Abstract
In the solid state, some 3-substituted 4-hydroxycoumarins β-ketoester enols form infinite translational hydrogen-bonded β-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·OH-bond contacts. Four distinctive features characterize these structures: (1) moderately delocalized β-ketoester enol structures, (2) translational misalignment angles between oxygen donors and acceptors less than 10°, (3) buttressing intermolecular C–H·O contacts co-planar with and near the intermolecular O–H·O interactions, and (4) fully extended ketoester enol hydrogen-bond (ap-anti-anti) geometries. For non-polar β-chains in related coumarin systems, β-ketoester enol alignments are typically poorer, involve hydrogen-bonding between glide relatives, ap-syn-(anti) geometry, and the intermolecular O·OH-bond contacts are longer. Substituted 4-hydroxycoumarins related to phenprocoumon can form well-aligned polar translational β-chains between enolones showing resonance assisted Hydrogen-bonding and a 717 pm repeat along a crystallographic axis.
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