as C60‚(S8)2,28
C60‚(P4)2,29 C60‚I2‚C6H5CH3,30 C60‚{(η5C5H5)2Fe}2,31 C60‚
{(η5C5H5)4Fe4(CO)4}‚3C6H6,32 C60‚4 C6H6,33 C60‚CH2I2‚C6H6,34
and C60‚{bis(dimethylthieno)tetratellurafulvalene}‚CS235 where
the other component is drawn from the inorganic, organome-
tallic, or organic classes. The ter-molecular solid, 7, belongs
to this latter classification.
Experimental Section
Preparation of Compounds. Bis(benzonitrile)palladium(II) dichlo-
ride was prepared as described in the literature.36
Pd6Cl12 (1). A solution of 5.5 mg (1.43 × 10-5 mol) of bis-
(benzonitrile)palladium(II) dichloride in 0.5 mL of benzene was
transferred to a 20 cm × 6 mm inside diameter glass tube that was
sealed at one end. The solution was red-orange in color. Chloroform
(0.5 mL) was added drop by drop to the solution in the glass tube. The
chloroform settled to the bottom of the tube and the color of the solution
immediately turned to orange-yellow. The tube was sealed with a
rubber septum and set aside for 24 h. Dark red rhombohedral prisms
of Pd6Cl12 formed: yield 1 mg, 39.5%.
(27) Rosseinsky, M. J. J. Mater. Chem. 1995, 5, 1497.
(28) Roth, G.; Adelmann, P. Appl. Phys. A 1993, 56, 169.
(29) Douthwaite, R. E., Green, M. L. H.; Heyes, S. J.; Rosseinsky, M.
J.; Turner, J. F. C. J. Chem. Soc., Chem. Commun. 1994, 1367.
(30) Birkett, P. R.; Christides, C.; Hitchcock, P. B.; Kroto, H. W.;
Prassides, K.; Taylor, R.; Walton, D. R. M. J. Chem. Soc., Perkin Trans.
1993, 1407.
(31) Crane, J. D.; Hitchcock, P. B.; Kroto, H. W.; Taylor, R.; Walton,
D. R. M. J. Chem. Soc., Chem. Commun. 1992, 1764.
(32) Crane, J. D.; Hitchcock, P. B. J. Chem. Soc., Dalton Trans. 1993,
2537.
(33) Meidine, M. F.; Hitchcock, P. B.; Kroto, H. W.; Taylor, R.; Walton,
D. M. R. J. Chem. Soc., Chem. Commun. 1992, 1534. Balch, A. L.; Lee, J.
W.; Noll, B. C.; Olmstead, M. M. J. Chem. Soc., Chem. Commun. 1993,
56. Bu¨rgi, H. B.; Restori, R.; Schwarzenbach, D.; Balch, A. L.; Lee, J. W.;
Noll, B. C.; Olmstead, M. M. Chem. Mater. 1994, 6, 1325.
(34) Geiser, U.; Kumar, S. K.; Savall, M. B.; Harried, S. S.; Carlson, K.
D.; Mobley, P. R.; Wang, H. H.; Williams, J. M.; Botto, R. E.; Liang, W.;
Whangbo, M. H. Chem. Mater. 1992, 4, 1077.
Pd6Cl12‚(CH3)3C6H3 (2). A solution of 10 mg (2.61 × 10-5 mol)
of bis(benzonitrile)palladium(II) dichloride in 1.5 mL (1.07 × 10-2
mol) of mesitylene was transferred to a glass tube. The color of the
solution was orange. The tube was capped and set aside for 48 h.
Dark red crystals formed. The crystals were harvested by cracking
the tube: yield 1 mg, 19.5%.
