HYDROGEN-BOND PATTERNS OF DIALKYLPYRIDONE IRON CHELATORS AND THEIR 1-1 FORMIC-ACID SOLVATES - DESCRIPTION, PREDICTION, AND ROLE IN CRYSTAL PACKING

The crystal structures (determined from single-crystal X-ray diffraction studies) and hydrogen-bond patterns of three crystalline 1,2-dialkyl-3-hydroxy-4-pyridones and their 1:1 formic acid solvates are elucidated. The primary hydrogen-bond connectivities observed are explained by a model that predicts that the best donor bonds to the best acceptor. Relative hydrogen-bond donating and accepting abilities of the functional groups observed in these compounds are evaluated by a combination of pK(a)s, energy calculations, resonance arguments, and crystallographic evidence. The primary (O-H ... O) hydrogen-bond patterns are described by graph set notation, and brief explanations of the graph set assignments are also included. A total of 17 secondary (C-H ... O) hydrogen bonds are also observed in these six structures. Correlations are drawn between the observed C-H ... O hydrogen bonds and the molecular packing. The possible role of these secondary hydrogen bonds in influencing molecular packing is discussed.