K.-Y. Choi

A Planar {Mn19(OH)12}26+ Unit Incorporated in a 60‐Tungsto‐6‐Silicate Polyanion

Polyoxometalates (POMs) are discrete metal–oxo anions of early transition-metals in high oxidation states (e.g. W, Mo, V) and they are usually synthesized in aqueous, acidic medium. Most classical POMs are based on edgeand corner-shared MO6 octahedra. However, the recently discovered POM subclass of noble metalates comprises linked square-planar MO4 units (M = Pd , Au). Lacunary (vacant) POMs can be considered as inorganic, multidentate ligands, and hence they are good candidates for the encapsulation of large, multinuclear dand f-block metal–oxo fragments, sometimes resulting in compounds with interesting magnetic properties. A pioneering result in this area was the synthesis of [Mn12(CH3COO)16(H2O)4O12] (Mn12) by Lis in 1980, which was shown to exhibit single-molecule magnet (SMM) behavior by Gatteschi s group 13 years later. During the past two decades many high-nuclearity, transition-metal based, coordination complexes with interesting electronic and magnetic properties have been prepared. High-nuclearity manganese complexes have been amongst the most studied in this class, and there are examples containing up to 84 manganese ions. 6] To date there are only a few high-nuclearity manganese– oxo-containing POMs, such as {[XW9O34]2[Mn III 4Mn II 2O4(H2O)4]} 12 (X = Si, Ge) and [Mn13Mn O12(PO4)4(PW9O34)4] 31 . Herein we report the synthesis and structure as well as the magnetic and electrochemical properties of a 19 manganese(II) center containing 60-tungsto-6-silicate, [Mn19(OH)12(SiW10O37)6] 34 (1), which was isolated as a hydrated sodium salt, Na34[Mn19(OH)12(SiW10O37)6]·115H2O (Na-1). Single-crystal X-ray diffraction revealed that polyanion 1 consists of a cationic {Mn19(OH)12} 26+ (Mn19) assembly stabilized by six dilacunary [a-SiW10O37] 10 units resulting in a structure with S6 point-group symmetry (Figure 1, top). To the best of our knowledge, 1 is the highest nuclearity manganesecontaining POM known to date. All 19 Mn ions lie in the same plane forming a hexagonal structure based on edgeshared MnO6 octahedra. The Mn II ions in Mn19 are connected by a total of twelve m3-hydroxo bridges, as determined by bond valence sum (BVS) calculations (Supporting Information, Table S1). The discrete Mn19 nanosheet (Figure 1, bottom) is held in place by six dilacunary [a-SiW10O37] 10

Structural Tailoring Effects on the Magnetic Behavior of Symmetric and Asymmetric Cubane‐Type Ni complexes

Using two kinds of carboxylate ligands with small but significant differences in steric size, symmetric and asymmetric Fe(II) and Ni(II) cubanes have been synthesized in a controlled fashion. Fast sweeping pulsed field measurements showed magnetization hysteresis loops for two cubane-type molecular complexes, [Ni4(μ-OMe)4(O2CAr(4F-Ph))4(HOMe)8] and [Ni4(μ-OMe)4(O2CAr(Tol))4(HOMe)6], thus suggesting single-molecule magnet behavior. To differentiate the magnetic properties between the symmetric and asymmetric cubanes, detailed electron paramagnetic resonance (EPR) measurements were performed. From the EPR data, taken at various frequencies and temperatures, zero-field splitting parameters D, E, and other higher-order parameters for both cubane samples were extracted. Compared to the symmetric Ni-cubane, the asymmetric one shows an increase in the D and E values by about 20%, thereby suggesting structural engineering effects on the magnetic properties. By using the magnetic parameters determined by EPR, a static magnetization curve at 2 K and a temperature dependence of the magnetic susceptibility were simulated. A good agreement between theoretical and experimental data confirms the validity of the values obtained from EPR measurements.

Softened magnetic excitations in the s = 3/2 distorted triangular antiferromagnet α-CaCr2O4.

The spin dynamics and magnetic excitations of the slightly distorted triangular s = 3/2 system α-CaCr (2)O (4) are investigated by means of Raman spectroscopy and electron spin resonance (ESR) to elucidate its peculiar magnetic properties. Two-magnon excitations in circular RL symmetry show a multi-maximum structure with a dominant spectral weight at low energies. The temperature dependence of the ESR linewidth is described by a critical broadening ΔH(pp)(T) is proportional to (T-T(N ))(-p) with the exponent p = 0.38(5) - 0.48(3) for temperatures above T(N) = 42.6 K. The exponent is much smaller than that of other s = 3/2 triangular lattices. This is ascribed to soft roton-like modes, indicative of the instability of a helical 120° phase. As an origin we discuss a complex spin topology formed by four inequivalent nearest neighbor and sizable next-nearest neighbor interactions.

Anomalous frequency and intensity scaling of collective and local modes in a coupled-spin tetrahedral system Cu 2 Te 2 O 5 Cl 2

We report on the magnetic excitation spectrum of the coupled spin tetrahedral system Cu

Dimethylammonium copper formate ((CH3)2NH2)Cu(HCOO)3: A metal-organic framework with quasi-one-dimensional antiferromagnetism and magnetostriction

_{2}

Planare {Mn19(OH)12}26+-Einheit in einem 60-Wolframato-6-silicat- Polyanion†

Te

Mn55 NMR study of La1-xSrxMnO3(x=0.13)

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55Mn NMR study of La1-xSrxMnO3 (x = 0.13)

O

Muon spin relaxation study of spin dynamics in the extended kagome systems YBaCo4O7+δ (δ=0,0.1)

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Ferromagnetic quantum criticality in Sm1−xLaxNiC2 ( x=0.85 , 0.92, and 0.96)

Cl