Coordination Chemistry of Proton. In Situ Synthesis and X-Ray Structural Analysis of 2-Hydroxyethanaminium Picrate, HOCH2CH2NH3+*C6H2N3O7-

Article abstract of DOI:10.1246/bcsj.63.1512

2-Hydroxyethanaminium picrate, HOCH2CH2NH3+*C6H2N3O7-, is prepared through a metathetical reaction of Mg(Pic)2 and HOCH2CH2NH2 (2-aminoethanol, MEA) in ethanol through in situ generation of HPic.Orange yellow crystals (MEAH+Pic-) (mp 163 deg C) of the "Salt" are produced along with the colorless Mg(CH2NH2CH2O-)2, even when MEA is less than 1:1 with respect to Mg(Pic)2.The crystals are monoclinic, space group P2₁/c, a=11.797(4), b=14.288(3), c=7.124(2) Angstroem, β=97.63(2) deg, Z=4.D_cal=1.62 g cm^-3.Structural analysis from the 1617 reflection data (R=0.059, R_w=0.056) reveals that the picric acid proton is formally transferred to the MEA nitrogen (N-H, 0.968 Angstroem) and is merely bonded to the phenoxide of Pic(H...O-, 1.951 Angstroem) and weakly also to an oxygen of o-nitro group of the anion (H...ONO, 2.379 Angstroem).The transferred proton becomes and integral part of the cation MEAH+ and completes the fourth covalent bond of the sp³ N of MEA, and does not show any special affinity for the anionic oxygen of Pic; the N-H...O- (142.8 deg) and N-H...ONO (141.6 deg) angles are closely comparable.