We propose a high-pressure powder neutron diffraction study of the simple donor-acceptor complexes (C5D5N)...ICl and (C5D5N)...IBr . These are the simplest structurally characterised donor-acceptor complexes known between an aromatic amine and an interhalogen. At ambient pressure, both complexes exhibit short N...I contacts and unusually long I-Cl/I-Br bond lengths. The main objective of the proposed study will be an accurate determination of the changes in the N...I and I-Cl/I-Br distances over the pressure interval 0-5 GPa at 120 K, This will complement our earlier study involving aliphatic amines Whilst carrying out this main aim, we also intend to collect high-pressure diffraction data at temperatures between 120 and RT, which will permit the first systematic study of the effect of pressure and temperature on the structure and phase stability of these compounds