Designing Single-Ion Magnets and Phosphorescent Materials with 1-Methylimidazole-5-carboxylate and Transition-Metal Ions

Abstract

Detailed structural, magnetic, and photoluminescence (PL) characterization of four new compounds based on 1-methylimidazole-5-carboxylate (mimc) ligand and transition metal ions, namely [Ni(mimc)(HO)] (1), [Co(μ-mimc)] (2), {[Cu(μ-mimc)(HO)]·2HO} (3), and [Cd(μ-mimc)(HO)] (4) is reported. The structural diversity found in the family of compounds derives from the coordination versatility of the ligand, which coordinates as a terminal ligand to give a supramolecular network of monomeric entities in 1 or acts as a bridging linker to build isoreticular 2D coordination polymers (CPs) in 2-4. Magnetic direct-current (dc) susceptibility data have been measured for compounds 1-3 to analyze the exchange interactions among paramagnetic centers, which have been indeed supported by calculations based on broken symmetry (BS) and density functional theory (DFT) methodology. The temperature dependence of susceptibility and magnetization data of 2 are indicative of easy-plane anisotropy (D = +12.9 cm, E = +0.5 cm) that involves a bistable M = ±1/2 ground state. Alternating-current (ac) susceptibility curves exhibit field-induced single-ion magnet (SIM) behavior that occurs below 14 K, which is characterized by two spin relaxation processes of distinct nature: fast relaxation of single ions proceeding through multiple mechanisms (U = 26 K) and a slow relaxation attributed to interactions along the polymeric crystal building. Exhaustive PL analysis of compound 4 in the solid state confirms low-temperature phosphorescent green emission consisting of radiative lifetimes in the range of 0.25-0.43 s, which explains the afterglow observed during about 1 s after the removal of the UV source. Time-dependent DFT and computational calculations to estimate phosphorescent vertical transitions have been also employed to provide an accurate description of the PL performance of this long-lasting phosphor.

Coordination Polymers with Intriguing Photoluminescence Behavior: The Promising Avenue for Greatest Long‐Lasting Phosphors

“…A very weak RTP has been recently observed for the [Cd(µ‐MIMC) 2 (H 2 O)] n (10‐Cd hereafter, MIMC being 1‐methylimidazole‐5‐carboxylate) 2D sql layered CP . Exciting the polycrystalline sample of 10‐Cd with monochromatic 325 nm laser, it exhibits a broad band covering the whole visible spectrum (400–700 nm) in which two main peaks at 460 and 520 nm are distinguished, all of which explains well the multicolored emission shown by the crystals when illuminated at variable wavelength (Figure ).…”

“…micro‐PL images at different excitation lines; (b) experimental and TD‐DFT excitation and emission spectra; (c) schematic energy diagram of molecular orbitals involved in the fluorescence and phosphorescence emissions. Reproduced with permission from ref . Copyright 2017 American Chemical Society.…”

2D-Coordination polymers based on 1H-indazole-4-carboxylic acid and transition metal ions: magnetic, luminescence and biological properties

“…This behaviour is the first evidence of zero-field splitting (ZFS) in NiIJII) compounds. 7 In addition, the magnetization curve at 2 K saturates below 2μ B , which definitely confirms the presence of this effect (Fig. 6, inset).…”

“…In particular, the study of transition metal ion-based MOFs has evolved enormously in a great quantity of areas, and considering the advantage that ions have fairly predictable coordination spheres, it allows us to design materials with application for virtually all fields. In this sense, in recent years, our group and others have worked on the design of novel MOFs to study their properties in luminescence, 4 gas adsorption, 5 catalysis, 6 magnetism, 7 biology as drug-delivery systems, 8 cytotoxic agents 9 and sensing. 10 Bearing in mind the interest of our group in the study of MOFs based on nitrogen linkers with carboxylate groups, we decided to study the properties of this type of materials with the interesting 1H-indazole-4-carboxylic acid because, as far as we know, there are no coordination compounds synthesized with it.…”

Designing Single-Molecule Magnets as Drugs with Dual Anti-Inflammatory and Anti-Diabetic Effects

“…Results of the best fit are B Raman = 115(4) s -1 , n = 2.9(3), τ 0 = 1.69 × 10 -11 s and U eff = 71(4) K, which can be considered as relatively high compared to those previously reported for Co II based SIMs [39,40].…”