Assembly of Polyiodide Networks with Cu(II) Complexes of Pyridinol-Based Tetraaza Macrocycles

Abstract

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.

Bidimensional Polyiodide Netting Stabilized by a Cu(II) Macrocyclic Complex

“…2+ is redox stable in the presence of I − , but also that it readily binds to I − , giving a [Cu(L)I] + tecton of appreciable stability. This is in line with what was observed before with pyridine-bearing azacyclophanes [14,15] and, hence, allows for the usage of [Cu(L)I] + as a reliable building block for more complex polyiodides. Inset: sigmoidal profiles of spectral changes upon I − addition at selected wavelengths (730 nm, orange, and 420 nm, green).…”

“…2+ is redox stable in the presence of I − , but also that it readily binds to I − , giving a [Cu(L)I] + tecton of appreciable stability. This is in line with what was observed before with pyridine-bearing azacyclophanes [14,15] and, hence, allows for the usage of [Cu(L)I] + as a reliable building block for more complex polyiodides. Interestingly, despite this compound crystallizing in a chiral space group, the two nonequivalent complexes appear to be enantiomorphic, their overlaid conformations related by a pseudo mirror plane (Figure 7a).…”

“…The coordinated iodide, previously found to be a key element involved in Cu(II) complexes into polyiodide superstructures (rings, chains, etc.) [14,15], was not involved in superior polyiodides or I• • • I contacts. In this sense, it seems that the incorporation of aromatic sulfonamides, previously exploited as their S=O• • • HN H-bonding, offers the opportunity to panel polyiodides [16], and in this case, reduced the possibility of the coordinated iodide to participate in supramolecular architectures.…”

“…The involvement of metal centers in polyiodide stabilization could also be of high interest, both to exploit metal cations as structural elements and to, potentially, improve their thermal stability and tune the electronic properties of the material. Accordingly, we recently proposed Cu(II) complexes of tetraazacyclophanes [14,15], showing how the choice of substituents on the macrocycle could shift packing forces from an H-bond-based arrangement, featuring charge-dense, noninteracting polyiodides, to an I• • • I dominated crystal featuring polyiodide chains periodically decorated with Cu(II) complexes.…”

Fluorogenic Detection of Sulfite in Water by Using Copper(II) Azacyclam Complexes

“…Similarly to cyclam analogues, azacyclam complexes exhibit both a strong thermodynamic stability and inertness toward ligand dissociation [ 55 , 56 ]. Metal complexes of azacyclam and of other polyaza-macrocyclic ligands have been extensively investigated over the last years, finding application in different areas, including, for instance, metal-organic-framework (MOF) design [ 57 , 58 , 59 , 60 , 61 ], solid-state conducting materials [ 62 , 63 ], electrocatalysis [ 64 , 65 ], and chemosensors and optical probes [ 66 , 67 ].…”