Controlled aggregation of multiple guanidinium ions through a hydrogen bonded network assembly with deprotonated forms of Kemp's triacid

A series of five complexes that incorporate the guanidinium ion and various deprotonated forms of Kemp's triacid (H₃KTA) have been synthesized and characterized by single-crystal X-ray analysis. The complex [C(NH ₂)₃+]·[H₂KTA^-] (1) exhibits a sinusoidal layer structure with a centrosymmetric pseudo-rosette motif composed of two ion pairs. The fully deprotonated Kemp's triacid moiety in 3[C(NH ₂)₃⁺]·[KTA^3-] (2) forms a record number of eighteen acceptor hydrogen bonds, thus leading to a closely knit three-dimensional network. The KTA^3- anion adopts an uncommon twist conformation in [(CH₃)₄N⁺]· 2[C(NH₂)₃⁺]·[KTA^3-] ·2H₂O (3). The crystal structure of [(nC₃H ₇)₄N⁺]· 2[C(NH₂) ₃⁺]·[KTA^3-] (4) features a tetrahedral aggregate of four guanidinium ions stabilized by an outer shell that comprises six equatorial carboxylate groups that belong to separate [KTA^3-] anions. In 3[(C₂H₅)₄N⁺]· 20 [C(NH₂)₃⁺]·11 [H₂KTA ^2-]·[H₂KTA^-]· 17H₂O (5), an even larger centrosymmetric inner core composed of eight guanidinium ions and six bridging water molecules is enclosed by a crust composed of eighteen axial carboxyl/ carboxylate groups from six HKTA^2- anions.