Hierarchy of Hydrogen Bonding versus Anion Binding in Self

Hierarchy of Hydrogen Bonding versus Anion Binding in Self-Assembled Network ... or PF6, and it is argued that the hierarchy of control in the self-as...
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CRYSTAL GROWTH & DESIGN

Hierarchy of Hydrogen Bonding versus Anion Binding in Self-Assembled Network Structures of Silver(I)

2006 VOL. 6, NO. 4 974-982

Tara J. Burchell, Dana J. Eisler, and Richard J. Puddephatt* Department of Chemistry, UniVersity of Western Ontario, London, Canada, N6A 5B7 ReceiVed NoVember 1, 2005; ReVised Manuscript ReceiVed February 16, 2006

ABSTRACT: Reaction of the ligands 1,2-C6H4{NHC(dO)-4-C5H4N}2 (1) and 1,2-C6H4{NHC(dO)-3-C5H4N}2 (2) with silver(I) salts AgX, X ) CF3CO2, NO3, CF3SO3, and PF6, gave the corresponding complexes [(AgX)(µ-LL)]n, 3a-4d (3a-3d: LL ) 1; 4a-4d: LL ) 2; a, X ) CF3CO2; b, X ) NO3; c, X ) CF3SO3; d, X ) PF6). The complexes probably exist in solution primarily as the disilver(I) macrocyclic complexes [{AgX(µ-LL)}2] or [Ag2(µ-LL)2]X2, but in the solid state they may exist as either macrocycles or polymers [{AgX(µ-LL)}n] or [Agn(µ-LL)n]Xn. The silver(I) centers have distorted tetrahedral stereochemistry when X ) CF3CO2 or NO3 but roughly linear stereochemistry when X ) CF3SO3 or PF6, and it is argued that the hierarchy of control in the selfassembly process is by the bonds Ag-N > Ag-O > NH‚‚‚OdC when X ) CF3CO2 or NO3, but Ag-N > NH‚‚‚OdC > Ag‚‚‚O or Ag‚‚‚F when X ) CF3SO3 or PF6. In complexes 3a and 3b, macrocyclic complexes are connected to form polymers or sheets, respectively, through bridging anions, whereas polymers of 4a are connected through bridging anions to form a double-stranded polymer. In all these cases, network structures are formed through formation of intermolecular hydrogen bonds NH‚‚‚OdC, and these porous networks contain large solvent-filled channels. In the molecular materials assembled using the more weakly bonding anions (X ) CF3SO3 or PF6), the network structures are more compact, and they do not contain solvent molecules. Complexes 3c and 4d exist as polymers, whereas 4c exists as a macrocycle. These complexes are further connected through hydrogen bonding and through weak Ag‚‚‚O or Ag‚‚‚F interactions to form network structures. Complexes 3a-3c and 4a adopt the polar anti conformation of the two amidopyridyl units of the bidentate ligands, and 4d adopts a similar conformation with an intramolecular NH‚‚‚OdC bond, but complex 4c adopts the nonpolar syn conformation. Complex 4d is unusual because it undergoes spontaneous resolution to give crystals in which chiral polymers are self-assembled to give a chiral network. Introduction The combination of dynamic coordination chemistry and noncovalent interactions, such as hydrogen bonding, provides a powerful method for creating complex structures from simple building blocks.1,2 By incorporating hydrogen bonding amide groups into bis(pyridyl) ligands, it is possible to use the known patterns of self-assembly through hydrogen bonding between amide units to engineer the secondary and tertiary structures of the primary molecular materials, which are formed through dynamic coordination chemistry.3 It is natural to use silver(I) complexes in self-assembly because the coordination number and stereochemistry of silver(I) are variable, with linear (CN ) 2), trigonal (CN ) 3), and tetrahedral (CN ) 4) geometries all being common. Thus, a simple complex of empirical formula AgXL2 (X- ) anion, L ) neutral ligand) may be formed as [AgL2]+X-, [AgXL2], or [Ag2(µ-X)2L4] (Chart 1), depending primarily on the donor strength of the anion, and, if bridging multidentate ligands are used, correspondingly different molecular architectures may be formed.4 If the anion bridges between silver(I) centers, there may be an increase in dimensionality of the primary material.5 Most early studies of self-assembly of network structures of silver(I) used rigid, linear bipyridine derivatives.4,5 In a few cases, hydrogen bonding amide groups were incorporated into the bis(pyridine) ligands and shown to play a role in the selfassembly of the silver(I) coordination networks.6 For example, Lauher and Yip studied the self-assembly of network structures, in which the primary structures formed through the coordinate bonds were further aligned and associated by hydrogen bonding, using ligands in which ureas and oxalamides were derivatized * To whom correspondence should be addressed. Fax: (519) 661-3022. E-mail: [email protected].

Chart 1.

Some Common Coordination Geometries for Silver(I)

with pyridyl donor groups or with the ligands N,N′-bis(3pyridinecarboxamide)-1,2-ethane and N,N′-bis(3-pyridinecarboxamide)-1,6-hexane, respectively.6a,6b This article further demonstrates the potential of this approach to the engineering of the solid-state structures of silver(I) network materials by using the U-shaped bis(amidopyridyl) ligands 1 and 2. In these ligands, the amide groups prefer the trans HN-CdO orientation but can exist in several different conformations as a result of rotation of the amide unit with respect to the aromatic groups at either end. Thus, they can exist in the chiral C2-symmetric conformation A, B, the achiral conformation C, or, as shown in this work, the chiral conformation with an intramolecular hydrogen bond D (alternatively written as D-A, D-B) (Chart 2).2i,3a,3b These flexible ligands are also capable of forming either macrocyclic or polymeric complexes with silver(I), and the incorporation of both hydrogen bonding groups in the ligand and the weakly binding anions X- (donor strengths X- ) CF3CO2 > NO3 > CF3SO3 > PF6)6d in the silver(I) salts AgX creates a system with potential to form new and interesting network structures. A preliminary account of part of the present work has been communicated.3b

10.1021/cg050578q CCC: $33.50 © 2006 American Chemical Society Published on Web 03/16/2006

Self-Assembled Network Structures of Silver(I) Chart 2.

