Synthesis and characterisation of chiral metal phosphonates with applications in magnetism, catalysis and luminescence

Abstract

This thesis details an improved synthesis and full characterisation of a chiral phosphonic acid, (S)-[1,1’-binaphthalen]-2-ylphosphonic acid, (S)-bpa, derived from the commercially-available (R)-binol. From this sterically encumbered phosphonic acid ligand, a total of 27 new chiral metal phosphonates (11 first-row transition metal, 2 second-row transition metal and 14 lanthanide) have been prepared and characterised by single-crystal X-ray diffraction. Chapter 1 discusses the history of metal phosphonate chemistry and how reagents and conditions can be controlled in order to determine certain metal phosphonate structures. It also explains the nomenclature of phosphonate binding which will be used throughout the thesis. Chapter 2 discusses the synthesis of (S)-bpa and how it was optimised from the parent (R)-binol. The ligand was then reacted with Co(II) under different conditions in order to prepare three cobalt(II) phosphonates of remarkably different morphologies. Furthermore, (R)-bpa was synthesised and used to prepare the corresponding (R)- derivatives of the aforementioned three cobalt(II) phosphonates. One by-product of these reactions, the mononuclear Co(II) complex [Co(OAc)2(Py)2(H2O)2] (Py = pyridine) was found to exhibit slow relaxation after magnetic susceptibility measurements were conducted on it (Ueff = 25 cm-1 (36 K)). The magnetic susceptibility data for the other cobalt(II) phosphonates is pending. Chapter 3 further explores the versatility of (S)-bpa and details the preparation of nine transition metal phosphonates – seven first-row (Sc, two Mn, Fe, Ni, Cu and Zn) and two second-row (Y and Cd). In Chapter 4, we turn our attention to the lanthanides and the successful preparation and full characterisation of 14 (S)-bpa-lanthanide phosphonates (all except for promethium) is detailed. The structures adopt three different forms throughout the series – the first from La to Sm, the second from Eu to Tm and the third include Yb and Lu. Photophysical studies were conducted on the europium phosphonate and it was found to be fluorescent.