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

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)-1,2,4triazole 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(H2(P)O(4)) (4), H2L(H2PO4) 2 (5), [H2L](2)I-4 (6), H2L(NO3) 2 (7), H2L(SO4)center dot H2O (8), H2LSiF6 (9), H2LSiF6 center dot 2H2O (10), H2L(HF2) 2 (11), H3LI3 (12), H3L(BF4) 3 (13), H3L(ClO4) 3 (14), H3L(ClO4) 3 center dot 2H(2)O (15), and H3LH3O(SiF6) 2 center dot 2H(2)O (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 anionwater clusters ranging from a cyclic tetramer [(SO4)2-(H2O)(2)]4- and an octameric cluster [(SiF6)4-(H2O)4]88 - 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.

Automated summary

By reacting with acidic solutions, 16 new anion-mediated supramolecular entities with different molecular structures and geometric forms are obtained, which are assembled by hydrogen bonding.