3D structures constructed by π···π and C-H···π interactions. Synthesis, structures and selected guest molecule binding properties

Article abstract of DOI:10.1016/S1387-7003(03)00002-9

Syntheses and X-ray determined single-crystal structures of thermally stable palladium(II) compounds involving π···π and C-H···π interactions which show selectivity to small organic molecules.

Full text of DOI:10.1016/S1387-7003(03)00002-9

Inorganic Chemistry Communications 6 (2003) 455–458
www.elsevier.com/locate/inoche
3D structures constructed by p ꢀ ꢀ ꢀ p and C–H ꢀ ꢀ ꢀ p interactions.
Synthesis, structures and selected guest molecule
binding properties
a
a,
*
Sarah J. Carlson , Tongbu Lu a,b, Rudy L. Luck
a
Department of Chemistry, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA
b
Department of Chemistry, Zhongshan University, Guangzhou 510275, China
Received 3 January 2002; accepted 26 December 2002
Abstract
Syntheses and X-ray determined single-crystal structures of thermally stable palladium(II) compounds involving p ꢀ ꢀ ꢀ p and
C–H ꢀ ꢀ ꢀ p interactions which show selectivity to small organic molecules.
Ó 2003 Elsevier Science B.V. All rights reserved.
Keywords: Palladium(II) compounds; Selective absorption
Pronounced interest has recently been focused on the
construction of nanoporous frameworks organized by
coordinate covalent bonds [1] or noncovalent forces
such as hydrogen bonding [2] and p ꢀ ꢀ ꢀ p [3] interactions,
with potential usage for molecular absorption and
separation, ion exchange and catalysis. Some of the
metal-organic frameworks (MOFs) constructed by co-
ordination interactions show higher stability and zeolite-
like reversible guest absorption properties [1b,1g].
In this communication, we report on two thermally
stable 3D structures ½PdCl2ðdpbÞ2Š ꢀ 2Et2O, 1, and
½PdCl2ðdpbÞ2Š ꢀ 2DMF, 2 (dpb ¼ 4-(diphenylphosphino)
benzoate, Et2O ¼ ethyl ether, DMF ¼ N; N-dimethyl-
formamide), which are stabilized by p ꢀ ꢀ ꢀ p and
C–H ꢀ ꢀ ꢀ p interactions, respectively, and show selective
solvent binding properties.
Reaction of dpb with PdCl2ðPhCNÞ2 in a molar ratio
of 2:1 in acetonitrile gave a yellow powder. Crystals of 1
1
and 2 were obtained by diffusion of ethyl ether into
solutions of dichloromethane–acetonitrile and DMF–
acetonitrile of the yellow powder, respectively. X-ray
2
single-crystal analyses reveal that 1 and 2 have similar
structures. In both 1 and 2, the Pd(II) ions are four-
coordinated with two P atoms and two Cl anions in
trans positions (Figs. 1 and 2). The Pd–P and Pd–Cl
ꢀ
distances are 2.3496(8) and 2.2952(9) A in 1, and
ꢀ
2.3520(12) and 2.2945(12) A in 2, respectively. In 1, each
of the ‘‘front’’ phenyl ring of PdCl2ðdpbÞ2 interacts with
* Corresponding author. Tel.: +1-906-487-2309; fax: +1-906-487-
Crystal data for 1: triclinic, PI, a ¼ 9:8564ð9Þ, b ¼ 10:2628ð19Þ,
2
ꢁ
ꢀ
2061.
c ¼ 12:855ð2Þ A, a ¼ 76:526ð14Þ°, b ¼ 83:337ð14Þ°, c ¼ 69:168ð16Þ°,
ꢀ3
E-mail address: rluck@mtu.edu (R.L. Luck).
Synthesis of 1 and 2: a solution of dpb (0.061 mg, 0.2 mmol) in
V ¼ 1181:9ð4Þ A , Z ¼ 1, T ¼ 293 K. 3052 independent (Rint ¼ 0:0104)
1
with 2953 ½I > 2rðIފ observed data, R1 ¼ 0:0310, wR2 ¼ 0:0812,
GOF ¼ 1.048.
acetonitrile (2 ml) was added to a solution of PdCl2ðPhCNÞ (0.038
2
mg, 0.1 mmol) in acetonitrile (2 ml), the yellow solid formed was
dissolved by adding CH2Cl2 or DMF. Diffusion of ethyl ether into the
filtrate results in the formation of yellow crystals of 1 or 2. 1H NMR of
1 (DMSO-d6, ppm): d 7.98–8.00 (d, 2H, Ar–H), d 7.50–7.69 (m, 12H,
Ar–H), d 3.36–3.41 (m, 4H, –OCH2), d 1.07–1.11 (m, 6H, –CH3). 1H
NMR of 2 (DMSO-d6, ppm): d 7.98–8.00 (d, 2H, Ar–H), d 7.95 (s, 1H,
C–H), d 7.51–7.70 (m, 12H, Ar–H), d 2.89 (s, 3H, –CH3), d 2.73 (s, 3H,
–CH3).
Crystal data for 2: monoclinic, P21=c, a ¼ 8:138ð3Þ, b ¼ 15:944ð4Þ,
ꢀ
ꢀ3
c ¼ 16:371ð2Þ A, b ¼ 93:71ð2Þ°, V ¼ 2119:7ð11Þ A , Z ¼ 2, T ¼ 293 K.
3729 independent (Rint ¼ 0:0225) with 2376 ½I > 2rðIފ observed data,
R1 ¼ 0:0345, wR2 ¼ 0:0768, GOF ¼ 1.032.
Crystal data for 3: monoclinic, C m, a ¼ 16:585ð6Þ, b ¼ 11:269ð4Þ,
ꢀ
ꢀ3
c ¼ 12:661ð4Þ A, b ¼ 101:05ð3Þ°, V ¼ 2322:4ð15Þ A , Z ¼ 2, T ¼ 293
K. 1677 independent with 1377 ½I > 2rðIފ observed data, R1 ¼ 0:0650,
wR2 ¼ 0:167, GOF ¼ 1.107.
1387-7003/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S1387-7003(03)00002-9

