Structural control in Cu(II) coordination polymers through the conformational flexibility of a 2,3-dipyridyl ketone oxime ligand

Abstract

Four new compounds prepared from the ligand 2,3-dipyridyl ketone oxime (L23) with varying Cu(II) salts were synthesised and structurally characterised, {[Cu(L23)(L23-H)](ClO4)}∞ (1), {[Cu(L23)(L23-H)](BF4)¼(H2O)}∞ (2), [Cu3(L23-H)2(L23′)(NO3)2OH]2(NO3)2(C3H8O)6 (3) and [Cu(L23)Cl2]∞ (4). The effects of differing counterions, as well as the rotational conformational versatility of L23, were demonstrated by the differing polymeric structures that were observed. Complex 1 and 2 both existed as 1-D polymeric chains with L23 acting as a pseudo-tetradentate ligand through an oxime–oximato bridge. Complex 1 formed a helical arrangement while 2 formed a chiral chain with both 1 and 2 exhibiting similar chiral packing. Complex 3 formed an unusual inverse–9–metallacrown–3 complex, with one of the L23 ligands in a zwitterionic form. Complex 4 was present as a simple 1-D meso-helical chain.