Louis C. W. Baker

Exchange Interactions between Pairs of Differing Magnetic Spins in Heteropoly Complexes

Coupled pairs of differing magnetic spins in tungsto‐heteropoly complexes have been investigated by studying the magnetic susceptibility over the temperature range 2–300°K. The two sites of the magnetic ions are surrounded by oxygen ions in octahedral and tetrahedral coordinations with one oxygen ion in common. The ions studied were Co2+, Co3+, and Fe3+ in a total of six combinations on the two sites, offering a unique set of symmetries and ions for examining super‐exchange effects. A closed form for the susceptibility has been obtained on assuming the spin Hamiltonian H=β (g1S1+g2S2)· H‐JS1· S2, allowing for the possibility of g1≠ g2, S1≠ S2. Fitted values of J/k range from −6 to −70°K depending on the combinations of ions. The experimental agreement with the spin Hamiltonian for all cases studied is satisfactory for this system.

Magnetic exchange interactions in the heteropoly complexes [M4(H2O)2(PW9O34)2]10− [M=Co(II) and Cu(II)]

The magnetic properties of the heteropolyanions [M4(H2O)2(PW9O34)2]10− [M=Co(II) and Cu(II)] down to 4 K are reported. Their individual heteropoly molecules contain a rhomblike arrangement formed by four coplanar MO6 octahedra sharing edges. The magnetic properties support an intramolecular ferromagnetic exchange in the Co(II) tetramer, and antiferromagnetic exchange in the Cu(II) tetramer. These behaviors are discussed assuming anisotropic exchange in the Co(II) compound, and Heisenberg exchange in the Cu(II) compound.

Magnetic measurements with a SQUID magnetometer: Possible artifacts induced by sample-holder off-centering

Asymmetries in sample holders used for magnetic measurements on magnetometers based on induction methods, such as those equipped with SQUID sensors, can lead to substantial errors and/or important artifacts which resemble phase transitions. They occur under the conditions for which sample and/holder have signals of opposite sign, but are nearly equal in magnitude. The most serious errors can occur often, but not exclusively, for compounds having intermediate magnetic dilution. We present here a general discussion of the problem illustrated by measurements of a polyoxometallate with the known Keggin structure K6[Fe(III)W12O40]⋅nH2O, done on a SHE VTS model 905. While one of the obvious solutions to this problem is the use of holders with a signal much smaller than that of the sample, it would be preferable if, in addition, the holder had a response of the same sign as that of the sample, for all temperatures and fields measured.

Useful chemical information obtained by use of common counterions as internal calibrants in X-ray photo-electron spectra of inorganic complex ions

Abstract It is shown that the accuracy and precision, and hence the value for bonding-structure studies, in relative binding energy measurements can be enhanced if a common counterion is employed. The differences in chemical shifts between the peaks for the atoms under consideration and for a common counterion in twenty-nine compounds are measured. This technique reduces charging effect errors, which otherwise often occur when non-conducting samples (e.g., salts) are measured relative to a traditional external calibrant. The improvements in accuracy and precision are demonstrated by using the cesium salt of twenty-nine heteropoly and isopoly anions in more than seventy-five different runs. Oxygen 1 s , tungsten 4 d , and molybdenum 3 d binding energies are measured relative to the cesium 3 d ionization potential. In this work the cesium counterion is assumed to be chemically invariant. For the relative binding energies that are studied, no dependence on the charge of the anion is observed. A linear relation seems to exist between the oxygen Is binding energies (measured relative to Cs) and the oxygen-to-tungsten ratio in five isopoly anions. This latter finding may serve as a useful aid in studies related to the synthesis of new compounds.

Blue Electron Distributions in Diamagnetic Reduced Heteropoly Tungstates. Insights Concerning Conduction Pathways and Spin Coupling Patterns. 183W NMR Chemical Shift Calculations

This is a paper in a continuing series about roles played by delocalized “blue” electrons and by unpaired electrons in determining properties and structures of heteropoly complexes and their blue reduction products. 183W NMR data for α-[SiW12O40]4-, α-[P2W18O62]6-, α-[P2Mo3W15O62]6-, α-[P2Mo6W12O62]6-, α1-[P2MoW17O62]6-, and α2-[P2MoW17O62]6- and the diamagnetic 2-electron reduction products of these, are combined with our earlier interpretations, yielding new insights about blue electron distributions, pathways for blue electron conduction and delocalization, and energy factors that determine these. MoVI is more easily reduced than WVI. Therefore, in each diamagnetic completely spin-coupled 2e-reduction product of the monomolybdenum derivatives, one of the added electrons is “anchored” on the Mo while the other is rapidly thermally hopping among several belt W’s.