.The effect of pressure on halogen and hydrogen bonds in the pyroelectric material N-iodo succinimide.

We will study the effect of pressure on the halogen and hydrogen bonds in the pyroelectric material N-iodosuccinimide. This compound crystalizes in the tetragonal space group P41 and shows in addition to its electrical properties, marked anisotropy in its thermal expansion properties, with negative thermal expansion along the unique axis and thermal expansion along a and b. The structure consists of helical chains along c which are formed by N-I---O=C halogen bonds. These chains are linked by weak C-H hydrogen bonds. This study will build upon our recently published studies on the effect of pressure on 1,4 dioxane monochloride(Diox-ICl), and trimethylamine and iodine monochloride/iodine TMA-ICl, TMA-I2. These studies showed how pressure could be utilized to modify the halogen and hydrogen bonds causing a sequence of phase transitions in diox-ICl in which C-H---Cl interactions became dominant at elevated pressures. However the TMA complexes behaved differently. In TMA-ICl at high pressure a zwitterionic species was formed, whilst in TMA-I2 no changes was observed. We ascribed this to an electronegativity difference between chlorine and iodine. Consequently this experiment will not just enable us to understand the effect of pressure on halogen bonds but deepen our understanding its connection with other physical properties providing a model for the construction of functional organic materials.