Magnetic moments of metal

Figure 7.9 Examples of calculating the magnetic moments of metal ions for and high-...

Metal clusters are compounds with metal-metal bonds. In the last few decades, the preparation and stractural determination of such species has been a very active field of inorganic chemistry. Almost all transition metals form such compounds. There is also a tendency of transition metals to form bonds with themselves. An extensive overlap of d orbitals is required for the formation of such compounds, and the bonding is best accounted for in terms of the molecular orbital theory." The short distances between metal atoms and the low magnetic moments of metal clusters speak in favor of metal-metal bonding, but the X-ray structural determinations have provided an unambiguous evidence. 

Figure 5b. Variation in the magnetic properties of metal clusters are investigated by measuring the depletion of a highly collimated cluster beam by an inhomogeneous magnetic field. Fe clusters and their oxides (FexO and Fex02) at several applied fields. The uniform depletion of Fe clusters indicates that their magnetic moments increase approximately linearly with number of atoms, as would be anticipated for incipient ferromagnetic iron. Unexpected, however, is the much larger depletion of iron oxide clusters.

Two copper(II) complexes of 2-acetylpyridine thiosemicarbazone, 8, were included in a study of complexes of 2-formylpyridine thiosemicarbazone [169]. [Cu(8-H)OAc] has a magnetic moment consistent with a monomeric copperfll) center and both it and [Cu(8)Cl2] have d,2-y2 ground state ESR spectra (Table 2). A d-d envelope and a magnetic moment of 1.68 B.M. have led others [178] to propose a distorted tetrahedral environment with metal-metal interaction for the brown complex, [Cu(8)Cl2]. 

Formylisoquinoline S-methyldithiocarbazate, 19, forms green [Cu(19-H)Cl], and its magnetic moment of 1.80 B.M. and v(d-d) = 16000 cm are cited as evidence for planar stereochemistry [146]. It and the analogous zine complex showed the greatest antitumor activity of metal eomplexes tested. 

Methyl-5-amino-l-formylisoquinoline thiosemicarbazone, 22, also yields cobalt(II) complexes from unheated methanol solution [202]. However, due to this ligand s added steric requirements, a complex, [Co(22)Cl2], with one ligand per metal ion center is formed. This brown solid has a magnetic moment of 4.42 B.M., is a non-electrolyte, has coordination of a neutral NNS ligand, and the electronic spectrum indicates approximate trigonal bipyramidal stereochemistry. 

Fe(6-Mepy)2(py)tren] (004)2 Doped in PSS. Magnetic susceptibilities measured for a microcrystalline sample of the complex produce a magnetic moment value = 0.36 pg at 10 K and 0.61 pg at 150 K, followed by a gradual increase to Peff = 2.80 pe at 311 K [138]. Thus 26% of the complexes are in the HS state at 300 K if a magnetic moment of 5.1 Pe is assumed for the pure HS compound. On the other hand, the complex doped into a polystyrene sulfonate (PSS) film does not provide any evidence for a thermal population of the HS state up to 340 K as demonstrated by variable-temperature UV-VIS and Mossbauer spectra. In fact, all the complexes doped into the PSS film are in the LS state at temperatures below 340 K. However, if irradiated by a single pulse of a Q-switched Nd/YAG laser (532 mp), the complex is excited from the LS ground state to the HS J2 states via an intermediate MLCT state and the metal states. The subsequent back relaxation from the excited T2 state to the... 

On the other hand, internal magnetic fields at the iron nucleus arising from the magnetic moments of unpaired valence electrons can be much stronger than any applied field and their effect can easily exceed the quadrupole interaction. For instance, Mossbauer nuclei in magnetic materials such as metals or oxides may experience fields of 30-50 T even without applied field. Similarly, the typical... 

Sauer et al. [185] determined the gyromagnetic ratio g(9/2)/g(7/2) and the magnetic moment of the 6.2 keV level in Ta in two ways, (1) from the Zeeman split velocity spectrum of a metal source in a longitudinal field versus a Ta... 

In the Introduction the problem of construction of a theoretical model of the metal surface was briefly discussed. If a model that would permit the theoretical description of the chemisorption complex is to be constructed, one must decide which type of the theoretical description of the metal should be used. Two basic approaches exist in the theory of transition metals (48). The first one is based on the assumption that the d-elec-trons are localized either on atoms or in bonds (which is particularly attractive for the discussion of the surface problems). The other is the itinerant approach, based on the collective model of metals (which was particularly successful in explaining the bulk properties of metals). The choice between these two is not easy. Even in contemporary solid state literature the possibility of d-electron localization is still being discussed (49-51). Examples can be found in the literature that discuss the following problems high cohesion energy of transition metals (52), their crystallographic structure (53), magnetic moments of the constituent atoms in alloys (54), optical and photoemission properties (48, 49), and plasma oscillation losses (55). 

---