Synthesis of an unusual, cage-functionalized molecular cleft

Article abstract of DOI:10.1023/A:1014311703618

The synthesis and X-ray crystal structure of a novel, cage-functionalized bis(α-diketone), 4, is described. A molecular cleft is formed by two parallel planar aromatic diketone units bridged by a polycarbocyclic cage. Crystal data: T = 100(1) K, monoclini

Full text of DOI:10.1023/A:1014311703618

C
Journal of Chemical Crystallography, Vol. 31, No. 3, March 2001 ( 2002)
Synthesis of an unusual, cage-functionalized
molecular cleft
A. Alan Pinkerton,(1)* Michaele J. Hardie,(1)† Alan P. Marchand,(2)
and Kaipenchery A. Kumar(2)
Received February 23, 2001
The synthesis and X-ray crystal structure of a novel, cage-functionalized bis( -diketone),
4, is described. A molecular cleft is formed by two parallel planar aromatic diketone units
bridged by a polycarbocyclic cage. Crystal data: T = 100(1) K, monoclinic, C2/c, a =
3
˚
˚
35.6383(2), b = 11.8110(1), c = 15.6319(2) A, = 110.7745(2) , V = 6152.04(9) A ,
Z = 12, R = 0.0691. Compound 4 is of potential interest as a new type of “host” molecule
for the study of host–guest interactions in solution.
KEY WORDS: X-ray structure; polycarbocyclic cage; cage-functionalized molecular cleft.
Introduction
Experimental section
As part of an ongoing program devoted to
Melting points are uncorrected. Elemental
microanalytical data was obtained by personnel
at M-H-W Laboratories, Phoenix, AZ.
the synthesis and chemistry of novel polycarbo-
cyclic “cage” compounds,1 we recently reported
the preparation of several examples of cage-
4
functionalized molecular clefts2
and crown
exo-8,exo-11-Bis(20-phenylethynyl)pentacyclo
[5.4.0.02,6.03,10.05,9]undecane-endo-8,endo-11-
diol (2)
ethers.5,6 Compounds of this type are of interest
as members of a new class of “host” systems for
the study of host–guest interactions (i.e., molecu-
lar recognition and inclusion phenomena). As an
extension of these past studies, our attention has
turned to the preparation and characterization of
an unusual, cage-functionalized molecular cleft, 4
(Scheme 1).
A solution of phenylacetylene (1.86 g,
18.2 mmol) in dry THF (20 mL) under argon
was cooled to 0 C via application of an exter-
nal ice-water bath. To this cooled solution was
added dropwise with stirring n-BuLi (7.3 mL
of 2.5 M solution in hexane, 18.3 mmol). Af-
ter all of the organometallic reagent had been
added, the reaction mixture was stirred at 5 C for
0.5 h. Pentacyclo[5.4.0.02,6.03,10.05,9]undecane-
8,11-dione (1, 793 mg, 4.55 mmol) then was
added to the reaction mixture in one portion,
and the resulting mixture was refluxed at ca.
60 C for 24 h. The reaction mixture was cooled
(1) Department of Chemistry, University of Toledo, Toledo, Ohio.
(2) Department of Chemistry, University of North Texas, Denton,
Texas.
*To whom correspondence should be addressed; e-mail: apinker@
uoft02.utoledo.edu.
†
Present address: School of Chemistry, The University of Leeds,
Woodhouse Lane, Leeds LS2 9JT, UK.
