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

摘要

A series of five complexes that incorporate the guanidinium ion and various deprotonated forms of Kemp's triacid (H_3KTA) have been synthesized and characterized by single-crystal X-ray analysis. The complex [C(NH _2)_3+]·[H_2KTA~-] (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 [(CH_3)_4N~+]· 2[C(NH_2)_3~+]·[KTA~(3-)] ·2H_2O (3). The crystal structure of [(nC_3H _7)_4N~+]· 2[C(NH_2) _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[(C_2H_5)_4N~+]· 20 [C(NH_2)_3~+]·11 [H_2KTA ~(2-)]·[H_2KTA~-]· 17H_2O (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.