Effect of anion on Ag(I) meso-helical chains formed with 4,4′-dipyridyl ketone: solvent versus anion bridging and anion effects on the strength of ligand binding

The synthesis and characterisation by IR spectroscopy and elemental analysis of ten new Ag(I)–L complexes are described. Of these complexes, nine are characterised by single crystal X-ray diffraction: {[Ag(L)](CF3SO3)·1/2H2O}∞ (1), {[Ag(L)](ClO4)·1/2H2O}∞ (2), {[Ag2(L)2(CH3CN)](ClO4)2·2CH3CN·H2O}∞ (3), {[Ag2(L)2(CH3CN)2](ClO4)2·CH3CN}∞ (4), {[Ag2(L)2(CH3CN)2](PF6)2·2CH3CN}∞ (5), {[Ag(L)2](CF3SO3)·1/2H2O}∞ (6), {[Ag(L)2](BF4)}∞ (7), {[Ag(L)2](PF6)}∞ (8) and {[Ag(L)2](PF6)·2CH3CN}∞ (9). The primary structures of 1–6 were meso-helical one-dimensional (1D) polymers, while 7 was a helical 1D polymer and 8 and 9 were (4,4) networks. Complexes 1–5 possessed 1 : 1 metal-to-ligand (M : L) ratios, while complexes 6–9 possessed 1 : 2 M : L ratios. The meso-helical chains of complexes 1 and 2 were di-μ-bridged at the Ag(I) nodes by the counteranions CF3SO3− and ClO4−, respectively, while the meso-helical chains of complexes 3–5 were di-μ-bridged at the Ag(I) nodes by the CH3CN molecules. The effect of counteranions and solvent molecules on delicate anion–Ag, π–π-stacking and argentophilic interactions was studied through complexes 1–5. The 1D chains of complexes 6 and 7 possessed monodentate L ligand side arms. The uncoordinated N-donors of these side arms were inclined towards the Ag(I) centre of the adjacent chains and demonstrated narrower Ag–Npy–Cg(pyridyl) angles. In the case of complexes 8 and 9, wider Ag–Npy–Cg(pyridyl) angles and stronger N⋯Ag interactions resulted in (4,4) nets. The effects of the size and the nature of the counteranions on the topology were studied through complexes 6–9.


Introduction
1D architectures form an extensively explored area of coordination polymer chemistry. About 40% of the total reported coordination polymers in the last decade are 1D in nature. Yet there have been very few reviews dedicated to 1D coordination polymers between the years 1993 and 2010, because many researchers perhaps consider 1D coordination polymers to be structurally less attractive than their higher dimensional counterparts. 1 However, through weaker interactions these simple and seemingly less attractive structures possess the ability to demonstrate unusual and interesting architectures. In this regard, Ag(I) is particularly useful, and a significant number of 1D coordination polymers contain Ag(I), as its low dimensional and accommodating stereochemistry often allows it to interact with additional donor atoms from solvent or a counteranion. 2 Rigid linear bridging ligands enable the formation of predictable arrays because of their configuration, coordination activity, and relative orientation of the donor groups. Rigid linear linking ligands such as 4,4′-bipyridine and pyrazine have already been extensively studied for designing linear 1D coordination polymers and higher dimensional networks. 3 Introduction of a bend in these ligands presents a new variable to the study of the coordinating aspects of these linear linkers. The bend provides an opportunity to study lower dimensional structures such as helical, 4 meso-helical, 5,6 zigzag 7-9 chains and other structures of current interest. 10 One simple bent ligand is 4,4′-dipyridyl ketone (L) (Fig. 1). In the solid state, L contains a chiral axis passing through the carbonyl group of the ligand. NDDO calculations reported for L determined that the two rotational energy maxima for rotation of both pyridine rings through or orthogonal to the molecular plane are approximately 45 and 20 kJ mol −1 , respectively. 