Carlos Cruz

Neutral 1D chains [RuCl₂(μ-ox)₂Ln(H₂O)_x(dmf)₄]_n [Ln = La, x = 1 (2); Ln = Dy, x = 0 (3)] were obtained by self-assembly from LnCl₃·nH₂O and (PPh₄)₂(H₃O)[RuCl₂(ox)₂]·4H₂O (1·4H₂O). Compounds 1 and 2 display field-induced slow magnetic relaxation dominated by Raman processes, whereas no such behavior is observed for the Dy-containing chain.

We report the synthesis, structure, and magnetic properties of a novel Co/Dy heterometallic complex, [Co^III ₄Co^II ₂Dy^III ₂(tea)₄(CH₃COO)₄(OH)₂(NO₃)₄]·2H₂O (1), the first structurally characterized example of a mixed-valent {Co^III ₄Co^II ₂Dy^III ₂} motif. It comprises two butterfly-like {Co^III ₂Co^IIDy^III} units linked by carboxylate and alkoxide bridges. X-ray diffraction shows unique Dy(III) and Co(II) sites, with Dy(III) nine-coordinated and Co(II) in a rhombic tetrahedral geometry. Magnetic data and quantum chemical calculations reveal weak Co(II)–Co(II) antiferromagnetic exchange, negligible Co(II)–Dy(III) interactions, and moderate Co(II) zero-field splitting (D ≈ 12–20 cm⁻¹), which drives single-molecule magnet behavior below 14 K. AC studies indicate multiple tunneling pathways and an Orbach barrier (U_eff ≈ 65 cm⁻¹) arising from Co(II), while Dy(III) ions remain largely magnetically decoupled.

We report two new cyanido-bridged Fe(II)-Ag(I) coordination polymers using different acetylpyridine isomers, {Fe(4acpy)₂[Ag(CN)₂]₂} 1 and {Fe(3acpy)[Ag(CN)₂]₂} 2 (4acpy = 4-acetylpyridine; 3acpy = 3-acetylpyridine) displaying thermally and photoinduced spin crossover (SCO). In both cases, the acetylpyridine ligand directs the coordination polymer structure and the SCO of the materials. Using 4-acetylpyridine, a two-dimensional (2D) structure is observed in 1 made of layers stacked on each other by silver-ketone interactions leading to a complete SCO and reversible thermally and photoswitching of the magnetic and optical properties. Changing the acetyl group to a 3-position, a completely different structure is obtained for 2. The unexpected coordination of the carbonyl group to the Fe(II) centers induces a three-dimensional (3D) structure, leading to statistical disorder around the Fe(II) with three different coordination spheres, [N₆], [N₄O₂], and [N₅O]. This disorder gives rise to an incomplete thermally induced SCO with a poor photoswitchability. These results demonstrate that the choice of the acetyl position on the pyridine dictates the structural characteristics of the compounds with a direct impact on the SCO behavior. Remarkably, this work opens interesting perspectives for the future design of Fe-Ag cyanido coordination polymers with judiciously substituted pyridine ligands to tune the thermally and photoinduced SCO properties.

The MOF [Ce₂Zn₃(oda)₆(H₂O)₆]·12H₂O displays field-induced slow magnetic relaxation and phonon-bottleneck effect. Ab initio calculations reveal strong mixing of spin–orbit levels in the Ce^III ground state and significant tunneling probability.

A new trinuclear Cu^II compound {[Cu₃(HL′)₂(H₂O)₂](ClO₄)₄}·(H₂O)₄ (1) was obtained and presented a trapped chiral hemiaminal (HL_2′ = [(5-amino-4H-1,2,4-triazol-3-yl)amino](1H-imidazol-4-yl)methanol)). Compound 1 shows an almost flat cationic structure [Cu₃(HL′)₂(H₂O)₂]⁴⁺ with a Cu₃ linear core reached by the double Cu-OR/NN-Cu triazole/alkoxo bridge of the hemiaminal molecule. The Cu^II spin carriers are antiferromagnetically coupled, presenting a spin doublet ground state (S = 1/2) with a magnetic coupling constant of −179 cm⁻¹. Moreover, DTF calculations show that the planarity of the compound permits a sigma-type overlapping between the unpaired electrons of the spin carriers and the p-type orbitals of the coordinated N and O atoms producing an electronic delocalization through the bridging ligand responsible for the strong antiferromagnetic interactions observed experimentally.