Ligands 1 and 2 and, below, Some Preferred Conformations

Crystal Growth & Design, Vol. 6, No. 4, 2006 975 Scheme 1

Results Reaction of equimolar amounts of the bis(amidopyridine) ligands 1 and 2 with silver(I) salts AgX, X ) CF3CO2, CF3SO3, NO3, and PF6 gave the corresponding complexes of formula [(AgX)(µ-LL)]n, 3a-4d (3: LL ) 1; 4: LL ) 2; a, X ) CF3CO2; b, X ) NO3; c, X ) CF3SO3; d, X ) PF6). The complexes were isolated as analytically pure, air stable, white solids that slowly decomposed in solution or upon exposure to light and that were insoluble in most common organic solvents. They were soluble in DMSO but with decomposition since DMSO is competitive with pyridine as a ligand for silver(I), and they were very sparingly soluble in the mixed solvent system CH2Cl2-methanol. Since the isolated complexes were so sparingly soluble, single crystals were grown by slow diffusion of a solution of the silver(I) salt into a solution of the ligand. The complexes 3a-4d were characterized in dilute solutions in CH2Cl2-methanol by 1H NMR spectroscopy and by ESIMS. The NMR spectra contain the expected resonances of the bis(pyridyl) ligands, with modest coordination shifts compared to the free ligand, and parameters are listed in Experimental Section. Since single resonances for each ligand hydrogen were observed, the spectra are consistent with the presence of macrocycles [Ag2X2(µ-LL)2] or [Ag2(µ-LL)2]X2 or with a dynamic equilibrium between macrocyclic and oligomeric isomers [{AgX(µ-LL)}n] or [{Ag(µ-LL)n]Xn but are not consistent with the existence of the compounds in solution as static, ring-opened oligomers. In the ESI-MS, most complexes gave peak envelopes centered at m/z ) 425, 531, 743, and 849 (reported for the 107Ag isotope), corresponding to the fragments [Ag‚LL]+, [Ag2‚(LL-H)]+, [Ag‚(LL)2]+ and [Ag2‚(LL)‚(LLH)]+ but no peaks corresponding to complex ions with three or more silver atoms. In addition to these peaks, most compounds gave peaks due to ions with anions incorporated. For example, the ESI-MS for the trifluoroacetate complexes 3a and 4a each showed additional peaks at m/z ) 645 and 963, corresponding to the fragments [Ag2‚X‚LL]+ and [Ag2‚X‚(LL)2]+ (X ) CF3CO2) 3a: LL ) 1, 4a: LL ) 2), and complex 4a gave an additional peak at m/z ) 955 corresponding to [Ag3‚(LL-H)2]+. The ESI-MS for the triflate complexes 3c and 4c each showed a peak at m/z ) 681 corresponding to the fragment [Ag2‚X‚ LL]+ (X ) CF3SO3), and the ESI-MS for the nitrate complexes 3b and 4b each contained a peak at m/z ) 594 corresponding to [Ag2‚X‚LL]+ (X ) NO3). Complex 4b also gave a peak from

the higher mass fragment [Ag2‚(LL)2‚NO3]+ at m/z ) 912. Overall, similar ESI-MS data were obtained for all complexes, with common fragments corresponding to [Ag‚LL]+, [Ag‚ (LL)2]+, and [Ag2‚X‚LL]+ or [Ag2‚X‚(LL)2]+, all of which could be derived from macrocycles [Ag2(µ-LL)2]2+, [Ag2X(µ-LL)2]+, or [Ag2X2(µ-LL)2]+. Only in the case of complex 4a was a peak observed corresponding to a complex containing three silver atoms. In contrast, it will be shown that the complexes 3c, 4a, and 4d exist in the solid state as polymers, and it is therefore likely that ring-opening polymerization occurs during crystallization. A schematic summary of the solid-state structures is shown in Scheme 1, and they are described in detail below. The ligands exist in the chiral conformations A and B in complexes 3a-3c and 4a, D-A and D-B in 4d but adopt conformation C in complex 4c (Chart 2). In all complexes, the primary structures are further assembled by intermolecular amide hydrogen bonds and in complexes 3c, 4c, and 4d other secondary bonding forces, such Ag‚‚‚O and Ag‚‚‚Ag interactions, also play a part in the final self-assembly process. Several of the crystalline complexes contained solvent molecules in open channels, but these solvent molecules were lost on drying the samples. Structures of the Trifluoroacetate Complexes 3a and 4a. The structure of complex 3a, studied as the dichloroethane solvate 3a‚2.5(ClCH2CH2Cl), is depicted in Figures 1 and 2. The bis(amido-4-pyridyl) ligands 1 and silver(I) ions form, as the primary structure, a 30-membered macrocycle [Ag2(µ-1)2]2+. The macrocyclic cavities are large and open, with a bis(pyridyl) bite distance N(1)‚‚‚N(1A) ) 8.49 Å and intramolecular silversilver distance Ag(1)‚‚‚Ag(1A) ) 10.44 Å. The macrocycles are connected by pairs of µ2-η1-trifluoroacetate anions and form the one-dimensional (1D) polymer [Ag2(µ-1)2(µ-CF3CO2)2]n, with tetrahedral silver(I) centers, as shown in Figure 1. Each macrocycle [Ag2(µ-1)2]2+ contains one ligand in conformation 1A and one in conformation 1B (Chart 2). The “polymers of macrocycles” shown in Figure 1 further associate through intermolecular amide-amide hydrogen bonds [N(2)‚‚‚O(1A) ) 2.788(4) Å] to give a three-dimensional (3D) network (Figure 2). The hydrogen bonding occurs between amide groups of ligands on adjacent chains in a manner analogous to the head-to-tail, ‚‚‚A‚‚‚B‚‚‚A‚‚‚B‚‚‚ pattern observed in the structure of the free ligand 1.2i Thus, A ligands of one polymer chain are sandwiched between B ligands from two

976 Crystal Growth & Design, Vol. 6, No. 4, 2006

Figure 1. A view of the structure of the macrocyclic complex 3a, further associated to form a 1D polymer by anion binding. Selected bond distances: Ag(1)-N(1) ) Ag(1)-N(1B) ) 2.245(4), Ag(1)O(50) ) 2.359(7), Ag(1)-O(50A) ) 2.494(7) Å; angles N(1)-Ag(1)N(1B) ) 125.6(2), N(1)-Ag(1)-O(50) ) 98.0(2), N(1)-Ag(1)O(50A) ) 123.7(2), N(1B)-Ag(1)-O(50) ) 126.3(2), N(1B)-Ag(1)O(50A) ) 97.2(2), O(50)-Ag(1)-O(50A) ) 78.9(3) °. Symmetry operators: x, -y + 1, z; -x + 2, -y + 1, -z + 2; -x + 2, y, -z + 2; -x + 3, y, -z + 3.

