Novel tripodal chelating ligand for appending and encapsulating metal ions. Crystal structure of a parachute-like hydrogen bonded complex

Article abstract of DOI:10.1039/b003694n

Tripodal ligand 1,3,5-tris(1-methylimidazol-2-ylmethyl)-2,4,6-trimethylbenzene (3) forms a parachute-like non-covalent complex with zinc tetrachloride, 5.[Zn₂Cl₆]_0.5, where the imidazoles of the ligand are protonated and bind to the metal ion through NH···Cl hydrogen bonds.

Full text of DOI:10.1039/b003694n

Novel tripodal chelating ligand for appending and encapsulating metal ions.
Crystal structure of a parachute-like hydrogen bonded complex
Wei-Yin Sun,*a Jin Xie,a Taka-aki Okamura,b Chang-Kang Huanga and Norikazu Ueyamab
a Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing
210093, China. E-mail: sunwy@netra.nju.edu.cn
b Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560,
Japan
Received (in Cambridge, UK) 9th May 2000, Accepted 19th June 2000
Tripodal ligand 1,3,5-tris(1-methylimidazol-2-ylmethyl)-
complexes.4 Up to now, tripodal ligands 1 and 2, and others also
having benzene or other arene as the ring core such as
2,4,6-tris(4-pyridyl)-1,3,5-triazine, 1,3,5-tris(pyrazol-1-ylme-
thyl)-2,4,6-triethylbenzene have been reported to form poly-
meric networks or multinuclear metallocages with metal ions.4,5
The ligand 3 was demonstrated for the first time to form a
parachute-like non-covalently bonded complex with zinc tetra-
chloride. [ZnCl4]22 has been used as a counterion for
crystallization of Ru(II) and Co(II) complexes.6,7 In the present
complex, this anion binds to 3 through NH…Cl interactions in
which the Cl atom acts as an acceptor of hydrogen bonds.
Assembly of 3† with ZnCl2 in hydrochloric acid solution
gave the hydrogen bonded complex, 5·[Zn2Cl6]0.5 (Scheme 1).‡
As shown in Fig. 1,§ all three imidazole groups of 3 are
protonated which was confirmed by IR spectral measurements.
The distances between each imidazole proton and Cl(12) ranges
from 2.32 to 2.45 Å which indicates the presence of triple N–
H…Cl hydrogen bonds. Therefore, 5 looks like a parachute in
which [ZnCl4]22 acts as an appending group. The atom Cl(12)
is located under 3 with a distance of 3.43 Å between Cl(12) and
the center of the benzene ring plane. Two adjacent molecules of
5 with normal and upside down orientations linked by hydrogen
bonds are illustrated in Fig. 2(a). There are four additional
hydrogen bonds in each [ZnCl4]22 unit excluding the triple N–
H…Cl(12) bonds described above: C(14)–H…Cl(11)
[rC(14)–Cl(11) = 3.517(8) Å], C(11A)–H…Cl(11) [rC(11A)–Cl(11)
= 3.707(6) Å], C(54)–H…Cl(13) [rC(54)–Cl(13) = 3.602(7) Å]
and C(101A)–H…Cl(14) [rC(101A)–Cl(14) = 3.768(8) Å]. The
unit shown in Fig. 2(a) can be repeated and joined by
2,4,6-trimethylbenzene (3) forms a parachute-like non-
covalent complex with zinc tetrachloride, 5·[Zn2Cl6]0.5
,
where the imidazoles of the ligand are protonated and bind
to the metal ion through NH···Cl hydrogen bonds.
Although biological systems efficiently organize simple units
into aggregates with intricate and wonderful functions by non-
covalent interactions, self-assembly of frameworks with spe-
cific topology, interesting properties and functions is still a
challenge for chemists.1 A number of hydrogen-bonded ag-
gregates have been obtained by self-organization of organic or
organic–inorganic components.1–3 We herein report a para-
chute-like complex obtained by assembly of organic tripodal
ligand
1,3,5-tris(1-methylimidazol-2-ylmethyl)-2,4,6-trime-
thylbenzene (3) and inorganic zinc tetrachloride. In this
complex, protonation of the imidazoles of the ligand and its
binding to the metal ion through NH…Cl hydrogen bonds
provides a good example of a dual role for a single ligand.
We are currently engaged in the systematic study of self-
assembly of tripodal ligands 1–4 (Scheme 1) with various metal
ions and are investigating the influence of linkage mode of
bridging ligands on the assembly process of supramolecular
Fig. 1 Crystal structure of 5, thermal ellipsoids are drawn at 50% probability
and the N–H…Cl hydrogen bonds are indicated by dashed lines. Selected
bond lengths (Å) and angles (°): Zn1–Cl11 = 2.269(1), Zn1–Cl12 =
2.360(1), Zn1–Cl13 = 2.242(2), Zn1–Cl14 = 2.249(2), N12–Cl12 =
3.199(4) [H1–Cl12 = 2.32], N32-Cl12 = 3.194(5) [H2-Cl12 = 2.40],
N52–Cl12 = 3.254(5) [H3–Cl12 = 2.45]; N12–H1–Cl12 = 163, N32–H2–
Cl12 = 154, N52–H3–Cl12 = 162, Cl12–Zn1–Cl11 = 104.64(5), Cl12–
Zn1–Cl13 = 105.86(6), Cl12–Zn1–Cl14 = 108.23(6), Cl11–Zn1–Cl13 =
113.71(6), Cl11–Zn1–Cl14 = 110.28(6), Cl13–Zn1–Cl14 = 113.49(6).
Scheme 1 Reagents: i, ZnCl2 + HCl; ii, Ru(DMSO)4Cl2. For details see
notes of preparations.
DOI: 10.1039/b003694n
Chem. Commun., 2000, 1429–1430
This journal is © The Royal Society of Chemistry 2000
1429

