Application of ‘molecular’ theories to the structure of the crystalline state
Recent years have seen the development of simple molecular orbital based ideas to view the structures of molecular ring, cage and cluster compounds. The principles of these methods are used here to demonstrate in a new way how the structures of solids depend on electronic configuration.
Coordination Number Pattern Recognition Theory of Carborane Structures
Publisher Summary In the early 1950s, the structures of the more common boranes were still a matter of debate. Although the hypothesis appeared to be a losing favor, there remained strong tendencies to anticipate and interpret borane structures as having mildly nonconforming hydrocarbon structures. As a number of boranes were verified as having polyhedral fragment configurations, the structural thread to hydrocarbon chemistry became weakened. Subsequently, many other boranes and carboranes were discovered, and a seemingly endless array of multifarious structural types had to be considered. Several schools of thought then arose. Members of one school treated each structure as a separate case, more or less succumbing to the thesis of an almost infinite variety of structural parameters. A second school took the view that although carborane structures were complex in nature, such structures could eventually be categorized or collated by improved theoretical treatments, which could be expected to become ever more accurate because of constantly improving computer systems.
An account of some computing experiences
is near ly normal (86 °) to the associated uranyl axis. The distances and bond angles within the group agree well with those observed in other acetates. The crude experimental determinat ion of the hydrogen coordinates places the H m a tom in the same plane as the carbon and oxygen atoms, and this feature was re ta ined in modifying the exper imental coordinates for the hydrogen atoms so as to give more reasonable C H distances and bond angles. H 0 distances outside a given aceta te group are all greater t h a n 2-7 /~, showing tha t there is no real bonding. The 0m--0~v distances are 2.21+0.05 /~ within and 2-76±0-05/~ between aceta te groups. These are alterna t ing edges of the near ly plane hexagon of oxygen atoms about the uran ium a tom shown in :Fig. 2.