Synthesis and characterisation of new Schiff-base metallo-supramolecular assemblies

Abstract

This thesis reports the design, synthesis and structural characterisations of new metallo-supramolecular assemblies, all incorporating a Schiff-base type ligand. The Schiff-base moiety was employed as it is widely documented in supramolecular architectures due to its ease of synthesis, interesting properties and its strong binding affinities to various metal ions. Small changes to the ligand, such as the addition of electron withdrawing or electron donating functional moieties were explored, as well as, shortening the ligand backbone in order to promote different rigidity of the ligand. The synthesis and characterisation have been communicated in each chapter and where possible physical properties have also been studied. In chapter two, a flexible N4O2-donor Schiff-base ligand incorporating an electron donating functional moiety (diethylamine) was employed. Four new complexes are presented containing metal centres (FeIII, CoIII, NiII and CuII). It was demonstrated that all complexes, except CuII, formed in a 1:1 ligand-to-metal (L:M) ratios, while the CuII complex exhibited an unexpected 3:2 (L:M) ratio due to the flexibility of the N4O2-donor Schiff-base ligand and CuII having the flexibility to form 4 or 5 coordinate bonds. In chapter three, adopting a similar flexible N4O2-donor Schiff-base as described in chapter two. The ligand utilised incorporated an electron withdrawing functional moiety (bromine) rather than an electron withdrawing functional moiety. Three new complexes ([FeL](BF4)2, [MnL](PF6) and [CoL]PF6) were reported and structural characterisation revealed all complexes exhibit a 1:1 (L:M) stoichiometric ratio in both the solid and liquid phase. In chapter four, a flexible N6-donor Schiff-base ligand incorporating thiazolyimine functional groups was synthesised, complexation resulted in the formation of a mononuclear complex ([FeL](BF4)2) that displayed a high-temperature spin transition. Structural characterisation revealed the complex exists in a 1:1 stoichiometric ratio in both the solid and liquid state. In chapter five, the backbone of the previous Schiff-base ligand (from chapter 4) was shortened and replaced by a hydrazine moiety in order to create a semi-flexible N3-donor Schiff-base ligand. Five new FeII complexes [FeL2](A)2 (A = BF4-, BPh4-, Cl-, Br- & I-) were reported. Structural characterisation was successful on four complexes and revealed that they exist in a 2:1 (L:M) stoichiometric ratio in both solid and liquid state.

Date of Award	2017
Original language	English