Els fonaments de la Química Bàsica 1

En aquest llibre es presenten els continguts fonamentals d'una part de la química general o química bàsica, el que correspon al programa de l'assignatura de Química Bàsica 1 del grau de química de la Universitat de Barcelona

Fonaments de Bioinorgànica

En aquest llibre s'analitzen diferents aspectes de la vida des de la vessant de la química inorgànica, fonamentalment des del punt de vista de la química de coordinació. Alguns temes en detall, des del punt de vista químic, d'altres més a nivell divulgació i de curiositat

Les reaccions Inorgàniques

En aquest llibre es presenten els dos grans tipus de reaccions inorgàniques, redox i no redox (diferents models àcid base). Es fa especial èmfasi a la química en solució i la formació de complexos, així com a la diferenciació i separació de compostos inorgànics. Hi ha una extensa col·lecció d'exercicis resolts i un capitol dedicat als pigments

New insights into the comprehension of the magnetic properties of dinuclear Mn(III) compounds with general formula [{MnL(NN)}2(μ-O)(μ-n-RC6H4COO)2]X2

Five new dinuclear Mn(III) compounds with benzoato derivative bridges [{Mn(bpy)L}2(μ-O)(μ-n-RC6H4COO)2]X2 (n-R = 3-MeO, 4-MeO and 4-tBu, X = NO3− and ClO4−) were synthesised and characterised. According to X-ray diffraction, the X anions tend to be coordinated to the Mn ions and may occupy the place of the monodentate ligand L. Two structural isomers that only differ in one of their monodentate ligands have been obtained with the 3-MeOC6H4COO− bridges. For all compounds, the Mn(III) ions display elongated octahedra with a pronounced rhombic distortion. To quantify these distortions separately, the elongation and rhombicity parameters Δ and ρ have been defined. The magnetic study shows a good relationship between the distortion of the coordination polyhedra and the zero field splitting parameters (DMn and EMn). From the magnetic data of a powder sample, it is possible to determine the sign and magnitude of DMn for ferromagnetic systems or weak antiferromagnetic systems with DMn < 0. For this kind of dinuclear compound, the R group at the meta position, the rhombic distortion of the octahedra, and large torsion angles between the Jahn-Teller axes lead to ferromagnetic interactions

Singlet ground state in compounds with [MnIII4O2]8+ core due to broken degeneration

Two new tetranuclear compounds with a formula [MnIII4(μ-O)2(μ-4-RC6H4COO)7−m(L)2m(phen)2](ClO4)1+m, where R = MeO or tBu and m = 0 or 1, were synthesised and studied structurally and magnetically. The core of these compounds comprises a central Mn2O2 rhombus to which two terminal ions are attached - one to each oxo bridge. There are two types of bridges that alternately bind the central and terminal ions, those having a triple (μ-O)(μ-RCOO)2 or a double (μ-O)(μ-RCOO) bridge. The fit of the magnetic data of analogous compounds has so far been performed considering two different magnetic interactions, that between central ions (J1) and those between terminal and central ions (Jct), leading to ground states with ST = 2 or 3, or to five energetically degenerate ground states with ST = 0-4, depending on the J1/Jct ratio. In contrast, the compounds presented herein show an isolated ST = 0 ground state, and it was necessary to distinguish the two types of magnetic interactions between central and terminal ions (J2 and J3) to achieve a good fit of the experimental data. The differentiation of these interactions causes a spin state redistribution: the degeneration of ST = 0-4 breaks and the states with ST ≠ 0 become unstable as J2 and J3 become more different. Nevertheless, the assignment of these states to a particular spin configuration was unachievable because the composition of these states changes upon decreasing the J3/J2 ratio. The importance of considering the relative orientation of Jahn-Teller axes is also highlighted

Determination of ZFS parameters from the EPR spectra of mono-, di- and trinuclear MnII complexes: impact of magnetic coupling

A family of new MnII compounds, consisting of seven dinuclear, three mononuclear, and four trinuclear ones, were synthesised using benzoic acid derivatives n-RC6H4COOH, where n-R = 2-MeO, 3-MeO, 4-MeO, or 4-tBu, and 2,2′-bipyridine (bpy) or 1,10-phenantroline (phen) as blocking ligands. The crystal structures of nine of these compounds and the magnetic studies of all of them are reported here. Each type of compound was formed depending on the presence or absence of ClO4− ions, the solvent used, and/or the presence of a small amount of water in the reaction medium. The use of the tert-buthylbenzoate ligand gave unexpected results, very likely due to the steric hindrance caused by the voluminous tBu groups. The EPR spectra of each type of compound give some peculiar features that allow its identification. Attempts to fit these spectra have been made in order to determine the ZFS parameters, D and E, of the MnII ion (for mononuclear and dinuclear systems) or of the ground state (for trinuclear systems). For trinuclear systems, the single-ion ZFS parameters estimated from those of the ground state provided a good simulation of the EPR spectra of these compounds. The EPR signals observed in each case have been rationalised according to the energy level distribution and the plausible population in the excited states. In some particular situations, the sign of DMn could be determined from the fit of the EPR spectra of the antiferromagnetic dinuclear compounds, the source of the difference between the spectra lying in the second excited state

