Discarding metal incorporation in pyrazole macrocycles and the role of the substrate on single-layer assemblies

Pyrazole derivatives are key in crystal engineering and liquid crystal fields and thrive in agriculture, pharmaceutical, or biomedicine industries. Such versatility relies in their supramolecular bond adaptability when forming hydrogen bonds or metal-pyrazole complexes. Interestingly, the precise structure of pyrazole-based macrocycles forming widespread porous structures is still unsolved. We bring insight into such fundamental question by studying the self-assembled structures of a bis-pyrazole derivative sublimed in ultra-high-vacuum conditions (without solvents) onto the three (111) noble metal surfaces. By means of high-resolution scanning tunneling microscopy that is validated by gas phase density functional theory calculations, we find a common hexagonal nanoporous network condensed by triple hydrogen bonds at the molecule-metal interface. Such assembly is disrupted and divergent after annealing: (i) on copper, the molecular integrity is compromised leading to structural chaos, (ii) on silver, an incommensurate new oblique structure requiring molecular deprotonation is found and, (iii) on gold, metal-organic complexes are promoted yielding irregular chain structures. Our findings confirm the critical role of these metals on the different pyrazole nanoporous structure formation, discarding their preference for metal incorporation into the connecting nodes whenever there is no solvent involved.

A whole zoo of hydrogen bonds in one crystal structure: tris(isonicotinium) hydrogensulfate sulfate monohydrate

Depending on the reaction partner, the organic ditopic molecule isonicotinic acid (Hina) can act either as a Brønsted acid or base. With sulfuric acid, the pyridine ring is protonated to become a pyridinium cation. Crystallization from ethanol affords the title compound tris(4-carboxypyridinium) hydrogensulfate sulfate monohydrate, 3C₆H₆NO₂⁺·HSO₄^-·SO₄^2-·H₂O or [(H₂ina)₃(HSO₄)(SO₄)(H₂O)]. This solid contains 11 classical hydrogen bonds of very different flavour and nonclassical C-H...O contacts. All N-H and O-H donors find at least one acceptor within a suitable distance range, with one of the three pyridinium H atoms engaged in bifurcated N-H...O hydrogen bonds. The shortest hydrogen-bonding O...O distance is subtended by hydrogensulfate and sulfate anions, viz. 2.4752 (19) Å, and represents one of the shortest hydrogen bonds ever reported between these residues.

Crystal structure of bis-(2-amino-anilinium) hydrogen phosphate

The asymmetric unit of the title compound, 2C6H9N2 (+)·HPO4 (2-), comprises two 2-amino-anilinium cations and one hydrogen phosphate dianion. In the crystal, the HPO4 (2-) dianions are linked by O-H⋯O hydrogen bonds into chains along [100]. The inorganic anionic chains and organic cations are linked by N-H⋯O and N-H⋯N hydrogen bonds, forming a two-dimensional supra-molecular network extending parallel to (001).

A series of coordination polymers based on varied polycarboxylates and different imidazole-containing ligands: syntheses, crystal structures and physical properties

To investigate the effect of organic ligands on the coordination frameworks, seven nickel(ii) coordination polymers, based on varied polycarboxylates and different imidazole-containing ligands, are synthesized under hydrothermal method.

Supramolecular assemblies of benzene-1,3,5-tricarboxylic acid and 3,5-substituted pyrazoles: formation and structural analysis

Reaction of benzene-1,3,5-tricarboxylic acid (H3BTC) with various 3,5-substituted pyrazoles resulted in different host guest assemblies. Theoretical calculations were used to calculate the interaction energy and their comparison with the experimental data obtained through thermogravimetric analysis.

New organic-inorganic frameworks incorporating iso- and heteropolymolybdate units and a 3,3',5,5'-tetramethyl-4,4'-bi-1H-pyrazole-2,2'-diium multiple hydrogen-bond donor

Poly[bis(3,3',5,5'-tetramethyl-4,4'-bi-1H-pyrazole-2,2'-diium) γ-octamolybdate(VI) dihydrate], {(C(10)H(16)N(4))(2)[Mo(8)O(26)]·2H(2)O}(n), (I), and bis(3,3',5,5'-tetramethyl-4,4'-bi-1H-pyrazole-2,2'-diium) α-dodecamolybdo(VI)silicate tetrahydrate, (C(10)H(16)N(4))(2)[SiMo(12)O(40)]·4H(2)O, (II), display intense hydrogen bonding between the cationic pyrazolium species and the metal oxide anions. In (I), the asymmetric unit contains half a centrosymmetric γ-type [Mo(8)O(26)](4-) anion, which produces a one-dimensional polymeric chain by corner-sharing, one cation and one water molecule. Three-centre bonding with 3,3',5,5'-tetramethyl-4,4'-bi-1H-pyrazole-2,2'-diium, denoted [H(2)Me(4)bpz](2+) [N···O = 2.770 (4)-3.146 (4) Å], generates two-dimensional layers that are further linked by hydrogen bonds involving water molecules [O...O = 2.902 (4) and 3.010 (4) Å]. In (II), each of the four independent [H(2)Me(4)bpz](2+) cations lies across a twofold axis. They link layers of [SiMo(12)O(40)](4-) anions into a three-dimensional framework, and the preferred sites for pyrazolium/anion hydrogen bonding are the terminal oxide atoms [N···O = 2.866 (6)-2.999 (6) Å], while anion/aqua interactions occur preferentially via μ(2)-O sites [O···O = 2.910 (6)-3.151 (6) Å].