Silver coordination networks and cages based on a semi-rigid bis(isoxazolyl) ligand

Abstract

The semi-rigid ligand 1,4-bis((3,5-dimethylisoxazol-4-yl)methyl)benzene (bisox) reacts with a range of silver(I) salts to give products in which the anions dictate the structure. The reactions with AgNO₃ and AgO₂CCF₃ both lead to compounds in which the anions are coordinated to the silver centres. Thus, the structure of [Ag₂(NO₃)₂(bisox)] 1 contains helical silver-nitrate chains that are linked into sheets by bridging bisox ligands, whereas the structures of [Ag(O₂CCF₃)(bisox)]·0.5X (2a, X = MeOH; 2b, X = MeCN) consist of sheets in which Ag₂(μ-O₂CCF₃)₂ dimers act as 4-connecting nodes. In these structures bisox adopts the S-conformation, with the nitrogen donor atoms anti to each other. The reactions of bisox with AgClO₄ and AgBF₄ in methanol give the compounds [Ag₂(bisox)₃]X₂ (3, X = ClO₄; 5, X = BF₄), the structures of which contain triply-interpenetrated sheets with Borromean links and ligands in the S-conformation. Recrystallisation of these compounds from acetonitrile–diethyl ether gives [Ag₂(bisox)₃]X₂·xEt₂O (4, X = ClO₄, x = 1; 6, X = BF₄, x = 1.2). The structures of 4 and 6 contain similar triply-interpenetrated sheets to those in 3 and 5, though these are sandwiched between sheets of discrete Ag₂(bisox)₃ cages, in which the bisox ligands are in the C-conformation, with the nitrogen donor atoms syn to each other. Diethyl ether molecules project through the faces of the cages and template cage formation. Both 4 and 6 lose diethyl ether on heating in vacuum, and convert into 3 and 5, respectively. This solid state transformation requires a change in conformation of half the bisox ligands, with conversion of 6 into 5 occurring more readily than conversion of 4 into 3. The reactions of bisox with AgPF₆ and AgSbF₆ in methanol give mixtures of products from which [Ag(bisox)₂]X·0.5bisox (7, X = PF₆; 8, X = SbF₆) can be isolated. Both 7 and 8 have structures containing one-dimensional chains, in which the bisox ligands adopt C-conformations and interconnect distorted tetrahedral silver centres in a pairwise manner generating macrocycles. Additional uncoordinated bisox molecules lie within half of these macrocyclic rings. Recrystallisation of the crude AgSbF₆/bisox reaction mixture from acetonitrile–diethyl ether gives [Ag(bisox)₂]SbF₆9, the structure of which consists of a triply-interpenetrated flattened diamondoid network. A similar structure was observed for [Ag(bisox)₂]CF₃SO₃10, which is formed from the reaction of AgO₃SCF₃ and bisox in methanol.