Chemical insight from crystallographic disorder-structural studies of supramolecular photochemical systems. Part 2. The beta-cyclodextrin-4,7-dimethylcoumarin inclusion complex: a new beta-cyclodextrin dimer packing type, unanticipated photoproduct formation, and an examination of guest influence on beta-CD dimer packing

As part of an ongoing structural study of supramolecular photochemical beta -cyclodextrin(beta-CD)-coumarin derivatives systems the crystal structure o f the beta-CD-4,7-dimethylcoumarin complex has been determined at 13 K and complemented with ab initio molecular orbital calculations on selected gues t coumarin molecules. The 4,7-dimethylcoumarin molecules form a crystalline 2:2 host-guest (H-G) complex with beta-CD that is appropriately described as a "reaction nano-vessel" in which the inter-molecular interactions of im port to the outcome of the reaction are confined to a single beta-CD dimer host. Structure determination of the isolated photoproduct showed the produ ct formed is the anti-HT photodimer. Production of this dimer is only possi ble with much rearrangement of the guests. This appears to occur because of a preferential spatial fit of this product to the beta-CD dimer cavity. Th e crystal structure reveals a new beta-CD dimer packing pattern, designated tetrad type, with reduced reaction tube intermolecular interactions among guest molecules. Tetrad packing is characterized in comparison with the pre viously reported beta-CD dimer packing types. Guest influence on packing of beta-CD dimers is examined in beta-CD inclusion complexes with different d erivatized coumarins. To probe basic molecular properties giving rise to in ter-molecular interactions influencing crystal packing, ab initio molecular orbital calculations for the guest coumarin molecules were carried out to examine electrostatic interactions.