Solvothermal synthesis, structure and properties of metal imidazolate polymers

Metal imidazolates [M(Im)2] have received much recent attention as a promising class of metal coordination polymer especially as microporous phases for separation technology. Notably they have chemical stability because of strong metal-nitrogen bonds which also leads to exceptional framework thermal stability of 300℃-500℃. They are also of interest as direct topological analogues of silica SiO2. Chapter One surveys the background to successful design and preparation of ZIFs and their potential application such as gas storage and separation. In Chapter Two a total of 17 phases, mostly new, were formed by varying a wide range of solvents in metal imidazolate and benzimidazolate systems. Importantly, solid-state phase transitions of metal imidazolates are possible and two examples of reconstructive and two examples of displacive types are given. Chapter Three explores the effect of imidazole 2-position substituent groups on framework topology. The 2-EtIm systems give three isostructural products [Zn(2-EtIm)2] 3-4, [Co(2-EtIm)2] 3-5 and [Cd(2-EtIm)2] 3-6. The 3-D frameworks formed are topological analogues of quartz.They exhibit phase transition to ‘high quartz’ type phases. The transition is principally entropy driven and involves rotation of ethyl groups. Chapter Four looks at asymmetric imidazoles. Asymmetry into each Im bridge can lead to three outcomes; amorphous phases, crystalline phases with 4,5-positional disorder or fully ordered crystalline phases. Hydrothermal reactions in the Cadmium 4-methylimidazolide system gives amorphous phases at lower temperatures, whilst 160℃ can lead to fully ordered system. Finally Chapter Five discusses metal imidazolide-hydroxides that can also form zeolite-like frameworks. Basic hydrothermal conditions gives Form I [Zn3(2-MeIm)5(μ-OH)]n 5-1 its polymorph Form II [Zn3(2-MeIm)5(μ-OH)]n 5-2. and [Zn2(2-EtIm)3(μ-OH)]n 5-6. They have lower thermal stability than [Zn(Im)2] type ZIFs, but are still stable to loss of channel solvent