Spin polarized neutron diffraction

It is a somewhat surprising fact that information about vibrational frequencies and bond lengths in very common and important ions is very sparse. Clearly, many more such determinations are necessary. Only this year, for example, have data become available which enable metal-ligand displacements on electron removal for the aquo Fe(II)/Fe(III) and Co(II)/Co(III) systems to be obtained. In view of the importance of these partially unpublished data, I have reproduced them in Table VI. The values of A for the Fe and Co systems are 0.128-0.137, and 0.208 8 respectively. The variability of the Fe results points to the fact that caution must be exercised in using data obtained in crystal lattices for a solution environment. Spin-polarized neutron diffraction studies on the structure of solu-... 

Papoular, R.J. and Gillon, B. (1990) Maximum entropy reconstruction of spin density maps in crystals from polarized neutron diffraction data, Europhys. Lett., 13(5), 429 134. 

Baron, V., Gillon, B., Plantevin, O. et al. (1996) Spin-density maps for an oxamido-bridged Mn(II)Cu(II) binuclear compound. Polarized neutron diffraction and theoretical studies, J. Am. Chem. Soc., 118, 11822-11830. 

Zheludev, A., Grand, A., Ressouche, E. et al. (1994) Experimental determination of the spin density in the tetracyanoethenide free radical, [TCNE]-, by single-crystal polarized neutron diffraction, a view of a 71 orbital, J. Am. Chem. Soc., 116,7243-7249. 

The joint use of X-ray and neutron diffraction data is particularly expedient. Firstly, the interaction between the magnetic moments of neutrons and electrons is the basis for polarized-neutron diffraction, from which the unpaired spin density in a system can be derived. The diffraction of spin-polarized neutrons is an important technique, beyond the scope of this volume. Secondly, the interaction between neutrons and the atomic nuclei, which is the basis for structure determination by neutron diffraction, leads directly to information on the positions and mean-square vibrations of the nuclei. 

A detailed study of the spin density and bonding of the [CrFel3- ion in K3[CrF6] has appeared.1067 The results of polarized neutron diffraction experiments1068 were reinterpreted. A chemically based model of the [CrF6]3- ion has been fitted to the 92 observed magnetic structure factors by a least squares procedure. The spin density in the chromium(III) orbitals has t2g symmetry 06spin density centred on the... 

The X-ray and neutron diffraction data mentioned previously have been used in conjunction with the technique of polarized neutron diffraction (at 4.2 K) to deduce spin-density distributions in [MnPc].519,520 In further investigations514 it proved possible to determine individual 3d and 4s orbital populations on the manganese ion together with an estimate of 24% for the d-orbital electron density delocalized in the macrocyclic ring. From these studies it appears that the charge on the manganese is approximately +1 this charge appears to be achieved primarily by the loss of a 3d electron rather than a 4s electron. 

Polarized neutron diffraction makes it possible to measure magnetic structure factors and thus to obtain the distribution of unpaired spins in magnetic materials (see, e.g., Ref. 201). Let us discuss here the use of this technique for the study of low-dimensional organic conductors. 

Cu(II) region. Such a view is supported by the spin density map of Fig. 29, deduced from a polarized neutron diffraction investigation (58). 

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