Neodymium 1D systems: targeting new sources for field-induced slow magnetization relaxation

Two non-isostructural homometallic 1D neodymium species dis- playing field-induced slow magnetization relaxations are presented together with theoretical studies. It is established that both systems are better described as organized 1D single molecule magnets (SMMs). Studies show great potential of NdIII ions to provide homometallic chains with slow magnetic relaxation

Biomimetic Mn-catalases based on dimeric manganese complexes in mesoporous silica for potential antioxidant agent

Two new structural and functional models of the Mn-catalase with formula [{MnIII(bpy)(H2O)}(μ-2-MeOC6H4CO2)2(μ-O){MnIII(bpy)(X)}]X, where X = NO3 (1) and ClO4 (2) and bpy = 2,2′-bipyridine, were synthesized and characterized by X-ray diffraction. In both cases, a water molecule and an X ion occupy the monodentate positions. The magnetic properties of these compounds reveal a weak antiferromagnetic behavior (2J = −2.2 cm 1 for 1 and −0.7 cm 1 for 2, using the spin Hamiltonian H = −2J S1·S2) and negative zero-field splitting parameter DMn (−4.6 cm 1 and −3.0 cm 1 for 1 and 2, respectively). This fact, together with the nearly orthogonal orientation of the Jahn Teller axes of the MnIII ions explain the unusual shape of χMT versus T plot at low temperature. Compound 1 presents a better catalase activity than 2 in CH3CN H2O media, probably due to a beneficial interaction of the NO3− ion with the Mn complex in solution. These compounds were successfully inserted inside two-dimensional hexagonal mesoporous silica (MCM-41 type) leading to the same hybrid material ([Mn2O]@SiO2), without the X group. The manganese complex occupies approximately half of the available pore volume, keeping the silica's hexagonal array intact. Magnetic measurements of [Mn2O]@SiO2 suggest that most of the dinuclear unit is preserved, as a non-negligible interaction between Mn ions is still observed. The X-ray photoelectron spectroscopy analysis of the Mn 3s peak confirms that Mn remains as MnIII inside the silica. The catalase activity study of material [Mn2O]@SiO2 reveals that the complex is more active inside the porous silica, probably due to the surface silanolate groups of the pore wall. Moreover, the new material shows catalase activity in water media, while the coordination compounds are not active

Magnetic behavior of heterometallic wheels having a [MnIV6M2O9]10+ core with M = Ca2+ and Sr2+

Two new heterometallic MnIV−M2+ compounds with formula [Mn6M2O9(4-tBuC6H4COO)10(4-tBuC6H4COOH)5] (M = Ca2+ (1), Sr2+ (2)) have been crystallized. The core of both compounds consists of a planar Mn6 ring, where the MnIV ions are alternatively bridged by (μ3-O)2(μ-RCOO) and (μ4-O)(μ-RCOO)2 ligands, and the two alkaline earth ions are located to both sides of the wheel, linked to the oxo bridges, generating three fused [Mn2M2O4]4+ cuboids. These compounds show a net antiferromagnetic behavior, more important for 2 (Sr2+) than for 1 (Ca2+). The fitting of the experimental data was performed with the support of DFT calculations, considering four different exchange pathways: two between adjacent MnIV ions (J1 and J2) and two between nonadjacent MnIV ions (J3 and J4). The results of the analysis show that J1 and J2 are of the opposite sign, the ferromagnetic contribution corresponding to the [Mn2(μ4- O)(μ-RCOO)2]4+ unit (J2). The influence of the M2+ ions in the magnetic behavior is analyzed for 1 and 2 and for three hypothetical models with the structural parameters of 1 containing Mg2+, Sr2+ or without the M2+ ions. In spite of the diamagnetic character of the alkaline earth ions, their influence on the magnetic behavior has been evidenced and correlated with their polarizing effect. Moreover, the magnetic interactions between nonadjacent ions are non-negligible