Bonding magnetic properties

J. M. Rawson and F. Palacio, Magnetic Properties of Thiazyl Radicals, Structure and Bonding, 100, 93 (2001). 

In his valence bond theory (VB), L. Pauling extended the idea of electron-pair donation by considering the orbitals of the metal which would be needed to accommodate them, and the stereochemical consequences of their hybridization (1931-3). He was thereby able to account for much that was known in the 1930s about the stereochemistry and kinetic behaviour of complexes, and demonstrated the diagnostic value of measuring their magnetic properties. Unfortunately the theory offers no satisfactory explanation of spectroscopic properties and so was... 

Apart from TiO and the lower halides already mentioned, the chemistry of these metals in oxidation states lower than 3 is not well established. Addition compounds of the type [TiCl2L2] can be formed with difficulty with ligands such as dimethylformamide and acetonitrile, but their magnetic properties suggest that they also are polymeric with appreciable metal-metal bonding. However, the electronic spectra of Ti in TiCl2/AlCl3 melts and also of Ti incorporated in NaCl crystals (prepared by... 

Until about 20 years ago, the valence bond model discussed in Chapter 7 was widely used to explain electronic structure and bonding in complex ions. It assumed that lone pairs of electrons were contributed by ligands to form covalent bonds with metal atoms. This model had two major deficiencies. It could not easily explain the magnetic properties of complex ions. 

A major weakness of valence bond theory has been its inability to predict the magnetic properties of molecules. We mentioned this problem in Chapter 7 with regard to the 02 molecule, which is paramagnetic, even though it has an even number (12) of valence electrons. The octet rule, or valence bond theory, would predict that all the electrons in 02 should be paired, which would make it diamagnetic. 

Relationships between covalency, interatomic distances and magnetic properties in halides and chal-cogenides. R. D. Shannon and H. Vincent, Struct. Bonding (Berlin), 1974,19,1-43 (50). 

One of the reasons for my having attacked this problem in 1938 was that I was thoroughly dissatisfied with the claim of some physicists that only the s electrons were involved in the cohesion of the transition metals the observed magnetic properties were said to show that the bonding in Ni involves 0.61 s electrons per atom, that in Co involves 0.71, that in Fe involves 0.22, and that in Cu involves 1 (the d shell for copper having its full complement of 10 electrons). The physical properties of these 297 0022-4596/84 3.00... 

Chapter 11. Hemoglobin Oxygen Bonding and Magnetic Properties 849... 

Complexes. The structure of an n a charge-transfer complex between quinoxaline and two iodine atoms has been obtained by X-ray analysis and its thermal stability compared with those of related complexes. The hydrogen bond complex between quinoxaline and phenol has been studied by infrared spectroscopy and compared with many similar complexes. Adducts of quinoxaline with uranium salts and with a variety of copper(II) alkano-ates have been prepared, characterized, and studied with respect to IR spectra or magnetic properties, respectively. 

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