Figure 2. 3D network of macrocycles of 3a, showing the dichloroethane filled channels formed by intermolecular N-H‚‚‚OdC hydrogen bonding between macrocycles. Only the bridging oxygen atoms of the anions are shown.

adjacent polymer chains and vice versa, so that propagation occurs in a second dimension in an ‚‚‚A‚‚‚B‚‚‚A‚‚‚B‚‚‚ fashion, creating channels that host solvent molecules of crystallization (Figure 2). Because each polymer hydrogen bonds to polymers at the top (A ligands) and bottom (B ligands) of the chain, propagation of the network also occurs in the third dimension, and a beautiful 3D network is formed (Figure 2). According to the hierarchical sequence of increasing dimensionality described above, the primary macrocyclic structure of 3a is formed by the silver(I) ions and the bis(pyridyl) ligands, the secondary polymeric structure is then formed by additional anion binding, and the final tertiary network structure is formed by hydrogen bonding between amide groups. The description of anion binding having higher priority than hydrogen bonding is arbitrary, and an alternate description would be to describe the primary structure as before but with the secondary structure being a sheet of macrocycles formed by hydrogen bonding between amide groups and the tertiary network structure formed by anion bonding to link these sheets (Figure 2). The relative contributions to the overall bonding from anion binding and

Burchell et al.

Figure 3. View of the 1D, double-stranded polymeric structure of complex 4a. Selected bond distances: Ag(1)-N(1) ) 2.199(4), Ag(1)N(4A) ) 2.232(4), Ag(1)-O(50) ) 2.412(3), Ag(1)-O(50A) ) 2.584(3) Å; angles N(1)-Ag(1)-N(4A) ) 142.6(2), N(1)-Ag(1)O(50) ) 123.0(1), N(1)-Ag(1)-O(50A) ) 90.8(1), N(4A)-Ag(1)O(50) ) 92.0(1), N(4A)-Ag(1)-O(50A) ) 101.9(1), O(50)-Ag(1)O(50A) ) 91.73(1)°. Symmetry operators: x, y, z + 1; -x + 3, -y, -z + 1; -x + 3, y + 2, -z; x, y, z - 1.

Figure 4. 3D network of double-stranded polymers of 4a, formed by intermolecular N-H‚‚‚OdC hydrogen bonding between ligands in adjacent polymer chains, showing only the bridging oxygen atoms of the anions. The network channels are occupied by dichloromethane (green Cl) and methanol (red O) solvent molecules.

hydrogen bonding will clearly vary as a function of the donor power of the anion. The structure of complex 4a, studied as the solvate 4a‚1.5(CH2Cl2)‚(MeOH), is shown in Figures 3 and 4. The primary structure formed from the bis(amido-3-pyridyl) ligands, 2, and silver(I) ions is the polymeric chain [Ag(µ-2)]nn+ in which all ligands have the same chiral conformation 2A or 2B. Because the nitrogen atoms of the 3-pyridyl rings in 4a point in opposite directions, the ligand N‚‚‚N separation [N(1)‚‚‚N(4) ) 8.75 Å] and intramolecular silver-silver distance [Ag(1)‚‚‚Ag(1A) ) 12.40 Å] are larger in the 3-pyridyl complex 4a than in the analogous 4-pyridyl complex 3a. Pairs of polymer chains in 4a are connected, through binding by the µ2-η1-trifluoroacetate anions, to form the double-stranded polymer chains shown in Figure 3, in which the silver(I) centers have distorted tetrahedral stereochemistry. Since each double-stranded polymer contains

Self-Assembled Network Structures of Silver(I)

Crystal Growth & Design, Vol. 6, No. 4, 2006 977

Figure 6. 3D network of macrocycles of 3b. The network is formed through intermolecular amide-amide hydrogen bonds and contains channels that host disordered methanol solvent molecules. Figure 5. Top: A view of the structure of the macrocyclic complex 3b. Selected bond parameters: Ag(1)-N(1) ) 2.274(3), Ag(1)-N(4A) ) 2.241(3), Ag(1)-O(3A) ) 2.487(3), Ag(1)-O(5) ) 2.568(3) Å, N(1)-Ag(1)-N(4A) ) 134.4(1), N(1)-Ag(1)-O(5) ) 99.5(1), N(1)Ag(1)-O(3A) ) 99.3(1), N(4A)-Ag(1)-O(5) ) 108.6(1), N(4A)Ag(1)-O(3A) ) 115.3(1) °. Symmetry operators: -x, -y + 1, -z; -x - 1/2, y, z - 1/2; -x - 1/2, y, z + 1/2. Bottom: The 2D sheet of macrocycles in which the macrocycles are connected by nitrate anions.

one strand containing only ligands 2A and one containing only ligands 2B, the overall double stranded polymeric structure is racemic. Finally, the double-stranded polymer chains in 4a associate through intermolecular amide-amide hydrogen bonds [N(2)‚‚ ‚O(2A) ) 2.785(5) Å, N(3)‚‚‚O(1A) ) 2.762(5) Å] to form a 3D network (Figure 4). The hydrogen bonding occurs in a very similar head-to-tail, ‚‚‚A‚‚‚B‚‚‚A‚‚‚B‚‚‚ pattern as found in complex 3a (compare Figures 2 and 4), with propagation in the second and third dimensions, and so a related network structure is formed. Furthermore, the hydrogen bonded network contains large open channels, as in complex 3a, that encapsulate solvent molecules. An alternative description of the structure would be to consider the primary polymer chains to be connected through hydrogen bonding to give sheets of polymers, followed by anion binding to connect the sheets and give the final network structure of Figure 4. Structure of the Nitrate Complex 3b. The solid-state structure of complex 3b, studied as the solvate 3b‚2(MeOH), is shown in Figures 5 and 6. The bis(amido-4-pyridyl) ligands and silver(I) ions form a 30-membered macrocycle [Ag2(µ-1)2]2+ (Figure 5, top). These macrocycles resemble those in the trifluoroacetate complex 3a but have shorter N‚‚‚N separation and intramolecular silver‚‚‚silver distances [N(1)‚‚‚N(4A) ) 6.84 Å, Ag(1)‚‚‚Ag(1A) ) 8.47 Å]. The nitrate anions are coordinated to the silver(I) centers as µ2-η2-O,O′ donors, and

Figure 7. View of the 1D zigzag, polymeric structure of complex 3c, with weakly coordinated triflate anions. There are alternating ligand conformers I, containing donor atoms N(1) and N(4), and II, containing donor atoms N(5) and N(8). Selected bond distances: Ag(1)-N(8A) ) 2.126(8), Ag(1)-N(1) ) 2.153(8), Ag(2)-N(4) ) 2.164(8), Ag(2)N(5) ) 2.151(8) Å; angles N(8A)-Ag(1)-N(1) ) 178.2(3), N(4)Ag(2)-N(5) ) 170.1(3)°. Symmetry operators: -x, -y + 1, -z + 1; -x, -y, -z + 1; x, y - 1, z - 1; x, y, z - 1; x, y, z + 1.

they bridge between silver(I) centers to form a sheet of macrocycles as shown in Figure 5, bottom. Each macrocycle in 3b contains one ligand in conformation A and one in conformation B. Further self-assembly of the sheets of macrocycles occurs through head-to-tail, amide-amide hydrogen bonding [N(2)‚‚‚O(1A) ) 2.7644 Å, N(3)‚‚‚O(2A) ) 2.779(4) Å] in the sequence ‚‚‚A‚‚‚B‚‚‚A‚‚‚B‚‚‚, to give the network structure shown in Figure 6. The channels in the stacked macrocycles are occupied by methanol solvent molecules (Figure 6). Structures of the Triflate Complexes 3c and 4c. The structure of complex 3c is shown in Figures 7 and 8. The bis(amido-4-pyridyl) ligands and silver(I) ions self-assemble to form a 1D zigzag polymer [Ag(µ-1)]nn+ as shown in Figure 7.

