Control of crystal structure using temperature and time

Three novel crystal structures were obtained from iron(III) acetylacetonate and 2,6-pyridinedicarboxylic acid. The structures elucidated were found to be dependent on the temperature and length of time allowed for the reaction. The product of the reaction between iron(III) acetylacetonate and 2,6-pyridinedicarboxylic acid in acetonitrile at room temperature is [FeC₁₂H₁₂NO₇]·CH₃CN, (I). When the reaction temperature was increased to 60°C, FeC₁₂H₁₀NO₆, (II), was isolated after 2 h and [FeC₁₂H₁₀NO₆]₄, (III), was isolated after 24 h. (I) is a discrete complex, whereas (II) and (III) form tetramers.