Single-crystal neutron diffraction structure of sodium pentacyanonitrosylferrate(2-) (sodium nitroprusside) dihydrate

Na2[Fe(CN)sNOI.2H20, M r= 297.973, orthorhombic, Pnnm (No. 58), a=6.219(8), b= 11.947(11), c= 15.587(12)A, V= 1158(4)A 3, Z =4,Dx= 1.69gcm 3,2=0.831 (1),/k,/t = 0.585 cm -~ (evaluated), F(000)= 43.2, room temperature, final R factor 0.046 for 1557 observed reflections, wR = 0.015. The structure is essentially the same as that determined by X-ray diffraction" the nitroprusside anion presents the usual distorted octahedral geometry with the Fe atom 0-261 (1) A out of the equatorial least-squares mean plane (defined with cis CN ligands). The Fe-C and C-N bond lengths are in the ranges 1.929 (2)-1.945 (1) and 1. 155 (1)-1. 158 (1) ,/k respectively, the Fe-N distance is 1.667 (1) A and the Fe-N-O angle is 176.2 (1) °. The water molecules are tetrahedrally coordinated, the H(1)-O(2)-H(2) angle is 105.4 (4) ° and the O(2)-H distances 10.925 (4) and 0.939 (4) AI are slightly shorter than the average value 10.945 AI found for N-acceptors.