The Crystal and Molecular Structure of the Sodium Salt of Xanthine

The crystals of sodium salt of xanthine, C5H3N4O2Na·4H2O, are monoclinic with four molecules in a unit cell of dimensions; a=7.31, b=19.52, c=7.17 Å, β=100.0°, space group P21⁄c. The structure has been determined by application of the sign relationship S(hkl)S(h′k′l′)∼S(h+h′,k+k′,l+l′) from (hk0) intensity data and refined by three-dimensional least-squares methods. The positions of the hydrogen atoms were determined by a three-dimensional difference Fourier analysis, and it was confirmed that deprotonation took place at the position of the imino N(3)H of the xanthine molecule. Each Na+ cation is surrounded by six water molecules and each xanthine anion participates in ten hydrogen bonds, forming a close-packed system.