11 In solution, these two enantiomers readily interconvert from one form to another because of the low energy of conversion, effectively making them appear achiral. 12,13 However in the solid state, the conjugating effect between CO and Py-rings and the hydrogen repulsion in the planar form provide resonance stability to this ligand. 11 The process of stabilisation "freezes" the racemates making L behave as a two-bladed chiral molecular propeller in the solid state. 14 An analogous ligand, 4,4′-dipyridyl amine, acts in a similar fashion as a two-bladed molecular propeller. 15 13 The L ligand formed a pair of 1D meso-helical chains di(μ:κ 2 O,O′)-bridged at the Ag(I) nodes when a CF 3 COO − counteranion was employed. These chains extended their framework by virtue of weak π-π interactions. 17 Linear and zigzag polymers are widely encountered in the literature. Helical polymers have gained added interest in the past decade because of their inherent chirality, 18 while meso-helical polymers remain relatively uncommon. A meso-helix represents an alternative way, compared to a helix, of combining chiral components into an extended structure. 19 Thus, a lemniscate (∞) or figure of eight can be converted into a meso-helix by transforming it into the third dimension (Fig. 2). 20 This achiral 1D strand consists of alternate linkages of the Mand P-forms of the ligands to the metal centre (M). The chain is thus represented as -M-(M)-P-(M)-M-(M)-Pand can sometimes be misinterpreted as a zigzag chain. 21,22 Herein, we describe the use of the bent bridging ligand L to form two series of related coordination polymers of Ag(I) salts with varying M : L ratios (1 : 1 and 1 : 2). These coordination polymers were structurally characterised by single crystal X-ray diffraction, IR spectroscopy and elemental analysis. The first Ag(I) series comprised six 1 : 1 complexes (1-3, 3a, 4, and 5) generated by employing the counteranions CF 3  . Since all of the 1 : 1 Ag-L complexes were meso-helical 1D chains, the diversity in counteranions did not play a profound role in determining the primary structure. However, these coordination polymers provided an opportunity to study the delicate anion-Ag versus CH 3 CN-Ag bridging interactions and their consequences for π-π-stacking and argentophilic interactions in this series of related 1D meso-helical chains. The second Ag(I) series comprised four related 1 : 2 complexes (6-9) generated by employing the counteranions CF 3 SO 3 − , PF 6 − and BF 4 − . In contrast to the first series, the primary structure of these coordination polymers was influenced by the nature of the counteranion, which moderated the extent of interaction between the N-pyridyl (N py ) donor on the peripheral arms and the Ag(I) ion. The counteranion did not directly interact with the Ag(I) ion.

Results and discussion
Coordination polymers 1-9 were all prepared using the same 1 : 1 v/v CH 3 CN : CH 3 OH solvent system. Reactions were carried out in 1 : 1 and 1 : 2 M : L molar ratios. The products formed showed a considerable degree of sensitivity towards the nature of the counteranion and also the M : L ratio. For AgCF 3 SO 3 and AgBF 4 , two products were isolated and the final products had M : L ratios in agreement with the starting ratios as determined by microanalyses. For AgPF 6 , regardless of the M : L ratio used, a mixture of products was formed and a 1 : 1 and two 1 : 2 pseudo-polymorphic coordination polymers were isolated. For AgClO 4 , regardless of the M : L ratio, only polymorphic 1 : 1 products could be isolated. Even when a 2 : 1 M : L ratio was used, only a 1 : 1 product was formed which was found to be a pseudo-polymorph of the other two 1 : 1 AgClO 4 products.
