DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, 3927–3933 3927 Synthesis and crystal structures of silver(I) and palladium(II) complexes of new bis(2-pyridyloxy)benzenes and methylene extended analogues Chris M. Hartshorn and Peter J. Steel * Chemistry Department, University of Canterbury, Christchurch, New Zealand. E-mail: p.steel@chem.canterbury.ac.nz Received 22nd September 1998, Accepted 24th September 1998 Four new ligands, 1,3-bis(2-pyridyloxy)benzene II, 1,2-bis(2-pyridyloxy)benzene III, 1,4-bis(2-pyridyloxymethyl)- benzene IV and 1,4-bis(2-pyridylmethoxy)benzene V, have been prepared, and their complexes with silver(I) nitrate and palladium(II) chloride synthesized.The silver complex of ligand II is shown, by a crystal structure determination, to be a M2L2 20-membered macrocycle with close p–p stacking of the benzene rings of the ligands, similar to the analogous complex of the para substituted isomer of this ligand. The structure of the mononuclear palladium complex of ligand III shows the ligand co-ordinated to the metal in a nine-membered chelate ring, with evidence for a weak interaction between the metal and the central benzene ring. Structures of the silver complexes of ligands IV and V reveal that these are polymeric species, with the molecular packing controlled by p–p stacking interactions between aromatic rings.The crystal structure of the palladium complex of ligand V shows that it self-assembles into a M2L2 26-membered macrocycle, but without intramolecular p–p stacking.Introduction The term metallosupramolecular chemistry was introduced by Constable 1 to describe the self-assembly of larger molecular aggregates from combinations of transition metal ions and polydentate ligands. Often this involves the use of metal ions that have defined co-ordination numbers and stereochemical preferences, to encode the rational assembly of specific molecular architectures by recognition of the inherent properties of logically designed ligands.In this way, many recent reports 2 have described the formation of numerous metallosupramolecular species with novel topological structures, such as squares, cages, ladders, bricks, helicates and polycatenates, some of which contain interlocking rings and interpenetrating 3-D networks, much of which has provided useful information for the rapidly expanding area of crystal engineering.3 However, this approach imposes natural restrictions on the architectures available, due to the limited range of angular motifs available from stereorigid metals.Thus, we are presently studying the chemistry of metal ions that have less well defined coordination numbers and geometries. For example, the d10 metal silver(I) forms complexes with various co-ordination numbers, and, within a given co-ordination number, has very flexible geometrical requirements. Previously, we reported the synthesis of the new ligand I and its reaction with silver nitrate to produce the novel M2L2 dimetalloparacyclophane 1 containing a p–p stacked subunit (Scheme 1).4 We were curious to know whether this was simply a serendipitous event or a more general reaction that would apply to other structurally related ligands.Specifically, we were interested to determine the extent to which the p–p stacking was responsible for the self-assembly of this dimeric structure and whether the oxygen atoms of the ligand played a role in the dimer formation.Accordingly, we have now synthesized four new ligands and studied their reactions with silver(I) nitrate and, for comparative purposes, palladium(II) chloride. Since our previous report of the reaction of I, a number of structurally related M2L2 dimers of various ligands with silver 5 and other metals 6 have been reported; however none of these displays such intimate p–p stacking of aromatic rings. Results and discussion Two approaches were adopted for structural modification of the ligand I, in order to assess the generality of the dimer formation.First, the para substitution in the benzene ring was replaced by the meta and ortho isomers and, secondly, methylene spacer groups were introduced on either side of the oxygen atoms. Thus, the four new ligands II–V were synthesized, all by nucleophilic