lower field signals at the end point. We suggest that a 2 : 1 complex
32–Ag+ is initially formed at the higher ligand concentrations used
for the NMR experiment. As additional Ag+ is added, this complex
dissociates into the 1 : 1 3–Ag+ complex 6 observed at low overall
concentrations using absorption spectroscopy.
photophysical properties of such conjugated heterocycles and the
effective coordination observed for this ligand are likely to inspire
the preparation and study of related systems.
We thank the National Institutes of Health (GM 069773) and
National Science Foundation (CHE 0213323) for support.
Addition of 1 equivalent of silver perchlorate in acetonitrile
to a solution of 3 in chloroform results in the formation of a
white precipitate (Scheme 1). 1H NMR spectra of the free ligand
and the isolated complex in both acetonitrile and DMSO† reveal
comparable patterns and chemical shifts changes to the ones
observed in the titration experiments described above, supporting
the coordination of a single Ag+ ion to ligand 3. 13C NMR
spectroscopy shows a small upfield shift of the alkyne carbons
upon metal coordination (Dd = 1.5 ppm), in agreement with
previous observations of Ag+-coordinated alkynes.14–16
Large single crystals of the complex 6, suitable for X-ray
crystallography, were obtained by slowly diffusing isopropyl ether
into a solution of the complex in acetonitrile. As seen in the solved
structure (Fig. 4),‡ the metal ion is coordinated in a distorted
square planar fashion to the alkyne, the quinolyl nitrogens
and a single acetonitrile molecule. The coplanarity of the two
coordinating rings is evident by the small dihedral angle (1◦)
between the aromatic moieties. Of interest is the distance between
Notes and references
‡ Crystallographic data. 3: C20H12N2 (280.32), monoclinic, space group
◦
−1
˚
˚
˚
C2/c, a = 15.◦582(5) A,◦b = 8.095(3) A, c = 12.481(4) A, a = 90 ,
3
˚
b = 117.326(4) , c = 90 , V = 1398.2(8) A , Z = 4, l = 0.079 mm
,
D = 1.332 g cm−3, T = 208(2) K, F(000) = 584. 4647 reflections (1639
independent), R(int) = 0.0295, final R indices [I > 2r(I)] are R1 =
0.0449, wR2 = 0.1236, R indices (all data) R1 = 0.0551, wR2 = 0.1321.
6: C22H15AgClN3O4 (528.69), monoclinic, space group P2(1)/c, a =
◦
◦
˚
˚
˚
6.8416(17) A, b = 23.779(6) A, c = 12.724(4) A, a = 90 , b = 105.290(4) ,
◦
3
c = 90 , V = 1996.7(9) A , Z = 4, l = 1.180 mm−1, D = 1.759 g cm−3, T =
˚
213(2) K, F(000) = 1056. 12985 reflections (3925 independent), R(int) =
0.0394, final R indices [I > 2r(I)] are R1 = 0.0606, wR2 = 0.1441, R indices
(all data) R1 = 0.0725, wR2 = 0.1492. CCDC reference numbers 600754
and 600755. For crystallographic data in CIF or other electronic format
see DOI: 10.1039/b603983a
1 H. Lang, K. Ko¨hler and S. Blau, Coord. Chem. Rev., 1995, 143, 113–168
and references cited therein.
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1996, 118, 4817–4829.
˚
the silver(I) ion and the alkyne moiety (2.73 A Ag–C11/C10).
While somewhat long, this distance falls within the range seen in
11
˚
related Ag–ethyne interactions (2.16–2.91 A). To accommodate
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the silver cation, the cavity of 3 opens up slightly as evident by the
difference in distances between the two bridging aromatic carbons
˚
˚
(4.06 A C12–C9) and the coordinating nitrogen atoms (4.46 A
N1–N2), as well as by the cavity side angles (94.18◦ N2–C12–C9
and 95.26◦ N1–C9–C12). The opening of 3 pushes N1 and N2
away from the silver cation and brings the alkyne closer to the
coordinated ion.17,18
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13 Jpn. Pat., 011 337, 2004.
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17 The packing of each complex in the crystal lattice shows an intriguing
pattern, governed by p stacking between the aromatic ligands (see
ESI†).
Fig. 4 Thermal ellipsoid plot (50% probability) of [Ag(3)(CH3CN)]-
(ClO4). Perchlorate anions and hydrogen atoms were removed for clarity.
18 The external angle created by C9–C10–C11 and C12–C11–C10 de-
creases from 179.2◦ in the free ligand 3, to 176.9◦ in the silver complex
6, pushing the alkyne toward the coordinated ion.
Ligand 3 represents a prototypical structure of a family of
accessible alkyne-containing chelating ligands. The favorable
2290 | Dalton Trans., 2006, 2288–2290
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