The crystal and molecular structure of the disodium salt of 2,4,6,8-tetrahydroxypyrimido[5,4-d]pyrimidine (2,6,8,10-tetrahydroxyhomopurine)

Abstract

The crystal structure of the title compound, C₆H₂N₄O₄Na₂,4H₂O, at room temperature, has been determined by three-dimensional methods. There are two formula units in the monoclinic unit cell, a= 3·57, b= 15·36, c= 10·54 Å, β= 98° 30′, with space group P2₁/c. The disodium salt is formed by the neutralisation of the two β-hydroxy-groups. The molecule is planar but only partly aromatic: the α-oxygen atoms are in the carbonyl form, the carbon–carbon central bond has a high double-bond character, and the other carbon–carbon a high single-bond character; the carbon–nitrogen distances vary from 1·37 to 1·40 Å. Each sodium atom is surrounded by an octahedron of six oxygen atoms, three from water and three from homopurine molecules. The water molecules are arranged in such a manner as to form donor–acceptor hydrogen bonds with the α-oxygen and nitrogen atoms of the molecule.