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

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^–).