978 Crystal Growth & Design, Vol. 6, No. 4, 2006

Burchell et al.

Figure 8. View of the double-stranded polymers of 3c, formed by intermolecular hydrogen bonding between amide groups (IA‚‚‚IIA and IB‚‚‚IIB), and the association of the double-stranded polymers into sheets through CdO‚‚‚Ag and π-stacking (reinforced by triflate ion bridging which is not shown).

The triflate anions are more weakly coordinated to the silver centers in 3c [Ag(2)‚‚‚O(8) ) 2.76 Å, Ag(1)‚‚‚O(5) ) 2.62 Å] compared to the trifluoroacetate anions in complex 3a [Ag-O ) 2.359(7) Å, 2.404(7) Å]. The silver(I) centers have approximate T-shaped coordination geometry (Figure 7). The structure of complex 3c is interesting because within each polymer chain there are equal amounts of two different conformers of the ligand 1, labeled I and II in Figure 7. The two forms differ such that, in one conformer of the ligand (I), the two pyridyl groups are parallel to one another while, in the other form (II), one of the pyridyl groups is twisted by 64° with respect to the other (Figure 7). The N‚‚‚N separations [N(1)‚‚‚N(4) ) 7.65 Å in I; N(5)‚‚‚N(8) ) 7.42 Å in II], and intermolecular silver-silver distances [Ag(1)‚‚‚Ag(2) ) 9.61 Å bridged by I; Ag(1)‚‚‚Ag(2A) ) 9.27 Å bridged by II] in complex 3c are all smaller than in the trifluoroacetate complex 3a. Each of the two ligand forms I and II exists in the chiral conformation A or B, and each polymer chain contains an equal number of A and B conformers (Chart 2). Half of the chains assemble in the manner -IA-Ag-IIB-Ag-IA-Ag-IIB-Ag-, while the other half assemble as the mirror image -IB-Ag-IIA-AgIB-Ag-IIA-Ag-, such that each polymer chain is conformationally chiral, but the overall network structure is racemic. The polymers are further associated through intermolecular amide hydrogen bonds, but rather than associating in the usual headto-tail ‚‚‚A‚‚‚B‚‚‚A‚‚‚B‚‚‚ fashion two polymer chains align in a head-to-head, tail-to-tail manner and associate through pairwise IA‚‚‚IIA and IB‚‚‚IIB amide hydrogen bonds [N(2)‚‚‚O(3A) ) 2.78(1) Å, N(7A)‚‚‚O(2) ) 2.88(1) Å] and form a doublestranded polymer (pairs of chains in same color in Figure 8). Because the triflate anions bind only weakly to silver(I) and form weak O‚‚‚HN hydrogen bonds, the hierarchy of selfassembly is assigned as coordinate Ag-N bonds > amideamide hydrogen bonds > anion binding in 3c. Half of the N-H groups in 3c, which are not involved in the amide‚‚‚amide hydrogen bonds, are hydrogen bonded to oxygen atoms of the

Figure 9. Solid-state structure of complex 4c. Top: The disilver macrocycle with weakly coordinating CF3SO3- anions. Selected parameters: Ag(1)-N(1) ) 2.152(4), Ag(1)-N(4A) ) 2.156(4) Å, N(1)-Ag(1)-N(4A) ) 163.9(1)°. Symmetry operator: -x + 1, -y, -z + 1. Bottom: The 2D sheet of rings formed by intermolecular amide-amide hydrogen bonds.

triflate anions [N(3)‚‚‚O(5) ) 2.89(1) Å] (not shown), which are also weakly coordinated to silver atoms of adjacent chains [O(5)‚‚‚Ag(1A) ) 2.62 Å] to form a sheet of double-stranded polymers. The association of the double-stranded polymers is aided by the formation of secondary CdO‚‚‚Ag bonds [Ag(1)‚ ‚‚O(1A) ) 2.71 Å] and through π-stacking of pyridyl groups (Figure 8). The structure of complex 4c is shown in Figures 9 and 10. The bis(amido-3-pyridyl) ligands and silver(I) ions self-assemble to form a 26-membered macrocycle [Ag2(µ-2)2]2+ in a chair conformation (Figure 9, top). The triflate anions are weakly coordinated to the silver(I) centers [Ag(1)‚‚‚O(4) ) 2.80 Å, Ag(1)‚‚‚O(5B) ) 2.84 Å (not shown)] (Figure 9, top), and they bridge between macrocycles. In each macrocycle, the ligands 2 adopt the achiral conformation C (Chart 2). The macrocycles self-assemble through intermolecular ligand N-H‚‚‚OdC hydrogen bonds [N(2)‚‚‚O(1) ) 2.873(5) Å, N(3)‚‚‚O(2) ) 2.843(4) Å], with the ligand units aligned in the usual headto-tail manner, to give a two-dimensional (2D) sheet structure (Figure 9, bottom). The macrocyclic cavities of 4c are large and open, but the ligand N‚‚‚N separation and intramolecular Ag‚‚‚Ag distances [N(1)‚‚‚N(4) ) 7.47 Å, Ag(1)‚‚‚Ag(1A) ) 8.07 Å] are much smaller than in complex 4a. The macrocycles form narrow channels, but they are partly blocked by phenylene groups of overlapping macrocycles, and so they do not accommodate guest molecules.

Self-Assembled Network Structures of Silver(I)

Crystal Growth & Design, Vol. 6, No. 4, 2006 979

Figure 12. View of the 2D sheet structure of complex 4d. The sheet is formed by a combination of N-H‚‚‚OdC hydrogen bonds, Ag‚‚‚ OdC interactions, and π-π interactions.

