Self-assembly of Nickel(II) Complexes of New Bis-Dentate Schiff Base Ligands

Nickel(II) complexes derived from three new bis-bidentate Schiff bases, H2L1-3, 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 moieties, are described. The pyridine adduct of the complex with the shorter spacer forms a cyclic trinuclear structure, [Ni3(L1)3(py)6] (2), in the solid state, where each NiII ion is octahedrally coordinated by two N,O-bidentate arms of two different ligands and two pyridine nitrogens. The base with n = 8 leads to the double-helical dinuclear complex, [Ni2(L2)2]·THF (3), which is the first example of a structurally characterised helicate based on a square-planar N2O2 coordination geometry. In CHCl3 solution, 3 undergoes a disassembly process which results in an equilibrium mixture where the mononuclear species is largely predominant.