Synthesis of ligands containing N-oxide donor atoms and their assembly into metallosupramolecular structures

Abstract

A series of ligands that contain both N-donor and N-oxide donor atoms have been synthesised and ligands L⁵55, L⁶66, L⁷77 and L⁸888 contain, 4, 6, 5, and 6 donor atoms respectively. The smallest ligand L⁵55 forms a mononuclear complex with Cu²⁺ ([Cu(L⁵)(ClO₄)₂(MeCN)]) whereas L⁶66 and L⁷77 form dinuclear double helicates with Ni²⁺ and Cu²⁺ respectively ([Ni₂(L⁶66)₂]⁴⁺ and [Cu₂(L⁷77)₂]⁴⁺). L⁸888 forms a tetranuclear cyclic helicate upon reaction with Co²⁺ ([Co₄(L⁸888)₄]⁸⁺) and in all cases the complexes are characterised by single-crystal X-ray diffraction and ESI-MS. The N-oxide units imparts flexibility in the ligand strand and where the unoxidised ligand strand forms a cyclic helicate, the incorporation of an N-oxide unit allows the formation of the dinuclear double helicate.