J.-M. Lehn et al.
Table 2. Control of strand shape and motion amplitude by the nature of
the heterocyclic units.
decrease of the amplitude of the subsequent molecular mo-
tions, as well as a change in the nature of relative motions
of the branches connected to these rings, from “flapping”-
type (dis-sense) motions (pym) to “twirling”-type (con-
sense) motions (pz). The combination within ligands of dif-
ferent encoding units allows the generation of hybrid strand
folding as well as of combined molecular motions.
Sequence
(pym-hyz)n
(pz-hyz)n
(pz-hyz-pym-hyz)n
Strand shape
Complex shape
Amplitude
N
helical
linear
undulating
linear (“syn”)
linear (“anti”)
linear
large
small
intermediate
G
(ligand strand 3) to 18.6 ꢅ (ligand strand 4). On the other
hand, both hyz-pym and hyz-pz act as linearity codons on
coordination, and consequently the replacement of the cen-
tral pym (ligand 3) by a pz unit (ligand 4) led to a stick-like
tetranuclear complex 4-Zn4 having globally a length very
close to that of its pym analogue 3-Pb4.
The lengths of stick-like tetranuclear complexes of ligands
3 and 4 are similar (l3 ꢁl4), although the lengths of the free
ligands are different (l1 ¼l2). It thus becomes possible to
change the motional amplitude by changing the central unit.
The two amplitudes may be defined as Dlpym =l3ꢀl1 and
Dlpz =l4ꢀl2. But l3 and l4 being almost equal, the amplitude
depends only on the length of the free ligands, l1 and l2,
which itself depends on the nature of the central heterocycle
(Figure 7).
Experimental Section
Materials and general methods: The following compounds were prepared
as previously described: 1,[10b] 2,[13a] 3,[10b] 6,[10b] 7,[10b] 9,[17] 10,[18] 1-Pb2,[11b]
3-Pb4,[11b] 1-[Ru(terpy)]2,[13a] 2-[Ru(terpy)]2,[13a] and [Ru(terpy)]Cl3.[26] The
ACHTUNGTRNENNUG ACHTNUGTRENNUNG ACTHNUGTRENNGUN
following reagents were purchased from commercial sources: RuCl3 (Al-
drich, Avocado), terpy (Aldrich, Avocado), 2,5-dimethylpyrazine (Al-
drich), benzaldehyde (Aldrich), and benzoic anhydride (Aldrich).
400 MHz 1H NMR spectra were recorded on
a Bruker Ultrashield
Avance 400 spectrometer and 300 MHz 1H NMR spectra were recorded
on a Bruker 300 spectrometer. The solvent residual signal was used as an
1
internal reference for H NMR spectra (CHCl3 d=7.26 ppm, CH3CN d=
1.94 ppm). The following notation is used for the 1H NMR spectral split-
ting patterns: singlet (s), doublet (d), triplet (t), multiplet (m). The 2D-
NMR experiments employed were COSY (correlation spectroscopy) and
NOESY (nuclear Overhauser enhancement spectroscopy or nuclear
Overhauser and exchange spectroscopy); they were carried out on
300 MHz Bruker spectrometers. ESIMS measurements were performed
by the Service de Spectromꢁtrie de Masse, Universitꢁ de Strasbourg.
CCDC-743475 (2-Pb2) and 743476 (4-Zn4) contain the supplementary
crystallographic data for this paper. These data can be obtained free of
charge from the Cambridge Crystallographic Data Centre via
Ligand and complex synthesis and characterisation
4: A solution of 10 (114.1 mg, 0.84 mmol) and 7 (436 mg, 1.7 mmol) in
CH2Cl2 (25 mL) and EtOH (10 mL) was stirred at 368C during 6 h. The
yellow solid that precipitated was separated by centrifugation, washed
1
with CH2Cl2 and dried under vacuum to yield 4 (431 mg, 83%). H NMR
(CDCl3, 400 MHz, reference: solvent residual peak, d=7.26 ppm): d=
9.39 (s, 2H; Hm), 8.63–8.59 (m, 2H; Ha), 8.50 (s, 2H; Hi), 8.20 (d, J=
8.8 Hz, 2H; Hd), 7.99 (s, 2H; Hg), 7.99–7.91 (m, 2H; Hc), 7.90 (s, 2H;
Hk), 7.87 (s, 2H; He), 3.78 (s, 6H; Hh), 3.71 ppm (s, 6H; Hf); Hb is hidden
by the residual CHCl3 peak. The solubility of this ligand in CDCl3 is too
low to allow NOESY, so C2Cl4D2 was used for this purpose, heated at
608C. HR-ESIMS: m/z: calcd for [C30H30N16 +Li]+: 621.299 [M+Li]+;
found: 621.306.