Figure 10. 3D network of macrocycles of 4c. The network is formed by linking hydrogen bonded sheets of macrocycles through weak Ag‚ ‚‚Ag and Ag‚‚‚anion‚‚‚Ag interactions.

Figure 11. View of the 1D polymeric structure of complex 4d, showing the intra-ligand N-H‚‚‚OdC hydrogen bond. Selected bond distances: Ag(1)-N(1) ) 2.142(6), Ag(1)-N(4A) ) 2.156(5) Å; angle N(1)-Ag(1)-N(4A) ) 174.0(3)°. Symmetry operators: x, y + 1, z; x, y - 1, z.

The 2D hydrogen bonded sheets are further assembled through weak Ag‚‚‚Ag interactions [Ag(1)‚‚‚Ag(1B) ) 3.74 Å], supported by the weakly bridging triflate anions, to give a 3D network of disilver rings (Figure 10). The bond angle at silver(I) deviates significantly from linearity [N(1)-Ag(1)-N(4A) ) 163.9(1) °], as a result of these secondary bonding interactions. Structure of the Hexafluorophosphate Derivative 4d. The structure of complex 4d is shown in Figures 11-13. The primary structure formed from the bis(amido-3-pyridyl) ligands and silver(I) ions is a polymer [Ag(µ-1)]nn+ with essentially linear silver(I) centers (Figure 11). The pyridyl groups of the ligands are directed away from each other, and so the N‚‚‚N and silver‚‚‚silver separations [N(1)‚‚‚N(4) ) 9.49 Å, Ag(1)‚‚ ‚Ag(1A) ) 13.71 Å] are larger than in the other 3-pyridyl complexes 4a and 4c. The amido(pyridyl) arms of the ligands are twisted such that there is an intramolecular N-H‚‚‚OdC hydrogen bond [N(3)‚‚‚O(1) ) 2.659(6) Å], defining the chiral conformation 2D (Chart 2). All ligands 2 in a given polymer chain have the same chiral conformation, which can be labeled 2D-A and 2D-B (Figure 11). Because there is an intramolecular hydrogen bond (Figure 11), only one N-H and CdO pair are available for interchain hydrogen bonding. This interchain hydrogen bonding [N(2)‚‚‚ O(2A) ) 2.937(6) Å] leads to formation of a double-stranded polymer of a new type, in which both polymer strands contain all ligands in the same chiral conformation 2D-A or 2D-B, as shown in Figure 12. Furthermore, each polymer chain is also associated with a second chain of like chirality through the

formation of interchain silver-oxygen bonds [Ag(1)‚‚‚O(1A) ) 2.73 Å] between silver(I) centers and carbonyl groups and through π-π interactions between 3-pyridyl groups, with a centroid-to-centroid distance of 3.69 Å (Figure 12). Overall, the combination of N-H‚‚‚OdC hydrogen bonds, Ag‚‚‚OdC and π-π interactions leads to the formation of the chiral 2D sheet shown in Figure 12, in which all ligands 2 have the same chiral conformation 2D-A or 2D-B. The chiral sheets in 4d are further associated through weak interactions with the hexafluorophosphate counteranions to form a network structure. The anions [PF6]- are often noncoordinating, but, in this case, there are weak interactions between fluorine atoms and silver(I) atoms [Ag(1)‚‚‚F1(A) ) 2.84 Å, Ag(1)‚‚‚F2(A) ) 2.83 Å] such that the hexafluorophosphate ions bridge between the chiral sheets to form a 3D network, in which all of the ligands of the network adopt the same chiral conformation. From the above discussion, it appears that the complex 4d crystallized with spontaneous resolution to give crystals containing all ligands 2D-A or 2D-B,7 and this was consistent with the observed noncentrosymmetric space group P21. However, the crystallographic Flack parameter, which is a measure of the relative amounts of a structure and its inverse,8 refined to a value of 0.24(4), indicating that molecules of both enantiomeric conformations are present with approximately 76% of the molecules containing ligands of one chiral conformation. X-ray diffraction data were collected for another crystal of 4d and, in this case, the Flack parameter refined to 0.40(5), suggesting a 60% excess of one chiral conformation. Therefore, it appears that the spontaneous resolution was only partial, with each crystal containing different amounts of enantiomeric molecules. This apparent partial resolution is attributed to inversion twinning of chiral crystals. In the lattice of complex 4d, the secondary bonding interactions within a sheet are both directional and strong and will be expected to give rigid order, but the intersheet forces are weaker, and it is easy to envisage an occasional break in the intersheet order. Discussion The silver(I) complexes 3a-4d, which were prepared from the flexible bis(amidopyridyl) ligands 1 and 2, appear to exist primarily as the macrocyclic isomers in solution, but they may occur as either macrocycles (complexes 3a, 3b, and 4c) or as polymers (complexes 3c, 4a, and 4d) in the solid state. It is interesting to ask why, although it must be recognized that there will be some uncertainty when a number of different secondary bonding forces accompany the primary bonding of the silver(I) ions with the pyridyl groups. Some mean bond parameters from

980 Crystal Growth & Design, Vol. 6, No. 4, 2006

Burchell et al.

Table 1. Mean Bond Parameters for the Complexesa

Ag-N/Å Ag-O/Å N-Ag-N/° N‚‚‚N/Å Ag‚‚‚Ag/Å

Ag-N/Å Ag-O/Å N-Ag-N/° N‚‚‚N/Å Ag‚‚‚Ag/Å a

3a, R

3b, R

3c, P

2.24 2.43 126 8.49 10.44

2.26 2.53 134 6.84 8.47

2.15 2.69 174 7.53 9.44

4a, P

4c, R

4d, P

2.22 2.50 143 8.75 12.40

2.15 2.82 164 7.47 8.07

2.15 2.83a 174 9.49 13.71

R ) ring; P ) polymer. b Mean Ag-F distance.

