The aim of this proposal is to perform a neutron diffraction determination of the first perdeuterated Mn-Prussian Blue (PB) analogue of composition: Mn(II)3 [Mn(III)(CN)6]2 ¿(D2O)6.xD2O (x = 6-10) . Air-stable, cubic crystals of ~1.5 mm edges suitable for measurements on the instrument SXD, have been recently obtained by in-gel crystallization. A preliminary characterization has shown a magnetic ordering temperature around 30K, therefore we ask for a total of 8 days of beamtime on SXD in order to determine the structure of this compound at 50 and at 15K, i.e. above and below the magnetic transition.