Ab initio structure determination of kidney stone potassium quadriurate from synchrotron powder diffraction data, a 150 year problem solved

The structure of potassium urate, co-crystallized with uric acid K(C5H3N4O3)(C5H4N4O3), from human kidney stones, is determined ab initio from synchrotron powder diffraction data, space group P21/c, a = 3.60504(9) Å, b = 19.9293(7) Å, c = 18.4841(6) Å, β = 100.503(2)°, Z = 4. Each uric acid molecule is connected to a urate anion through three hydrogen bonds, both molecules are related by a pseudo-inversion center and are randomly distributed in the crystal. Two of the oxygen atoms of the uric acid molecule and two of the urate anions are involved in the potassium coordination forming KO7 monocapped trigonal prisms sharing their triangular bases, building infinite chains extending along the short a axis. Such a formulation, though controversial, has been claimed to exist since 1862 and named potassium quadriurate. The crystal structure is optimized by energy minimization (DFT) in the solid state, using a hybrid PBE0 functional. The capacity of the urate anion to connect by strong hydrogen bonds to a uric acid molecule has implications concerning the uric acid transport in biological media.