Synthesis And Coordination Chemistry Of Ligands Capable Of Simultaneously Coordinating Metal Ions And Binding Anions

Abstract

This thesis is concerned with the synthesis of ditopic ligands than can both coordinate transition metal ions and interact with anions. All the ligands contained two or more bidentate thiazole-pyridyl N-donor coordination domains and two or more secondary amine units which have shown to interact well with anions.

In Chapter 2 the bidentate thiazole-pyridyl ligands (L ^2.1 , L ^2.2 and L ^2.3) were synthesised in moderate yields via diamine starting materials following a simple three step procedure. This involved, benzoylisothiocyanation, base hydrolysis and finally a Hantzsch thiazole ring closure reaction. Each of the three ligands have the same basic functionality with two thiazole-pyridyl domains separated by a spacer unit. L ^2.1 contains a diamino 1,2-ethyl central spacer unit, L ^2.2 a diamino 1,4-butyl central spacer unit and L ^2.3 a diamino cis-1,4-but-2-ene central spacer unit. The coordination chemistry of L ^2.1, L^2.2 and L ^2.3 with Cu(II) metal salts (usually as the ClO4 - , BF4 - and triflate salts) was examined, as well as other selected counter anions. For L ^2.1 six different helicate architectures were determined by single crystal X-ray diffraction as well as being confirmed in the gas phase by ESI-MS for the systems concerning. These included the dinuclear double helicates; [(L ^2.1)₂Cu₂(trif)₂] ²⁺, [(L ^2.1)₂Cu₂(H₂O)₂(NO₃)₄], [(L ^2.1)₂Cu₂] ²⁺ , [(L ^2.1)₂Cu₂(OSe(OMe)₂)]²⁺ and [(L ^2.1)₂Cu₂(H₂PO₄)(trif)]²⁺. In addition to this the trinuclear helicate [(L ^2.1)₃Cu₃(PO₄BF₃)]³⁺ was also isolated, where the coordinated dihydrogen phosphate underwent reaction with the tetrafluoroborate anion. For ligand L ^2.2 two different dinuclear double helicate structures were formed which included [(L ^2.2)₂Cu₂(H₂PO₄)(trif)₂] ²⁺ and [(L ^2.2)₂Cu₂(PO₄(BF₃)₂)]⁺ with the latter species arising from reaction of dihydrogen phosphate with the tetrafluoroborate anion. For the alkene-containing ligand L ^2.3 two isomeric helicate structures were obtained with Cu(trif)₂ that differ in the coordination of the triflate anion.

A similar synthesis route was used to produce the bis-bidentate ligand L ^3.1 which comprised of a 2,2’- phenylene central spacer unit linking the two thiazole-pyridyl domains. Again, L ^3.1was reacted with a series of Cu(II) metal salts and the resulting structures determined by single crystal X-ray diffraction as well as being confirmed in the gas phase by ESI-MS. Two different structures were observed for this system, the mono-nuclear [(L ^3.1)Cu](ClO₄)₂ and the tetranuclear circular head-to-tail helicate [(L ^3.2 )₄Cu₄](trif)₈. In the latter the ligand was observed to undergo a reaction at one of the two amine units with a molecule of the acetonitrile solvent to give a new amidine-containing R₂N-C=NH(CH)₃ unit. This resulted in the ligand system re-programming itself to give the unsymmetrical bidentate/tridentate ligand L ^3.2 and consequently forming the tetranuclear head-to-tail circular helicate [(L ^3.2 )₄Cu₄] ⁸⁺ .

The final chapter is concerned with the tripoidal ligand L ^4.1 which was synthesised in a similar fashion to the previous ligands. However, the ligand contained three bidentate thiazole-pyridyl domains linked by a tris-(aminoethyl)amine (tren) central spacer unit. L ^4.1 was reacted with a series of Cu(II) metal salts ((ClO₄ - , BF₄ - and triflate) and the resulting structures were determined by single crystal X-ray diffraction as well as being confirmed in the gas phase by ESI-MS. Sixteen different anion containing crystal structures were obtained for this system, where 13 of which adopted the [(L ^4.1)₂Cu₃A]ⁿ⁺ trinuclear capsule type motif (i.e. BF₄ˉ, Brˉ, Iˉ, CO₃ ^{2 ˉ}, SiF₆ ^{2 ˉ}, VO₄ ^{3 ˉ}, WO₄ ^{2 ˉ}, CrO₄ ^{2 ˉ}, SO₄ ^{2 ˉ}, AsO₄ ^{3 ˉ}, SeO₄ ^{2 ˉ}, SeO₃ ^{2 ˉ} and PO₄ ³ ˉ). The larger octahedral iodate anion gave the expanded tetranuclear species [(L ^4.1)₂Cu₄(IO₆)(H₂O)₂] ⁴⁺ and dependant on stoichiometry the third row chalcogenide selenite gave the remarkably different [(L ^4.1)₄Cu₈(SeO₃)₄] ⁸⁺ cage type assembly. UV-Vis experiments showed that the self-assembled host ([(L ^4.1)₂Cu₃] ⁶⁺) displayed a high degree of selectivity to shape, size and charge of the guest anion, with the highly charged phosphate anion encapsulated in preference to most common anions. Importantly, gravimetric and ion chromatography experiments showed that the [(L ^4.1)₂Cu₃] ⁶⁺ host system is capable of both forming and encapsulating phosphate anions in a competitive aqueous solvent (i.e. water) and removing them in a virtually stoichiometric manner resulting in
concentrations < 0.1 ppm.

Date of Award	7 Mar 2019
Original language	English
Supervisor	Craig Rice (Main Supervisor) & Mark Heron (Co-Supervisor)