Self-assembly of nickel(II) complexes of new bis-bidentate Schiff base ligands

Nickel(II) complexes derived from three new bis-bidentate Schiff bases, H2L 1-3, having two N-n-propyl-salicylaldiminate units linked by an O-(CH2)(n)- O spacer (n = 4, 8, 12, respectively) at the 3-position of the salicyl moie ties, are described. The pyridine adduct of the complex with the shorter sp acer forms a cyclic trinuclear structure, [Ni-3(L-1)(3)(PY)(6)] (2), in the solid state, where each Ni-II ion is octahedrally coordinated by two N,O-b identate arms of two different ligands and two pyridine nitrogens. The base with n = 8 leads to the double-helical dinuclear complex, [Ni-2(L-2)(2)]. THF (3), which is the first example of a structurally characterised helicat e based on a square-planar N2O2 coordination geometry. In CHCl3 solution, 3 undergoes a disassembly process which results in an equilibrium mixture wh ere the mononuclear species is largely predominant.