Cr(VI) represents a worldwide issue due to its carcinogenicity and toxicity, and its removal from water/waste-water is of great relevance for the protection of the human health and of the...

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Rare-earth elements are widely used in high-end technologies, the production of permanent magnets (PMs) being one of the sectors with the greatest current demand and likely greater future demand. The combination of Nd and Dy in NdFeB PMs enhances their magnetic properties but makes their recycling more challenging. Due to the similar chemical properties of Nd and Dy, their separation is expensive and currently limited to the small scale. It is therefore crucially important to devise efficient and selective methods that can recover and then reuse those critical metals. To address these issues, a series of heptadentate Trensalbased ligands were used for the complexation of Dy 3+ and Nd 3+ ions, with the goal of indicating the role of coordination and solubility equilibria in the selective precipitation of Ln 3+ −metal complexes from multimetal non-water solutions. Specifically, for a 1:1 Nd/Dy mixture, a selective and fast precipitation of the Dy complex occurred in acetone with the Trensal p-OMe ligand at room temperature, with a concomitant enrichment of Nd in the solution phase. In acetone, complexes of Nd and Dy with Trensal p-OMe were characterized by very similar formation constants of 7.0(2) and 7.3(2), respectively. From the structural analysis of an array of Dy and Nd complexes with Trensal R ligands, we showed that Dy invariably provided complexes with coordination number (cn) of 7, whereas the larger Nd experienced an expansion of the coordination sphere by recruiting additional solvent molecules and giving a cn of >7. The significant structural differences have been identified as the main premises upon which a suitable separation strategy can be devised with these kind of ligands, as well as other preorganized polydentate ligands that can exploit the small differences in Ln 3+ coordination requirements.

Weak interactions (hydrogen bonds, halogen bonds, CH···π and π–π stacking) can play a significant role in the formation of supramolecular assemblies with desired structural features. In this contribution, we report a systematic investigation on how a halogen bond (XB) can modulate the structural arrangement of silver supramolecular complexes. The complexes are composed of X-phenyl­(bispyrazolyl)­methane (X = Br, I) and I-alkynophenyl­(bispyrazolyl)­methane ligands functionalized in meta (L3Br, L3I) and para (L4Br, L4I, L4CCI) positions on a phenyl ring with the purpose of providing different directionalities of the X function with respect to the N,N coordination system. The obtained [Ag­(L)2]+ moieties show remarkable geometric similarities, and the L4Br, L4I, and L4CCI ligands exhibit the most conserved types of supramolecular arrangement that are sustained by XB. The increased σ-hole in L4CCI with respect to L4I leads to an occurrence of short (and strong) XB interactions with the anions. [Ag­(L4I)2]­PF6 and [Ag­(L4I)2]­CF3SO3 are characterized by the presence of three different phases, and the single-crystal evolution from phase-1 (a honeycomb structure with large 1D cavities) to phase-3 (solventless) occurs by a stepwise decrease in the crystallization solvent content, which promotes an increase in XB interactions in the lattice. The present paper aims to provide useful tools for the selection of appropriate components for the use of coordination compounds to build supramolecular systems based on the halogen bond.