Dmitrii Yu. Naumov

Zinc(II) complexes with an imidazolylpyridine ligand: luminescence and hydrogen bonding

ZnLCl and [H2L]2[ZnCl4], based on 2-(1-hydroxy-4,5-dimethyl-1H-imidazol-2-yl)pyridine (HL), have been synthesized. There is a short intraionic O–H···N hydrogen bond between the hydroxyimidazolyl and pyridyl of H2L+ cations (N···O 2.608(2) Å) in the structure of [H2L]2[ZnCl4]. The formation of this rather strong hydrogen bond is confirmed by IR spectroscopy through a broad band at 3200–2200 cm−1 and a band at 1655 cm−1. HL crystallizes in the form of a hemihydrate, HL·0.5H2O. HL assemble into infinite helical chains due to N–H···O intermolecular hydrogen bonds between the NH of imidazole and O of the N-oxide (O···N 2.623(2) Å). An unusual mid-IR pattern with three broad bands at 3373, 2530, and 1850 cm−1 is typical for strong hydrogen bonds, explained by resonance-assisted hydrogen bonding occurring in the helical chains. On cooling to 5 K, noticeable changes in the IR spectra of [H2L]2[ZnCl4] and HL·0.5H2O were observed. ZnLCl and [H2L]2[ZnCl4] exhibit bright photoluminescence with maxima of emission at 458 nm (for ZnLCl) and 490 nm (for [H2L]2[ZnCl4]). Graphical Abstract

The crystal structure of kelyanite, (Hg2)6(SbO6)BrCl2

Abstract The crystal structure of kelyanite, a rare mercury mineral that was found in oxidized mercuryantimony ores in the Kelyana deposit (Buryatia, Russia), has been determined. The preliminary formula of kelyanite was Hg34Sb3Cl3Br1O28 (assuming the presence of both the Hg1+ and Hg2+). In contrast to this assumption, kelyanite appears to contain only monovalent Hg and its revised formula is (Hg2)6(SbO6) BrCl2. Kelyanite is trigonal, space group P3, a = 13.560(4), c = 10.004(6) Å, V = 1593(1) Å3, and Z = 3. In the structure, Hg atoms form six crystallographically independent pairs [dumbbells of composition (Hg2)2+] with Hg-Hg distances of 2.482(3)-2.519(2) Å. The Hg and O atoms form O-Hg-Hg-O systems with Hg-O bond lengths of 1.98(3)-2.33(3) Å and HgHgO angles of 140.3(7)-168.3(9)°. Mercury atoms in the (Hg2)2+ dumbbells have additional coordination to O, Cl, and Br atoms [Hg-O 2.62(2) Å, Hg-Cl 2.68(1)-2.97(1) Å, and Hg-Br 3.00(1)-3.55(1) Å]. Three crystallographically independent Sb atoms are octahedrally coordinated by O atoms with Sb-O distances of 1.96-2.14 Å. The (Hg2)2+ dumbbells link the (SbO6) octahedra in a 3D structure.

Excitation-Wavelength-Dependent Emission and Delayed Fluorescence in a Proton-Transfer System

Manipulating the relaxation pathways of excited states and understanding mechanisms of photochemical reactions present important challenges in chemistry. Here we report a unique zinc(II) complex exhibiting unprecedented interplay between the excitation-wavelength-dependent emission, thermally activated delayed fluorescence (TADF) and excited state intramolecular proton transfer (ESIPT). The ESIPT process in the complex is favoured by a short intramolecular OH⋅⋅⋅N hydrogen bond. Synergy between the excitation-wavelength-dependent emission and ESIPT arises due to heavy zinc atom favouring intersystem crossing (isc). Reverse intersystem crossing (risc) and TADF are favoured by a narrow singlet-triplet gap, ΔEST ≈10 kJ mol-1 . These results provide the first insight into how a proton-transfer system can be modified to show a synergy between the excitation-wavelength-dependent emission, ESIPT and TADF. This strategy offers new perspectives for designing ESIPT and TADF emitters exhibiting tunable excitation-wavelength-dependent luminescence.