(Di)-aminoguanidine Functionalization through Transamination: An Avenue to an Auspicious Class of Supramolecular Synthons

Abstract

N-4H-1,2,4-Triazol-4-yl-guanidine hydrochloride (L1) and a heterocyclized 3,4-diamino-4H-1,2,4-triazole hydrochloride (L2) were synthesized in good yields thanks to a transamination reaction of aminoguanidine and diaminoguanidine hydrochlorides, whose mechanism is presented. L1 and L2 crystallize in monoclinic (P21/a) and triclinic (P1) space groups, respectively. Hydrogen bonding interactions dictated by H-donor, acceptor rich ligand framework together with lattice chloride ions in L1 and L2 organize the crystal packing into a three-dimensional (3D) supramolecular network. The crystal structure of L1 is the first one for a 1,2,4-triazole ligand constructed from aminoguanidine. Both L1 and L2 that exist in monocationic form were introduced as supramolecular synthons to prepare Zn(II) complexes. Scanning electron microscopy (SEM) images on a bulk sample of [Zn(L1)2Cl2]Cl2·H2O (1) reveals a spontaneous aggregation of porous balls of coccolith morphology with surface decorated sickle-shaped particles of 100 nm thickness, whereas a powder sample of [Zn(L2)2Cl2]·H2O (2) shows neat rectangular blocks of 470 nm thickness. Colorless crystals of 2 crystallize in a monoclinic space group (C2/c). Zn(II) ions bound chloride with NH6B···Cl(1) = 2.495(2) A and N···H type bonding (N6···H3C3 = 2.743(2) A; N2···H7N7 = 1.989(2) A) affording a 3D supramolecular network. The degree of pyramidality, ΣN = 38°, observed at one of the terminal amines in L2 is still retained in 2, but “flipping” of orientation of attached protons due to directional H-bonding is observed too. Porosity partitioning by mercury porosimetry measurements on 1 and 2 reveals interparticular porosities between 7 and 15 μm. N2(g) and H2(g) gas adsorption capacities of 1 and 2 were measured by BET which shows no preference for N2(g) but a low irreversible H2(g) uptake of 3 cm3/g.