Development of Imide Coordination Chemistry

Abstract

This work provides a comprehensive review of structurally characterised imide based complexes (Chapter 1) and the developments of imide chemistry achieved during the course of this work. Individual chapters have their own abstracts to provide details of the material within. Key findings are summarised here.

An investigation into methylene and ethylene linked amide based ligands for the formation of grid type complexes is reported in Chapter 2. Four amide based ligands were prepared namely: N,N’-bis(2-pyrazylmethyl)pyrazine-2,3-dicarboxamide (H2LMpz1), N,N’-bis(2-pyrazylethyl)-pyrazine-2,3-dicarboxamide (H2LMpz2), N,N’-bis(2-pyrazylmethyl)pyrazine-2,5-dicarboxamide (H2LSpz1) and N,N’-bis(2-pyrazylethyl)pyrazine-2,5-dicarboxamide (H2LSpz2). During complexation reactions it was found that in some cases the methylene linked ligands (H2LMpz1 and H2LSpz1) partially oxidised to the imide analogues. This prompted the deliberate preparation and investigation of imide based ligands, which makes up the remainder of this work (Chapters 3-7). Complexes of the analogous ethylene linked amide ligand (H2LMpz2 and H2LSpz2) were generated with cobalt(II), nickel(II), copper(II) and zinc(II). The first row transition metal coordination chemistry of the non-symmetric pyrazine/pyridine imide ligand Hpypzca (N-(2-pyrazylcarbonyl)-2-pyridinecarboxamide), prepared in this work, is presented and discussed in Chapter 3. The reported complexes include: [MII(pypzca2)], M = Zn, Cu, Ni, Co, Fe; [MIII(pypzca)2]Y, M = Co and Y = BF4, M = Fe and Y = ClO4; [CuII(pypzca)(H2O)2]BF4, HNEt3[MnII(pypzca)(Cl)2]. The properties of these complexes are reported, with particular attention given to the reversible electrochemical properties. The first row transition metal coordination chemistry of the symmetric pyrazine/pyrazine imide ligand Hdpzca (N-(2-pyrazylcarbonyl)-2-pyrazinecarboxamide), prepared in this work, is presented and discussed in Chapter 4. The reported complexes include: [MII(dpzca)2], M = Fe, Co, Ni, Cu, Zn; [CuII(dpzca)(H2O)3](1 or 2)X, where X = BF4- or SiF62-, respectively. The properties of these complexes are reported, with particular attention given to the electrochemical properties. The properties of the triply switchable complex [CoII(dpzca)2] are explored in detail in Chapter 5. This includes analysis of temperature induced hysteretic spin crossover, pressure induced spin crossover and reversible electrochemical behaviour. The complexes [CoII(dpzca)2] and [NiII(dpzca)2] have been used as building blocks to produce two three-dimensional coordination polymers which are presented and discussed in Chapter 6: {[CoIII(dpzca)2AgI](BF4)2·2(H2O)}{∞ (1·2(H2O)) and {[NiII(dpzca)2AgI]-BF4·0.5(acetone)}∞ (2·0.5(acetone)). To the best of our knowledge these complexes are the first examples of isostructural frameworks with different overall charges resulting from alteration of the framework charge rather than that of the guest counterions. The surface area of 1 (5.6 m2 g-1) and 2 (3.5 m2 g-1) was evaluated by Ar and H2 adsorption isotherms. The guest exchange behaviour of the evacuated frameworks at 298 K has been studied with N2, CO2, CH4, H2O, CH3OH and CH3CN. These studies revealed an significant selectivity for the adsorption of carbon dioxide over other gases. Also detailed are attempts to prepare analogues of these systems using the [MII(dpzca)2] building blocks (MII = Fe, Cu, Zn). Attempts to produce analogues of 1 and 2 with different anions, by use of silver(I) nitrate, perchlorate, triflate and sulphate, are also detailed. The structural features of the three-dimensional framework {[CoIII(dpzca)2AgI](NO3)2·2(H2O)}∞ (3·2(H2O)) and the two-dimensional polymer {[NiII(dpzca)2AgI]NO3·x(solvent)}∞ 4·x(solvent) are also presented and discussed.