substitution reactions. By analogy with the method used to prepare the para isomer I,4 2-bromopyridine was treated with 1,3-dihydroxybenzene (resorcinol) and 1,2-dihydroxybenzene (catechol), in the presence of potassium carbonate, to give the meta and ortho isomers II and III, respectively.The methylene extended homologue IV was prepared by reaction of 2-bromopyridine with 1,4- benzenedimethanol, in an adaptation of a reported method for the synthesis of benzyl 2-pyridyl ether.7 The isomer V was prepared by reaction of 1,4-dihydroxybenzene (hydroquinone) with 2-chloromethylpyridine under phase-transfer catalysed conditions.The 1H and 13C NMR spectra of all four ligands were fully assigned, by a combination of 1- and Scheme 1 O O N N O O N N O O N N Ag Ag OH2 H2O ONO2 O2NO I 1 AgNO33928 J. Chem. Soc., Dalton Trans., 1998, 3927–3933 2-D NMR techniques, and are given in the Experimental section. The ligands II–V reacted smoothly with silver nitrate, under similar conditions to those used to prepare 1, to give complexes 2–5, in excellent yields. The crystal structures of three of these are described below.In order to determine whether stereochemically less flexible metals would also form the M2L2 dimers, palladium(II) was chosen as a representative square-planar co-ordinating metal, which has been much used in metallosupramolecular self-assemblies.8 Reactions of I and II–V with palladium chloride aVorded complexes 6–10 of 1 : 1 stoichiometry, in excellent yields. Unfortunately, only two of these complexes were suYciently soluble for NMR studies and for recrystallisation to furnish X-ray quality crystals.The crystal structures of these are also described below. The silver nitrate complex 2, of 1,3-bis(2-pyridyloxy)benzene II, crystallises in the monoclinic space group C2/c. Like 1, it is a M2L2 dimeric macrocycle, but in this case has C2 crystallographic symmetry, rather than a centre of inversion. Fig. 1 shows a perspective view of the structure, with atom labelling of the asymmetric unit.Selected interatomic distances and angles are also listed. To each silver atom are co-ordinated two pyridine nitrogens and a water oxygen atom. The silver–donor bond distances are similar to those of 1, although the Ag– O(100) distance [2.486(2) Å] is slightly shorter than the analogous bond in 1 [2.528(2) Å]. The geometry at the silver atom is distorted T-shaped with a similar N–Ag–N angle [158.08(6)8] to that in 1. However, whereas in 1 the water oxygen bisects this angle, in the case of 2 it subtends two very diVerent O–Ag–N angles [109.17(6) and 92.75(6)8].As with 1, the co-ordinated water hydrogen atoms are hydrogen-bonded to oxygen atoms of two diVerent nitrate anions, with O ? ? ? O separations of 2.878(3) and 3.034(3) Å. The intramolecular Ag ? ? ? Ag separation [9.405(1) Å] in the 20-membered macrocycle 2 of the meta Fig. 1 Perspective view and atom labelling of the crystal structure of complex 2. Selected interatomic distances (Å) and angles (8): Ag(1)– N(11) 2.196(2), Ag(1)–N(31A) 2.218(2), Ag(1)–O(100) 2.486(2), Ag(1) ? ? ? O(10) 3.063(2), Ag(1) ? ? ? O(30A) 2.899(2); N(11)–Ag(1)– N(31A) 158.06(6), N(11)–Ag(1)–O(100) 109.17(6), N(31A)–Ag(1)– O(100) 92.75(6).O O N N O O N N O O N N O O N N IV II III V isomer is considerably less than that [10.384(1) Å] in the 22- membered macrocyclic complex of the para disubstituted ligand.4 The benzene and two pyridine rings are each planar, but, as was observed with complex 1, the oxygen linking atoms, O(10) and O(30), are both significantly out of the plane of the benzene ring [0.088(4) and 0.163(4) Å, respectively].Again, this distortion is towards the proximate silver atom, which, in combination with the O ? ? ? Ag distances [2.899(2) and 3.063(2) Å], suggests the existence of weak ether–oxygen–silver interactions. The change in topology of the ligand from 1,4- to 1,3- disubstitution also changes the relative inclinations of the various aromatic rings.The mean planes of the pyridine rings are now inclined at angles of 83.6(1) and 103.9(1)8 to that of the linking benzene ring, while the two pyridine ring mean planes at each silver atom are inclined to one another at an angle of 17.5(1)8. Again, the silver atom is significantly