Insights into supramolecular design from analysis of halide coordination geometry in a protonated polyamine matrix

Single-crystal X-ray diffraction analysis at 100 K of nineteen hydrogen bonded structures formed from reaction of five aliphatic polyamines with hydrochloric, hydrobromic and hydriodic acid is reported. The polyamines included are diethylenetriamine, H2N(CH2)2NH(CH2)2NH2  1, N-(2-aminoethyl)propane-1,3-diamine, H2N(CH2)3NH(CH2)2NH2  2, triethylenetetramine, H2N(CH2)2NH(CH2)2NH(CH2)2NH2  3, N,N′-bis(3-aminopropyl)ethylenediamine, H2N(CH2)3NH(CH2)2NH(CH2)3NH2  4 and 2,2′,2″-triaminotriethylamine, N[(CH2)2NH2]3  5. The anions interact ia hydrogen bonds with the protonated amines in a variety of complexation geometries and coordination numbers. A marked deviation from the extended all-anti conformation is observed for some of the polyammonium cations, depending on their shape, protonation sites, the polyammonium cation:anion ratio and the size of the amines and the complexed halides. The analysis of the crystal structures showed some preference for three- and four-coordinate N–H···X− hydrogen bonded geometries for the complexed halides, with additional longer interactions, including C–H···X− hydrogen bonds and N+···X− electrostatic interactions. Some chelate effects were also observed. To a first approximation, however, the halides act as spherical charges and their coordination sphere is highly flexible. In general, solid-state self-assembly occurs in such a way as to maximise the number and strength of hydrogen bonds and non-directional interactions in the system as a whole.