Synthesis and structure of {[Ag(L)](CF 3 SO 3 )·1/2H 2 O} ∞ , 1 The 1 : 1 molar reaction between AgCF 3 SO 3 and L resulted in a tan solid. The microanalysis was consistent with the 1 : 1 formulation. Infrared studies of these samples confirmed the  presence of L as the peaks at 1682 (ketonic CO group), 3124-3053 (aromatic C-H stretching), 1611 and 1555 (CC bending) and 759-660 cm −1 (aromatic C-H bending) were observed. The peak corresponding to the CO moiety of this complex was lower (1682 cm −1 ) than that observed in the free ligand (1731 cm −1 ). The peaks corresponding to the stretching of the SO, C-F, S-O and C-S bonds of the CF 3 SO 3 − counteranion were observed at 1330-1271, 1236-1018, 940-844 and 759-572 cm −1 , respectively. In infrared studies of AgCF 3 SO 3 , Johnston and Shriver have demonstrated that the peak at 1271 cm −1 arises from asymmetric SO 3 stretching, at 1236 cm −1 from symmetric CF 3 stretching and at 760 cm −1 due to the CF 3 angle deformation and the symmetric C-S stretching. 23 Complex 1 crystallised in the monoclinic space group C2/c with one Ag(I) cation, one complete L ligand, one CF 3 SO 3 − counteranion and half a H 2 O of crystallisation in the asymmetric unit. Complex 1 formed a 1D meso-helical strand running along the [1 0 1] diagonal axis (Fig. 3). The Ag(I) ion was essentially linear with an N-Ag-N angle of 175.72(6)°. The slight bend was a consequence of weak interactions between the Ag(I) cation and the O-atoms of adjacent CF 3 SO 3 − anions ( Fig. 3). 24 The pyridyl rings of L formed a two-bladed chiral propeller at an angle between the rings of 50.37(9)°and generated 1D strands. From the viewpoint of chirality, these 1D strands consisted of alternate linkages of the Mand P-forms of the ligands with the Ag(I) ions. The chain was thus represented as -M-(Ag)-P-(Ag)-M-(Ag)-P-, resulting in a meso-helical structure. 19 Adjacent meso-helical chains were formed into antiparallel pairs through a weak π-π interaction [centroid-to-centroid distance 3.803(2) Å; inter-planar dihedral angle 9.80(9)°, minimum interatomic distance 3.615(2) Å; minimum ring slippage between planes 1.664 Å]. The pairs of chains were di(μ:κ 2 O,O′)-bridged by weak Ag⋯OSO 2 CF 3 interactions which appeared to pull the Ag(I) ions closer together. The Ag⋯Ag distance was found to be 3.4704 (16)  Evaporation of the solvents from a 2 : 1 molar reaction between AgClO 4 and L resulted in X-ray quality colourless crystals of 2. However, the microanalysis was consistent with a 1 : 1 formulation. Infrared studies of these samples confirmed the presence of L as the peaks at 1680 (ketonic CO group), 3095 (aromatic C-H stretching), 1612-1555 (CC bending) and 759-657 cm −1 (aromatic C-H bending) were observed. The presence of peaks at 1285, 1055, 952 and 691-619 cm −1 indicated the presence of ClO 4 − . Complex 2 crystallised in the monoclinic space group C2/c with one Ag(I) cation, one complete L ligand, one ClO 4 − counteranion and half a H 2 O of crystallisation in the asymmetric unit. It formed infinite 1D meso-helical strands running along the [1 0 1] diagonal axis (Fig. 4). The Ag(I) ion was essentially linear with an N-Ag-N angle of 170.12(6)°. 24 The slight bend indicated a relatively weak interaction between an adjacent ClO 4 − anion at 2.727(2) Å and the Ag(I) cation.
The Ag⋯OClO 3 interactions fell in the middle of the range of Ag⋯O contact lengths [2.291-3.238 Å] for similar twocoordinated Ag⋯OClO 3 complexes as indicated in the CSD database (version 5.33). 25,26 The pyridyl rings of L formed a two-bladed chiral propeller and registered an angle of 53.37 (8)°between the planes of the rings. This complex possessed achiral meso-helical 1D chains similar to 1.
The adjacent meso-helical chains were formed into antiparallel pairs through two complementary interactions. One of which was weak π-π-interactions involving all of the pyridine rings of the adjacent chain [centroid-to-centroid anions on each side of the meso-helical pair (Fig. 4) Slow evaporation of the solvents from a 1 : 2 molar reaction between AgClO 4 and L resulted in X-ray quality colourless crystals of 3. Again, the microanalysis was consistent with a 1 : 1 formulation. Infrared analysis revealed that the peak corresponding to the CO moiety of this complex was lower (1665 cm −1 ) than that observed in 2 (1680 cm −1 ). The peaks corresponding to the stretching and bending of aromatic rings of L and those for ClO 4 − were similar to 2. Slow evaporation of the solvents from a 1 : 1 molar reaction between AgBF 4 and L resulted in colourless crystals of {[Ag 2 (L) 2 (CH 3 CN) 2 ](BF 4 ) 2 ·CH 3 CN·H 2 O} ∞ (3a) which were found to be isomorphous with 3 (experimental section). Complex 3 formed infinite 1D meso-helical strands along the c axis which through bridging interactions were formed into two-dimensional (2D) sheets in the ac plane.
