A 3D coordination polymer of Tb( iii ) of formula [Tb(bttb) _0.5 (2,5-pzdc) _0.5 ] _n , where two polycarboxylate ligands act as linkers, exhibits a maximum relative sensitivity of 0.76% K ⁻¹ at 295 K.

In this work, we present the synthetic pathway, a refined structural description, complete solid-state characterization and the magnetic properties of four new cobalt(II) compounds of formulas [Co(H₂O)₆][Co₂(H₂mpba)₃]∙2H₂O∙0.5dmso (1), [Co(H₂O)₆][Co₂(H₂mpba)₃]∙3H₂O∙0.5dpss (2), [Co₂(H₂mpba)₂(H₂O)₄]_n∙4nH₂O (3), and {[Co₂(H₂mpba)₂(CH₃OH)₂(H₂O)₂]_n∙0.5nH₂O∙2ndpss (4) [dpss = 2,2’-dipyridyldisulfide and H₄mpba = 1,3-phenylenebis(oxamic) acid], where 2 and 4 were obtained by using [Co(dpss)Cl₂] (Pre-I) as source of cobalt(II). All four compounds are air-stable and were prepared under ambient conditions. 1 and 2 were obtained by a slow diffusion method [cobalt(II):H₂mpba^2– molar ratio used 1:1] and their structures are made up of [Co₂(H₂mpba)₃]^2– anionic helicate units and [Co(H₂O)₆]²⁺ cations, exhibiting supramolecular three-dimensional structures. Interestingly, a supramolecular honeycomb network between the helicate units interacting each other through R₂ ²(10) type hydrogen bonds occurs in 2 hosting one co-crystallized dpss molecule. On the other hand, for the first time, linear (3) and zigzag (4) cobalt(II) chains were isolated by slow evaporation at room temperature of stirred solutions of mixed solvents with cobalt(II):H₂mpba^2– 1:2 molar ratio. Magnetic measurements of Pre-I revealed a quasi magnetically isolated S = 3/2 spin state with a significant second-order spin-orbit contribution as expected for tetrahedrally coordinated cobalt(II) ions. The analysis of the variable temperature static (dc) magnetic susceptibility data through first- (1 and 3) and second-order spin-orbit coupling models (2 and 4) reveals the presence of magnetically non-interacting high-spin cobalt(II) ions with easy-axis (1 and 4)/easy-plane magnetic anisotropies (2 and 4) with low rhombic distortions. Dynamic (ac) magnetic measurements for Pre-I and 1-4 below 8.0 K show they are examples of field-induced Single-Ion Magnets (SIMs).

Herein, we describe the synthesis, crystal structure, and electronic properties of {[K₂(dmso)(H₂O)₅][Ni₂(H₂mpba)₃]·dmso·2H₂O}_n (1) and [Ni(H₂O)₆][Ni₂(H₂mpba)₃]·3CH₃OH·4H₂O (2) [dmso = dimethyl sulfoxide; CH₃OH = methanol; and H₄mpba = 1,3-phenylenebis(oxamic acid)] bearing the [Ni₂(H₂mpba)₃]²⁻ helicate, hereafter referred to as {Ni^II₂}. SHAPE software calculations indicate that the coordination geometry of all the Ni^II atoms in 1 and 2 is a distorted octahedron (O_h) whereas the coordination environments for K1 and K2 atoms in 1 are Snub disphenoid J84 (D_2d) and distorted octahedron (O_h), respectively. The {Ni^II₂} helicate in 1 is connected by K⁺ counter cations yielding a 2D coordination network with sql topology. In contrast to 1, the electroneutrality of the triple-stranded [Ni₂(H₂mpba)₃] ²⁻ dinuclear motif in 2 is achieved by a [Ni(H₂O)₆]²⁺ complex cation, where the three neighboring {Ni^II₂} units interact in a supramolecular fashion through four R₂²(10) homosynthons yielding a 2D array. Voltammetric measurements reveal that both compounds are redox active (with the Ni^II/Ni^I pair being mediated by OH^– ions) but with differences in formal potentials that reflect changes in the energy levels of molecular orbitals. The Ni^II ions from the helicate and the counter-ion (complex cation) in 2 can be reversibly reduced, resulting in the highest faradaic current intensities. The redox reactions in 1 also occur in an alkaline medium but at higher formal potentials. The connection of the helicate with the K⁺ counter cation has an impact on the energy levels of the molecular orbitals; this experimental behavior was further supported by X-ray absorption near-edge spectroscopy (XANES) experiments and computational calculations.

Carbon dioxide fixation by [Cu(bpca)(H₂O)]²⁺ resulted in a chain having CO₃²⁻ and HCO₃⁻ as ligands that shows a weak intrachain ferromagnetic interaction.

The heterobimetallic 15-MC-5 metallacrown of formula [CeCu₅(5mpzHA)₅(NO₃)(H₂O)₇]·2NO₃·7H₂O, designated MC-Ce, was synthesized using 5-methyl-2-pyrazinehydroxamic acid (5mpzHA) as a linker, reacting with Ce^III and Cu^II salts under mild conditions. Single-crystal X-ray diffraction analysis reveals a crown-like [Cu₅Ce(5mpzHA)₅] core, characteristic of a 15-MC-5 system, with five Cu^II atoms at the rim of the crown and the Ce^III ion occupying the dome of the crown, with water molecules, oxygen atoms and one nitrate anion filling the nine-coordination sphere around the Ce^III ion, which exhibits a distorted spherical tricapped trigonal prism geometry. The thermogravimetric analysis evidences successive mass losses due to the removal of water molecules and decomposition of the structure after 217 °C, whereas the PXRD analysis of the thermal decomposition residue reveals the presence of copper and copper/cerium oxide particles. These nanocomposite materials were also synthesized using the metallacrown MC-Ce under a hydrothermal method in the presence of multi-walled carbon nanotubes (MWCNTs), affording insights that this metallacrown can act as a source precursor for the synthesis of these mixed cerium/copper oxide nanomaterials. The experimental χMT value in MC-Ce at room temperature is 3.175 cm³ mol⁻¹ K, which is higher than the calculated one for one magnetically isolated Ce^III plus five Cu^II ions, probably due to the antiferromagnetic interactions among Cu^II ions within the metallacrown hoop plus the thermal depopulation of JZ sublevels of Ce^III ground state (5/2), which exhibit a small splitting under the anisotropic ligand field effects. The χMT decreases continuously until it reaches the value of 0.80 cm³ mol⁻¹ K at 10 K, reinforcing the presence of intramolecular antiferromagnetic interactions.