Silver coordination networks and cages based on a semi-rigid bis(isoxazolyl) ligand
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 AgO 2CCF3 both lead to compounds in which the anions are coordinated to the silver centres. Thus, the structure of [Ag 2(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(¿- 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 AgBF 4 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]X 2.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 AgSbF 6/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. The Royal Society of Chemistry.
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