It crystallised in the monoclinic space group P2 1 /c with two crystallographically distinct Ag(I) cations, two complete L ligands, two ClO 4 − counteranions, three CH 3 CN molecules and a H 2 O of crystallisation in the asymmetric unit. The crystallographically distinct Ag(I) cations were present in different 1D meso-helical polymeric strands running parallel to each other along the c axis (Fig. 5). One Ag(I) cation possessed a linear geometry by coordinating with two N-donors of the L ligand, while the other Ag(I) cation possessed a T-shaped geometry by exhibiting additional coordination to a CH 3     The linear and T-shaped Ag(I) ions were present in separate strands and formed a pair of dissimilar strands. This pair of strands was di(μ:κ 2 N)-bridged by the CH 3 CN molecules ( Fig. 5) and displayed weak π-π-stacking interactions [the centroid-to-centroid distances were 3.717(3) Å (inter-planar dihedral angle 5.5(2)°, minimum interatomic distance 3.601(3) Å; minimum ring slippage between planes 1.293 Å) and 3.749(2) Å (inter-planar dihedral angle 1.8(2)°, minimum interatomic distance 3.701(2) Å; minimum ring slippage between planes 1.600 Å)]. These distances were registered every alternate pyridine ring throughout the pair of strands. Slow evaporation of solvent from a solution of AgClO 4 and L in a 1 : 1 M : L ratio resulted in X-ray quality colourless crystals of 4. The infrared spectrum revealed that the peaks corresponding to the ketonic CO group, stretching and bending of aromatic rings of L and ClO 4 − were similar to those of 2. Complex 4 formed infinite 1D meso-helical strands along the c axis which through bridging interactions were formed into 2D sheets in the ac plane. It crystallised in the monoclinic space group P2 1 /c with two crystallographically distinct Ag(I) cations, two complete L ligands, two ClO 4 − counteranions and three CH 3 CN molecules in the asymmetric unit. The crystallographically distinct Ag(I) cations were present in different 1D meso-helical polymeric strands running parallel to each other along the c axis ( Fig. 6). One Ag(I) cation possessed a linear geometry by coordinating with two N-donors of the L ligand, while the other Ag(I) cation possessed a four-coordinated geometry by exhibiting additional coordination to two CH 3 CN molecules. The linear Ag(I) cation displayed a slight bend and the N py -Ag1-N py angle measured 165.85 (18) Å. This bend may have been a consequence of the weak N⋯Ag interactions with the three CH 3 CN molecules [the N⋯Ag contacts ranged between 2.887(7) and 3.043(6) Å]. 25,26 The four-coordinated Ag(I) cation adopted a geometry between a seesaw and a trigonal pyramid as evidenced by a τ 4 value of 0.70. 27 The N5-Ag2 and N7-Ag2 distances were 2.414(6) Å and 2.657(6) Å, respectively. The   (7) 6). This asymmetric bridging was augmented by virtue of weak π-π-stacking interactions [centroid-to-centroid distance was 3.884 (4)  A bulk reaction with a 1 : 2 M : L ratio of AgPF 6 and L resulted in the formation of a brown crystalline precipitate in moderate yield. However, the microanalysis of the bulk sample was consistent with a 1 : 1 formulation. Infrared studies of these samples confirmed the presence of L as the peaks at 1675 (ketonic CO group), 1612 and 1555 (CC bending) and 757-651 cm −1 (aromatic C-H bending) were observed. The very strong sharp peak at 821 cm −1 and strong sharp peak at 555 cm −1 indicated the presence of PF 6 − counteranions. 28 Complex 5 formed infinite 1D meso-helical strands along the b axis which through bridging interactions were formed into 2D sheets in the ab plane. It crystallised in the monoclinic space group P2 1 /c and the asymmetric unit consisted of two crystallographically distinct Ag(I) cations, two complete L ligands, two PF 6 − counteranions and four CH 3 CN molecules.
The two crystallographically distinct Ag(I) cations and ligands were alternately present in the same 1D meso-helical strand despite it running along the crystallographic b axis (Fig. 7). The Ag(I) cations displayed a pseudo T-shaped three-coordinated geometry by coordinating with two N py -donors of two distinct L ligands and a CH 3   alternate Ag(I) nodes by the bound CH 3 CN molecules generating a 2D sheet in the ab plane (Fig. 7).  The pyridyl rings of L formed a two-bladed chiral propeller. The L ligands which formed the polymeric backbone registered an angle of 48.8(4)°, while the decorated L arms registered an angle of 58.6(4)°between the planes of the pyridine rings. The uncoordinated N2 of the dipyridyl ketonic arms showed a slight inclination towards Ag1 of an adjacent chain with N2⋯Ag1 contact of 3.153(8) Å 29,30 and registered an angle of 111.95°between the Ag(I)-N2 py -Cg py . This long contact distance and very narrow angle indicated that there is essentially no interaction between pyridyl N2 and Ag1 (Fig. 9). The arrangement of the decorated arms created a cavity encompassing two CF 3 SO 3 − counteranions.

