Organized assemblies of lead(II) complexes of a tetraiminodiphenol macrocyclic ligand: manifestation of weak metal-anion interactions and the directional influence of anions

Abstract

The syntheses and crystal structures of the lead(II) complexes [Pb(LH₂)(ClO₄)][ClO₄], [Pb(LH₂)(NO₃)₂] and [Pb₂L(NO₃)₂] of the tetraiminodiphenol macrocyclic ligand (H₂L) derived from a [2+2] condensation reaction between 2,6-diformyl-4-methylphenol and 1,3-diaminopropane are reported. In the mononuclear complexes, the two uncoordinated imino nitrogens are protonated and are hydrogen bonded to the phenolate oxygens. A supramolecular assembly occurs for [Pb(LH₂)(ClO₄)][ClO₄], due to weak interactions between the metal and three oxygen atoms of three different symmetry-related perchlorates, thereby forming a hexameric species with a propeller structure. [Pb(LH₂)(NO₃)₂], however, is a monomer with normal bidentate binding modes for the nitrates. By contrast, [Pb₂L(NO₃)₂] exhibits a 2-D structural network comprising parallel chains from two independent [Pb2L]2+ units, to which the nitrate anions are associated rather unconventionally: one oxygen is coordinated to two symmetry-related metal centres, another oxygen to a single lead, while the third oxygen remains free. The structural features of the complexes in solution have been investigated by ¹H NMR spectroscopy.