The lock-in phase in the urotropine-sebacic acid system

The 1,10-decane­dioic acid-1,3,5,7-tetra­aza­tri­cyclo­[3.3.1.1^3,7]­decane (1/1) system, C₁₀H₁₈O₄·C₆H₁₂N₄, was studied at 215 (2) K. Its analysis provides important information with regard to the long-standing acid-carboxyl­ate controversy in the urotropine-alkanedioic acid system. In the present structure, all the chain end-groups display a clear acid character. The asymmetric unit of this commensurate modulated phase contains two mol­ecules of diacid as well as two mol­ecules of urotropine. Furthermore, the chain packing suggests a possible order parameter for the lock-in transition.