The crystal structures of Mn, Zn, and Cd nitroprussides in their anhydrous state,
(M=Mn, Zn, Cd), were refined from XRD powder patterns using the Rietveld method. These compounds have a porous framework useful for adsorption and storage of small molecules. Water crystallization can be removed by heating below 100 °C without disrupting the 3D network by introducing certain structural modification mainly around the M site (Mn, Zn, Cd). For M=Mn and Cd, the compounds were found to be orthorhombic with space group Pnma [Mn:a=13.7844(1), b=7.3750(2), c=10.9470(2) Å, V=1112.8(1) Å3, Z=4; Cd:a=13.9566(3), b=7.5040(4), c=11.0230(2) Å, V=1154.4(1) Å3, Z=4]. Anhydrous zinc nitroprusside crystallizes in rhombohedral with space group R3 [a=b=19.2525(1), c=17.7107(2) Å, γ=120.0°, V=5685.1(1) Å3, Z=18]. When exposed to humid air, these anhydrous compounds become hydrated. The XRD powder patterns were recorded under vacuum on samples dehydrated in situ. The structural information from XRD was complemented with thermo-gravimetric, infrared, and Mössbauer data.