Pd6Cl12‚(CH3)3C6H3‚0.5C6H6 (3). A solution of 10 mg (2.61 ×
10-5 mol) of bis(benzonitrile)palladium(II) dichloride in 0.5 mL of
benzene was added to 0.5 mL (3.58 × 10-3 mol) of mesitylene. The
color of the solution turned from red-orange to orange upon the addition
of mesitylene, and after stirring, the solution was transferred to a glass
tube. The tube was capped and set aside for 24 h. Dark red plates
formed: yield 1 mg, 20%.
Pd6Cl12‚(CH3)4C6H2 (4). A solution of 10 mg (2.61 × 10-5 mol)
of bis(benzonitrile)palladium(II) dichloride in 0.5 mL of benzene was
(35) Wang, P.; Lee, W.-J.; Shcherbakova, I.; Cava, M. P.; Metzger, R.
M. Syn. Metals 1994, 64, 319.
(36) Anderson, G. K.; Minren, L. Inorg. Synth. 1990, 28, 61.

Supramolecular Aggregation of Pd6Cl12
J. Am. Chem. Soc., Vol. 118, No. 33, 1996 7745
transferred to a glass tube. A solution of 100 mg (7.5 × 10-4 mol) of
1,2,4,5-tetramethylbenzene in 1 mL of benzene was added drop by drop
to this solution. The color of the solution at the interface of the red-
orange bis(benzonitrile)palladium(II) dichloride solution and the color-
less tetramethylbenzene solution was light yellow. The tube was capped
and set aside for 48 h. Dark red prismatic crystals formed: yield 1.3
mg, 25%.
of SHELXTL Plus, VMS version, and refined by use of the program
SHELXTL-93 (based on F2). An absorption correction was applied
to the structures with the program XABS2 which calculates 24
coefficients from a least-squares fit of (1/A vs sin2(q)) to a cubic
2
equation in sin2(q) by minimization of Fo and Fc2 differences.39
Hydrogen atoms were added geometrically and refined with a riding
model. All non-hydrogen atoms were refined with anisotropic thermal
parameters. No disorder was present in any of the structures except
for that of 7. For 7 there is severe disorder in the fullerene portions.
There are two sites with 2/m symmetry that are occupied by disordered
Pd6Cl12‚1.5(CH3)6C6 (5). A solution of 10 mg (2.61 × 10-5 mol)
of bis(benzonitrile)palladium(II) dichloride in 0.5 mL of benzene was
transferred to a glass tube. A solution of 50 mg (2.06 × 10-4 mol) of
hexamethylbenzene in 1 mL of benzene was added drop by drop to
this solution. The color of the solution at the interface of the red-
orange bis(benzonitrile)palladium(II) dichloride solution and the color-
less hexamethylbenzene solution turned brown. The tube was capped
and set aside for 48 h. Dark red, hexagonal needles formed: yield 3.3
mg, 59%.
fullerene molecules. Similar disorder has been observed in (C60)1.5
-
40
(cyclotriveratrylene)(toluene)0.5
.
Crystal data and some details of the
refinements are given in Table 2.
Electronic Structure Calculations. Standard SCF-XR-SW cal-
2-
culations were performed on PdCl2 (C2V symmetry), PdCl4 (D4h
symmetry), and Pd6Cl12 (Oh symmetry).41 In all cases, the Cl-Pd-Cl
angles were taken as 90° (and 180°) and the Pd-Cl bond lengths as
2.3065 Å, which correspond to the average values found in crystals of
Pd6Cl12. Atomic exchange parameters were taken from Schwarz,42 with
the valence electron weighted average used in the interatomic and outer
regions. The Norman criterion was used to determine atomic sphere
radii.43 The outer sphere was reduced from tangency with the most
distant atomic sphere by 0.1 bohr. A Watson sphere of charge +2
was used for PdCl42-. The partial wave bases used lmax equal to 6 on
the outer sphere, 3 on Pd, and 2 on Cl. The SCF calculations were
spin restricted, used the quasirelativistic option for Pd, and treated the
core levels ([Kr] for Pd and [Ne] for Cl) as single atom functions.