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S. Carlson et al. / Inorganic Chemistry Communications 6 (2003) 455–458
total) by using the PLATON program (VOID) [4].
Differential scanning calorimetry (DSC) measurement
reveals that the guest ethyl ether molecules are liberated
at 99 °C, a temperature much higher than its boiling
point. After loss of the ethyl ether molecules, 1 melted at
233 °C, and then decomposed at 270 °C. Compound 2
has a different packing arrangement to 1. In 2,
PdCl2ðdpbÞ2 monomers are combined through C–H
ꢀ ꢀ ꢀ p interactions of the phenyl rings parallel to the c axis
to form a 3D network with 1D channels along the a
axis (Fig. 4). The channel volume per unit is estimated to
ꢀ3
be 471 A (22.2% of the total) by using the PLATON
program (VOID) [4]. The channels are filled with DMF
guest molecules, which are also linked to the O1 atoms
through hydrogen bonding interactions (O1 ꢀ ꢀ ꢀ O55a ¼
a
ꢀ
2:5807 A, O1–H1 ꢀ ꢀ ꢀ O55 ¼ 160:00°, a ¼ 1 þ x; y; z).
DSC result indicates that the DMF molecules are lost
from 2 at 140 °C, and then it melts at 250 °C, followed
by decomposition.
When 1 was dried at 120 °C under vacuum (2 Torr)
for 5 h to remove ethyl ether molecules, the resulting
dried solids can selectively bind guest molecules con-
taining oxygen atoms such as THF and ether. The ex-
periment was done by suspending dried solids in a 1:1
mixture of THF/ether, ether/benzene or ether/CH2Cl2,
and allowing to stand overnight. After filtration and
drying, the solids were dissolved in DMSO-d6. The re-
Fig. 1. ORTEP drawing for 1.
1
sults of H NMR spectra indicated that compounds of
stoichiometry ½PdCl2ðdpbÞ2Š ꢀ 1:5THF ꢀ 0:5Et2O, ½PdCl2
ðdpbÞ2Š ꢀ 2Et2O ꢀ 0:5C6H6 and ½PdCl2ðdpbÞ2Š ꢀ 1:7Et2O ꢀ
0:4CH2Cl2 were obtained. The X-ray powder pattern of
dried 1 (obtained using the conditions stated above) did
not differ substantially from that of the crystals of 1.
This suggests that some of the structural integrity of
the sample was maintained after the lattice solvent was
removed.
the ‘‘behind’’ phenyl ring of the adjacent PdCl2ðdpbÞ2
by weak p ꢀ ꢀ ꢀ p interactions (the shortest atom–atom
ꢀ
distance between the two phenyl rings is 3.9 A, and the
shortest distance between the two phenyl planes is 3.0
ꢀ
A), resulting in a 1D rhombus channel with a dimension
ꢀ
of 9:9 Â 9:9 A (Fig. 3). Ethyl ether molecules fill the
voids of the channels, and they are linked with O2 atoms
through hydrogen bonding interactions (O2 ꢀ ꢀ ꢀ O3 ¼
The DMF molecules in 2 were removed by drying the
crystals of 2 at 175 °C under vacuum (2 Torr) for 5 h,
and the solubility of the dried solid from 2 is greater
ꢀ
2:6754 A), O2–H1 ꢀ ꢀ ꢀ O3 ¼ 175:55°). The channel vol-
ꢀ3
ume per unit is estimated to be 422 A (35.7% of the
Fig. 2. ORTEP drawing for 2.

