Crystal structures of ammonium citrates. Issue 1 (11th December 2018)

• Record Type: Journal Article
• Authors: Wheatley, Austin M.; Kaduk, James A.
• Is Part Of: Powder diffraction. Volume 34:Issue 1(2019)
• Page Start: 35
• Page End: 43
• Publication Date: 2018-12-11
• Subjects: ammonium, -- citrate, -- powder diffraction, -- Rietveld refinement, -- density functional theory; Powder metallurgy -- Periodicals; Materials -- Analysis -- Periodicals; 620.1127
• DOI: 10.1017/S0885715618000829
• Languages: English
• ISSNs: 0885-7156

Abstract

Abstract : The crystal structures of (NH4 )H2 C6 H5 O7 and (NH4 )3 C6 H5 O7 have been determined using a combination of powder and single crystal techniques. The structure of (NH4 )2 HC6 H5 O7 has been determined previously by single crystal diffraction. All three structures were optimized using density functional techniques. The crystal structures are dominated by N-H⋅⋅⋅O hydrogen bonds, though O-H⋅⋅⋅O hydrogen bonds are also important. In (NH4 )H2 C6 H5 O7 very strong centrosymmetric charge-assisted O-H-O hydrogen bonds link one end of the citrate into chains along the b -axis. A more-normal O-H⋅⋅⋅O hydrogen bond links the other end of the citrate to the central ionized carboxyl group. In (NH4 )2 HC6 H5 O7, the very strong centrosymmetric O-H-O hydrogen bonds link the citrates into zig-zag chains along the b -axis. The citrates occupy layers parallel to the bc plane, and the ammonium ions link the layers through N-H⋅⋅⋅O hydrogen bonds. In (NH4 )3 C6 H5 O7, the hydroxyl group forms a hydrogen bond to a terminal carboxylate, and there is an extensive array of N-H⋅⋅⋅O hydrogen bonds. The energies of the density functional theory-optimized structures lead to a correlation between the energy of an N-H⋅⋅⋅O hydrogen bond and the Mulliken overlap population: E(N-H⋅⋅⋅O) (kcal/mole) = 23.1(overlap) ½ . Powder patterns of (NH4 )H2 C6 H5 O7 and (NH4 )3 C6 H5 O7 have been submitted to International Centre for Diffraction Data for inclusion in the powder diffraction file.