Exploring “Triazole-Thiourea” Based Ligands for the Self-Assembly of Photoluminescent Hg(II) Coordination Compounds

Abstract

This study represents the first explorative investigation on the supramolecular structural diversity in Hg­(II) coordination chemistry with triazole-thiourea ligands leading to a variety of mononuclear, binuclear, and coordination polymers: {[Hg­(L1)2(L1 – )2]} (1), {[Hg2(L1)2­(μ2-I)2I2]­·DMSO} (2), {[Hg­(L2)­(μ2-I)­I]­·MeOH}∝ (3), {[Hg2(μ-L3 –)4]}∝ (4), {[HgCl­(L4 –)L4]­·MeOH} (5), {[Hg2(L4)2­(μ2-I)2(I)2]­·2MeOH} (6), {[Hg2(μ2-L5 – )4]}∝ (7), {[Hg2(μ2-Cl)2­(L6 – )2(L6)2]} (8), {[Hg2(μ2-Br)2­(L6 – )2(L6)2]} (9), and {[Hg2(μ2-I)2­(L6 –)2(L6)2]} (10). A reaction mechanism was suggested for the unexpected ligand rearrangement occurring in {[Hg2I3(μ3-L5′)]}∝ (11). The ligands were fully characterized including by X-ray crystallography and computational means. This includes six new triazole-thiourea based ligands, namely, 1-R-3-(4H-1,2,4-triazol-4-yl)­thiourea (where R = methyl (L1), ethyl (L2), propyl (L3), isopropyl (L4), and its polymorph (L4-poly), allyl (L5), ethyl acetate (L6), and its solvate (L6_MeOH)). Under UV light excitation, 7, 10, and 11 exhibit visible photoluminescence of wide origin, ranging from ligand-centered (LC) fluorescence combined with organic-ligand-to-metal charge transfer (LMCT) emissive states in 7 and 10, up to halide-to-metal charge transfer (XMCT) combined with halide-to-ligand charge transfer (XLCT) emissive states in 11. The variable emission mechanisms in the obtained coordination polymers were elucidated by experimental proofs confronted with theoretical calculations of the electronic densities of states, proving that Hg­(II) halide coordination polymers involving flexible 1,2,4-triazole-based ligands form a promising class of luminescent molecular materials.

Multifunctional Crystalline Coordination Polymers Constructed from 4,4′-Bipyridine-N,N′-dioxide: Photochromism, White-Light Emission, and Photomagnetism

“…Thus, the emission peak at 440 nm can be assigned to ligand-centered emission. Compared with free ligand bpdo, the new shoulder peak at 540 nm in compound 1 can be ascribed to the excited state of the ligand-to-metal charge transfer (LMCT) …”

“…Compared with free ligand bpdo, the new shoulder peak at 540 nm in compound 1 can be ascribed to the excited state of the ligand-to-metal charge transfer (LMCT). 21…”

Heterocycles as supramolecular handles for crystal engineering: a case study with 7-(diethylamino)coumarin derivatives

“…Since the molecular packing of 1,2,4-triazole derivatives tends to be directed by H-bonding interactions, it allows the controlled bottom-up construction of MOFs and it has been applied to Fe(II) coordination polymers that present spin-crossover behavior. [32][33][34][35][36][37] In light of the aforementioned considerations, the impact of incorporating a 4-amino-1,2,4-triazole (51) moiety into the 7-DAC nucleus was investigated to assess its inuence on the solid-state organization. 27,31,38 The amino group (-NH 2 ) is a plausible precursor to an imine or Schiff base p-bridge for the targeted derivative (Scheme 1).…”

Coordination Complexes Built from a Ditopic Triazole-Pyrazole Ligand with Antibacterial and Antifungal Performances

“…Motivated by those applications and properties, triazoles kept sparking the interest and curiosity of our group [25]. Thus, we established a new path towards auspicious novel triazole-based compounds.…”