Notes and references
† The ligand 3 was prepared from 1,3,5-tris(bromomethyl)-2,4,6-tri-
methylbenzene, 1-methylimidazole and n-BuLi using standard Schlenk
techniques in 45% isolated yield. dH(CDCl3): 7.05 (s, 3H), 6.91 (s, 3H), 4.24
(s, 6H), 3.90 (s, 9H), 2.07 (s, 9H).
‡ Experimental: a solution of 3 (40.2 mg, 0.1 mmol) in MeOH (5 ml) was
added to a 1 M HCl (10 ml) solution of ZnCl2 (40.8 mg, 0.3 mmol) at room
temperature. The mixture was filtered after stirring for about 10 min and the
filtrate was stood at ca. 40 °C for several days. Light yellow crystals were
collected in ca. 60% yield. Macroanal. Found: C, 36.64; H, 4.22; N, 10.66.
C
24H33N6Cl7Zn2 requires C, 36.75; H, 4.24; N, 10.71%. dH(D2O, 298 K):
7.32 (s, 3H), 7.12 (s, 3H), 4.42 (s, 6H), 3.83 (s, 9H), 2.05 (s, 9H).
§ Crystal data for 5·[Zn2Cl6]0.5 (C24H33N6Cl7Zn2): M = 784.50, triclinic,
¯
space group P1, a = 13.593(4), b = 13.788(4), c = 10.821(3) Å, a =
108.41(2), b = 112.25(2), g = 104.09(2)°, U = 1621(1) Å3, Z = 2, Dc
=
1.606 g cm23, m = 2.081 mm21, F(000) = 796, T = 296(1) K. The data
collection was carried out on a Rigaku AFC5R four-circle diffractometer by
w 2 2q scan techniques using graphite-monochromated Mo-Ka radiation
(l = 0.7107 Å). Total 7720 reflections were collected of which 7408 are
independent (Rint = 0.017). The structure was solved by direct methods
with SIR92 and refined by full-matrix least-squares calculations. The final
Fig. 2 Two adjacent parachute-like molecules with normal and upside down
orientations (a) and one-dimensional chain (b) linked by hydrogen bonds.
[Zn2Cl6]22 through hydrogen bonds to generate an infinite one-
dimensional chain [Fig. 2(b)]: C(301A)–H…Cl(22)
R1 = 0.0431[I > 2s(I)], max., min. residual density: +0.80, 20.96 e Å23
.
CCDC 182/1693. See http://www.rsc.org/suppdata/cc/b0/b003694n/ for
crystallographic files in .cif format.
[rC(301A)–Cl(22)
=
3.620(8) Å] and C(21A)–H…Cl(22)
[rC(21A)–Cl(22) = 3.530(8) Å].
¶ A solution of 3 (40.2 mg, 0.1 mmol) and Ru(DMSO)4Cl2 (48.9 mg, 0.1
mmol) in EtOH–H2O (1 3, 15 ml) was refluxed for 10 h. After filtration, the
filtrate was stood at room temperature for several days and a brown powder
was obtained. dH(D2O, 313 K): 7.36 (s, 3H), 7.03 (s, 3H), 4.47 (s, 6H), 3.96
(s, 9H), 2.25 (s, 9H).
Another coordination mode of such a tripodal ligand is the
encapsulation of the metal ion with additional coordination to
