Ligand flexibility and dual complexation modes on reaction of 1,2-bis(2′-pyridylethynyl)benzene with copper(I) halides

The reaction of the bidentate ligand 1,2-bis(2'-pyridylethynyl)benzene with copper(l) halides reveals the rich coordination chemistry of the ligand. The reaction with copper(l) iodide yields a linear I D coordination polymer. The polymer features a series of rhomboid CuI2Cu centers bridged by two of the bipyridyl ligands. A tetramer is formed with copper(I) bromide where the ligand adopts two distinct conformations. One pair of ligands bridges two rhomboid CuBr2Cu centers and the second pair of ligands end-caps the two copper centers. The end capping ligands in the copper(I) bromide structure have pyridyl rings flexed with torsional angles of 11 and 28degrees with respect to the central benzene ring. A 2: 4 complex is formed on reaction with copper(l) chloride. In this structure both pyridyls complex the same copper atom and are twisted out of planarity with the benzene ring with one alkyne coordinated to the second copper atom.