S. Carlson et al. / Inorganic Chemistry Communications 6 (2003) 455–458
457
Fig. 3. Structure views of 1 along the c axis, showing the 1D channels. (a) The molecular packing arrangement. (b) A space-filling model. All ethyl
ether molecules are omitted for clarity.
than that of dried 1, for example, 1 is insoluble in a 1:1
mixture of THF/ether, ether/benzene or ether/CH2Cl2,
while 2 is soluble in these solvent mixtures, and even
slightly soluble in the 1:4 mixture of THF/ether. This
can be attributed to weaker C–H ꢀ ꢀ ꢀ p interactions in 2.
Material from dried 2 was immersed in the 1:4 mixture
of THF/ether. After about 20 h, the solid was filtered,
dried, and then dissolved in DMSO-d6. The results of
1H NMR spectra indicated that a compound of stoi-
chiometry ½PdCl2ðdpbÞ2Š ꢀ THF ꢀ 0:7Et2O was formed.
More interestingly, when dried 2 was suspended in a 1:4
mixture of THF/ether, a few single crystals which turned
out to be ½PdCl2ðdpbÞ2Š ꢀ THF, 3, were obtained from
the solution. X-ray analysis 2 indicates that the network
structure of 3 is constructed by p ꢀ ꢀ ꢀ p interactions to
form 1D channels along the c axis (Fig. 5), similar to
that of 1. The channel volume per unit is estimated to be
842 A (36.3% of the total) by using the PLATON
program (VOID) [4]. The channels are filled with THF
guest molecules. Crystals of 3 were probably formed
ꢀ3
Fig. 4. Structure views of 2 along the a axis, showing the 1D channels. (a) The molecular packing arrangement. (b) A space-filling model. All DMF
molecules are omitted for clarity.

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S. Carlson et al. / Inorganic Chemistry Communications 6 (2003) 455–458
Fig. 5. Structure views of 3 along the c axis, showing the 1D channels. (a) The molecular packing arrangement. (b) A space-filling model. All THF
molecules are omitted for clarity.
from dried 2 dissolving in the 1:4 mixture of THF/ether
upon suspension in this solution, and then crystallizing
to form 3. Crystals of 1 were formed from a solution
mixture of acetonitrile, dichloromethane and ethyl
ether, and only ethyl ether molecules were bonded in the
crystals. When the crystals were obtained from a solu-
tion mixture of acetonitrile, DMF and ethyl ether, DMF
molecules cocrystallized as evident in the structure of 2.
When dried solid from 2 was immersed in a 1:4 solution
of THF and ethyl ether, crystals containing THF mol-
ecules were obtained as the structure of 3 indicated.
From these and the 1H NMR results it can be concluded
that the order of selectivity is THF, DMF >
ethyl ether > CH2Cl2, benzene. These selected guest
molecule binding properties are attributed to hydrogen
bonding interactions between the oxygen atoms of these
molecules and the carboxylic acid moiety of the dpb
ligand.
Acknowledgements
This work was supported by the NSF (CHE-0079158).
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constructed via p ꢀ ꢀ ꢀ p or C–H ꢀ ꢀ ꢀ p interactions, and can
selectively absorb small organic molecules. The results
indicate that the guest molecules can affect network
structures, and that the solubility is affected by the
network structures.
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