135
C
1074-1542/01/0300-0135/0 2002 Plenum Publishing Corporation

136
Pinkerton, Hardie, Marchand, and Kumar
Scheme 1
to 0 and then quenched via addition of sat-
urated aqueous NH4Cl (20 mL). The resulting
aqueous suspension was extracted with EtOAc
(2 40 mL). The combined extracts were washed
with water (20 mL), dried (MgSO4), and filtered,
and the filtrate was concentrated in vacuo. The
residue was purified via fractional recrystalliza-
tion from acetone–hexane, thereby affording 2
(1.06 g, 62%) as a colorless microcrystalline solid:
mp 186–187 C; IR (KBr): 3000–3300 (br, m),
acid (TsOH, 50 mg, catalytic amount). The re-
sulting mixture was refluxed in a Dean-Stark ap-
paratus until the distillate was no longer cloudy
(ca. 4 h). The reaction mixture was allowed to
cool gradually to ambient temperature and was
washed successively with 10% aqueous NaHCO3
(10 mL) and water (10 mL). The organic layer
was dried (MgSO4) and filtered, and the fil-
trate was concentrated in vacuo. The residue
was purified via column chromatography on neu-
tral alumina by eluting with 1:1 CH2Cl2–hexane.
Pure 3 (385 mg, 81%) was thereby obtained
as a colorless microcrystalline solid: mp 114.0–
114.5 C; IR (KBr): 2963 (m), 2860 (w), 1491
2977 (m), 2867 (w), 1491 (s), 1132 (s), 1063 (m),
1
752 cm
(vs); 1H NMR (CDCl3):
1.19
(AB, JAB = 10.3 Hz, 1H), 1.72 (AB, JAB
=
10.3 Hz, 1H), 2.63–3.04 (m, 8H), 4.70–6.01 (br,
2H, peak disappeared when sample was shaken
with D2O), 7.22–7.46 (m, 10H); 13C NMR
(CDCl3): 34.1 (t), 39.9 (d), 45.1 (d), 45.8 (d),
52.0 (d), 74.2(s), 84.0 (s), 92.5(s), 122.8(s), 128.2
(2 C, d, determined via integration of the gated-
decoupled 13C NMR spectrum), 131.6 (d). Anal.
Calcd for C27H22O2: C, 85.69; H, 5.86. Found: C,
85.43; H, 5.59.
1
(m), 1374 (s), 1174 (s), 856 (s), 725 cm (s);
1H NMR (CDCl3): 1.63 (AB, JAB = 10.1 Hz,
1H), 1.99 (AB, JAB = 10.1 Hz, 1H), 2.66–
3.17 (m, 8H), 7.18–7.51 (m, 10H); 13C NMR
(CDCl3): 42.0 (d), 43.4 (t), 44.5 (d), 52.1 (d),
61.7 (d), 85.8 (s), 87.3 (s), 87.4 (s), 122.6 (s),
128.2 (d), 128.4 (d), 131.7 (d). Anal. Calcd for
C27H20O: C, 89.97; H, 5.59. Found: C, 89.72;
H, 5.80.
3,5-Bis(20-phenylethynyl)hexacyclo[5.4.1.0.02,6
3,10.05,9]dodecane (3)
.
0
Oxidation of 3
To a solution of 2 (500 mg, 1.32 mmol) in
drybenzene(50mL)wasadded p-toluenesulfonic
To a solution of 3 (1.10 g, 3.05 mmol) in
dry CH2Cl2 (100 mL) under argon was added

Cage-functionalized molecular cleft
137
Table 1. Crystal Data and Summary of Intensity Data Collection
sequentially KMnO4 (8.70 g, 55 mmol), ben-
zyl tri(n-butyl)ammonium bromide (TEBAC,
200 mg, catalytic amount), and HOAc (3.30 g,
55 mmol), and the resulting mixture was refluxed
for 4 h. The reaction mixture then was cooled
to 5 C via application of an external ice-water
bath. To this cooled solution was added portion-
wise solid Na2S2O5 (10 g, 53 mmol) with stir-
ring. After all of the Na2S2O5 had been added, the
reaction mixture was stirred at 5 C for 20 min,
at which time water (25 mL) and 10% aque-
ous H2SO4 (10 mL) were added sequentially
to the reaction mixture. The organic layer was
separated, washed with water (10 mL), dried
(MgSO4), and filtered, and the filtrate was con-
centrated in vacuo. The residue was purified via
column chromatography on silica gel by elut-
ing with 1:1 CH2Cl2–hexane). Pure 4 (866 mg,
67%) was thereby obtained as a pale yellow mi-
crocrystalline solid: mp 112–113 C; IR (KBr):
2998 (w), 2984 (w), 2867 (w), 1720 (s), 1678
(vs), 1594 (m), 1443 (m), 1264 (m), 787 (m),
and Structure Refinement
Compound
4
Formula
C
27H20O5
CCDC deposit no.
