Combined experimental and theoretical investigation on the magnetic properties derived from the coordination of 6-methyl-2-oxonicotinate to 3d-metal ions

Five new compounds are reported herein starting from 2-hydroxy-6-methylnicotinic acid (H2h6mnic) and first-row transition metal ions, although H2h6mnic shows a prototropy in solution to lead to the 6-methyl-2-oxonicotinate (6m2onic) ligand that is the molecule eventually present in the compounds. The structural and chemical characterization reveals the following chemical formulae: {[MnNa(μ₃-6m2onic)₂(μ-6m2onic)(MeOH)]·H₂O·MeOH}_n (1Mn), {[M₂Na₂(μ₃-6m2onic)₂(μ-6m2onic)₂(μ-H₂O)(H₂O)₆](NO₃)₂}_n [M^II = Co (2Co) and Ni (3Ni)], 2[Cu₂(6m2onic)₃(μ-6m2onic)(MeOH)]·[Cu₂(6m2onic)₂(μ-6m2onic)₂]·2[Cu(6m2onic)₂(MeOH)]·32H₂O (4Cu) and {[Cu(μ-6m2onic)₂]·6H₂O}_n (5Cu) (where 6m2onic = 6-methyl-2-oxonicotinate). An unusual structural diversity is observed for the compounds, ranging from isolated complexes (in 4Cu), 1D arrays (in 1Mn and 5Cu) and 3D frameworks (in 2Co and 3Ni). Magnetic properties have been studied for all compounds. Analysis of the magnetic dc susceptibility and magnetization data for 4Cu and 5Cu suggests the occurrence of ferromagnetic exchange, which is well explained by broken-symmetry and CASSCF calculations. The sizeable easy-plane magnetic anisotropy present in compound 2Co allows for a field-induced magnet behaviour with an experimental effective energy barrier of 16.2 cm^-1, although the slow relaxation seems to be best described through Raman and direct processes in agreement with the results of ab initio calculations.

Calcium-Based Metal-Organic Frameworks and Their Potential Applications

Metal-organic frameworks (MOFs) built on calcium metal (Ca-MOFs) represent a unique subclass of MOFs featuring high stability, low toxicity, and relatively low density. Ca-MOFs show considerable potential for molecular separations, electronic, magnetic, and biomedical applications, although they are not investigated as extensively as transition metal-based MOFs. Compared to MOFs made of other groups of metals, Ca-MOFs may be particularly advantageous for certain applications such as adsorption and storage of light molecules because of their gravimetric benefit, and drug delivery due to their high biocompatibility. This review intends to provide an overview on the recent development of Ca-MOFs, including their synthesis, crystal structures, important properties, and related applications. Various synthetic methods and techniques, types of building blocks, structure and porosity features, selected physical properties, and potential uses will be discussed and summarized. Representative examples will be illustrated for each type of important applications with a focus on their structure-property relations.

Tuning the porosity through interpenetration of azobenzene-4,4′-dicarboxylate-based metal–organic frameworks

Pore size is tuned in a series of azobenzene-4,4′-dicarboxylate/3,6-bis(4-pyridyl)-1,2,4,5-tetrazine/Zn or Cd based MOFs through a variable interpenetration degree. These structural features promote subtle shifts in the blue emission of the compounds.

Enhancing luminescence properties of lanthanide(iii)/pyrimidine-4,6-dicarboxylato system by solvent-free approach

Solvent-free reaction between lanthanide nitrates and pyrimidine-4,6-dicarboxylic acid led to 3D frameworks with coordinated nitrates showing a photoluminescence improvement and waveguiding behaviour.