Pre-organisation or a hydrogen bonding mismatch: silver(I) diamide ligand coordination polymers versus discrete metallo-macrocyclic assemblies

Abstract

The investigation of novel motifs to selectively complex anions is an area of considerable importance due to the significant environmental, biological and medicinal roles of anions. The synthesis of discrete metallo-macrocyclic compounds or coordination polymers displaying anion-binding pockets can generate specific anion receptors from relatively simple components. Here, we examine the self-assembly of a series of flexible diamide compounds L1–L5 with silver(I) metal salts. A new diamide ligand, 2,6-[N,N′-bis(di-(pyridin-2-yl)methyl)pyridine]-2,6-dicarboxamide (L5), with two chelating di-2-pyridylmethyl donor groups, was also prepared. Compounds L1–L3, lacking the pre-organising effect of a central 2,6-pyridine dicarboxamide core, form 1D coordination polymers {[Ag(L1)(CH3CN)](PF6)} n (6), {[Ag(L2)](NO3)·(H2O)]} n (7) and {[AgNO3(L3)]·(CH3OH)]} n (9) which in turn form 2D and 3D hydrogen-bonded networks through orthogonal hydrogen bonding. In one instance, L2 gives rise to a dinuclear metallo-macrocycle in the solid state, [Ag2(CF3CO2)2(L2)2][Ag2(μ2-CF3CO2)2(L2)2] (8). Both diamide ligands L4 and L5 form dinuclear metallo-macrocycles, [Ag2(NO2)2(L4)2] (10) and [Ag2(L5)2](NO3)2·2CH3OH·2H2O (11), in solution and in the solid state. Where possible, all compounds were investigated in solution and their solid-state structures were determined using X-ray crystallography. This enabled the effect of competing supramolecular synthons, covalent M–L bonding and hydrogen bonding, to be examined by comparing the solution and solid-state behaviour of each metal–ligand combination.