Color/shape
Formula weight
Temperature, K
Crystal system
Space group
CCDC-1003/6014
Colorless/plate
424.46
100(1)
Monoclinic
C2/c
˚
˚
Unit cell dimensions
(8192 reflections in full
range)
a = 35.6383(2) A
b = 11.8110(1) A
˚
c = 15.6319(2) A
= 110.7745(2)
3
˚
Volume, A
6152.04(9)
Z
12
1.375
0.095
Density (calculated), Mg/m3
Absorption coefficient, mm
Diffractometer/scan
1
Siemens SMART/1k CCD
area detector/ω scan
˚
Radiation, graphite
monochromator
Mo K , 0.71073 A
range for data collection, deg
Reflections measured
2.16–28.29
19839
Independent/observed reflections
7597 (R = 0.0465)/5203
int
[I > 2 (I)]
Data/restraints/parameters
Goodness of fit on F2
Final R indices [I > 2 (I)]
R indices (all data)
7597/0/562
1.030
1
1
718 cm (m); H NMR (CDCl3): 1.64 (AB,
JAB = 10.1 Hz, 1H), 2.02 (AB, JAB = 10.1 Hz,
1H), 2.71–3.42 (m, 8H), 7.34–7.81 (m, 10H); 13C
NMR (CDCl3): 42.6 (d), 43.5 (t), 45.5 (d),
50.4 (d), 59.1 (d), 99.5 (s), 128.7 (d), 129.6 (d),
132.0 (s), 134.6 (d), 193.2 (s), 201.6 (s). Anal.
Calcd for C27H20O5: C, 76.40; H, 4.75. Found: C,
76.62; H, 4.87.
R1 = 0.0691, wR2 = 0.1849
R1 = 0.1000, wR2 = 0.2043
anisotropic displacement parameters. Positional
parameters and isotropic displacement parameters
were refined for all hydrogen atoms. Structure so-
lution and refinement are summarized in Table 1,
final refined coordinates are reported in Table 2,
and selected distances and angles in Table 3.
Crystallography
A colorless fragment of 4 was mounted on a
fine glass fiber with epoxy resin. Preliminary ex-
amination and data collection were carried out at
100(1) K on a Siemens SMART 1k CCD Platform
diffractometer. 0.1 ω scans with 60 sec. exposure
time were carried out at three different settings
corresponding to a nominal hemisphere of data.
The intensities were corrected for absorption and
decay (SADABS7). The structure was solved by
direct methods (SHELXS-868) in the space group
C2/c. All non-hydrogen atoms were refined using
full-matrix least-squares (SHELXL-939) with
Results and discussion
The procedure that we employed to prepare
4 is analogous to a portion of the reaction
sequence used recently to synthesize “alba-
trossenes,” a class of molecular clefts that
contain large benzenoid aromatic groups attached
to -diketone “arms.”10 Thus, reaction of a
readily available pentacyclic cage diketone, i.e.