Figure 7. Control of the amplitude of motion on cation coordination, de-
pending on the nature of the central ring: pym for 3 and pz for 4.
One may also note that ligand 4, which combines pym
and pz groups, contains local domains that will behave, in
terms of relative displacements, either in the syn or anti
fashion, as in the model ligands 1 and 2 (see also Scheme 3).
Ligand 4 thus illustrates the ability to control both the local
shape and local motion through appropriate selection of the
heterocyclic components.
2-Pb2: PbACHTUNGRTNEUNG(CF3SO3)2 (4 mg, 2.2 equiv) in CD3CN (0.4 mL) was added to a
suspension of ligand 2 (1.26 mg, 1 equiv) in CD3CN (0.4 mL). 1H NMR
(CD3CN, 400 MHz, reference: solvent residual peak, d=1.94 ppm): d=
9.31 (s, 2H; Hk), 8.61 (s, 2H; Hj), 8.58 (d, J=4.9 Hz, 2H; Ho), 8.12–8.04
(m, 2H; Hm), 7.55 (d, J=8.8 Hz, 2H; Hl), 7.40–7.35 (m, 2H; Hn),
3.75 ppm (s, 6H; Hi). After about 5 min, the complex crystallised out of
the solution. Crystal data for 2-Pb2: formula C26H28F12N10O14Pb2S4; for-
¯
mula weight: 1475.19; triclinic; space group: P1 (No.2); a=9.7810(1),
Conclusion
b=11.2120(1), c=11.9373(2) ꢅ; a=63.140(5), b=82.711(5), g=
70.578(5)8; V=1100.98(7) ꢅ3; Z=1; 1calcd =2.219 gcmꢀ3
; mACHTUNGTRENNUNG
7.949 mmꢀ1; F
ACHTUNGTRENNUNG
The present results demonstrate the possibility of enforcing
the global shape of a molecular ligand strand (folded helix
versus undulating zigzag) by selecting and combining appro-
priate heterocyclic units. Furthermore, the grafting of given
het-hyz sequences on a central core heterocyclic unit allows
the control of both the amplitude and especially of the rela-
tive direction of the motions generated on metal-ion bind-
ing. In particular, the replacement of a central 4,6-disubsti-
tuted pyrimidine by a 2,5-disubstituted pyrazine produces a
qꢂ30.08; dataset hkl: ꢀ13, 13; ꢀ15, 15; ꢀ15, 16; total unique data, R-
(int)=10331, 6397, 0.030; observed data with [I>2s(I)]: 5785; Nref
,
N
par =5785, 307; R=0.0210, wR2=0.0330, S=1.05; GOF=1.055; min.
and max. residual density=ꢀ0.23, 0.82 eAꢀ3
.
4-Zn4: Ligand 4 (1.9 mg, 3.1 mmol, 1 equiv) and ZnACTHUNGTRENUNG(CF3SO3)2 (4.5 mg,
12.4 mmol, 4 equiv) were mixed with CD3CN (0.6 mL) until dissolution.
1H NMR (CD3CN, 400 MHz, reference: solvent residual peak, d=
1.94 ppm): d=9.33 (s, 2H), 8.85 (s, 2H), 8.74 (d, J=5.0 Hz, 2H), 8.59 (s,
2H), 8.32 (s, 2H), 8.29 (td, J=7.8, 1.0 Hz, 2H), 7.98 (d, J=7.8 Hz, 2H),
7.84 (dd, J=7.8, 5.0 Hz, 2H), 7.01 (s, 2H), 3.88 (s, 6H), 3.81 ppm (s, 6H);
5376
ꢃ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 5369 – 5378