Pd6Cl12‚(C6H5)2 (6). A solution of 10 mg (2.61 × 10-5 mol) of
bis(benzonitrile)palladium(II) dichloride in 0.5 mL of benzene was
transferred to a glass tube. A solution of 50 mg (3.24 × 10-4 mol) of
biphenyl in 1 mL of benzene was added drop by drop to this solution.
The color of the solution at the interface of the red-orange bis-
(benzonitrile)palladium(II) dichloride solution and the colorless biphenyl
solution was light yellow. The tube was capped and set aside for 48
h. Dark red crystals formed. The crystals were harvested by cracking
the tube: yield 1.7 mg, 32%.
Pd6Cl12‚0.5C60‚1.5 C6H6 (7). A solution of 0.25 mg (3.47 × 10-7
mol) of C60 in 0.75 mL of benzene was added to 5 mg (1.31 × 10-5
mol) of bis(benzonitrile)palladium(II) dichloride. The color changed
from magenta to red brown upon dissolution of the bis(benzonitrile)-
palladium(II) dichloride in the C60 benzene solution. This solution was
transferred to a glass tube. A 1-mL portion of n-hexane was added
drop by drop to the tube. The tube was set capped and set aside for
14 h. Dark needles formed; yield 1.7 mg, 65.4%.
X-ray Crystallography. The crystals were removed from the glass
tubes together with a small amount of mother liquor and immediately
coated with a hydrocarbon oil on the microscope slide.37 Suitable
crystals were mounted on glass fibers with silicone grease and placed
in the cold stream of either a Siemens R3m/V diffractometer equipped
with an Enraf-Nonius low temperature apparatus (1-3, 5) or a Siemens
P4 diffractometer equipped with an LT-2 low temperature device (4,
7). The former diffractometer utilized a sealed Mo tube that operated
at 2 kW and a graphite monochromator, while the latter employed a
rotating Mo anode that operated at 15 kW and a Zr filter. All the data
sets were collected at 130 K except for that of 3 which was collected
at 198 K in order to avoid the cracking that occurred upon further
cooling. 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.38 The
structures were solved by Patterson or direct methods using the software
Acknowledgment. We thank the National Science Founda-
tion (Grant CHE 9321257) for support and Johnson Matthey,
Inc. for a loan of palladium chloride.
Supporting Information Available: Tables including a full
listing of data collection and structure refinement details, atomic
coordinates, bond distances and angles, anisotropic thermal
parameters, and hydrogen atom coordinates for compounds 1-7
(56 pages). See any current masthead page for ordering and
Internet access instructions.
JA960939D
(38) International Tables for X-ray Crystallography, D. Reidel Publishing
Co.; Boston, MA, 1992; Vol. C.
(39) XABS2, An empirical absorption correction program. Parkin, S.
R.; Moezzi, B.; Hope, H. J. Appl. Crystallogr. 1995, 28, 53-56.
(40) Steed, J. W.; Junk, P. C.; Atwood, J. L.; Barnes, M. J.; Raston, C.
L.; Burkhalter, R. S. J. Am. Chem. Soc. 1994, 116, 10346.
(41) (a) Johnson, K. H. AdV. Quantum Chem. 1973, 7, 143. (b) Slater, J.
C. Quantum Theory of Molecules and Solids; McGraw-Hill: New York,
1974. (c) Case, D. A. Annu. ReV. Phys. Chem. 1982, 33, 151. (d) The
program was written by M. Cook and D. A. Case and obtained from the
QCPE.
(37) Hope, H. In ACS Symposium Series; Wayda, A. L., Darensbourg,
M. Y., Eds.; American Chemical Society: Washington, DC, 1987; Vol.
357, pp 257-262.
(42) Schwarz, K. Phys. ReV. B 1972, 5, 2466.
(43) Norman, J. G. Mol. Phys. 1976, 31, 1191.