out of the extended mean planes of the co-ordinated pyridine rings to the extent of 0.164(2) and 0.121(2) Å. An important feature of this structure is the preservation of the p–p stacking of the benzene rings.In particular, it is interesting that this complex crystallises in a conformation with the two meta disubstituted benzene rings oriented in the same direction (with C2v molecular symmetry), rather than an alternative possible orientation with one of the benzene rings inverted (with C2h symmetry). We believe that the observed orientation occurs in order to maximise the favourable p–p stacking interaction. Nevertheless, unlike the centrosymmetric isomer 1, in the structure of 2 the benzene rings are not parallel, with mean planes inclined at an angle of 9.18.However, despite this slight splaying of the benzene rings away from each other, they are still displaced from one another in the same manner as in 1, with the centroid of one ring lying above an atom of the other ring, as shown in the alternative view of the structure displayed in Fig. 2. We have previously noted that this seems to be the most favourable orientation for parallel stacked aromatic rings, as has been suggested by computational studies.9 The spacing between the two parallel benzene rings in 1 is 3.33(1) Å; in 2 the slight splaying of the rings has the result that the corresponding values range from 3.343(3) Å, for C(2), to 3.777(3) Å, for C(5).Thus, the formation of a second M2L2 dimer has demonstrated that the structure 1 was not a fortuitous singularity and may represent a general self-assembly process, controlled by the p–p stacking interaction.Attention, therefore, was turned to the ortho isomer III. Unfortunately, the silver nitrate complex of this ligand failed to provide crystals suitable for X-ray analysis. Elemental analysis suggested an intriguing M5L4 stoichiometry; however, this complex was not able to be characterised further. Reaction of palladium chloride with III provided a 1 : 1 complex 8 which was more amenable to study, being soluble in dichloromethane, suggestive of a monomeric structure.The 1H NMR spectrum in CD2Cl2 shows only six signals, which indicates the complex has two-fold symmetry. Significant coordination- induced changes in chemical shift are observed in comparing the spectra of III and 8 in CD2Cl2. In particular, the two pairs of benzene hydrogens have the same chemical shift (d 7.27) for free III, while diVerent chemical shifts downfield of Fig. 2 Top view of complex 2 showing the relationship of the p–p stacked benzene rings.J.Chem. Soc., Dalton Trans., 1998, 3927–3933 3929 this are observed for complex 8 (d 7.32 and 7.59). Such changes in chemical shift can result from a number of factors such as a change in the conformation of the ligand upon co-ordination and through-space ring-current anisotropy eVects.10 Assuming cis co-ordination by the two pyridine nitrogens, this complex would possess a nine-membered chelate ring. Furthermore, two distinct structures are possible, depending upon whether the benzene ring is proximate (8a) or distal (8b) to the palladium atom.Inspection of molecular models suggested that interconversion between these two isomers would not be a facile process. Significantly, no NOE enhancement of any pyridine hydrogen signal was observed upon irradiation of either benzene hydrogen signal. Inspection of molecular models showed that this would be so only for isomer 8a, which in turn raises the interesting possibility that there may also be an interaction between the palladium atom and the benzene ring.Thus a crystal structure determination of 8 was carried out. The palladium complex 8 crystallises in the monoclinic space group P21/c. Fig. 3 shows a perspective view and atom labelling of the structure, along with selected bonding geometry. The ligand, III, is indeed cis-chelated to the palladium, producing a nine-membered chelate ring. A search of the Cambridge Structural Database revealed that this is the first structure involving palladium in a nine-membered chelate ring with N,N-donors, although analogous structures with P,P-donors are known.11 The Pd–N and Pd–Cl distances are within the range of values previously