the structure determinations are listed in Table 1, and are useful in discussing the structures shown in Figures 1-13. The relative stability of macrocycle versus polymer is most easily explained for complexes 3, which are derivatives of the bis(4-pyridyl) ligand 1. For this ligand, provided that it retains the trans orientation of the HN-CdO groups (Chart 2), the orientation of the two 4-pyridyl groups is not greatly affected by rotation about the aryl-NH or pyridyl-CO bonds (Chart 2), and a conformation in which they are oriented parallel to one another is highly strained. Hence, a macrocyclic structure is not favorable if the metal ion has linear (N-Ag-N) stereochemistry. This is the case with the triflate derivative 3c, since triflate is a weak donor, and so 3c forms a polymeric structure in the solid state. With the more strongly coordinating trifluoroacetate and nitrate anions, the silver(I) centers adopt a distorted tetrahedral stereochemistry, and the macrocycles are then favored in 3a and 3b, with angles N-Ag-N of 126 and 134°, respectively. It was not possible to grow crystals of the hexafluorophosphate derivative 3d, but it can be predicted that it will have a polymeric structure in the solid state, based on the poor donor properties of the anion. In 3a, 3b, and 3c the conformation of the ligand was 1A/1B in each case, and the range of distances between the two pyridyl donors N‚‚‚N and the associated distances between the coordinated silver atoms Ag‚‚‚Ag was narrow (spread of less than 2 Å, Table 1). The structures formed by ligand 2 are less predictable. The conformation of the ligand varies from 2A/2B in 4a, to 2C in 4c to 2D in 4d. In addition, rotation about the pyridyl-CO bond has a very large effect on the orientation of the pyridyl donors. The result is that the ligand can adapt to the stereochemistry of the metal ion. Thus the pyridyl donors are aligned parallel in forming 4c, which has roughly linear coordination at silver. In contrast, the pyridyl ligands are directed apart in forming the polymers 4a, with distorted tetrahedral silver(I), and 4d, with roughly linear silver(I) centers. Clearly, the anion has an effect, but this effect is not solely dependent on the strength of the coordination of the anion to silver(I). Thus, the strongest (trifluoroacetate) and weakest (hexafluorophosphate) donor anions form polymers, while the intermediate donor (triflate) forms a macrocycle. In the hierarchy of self-assembly, the macrocyclic or polymeric structure defined by the bis(pyridyl) ligand and silver(I), formed through Ag-N coordinate bonds, is considered as the primary structure. For the trifluoroacetate and nitrate complexes, the anion plays an important role in controlling the selfassembly. In both trifluoroacetate complexes 3a and 4a, the trifluoroacetate anions act as µ2-η1 ligands, forming Ag2(µ-X)2 units, and the anions naturally assemble the macrocycle 3a into a linear polymer of macrocycles (Figure 1) or the polymer 4a into a double-stranded polymer (Figure 3). However, the nitrate

Figure 13. Side view of the 3D network complex 4d. 2D sheets are connected via weak Ag‚‚‚F interactions to form the overall 3D network.

ions in 3b act as µ2-η2 ligands and, as a consequence, they assemble the macrocycles into sheets (Figure 5), in contrast to the polymers in the µ2-η1-trifluoroacetate complex 3a. The binding of the trifluoroacetate and nitrate anions to silver(I) is indicated by the stereochemistry at silver, which is distorted tetrahedral in 3a, 3b, and 4a (Table 1). The anions triflate and hexafluorophosphate coordinate much more weakly, giving distorted linear stereochemistry at silver(I) in 3c, 4c, and 4d (Table 1). However, they can still influence the self-assembly, as shown by the different structures of 4c (macrocycle) and 4d (polymer). In the complexes with trifluoroacetate or nitrate anions, 3a, 3b, and 4a, the bis(pyridyl) ligands adopt the chiral conformations A and B (Chart 2), and they each associate through hydrogen bonding between amide groups to give the network structures shown in Figures 2, 4, and 6. The intermolecular N-H‚‚‚OdC hydrogen bonding between amide groups occurred in the same head-to-tail, ‚‚‚A‚‚‚B‚‚‚A‚‚‚B‚‚‚ fashion as observed in the free ligand 1, and so it can be claimed that these solidstate structures were partly engineered. It is noteworthy that the structures of these complexes 3a, 3b, and 4a all contain solvent-filled channels, and it is possible that the solvents play a role as templates during the network self-assembly process. Certainly, there is a synergy between formation of the complementary ‚‚‚A‚‚‚B‚‚‚A‚‚‚B‚‚‚ hydrogen bonds, which stack the primary building block units directly above one another in the final network structure, with the formation of channels which will naturally accommodate solvent molecules. The hierarchy of self-assembly appears to switch from Ag-N > Ag-O > NH‚‚‚OdC in the trifluoroacetate and nitrate derivatives 3a, 4a, and 3b to Ag-N > NH‚‚‚OdC > Ag‚‚‚O (and Ag‚‚‚Ag in 4c, Ag‚‚‚F in 4d) in the triflate and hexafluorophosphate derivatives 3c, 4c, and 4d. In these complexes with weakly binding anions, the structures are compact and do not include solvent guest molecules. In complex 3c, there are double-stranded polymers, while in complex 4c there are sheets of macrocycles and in 4d there are sheets of polymers. While complex 3c contains the bis(pyridine) ligands in two different conformations A and B, complex 4c contains ligands in conformation C, and 4d contains ligands in conformation D. These patterns of self-assembly were not predicted and are not easily rationalized.

Self-Assembled Network Structures of Silver(I)

Crystal Growth & Design, Vol. 6, No. 4, 2006 981

Table 2. Crystallographic Data for Complexes 3a, 4a, 3b, 3c, 4c, 4d 3a‚2.5(ClCH2CH2Cl)

4a‚1.5(CH2Cl2)‚(MeOH)

3b‚2(MeOH)

3c

4c

4d

formula

C45H36Ag2Cl5F6N8O8

C42.50H35Ag2Cl3F6N8O9

C20H22AgN5O7

fw space group a (Å) b (Å) c (Å) R (°) β (°) γ (°) T (K) λ (Å) V (Å3) Z Dcalc (Mg/m3) µ (mm-1) R1, wR2 [I >2σ(I)] R1, wR2 (all data)

1323.81 C2/m 9.4067(19) 24.330(5) 11.965(2) 90 98.8(3) 90 150 0.71073 2704.8(9) 2 1.625 1.048 0.0552, 0.1576

1237.88 P1h 9.3701(19) 12.076(2) 12.400(3) 88.01(3) 85.14(3) 73.19(3) 150 0.71073 1338.4(5) 1 1.536 0.958 0.0612, 0.1700

552.3 Pccn 19.253(4) 24.785(5) 9.6781(19) 90 90 90 150 0.71073 4618.3(16) 8 1.589 0.923 0.0478, 0.1233

C38H28Ag2F6N8O10S2 1150.54 P1h 10.719(2) 10.728(2) 18.594(4) 84.66(3) 84.95(3) 79.61(3) 150 0.71073 2088.5(7) 2 1.830 1.133 0.0562, 0.1228

C19H14AgF3N4O5S 575.27 P2(1)/c 11.470(2) 19.039(4) 9.852(2) 90 99.69(3) 90 150 0.71073 2120.7(7) 4 1.802 1.116 0.0477, 0.0981

C18H14AgF6N4O2P 571.17 P2(1) 8.7166(17) 13.711(3) 9.2663(19) 90 112.10(3) 90 150 0.71073 1026.2(4) 2 1.849 1.138 0.0466, 0.1168

