Anion binding by Ag(I) complexes of urea-substituted pyridyl ligands

A series of Ag(I) complexes of ureidopyridyl ligands 1 and 2 have been prepared from oxo-anion salts. In all cases the new materials contain the AgL(2)(+) cation interacting with oxo-anions via the urea moiety. The complexes containing the para ligand 2: [Ag(2)(2)]CF(3)SO(3).2H(2)O (3), [Ag(2)(2)]CH(3)CO(2).1.33H(2)O.MeOH (4) and [Ag(2)(2)]NO(3).H(2)O (5), all exhibit remarkably similar chain-like structures based around a linear Ag(I) centre, despite the change in the counter-ion. A recurring R(2)(2)(8) hydrogen-bonding ring motif between the urea group and the oxo-anion is observed in almost all cases. An exception to this trend is the anhydrous nitrate structure [Ag(2)]NO(3) (6) in which the nitrate is coordinated in a bridging position between two silver centres, which adopt distorted trigonal pyramidal geometries. Structures containing the ligand 1, [Ag(1)(2)]CF(3)SO(3).0.5H(2)O (7), [Ag(1)(2)]CF(3)SO(3).H(2)O.MeCN (8), [Ag(1)(2)](2)SO(4) (9), [Ag(1)(2)]NO(3).MeOH (10) and [Ag(1)(2)]NO(3).0.5MeOH.0.5MeNO(2) (11), display very different geometries, although the R(2)(2)(8) is observed to persist throughout. The most notable of these structures are 10 and 11 in which the nitrate anion is chelated within a 'pincer' arrangement by the silver complex. The nitrate anion is situated asymmetrically within the cavity of the host complex. This discrete nitrate complex persists in solution with strong nitrate binding by the [Ag(1)(2)](+) host compared to other anions being observed.