Photocrystallography is a rapidly developing technique in modern structural chemistry which will result in a paradigm shift in the way that the crystallographic method is employed. The most recent and impressive developments of this technique have been in small molecule the X-ray study of metastable state structures with very short lifetimes. Recently, we have used this method to monitor solid-state reactions. The nitro group in [Ni(dppe)(n1-NO2)Cl] reversibly converts to the nitrito isomer [Ni(dppe)(n1-ONO)Cl] upon irradiation with 400 nm light at temperature between 100 ¿ 160 K. Photocrystallography is well developed for neutrons and we have chosen the mentioned system to develop this technique using SXD with the aim of becoming more routine and enabling charge density studies using neutron coordinates. We request 7 days on SXD to obtain the structures prior and after photoexcitation.