reported for related structures.12 In the solid state, the twofold symmetry observed in solution is not crystallographically present, with the mean planes of the two pyridine rings inclined at angles of 90.6(1) and 119.8(1)8 to the benzene ring, and at 79.7(1)8 to each other.As suggested by the NMR experiments, the complex exists as isomer 8a.We believe that this is due to a weak interaction Fig. 3 Perspective view and atom labelling of the crystal structure of complex 8. Selected interatomic distances (Å) and angles (8): Pd(1)– N(11) 2.059(2), Pd(1)–N(21) 2.040(2), Pd(1)–Cl(1) 2.2831(7), Pd(1)– Cl(2) 2.2871(7); N(11)–Pd(1)–N(21) 88.33(8), N(11)–Pd(1)–Cl(1) 90.77(6), N(21)–Pd(1)–Cl(2) 89.07(6), Cl(1)–Pd(1)–Cl(2) 91.67(3), N(11)–Pd(1)–Cl(2) 176.63, N(21)–Pd(1)–Cl(1) 175.78(6). O O N N Pd Cl Cl O N Pd Cl Cl O N 8a 8b between the palladium atom and the benzene ring, as indicated by certain features of the structure.The palladium atom lies at a distance of 2.879(3) Å from the centre of the C(1)–C(2) bond. This interaction is suYcient slightly to pyramidalise the squareplanar palladium, by pulling it out of the co-ordination plane and towards the benzene ring. In turn, the oxygen atoms are displaced, by 0.134(4) and 0.142(4) Å [O(10) and O(20), respectively], on the opposite side of the plane of the benzene ring, indicating pyramidalisation of the attached carbons.This intramolecular interaction between the benzene p orbitals and the palladium dz2 orbital is analogous to those proposed to account for the intermolecular packing of palladium complexes containing aromatic ligands. Thus III represents an interesting new chelating ligand. As described above, the two methylene extended ligands IV and V were prepared to determine whether they would selfassemble into larger dimeric macrocycles, and to examine the possible role of the oxygen atoms in this process.Each of these ligands was treated with silver nitrate to produce, in excellent yields, crystalline complexes (4 and 5), suitable for structure determination. The complex 4 crystallises in the monoclinic space group C2/c, and is a metallopolymer, rather than a dimetallocycle. The asymmetric unit contains half of the ligand IV, positioned about a centre of inversion, that is co-ordinated to a silver atom, which, in turn, lies on a twofold rotation axis.The chelated nitrate ion, which is disordered over two orientations, also lies with two atoms on this axis. Fig. 4 shows the labelled contents of the asymmetric unit, together with adjacent groups and selected interatomic distances and angles. The silver atom is coordinated to two pyridine nitrogens with non-linear geometry [N(11)–Ag(1)–N(11B) 139.6(2)8].The silver–donor bond distances are similar to those in related literature compounds.13 The mean plane of the pyridine ring is inclined to that of the benzene at an angle of 46.5(6)8, while the two pyridine ring mean planes at each silver atom are inclined to one another at an angle of 62.8(6)8. Although this ligand does not produce a dimeric structure, it is interesting that both of the types of interaction discussed above are still found in the extended structure of complex 4.Specifically, the ether oxygen shows a similar weak interaction with the silver atom [Ag(1) ? ? ? O(10) 2.874(4) Å], being pulled towards the silver as seen in the distortion from ideal geometry around C(12) [O(10)–C(12)–N(11) 111.4(7), O(10)–C(12)– C(13) 125.1(8)8]. Also, the packing of the metallopolymeric structure still appears to be controlled in part by p–p interactions, but, in this case, between pyridine and benzene rings of adjacent units, rather than the benzene–benzene stacks of 1 and 2.As shown in Fig. 5, the zigzag shaped chain of the polymer is Fig. 4 Perspective view and atom labelling of the crystal structure of complex 4. Selected interatomic distances (Å) and angles (8): Ag(1)– N(11) 2.216(5), Ag(1)–O(1) 2.545(3), Ag(1)–O(1A) 2.503(4), Ag(1) ? ? ? O(10) 2.874(4); N(11)–Ag(1)–N(11B) 139.6(2), N(11)–Ag(1)– O(1) 97.0(2), N(11)–Ag(1)–O(1A) 120.0(2).3930 J. Chem. Soc., Dalton Trans., 1998, 3927–3933 such that each benzene ring exhibits p–p stacking with two pyridine rings that are inclined at an angle of 17.9(8)8.The structure of the silver complex 5 of the isomeric ligand V is somewhat similar. It crystallises in the monoclinic space group P21/c and is also a one dimensional metallopolymer. Fig. 6 shows the labelled contents of the asymmetric unit, along with selected adjacent groups. The silver atom is co-ordinated to two pyridine nitrogens and in half of the units to an oxygen of the nitrate counter ion, which is again disordered over two equally occupied sites.The silver–donor bond distances are again in agreement with the distances of related literature compounds. 