Reversible Cu4 ↔ Cu6 Core Interconversion and Temperature Induced Single-Crystal-to-Single-Crystal Phase Transition for Copper(I) Carboxylate

Copper(i)–iodide cluster structures as functional and processable platform materials

This review provides a complete overview of the progress towards implementation of CuI-nanoclusters in functional materials and devices.

On the Nature of Luminescence Thermochromism of Multinuclear Copper(I) Benzoate Complexes in the Crystalline State

A model luminescent [(PhCO2)4Cu4] (Cu4) complex in the crystalline state was investigated via combined crystallographic and spectroscopic techniques contributed substantially by theoretical modelling. The complex appeared to exhibit luminescence thermochromism, i.e., red phosphorescence at room temperature which changes to green when lowering the temperature to 90 K. The low-energy emissive state was assigned as a cluster-centred triplet, 3CC. The emission from this state predicted in TDDFT (~635 nm) matches the experimental red band observed at 660–715 nm. In contrast, the nature of the high-energy “green” band was less straightforward. The next reached cluster-centred triplet excited state occurred to be energetically close to the experimental value of ~545 nm. The two excited states also exhibit significant metal-to-ligand and ligand-to-metal charge transfer characteristics, especially for solid-state distorted geometries. In both cases the cluster core was expected to become notably contracted when compared to the ground state. Time-resolved photocrystallographic results supported the computationally predicted core contraction upon excitation. Additionally, the differences between the spectroscopic behaviour of the related tetra- and hexanuclear copper(I) complexes, Cu4 and Cu6 (i.e., [(PhCO2)6Cu6]) in the crystalline state were discussed and examined. It appeared that crystal packing may constitute an important factor as far as the lack of luminescence thermochromism in the latter case is concerned. Synopsis: Structure–property relationships characterising a model luminescent [(PhCO2)4Cu4] (Cu4) complex in the crystalline state were investigated via combined crystallographic and spectroscopic techniques contributed by theoretical modelling, and compared with the properties of the related [(PhCO2)6Cu6] (Cu6) complex.

Enantiopure versus Racemic Mixture in Reversible, Two-Step, Single-Crystal-to-Single-Crystal Transformations of Copper(II) Complexes

The reaction of chiral sodium complexes, ¹_∞ [Na(S-valmetH)]⋅H₂ O (1-S) and ¹_∞ [Na(R-valmetH)]⋅H₂ O (1-R), with copper(II) acetate affords chiral one-dimensional coordination polymers with the formulas ¹_∞ [Cu(S-valmet)(H₂ O)]⋅H₂ O (2-S) and ¹_∞ [Cu(R-valmet)(H₂ O)]⋅H₂ O (2-R) (R/S-valmetH₂ are Schiff base proligands resulting from the condensation reactions between o-vanillin and R/S-methionine). The copper ions are connected by the carboxylato groups belonging to the amino-acid moieties, resulting in infinite chains showing syn-anti out-of-plane bridging mode. The circular dichroism spectra of 1-S, 1-R, 2-S, and 2-R confirm their enantiomeric nature. Compounds 2-S and 2-R undergo a two-step single-crystal-to-single-crystal transformation, with the elimination of the lattice and coordinated water molecules: ¹_∞ [Cu(S-valmet)(H₂ O)]⋅H₂ O (2-S)→¹_∞ [Cu(S-valmet)]⋅H₂ O (3-S⋅H₂ O)→¹_∞ [Cu(S-valmet)] (3-S) and ¹_∞ [Cu(R-valmet)(H₂ O)]⋅H₂ O (2-R)→¹_∞ [Cu(R-valmet)]⋅H₂ O (3-R⋅H₂ O)→¹_∞ [Cu(R-valmet)] (3-R), respectively. During these transformations, every pair of face-to-face chains present in 2-S (or 2-R) has been "zipped up" into a chiral double chain through the removal of the aqua ligands and their replacement by the carboxylato oxygen atoms from the neighboring chain. Consequently, each carboxylato group now bridges three copper ions. The conversion of the single chains, 2-S and 2-R, into the double chains, 3-S and 3-R, is accompanied by a change of the strength of the exchange interactions between the copper ions: weak antiferromagnetic couplings are observed in compound 2-S (J/k_B =-1.23(5) K, H=-2J ΣS_i S_i+1 ) and relatively strong in compound 3-S (J/k_B =-76.0(8) K). When the racemic mixture of the ligands, R,S-valmetH₂ , is employed, in the same experimental conditions, a racemic mixture of mononuclear compounds, [Cu(R,S-valmet)(H₂ O)₂ ]⋅H₂ O (4-RS), is obtained. Compound 4-RS also undergoes a SCSC transformation with the elimination of the lattice and one of the coordinated water molecules, resulting in a racemic mixture of chiral chains, ¹_∞ [Cu(R-valmet)(H₂ O)]⋅¹_∞ [Cu(S-valmet)(H₂ O)] (5-RS). In this compound, the coupling of the copper(II) ions within the chains is weak and ferromagnetic (J/k_B =+0.10(2) K). These results prove that the chirality of the valmetH₂ ligands (optically pure or racemic mixture) plays a key role in the self-assembly process of the copper(II) complexes.