Crystal and Species Engineering with Semi‐Flexible Nitrogen Containing Organic Cations: Generation of [H 13 O 6 ] + Ions with the Unfavoured Unbranched Topology by Enclosing Hydrochloric Acid in a Porous Inorganic‐Organic Hybrid Material

The reaction of rhodium(III) chloride trihydrate with 1, 4‐diazacycloheptane in concentrated hydrochloric acid results in the formation of tris(1, 4‐diazoniacycloheptane) hexaaquahydrogen(1+) bis(hexachlororhodate(III)) chloride, [C 5 H 14 N 2 ] 3 [H 13 O 6 ][RhCl 6 ] 2 Cl ( 1 ). Dark red crystals of 1 are obtained by diffusion‐controlled crystallization at room temperature. Slow evaporation of the mother liquor over a period of several days yields a few tiny crystals of the bis(1, 4‐diazoniacycloheptane) hexachlororhodate(III) chloride hydrate, [C 5 H 14 N 2 ] 2 [RhCl 6 ]Cl ˙ 1.75 H 2 O ( 2 ), as red thin squared plates. In the context of crystal engineering, compounds 1 and 2 are inorganic‐organic hybrid materials built up from octahedral [RhCl 6 ] 3‐ , simple Cl ‐ and semi‐flexible heterocyclic 1, 4‐diazoniacycloheptane ions, incorporating either the [H 13 O 6 ] + and further Cl ‐ ions or portions of simple water molecules. Both compounds crystallize in the space group type P 2 1 / c . Compound 1 contains isolated [H 13 O 6 ] + ions with a linear chain‐like configuration enclosed in the cavities of the inorganic‐organic framework. The presence of a strong central O···H···O hydrogen bond within the [H 13 O 6 ] + ions in 1 is confirmed by the short O···O separation of 2.47Å and by characteristic IR absorption bands at 1626 (s), ∼ 1250 (m) and 668 (m) cm ‐1 . During the thermal decomposition, compound 1 looses at first five equivalents of water and one equivalent of hydrochloric acid in a two‐step process at 37 °C and 67 °C. This is followed by the decomposition of the 1, 4‐diazoniacycloheptane cations and the hexachlororhodate(III) anions, starting at 190 °C and proceeding intensified at 240 °C.