In this work we report the synthesis, crystal structures, and magnetic behavior of 2p-3d-4f heterospin systems containing the nitroxide radical 4-azido-2,2,6,6-tetramethylpiperidine-1-oxyl radical (N3tempo). These compounds were synthesized through a one-pot reaction by using [Cu(hfac)2], [Ln(hfac)3] (hfac = hexafluoroacetylacetonate, Ln = Dy(III), Tb(III) or Gd(III)), and the N3tempo radical. Depending on the stoichiometric ratio used, the synthesis leads to penta- or trimetallic compounds, with molecular formulas [Cu3Ln2(hfac)8(OH)4(N3tempo)] (Ln = Gd, Tb, Dy) and [CuLn2(hfac)8(N3tempo)2(H2O)2] (Ln = Gd, Dy). The magnetic properties of all compounds were investigated by direct current (dc) and alternating current (ac) measurements. The ac magnetic susceptibility measurements of Tb(III)- and Dy(III)-containing compounds of both families revealed slow relaxation of the magnetization, with magnetic quantum tunneling in zero field.

A new family of binuclear complexes [MnLn(dpm)(MeO)(MeOH)] is reported (where Ln = La (1), Pr (2), and Eu(3)). These compounds were obtained from a one-pot reaction between 2,2,6,6-tetramethyl-3,5-heptanodione (Hdpm), Mn, and the respective Ln salt in the presence of sodium methoxide. The derivative containing the diamagnetic ion La has been synthesized in order to characterize the local anisotropy of the Mn ion. High-field electron paramagnetic resonance (HFEPR) spectroscopy shows that the Mn ion, with an elongated octahedral geometry in all compounds, has a significant axial zero-field splitting and a small rhombic anisotropy. Additionally, the HFEPR measurements indicate that there is almost no exchange between the spin carriers in these compounds, all of which exhibit field-induced slow relaxation of the magnetization.

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Two tetranuclear compounds with a cubanelike structure were synthesized from a one-pot reaction between Ni II and 2,2,6,6-tetramethyl-3,5-heptanedione (Hdpm) for 1 or 4,4,4-trifluoro-1-phenyl-1,3-butanedione (Hbta) for 2 in the presence of sodium methoxide. The crystal structures of both compounds have been determined by single-crystal X-ray diffraction, and their magnetic properties have been studied by SQUID magnetometry as well as by high-field electron paramagnetic resonance (HFEPR) spectroscopy. For 1, the temperature dependence of the magnetic susceptibility can be fitted by taking into account Ni•••Ni ferromagnetic interactions, which leads to an S = 4 ground-state spin. For 2, both antiferromagnetic and ferromagnetic interactions are present. However, the latter are dominant, which also leads to an S = 4 ground-state spin, in good agreement with the HFEPR study.

Recently, spin-crossover compounds were pointed out as strong candidates for working as refrigerant materials due to their huge barocaloric effect. In this work, we report the giant isothermal entropy change (ΔST) and adiabatic temperature change (ΔTad) upon moderated pressure variation in the spin-crossover complex [CrI2(depe)2], where depe = 1,2-bis(diethylphosphino)ethane. This complex was investigated considering three main contributions for total entropy: configurational, magnetic, and phonon entropies, which were simulated using proper microscopic parameters. The high values of ΔST = 40 J kg−1 K−1 and ΔTad = 10.6 K for ΔP = 2 kbar were obtained around low ↔ high spin phase transition temperature (T1/2). Besides, due to the large barocaloric shift parameters (δT1/2/δP ∼ 52 K/kbar), a giant refrigerant capacity (RC = 3583 J kg−1) was established for [CrI2(depe)2].

Using the 1-(m-tolyl)-1H-1,2,3-triazole-4-(4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) (TlTrzNIT) radical and metal β-diketonate complexes [M­(hfac)2(H2O)2], where hfac is hexafluoroacetylacetonato, three new 2p–3d heterospin complexes were synthesized. Their structures were solved using single crystal X-ray diffraction data, and magnetic investigation was performed by DC and AC measurements and multifrequency EPR spectroscopy. Compounds 1 and 2 are isostructural complexes with molecular formula [M3(TlTrzNIT)2(hfac)6] (MII = Mn or Cu) while compound 3 is the mononuclear [Co­(TlTrzNIT)­(hfac)2] complex. In all complexes, the radical acts as a bidentate ligand through the oxygen atom of the nitroxide moiety and the nitrogen atom from the triazole group. Furthermore, in compounds 1 and 2, the TlTrzNIT is bridge-coordinated between two metal centers, leading to the formation of trinuclear complexes. The fitting of the static magnetic behavior reveals antiferromagnetic and ferromagnetic intramolecular interactions for complexes 1 and 2, respectively. The EPR spectra of 1 are well described by an isolated ferrimagnetic S = 13/2 (= 5/2 – 1/2 + 5/2 – 1/2 + 5/2) ground state with a biaxial zero-field splitting (ZFS) interaction characterized, respectively, by 2nd order axial and rhombic parameters, D and E, such that E/D is close to the maximum of 0.33. Meanwhile, EPR spectra for 2 are explained in terms of a ferromagnetic model with weakly anisotropic Cu–radical exchange interactions, giving rise to an isolated S = 5/2 (= 5 × 1/2) ground state with both an anisotropic g tensor and a weak ZFS interaction. Complex 2 represents one of only a few examples of Cu–radical moieties with measurable exchange anisotropy.

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A novel triazole bridged cobalt fluorophosphate coordination polymer with the formula {Co 5 (1,2,4-triazole) 2 (OH) 2 (PO 3 F) 4 } n has been synthesized. Single crystal X-ray studies reveal that the compound comprises of Co 5 clusters which ultimately build the whole framework, here all cobalt centers are in octahedral geometry established from continuous shape analysis. All the cobalt centers are in Co(II) oxidation state and the results are supported by the bond valence sum (BVS) calculation. The sample has been characterized by single crystal X-ray, powder X-ray, FTIR and TGA analysis. The compound was tested for olefin catalysis performance and magnetism. Magnetization measurements reveal overall antiferromagnetic interactions among the Co(II) ions. The compound is very active in the catalytic transformation of olefins to their corresponding epoxides. Catalytic epoxidation studies reveal that cyclohexene and styrene can be converted up to 97 % with almost 65 % selectivity of products with higher TON numbers.