13 The pyridine–silver–pyridine co-ordination geometry is non-linear, with the half occupancy co-ordinated oxygen bisecting the larger N–Ag–N angle. The mean planes of the pyridine rings are inclined at angles of 48.4(3) and 2.4(3)8 to that of the linking benzene ring. Since the ether oxygen atoms are no longer directly attached to the pyridine ring they do not interact with the silver atom.Once again the metallopolymer describes a zigzag shape, which results from p–p stacking interactions. As shown in Fig. 7, there is a weak p–p interaction between alternating pyridine rings in the polymer chain. Stronger interactions exist between diVerent strands of the polymer, with crystallographically equivalent pyridines of adjacent strands, related by a centre of inversion, being coplanar and separated by only 3.33(1) Å.Once again, the rings are displaced such that an atom of one ring lies over the centroid of the other ring, a relationship similar to that existing in complexes 1 and 2. Hence, p–p interactions appear to contribute to the assembly of the complex, and certainly to its crystal packing. The palladium chloride complex 10 of this ligand V was soluble and stable in DMSO, which allowed for characterisation by 1H NMR spectroscopy.The spectrum, with co-ordination induced shifts ranging between 0.10 and 0.57 ppm downfield from those of the non-co-ordinated ligand, showed that, in solution, the two pyridine rings are equivalent. Although the Fig. 5 View down the b axis of the polymeric chain structure of complex 4, with hydrogen and nitrate atoms omitted, showing the interligand p–p stacking of aromatic rings. Fig. 6 Perspective view and atom labelling of the crystal structure of complex 5. Selected interatomic distances (Å) and angles (8): Ag(1)–N(11) 2.203(3), Ag(1)–N(41A) 2.195(3), Ag(1)–O(3A) 2.557(5); N(11)–Ag(1)–N(41A) 150.3(1), N(11)–Ag(1)–O(3A) 104.9(1), N(41A)– Ag(1)–O(3A) 104.2(1).silver complexes of IV and V were polymeric, the solubility of 10 suggested that this was not a polymeric species and, hence, a crystal structure determination seemed worthwhile. Suitable crystals were obtained by vapour diVusion of acetone into a DMSO solution of the complex. The palladium complex 10 crystallises in the monoclinic space group C2/c, with the asymmetric unit containing one PdLCl2 moiety and half an acetone solvate molecule, the latter lying on a twofold rotation axis.The complex is a dimetalloparacyclophane incorporating a 26 membered macrocycle. Fig. 8 shows the structure with the asymmetric unit labelled and lists selected interatomic distances and angles. Unfortunately, the structure exhibits considerable disorder. As shown in Fig. 8, each chlorine atom is disordered over three sites. High thermal displacement parameters for some atoms of the ligand suggested that these too are disordered, but this was not included in the refinement model. Consequently, the bonding Fig. 7 Perspective view of complex 5, with hydrogen and nitrate atoms omitted, showing the intra- and inter-polymer p–p stacking of pyridine rings. Fig. 8 Perspective view and atom labelling of the crystal structure of complex 10. Selected interatomic distances (Å) and angles (8): Pd(1)– N(11) 2.03(1), Pd(1)–N(41A) 2.06(1), Pd(1)–Cl range 2.267(6)– 2.383(6); N(11)–Pd(1)–N(41A) 172.1(8), N(11)–Pd(1)–Cl range 86.9(4)–92.5(4), N(41A)–Pd(1)–Cl range 87.1(6)–92.1(4), Cl(1A)– Pd(1)–Cl(1B) 178.4(3), Cl(2A)–Pd(1)–Cl(2B) 171.8(7), Cl(3A)–Pd(1)– Cl(3B) 178.6(5).J.Chem. Soc., Dalton Trans., 1998, 3927–3933 3931 geometry parameters are less well determined than in the other structures. Each palladium atom is approximately square planar and is trans