CH···N Bonds and Dynamics in Isostructural Pyrimidine Polymorphs

In
the crystalline pyrimidine, the most basic building block of
biochemical systems, the changes of entropy and enthalpy combine into
a series of discrete structural transitions that have defied detection
until now. The counterintuitive fully isostructural polymorphs of
pyrimidine differ mainly by entropy, while the varied space occupied
by molecules in partly isostructural polymorphs can be connected to
the molecular dynamics, too. The interplay of thermodynamic and structural
features affects the molecular interactions and environment and is
most relevant to the functions of all organic compounds in the living
tissue. The single crystals of four pyrimidine polymorphs have been
grown at isobaric, isothermal, and isochoric conditions, and their
structures have been determined by X-ray diffraction.