pentacyclo [ 5.4.0.02,6.03,10.05,9] undecane - 8,11 -
dione (1)11 with excess 1-lithio-2-phenylethyne

138
Pinkerton, Hardie, Marchand, and Kumar
a
˚
Table 3. Bond Lengths (A) and Angles (deg) for 4
Table 2. Atomic Coordinates and Equivalent Isotropic Displace-
2
˚
ment Parameters (A ) for 4
Molecule 1
Molecule 2
a
x
y
z
Ueq
Bond length
----
----
O1
O2
O3
O4
O5
O6
O7
O8
C1
C2
C3
C4
C5
C6
C7
C8
0.16927(4)
0.15894(5)
0.22483(4)
0.17970(5)
0.11144(4)
0.0000
0.20348(11) 0.25468(9) 0.0199(3)
0.14502(13) 0.02803(11) 0.0362(4)
0.31059(13) 0.14519(12) 0.0364(4)
0.15128(12) 0.48265(10) 0.0298(4)
0.30644(12) 0.36845(11) 0.0294(4)
O1 C4
1.441(2) C28 C29
1.442(4)
1.415(4)
1.538(3)
1.507(3)
1.543(2)
1.564(3)
1.558(2)
1.496(2)
1.564(3)
1.536(3)
1.414(4)
1.922(4)
1.536(3)
1.480(2)
1.398(3)
1.395(3)
1.383(3)
1.390(3)
1.393(3)
1.393(3)
I
----
----
O1 C9
1.439(2) C28 C33
----
----
O2 C12
1.211(2) C29 C30
----
----
O3 C13
1.222(2) C29 C33
----
----
O4 C20
1.214(2) C30 C31
I
I
----
----
0.31017(14) 0.2500
0.0167(4)
O5 C21
1.217(2) C30 C32
----
----
0.01149(4)
0.05612(4)
0.12554(7)
0.14452(6)
0.13277(6)
0.16893(5)
0.20498(6)
0.18971(6)
0.14372(7)
0.13196(6)
0.16855(6)
0.20430(6)
0.18892(6)
0.16998(6)
0.18837(6)
0.16162(5)
0.17825(6)
0.15354(7)
0.11233(7)
0.09561(6)
0.12025(6)
0.16786(5)
0.14757(6)
0.17257(6)
0.21373(6)
0.23673(6)
0.21843(7)
0.17763(7)
0.15459(6)
0.04195(11)
0.02226(6)
0.03586(5)
0.00012(5)
0.03649(5)
0.02296(6)
0.00051(5)
0.01993(5)
0.00580(5)
0.01139(6)
0.01236(7)
0.05351(7)
0.07095(6)
0.04705(6)
0.36402(12) 0.47805(9) 0.0263(3)
0.20547(12) 0.36355(11) 0.0302(4)
O6 C31
1.442(2) C31 C32
----
----
O7 C34
1.212(2) C31 C34
----
----
0.1477(2)
0.0794(2)
0.0441(2)
0.1216(2)
0.0423(2)
0.0805(2)
0.0765(2)
0.0461(2)
0.1238(2)
0.0444(2)
0.0787(2)
0.1854(2)
0.3044(2)
0.4032(2)
0.5121(2)
0.6061(2)
0.5924(2)
0.4849(2)
0.3896(2)
0.1893(2)
0.3057(2)
0.4076(2)
0.3995(2)
0.4970(2)
0.6026(2)
0.6114(2)
0.5142(2)
0.6641(3)
0.5934(2)
0.2219(2)
0.0309(5)
O8 C35
1.217(2) C32 C30
----
----
0.16487(15) 0.0272(4)
0.17508(14) 0.0209(4)
0.18613(13) 0.0191(4)
0.23626(14) 0.0252(4)
0.2242(2)
0.3085(2)
0.27503(13) 0.0213(4)
0.32372(13) 0.0199(4)
0.33540(14) 0.0245(4)
0.32501(14) 0.0283(5)
0.10419(14) 0.0232(4)
