The solid-state behaviour of 4,6-dioxo-5,5-diethylenepyrimidine-2-isobutylurea

Abstract

The solid-state behaviour of 4,6-dioxo-5,5-diethylenepyrimidine-2-isobutylurea (PIBU) has been investigated. Two polymorphic forms have been identified, a monoclinic α form and a triclinic γ form, both of which undergo a destructive phase transition below 165 K. The α form undergoes an additional temperature-dependent phase transition at approximately 250 K to give the β form. All three forms of PIBU have been structurally characterised by X-ray diffraction. In all three crystal structures the PIBU molecules are organised into dimer units, which are stabilised by a self-complementary AADD quadruple hydrogen bond array.