co-ordinated to two pyridine nitrogens and two disordered chlorine atoms.The Pd–N and Pd–Cl distances are within the range of reported values for related structures.14 Within the ligand, the mean planes of the pyridine rings are inclined at angles of 25(1) and 47(1)8 to that of the benzene ring, while two pyridines co-ordinated to the same palladium atom are inclined at an angle of 15(1)8. The intramolecular Pd ? ? ? Pd separation in the macrocycle is 11.269(2) Å.This is significantly larger than those of the silver structures described above, as a result of the additional methylene groups incorporated in the ligand. The two non-stacked benzene rings are inclined at an angle of 44(1)8 to each other, with their centroids separated by 6.45(3) Å, which indicates that this dimension of the macrocycle is also enlarged from the earlier structures. The overall shape of the macrocycle is curved (Fig. 9). This is as a result of hydrogen bonding interactions between a co-ordinated chlorine and the acetone solvate molecule [closest Cl ? ? ? H distance 2.59(2) Å].This has the eVect of wrapping the macrocycle around the solvate to give the concave curvature. Although there are no intramolecular p–p interactions, the molecular packing involves weak intermolecular p–p stacking interactions between the rings of adjacent molecules. Conclusion The four new ligands, 1,3-bis(2-pyridyloxy)benzene II, 1,2-bis- (2-pyridyloxy)benzene III, 1,4-bis(2-pyridyloxymethyl)benzene IV and 1,4-bis(2-pyridylmethoxy)benzene V, have been shown to form complexes with silver nitrate and palladium chloride, in excellent yields.Crystal structure determinations have shown a variety of modes of co-ordination by these ligands, including the formation of a mononuclear chelated complex, bridged binuclear cyclic dimers and bridged polymeric structures. Further experiments designed to rationalise the behaviour of these ligands will be reported subsequently.For example, the accompanying paper describes the silver complexes of structurally related ligands incorporating sulfur atoms rather than oxygen linking groups. Experimental General The 1H NMR spectra were recorded on a Varian 300 Unity spectrometer with a 3 mm probe operating at 300 MHz, 13C NMR spectra on a Varian 300 Unity or XL-300 spectrometer with a 3 or 5 mm probe, respectively, operating at 75 MHz. Spectra were referenced relative to internal Me4Si.Melting points were determined using an Electrothermal melting point apparatus and are uncorrected. Elemental analyses were performed by the Chemistry Department, University of Otago, Dunedin. Solvents were purified according to literature pro- Fig. 9 Side view of complex 10 showing the macrocycle wrapping around the hydrogen-bonded acetone. All hydrogens except those of the acetone are omitted for clarity. cedures. Unless otherwise stated, reagents were obtained from commercial sources.Ligand preparations 1,3-Bis(2-pyridyloxy)benzene II. A mixture of 1,3- dihydroxybenzene (1.15 g, 10.4 mmol), 2-bromopyridine (3.31 g, 21.0 mmol) and potassium carbonate (2.90 g, 21.0 mmol) was heated, with stirring, at 210–220 8C for 5 h. The resulting tar was extracted several times with diethyl ether; the extracts were combined and washed with aqueous sodium hydroxide (40%), then water. The solvent was then removed to give a brown oil.Crystallisation of this oil from light petroleum–ethyl acetate (2 : 1) aVorded pure compound II (1.06 g, 39%) as colourless crystals, mp 50–51 8C (Found: C, 72.90; H, 4.76; N, 10.56. C8H6NO requires C, 72.72; H, 4.58; N, 10.60%). 1H NMR (CDCl3): d 6.93 (2 H, d, H39), 6.96 (1 H, s, H2), 6.99 (2 H, dd, H4,6), 7.00 (2 H, t, H59), 7.40 (1 H, t, H5), 7.68 (2 H, t, H49), 8.21 (2 H, d, H69). 13C NMR (CDCl3): d 111.48 (C39), 113.88 (C2), 116.81 (C4,6), 118.56 (C59), 129.92 (C4), 139.26 (C49), 147.53 (C69), 154.98 (C1,3), 163.07 (C29). 1,2-Bis(2-pyridyloxy)benzene III. 1,2-Dihydroxybenzene was treated as above and gave crude compound III as a white solid. Recrystallisation from light petroleum (bp 40–60 8C)–ethyl acetate (2 : 1) aVorded pure III (0.87 g, 32%) as colourless crystals, mp 97–98 8C (Found: C, 72.55; H, 4.69; N, 10.70). 