Both helical enantiomers are present in the respective centrosym-
metric crystal structures, and in both cases a bipyridyl strand of one
enantiomer slots into the ‘groove’ created by two strands of the
complementary enantiomer. In the metal complex structure there
are two crystallographically independent complexes, each located
on a three fold axis, that effectively form a dimeric unit linked by
the groove interaction. In the free ligand structure, 50% of the cage
molecules accommodate a toluene guest, and it appears that the
nestling of a helical molecule into the grove of neighbour
containing a bound toluene molecule precludes solvate binding in
the former molecule. The independent angles subtended by the
principal cage axis and the bi-pyridyl axis are 38.71(1) and
38.10(1)° in the two metal complexes, and 22.81(6), 30.33(1) and
25.26(1)° for the three strands of the free ligand. The apical
nitrogen–nitrogen separation is 13.267(7) Å in the free ligand, and
13.446(6) and 12.571(6) Å in the two independent nickel
complexes. The t-Bu to t-Bu distances along a ligand strand are
respectively 21.938(6) and 21.562(10) Å in the two Ni complexes,
and 21.578(10), 21.656(11) and 21.573(10) Å in the three strands of
the free ligand. One end of the metal complex molecule is more
open than its counterpart; the three t-Bu residues in the two
complexes are respectively 6.17(2) and 6.623(7) Å apart at one end,
and 7.004(14) and 8.056(8) Å apart at the opposite end. The nickel
ion coordination is pseudo-octahedral, with negligible trigonal
twist. The terminal nitrogens are 6.589(4) and 6.857(4) Å from the
metal ion in one complex, and 5.943(P4) and 6.629(4) Å in the
second complex. The metal complex structure closely matches that
predicted by CPK models. Clearly it is the tendency of the capping
groups to twist into a propeller-like configuration (left- or right-
handed) coupled with the chiral octahedral coordination geometry
adopted by the central nickel on coordination to the three bipyridyl
residues that promotes and enhances the helical twist along the
length of individual complex cations.
Advanced Photon Source is supported by the U.S. Department of
Energy, Basic Energy Sciences, Office of Science, under Contract
No. W-31-109-Eng-38.
Notes and references
† Dialdehyde 4 was prepared in 60% yield by alkylation of 5-tert-
butylsalicylaldehyde with 5,5A-bis(bromomethyl)-2,2A-bipyridine5 under
phase transfer conditions (toluene–H2O–NaOH–Bu4NBr).
‡ Synthesis of [NiL](PF6)2 (L = 3, R = t-Bu): Dialdehyde 4 (0.25 g, 0.466
mmol) and Ni(NO3)2·5H2O (0.042 g, 0.154 mmol) were dissolved in
acetonitrile (400 cm3) and stirred at 50 °C for 20 min. The solution was
filtered into a dropping funnel and added dropwise over 3 h to a vigorously
stirred solution of ammonium acetate (0.18 g, 2.33 mmol) and sodium
cyanoborohydride (0.15 g, 2.33 mmol) in acetonitrile (500 cm3) warmed at
50°. The reaction was stirred at 50° for a further 1 h and the solvent then
removed in vacuo. Routine workup yielded a salmon-pink solid which was
recrystallised from acetonitrile–ether to give title complex (0.22 g, 0.116
mmol, 75%), mp
> 250°. Found: C, 64.33; H, 5.80; N, 5.90;
C102H114F12N8NiO6P2 requires: C, 64.59; H, 5.80; N, 5.91%; ESMS, found:
M2+ (22PF62) 802.4, C102H114N8NiO62+ requires 802.41.
§ Modelling studies indicate this is not so for the analogous 6,6A-substituted
2,2A-bipyridyl cage in which the cavity is significantly larger than is ideal for
transition metal ions; the calculations for metal-free 3 also suggested that
there is little difference in the energies of the exo-exo and endo-endo
bridgehead nitrogen arrangements for this cage.
¶
Free ligand 3: data from ChemMatCARS Advanced Photon Source,
model formula C112.50H126N8O6.50, M 1694.21, triclinic, space group
¯
P1(#2), a 15.555(4), b 16.622(2), c 23.495(6) Å, a 71.105(11), b 78.998(8),
g70.890(11)°, V 5406(2) Å3, Z 2, temperature 123(2) Kelvin, l(synchrotron)
0.56356 Å, m 0.042 mm21, 2qmax 36.48, N 101066, Nind 14377(Rmerge
0.0877), Nobs 10853(I > 2s(I)), R1(F) 0.1613, wR2(F2) 0.437.7,8,9 Poor
diffraction, rigid bodies for pyridyl and toluene molecules.
Complex [Ni(3)](PF6)2: Data from Bruker SMART 1000, model formula
¯
C
104.50H117.75F12N9.25NiO8P2, M 1979.98, trigonal, space group P3 (#147),
a 15.9763(19), b 15.9763(19), c 51.131(9) Å, g 120.00°, V 11302(3) Å3, Z
4, temperature 173(2) Kelvin, l(MoKa) 0.71073 Å, m(MoKa) 0.273 cm21
,
We thank the Australian Research Council for support. Use of
the ChemMatCARS Sector 15 beamline at the Advanced Photon
Source, was supported by the Australian Synchrotron Research
Program, which is funded by the Commonwealth of Australia under
the Major National Research Facilities Program. ChemMatCARS
Sector 15 is also supported by the National Science Foundation/
Department of Energy under grant numbers CHE9522232 and
CHE0087817 and by the Illinois board of higher education. The
2qmax 63, N 136109, Nind 24406 (Rmerge 0.0509), Nobs 18113(I > 2s(I)),
R1(F) 0.0750, wR2(F2) 0.2398.7,8,9 Two independent complexes each on
three fold axis. Twinned with (y,x,2z). CCDC 222140 and 222141. See
.cif or other electronic format.
1 J.-M. Lehn, Supermolecular Chemistry, VCH, Weinheim, 1996.
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Sobolev and A. H. White, Aust. J. Chem., 1994, 47, 1155; K. R. Adam,
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3 R. J. A. Janssen, L. F. Lindoy, O. A. Matthews, G. V. Meehan, A. N.
Sobolev and A. H. White, J. Chem. Soc., Chem. Commun., 1995, 735.
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Matthews and G. V. Meehan, J. Chem. Soc., Perkin Trans. 1, 1997,
295.
5 U. S. Schubert, C. Eschbaumer and G. Hochwimmer, Synthesis, 1999,
779.
6 L. F. Lindoy and I. M. Atkinson, Self-assembly in Supramolecular
Chemistry, Royal Society of Chemistry, Cambridge, UK, 2000, pp.
138–178.
7 Bruker (1995). SMART, SAINT and XPREP. Area detector control and
data integration and reduction software. Bruker Analytical X-ray
Instruments Inc., Madison, Wisconsin, USA.
8 A. Altomare, M. Cascarano, C. Giacovazzo and A. J.Guagliardi, Appl.
Cryst., 1993, 26, 343.
9 G. M. Sheldrick, SHELXL97, Program for crystal structure refinement,
University of Göttingen, Germany, 1997.
Fig. 1 Space-filling depictions highlighting the helical disposition of the
ligand in the crystal structures of (a) free ligand 3, (b) free ligand 3 with
toluene guest and (c) the complex cation of [Ni(3)](PF6)2.
C h e m . C o m m u n . , 2 0 0 4 , 1 5 2 – 1 5 3
153