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Crystal structure and hydrogen bonding of magnesium ammonium sulfate hexahydrate*

1962; De Gruyter; Volume: 117; Issue: 5-6 Linguagem: Inglês

10.1524/zkri.1962.117.5-6.344

2366-1798

T. N. Margulis, David H. Templeton,

Crystal structures of chemical compounds

The structure of Mg(NH4)2(SO4)2 · 6H2O has been redetermined in order to assign the hydrogen bonds. The crystals are monoclinic, space group P21/a, with a = 9.324, b = 12.597, c = 6.211 Å, and β = 107.14°. The structure previously reported by Hofmann has nearly correct coordinates for the Mg, S, and N atoms, but incorrect coordinates for the oxygen atoms. Three-dimensional x-ray diffraction data were taken with the General Electric goniostat. The structure, including hydrogen atoms, was determined by Fourier and least-squares methods. The magnesium atom is surrounded by an octahedron of water molecules, each forming two hydrogen bonds to oxygen atoms of the sulfate ions. Three hydrogen atoms of each ammonium ion are bonded to sulfate-oxygen atoms, but the fourth is equidistant from two sulfate-oxygen atoms with the geometry which previous authors have called a "bifurcated hydrogen bond". Average interatomic distances (uncorrected for thermal motion) are: Mg–O = 2.07 Å, S–O = 1.47 Å, O–O (hydrogen bonded) = 2.77 Å, N–O (hydrogen bonded) = 2.90 Å, and N–O (bifurcated bond) = 3.08 Å. The average S–O bond length after correction for thermal motion is 1.49 Å.