Crystal-to-crystal transformations in heterometallic yttrium(iii)–copper(i) iodide derivatives in a confined solvent-free environment: Influence of solvated yttrium cations on the nuclearity and dimensionality of iodocuprate clusters

Abstract

The solvated yttrium iodide precursors [Y(L)₈]I₃ (L = DMSO or DMF), prepared in situ by stirring YI₃(PrⁱOH)₄ in DMSO or DMF, react with CuI in the presence of NH₄I to give ionic hetero-metallic species [Y(DMSO)₈][Cu₂(µ-I)I₄] (1) and [Y(DMF)₈][Cu₄(µ₃-I)₂(µ-I)₃I₂] (2) in excellent yields. Re-crystallization of 1 from DMF afforded the mixed-solvate complex [Y(DMSO)₆(DMF)₂][CuI₃][I] (3). Compounds 2 and 3 undergo unique crystal-to-crystal transformation via progressive substitution of DMF by water molecules in a confined, solvent-free environment. Thus, crystals of 3 transform into [Y(DMSO)₆(H₂O)₂][CuI₃][I] (4), whereas a discrete ion-pair assembly of 2 is first converted into a 1-D zig-zag structure [Y(DMF)₆(H₂O)₂]³⁺[Cu₇(µ₄-I)₃(µ₃-I)₂(µ-I)₄(I)]_1∞³⁻ (5) and finally into a 2-D sheet containing mixed-valent copper atoms, [Y(DMF)₆(H₂O)₃]³⁺[Cu^I₇Cu^II₂(µ₃-I)₈(µ-I)₆]_2∞³⁻ (6). The bi- and tetrafurcate H-bonding between water ligands on yttrium and iodides of the Cu–I cluster plays a pivotal role in the evolution of structures 4–6. Formation of a wide range of iodocuprate structures in 1–6, from discrete mono-, di- or tetranuclear units to one- and two-dimensional extended arrays, reflects the influence of solvated yttrium cations on the nuclearity and dimensionality of Cu–I clusters. TG-DTA-MS studies and DFT calculations for these complexes have also been carried out in order to determine their thermal stability and have insight about aforesaid transformations.