Neutron structure of strontium pentacyanonitrosylferrate(II) tetrahydrate below the 153 K phase transition

The average structure in the space group C2/m at 130 K of strontium pentacy anonitrosylferrate(II) tetrahydrate (strontium nitroprusside tetrahydrate, Sr[Fe(CN)(5)NO].4H(2)O, space group P2/m, monoclinic, Z=4, a=19.816(24), b= 7.563(7), c=8.406(9) Angstrom, beta=99.02 degrees, V=1244(24) Angstrom(3)) has been determined using neutron diffraction. A final R factor 0.061 was o btained using 665 observed structure factors. When going from room temperature to 130 K the space group C2/m changes to P 2/m. A rearrangement of hydrogen atoms is produced due to 14.3, 17.2, 5.9 a nd 26 degrees rotations of the planes of W1, W2, W3 and W4 water molecules, respectively. As a consequence of this structural modification, the weaken ing of some hydrogen bonds related to the W4 molecule and the reinforcement of the hydrogen bonds of the W2 molecule along the [0 1 0] direction are o bserved.