0.12251(14) 0.0242(4)
0.10975(13) 0.0198(4)
0.11938(15) 0.0259(4)
C1 C2
1.526(3) C32 C33
I
I
----
----
C2 C3
1.542(3) C33 C28
----
----
C3 C4
1.539(3) C33 C29
----
----
C5 C4
1.558(3) C34 C35
----
----
0.0288(5)
0.0280(5)
C5 C6
1.537(3) C35 C36
----
----
C5 C10
1.559(3) C36 C37
----
----
C6 C2
1.547(3) C36 C41
----
----
C9
C6 C11
1.586(3) C37 C38
----
----
C10
C11
C12
C13
C14
C15
C16
C17
C18
C19
C20
C21
C22
C23
C24
C25
C26
C27
C28
C29
C30
C31
C32
C33
C34
C35
C36
C37
C38
C39
C40
C41
C7 C1
1.529(3) C38 C39
----
----
C7 C8
1.546(3) C39 C40
----
----
C7 C11
1.539(3) C40 C41
----
C8 C3
1.573(3)
1.555(3)
1.540(2)
1.502(3)
1.543(3)
1.498(3)
1.534(3)
1.475(3)
1.403(3)
1.399(3)
1.385(3)
1.393(3)
1.389(3)
1.397(3)
1.532(2)
1.477(3)
1.398(3)
1.398(3)
1.391(3)
1.392(3)
1.387(3)
1.389(3)
----
C8 C9
----
C9 C10
----
0.1055(2)
0.0291(5)
C9 C20
----
0.08287(15) 0.0280(5)
0.07398(14) 0.0249(4)
0.08761(14) 0.0222(4)
0.40553(13) 0.0202(4)
0.38621(13) 0.0205(4)
0.39371(13) 0.0202(4)
0.41072(14) 0.0236(4)
0.4198(2)
0.4117(2)
0.3949(2)
C10 C11
----
C12 C4
----
C12 C13
----
C13 C14
----
C14 C15
----
C14 C19
----
C15 C16
----
0.0291(5)
0.0305(5)
0.0292(5)
C16 C17
----
C17 C18
----
C18 C19
----
0.38552(14) 0.0239(4)
0.2833(3)
0.3298(2)
C20 C21
----
0.0194(7)
0.0283(5)
C21 C22
----
C22 C23
----
0.46981(15) 0.32996(12) 0.0159(4)
0.39117(14) 0.31897(12) 0.0159(4)
0.46971(15) 0.26956(13) 0.0161(4)
C22 C27
----
C23 C24
----
C24 C25
----
0.5930(2)
0.32637(15) 0.40087(13) 0.0182(4)
0.2084(2) 0.38246(13) 0.0196(4)
0.10730(15) 0.39278(13) 0.0190(4)
0.2926(2)
0.0333(5)
C25 C26
----
C26 C27
Bond angle
I
---- ----
----
----
----
----
----
----
C9 O1 C4
96.95(13) C29 C28 C33
84.6(2)
0.0004(2)
0.0960(2)
0.0848(2)
0.0220(2)
0.1184(2)
0.38452(15) 0.0234(4)
0.3973(2) 0.0285(5)
0.41887(15) 0.0284(5)
0.42653(14) 0.0254(4)
0.41324(13) 0.0209(4)
---- ----
C7 C1 C2
----
95.2(2)
104.3(2)
103.2(2)
102.1(2)
109.1(2)
102.6(2)
C28 C29 C30 109.9(2)
---- ----
----
C1 C2 C3
C28 C29 C33 116.9(2)
I
---- ----
C6 C2 C1
----
C30 C29 C33
83.31(14)
---- ----
----
C6 C2 C3
C30 C29 C33 106.9(2)
I
---- ----
----
----
C2 C3 C4
C33 C29 C33
90.3(2)
P P
---- ----
C8 C3 C2
---- ----
C29 C30 C31 108.81(14)
aUeq = (1/3)
j Ui j ai aj ai aj .
