1
Department of Chemistry, College of Science, University of Canterbury, Christchurch, New
Zealand.
Abstract
Reaction of silver nitrate with
1,4-bis(2-quinolyloxy)benzene ( 4 ) gave a onedimensional coordination polymer ( 5 ) in which there is extensive   stacking of the quinoline units.
Keywords : Silver; Coordination polymer;
  Stacking; N Ligands; Quinoline
For several years we have been involved in the synthesis and study of an extensive library of bridging ligands characterised by the schematic representation 1 [1,2]. These are comprised of a central arene core to which are appended a number ( n ) of heterocyclic rings attached via spacer groups (X). Variation of the arene core, the spacer group, the nature of the heterocycle and the number n has led to an extensive array of compounds that we have used for the construction of a diverse range of 1-, 2- and 3-D metallosupramolecular assemblies with various topological architectures. For example, 1,4-bis(2-pyridyloxy)benzene, which has a benzene core, an ether oxygen as spacer and ( n = 2) 2-substituted pyridines as the appended heterocycles, upon reaction with silver(I) nitrate led to the dimetallocyclophane 2 , the structure of which is stabilised by intimate internal π-π stacking of the central benzene rings
[3]. The meta -isomer of the ligand produced a very similar product [4] and the analogous ligand ( 3 ) with a 2,6-disubstituted naphthalene core also gave a similar dimetallocycle with π-

2
π stacking of the central naphthyl groups [5]. We now report that replacement of the terminal pyridyl groups in the ligand leading to ( 2 ) with quinoline substituents (ligand 4 ) results in a totally different assembly due to a reprioritisation of the π-π stacking interactions. core
X spacer
( 1 )
N heterocycle n = 2-8
N
Ag
N
O
O
( 2 )
O
O
N
Ag
N
O N
N O
N
O O
N
( 3 ) ( 4 )
The new ligand 2,7-bis(2-quinolyloxy)naphthalene ( 4 ) was prepared by reaction of hydroquinone with two equivalents of 2-chloroquinoline in refluxing DMF in the presence of potassium carbonate, albeit in modest yield [6]. Reaction of 4 with one equivalent of silver nitrate gave, in good yield, the complex 5 , which elemental analysis showed to have 1:1 metal:ligand stoichiometry [7]. Crystals suitable for X-ray structure determination were obtained directly from the reaction mixture [8].
The complex 5 has a one-dimensional metallopolymer structure and crystallises in the centrosymmetric triclinic space group P-1. The asymmetric unit contains two half molecules of the ligand, 4 , each of which lies about a centre of inversion, a silver nitrate and one molecule of water. The water and nitrate anion are each disordered over two sites. The labelled asymmetric unit is shown in Fig. 1, while a section of the polymeric chain is shown in Fig. 2.
[Figs 1 and 2 here]
Each ligand is bidentate and bridges two silver atoms, which in turn are coordinated to two quinoline nitrogens and to a nitrate oxygen or a water oxygen. The coordinated nitrate and the coordinated water each have an occupancy of 0.5 (as do the non-coordinated nitrate and the non-coordinated water), so any silver atom is only ever coordinated to one oxygen

3 atom. Thus, the geometry at silver is distorted T-shaped. The meanplanes of the two quinolines coordinated to a silver are inclined to each other at an angle of 10.1(3) º. The silver-donor bond lengths are similar to those reported for similar silver complexes [3,4,9].
The polymer chain propagates along the crystallographic a axis, with the result being that the silver-silver separation along the edge of the polymer (Ag1···Ag1C) is 9.720(1) Å, which is the a dimension of the unit cell. A ligand, of the type containing N1', bridges two silvers with a separation of 10.886(1) Å (Ag1···Ag1A), while a ligand, of the type containing
N1", bridges two silvers with a separation of 10.761(1) Å (Ag1-Ag1B). These distances are similar to the silver-silver separation (10.384 Å) in complex 2 [3]. However, unlike 2 , which has a discrete [2+2] macrocyclic structure, in 5 there is no   stacking of the benzene rings, which are well displaced so that the rings do not lie over each other. Instead, in the metallopolymer there are   stacking interactions between quinoline units, both intra-chain and inter-chain. Two quinolines (each of different nature) from adjacent ligands in the polymer have their mean-planes inclined to each other at 10.1 º and separated by 3.79(1) Å.
They are positioned so that both rings of each quinoline are involved in the stacking interaction (Fig. 2), with the rings offset so that the centroid of one ring sits over an atom of the other quinoline. An intra-chain   stacking interaction occurs between two quinolines of the type containing N1'. These two quinolines are related by a centre of inversion, and so are necessarily parallel, and are separated by only 3.36(1) Å. Only the nitrogen-containing rings of the quinolines are involved in this latter interaction, and are offset in the usual fashion with an atom of one ring lying over the centroid of the other ring.
In summary, the replacement of the pyridine rings in the ligand leading to the dimetallocyclophane 2 by quinoline units leads to a coordination polymer. This appears to be due to a reprioritisation of the   stacking interactions, wherein the stacking of the internal benzene rings is replaced by more stablising stacking of the external quinoline units. Silver coordination polymers are the subject of considerable current interest [10].