1H NMR (CDCl3): d 6.70 (2 H, d, H39), 6.90 (2 H, t, H59), 7.28 (4 H, s, H3–6), 7.56 (2 H, t, H49), 8.10 (2 H, d, H69). 13C NMR (CDCl3): d 110.73 (C39), 118.17 (C59), 123.60 (C3,6), 125.73 (C4,5), 138.96 (C49), 145.66 (C1,2), 147.31 (C69), 163.06 (C29). 1,4-Bis(2-pyridyloxymethyl)benzene IV. A mixture of 1,4- benzenedimethanol (0.57 g, 4.1 mmol), 2-bromopyridine (1.31 g, 8.3 mmol) and potassium hydroxide (1.86 g, 33.2 mmol) was refluxed in toluene (20 ml) for 42 h. The solvent was then removed and the residue divided between chloroform (15 ml) and aqueous (30 ml) layers. The organic layer was then separated, dried (Na2SO4) and concentrated to give crude compound IV.Unchanged 2-bromopyridine was removed under vacuum at room temperature for 30 min. Trituration of the remaining residue with ice-cold methanol gave a white precipitate which was filtered oV to give IV (0.41 g, 34%), mp 67–68 8C (Found: C, 72.03; H, 5.55; N, 9.17. C18H16N2O2?0.5H2O requires C, 71.75; H, 5.69; N, 9.30%). 1H NMR (CDCl3): d 5.38 (4 H, s, CH2), 6.80 (2 H, d, H39), 6.87 (2 H, t, H59), 7.47 (4 H, s, H2,3,5,6), 7.57 (2 H, t, H49), 8.17 (2 H, d, H69). 13C NMR (CDCl3): d 67.11 (CH2), 111.19 (C39), 116.79 (C59), 127.96 (C2,3,5,6), 136.87 (C1,4), 138.48 (C49), 146.70 (C69), 163.45 (C29). 1,4-Bis(2-pyridylmethoxy)benzene V. A mixture of 1,4- dihydroxybenzene (2.05 g, 18.6 mmol), 2-chloromethylpyridine hydrochloride (6.11 g, 37.2 mmol) and 40% aqueous tetrabutylammonium hydroxide (4 drops) was refluxed in benzene (40 ml) and 40% aqueous sodium hydroxide (8 ml) for 24 h. The organic layer was then separated, dried (Na2SO4) and concentrated to give crude compound V.Recrystallisation from light petroleum–ethyl acetate (10 : 1) gave pure V (2.63 g, 48%), mp 106 8C (Found: C, 73.55; H, 5.51; N, 9.46. C9H8NO requires C, 73.96; H, 5.52; N, 9.58%). 1H NMR (CDCl3): d 5.16 (4 H, s, CH2), 6.92 (4 H, s, H2,3,5,6), 7.23 (2 H, t, H59), 7.53 (2 H, d, H39), 7.72 (2 H, t, H49), 8.60 (2 H, d, H69). 13C NMR (CDCl3): d 71.14 (CH2), 115.69 (C2,3,5,6), 121.24 (C39), 122.54 (C59), 136.78 (C49), 149.16 (C69), 152.81 (C1,4), 157.43 (C29).Silver nitrate complexes [Ag2(II)2(H2O)2][NO3]2 2. Reaction of compound II (70 mg, 0.26 mmol), dissolved in methanol (8 ml), with silver nitrate (54 mg, 0.31 mmol), dissolved in water (5 ml), gave, over a period of several days at room temperature, complex 2 as colourless crys-3932 J. Chem. Soc., Dalton Trans., 1998, 3927–3933 Table 1 Crystal data and details of data collections and structure refinements for complexes 2, 4, 5, 8 and 10 Formula Formula weight Crystal system a/Å b/Å c/Å b/8 V/Å3 Space group Z Dc/Mg m23 F(000) T/K Crystal form Crystal size/mm m/mm21 2q range/8 Reflections collected Unique reflections (Rint) Parameters DiVerence peaks/e Å23 Goodness of fit Ra [I > 2s(I)] wRb (all data) 2 C32H28Ag2N6O12 904.34 Monoclinic 20.751(4) 9.311(1) 18.659(3) 113.21(1) 3313.4(9) C2/c 4 1.81 1808 158(2) Colourless block 0.56 × 0.49 × 0.31 1.26 4–55 4620 3797 (0.023) 243 0.427 1.074 0.0235 0.0623 8 C16H12Cl2N2O2Pd 441.58 Monoclinic 8.512(1) 17.845(1) 11.172(1) 106.41(1) 1627.9(3) P21/c 4 1.80 872 168(2) Orange block 0.60 × 0.19 × 0.16 1.48 4–50 3076 2874 (0.014) 208 0.428 0.940 0.0213 0.0523 4 C18H16AgN3O5 462.21 Monoclinic 15.793(2) 12.699(1) 10.959(1) 128.283(8) 1725.3(4) C2/c 4 1.78 928 188(2) Colourless block 0.52 × 0.28 × 0.19 1.21 4–50 1570 1513 (0.034) 126 0.766 1.068 0.0475 0.1182 5 C18H16AgN3O5 462.21 Monoclinic 12.235(1) 9.050(1) 15.820(2) 97.36(1) 1737.3(3) P21/c 4 1.77 928 130(2) Colourless block 0.31 × 0.15 × 0.12 1.20 4–50 3209 3057 (0.024) 280 0.654 0.766 0.0281 0.0441 10 C39H38Cl4N4O5Pd2 997.34 Monoclinic 15.428(4) 7.921(2) 32.63(1) 97.86(3) 3950(2) C2/c 4 1.68 2000 132(2) Yellow plate 0.68 × 0.41 × 0.03 1.23 4–48 3553 3083 (0.069) 254 0.964 0.807 0.0622 0.1874 a R = S(|Fo| 2 |Fc|)/S|Fo|.b wR = [Sw(Fo 2 2 Fc 2)2/Sw(Fo 2)2]� �� . tals suitable for single crystal structure determination (96 mg, 83%), mp 185–186 8C (Found: C, 42.61; H, 3.29; N, 9.16.C32H24Ag2N6O10?2H2O requires C, 42.50; H, 3.12; N, 9.29%). [Ag(NO3)5](III)4(H2O)2 3. Reaction of compound III (70 mg, 0.26 mmol), dissolved in methanol (5 ml), with silver nitrate (54 mg, 0.31 mmol), dissolved in methanol (5 ml), gave a colourless solution. This was