Sequential structural transformations via pseudohalide-anion exchange reactions in Cu(II) supramolecular complexes

Abstract

We report here the first example of sequential post-synthetic structural transformations via pseudohalide anion exchanges. Assembly of a rigid angular ligand 3-phenyl-5-(2-pyridyl)-4-(4-pyridyl)-4H-1,2,4-triazole (L240) with CuBr2 results in a 1D crystalline material {[Cu(L240)(Br)2](DMF)(H2O)}n (1). Immersing the green microcrystalline sample of 1 into an aqua solution of NaN(CN)2 (Na(dca)), the partly exchanged blue species {[Cu(L240)(dca)Br](H2O)}n (2) is obtained after ca. a week. Then, the fully exchanged green [Cu(L240)(dca)2]n (3) occurs after about ten days and 2 gradually disappears. Further immersing 1 or 3 into the solution of NaN3, a new deep green material defined as [Cu(L240)(N3)2]2 (4) can be obtained. These structural transformations can be ascribed to the solvent-mediated structural transformation, accompanied the change of crystallinity, shape, size, and color. Notably, 2–4 cannot be synthesized by direct assembly of L240 and Cu salts with those pseudohalide (dca– or N3–).