Controlling copper(I) halide framework formation using N-donor bridging ligand symmetry: use of 1,3,5-triazine to construct architectures with threefold symmetry

The formation of co-ordination polymers between copper(I) halides and 1,3,5 -triazine (tri), a potentially tridentate N-donor bridging ligand with thre efold symmetry, has been studied. Complexes with both 3:1 and 2:1 molar rat ios are formed by both CuBr and CuI. The compounds [Cu3X3(tri)](infinity) ( X=Br or I) are structurally similar, despite crystallising in different spa ce groups. They are composed of (CuX)(infinity) columns linked by triazine molecules to generate three-dimensional constructions with non-crystallogra phically imposed threefold symmetry. The (CuX)(infinity) columnar motif can be described as a series of perpendicularly stacked Cu3X3 chairs, alternat ely rotated by 60 degrees and linked by Cu-X contacts. The tetrahedral co-o rdination geometry of the copper centres is completed by a tridentate triaz ine bridge which links two copper atoms in separate columns. Thus, each (Cu X)(infinity) column is linked to six adjacent (CuX)(infinity) columns. The structure of [Cu2Br2(tri)](infinity) comprises (CuBr)(infinity) columns and castellated (CuBr)(infinity) chains linked by triazine molecules to genera te a construction with crystallographically imposed threefold symmetry. The (CuBr)(infinity) columns are similar to but more regular than those found in [Cu3Br3(tri)](infinity). In this case, however, each column is linked to six adjacent chains. The (CuBr)(infinity) castellated chain motif is very unusual. The tetrahedral copper centres are co-ordinated by two adjacent br omide anions and by two triazine molecules each of which links a second cha in and a column. Consequently, each chain is linked to four neighbouring ch ains and two neighbouring columns. Despite a stoichiometry identical to tha t of [Cu2Br2(tri)](infinity), [Cu2I2(tri)](infinity) has a completely diffe rent structure. The triazine molecules act as bidentate bridging ligands to link (CuI)(infinity) layers thereby giving alternating inorganic and organ ic layers. The tetrahedral co-ordination geometry of the copper centres in the (CuI)(infinity) layers, which are effectively undulating hexagonal nets , is provided by three iodide anions from the layers and by a bridging tria zine molecule.