Applications of low-temperature crystallography

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg for the Degree of Master of Science January, 1991.Two cryostats, a liquid nitrogen gas flow cryostat and a Be walled flow cryostat, suitable for use on Enraf Nonlus CAD4 four circle diffractometers have been commissioned and tested. The necessary techniques relating to crystal mounting and centring tor low-temperature data collection were also developed, The complete experimental procedure was tested by determining the crystal structures of the following three compounds at low-temperatures:N-arylpyrrolidin-2-one,4-p-hydroxyphenyl- 9,10,11-trihydroxy-8-ethyl-1,7-dioxaspiro[4,4]-nona-2,6-dione and 5,6-trans-Bromo- 5-hydroxy-3-nitrobicyclo[2,2.2]oct-2-ene.ln performing these structure determinations, some of the applications of low-temperature crystallography were considered

Poly[1,4-bis­(ammonio­meth­yl)cyclo­hexane [di-μ-iodido-diiodido­plumbate(II)]]

The title compound, {(C8H20N2)[PbI4]}n, is an inorganic–organic hybrid. The structure is composed of alternate layers of two-dimensional corner-sharing PbI6 octa­hedra ( symmetry) and 1,4-bis­(ammonio­meth­yl)cyclo­hexane cations ( symmetry) extending parallel to the bc plane. The cations inter­act with the inorganic layer via N—H⋯I hydrogen bonding in the right-angled halogen sub-type of the terminal halide hydrogen-bonding motif

Poly[1,4-bis­(ammonio­meth­yl)cyclo­hexane [di-μ-bromido-dibromido­plumbate(II)]]

The title compound, {(C8H20N2)[PbBr4]}n, crystallizes as an inorganic–organic hybrid with alternating layers of diammonium cations and two-dimensional corner-sharing PbBr6 octa­hedra extending parallel to the bc plane, which are eclipsed relative to one another. Both PbBr6 octa­hedra and the organic cation exhibit symmetry. The cations inter­act via N—H⋯Br hydrogen bonding in the right-angled halogen sub-type of the terminal halide hydrogen-bonding motif

Poly[1,4-bis(ammoniomethyl)cyclohexane [di-μ-chlorido-dichloridoplumbate(II)]]

The title compound, {(C8H20N2)[PbCl4]}n, crystallizes as an layered inorganic–organic hybrid perovskite-type structure. Corner-sharing PbCl6 octahedra extend parallel to the ac plane. Adjacent layers are staggered relative to one another, with diammonium cations separating these layers. The cations exhibit overline{1} symmetry and interact with the inorganic sheets via N—H...Cl hydrogen bonding in the right-angled halogen sub-type of the terminal halide hydrogen-bonding motif