Analysis of ion-ion interactions in the crystal structure of triazaphenalenium hexahydropyrimidopyrimidinium bistosylate.

The solid-state structure of triazaphenalenium hexahydropyrimidopyrimidinium bistosylate has been determined by single-crystal X-ray crystallography (Cc, Z = 4, a = 8.407(2) Å, b = 8.407(2) Å, c = 25.678(6) Å, β = 92.610(4)°, R₁ = 0.0583), marking the first time that a tricyclic guanidinium-type carbocation has been structurally characterized. The orthoamide moiety in the triazaphenalenium ion was planar, and density functional theory calculations on the free triazaphenalenium ion indicated that the central carbon was the locus of positive charge in this ion. Hirshfeld surfaces and fingerprint plots of the packing in this structure revealed numerous weak (e.g., C-H···O, C-H···π) interactions among the ions in the compound. These ions were arranged in columns, each consisting of tosylate ions interdigitated with either triazaphenalenium or hexahydropyrimidopyrimidinium ions. These columns were linked by N–H···O hydrogen bonds between the hexahydropyrimidopyrimidinium moiety in one column and one of the two tosylates in a neighboring column. The net result of these packing forces was a layering of these columns in the bulk, with a polar (sulfonate-dominated) surface on one face of each layer and a nonpolar (methylene-dominated) surface on the opposite face. [ABSTRACT FROM AUTHOR]