the benzene ring as demonstrated by Hartshorn and Steel.6 We
are also studying the reactions of 3 with other metal salts. The
reaction between 3 and Ru(DMSO)4Cl2 was investigated by
electrospray mass (ES-MS) spectrometry and NMR spectros-
copy.¶ Four main peaks at m/z 202.3, 252.3, 403.4 and 420.8
were observed which correspond to [3 + 2H]2+, [Ru(3)]2+, [3 +
H]+ and [3 + H2O + H]+, respectively. All these assignments
were confirmed by good agreements between the observed and
calculated isotopic distributions. The results of ES-MS imply
that only the mononuclear Ru(II) complex is formed by the
reaction of 3 with Ru(DMSO)4Cl2. In the 13C NMR spectrum of
6·Cl2, the benzene ring carbons were shifted upfield by ca. 32
ppm compared with the corresponding signals of 3. The NMR
study suggests the coordination of Ru to the benzene ring of 3.6¶
This means that 3 may encapsulate the Ru(II) ion (6) as shown
in Scheme 1.
1 See, for example: F. Zeng and S. C. Zimmerman, Chem. Rev., 1997, 97,
1681.
2 For example: A. Marsh, M. Silvestri and J.-M. Lehn, Chem. Commun.,
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Chem., Int. Ed. Engl., 1997, 36, 102; D. J. Pesak and J. S. Moore, Angew.
Chem., Int. Ed. Engl., 1997, 36, 1633; A. Kraft and R. Fröhlich, Chem.
Commun., 1998, 1085.
3 For example: D. S. Lawrence, T. Jiang and M. Levett, Chem. Rev., 1995,
95, 2229; G. M. Whitesides, E. E. Simanek, J. P. Mathlas, C. T. Seto,
D. N. Chin, M. Mammen and D. M. Gordon, Acc. Chem. Res., 1995, 28,
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5 C. M. Hartshorn and P. J. Steel, Chem. Commun., 1997, 541; M. Fujita,
D. Oguro, M. Miyazawa, H. Oka, K. Yamaguchl and K. Ogura, Nature,
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In conclusion, the present study shows that the novel tripodal
ligand 3 can append to the metal ion through non-covalent
interactions and encapsulate the metal ion through chelation and
6
h -arene coordination.
The authors are grateful for funding from the National Nature
Science Foundation of China for financial support of this
work.
6 C. M. Hartshorn and P. J. Steel, Angew. Chem., Int. Ed., Engl., 1996, 35,
2655, and references therein.
7 D. A. House and P. J. Steel, Inorg. Chim. Acta, 1999, 288, 53.
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Chem. Commun., 2000, 1429–1430