A new tetraaza-pyridinophane macrocycle (L1) N-alkylated with two isopropyl and one methyl groups symmetrically disposed has been prepared and its behavior compared with those of the unsubstituted pyridinophane (L3) and the related compound with three methyl groups (L2). The protonation studies show that, first, a proton binds to the central methylated amine group of L1, while, second protonation leads to a reorganization of the protons that are at this stage attached to the lateral isopropylated amines. The X-ray structure of [HL1] agrees with the UV-vis and NMR studies as well as with the results of DFT calculations. The stability of the Cu complexes decreases on increasing the bulkiness of the alkyl substituents of the amine groups. The crystal structures of [CuL1Cl](ClO) and [CuL1(HO)](ClO)·HO show square pyramidal coordination geometries with the ligands disposed in a bent L-shaped conformation. Kinetic studies indicate that the rates of both complexation and ligand dissociation decrease with the bulkiness of the substituents, so that the stability changes are surely the results of compensating effects, complex formation dominating over complex dissociation. The pH dependence of the rate constants for complex formation cannot be explained by consideration of rapid pre-equilibria involving the different protonated forms of the ligand, and it has been interpreted in terms of a mechanism involving an acid-base equilibrium for a reaction intermediate. NBT SOD studies show that the Cu complex of the bulkiest L1 ligand is the one having the highest activity (IC = 0.26(5) μM, k = 13.7 × 10 M s) which can be associated with the poorer σ-donor ability of the tertiary amino groups, and the rigidity of the system, caused by the bulky isopropyl groups.

Polyiodide chemistry is among the first historically reported examples of supramolecular forces at work. To date, owing to the increasingly recognized role of halogen bonding and the incorporation of iodine-based components in several devices, it remains an active field of theoretical and applied research. Herein we re-examine azacyclophanes as a class of ligands for the stabilization of iodine-dense three-dimensional networks, showing how we devised novel possible strategies starting from literature material. The new set of azacyclophane ligands affords novel crystal structures possessing intriguing properties, which develop on a double layer. At a macroscopic level, the obtained networks possess a very high iodine packing density (less than 2 times more diluted than crystalline I2): a simple parameter, IN, is also introduced to quickly measure and compare iodine packing density in different crystals. On the microscopic level, the present study provides evidence about the ability of one of the ligands to act as a three-dimensional supramolecular mold for the template synthesis of the rarely observed heptaiodide (I7−) anion. Therefore, we believe our approach and strategy might be relevant for crystal engineering purposes.

Ordered polyiodide networks have recently gathered considerable attention as electronic materials, a field historically dominated by metals. Could we incorporate metal cations into polyiodide frameworks in a controlled manner to...

Tetraaza-macrocyclic pyridinophane L-Ts, decorated with a p-toluenesulfonyl (tosyl; Ts) group, appear to be a useful tool to provide evidence on how the interplay of various supramolecular forces can help stabilise exotic anionic species such as tribromide (Br3−) anions. Indeed, crystals of (H2L-Ts)(Br3)1.5(NO3)0.5 unexpectedly grew from an acidic (HNO3) aqueous solution of L-Ts in the presence of Br− anions. The crystal structure of this compound was determined by single crystal XRD analysis. Hydrogen bonds, salt-bridges, anion-, - stacking, and van der Waals interactions contribute to stabilising the crystal lattice. The observation of two independent Br3− anions stuck over the π-electron densities of pyridine and tosyl ligand groups, one of them being sandwiched between two pyridine rings, corroborates the significance of anion-π interactions for N-containing heterocycles. We show herein the possibility of detecting anion-π contacts from fingerprint plots generated by Hirshfeld surface analysis, demonstrating the effective usage of this structural investigation technique to further dissect individual contributions of stabilising supramolecular forces.

The binuclear Cu2+ complex of a pyridinophane polyamine ligand ranking amongst the fastest SOD mimetics so far reported displays a remarkable SOD activity enhancement when grafted to the surface of boehmite (γ-AlO(OH)) nanoparticles (BNPs).

One of the first theoretical studies of the reaction mechanism of a small superoxide dismutase mimetic reveals the key role played by the metal bound water molecule and the molecular organisation.

Polyiodide networks are currently of great practical interest for the preparation of new electronic materials. The participation of metals in the formation of these networks is believed to improve their mechanical performance and thermal stability. Here we report the results on the construction of polyiodide networks obtained using Cu(II) complexes of a series of pyridinol-based tetraazacyclophanes as countercations. The assembly of these crystalline polyiodides takes place from aqueous solutions on the basis of similar structural elements, the [CuL] 2+ and [Cu(H –1 L)] + (L = L2 , L2-Me , L2-Me 3 ) complex cations, so that the peculiarities induced by the increase of N-methylation of ligands, the structural variable of ligands, can be highlighted. First, solution equilibria involving ligands and complexes were analyzed (potentiometry, NMR, UV–vis, ITC). Then, the appropriate conditions could be selected to prepare polyiodides based on the above complex cations. Single-crystal XRD analysis showed that the coordination of pyridinol units to two metal ions is a prime feature of these ligands, leading to polymeric coordination chains of general formula {[Cu(H –1 L)]} n n + (L = L2-Me , L2-Me 3 ). In the presence of the I – /I 2 couple, the polymerization tendency stops with the formation of [(CuL)(CuH –1 L)] 3+ (L = L2-Me , L2-Me 3 ) dimers which are surrounded by polyiodide networks. Moreover, coordination of the pyridinol group to two metal ions transforms the surface charge of the ring from negative to markedly positive, generating a suitable environment for the assembly of polyiodide anions, while N-methylation shifts the directional control of the assembly from H-bonds to I···I interactions. In fact, an extended concatenation of iodine atoms occurs around the complex dimeric cations, the supramolecular I···I interactions become shorter and shorter, fading into stronger forces dominated by the orbital overlap, which is promising for effective electronic materials.

Binuclear Cu2+ complexes of a pyridinophane polyamine ligand grafted to boehmite nanoparticles show a remarkable increase in SOD activity, which can be ascribed to the positive ζ-potential of the nanoparticles.