Inorganic Anion-Mediated Supramolecular Entities of 4-Amino-3,5-Bis(4-Pyridyl)-1,2,4-Triazole Salts Assisted by the Interplay of Noncovalent Interactions

Abstract

The development of new families of synthetic molecular systems projecting neutral, bi-, or multi-H-bonding donor units is significant to acquire the desired selectivity within the fascinating area of anion recognition. Here, we illustrate the reaction between a neutral 4-amino-3,5-bis(4-pyridyl)-1,2,4-triazole ligand (L) with acidic solutions containing either chloride, bromide, nitrate, phosphate, iodide, sulfate, hexafluorosilicate, fluoride, tetrafluoroborate or perchlorate anions, yielding 16 new anion-mediated supramolecular entities, H2LCl2 (1), H2LBr2 (2), H2L(NO3)2 (3), HL(H2PO4) (4), H2L(H2PO4)2 (5), [H2L]2I4 (6), H2L(NO3)2 (7), H2L(SO4)·H2O (8), H2LSiF6 (9), H2LSiF6·2H2O (10), H2L(HF2)2 (11), H3LI3 (12), H3L(BF4)3 (13), H3L(ClO4)3 (14), H3L(ClO4)3·2H2O (15), and H3LH3O(SiF6)2·2H2O (16), thoroughly examined by elemental analyses, Fourier transform-attenuated total reflectance-infrared (FT-ATR-IR), thermal analysis, powder diffraction, and single-crystal X-ray diffraction. We identified the propensity of H2PO4– into a cyclic hexameric cluster (H2PO4–)6 stabilized by a bent ligand L via a combination of functionalities such as an amino group, pyridyl terminals, and a triazolyl core. Additionally, we also found the anion–water clusters ranging from a cyclic tetramer [(SO4)2–(H2O)2]4– and an octameric cluster [(SiF6)4–(H2O)4]∞8– to an acyclic tetramer [(ClO4–)2(H2O)2]. As shown by the study, subtle modulation in the crystallization environment offers the possibility to yield entirely distinctive forms of molecular salts comprising both anhydrous and a few hydrates with different protonated numbers (mono-, di- or triprotonated). A systematic study indicates that the molecular salts obtained from different anions construct diverse supramolecular extended architectures (e.g., bricklayer, columns, zig-zag, stair-steps, wave-like, helical, double chain, and criss-cross orientation) self-assembled by a combination of noncovalent interactions, constituting distinct H-bonded geometry patterns, essentially depending on the molecular conformation of the bent ligand and the type of the anion utilized (linear, spherical, triangular, tetrahedral, and octahedral) in the preparation of salts.