Synthesis and structure of {[Ag(L) 2 ](BF 4 )} ∞ , 7
Slow evaporation of solvents from a solution of AgBF 4 and L in a 1 : 2 M : L ratio resulted in X-ray quality colourless crystals of 7. The microanalysis of the bulk reaction with similar molar and solvent ratios was consistent with a 1 : 2 formulation. Infrared studies of these samples confirmed the presence of L as the peaks at 1677 (ketonic CO group), 3106-3054 (aromatic C-H stretching), 1608-1555 (CC bending) and 756-660 cm −1 (aromatic C-H bending) were observed. The peaks at 1032, 756 and 520 cm −1 confirmed the presence of the BF 4 − counteranion.
Complex 7 crystallised in the monoclinic space group P2 1 /c to form infinite polymeric chains along the b axis. Each asymmetric unit contained one Ag(I) cation, two L ligands and one BF 4 − counteranion (Fig. 10). One L ligand bridged the three coordinated Ag(I) nodes and extended the polymer to a 1D chain, while the second L ligand interacted with Ag(I) through monodentate interactions and formed decorating side arms  This journal is © The Royal Society of Chemistry 2014 of the chain. Surprisingly, the 1D chain of 7 existed as a helix rather than a meso-helix. This was the only example of a helical chain for this entire series of compounds. Of necessity, both M and P forms of the helices were present in the centrosymmetric structure. The uncoordinated N2 of these side arms resided in the vicinity of Ag1 of the adjacent chain. The Ag1 bond distances to the other N py -donors of 2.2121-2.3861(17) Å were within the normal range. The Ag(I) cation adopted a slightly distorted trigonal-planar geometry with three N py at the angle of 109.33(6)°, 149.54(6)°and 99.89(6)°f or N3-Ag1-N4, N1-Ag1-N3 and N1-Ag1-N4, respectively. The Ag(I) ion deviated by 0.133 Å from the plane of three bound N-donors. The pyridyl rings of L formed a two-bladed chiral propeller. The L ligands which formed the polymeric backbone registered an angle of 57.50(10)°, while the decorated L arms registered an angle of 65.49(10)°between the planes of the rings. The two crystallographically distinct L ligands were pseudo enantiomers of each other. The uncoordinated N2 of the L side arm showed a significant inclination towards Ag1 with a N2⋯Ag1 contact of 2.6582(18) Å 29,30 and registered an angle of 138.80°between the Ag(I)-N py -Cg py . 31 A search of the CSD database identified 12 complexes with Ag(I)⋯N(pyridine) contacts in the range of 2.60-2.70 Å. For 11 of these complexes, the Ag(I)-N py -Cg py angle ranged from 132 to 141°, while one had a value of 125°. The consistency of the angles within this range suggested the presence of a weak interaction between pyridyl N and Ag(I). By virtue of this close contact and the positioning of the decorated arms on the adjacent chains, cavities existed in what appeared to be a pseudo (4,4) rhombic network (Fig. 10). The four Ag1 ions occupied the corners of the rhombus, and the adjacent sides of the network measured 11.102 Å and 11.471 Å. The four ligands of the rhombus were arranged such that two CO groups of the opposite ligands, which were pseudo enantiomers of each other, pointed above the plane of the rhombus and towards each other, while the remaining two CO groups of the ligands, which were also pseudo enantiomers, pointed below the plane and splayed away from each other (Fig. 10). This arrangement caused the pseudo (4,4) network to be flat and achiral. The weak CH-π-interactions between C-H25⋯Cg2 (N2 containing pyridine) [the distance between H-centroid was 2.72 Å] 32 and the weak π-π-interactions [the Cg2⋯Cg2 contact was 3.7572(16) Å, inter-planar dihedral angle 0°, minimum interatomic distance 3.736(16) Å; ring slippage between planes 1.525 Å] 33   generated (Fig. 11). The adjacent sides of the network measured 11.070(3) Å and 11.651(3) Å. The four ligands of the rhombus were arranged in an irregular way such that the CO groups of three of the ligands pointed above and one pointed below the plane of the rhombus (Fig. 11). The three ligands with the CO groups which pointed above were of the same pseudo enantiomeric form, while the one with the CO group pointing below was of the other pseudo enantiomeric form.  35 and weak π-πinteractions [Cg4⋯Cg2 contact was 3.899(3) Å, inter-planar dihedral angle 12.50(17)°, minimum interatomic distance 3.739(3) Å; minimum ring slippage between planes 0.9035 Å]. 