5-amino-2-methylpyridinium hydrogen fumarate: an XRD and NMR crystallography analysis.

Single-crystal X-ray diffraction structures of the 5-amino-2-methylpyridinium hydrogen fumarate salt have been solved at 150 and 300 K (CCDC 1952142 and 1952143). A base-acid-base-acid ring is formed through pyridinium-carboxylate and amine-carboxylate hydrogen bonds that hold together chains formed from hydrogen-bonded hydrogen fumarate ions. H-1 and C-13 chemical shifts as well as N-14 shifts that additionally depend on the quadrupolar interaction are determined by experimental magic angle spinning (MAS) solid-state nuclear magnetic resonance (NMR) and gauge-including projector-augmented wave (GIPAW) calculation. Two-dimensional homonuclear H-1-H-1 double-quantum (DQ) MAS and heteronuclear H-1-C-13 and N-14-H-1 spectra are presented. Only small differences of up to 0.1 and 0.6 ppm for H-1 and C-13 are observed between GIPAW calculations starting with the two structures solved at 150 and 300 K (after geometry optimisation of atomic positions, but not unit cell parameters). A comparison of GIPAW-calculated H-1 chemical shifts for isolated molecules and the full crystal structures is indicative of hydrogen bonding strength.