We propose a high-pressure powder neutron diffraction study of the archetypal donor-acceptor complexes (CD3)3N...I2 and (CD3)3N...ICl . These are the simplest structurally characterised donor-acceptor complexes known between an amine and a halogen/interhalogen. At ambient pressure, both complexes exhibit short N...I contacts and unusually long I-I/I-Cl bond lengths. The main objective of the proposed study will be an accurate determination of the changes in the N...I and I-I/I-Cl distances over the pressure interval 0-5 GPa at 120 K, which will constitute the first such study on a simple donor-acceptor system. 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 systems.