i

Cage-functionalized molecular cleft
139
Table 3. Continued
Table 3. Continued
Molecule 2
Molecule 1
Molecule 2
Molecule 1
I
---- ----
C8 C3 C4
----
----
----
----
----
----
----
----
----
----
----
----
100.89(15) C29 C30 C32 96.60(15)
C22 C23 C24 120.2(2)
I
---- ----
O1 C4 C3
---- ----
105.56(14) C31 C30 C32 101.15(14)
C23 C24 C25 119.5(2)
---- ----
O1 C4 C5
---- ----
103.99(15) O6 C31 C30 105.07(13)
C24 C25 C26 120.7(2)
---- ----
O1 C4 C12
107.56(15) O6 C31 C32 104.29(13)
---- ----
C25 C26 C27 119.9(2)
---- ----
C22 C27 C26 120.0(2)
---- ----
C5 C4 C3
101.97(15) O6 C31 C34 107.68(14)
---- ----
----
----
C5 C4 C12
117.8(2)
118.5(2)
108.2(2)
90.4(2)
C30 C31 C32 102.08(14)
---- ----
---- ----
aSymmetry operation to generate equivalent atoms: I x, y,
z+ 1/2.
C12 C4 C3
C30 C31 C34 118.2(2)
---- ----
----
----
----
C6 C5 C4
C32 C31 C34 118.05(14)
I
---- ----
C6 C5 C10
----
C31 C32 C30 100.99(13)
---- ----
C10 C5 C4
----
----
----
----
100.92(14) C31 C32 C33 108.16(14)
I
---- ----
----
C5 C6 C2
108.3(2)
89.8(2)
C33 C32 C30 96.8(2)
afforded the corresponding cage diol 2 (62%
yield). Subsequent acid promoted cycloelimi-
nation of water from 2 afforded 3,5-bis(20-phenyl-
ethynyl)hexacyclo[5.4.1.0.02,6.03,10.05,9]dodeca-
ne (3, 81% yield). Finally, application of the
oxidation procedure described by Pascal et al.7
converted 3 into the target tetraketone 4 (67%
yield). The structure of 4 was established
unambiguously via application of X-ray crystal-
lographic techniques.
I
---- ----
C5 C6 C11
----
C28 C33 C29 116.7(2)
---- ----
----
----
----
----
----
----
----
C11 C6 C2
102.4(2)
103.7(2)
102.4(2)
103.2(2)
C28 C33 C32 110.5(2)
I
---- ----
----
C8 C7 C1
C29 C33 C29 89.7(2)
---- ----
----
C8 C7 C11
C29 C33 C32 107.3(2)
I
---- ----
----
C11 C7 C1
C32 C33 C29 83.31(15)
---- ----
C7 C8 C3
----
102.90(15) O7 C34 C31 123.8(2)
---- ----
----
C7 C8 C9
107.9(2)
O7 C34 C35 119.7(2)
---- ----
---- ----
C9 C8 C3
100.82(15) C31 C34 C35 116.4(2)
---- ----
---- ----
O1 C9 C8
104.70(14) O8 C35 C34 116.1(2)
---- ----
---- ----
O1 C9 C10
104.66(15) O8 C35 C36 124.4(2)
---- ----
---- ----
O1 C9 C20
108.15(15) C34 C35 C36 119.4(2)
---- ----
C8 C9 C10
----
----
----
102.4(2)
117.2(2)
118.4(2)
C35 C36 C37 119.4(2)
---- ----
----
C8 C9 C20
C35 C36 C41 120.7(2)
---- ----
---- ----
C10 C9 C20
C37 C36 C41 119.9(2)
---- ----
----
----
C5 C10 C9
---- ----
101.30(15) C36 C37 C38 120.3(2)
----
----
----
C5 C10 C11
---- ----
90.6(2)
108.3(2)
102.7(2)
89.2(2)
108.2(2)
123.0(2)
120.8(2)
116.1(2)
116.7(2)
124.2(2)
C37 C38 C39 119.8(2)
----
C9 C10 C11
---- ----
C38 C39 C40 120.5(2)
---- ----
C6 C11 C7
---- ----
C39 C40 C41 119.8(2)
---- ----
C6 C11 C10
---- ----
C36 C41 C40 119.7(2)
C7 C11 C10
---- ----
O2 C12 C4
---- ----
O2 C12 C13
---- ----
C13 C12 C4
---- ----
O3 C13 C12
---- ----
O3 C13 C14
---- ----
C12 C13 C14 119.1(2)
---- ----
C13 C14 C15 118.9(2)
---- ----
C13 C14 C19 121.1(2)
---- ----
C15 C14 C19 120.0(2)
