NEUTRON-DIFFRACTION STUDY ON SINGLE-CRYSTALS OF STRONTIUM PENTACYANONITROSYL FERRATE(II) TETRAHYDRATE (STRONTIUM NITROPRUSSIDE TETRAHYDRATE)

The crystal structure of strontium nitroprusside tetrahydrate, Sr[Fe(C N)(5)NO]. 4H(2)O, has been redetermined by neutron diffraction measure ments on single crystals at room temperature (monoclinic, space group C2/m, (No, 12) a = 20.07(2), b = 7.591(8), c = 8.397(9) Angstrom, beta = 98.7(5)degrees, V = 1260(4) Angstrom(3)). Refinements of the struct ure using 867 observed structure factors converged to the final R = 0. 064, Results confirm the oxygen-water disorder found by the X-ray diff raction study; i,e,, the oxygen atom of one water molecule is located on two different sites, corresponding to general positions within the asymmetric unit, with occupation factors of 2/3 and 1/3. An infinie hy drogen bond network links the strontium coordination polyhedra along t he [010] direction, All sites occupied by hydrogen atoms of the only w ater molecule not coordinated to a strontium ion, and accepters of hyd rogen bonds in this network, could not be determined, This fact sugges ts that this water molecule is affected by structural disorder and tha t it has free unabridged hydrogens. The water molecule, which does not belong to the hydrogen-bond network, is disordered on the symmetry pl ane m, previous assignments of water IR absorption bands have been rev ised and improved on the basis of the new structural data. (C) 1996 Ac ademic Press, Inc.