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

Samantha J Bullock,Andrew Mills,Martina Whitehead,Michelle P Moore,Sean A F Piela,Lindsay P Harding,Craig R Rice,Liz Towns-Andrews

doi:10.1039/c3dt00090g

Abstract

A series of ligands that contain both N-donor and N-oxide donor atoms have been synthesised and ligands L5, L6, L7 and L8 contain, 4, 6, 5, and 6 donor atoms respectively. The smallest ligand L5 forms a mononuclear complex with Cu2+ ([Cu(L5)(ClO4)2(MeCN)]) whereas L6 and L7 form dinuclear double helicates with Ni2+ and Cu2+ respectively ([Ni2(L6)2]4+ and [Cu2(L7)2]4+). L8 forms a tetranuclear cyclic helicate upon reaction with Co2+ ([Co4(L8)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.

Highlights

To achieve the formation of metallosupramolecular architectures such as linear or circular helicates careful consideration has to go into ligand design.[1,2,3,4,5,6] These ligands must contain the correct number and arrangement of donor atoms such that the formation of the entropically favoured mononuclear assembly is prevented but the binding domains are sufficiently arranged so that a discrete self-assembled species is formed.[7]
We showed that incorporation of a 1,3-phenylene spacer unit, within a potentially hexadentate ligand, can give different self-assembled species dependent upon the ionic radius of the metal ion used to coordinate the ligand strand
It is somewhat surprising that this ligand gives a dinuclear double helicate with Cu2+ as we have previously shown that this type of ligand usually produces a pentanuclear cyclic helicate upon coordination with first-row transition metal ions

Summary

Introduction

To a suspension of 1-N-oxide-2,2′-bipyridine-6′-thioamide (3) (0.1 g, 0.43 mmol) in EtOH (20 ml) was added the thiazole-containing α-bromoacetyl (8) (0.15 g, 0.42 mmol) and the reaction refluxed for 8 hours, during which time all the reactants dissolved. In the solid state there are two different molecules in the unit cell, each of which contains a 6-coordinate metal centre formed by coordination of one ligand strand, two perchlorate counter ions and either a water molecule or a molecule of acetonitrile giving the simple mononuclear species [Cu(L5)(ClO4)2(sol)] where sol = H2O or MeCN (Fig. 2)

Results

Conclusion