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

摘要

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 AgNO_3 and AgO _2CCF_3 both lead to compounds in which the anions are coordinated to the silver centres. Thus, the structure of [Ag _2(NO_3)_2(bisox)] 1 contains helical silver-nitrate chains that are linked into sheets by bridging bisox ligands, whereas the structures of [Ag(O_2CCF_3)(bisox)]·0.5X (2a, X = MeOH; 2b, X = MeCN) consist of sheets in which Ag2(μ- O_2CCF_3)_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 AgClO_4 and AgBF _4 in methanol give the compounds [Ag_2(bisox) _3]X_2 (3, X = ClO_4; 5, X = BF_4), 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 [Ag_2(bisox)_3]X _2·xEt_2O (4, X = ClO_4, x = 1; 6, X = BF_4, 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 Ag_2(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 AgPF_6 and AgSbF_6 in methanol give mixtures of products from which [Ag(bisox)_2]X·0.5bisox (7, X = PF_6; 8, X = SbF_6) 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 AgSbF _6/bisox reaction mixture from acetonitrile-diethyl ether gives [Ag(bisox)_2]SbF_69, the structure of which consists of a triply-interpenetrated flattened diamondoid network. A similar structure was observed for [Ag(bisox)_2]CF_3SO_310, which is formed from the reaction of AgO_3SCF_3 and bisox in methanol.