catena-Poly[[silver(I)-μ-4-aminopyridine] perchlorate]: a 1-D staircase coordination polymer

Reaction of 4-aminopyridine with silver(I) perchlorate leads to a one-dimensional coordination polymer, {[Ag(C5H6N2)]ClO4}n, in which the aminopyridine binds through both N atoms. The perchlorate anion is hydrogen bonded to the amino H atoms and interacts weakly with the silver(I) atoms (Ag—O > 2.70 Å), both located on inversion centres, and some aromatic H atoms (O—H > 2.55 ÅA), thereby extending the dimensionality of the assembly. This is the first silver complex in which this ligand acts in a bridging mode.

Reaction of 4-aminopyridine with silver(I) perchlorate leads to a one-dimensional coordination polymer, {[Ag(C 5 H 6 N 2 )]-ClO 4 } n , in which the aminopyridine binds through both N atoms. The perchlorate anion is hydrogen bonded to the amino H atoms and interacts weakly with the silver(I) atoms (Ag-O > 2.70 Å ), both located on inversion centres, and some aromatic H atoms (O-H > 2.55 Å A), thereby extending the dimensionality of the assembly. This is the first silver complex in which this ligand acts in a bridging mode.

Comment
For some time we have been involved in the study of metallosupramolecular assemblies derived from bridging heterocyclic ligands (Steel, 2005). In recent years we have focused on the use of silver(I) for the self-assembly of both discrete and polymeric aggregates with diverse molecular architectures (Fitchett & Steel, 2006;O'Keefe & Steel, 2007). In this context, we have recently reviewed the use of pyrazine and analogues as bridging ligands for silver(I)-based assemblies (Steel & Fitchett, 2008). 4-Aminopyridine (1) is a less symmetrical ligand that can potentially act as a bridge between metal centres.
X-ray structures have been reported for complexes of (1) with silver nitrate (Kristiansson, 2000;Abu-Youssef et al., 2006), silver bicarbonate (Liu et al., 2005), silver trifluoroacetate (Zhu et al., 2003a), silver trifluoromethanesulfonate (Zhu et al., 2003b;Liu et al., 2005), silver terephthalate (Li et al., 2005) and silver 3-nitrobenzoate (Ma et al., 2004). However, in all these cases the ligand acts as a monodentate ligand binding through the pyridine nitrogen only and therefore forms discrete coordination complexes. We now describe a one-dimensional coordination polymer, obtained from reaction between this ligand and silver perchlorate, in which ligand (1) acts in a bridging bidentate mode.
The complex (2) crystallizes in the triclinic space group P-1 with a full 4-aminopyridine ligand, two half silver atoms and a perchlorate anion in the asymmetric unit (Fig. 1). The two independent silver atoms each lie on crystallographic centres of inversion and therefore act as linear connectors resulting in a 1-D coordination polymer. Ligand (1) coordinates to Ag1 through two pyridine N atoms and to Ag2 via two amino N atoms. The resulting coordination polymer has a staircase-type structure that results from the fact that the amino nitrogen introduces an angular turn (C4-N2-Ag2 111.9 (1)°) into the polymer chain.
Both of the amino group H atoms are hydrogen bonded (Table 1) to adjacent perchlorate counterions, which in turn serve to bridge adjacent chains through two such hydrogen bonds (Fig. 2). The perchlorate O atoms are also involved in weak interactions with the silver atoms, which in the case of Ag2 leads to a pseudo-octahedral coordination environment for this atom. The perchlorate O atoms make weak contacts with some CH H atoms. These additional interactions increase the dimensionality of the overall assembly. This structure represents the first example in which ligand (1) acts as a bridging ligand for silver(I).

Experimental
The title compound was prepared by slow evaporation of an acetone solution containing an equimolar ratio of 4-aminopyridine and silver perchlorate.

Refinement
CH hydrogen atoms were introduced in calculated positions as riding atoms, with U iso (H) = 1.2U eq (C). The NH H atoms were located from a difference Fourier map and their positions refined with U iso (H) = 1.2U eq (N).  Fig. 1. The molecular structure of (2), showing displacement ellipsoids at the 50% probability level. Fig. 2. Extended structure of (2), showing the staircase structure and the hydrogen bonding interactions.

catena-Poly[[silver(I)-µ-4-aminopyridine] perchlorate]
Crystal data [Ag(C 5  as those based on F, and R-factors based on ALL data will be even larger.