Magnetism and Spin States

Spin Quantum Number, S Number of Unpaired Electrons Multiplicity Magnetic Moment (Bohr Magnetons)  

FIGURE 15.1 A model for discussion of open-shell organometaUic compounds (dppe = Ph2CH2CH2PPh2). (a) Number of nonbonding levels (dotted box) depends on the coordination number, m. The number of electrons, n, available to fill these levels depends on the tf configuration. (b,c) For six- and seven-coordinate species, such as the ones shown, two spin states are possible, 5 = 0 and 5 = 1. Thick lines denote sets of orbitals. 

Influence of Spin State Changes on Kinetics and Thermodynamics 

one spin state may be very reactive, the other not. Where alternate spin states are possible, there may be a change of spin state in a 

FIGURE 15.2 (a) A single n-donor lone pair of PPI12 splits the d orbitals so that the four d electrons prefer to occupy the two lower levels leading to an 5 = 0 state, (b) The pair of ii-donor lone pairs of Cl split the d orbitals so that the four d electrons now prefer to occupy the three lower levels as shown, leading to an 5 = 1 state. TTie two unpaired electrons are parallel according to Hund s rule. 

Diamagnetic materials are weakly repelled by a magnetic field gradient while paramagnetic ones are attracted. From the weight change of a sample in the 

As discussed by Poli, a simple picture, based on the ionic model, starts from the coordination number, represent in what follows by the symbol m, a value determined by Eq. 15.1 for Ae complex Of die nine valence orbitals 

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Intermediate phases between these two extremes can be formed. The most stable of these are Sr5Mn50i3 and Sr7Mn7019. In both of these phases the structure consists of both square pyramids, containing Mn3+ and octahedra containing Mn4+ (Fig. 9.8c and 9.8d). These structures exhibit charge ordering, but the magnetic and spin states of the Mn ions has yet to be resolved. 

The description of the orbital and spin states of an electron in terms of the quantum numbers n, /, m, and s, and the calculation of the total angular momentum of a number of electrons in an atom in terms of J are outlined in Chapter 2. From that discussion, together with the above, it follows that an electron with orbital quantum number / possesses a total magnetic moment /(/ + and this can be oriented with respect to a magnetic field in... 

The Mossbauer effect is sensitive to the oxidation and spin state of iron and the environment around the iron nucleus therefore different chemical species yield different Mossbauer spectra. Furthermore all spin states and oxidation states of iron are accessible to the technique. There are three main components of a Mossbauer spectrum. The isomer shift arises from the electron density at the 57Fe nucleus the quadrupole splitting results from the electric field gradient produced by electrons and ions around the 57Fe nucleus, and the nuclear Zeeman splitting is sensitive to the spin state and magnetic coupling of the iron. 

The non-diffusional methods of bringing D and A together may also result in payment of an ultimate price of diminished overall efficiency since BET within contact ion pairs is usually more rapid than in solvent separated ion pairs (see below). Indeed, the most important aspect of the forward electron transfer is that it presets the conditions for the competition between BET and the fragmentation reaction. The reactive intermediates (ion pairs) are generated in specific solvation and spin states. That state can be controlled or at least influenced by a selection of the excited state component, the ground state component and solvent [20], as well as by magnetic and electric fields [36]. 

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