The crystal and molecular structure of photoaldrin, C₁₂H₈Cl₆

Generalization of Baur's correlations between bond length and bond strength in inorganic structures

“…[for Si-O see also Baur (1971)]. An analogous relationship has been obtained between the length D...A of hydrogen bonds and the corresponding value of (Po-PA), where A (acceptor) is always oxygen and D (donor) may be either oxygen (Baur, 1970) or an ammonium group (Khan & Baur, 1972). Although the scatter of experimental points around the fitted straight lines is often appreciable, particularly for cations with a formal charge less than 3, relation (2) is useful, at least qualitatively, in several cases ; e.g., it can justify irregular coordination polyhedrat and can provide a test for doubtful features of crystal structures, such as the possible existence of hydrogen bonds [see, e.g., Ferraris & Franchini-Angela (1973)].…”

The crystal structure of magnesium diethyl phosphate, Mg[PO2(OC2H5)2]2

“…The angles, 107.7 °, 109.6 ° and 111.1° are close to those of a regular tetrahedron. The magnesium atom is usually found in an octahedral coordination (Vijayan & Viswamitra, 1967;Nyborg & Danielson, 1970;Khan & Baur, 1972) and occasionally in fivefold coordination (Calvo, 1967;Nord & Kierkegaard, 1968;Vallino, 1969;Toney & Stucky, 1971) or eightfold coordination (Zeman & Zeman, 1961;Gibbs & Smith, 1965). The existence of four-coordinated magnesium ions has been observed in the crystal structures of spinel oxides (MgAl204: Bacon, 1952;MgV204: Reuter & Riedel, 1969), melilite (Smith, 1953) and several Grignard reagents: phenyl magnesium bromide dietherate (Stucky & Rundle, 1964), ethyl magnesium bromide dietherate (Guggenberger & Rundle, 1968), and magnesium bromide diethyl etherate (Schibilla & LeBihan, 1967).…”

Refinement of the crystal structures of ammonium dihydrogen phosphate and ammonium dihydrogen arsenate

“…As c/a is lowered the coordination number of the ammonium ion tends towards eight, as in the alkali dihydrogen phosphates and arsenates. This is analogous to the increasing coordination numbers of NH4 + with rising temperature in the transition of (NH4)_,SO4 (Schlemper & Hamilton, 1966;Khan & Baur, 1972) and is an indication of the increasing alkali ion character of NH + with increasing temperature.…”

“…Neutron-diffraction work on ADP by Tenzer et al (1958) provides a direct evidence of the N-H... O(f) bonds. This is a specific example of the tendency of the NH + ions towards displaying smaller coordination numbers than the corresponding alkali compounds (Khan & Baur, 1972). The effect of these N-H... O bonds is reflected in the cell parameters and in the thermal expansion behavior of ADP and ADA.…”

“…The c/a ratios vs. ionic radii of K ÷, Rb ÷, Cs + and NH + cations in KDP-type structures. Ionic radii for the alkali atoms in eightfold coordination are from Shannon & Prewitt (1969) and for NHg ions in fourfold coordination from Khan & Baur (1972).…”