Acknowledgements
4
We thank the Royal Society of New Zealand for funding through the Marsden Fund and a
James Cook Research Fellowship.
Supplementary material
Crsytallographic data for 5 have been deposited with the Cambridge Crystallographic
Data Centre (CCDC
620553). Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: +44 1223 336033; Email: deposit@ccdc.cam.ac.uk
. Supplementary data associated with this article can be found, in the online version, at:doi:10.1016/j.inoche.xxxx
.
References
[1] (a) P. J. Steel, Acc. Chem. Res. 38 (2005) 243-250;
(b) P. J. Steel, Molecules 9 (2004) 440-448.
[2] M. R. A. Al-Mandhary and P. J. Steel, Eur. J. Inorg. Chem. (2004) 329-334, and references therein.
[3] C. M. Hartshorn and P. J. Steel, Inorg. Chem. 35 (1996) 6902-6903.
[4] C. M. Hartshorn and P. J. Steel, J. Chem. Soc, Dalton Trans. (1998)
3927-3934.
[5] B. J. O’Keefe and P. J. Steel, CrystEngComm, submitted.
[6]
Reaction of 1,4-dihydroxybenzene (0.55 g, 5.0 mmol), 2-chloroquinoline (1.64 g, 10.0 mmol), potassium carbonate (1.38 g, 10.0 mmol) in refuxing DMF for 72 hours gave a crude product that was recrystallised from acetone/water to give pure 4 as colourless crystals (0.602 g, 33%), m.p. 197-199 ºC (Found: C, 79.00; H, 4.34; N, 7.43.
C
24
H
16
N
2
O
2
requires C, 79.11; H, 4.43; N, 7.69. Found M +.
, 364.1214. C
24
H
16
N
2
O
2 requires M +.
, 364.1212). 1 H NMR (CDCl
3
)

: 7.14, 2H, d, H3'; 7.32, 4H, s, H2, H3, H5,
H6; 7.43, 2H, t, H6'; 7.64, 2H, t, H7'; 7.77, 2H, d, H5'; 7.88, 2H, d, H8', 8.15, 2H, d,
H4'. 13 C NMR (CDCl
3
)

: 112.66, C3'; 122.56, C2, C3, C5, C6; 124.87, C6'; 125.69,

5
C4a'; 127.33, C5'; 127.85, C8'; 129.89, C7'; 139.86, C4'; 146.36, C8a'; 150.40, C1, C4;
161.78, C2'.
[7] Reaction of 4 (80 mg, (0.22 mmol) dissolved in acetone (40 mL) with silver nitrate (38 mg, 0.22 mmol) gave 5 as colourless crystals suitable for single-crystal X-ray structure determination (89 mg, 74%), m.p. 265-266 °C (Found C, 53.19; H, 3.13; N, 7.44.
C
24
H
16
N
3
O
5
Ag.½(H
2
O) requires C, 53.06; H, 3.15; N, 7.73).
[8] Crystallographic data for 5 : C
24
H
18
AgN
3
O
6
, Fw 552.28, triclinic, P-1, a = 9.720(1), b =
10.765(1), c = 11.154(1) Å,

= 67.55(1),

= 87.86(1),

= 80.53(1) o , V =
1063.5(2)
Å 3 , Z = 2, F(000) = 556, Siemens P4s diffractometer, T = 163(2) K, 0.67 x 0.22 x 0.16 mm,

= 0.997 mm -1 , D x
= 1.725 g cm -3 , 2

-range 4-54 °, 4673 unique reflections, 4536 with I > 2
0.0362.
 GoF = 1.041, wR (all data) 0.079, R1 [I > 2

[9] (a) M. Hedrich and H. Hartl, Acta Cryst., Sect. C 39 (1983) 1649-1652;
(b) L. M. Engelhardt, C. Pakawatchai, A. H. White and P. C. Healy, J. Chem. Soc.,
Dalton Trans. (1985) 117-123;
(c) G. Smith, A. N. Reddy, K. A. Byriel and C. H. Kennard, Polyhedron 13 (1994)
2425-2430, and references therein;
(d) C. Richardson and P. J. Steel, Inorg. Chem. Commun. 1 (1998) 260-262;
(e) C. M. Hartshorn and P. J. Steel, J. Chem. Soc., Dalton Trans. (1998) 3935-3940;
(f) C. Richardson and P. J. Steel, Eur. J. Inorg. Chem. (2003) 405-408;
[10] (a) M. Munakata, L. P. Wu and T. Kuroda-Sowa, Adv. Inorg. Chem. 46 (1999) 173-303;
(b) A. N. Khlobystov, A. J. Blake, N. R. Champness, D. A. Lemenovskii, A. G.
Majouga, N. V. Zyk and M. Schröder, Coord. Chem. Rev. 222 (2001) 155-192;
(c) S.-L. Zheng, M.-L. Tong and X.-M. Chen, Coord. Chem. Rev. 246 (2003) 185-202;
(d) C.-L. Chen, B.-S. Kang and C.-Y. Su, Aust. J. Chem. 59 (2006) 3-18;
(e) C. M. Fitchett and P. J. Steel, Aust. J. Chem. 59 (2006) 19-21;
(f) D. B. Cordes, L. R. Hanton and M. D. Spicer, Inorg. Chem. 45 (2006) 7651-7664.

6
Fig. 1. Labelled asymmetric unit of 5
. Selected bond lengths (Å) and bond angles (º): Ag1-
N1' 2.196(3), Ag1-N1" 2.192(3), Ag1-O11 2.575(5), Ag1-O14 2.561(8); N1'-Ag1-N1"
163.9(1), N1'-Ag1-O11 99.1(2), N1'-Ag1-O14 87.1(2), N1"-Ag1-O11 95.0(2), N1"-Ag1-O14
108.4(2).
Fig. 2. Perspective view of a section of the polymeric chain of 5 . The hydrogen atoms, water molecules and non-coordinated nitrates have been omitted for clarity and π-π stacking interactions are shown as dashed lines.