0.0711, 0.1675

0.0781, 0.1822

0.0949, 0.1462

0.0891, 0.1426

0.0912, 0.1148

0.0552, 0.1237

Chart 3

The hexafluorophosphate complex 4d is unique because it underwent spontaneous resolution upon crystallization. It forms conformationally chiral 1D polymers (Figure 11), which assemble into chiral sheets and then more weakly into a chiral network. Overall, this work supports the view that the strategy of combining dynamic coordination chemistry with hydrogen bonding to assemble multidimensional networks has great potential in the design of novel supramolecular materials.2,3,6 Experimental Section NMR spectra were recorded using a Varian Inova 400 spectrometer, with 1H and 13C chemical shifts reported relative to tetramethylsilane. ESI mass spectra were recorded using a Micromass LCT spectrometer. The ligands 1 and 2 were prepared as described previously.2i,3b The 1H NMR labeling scheme is shown below for ligand 2 (Chart 3). [{µ-1,2-C6H4(NHC(O)-4-C5H4N)2}(AgCF3CO2)]n, 3a. AgCF3CO2 (0.0220 g, 0.100 mmol) was added to a solution of 1 (0.0318 g, 0.100 mmol) in CH2Cl2/MeOH. After several minutes of stirring, the complex precipitated as a white solid, which was collected by filtration and dried under vacuum. Yield: 0.0392 g, 73%. 1H NMR (CD2Cl2/methanold4): 8.71 (d, 3JHH ) 6 Hz, 4H, H2,6 py); 7.94 (d, 3JHH ) 6 Hz, 4H, H3,5 py); 7.62 (m, 2H, H4,5 Ph); 7.35 (m, 2H, H3,6 Ph). ESI-MS (reported for 107Ag isotope): m/z ) 425, 645, 743, 963. Anal. Calcd. for C20H14N4AgF3O4: C, 44.55; H, 2.62; N, 10.39. Found: C, 44.10; H, 2.41; N, 10.23%. [{µ-1,2-C6H4(NHC(O)-4-C5H4N)2}(AgNO3)]n, 3b. This was prepared similarly from AgNO3 (0.0212 g, 0.125 mmol) and 1 (0.0397 g, 0.125 mmol). Yield 0.0468 g, 77%. 1H NMR (CD2Cl2/methanol-d4): 8.67 (d, 3JHH ) 6 Hz, 4H, H2,6 py); 7.84 (d, 3JHH ) 6 Hz, 4H, H3,5 py); 7.61 (m, 2H, H4,5 Ph); 7.34 (m, 2H, H3,6 Ph). ESI-MS (reported for 107 Ag isotope): m/z ) 425, 594, 743. Anal. Calcd. for C18H14N5AgO5: C, 44.28; H, 2.89; N, 14.35. Found: C, 43.76; H, 2.78; N, 13.95%. [{µ-1,2-C6H4(NHC(O)-4-C5H4N)2}(AgCF3SO3)]n, 3c. This was prepared similarly from AgCF3SO3 (0.0321 g, 0.125 mmol) and 1 (0.0397 g, 0.125 mmol). Yield: 0.0568 g, 79%. 1H NMR (CD2Cl2/ methanol-d4): 8.69 (d, 3JHH ) 6 Hz, 4H, H2,6 py); 7.94 (d, 3JHH ) 6 Hz, 4H, H3,5 py); 7.62 (m, 2H, H4,5 Ph); 7.35 (m, 2H, H3,6 Ph). ESI-

MS (reported for 107Ag isotope): m/z ) 425, 681, 743. Anal. Calcd. for C19H14N4AgF3O5S: C, 39.67; H, 2.45; N, 9.74. Found: C, 39.37; H, 2.13; N, 10.01%. [{µ-1,2-C6H4(NHC(O)-4-C5H4N)2}(AgPF6)]n, 3d. This was prepared similarly in THF from AgPF6 (0.0505 g, 0.200 mmol) and 1 (0.0636 g, 0.200 mmol). Yield 0.0902 g, 80%. 1H NMR (DMSO-d6): 10.22 (s, 2H, NH); 8.75 (d, 3JHH ) 6 Hz, 4H, H2,6 py); 7.84 (d, 3JHH ) 6 Hz, 4H, H3,5 py); 7.64 (m, 2H, H4,5 Ph); 7.31 (m, 2H, H3,6 Ph). ESIMS (reported for 107Ag isotope): m/z ) 425, 531, 743, 849, 994. Anal. Calcd. for C18H14N4AgF6PO2: C, 37.85; H, 2.47; N, 9.81. Found: C, 38.22; H, 2.19; N, 9.58%. [{µ-1,2-C6H4(NHC(O)-3-C5H4N)2}(AgCF3CO2)]n, 4a. This was prepared similarly from AgCF3CO2 (0.0220 g, 0.100 mmol) and 2 (0.0318 g, 0.100 mmol). Yield 0.0369 g, 68%. 1H NMR (CD2Cl2/ methanol-d4): 9.09 (br, 2H, H2 py); 8.67 (d, 3JHH ) 5 Hz, 2H, H6 py); 8.33 (d, 3JHH ) 7 Hz, 2H, H4 py); 7.61 (m, 2H, H4,5 Ph); 7.53 (m, 2H, H5 py); 7.33 (m, 2H, H3,6 Ph). ESI-MS (reported for 107Ag isotope): m/z ) 425, 645, 743, 849, 963, 955. Anal. Calcd. for C20H14N4AgF3O4: C, 44.55; H, 2.62; N, 10.39. Found: C, 43.98; H, 2.39; N, 9.95%. [{µ-1,2-C6H4(NHC(O)-3-C5H4N)2}(AgNO3)]n, 4b. This was prepared similarly from AgNO3 (0.0212 g, 0.125 mmol) and 2 (0.0397 g, 0.125 mmol). Yield 0.0274 g, 45%. 1H NMR (CD2Cl2/methanol-d4): 9.06 (s, 2H, H2 py); 8.66 (d, 3JHH ) 6 Hz, 2H, H6 py); 8.29 (d, 3JHH ) 7 Hz, 2H, H4 py); 7.61 (m, 2H, H4,5 Ph); 7.49 (m, 2H, H5 py); 7.33 (m, 2H, H3,6 Ph). ESI-MS (reported for 107Ag isotope): m/z ) 425, 594, 743, 849, 912. Anal. Calcd. for C18H14N5AgO5: C, 44.28; H, 2.89; N, 14.35. Found: C, 43.98; H, 2.83; N, 13.96%. [{µ-1,2-C6H4(NHC(O)-3-C5H4N)2}(AgCF3SO3)]n, 4c. This was prepared similarly from AgCF3SO3 (0.0321 g, 0.125 mmol) and 2 (0.0397 g, 0.125 mmol). Yield 0.0715 g, 99%. 1H NMR (CD2Cl2/ methanol-d4): 9.06 (s, 2H, H2 py); 8.66 (d, 3JHH ) 5 Hz, 2H, H6 py); 8.31 (d, 3JHH ) 7 Hz, 2H, H4 py); 7.60 (m, 2H, H4,5 Ph); 7.51 (m, 2H, H5 py); 7.33 (m, 2H, H3,6 Ph). ESI-MS (reported for 107Ag isotope): m/z ) 425, 681, 743, 1061. Anal. Calcd. for C19H14N4AgF3O5S: C, 39.67; H, 2.45; N, 9.74. Found: C, 40.27; H, 2.25; N, 10.37%. [{µ-1,2-C6H4(NHC(O)-3-C5H4N)2}(AgPF6)]n, 4d. This was prepared similarly in THF from AgPF6 (0.0505 g, 0.200 mmol) and 2 (0.0636 g, 0.200 mmol). Yield 0.0814 g, 72%. 1H NMR (CD2Cl2/ methanol-d4): 9.07 (s, 2H, H2 py); 8.66 (d, 3JHH ) 6 Hz, 2H, H6 py); 8.28 (d, 3JHH ) 7 Hz, 2H, H4 py); 7.61 (m, 2H, H4,5 Ph); 7.48 (m, 2H, H5 py); 7.32 (m, 2H, H3,6 Ph). ESI-MS (reported for 107Ag isotope): m/z ) 425, 531, 743, 849, 994. Anal. Calcd. for C18H14N4AgF6O2P: C, 37.85; H, 2.47; N: 9.81. Found: C, 38.17; H, 2.37; N, 9.48%. X-ray Structure Determinations. A crystal suitable for X-ray analysis was mounted on a glass fiber. Data were collected using a Nonius-Kappa CCD diffractometer using COLLECT (Nonius, B. V. 1998) software. The unit cell parameters were calculated and refined from the full data set. Crystal cell refinement and data reduction were carried out using the Nonius DENZO package. The data were scaled using SCALEPACK (Nonius, B. V. 1998). The SHELX-TL V5.1 and SHELX-TL V6.1 (Sheldrick, G. M.) program packages were used to

