Sodium silicate hydrates. IV. Location of hydrogen atoms in Na2O.Si02.6H20 by neutron diffraction

Abstract

The hydrogen atoms in the silicate Na20. SiO2.6H20 were located using neutron diffraction. The Si-O and Na-O bond lengths obtained from the refinement are compared with those given in the original X-ray structure determination, and also with the results of a completely new X-ray structure determination performed utilizing a chip from the crystal used for neutron diffraction. Some comments are made on the accuracy of the various results.

Location and anisotropic refinement of deuterium atoms in disodium dideuteriumsilicate heptahydrate (D2O) by neutron diffraction; hydrogen bonding at 296 K and thermal properties

“…D-O-D angles in Na2[SiO2(OD)2].7D20 range between 106 and 109 ° and are therefore more consistent compared with the corresponding data given for Na2[SiO2(OH)2].5H20 by Williams & Dent Glasser (1971) which range between 100 and 113 ° (see Table 2). The Na-O polyhedra in Na2[SiO2(OD)2].7D20 are almost regular octahedral (CN = 6) with Na-O bonds which are significantly shorter than in Na2[SiO2(OH)2].8H20 (Jamieson & Dent-Glasser, 1966a,b;Schmid, Felsche & Mclntyre, 1984) and are similar to those observed in Na 2-[SiOz(OH)2].5H20 (Williams & Dent-Glasser, 1971). Whereas in the octahydrate no Na-O bonds shorter than 2.4 !k are observed, about half of these bonds in the heptahydrate are shorter than 2.4 ,&.…”

An X-ray and neutron diffraction study of mercury(II) sulphate monohydrate

“…The O-H distances are 0.955 (5) .. H distance of 1.90 A and for an acceptor distance of 2.26 A a much more bent hydrogen bond is suggested than that found in the present structure. A weak hydrogen bond with a similar geometry is however found in NaEH2SiO4.5H20 (Williams & Dent Glasser, 1971) (Fig. 2), linked in the y direction by the very weak hydrogen bond O(W)... O(W).…”

Location and anisotropic refinement of hydrogen atoms in disodium dihydrogensilicate tetrahydrate, Na2H2SiO4.4H2O, by neutron diffraction; hydrogen bonding at 173 K

“…This fact reduces the force of repulsion between the O atoms to a minimum which accounts for the low HO-Si-OH angle of 101.3 (1) °. In Na2H2SiO4.8H20 with its isolated [H2SiO4] 2-tetrahedron (Schmid, Felsche & Mclntyre, 1984), bonded to neighbouring ones by means of hydrogen bonds from the hydroxyl groups which are in this case arranged in a neighbouring position (Williams & Dent-Glasser, 1971), this force of repulsion between both OH groups is higher and results in a larger HO-Si-OH angle.…”

“…The Na--O polyhedra in Na2H2SiO4.4H20 show almost trigonal-bipyramidal geometry (CN = 5) which is a striking difference between this structure and those of the higher hydrates of the l: 1 series, all of which show octahedral coordination (CN=6) for their Na-O polyhedra (Williams & Dent-Glasser, 1971;Jamieson & Dent-Glasser, 1967;Dent-Glasser & Jamieson, 1976;Schmid, Felsche & McIntyre, 1984). Taking into account bond-length-bond-strength considerations, bond-valence sums give 1 for both Na atoms.…”