concentrated to approximately 5 ml. Subsequent vapour diVusion of diethyl ether into this solution gave microcrystals of complex 3 (101 mg, 80%), mp > 130 8C (Found: C, 39.76; H, 2.50; N, 9.21.C64H48Ag5N13O23?2H2O requires C, 39.57; H, 2.70; N, 9.37%). [Ag(IV)(NO3)]n 4. Reaction of compound IV (50 mg, 0.17 mmol) dissolved in acetone (7 ml) with silver nitrate (29 mg, 0.17 mmol), dissolved in water (3 ml), gave, after slow evaporation at room temperature, colourless crystals of complex 4, suitable for single crystal structure determination (63 mg, 79%), mp 187–188 8C (Found: C, 46.68; H, 3.39; N, 9.15. C18H16Ag- N3O5 requires C, 46.78; H, 3.49; N, 9.09%).[Ag(V)(NO3)]n 5. Reaction of compound V (50 mg, 0.17 mmol), dissolved in methanol (10 ml), with silver nitrate (29 mg, 0.17 mmol), dissolved in water (10 ml), gave colourless needles of complex 5, after 15–30 min, which were filtered oV and washed with methanol (65 mg, 82%). Slow evaporation of an acetonitrile solution of 5 gave crystals suitable for single crystal structure determination, mp > 190 8C (Found: C, 46.72; H, 3.53; N, 9.23. C18H16AgN3O5 requires C, 46.78; H, 3.49; N, 9.09%).Palladium chloride complexes Pd(I)Cl2 6. Reaction of compound I (46 mg, 0.17 mmol), dissolved in hot methanol (5 ml), with palladium chloride (31 mg, 0.17 mmol), dissolved in hot aqueous hydrochloric acid (5 ml, 2 M), gave complex 6 as an orange precipitate (67 mg, 88%), mp > 300 8C (Found: C, 43.35; H, 2.80; Cl, 15.87; N, 6.26. C16H12Cl2N2O2Pd requires C, 43.52; H, 2.74; Cl, 16.06; N, 6.34%). Pd(II)Cl2 7. Reaction of compound II (60 mg, 0.23 mmol), dissolved in hot methanol (5 ml), with palladium chloride (40 mg, 0.23 mmol), dissolved in hot aqueous hydrochloric acid (5 ml, 2 M), gave crude complex 7 as an orange precipitate.This was subsequently recrystallised by vapour diVusion of acetone into a DMSO solution of the crude product to give 7 (82 mg, 81%), mp > 235 8C (decomp.) (Found: C, 41.29; H, 3.41; Cl, 14.72; N, 5.98. C16H12Cl2N2O2Pd?H2O?0.25(CH3)2SO requires C, 41.36; H, 3.26; Cl, 14.80; N, 5.85%). Pd(III)Cl2 8.Reaction of compoI (61 mg, 0.23 mmol), dissolved in hot methanol (5 ml), with palladium chloride (41 mg, 0.23 mmol), dissolved in hot aqueous hydrochloric acid (5 ml, 2 M), gave complex 8 as orange crystals suitable for single crystal structure determination (79 mg, 78%), mp > 260 8C (decomp.) (Found: C, 43.25; H, 2.65; Cl, 16.00; N, 6.38. C16H12Cl2N2O2Pd requires C, 43.52; H, 2.74; Cl, 16.06; N, 6.34%). 1H NMR (CD2Cl2): d 7.12 (2 H, t, H59), 7.16 (2 H, d, H39), 7.32 (2 H, dd, H4,5), 7.59 (2 H, dd, H3,6), 7.84 (2 H, t, H49), 8.69 (2 H, d, H69).Pd(IV)Cl2 9. Reaction of compound IV (60 mg, 0.21 mmol), dissolved in hot methanol (5 ml), with palladium chloride (36 mg, 0.21 mmol), dissolved in hot aqueous hydrochloric acid (5 ml, 2 M), gave complex 9 as an orange precipitate, which was filtered oV and washed with hot ethanol (89 mg, 87%), mp > 220 8C (decomp.) (Found: C, 44.26; H, 3.59; Cl, 14.62; N, 5.60. C18H16Cl2N2O2Pd?H2O requires C, 44.22; H, 3.72; Cl, 14.54; N, 5.74%). Pd(V)Cl2 10.Reaction of compound V (45 mg, 0.15 mmol), dissolved in hot methanol (5 ml), with palladium chloride (27 mg, 0.15 mmol), dissolved in hot aqueous hydrochloric acid (5 ml, 2 M), gave complex 10 as an orange precipitate (59 mg, 82%), mp > 300 8C. Vapour diVusion of acetone into a dimethyl sulfoxide solution of 10 gave crystals suitable for single crystal structure determination (Found: C, 46.68; H, 3.63; Cl, 14.40; N, 5.70.C36H32Cl4N4O4Pd2?CH3COCH3 requires C, 46.97; H, 3.84; Cl, 14.22; N, 5.62%). 1H NMR (DMSO): d 5.47 (8 H, s, CH2), 7.16 (8 H, s, H2,3,5,6), 7.93 (4 H, t, H59), 8.06 (4 H, d, H39), 8.49 (4 H, t, H49), 8.92 (4 H, d, H69). X-Ray crystallography The crystal data and details of the data collections and refinements for the five structures are listed in Table 1. All measure-J. Chem. Soc., Dalton Trans., 1998, 3927–3933 3933 ments were made with a Nicolet P4s diVractometer using graphite monochromatized Mo-Ka (l = 0.71073 Å) radiation.Cell parameters were determined by least-squares refinement on diVractometer angles for at least 20 accurately centred reflections. 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