982 Crystal Growth & Design, Vol. 6, No. 4, 2006 solve and refine the structures. The structures of complexes 3b, 3c, 4c, 4d, and 5d were solved by direct methods, while the structures of complexes 3a and 4a were solved by the automated Patterson routine of the SHELX-TL software package. Except as mentioned, all nonhydrogen atoms were refined with anisotropic thermal parameters. The hydrogen atoms were calculated geometrically and were riding on their respective carbon atoms. Crystal data are summarized in Table 2. All thermal ellipsoid diagrams are shown at 30% probability. [{µ-1,2-C6H4(NHC(O)-4-C5H4N)2}(AgCF3CO2)]n, 3a‚2.5(ClCH2CH2Cl). Crystals of 2[C20H14AgF3N4O4]‚2.5(ClCH2CH2Cl) were grown in situ from diffusion of a THF solution of AgCF3CO2 into a dichloroethane/methanol solution of the ligand 1. The trifluoroacetate group was disordered over a symmetry element and was modeled as a 50:50 isotropic mixture with geometric restraints. The solvent molecules were modeled isotropically with geometric restraints. One of the solvent molecules was disordered across a symmetry element and was modeled without hydrogen atoms. The largest residual electron density peak (1.754 e/Å3) was associated with a solvent molecule. [{µ-1,2-C6H4(NHC(O)-4-C5H4N)2}2(AgNO3)2], 3b‚2(CH3OH). Crystals of [C18H14AgN5O3]‚2(CH3OH) were grown in situ from diffusion of a methanol/acetonitrile solution of AgNO3 into a tetrahydrofuran/ methanol solution of the ligand 1. The methanol solvent molecules were disordered and were modeled as 55:45 and 50:50 isotropic mixtures. The largest residual electron density peak (0.611 e/Å3) was associated with one of the solvent molecules. [{µ-1,2-C6H4(NHC(O)-4-C5H4N)2}(AgCF3SO3)]n 3c. Crystals of [C38H28Ag2F6N8O10S2] were grown in situ from diffusion of a dichloromethane/methanol solution of AgCF3SO3 into a dichloromethane/ methanol solution of the ligand 1. The crystal was twinned around the 1h 1 0 reciprocal axis, as determined by the twin determination program ROTAX,10a and WIN-GX10b was used to prepare the HKLF5 file for further refinement. The largest residual electron density peak (1.19 e/Å3) was associated with the atom Ag(1). [{µ-1,2-C6H4(NHC(O)-3-C5H4N)2}(AgCF3CO2)]n, 4a‚1.5(CH2Cl2)‚ (MeOH). Crystals of 2[C20H14AgF3N4O4]‚1.5(CH2Cl2)‚(MeOH) were grown in situ from diffusion of a THF solution of AgCF3CO2 into a dichloromethane/methanol solution of the ligand 2. The trifluoroacetate groups were modeled as a four part disorder (30:30:20:20) with geometric restraints applied and refined isotropically. The solvent molecules were also disordered and each was modeled isotropically with geometric restraints. The largest residual electron density peak (1.963 e/Å3) was associated with a solvent molecule. [{µ-1,2-C6H4(NHC(O)-3-C5H4N)2}2(AgCF3SO3)2], 4c. Crystals of [C19H14AgF3N4O5S] were grown in situ from diffusion of a methanol solution of AgCF3SO3 into a dichloromethane/methanol solution of the ligand 2. The molecule was well ordered. The largest residual electron density peak (0.537 e/Å3) was associated with the Ag(1) atom. [{µ-1,2-C6H4(NHC(O)-3-C5H4N)2}(AgPF6)]n, 4d. Crystals of [C18H14AgF6N4O2P] were grown in situ from diffusion of a methanol solution of AgPF6 into a dichloromethane/methanol solution of the ligand 2. The fluorine atoms of the PF6- moiety were disordered and were modeled as a 60:40 isotropic mixture. Inversion twinning was observed and the Flack parameter was 0.24(4). The largest residual electron density peak (0.952 e/Å3) was associated with the atom Ag(1).

Acknowledgment. We thank the NSERC Canada for financial support. R.J.P. thanks the Government of Canada for a Canada Research Chair.

Burchell et al.

(2)

(3)

(4)

(5)

(6)

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(8)

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Supporting Information Available: Crystal and refinement data and tables of parameters in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org. (10)

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CG050578Q