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

Two novel constrained cyclam compounds, [H2L]Br-2 center dot 2H(2)O (1) and [H4L]Br-4 center dot 4H(2)O (2) (L = C20H40N4 = 3,14-dimethyl-2,6,13,17-tetraazatricyclo(16.4.0.0(7,12))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 center dot center dot center dot O, O-H center dot center dot center dot Br, and N-H center dot center dot center dot Br hydrogen bonds, thus forming a three-dimensional structure. Especially, the endodentate conformation of 1 is stabilized by intramolecular N-H center dot center dot center dot N hydrogen bonding. The Hirshfeld surface analysis and fingerprint plots reveal that the crystal packing in the two compounds is dominated by H center dot center dot center dot H, Br center dot center dot center dot H/H-Br and O center dot center dot center dot H/O center dot center dot center dot H contacts. (C) 2021 Elsevier B.V. All rights reserved.