L. Jos de Jongh

Mononuclear Manganese(III) Complexes as Building Blocks for the Design of Trinuclear Manganese Clusters: Study of the Ligand Influence on the Magnetic Properties of the [Mn3(μ3-O)]7+Core

The synthesis, crystal structure, and magnetic properties of three new manganese(III) clusters are reported, [Mn 3(mu 3-O)(phpzH) 3(MeOH) 3(OAc)] (1), [Mn 3(mu 3-O)(phpzMe) 3(MeOH) 3(OAc)].1.5MeOH (2), and [Mn 3(mu 3-O)(phpzH) 3(MeOH) 4(N 3)].MeOH (3) (H 2phpzH = 3(5)-(2-hydroxyphenyl)-pyrazole and H 2phpzMe = 3(5)-(2-hydroxyphenyl)-5(3)-methylpyrazole). Complexes 1- 3 consist of a triangle of manganese(III) ions with an oxido-center bridge and three ligands, phpzR (2-) (R = H, Me) that form a plane with the metal ions. All the complexes contain the same core with the general formula [Mn 3(mu 3-O)(phpzR) 3] (+). Methanol molecules and additional bridging ligands, that is, acetate (complexes 1 and 2) and azide (complex 3), are at the terminal positions. Temperature dependent magnetic susceptibility studies indicate the presence of predominant antiferromagnetic intramolecular interactions between manganese(III) ions in 1 and 3, while both antiferromagnetic and ferromagnetic intramolecular interactions are operative in 2.

High nuclearity manganese(III) compounds containing phenol-pyrazole ligands: the influence of the ligand on the core geometry

Three high-nuclearity manganese(III) clusters have been synthesized and characterized: [Mn₈(μ₄-O)₄(phpzH)₈(thf)₄] (1), [Mn₈(μ₄-O)₄(phpzH)₄(EtOH)₄]·2EtOH (2), and [Mn₆(μ₃-O)₄(μ₃-Br)₂(HphpzEt)₆(phpzEt)] (3). Compounds 1 and 2 contain a [Mn₈(μ₄-O₄)(phpzH)₈] core in which antiferromagnetic interactions between the manganese(III) ions are found. Compound 3 is a hexanuclear manganese(III) cluster in which weak ferromagnetic interactions appear to be operative. The formation and the stability of the cluster cores in relation to the type of phenol-pyrazole ligand and the reaction conditions are discussed.

Mononuclear and dinuclear manganese compounds stabilized by supramolecular interactions

New manganese compounds [Mn(HphpzMe)(2)(H(2)phpzMe)(HCO(2))] (1), [Mn(2)(phpzMe)(2)(HphpzMe)(2)(OCH(3))]·2CH(3)OH (2), Na{[Mn(HphpzPh)(phpzPh)(MeOH)(2)](2)}(HCO(2)) (3), [Mn(HphpzPh)(2)(EtOH)(2)]ClO(4)·2EtOH (4) and [Mn(HphpzPh)(2)N(3)] (5) were synthesized and characterized with various techniques. 1, 4 and 5 are mononuclear manganese(III) compounds, 2 is a mixed-valence dinuclear manganese(III/IV) compound, and 3 is a trinuclear compound containing two manganese(III) ions and a sodium(I) ion. A remarkable feature is the spontaneous formation of the formate ion as a result of the methanol or methoxide oxidation in compounds 1 and 3. Using ethanol precludes the formation of the formate and compound 4 is obtained. The molecular structure of all compounds is stabilized by supramolecular interactions, including strong hydrogen bonding and π-π interactions.

Analytical approach to the t—t′—J model: Quasi-particle dispersion, Fermi surface and optical conductivity

An approximate, analytically solvable ansatz for the self-energy of a single hole in the 2-dimensional t—t′—J model, at t ⪢ J, t′, is proposed: 〈M2q,Q〉Q(f(ω)+iΓ(ω)). It features consistently: 1) the incoherence of a substantial part of the hole spectral weight, asymmetrically stretched over an energy interval of width ∼ t; 2) the collective nature of the quasi-particle dispersion, ϵ(q), with q-dependence generated by the spin-hole scattering matrix element, and 3) the enhancement of the quasi-particle mass, m* ∼ (Jln(t/J))−1, i.e. a renormalization of the quasi-particle bandwidth: ∼ Jln(t/J). Our analytical result for ϵ(q) is in good accord with existing numerical data for the t-J model. Calculated optical conductivity exhibits single-hole/multimagnon resonances superimposed on a 1/ω tail of width ∼ t. A change of the curvature of the Fermi surface from hole-like to electron-like with doping is also found.