33 The two PF 6 − counteranions resided within the cavity being slightly above and below the plane of the rhombus by virtue of several weak anion-CH interactions [H⋯F contact distances between 2.44 and 2.97 Å] and strong anioncarbonyl interactions. The F11⋯C6 contact was 2.874(4) Å and the F14⋯C17 contact was 2.959(4) Å. A search of the CSD database suggested that for complexes containing pyridyl ketone like ligands, there were only two out of 204 observations which displayed a F⋯C CO contact below the van der Waals limit of 3.2 Å. 36,37 In total in the CSD there are 422 observations of general OC⋯F-PF 5 − interactions which range from 2.53 to 3.17 Å with a mean contact of 3.02 Å. 26,27 Complex 9 crystallised in the triclinic space group P1 to form an infinite 2D network in the ab plane. Each asymmetric unit comprised one Ag(I) cation, two L ligands, one PF 6 − counteranion and two CH 3 CN of crystallisation. The Ag(I) cation adopted a distorted tetrahedral geometry as evidenced by a τ 4 value of 0.91. 27 The four pyridine N-atoms coordinated to the Ag(I) ion at angles between 93.43 (12) and 119.90(12)°and interacted with the Ag(I) ions in the regular range of 2.268(4)-2.352(4) Å. These pyridyl rings demonstrated Ag(I)-N py -Cg py angles between 168.46 and 175.58°. The L ligand formed a two-bladed chiral molecular propeller, and the pyridyl rings of L registered angles of 53.78 (14)°and 77.2(9)°b etween the planes of the rings. The two crystallographically distinct L ligands were of the same pseudo enantiomeric form. Both the L ligands bridged the Ag nodes perpendicular to each other and a regular (4,4) rhombic network was generated (Fig. 12). The adjacent sides of the network measured 10.950(7) Å and 11.108(7) Å. These distances corresponded to the length of crystallographic a and b axes. The four ligands of the rhombus, all of the same pseudo enantiomeric form, were arranged such that the CO groups of the two ligands pointed above and two pointed below the plane of the rhombus (Fig. 12). This arrangement gave a more regular network which was also chiral. 38,39 The adjacent sheets of the (4,4) network, which were enantiomers of each other, were interdigitated and stacked on top of each other in a -A-B-Afashion along the c axis.
No other noteworthy π-π-stacking and H-bonding interactions were observed.

Comparison of structures
In structures 1-9, the coordination environment of the Ag(I) ions ranged from linear to trigonal pyramidal. The L ligand bridged the Ag(I) cores and generated the primary structure of 1D meso-helical chains in complexes 1-6, a helical 1D chain in complex 7 and 2D networks in complexes 8 and 9. The 1D meso-helical polymers in 1 and 2 existed as pairs of chains di(μ:κ 2 O,O′)-bridged with counteranions, while in 3-5 they existed as 2D grids extended by bridging of the Ag(I) nodes of the 1D meso-helical polymers by counteranions and CH 3 CN molecules. Complex 6 existed as a genuine 1D meso-helical polymer, while complex 7 was a pseudo (4,4) network and complexes 8 and 9 were (4,4) networks. The L ligand also acted as a two-bladed chiral molecular propeller within each solid-state structure such that the planes of the two pyridine rings intersected each other at an angle summarised in Table 1. The average twist in the planes of the pyridine rings was 52.6°. It is interesting to note that the pseudo-polymorphous complexes 3 and 4 and complexes 8 and 9 displayed large variations in these angles for only one of the ligands incorporated in the structures.