---- ----
C14 C15 C16 119.8(2)
---- ----
C15 C16 C17 120.1(2)
---- ----
C16 C17 C18 120.5(2)
---- ----
C17 C18 C19 119.8(2)
---- ----
C14 C19 C18 119.7(2)
----
----
----
O4 C20 C9
123.4(2)
120.1(2)
116.3(2)
116.0(2)
124.9(2)
----
O4 C20 C21
---- ----
C9 C20 C21
---- ----
O5 C21 C20
---- ----
O5 C21 C22
---- ----
C20 C21 C22 119.1(2)
---- ----
C21 C22 C23 121.5(2)
---- ----
Fig. 1. Molecule 1 showing the cage and molecular cleft
and atom numbering (50% probability ellipsoids). Hydrogen
atoms have been omitted for clarity.
C21 C22 C27 118.9(2)
---- ----
C23 C22 C27 119.7(2)

140
Pinkerton, Hardie, Marchand, and Kumar
The structure consists of two crystallograph-
It is clearly shown in Fig. 1 that a molecular
cleft with potential for behaving as a host for a va-
riety of guest molecules is formed by two planar
aromatic diketone moieties linked by a polycar-
bocyclic cage. An indication of the size of the
cleft may be obtained from the distances between
pairs of atoms in the ordered molecule. The op-
posite pairs of carbonyl carbons are separated by
ically distinct molecules. The atoms of one
molecule (O1 O5, C1 C27) lie on general po-
sitions. The second molecule has a symmetry im-
posed disorder with the molecule lying across
the twofold axis with O6 lying on the twofold
axis. The CH2 group of the cage is disordered
with atoms C28, H28A, and H28B having 50%
site occupancies. The probability ellipsoids of
C29 and C33 are slightly elongated along the
C29 C33I and C33 C29I bonds as would be an-
ticipated for this type of disorder. A structurally
similar disorder was also apparent for the solution
obtained in the noncentrosymmetric space group
Cc, hence, the description in the centrosymmetric
space group is preferred. ORTEP plots of the two
molecules showing the atom numbering scheme
and the disorder model are shown in Figs. 1 and 2.
˚
4.738(3) and 4.833(3) A. Opposite pairs of phenyl
˚
carbons are separated by 4.403(3) to 4.738(3) A.
Acknowledgments
We thank the Robert A. Welch Foundation [Grant
B-963 (APM)], the Office of Naval Research [Grants
N00014-98-1-0478 (APM), N00014-95-1-0013, and
N00014-95-1-1252 (AAP)], the U.S. Department of
Energy [Grant DE-FG07-98ER14936 (APM)], and the
Texas Advanced Technology Program [Grant 003659-
0206-1999 (APM)] for financial support of this study.
Finally, we thank Dr Sulejman Alihodzic, University
of North Texas, for having kindly obtained the infrared
spectra of 2, 3, and 4.
Supplementary material
Crystallographic data (excluding structure
factors) for the structure reported in this paper
have been deposited with the Cambridge Crystal-
lographic Data Centre as supplementary publica-
tion CCDC-1003/6014. Copies of available mate-
rial can be obtained, free of charge, on application
to the CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (e-mail: deposit@ccdc.cam.ac.uk).
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