β-Chain Hydrogen-Bonding in 4-Hydroxycoumarins

In the solid state, some 3-substituted 4-hydroxycoumarins beta-ketoester enols form infinite translational hydrogen-bonded beta-chains with varying degrees of alignment between adjacent delocalized systems. Nine related structures have been studied. At the strongest, intermolecular associations are polar, purely translation neighbors interact essentially along a 717 pm crystallographic repeat with shortened 260 pm intermolecular O center dot O(H-bond)contacts. Four distinctive features characterize these structures: (1) moderately delocalized beta-ketoester enol structures, (2) translational misalignment angles between oxygen donors and acceptors less than 10 degrees, (3) buttressing intermolecular C-H center dot O contacts co-planar with and near the intermolecular O-H center dot O interactions, and (4) fully extended ketoester enol hydrogen-bond (ap-anti-anti) geometries. For non-polar beta-chains in related coumarin systems, beta-ketoester enol alignments are typically poorer, involve hydrogen-bonding between glide relatives, ap-syn-(anti)geometry, and the intermolecular O center dot O(H-bond)contacts are longer. [GRAPHICS] .