The influence of the coordinating ability of the anions on the stoichiometry of the resultant Ag(I) complexes was demonstrated by our closely related series of coordination polymers. [40][41][42] The weakly coordinating CF 3   along with the bifurcated bridging of a CH 3 CN molecule from the other side extended the structures of 3 and 4 to 2D grids. In 2 and 3, the meso-helical chains bridged by ClO 4 − recorded shorter Ag⋯Ag contact distances but weaker π-π-interactions than the meso-helical strands bridged by CH 3 CN. Surprisingly, the meso-helical strands of 4 demonstrated slightly tighter bridging by CH 3 CN molecules but higher Ag⋯Ag contact and weaker π-π-interactions than the pseudo-polymorphous 3. The CH 3 CN molecules of 5 bridged the pair of meso-helical chains more tightly as compared to the bridging observed in 3. This was evidenced by a shorter Ag⋯Ag contact in the case of 5 as compared to 3. However, the π-π-interactions were found to be weaker in 5. In 5, the Ag⋯Ag contact at the bridged nodes was considerably shorter than that at the unbridged nodes, thus highlighting the effect of CH 3  molecules, while in 1.6% of the complexes, the CH 3 CN molecules displayed di(μ:κ 2 N)-bridging of the Ag(I)ions (Fig. 13). 25,26 In the 1 : 2 M : L complexes 6 and 7, the uncoordinated N2 donor of the decorating L side arms of the strands displayed inclination towards the Ag(I) centre on the adjacent polymeric chain and forced an unusual geometry on that metal centre. The counteranions in both these complexes did not coordinate to the Ag(I) ion. However, the size of the counteranion played a critical role in elaborating the dimensionality of the chains. In the former complex, the bulkier CF 3 25,26 There were 2427 observations with Ag(I)-N py -Cg py angles between 144.6 and 180°and their Ag(I)⋯N py distances range within 2.084-2.399 Å. This shows that the wider the Ag(I)-N py -Cg py angle, the stronger the Ag(I)⋯N py interaction. The CO groups of the four ligands of the rhombus of 6 splayed outwards. In 7, the CO groups of the four ligands of the rhombus were arranged such that two CO groups of the opposite ligands, which were pseudo enantiomers, pointed above the plane of the rhombus and towards each other, while the two CO groups of the remaining ligands, which were also pseudo enantiomers, pointed below the plane and were splayed away from each other. This arrangement produced an achiral sheet. The rhombus of the 2D network of 9 has a regular orientation with two CO groups pointing up and two pointing down and two CH 3 CN molecules in each cavity. All four ligands of the rhombus were of the same pseudo enantiomeric form producing a chiral sheet. By contrast, the rhombus of the 2D network of 8 has an irregular orientation with three CO groups pointing up and one pointing down and no CH 3 CN molecules in the structure. Three ligands of the rhombus had the same pseudo enantiomeric form, while the remaining ligand was of the other pseudo enantiomeric form. This gave rise to an achiral sheet. Thus, the irregular orientation of the CO groups in 8 appeared to make the structure corrugated rather than flat, while the vacillations of the CO groups prevented the formation of true 2D networks in 6 and 7. These differences may have been the cause of the embedding of the counteranions and the solvent molecules in the network cavities.

Conclusions
In conclusion, we have described two series of related coordination polymers of Ag(I) salts and L ligand with varying M : L ratio (1 : 1 and 1 : 2). The primary structure of the first Ag(I) series was not sensitive to the counteranion. However, the delicate anion-Ag and CH 3 CN-Ag bridging interactions showed a subtle effect on π-π-stacking and argentophilic interactions.
Owing to these delicate interactions, a transition from 1D meso-helical chains to 2D grids was observed. The second Ag(I) series displayed a remarkable sensitivity to the counteranion showing a transition from ordered 1D meso-helical chains to 2D (4,4) nets.

Experimental section
Commercially available 4,4′-dipyridyl ketone was acquired from Chem Bridge. All chemicals were used as received without further purification. All solvents were of LR grade or above. The samples for microanalysis studies were dried under vacuum to remove volatile sample residues. Elemental microanalyses were carried out at the Campbell Microanalytical Laboratory, University of Otago. All measured microanalysis results were within an uncertainty of 0.4%. Infrared (IR) spectra were recorded on a Perkin-Elmer Spectrum BX FT-IR system. Caution! Although no problems were encountered in this work, transition metal perchlorates are potentially explosive. They should be prepared in small amounts and handled with care.