A study of the structural chemistry of coesite
Abstract
Because of their high symmetry, most of the silica polymorphs contain only a few nonequivalent Si–O distances. However, the structure of coesite contains two nonequivalent silicate tetrahedra, eight Si–O bonds, five Si–O–Si and twelve O–Si–O angles, thus making it an excellent candidate for testing Si–O bonding theory. In order to obtain the best possible set of Si–O distances, we refined the structure using single-crystal diffraction data from a synthetic crystal (unweighted R = 0.024). Cell parameters for this crystal are a = 7.135(1) Å, b = 12.372(1), c = 7.173(1), and β = 120.36(1).
A Mulliken population analysis was calculated with all Si–O bond lengths clamped at 1.614 Å and using the valence angles determined by Araki and Zoltai (1969) for which R = 0.076, and those obtained from the present experiment. The Si–O bond overlap populations calculated using the valence angles obtained for the new coordinates were found to be more highly correlated (r2 = 0.91 vs. r2 = 0.60 for the older data) with the observed Si–O bond lengths, suggesting that precise structural data are necessary to obtain a near-linear correlation between bond-overlap population and bond length. The individual Si–O bond lengths to the oxygen in the Si–O–Si linkages in coesite vary (1) non-lineary when plotted against Si–O–Si angle and (2) linearly when plotted against −1/cos [unk] (Si–O–Si), shorter bonds being associated with wider angles. Shorter bonds also tend to be involved in the wider O–Si–O angles. The results of this experiment show that there is no evidence for departure from stoichiometry, that there is no unusual thermal vibration of the oxygen atom in the linear Si–O–Si linkage, and that variations in individual Si–O distances are closely related to calculated bond-overlap populations, to the geminal nonbonded repulsions and to the charge of the oxygen atom.
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- Nyerereite: a new volcanic carbonate mineral from Oldoinyo Lengai, Tanzania
- The magnetic structures of NiWO4 and CoWO4
- A study of the structural chemistry of coesite
- Crystal structure of a synthetic, compositionally intermediate, hypersolvus alkali feldspar: evidence for Na, K site ordering
- Twinning and disorder in zinc perchlorate hexahydrate crystals
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Articles in the same Issue
- Zeitschrift für Kristallographie 1877–1977
- The Zeitschrift für Kristallographie and Professor Dr. G. Menzer
- Die Molekular- und Kristallstruktur von N,N′-Disalicyliden-meso-1,2-diphenyläthylendiamin*
- Quadratischer elektrooptischer Tensor des rhombischen Calciumformiats
- Die Kristallstruktur von Cu2As3O6CH3COO
- Die Bestimmung der Kristallstruktur von Trimerit CaMn2(BeSiO4)3 und das Trimeritgesetz der Verzwillingung
- Powder data for the chlorine derivatives of C.I. Pigment Red 9 and C.I. Pigment Brown 1
- Nyerereite: a new volcanic carbonate mineral from Oldoinyo Lengai, Tanzania
- The magnetic structures of NiWO4 and CoWO4
- A study of the structural chemistry of coesite
- Crystal structure of a synthetic, compositionally intermediate, hypersolvus alkali feldspar: evidence for Na, K site ordering
- Twinning and disorder in zinc perchlorate hexahydrate crystals
- Crystal data for the polymethine dye 1,3-bis (dimethylamino)-trimethinium perchlorate
- Unit-cell dimensions of Hofmann pyridine complexes
