The Ga(84)R(20)(4-) [R = N(SiMe(3))(2)] species, which represents the largest metalloid cluster entity structurally characterized so far, has been electronically and topologically modified: Via changing the redox potential of the reaction solution, crystals different from those containing the Ga(84)R(20)(4-) anion can be isolated, featuring similar Ga(84)R(20)(3-) entities. An accurate crystal structure analysis via synchrotron radiation is presented, which might be the first step toward an understanding of the metallic conductivity and superconductivity of the Ga(84)R(20)(4-) cluster compound, physical properties which are singular in the field of metalloid clusters so far.
The new spin cluster [MnII4MnIII3(teaH)3(tea)3](ClO4)2×3MeOH realizes a
topological structure of mixed-valence manganese clusters which is especially
favorable for a high-spin ground state. The magnetic properties of the spin
cluster are studied numerically by exact diagonalization of the spin
Hamiltonian. By magnetic susceptibility two exchange constants are found:
J1/kB = − 1.28 K and J2/kB = + 4.25 K, which lead
to a S = 11 high-spin ground state. Electron spin resonance (ESR) measurements
at three frequencies 95, 190 and 285 GHz confirm the large spin of the ground
state and reveal an Ising anisotropy of the ground state which is
characterized by the spin Hamiltonian
H = α(Sz)2 + β(Sz)4 with
α/h.c. = − 0.08 cm−1 and β = − 2.1 × 10−4 cm−1. Ac-susceptibility shows thermally activated relaxation of the
magnetization for temperatures above T = 1 K with an activation energy
of ΔE/kB = − 19.5 K and a relaxation time of τ0 ≈ 10−8 s.
This paper presents measurements of the angular variation of the position and width of ESR lines in three mutually perpendicular planes of a single crystal of in the temperature range 12 - 200 K at two widely differing microwave frequencies. The analysis is carried out in terms of the anisotropic exchange and anisotropic Zeeman interaction. The variations of the anisotropy of the linewidth can be attributed to a temperature dependence of the orientation and the principal values of the exchange tensor.
Wir beschreiben Synthese und Kristallstrukturen von fünf neuartigen Eisen/hpdta‐Komplexen [{FeIII4(μ‐O)(μ‐OH)(hpdta)2(H2O)4}2FeII(H2O)4]·21H2O (2), (pipH2)2[Fe2(hpdta)2]·8H2O (4), (NH4)4[Fe6(μ‐O)(μ‐OH)5(hpdta)3]·20, 5H2O (5), (pipH2)1, 5[Fe4(μ‐O)(μ‐OH)3(hpdta)2]·6H2O (7), [{Fe6(μ3‐O)2(μ‐OH)2(hpdta)2(H4hpdta)2}2]·py·50H2O (9) und diskutieren den Aufbau dieser Verbindungen im Kontext weiterer, bereits von uns veröffentlichter, hpdta‐Komplexe (H5hpdta = 2‐Hydroxypropan‐1, 3‐diamin‐N, N, N′, N′‐tetraessigsäure). Sowohl bei der Charakterisierung der Reaktivität gegenüber Substraten wie Dimethylacetamid und CO2, als auch beim sukzessiven Aufbau der mehrkernigen Oxo/Hydroxo‐verbrückten Aggregate, sind terminale Wasserliganden, die durch pH‐Änderungen funktionalisiert werden können, von Bedeutung. Die Bildung, der unter hydrolytischen Bedingungen dargestellten Substanzen kann formal durch Kondensationsreaktionen erklärt werden und der homologe Aufbau der Komplexe erlaubt es, den Magnetismus quantitativ bis hin zum sechskernigen Aggregat 5 zu erforschen. Die Eisenatome in 1‐7 sind antiferromagnetisch gekoppelt; die Komplexe weisen S=0 Spin‐Grundzustände auf. Ein Einschluss anorganischer Ionenfragmente durch dimere {M2hpdta}‐Einheiten, wie wir es unlängst für das AlIII /hpdta‐System beschrieben haben, wird auch im zwölfkernigen Eisen(III)‐Aggregat 9 beobachtet.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.