Structure of racemic calcium 5-methyltetrahydrofolate trihydrate from synchrotron powder diffraction data and density functional theory

The crystal structure of the racemic title compound, poly[[(μ-(2<i>S</i>)-2-{[4-({[(6<i>S</i>)-2-amino-5-methyl-1,4,5,6,7,8-hexahydropteridin-6-yl]methyl}amino)phenyl]formamido}pentanedioato)diaquacalcium(II)] monohydrate], {[Ca(C₂₀H₂₃N₇O₆)(H₂O)₂]·H₂O} _<i>n</i> (space group <i>P</i>2₁/<i>c</i>) has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional theory techniques. The structure consists of alternating hydro-philic (Ca/O) and hydro-phobic layers lying parallel to the <i>bc</i> plane. An extensive network of O-H⋯O hydrogen bonds link the Ca coordination spheres within the layers. The anions link the Ca²⁺ ions into chains propagating along the <i>b</i>-axis direction. N-H⋯O hydrogen bonds link the Ca/O units and the anion layers. The calcium ion is 6-coordinate (distorted octa-hedral), and is isolated. The coordination sphere consists of two water mol-ecules, a chelated carboxyl-ate group, a monodentate carboxyl-ate group, and a carbonyl group. Both the Ca coordination geometry and the extended structure are very different than that of the previously determined enanti-opure calcium l-5-methyl-tetra-hydro-folate trihydrate (Form I).