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

Matteo Savastano,Carla Bazzicalupi,Valeria Monini,Antonio Bianchi

doi:10.3390/inorganics10010012

Abstract

Iodine-dense polyiodide phases are interesting materials for a number of potential uses, including batteries and solid-state conductors. The incorporation of transition metal cations is considered a promising way to enhance the stability, tune the properties, and influence the architecture of polyiodides. However, several interesting metals, including Cu(II), may suffer redox processes, which generally make them not compatible with the I2/I− redox couple. Herein L, a simple derivative of cyclen, is proposed as a Cu(II) ligand capable of protecting the +2 oxidation state of the metal even in the presence of polyiodides. With a step by step approach, we report the crystal structure of free L; then we present spectrophotometric verification of Cu(II) complex stability, stoichiometry, and formation kinetic in DMF solution, together with Cu(II) binding mode elucidation via XRD analysis of [Cu(L)Cl]ClO4∙CH3CN crystals; afterwards, the stability of the CuL complex in the presence of I− is demonstrated in DMF solution, where the formation of a Cu:L:I− ternary complex, rather than reduction to Cu(I), is observed; lastly, polyiodide crystals are prepared, affording the [Cu(L)I]2I3I5 crystal structure. This layered structure is highly peculiar due to its chiral arrangement, opening further perspective for the crystal engineering of polyiodide phases.

Highlights

Polyiodide chemistry is a long-lasting research area
In terms of scientific interest, it has been tied throughout history with inorganic, theoretical, and supramolecular research, while it is well known that iodine and polyiodides were used in applications soon after iodine discovery [1,2]
Centrosymmetric conformation featuring the two tosyl rings observed in other studies dealing with polyiodide stabilization using similar moieties) [16]

Summary

Introduction

Polyiodide chemistry is a long-lasting research area. In terms of scientific interest, it has been tied throughout history with inorganic, theoretical, and supramolecular research, while it is well known that iodine and polyiodides were used in applications soon after iodine discovery (iodimetry, iodometry, Lugol solution, etc.) [1,2].Contemporary application-oriented research on polyiodides focuses on batteries, [3,4]solar cells [5,6], solid state conductors [7,8], and even high-energy, iodine-dispersing agents [9].Our contribution to the field has been mostly directed towards the supramolecular chemistry of polyiodides, aimed at obtaining ordered solids with high iodide density organized in extended networks. Polyiodide chemistry is a long-lasting research area. In terms of scientific interest, it has been tied throughout history with inorganic, theoretical, and supramolecular research, while it is well known that iodine and polyiodides were used in applications soon after iodine discovery (iodimetry, iodometry, Lugol solution, etc.) [1,2]. Our contribution to the field has been mostly directed towards the supramolecular chemistry of polyiodides, aimed at obtaining ordered solids with high iodide density organized in extended networks. With suitable organic ligands, it is possible to obtain crystal phase architectures featuring alternating planes of ligands and polyiodides [10], high density polyiodide-based clathrates self-assembled around suitable ligands [11,12], and even complex architectures such as solid-state pseudopolyrotaxanes with a [3]-catenane axle [13]. 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

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Conclusion