Crystal structure, endo/exodentate conformations, spectroscopic properties, and Hirshfeld surface analysis of two constrained cyclam compounds with bromides and hydrates

Abstract

Two novel constrained cyclam compounds, [H2L]Br2⋅2H2O (1) and [H4L]Br4⋅4H2O (2) (L = C20H40N4 = 3,14-dimethyl-2,6,13,17-tetraazatricyclo(16.4.0.07,12)docosane) were synthesized and characterized by single-crystal X-ray diffraction and molecular spectroscopic techniques. The asymmetric unit of 1 contains one half of [H2L]2+ dication, one bromide anion and one water molecule, whereas the asymmetric unit of 2 comprises one half of [H4L]4+ tetracation, two bromide anions and two water molecules. The [H2L]2+ of 1 adopts an endodentate conformation and trans-III configuration, meanwhile the [H4L]4+ of 2 has an exodentate (3,4,3,4)-D conformation. In the crystals of 1 and 2, the macrocyclic cations, water molecules and bromide anions are held together by N—H⋯O, O—H⋯Br, and N—H⋯Br hydrogen bonds, thus forming a three-dimensional structure. Especially, the endodentate conformation of 1 is stabilized by intramolecular N—H⋯N hydrogen bonding. The Hirshfeld surface analysis and fingerprint plots reveal that the crystal packing in the two compounds is dominated by H⋯H, Br⋯H/H⋯Br and O⋯H/O⋯H contacts.