This result is consistent with the cyclic structure 2 and inconsistent with a cyclic dimer, in which two stilbene units would be aligned in the base-stacked conformation and therefore exhibit excirner fluorescence.

Intermolekulare Wechselwirkungen werden traditionell nach der Art der zugrundeliegenden energetischen Beziehung klassifiziert: Wasserstoffbriickenbindungen, van-der-Waals-Wechselwirkungen, Charge-Transfer-Krafte etc. [

Dedicated to Professor Jack D. Dunitz on the occasion of his 80th birthdayIn this paper, we report the results of a study involving the coordination geometries of Cu ; n m 4; n 0 ± 4) to provide data on the structural and energetic changes that occur in isolated complexes when the oxidation state of the Cu ion is changed from II to I while the coordination number is conserved. The use of such simple ligands in these calculations eliminates constraints on the geometric changes that may be imposed by more-complicated ligands.

The system containing six benzylideneanilines (BA) has been studied: C--H---hal interactions, which may contribute to the planarity of the molecule. The structures in Group 2 crystallize in a monoclinic cell. space group P2Jc. The confornmtion is nonplanar and there are no intern~olecular halogen---halogen interactions. The abovementioned five atom pattern ring does not occur in these structures. These two groups of structures show that the type and mode of molecular substitution can lead to specific intermolecular interactions which in turn stabilize an otherwise unfavorable molecular conlbnnation.

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