The chemistry of a range of systems displaying superconductivity will be surveyed briefly. The main focus will be on the factors controlling superconductivity in iron arsenide and selenide superconductors, but the chemical ideas will be extended to the control of superconductivity in other systems, particularly layered chalcogenides. Synthetic methods for realising members of the class of iron based superconductors, and other classes of superconductor will be described. In particular the focus will be on compounds containing iron selenide layers with electropositive metals and small molecules such as ammonia in the interlamellar space, which have been characterised using neutron diffraction investigations [1,2] and in-situ X-ray powder diffraction investigations carried out during synthesis . The control of the physical properties through chemical transformations including absorption of small molecules [2,3] will be described, and the interplay of magnetism and superconductivity as a function of composition will be compared with that of the iron arsenide members of the class . These will be related to measurements on iron selenide films. Further new results relating to the use of detailed characterisation to correctly identify the superconducting phase in structurally complex mixtures will be discussed in the context of superconductors derived from bismuth selenide .
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