Predictable stereoselective formation of supramolecular assembly is generally believed to be an important but complicated process. Here, we show that point chirality of a ligand decisively influences its supramolecular assembly behavior. We designed three closely related chiral ligands with different point chiralities, and observe their self-assembly into europium (Eu) tetrametallic tetrahedral cages. One ligand exhibits a highly diastereoselective assembly into homochiral (either ΔΔΔΔ or ΛΛΛΛ) Eu tetrahedral cages whereas the two other ligands, with two different approaches of loosened point chirality, lead to a significant breakdown of the diastereoselectivity to generate a mixture of (ΔΔΔΔ and ΛΛΛΛ) isomers. The cages are highly emissive (luminescence quantum yields of 16(1) to 18(1)%) and exhibit impressive circularly polarized luminescence properties (|g
lum|: up to 0.16). With in-depth studies, we present an example that correlates the nonlinear enhancement of the chiroptical response to the nonlinearity dependence on point chirality.
In this work, we synthesized a series of lanthanide(III) β-diketonate complexes to investigate the induction of triboluminescence. Triboluminescence (TL) spectra, solid-state emission spectra, and luminescence lifetimes of the complexes were obtained to prove consistent emitting species for steady-state and triboluminescence measurements. Detailed analyses of the crystal lattice packing were conducted in an attempt to correlate crystal symmetry, gas discharge, and structural arrangements with "triboexcitation", and it is found that either noncentrosymmetric or centrosymmetic compounds can be TL-active. Furthermore, an intensely TL compound, Eu(dbm)TMP, was achieved, and its light emission can be seen under daylight upon mechanical stress.
Reactions of [M(H2O)n](+), M = Cr, Mn, Fe, Co, Ni, Cu, and Zn, n < 50, with CH3CN are studied in the gas phase by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Sequential uptake of 4-6 acetonitrile molecules is observed for all metals. Rate constants show a weak dependence on both the metal and the number of acetonitrile molecules already in the cluster. Nanocalorimetry yields the enthalpy of the first reaction step. For most metals, this is consistent with a ligand exchange of water against acetonitrile. For M = Cr, however, the strong exothermicity of ΔE(nc) = -195 ± 26 kJ mol(-1) suggests an electron transfer from Cr(+) to CH3CN. Exclusively for M = Zn, a relatively slow oxidation of the metal center to Zn(2+), with formation of ZnOH(+) and release of CH3CNH(•) or CH3CHN(•) is observed. Density functional theory molecular dynamics simulations and geometry optimizations show that charge transfer from Zn(+) to CH3CN as well as the subsequent proton transfer are associated with a barrier.
Discrete lanthanide(III) tetranuclear cubane-like clusters seldom occur throughout the Ln series and behave as single-molecule magnets (SMMs). Herein, a series of cubanes, [Ln(μ-OH)(μ-tfa)(hfa)(phen)] (1-9, Ln = La-Dy (except Pm), tfa = trifluoroacetate, hfa = hexafluoroacetylacetonate, phen = 1,10-phenanthroline), and dinuclear clusters, [Ln(μ-OH)(hfa)(phen)] (10-16, Ln = Tb-Lu), were synthesized and characterized. Two types of clusters were formed due to the change of preferred coordination geometry for lighter and heavier Ln ions which favor nine-coordinated cubanes and eight-coordinated dimers, respectively. A magnetic study shows that 8-Tb and 9-Dy are ferromagnetically coupled and SMM in nature because of the larger Ln···Ln distance compared to other discrete cubanes. The anisotropic barriers, U, of 9-Dy are determined to be 67.0 K. In addition, the photophysical properties of 6-Eu, 8-Tb, and 10-Tb owing to tfa, hfa, and phen sensitization and O-H quenching are discussed.
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