Manuel Prinz

Star-shaped molecule of MnII4O6 core with an St=10 high-spin state. A theoretical and experimental study with XPS, XMCD, and other magnetic methods.

We report a comprehensive study of the electronic and magnetic properties of a star-shaped molecule comprising a MnII4O6 core. One feature of this compound is weak magnetic coupling constants compared to other similar polyoxo compounds. This leads to complicated low-lying magnetic states in which the ground state is not well separated from the upper-lying states, yielding a high-spin molecule with a giant magnetic moment of up to 20 microB/formula unit. We apply X-ray diffraction and magnetometry as well as other X-ray spectroscopic techniques, namely, X-ray photoelectron spectroscopy, X-ray magnetic circular dichroism, and X-ray emission spectroscopy. We compare our experimental results with ab initio electronic band structure calculations as well as the localized electronic structure around the Mn2+ ions with charge-transfer multiplet calculations.

A Star-Shaped Heteronuclear CrIIIMnII3 Species and Its Precise Electronic and Magnetic Structure: Spin Frustration Studied by X-Ray Spectroscopic, Magnetic, and Theoretical Methods

Molecular magnets incorporate transition-metal ions with organic groups providing a bridge to mediate magnetic exchange interactions between the ions. Among them are star-shaped molecules in which antiferromagnetic couplings between the central and peripheral atoms are predominantly present. Those configurations lead to an appreciable spin moment in the nonfrustrated ground state. In spite of its topologically simple magnetic structure, the [Cr(III)Mn(II)(3) (PyA)(6)Cl(3)] (CrMn(3)) molecule, in which PyA represents the monoanion of syn-pyridine-2-aldoxime, exhibits nontrivial magnetic properties, which emerge from the combined action of single-ion anisotropy and frustration. In the present work, we elucidate the underlying electronic and magnetic properties of the heteronuclear, spin-frustrated CrMn(3) molecule by applying X-ray magnetic circular dichroism (XMCD), as well as magnetization measurements in high magnetic fields, density functional theory, and ligand-field multiplet calculations. Quantum-model calculations based on a Heisenberg Hamiltonian augmented with local anisotropic terms enable us not only to improve the accuracy of the exchange interactions but also to determine the dominant local anisotropies. A discussion of the various spin Hamiltonian parameters not only leads to a validation of our element selective transition metal L edge XMCD spin moments at a magnetic field of 5 T and a temperature of 5 K but also allows us to monitor an interesting effect of anisotropy and frustration of the manganese and chromium ions.

Electronic structure and soft-X-ray-induced photoreduction studies of iron-based magnetic polyoxometalates of type {(M)M5}12FeIII30 (M = MoVI, WVI)

Giant Keplerate-type molecules with a {Mo72Fe30} core show a number of very interesting properties, making them particularly promising for various applications. So far, only limited data on the electronic structure of these molecules from X-ray spectra and electronic structure calculations have been available. Here we present a combined electronic and magnetic structure study of three Keplerate-type nanospheres--two with a {Mo72Fe30} core and one with a {W72Fe30} core by means of X-ray absorption spectroscopy, X-ray magnetic circular dichroism (XMCD), SQUID magnetometry, and complementary theoretical approaches. Furthermore, we present detailed studies of the Fe(3+)-to-Fe(2+) photoreduction process, which is induced under soft X-ray radiation in these molecules. We observe that the photoreduction rate greatly depends on the ligand structure surrounding the Fe ions, with negatively charged ligands leading to a dramatically reduced photoreduction rate. This opens the possibility of tailoring such polyoxometalates by X-ray spectroscopic studies and also for potential applications in the field of X-ray induced photochemistry.

Magnetic and electronic properties of the iron-containing polyoxotungstate [Fe4(H2O)10(β-SbW9O33)2]6−

The magnetic and x-ray photoelectron spectroscopy (XPS) studies on the transition metal substituted, dimeric polyoxotungstate [Fe4(H2O)10(β-SbW9O33)2]6− are reported. The magnetic data were analyzed by using an isotropic Heisenberg Hamiltonian. The ground state of the frustrated molecule has a total spin of S=2. The XPS Fe 2p spectra suggest a 2+ formal valence state. The deviation from the contained Fe3+ ions can be explained by charge-transfer effects.

Synthesis, Structure, and Valency Verification of a Mn6IIIO2-Cluster

Abstract A new oxime-based hexanuclear MnIII complex containing the structural core [Mn6III(μ3-O)2] was synthesized through a general route. We describe the preparation and characterization of the manganese(III) complex [Mn6III(μ3-O)2(Salox)6(CH3CH2OH)4{(CH3)3CCOO}2] by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). Therefore we offer the first core level XPS, and XAS reference spectra of polynuclear complexes comprising only Mn(III) ions in octahedral surrounding.