Spin Density Distributions from Single Crystal Data

7 Spin Density Distributions from Single Crystal Data 

Experiments with powders yield (Sg) and in certain unusual situations, significant data on the shape of f[x) have been obtained. Even so, only a spherical average is generally determined which, although adequate to discuss the high spin and / materials studied [MnO (48) and BaTbOs (2S)], can conceal much interesting information. 

Single crystal experiments are essential in the detailed investigation of spin density distributions. The anisotropy in the form factor at a given x can be measured and if a fairly extensive set of information is collected the spin density may be determined by Fourier transformation techniques. 

In such work, particularly in the case of metals, the spin density at any position in the unit cell cannot be uniquely assigned to a particular atom ). The discussion of magnetic scattering given above implicitly assumes nonoverlapping spins, and 

1 ) It is, however, possible to determine in some instances than spin density has been transferred to formally nonmagnetic atoms by observing a magnetic component for reflections which otherwise should arise from nuclear scattering only [e.g., on F in Mnp2 (57) and 02- in Y.sFe50i2 (73) (see below)]. 

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The experimental techniques employed to resolve the hfc s are EPR, ENDOR and TRIPLE resonance (reviewed in ref. 4). Detailed results were obtained recently for D+ in RC single crystals of Rhodobacter (Rb.) sphaeroides. Unambiguous assignments of the hf tensors to specific nuclei were achieved by a comparison with the X-ray structure data of the RC and predictions from molecular orbital (MO) calculations.The results of this investigation show that the unpaired electron is asymmetrically distributed over the dimer halves Dl and Dj with approximately 68% of the spin density on Dl (L and M subscripts denote the protein subunits binding the BChls constituting the dimer). 

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