Scott P. Sellers

New Magnetically Coupled Bimetallic Complexes as Potential Building Blocks for Magnetic Materials

Long-lived organic cation radical species, [1I]−and [2I]−, are formed when bimetallic CoIII or VV(O) complexes of a new binucleating ligand are oxidized by one electron. The VV(O) complex, [2I]−, has a total spin, ST, of 1/2, while the robust CoIII complex, [1I]−, has ST=3/2. The figure shows the spin arrangement within the complexes as deduced from combined EPR and SQUID measurements. The ferrimagnetic system, [1I]−, has both CoIII spin centers aligned in a common direction, an important step towards building ferromagnetic or ferrimagnetic network solids.

Characterization and structures of the 2,2,7-trimethyl-3,5-octanedionate chelates of cerium(IV) and terbium(III)

Abstract The complexes Ce(tod)4 and Tb2(tod)6 were synthesized using hydrated metal nitrates and the β-diketone ligand H(tod), (tod=2,2,7-trimethyl-3,5-octanedione) with base neutralization. The metal complexes have been characterized by X-ray crystallography, elemental analysis, infrared spectroscopy, mass spectrometry, differential scanning calorimetry, and thermogravimetric analysis. The structure of Ce(tod)4 represents a new polymorph for tetrakis cerium chelates and Tb2(tod)6 is the first reported dimeric β-diketonate structure for terbium. These materials are promising precursor sources of cerium and terbium for thin film deposition, and are highly soluble in supercritical carbon dioxide, making them surrogates for hazardous waste remediation using supercritical fluid extraction.

An Internal Hyperfine Field of 62.4 T in Ferromagnetically Ordered α-Iron(II) Octaethyl-Tetraazaporphyrin

Abstract We report on the magnetic properties of the molecular solids derived from square-planar, neutral iron(II) octaethyltetraazaporphyrin, FeOETAP. This compound exists as two polymorphs, α and β. dc SQUID and ac susceptometry measurements (1–1000 Hz) show that the α polymorph orders as a soft molecular ferromagnet below TCurie = 2.8 K, whereas the β form, with the same number of unpaired spins and a similar g value, exhibits zero-field splitting to a non-magnetic ground state. 57Fe-Mossbauer spectroscopy indicates that α-FeOETAP exhibits a remarkably large internal hyperfine field, Hint, of 62.4 T. This, to our knowledge, is the highest value of Hint ever reported for Fe, regardless of its spin state.

Ac Susceptibility Studies of New and Familiar Magnetic Molecular Solids

ac Susceptometry has been used to study a number of magnetic molecular solids including a new compound, Mn(II) octaethyltetraazaporphyrin, {alpha}-MnOETAP, and decamethylmanganocenium tetracyanoethenide, Mn(Cp*){sub 2}{center_dot}TCNE, a previously reported molecule-based ferromagnet. Both of these compounds exhibit signatures of ferromagnetism including significant hysteresis below 2 K and rapidly increasing {chi}T (where {chi} is the molar susceptibility) with decreasing temperature. However, their ac susceptibility data show relatively strong dependence of {chi}{prime} and {chi}{double_prime} on the frequency of the applied field, indicating a spin-glass state. Other molecular ferromagnetic solids examined show much less sensitivity. These studies indicate that the standard practice of characterization by dc and ac susceptometry at a single frequency are clearly insufficient for identifying the magnetic state of a molecular solid.