Self-assembled dinuclear molecular box [Ag2L2]2+ and triple helicates [Co2L3]4+, [Ni2L3]4+ {L = bis[4-(2-pyridylmethyleneamino)phenyl] ether}

Abstract

The self-assembly and structural characterization of the new silver(I) molecular box [Ag₂L₂]²⁺ and cobalt(II), and nickel(II) molecular helices [Co₂L₃]⁴⁺ and [Ni₂L₃]⁴⁺ have been achieved. These complexes are derived from an inexpensive and easy-to-prepare bis-bidentate Schiff base ligand bis[4-(2-pyridylmethyleneamino)phenyl] ether (L). The cage-like cation [Ag₂L₂]²⁺ is located at an inversion center with two tetrahedrally co-ordinated silver(I) atoms and two ether oxygen atoms in the corner of a box. The edge length Ag⋯O is ca. 7.1 Å. Each silver(I) center is bound to two pyridylimine units, one from each ligand. One ligand passes above the silver(I)–silver(I) axis, while the other passes beneath, giving a non-helical metallo-cyclophane with Ag⋯Ag separation ca. 12.3 Å. Both triple helical [Co₂L₃]⁴⁺ and [Ni₂L₃]⁴⁺ cations contain two metal atoms and three ligands. Each metal center is bound to three pyridylimine units to attain a pseudo-octahedral co-ordination geometry. The ligand wraps in a helical arrangement around the two metal ions. Edge-to-face and face-to-face π–π interactions play important roles in the metal-assisted self-assembling process.