The Iron Group

Carbides of the Iron Group Metals. The carbides of iron, nickel, cobalt, and manganese have lower melting points, lower hardness, and different stmctures than the hard metallic materials. Nonetheless, these carbides, particularly iron carbide and the double carbides with other transition metals, are of great technical importance as hardening components of alloy steels and cast iron. 

Catalysts for SW tube formation are not confined to the iron-group metals. Some elements of the lanthanide series can catalyze the formation of SW tubes. 

Table 26.2 also reveals a diminished tendency on the part of these elements to form compounds of high coordination number when compared with the iron group and, apart from [Co(N03)4], a coordination number of 6 is rarely exceeded. There is also a marked reluctance to form oxoanions (p. 1118). This is presumably because their formation requires the donation of n electrons from the oxygen atoms to the metal and the metals become progressively... 

The complex cyanides of transition metals, especially the iron group, are very stable in aqueous solution. Their high co-ordination numbers mean the metal core of the complex is effectively shielded, and the metal-cyanide bonds, which share electrons with unfilled inner orbitals of the metal, may have a much more covalent character. Single electron transfer to the ferri-cyanide ion as a whole is easy (reducing it to ferrocyanide, with no alteration of co-ordination), but further reduction does not occur. 

Rosenblum M (1965) Chemistry of the iron group metallocenes (part I) Wiley, New Y ork... 

But similar calculations for the iron-group ions show marked disagreement with experiment, and many attempts were made to explain the discrepancies. The explanation is simple in many condensed systems the perturbing effect of the atoms or molecules surrounding a magnetic atom destroys the contribution of the orbital momentum to the magnetic moment, which is produced entirely by the spin moments of unpaired electrons.40... 

The whole question is clarified when considered in relation to the foregoing quantum mechanical treatment of the electron-pair bond. For the iron-group elements the following rules follow directly from that treatment and from the rules of line spectroscopy. 

Finally, the use of simple valence bond theory has led recently to a significant discovery concerning the nature of metals. Many years ago one of us noticed, based on an analysis of the experimental values of the saturation ferromagnetic moment per atom of the metals of the iron group and their alloys, that for a substance to have metallic properties, 0.72 orbital per atom, the metallic orbital, must be available to permit the unsynchronized resonance that confers metallic properties on a substance.34 38 Using lithium as an example, unsynchronized resonance refers to such structures as follows. 

For a review of cyclopentadienone derivatives and of attempts to prepare the parent compound, see Oglianiso, M.A. Romanelli, M.G. Becker, E.I. Chem. Rev., 1965,65,261. For a monograph on metallocenes, see Rosenblum, M. Chemistry of the Iron Group Metallocenes Wiley NY, 1965. For reviews, see Lukehart, C.M. Fundamental Transition... 

Rosenblum, M., Chemistry of the Iron Group Metallocenes. Wiley, New York. 1965. 

Rosenblum M, Abbate FW (1966) The problem of metal atom participation in electrophilic substitution reactions of the iron group metallocenes. J Am Chem Soc 88 4178 184... 

Experience shows that in the deposition of a number of metals (mercury, silver, lead, cadmium, and others), the rate of the initial reaction is high, and the associated polarization is low (not over 20 mV). For other metals (particularly of the iron group), high values of polarization are found. The strong inhibition of cathodic metal deposition that is found in the presence of a number of organic substances (and which was described in Section 14.3) is also observed at mercury electrodes (i.e., it can be also associated with the initial step of the process). 

The origin of chemical elements has been explained by various nuclear synthesis routes, such as hydrogen or helium burning, and a-, e-, s-, r-, p- and x-processes. "Tc is believed to be synthesized by the s (slow)-process in stars. This process involves successive neutron capture and / decay at relatively low neutron densities neutron capture rates in this process are slow as compared to /1-decay rates. The nuclides near the -stability line are formed from the iron group to bismuth. 

In the Galaxy, we know 93 (3 Cephei (Stankov Handler 2004) and about 100 SPB-type stars (De Cat et al. 2004). They fall within the instability strips predicted by the theory. The K-mechanism driving pulsations in (3 Cephei and SPB stars strongly depends on the abundance of the iron-group ions in the driving zone at temperatures around 2 x 105 K (Dziembowski Pamyatnykh 1993, Dziembowski et al. 1993). Theoretical models predict that pulsations of (3 Cephei and SPB-type vanish for Z = 0.01 and Z = 0.006, respectively (Pamyatnykh 1999). 

Refractory materials in primitive meteorites were investigated first as they have the best chance of escaping homogenization in the early solar system. Inclusions in C3 carbonaceous chondrites exhibit widespread anomalies for oxygen and the iron group elements. Only a few members, dubbed FUN (for Fractionated and Unknown Nuclear effects), also display anomalous compositions for the heavy elements. Anomalies in inclusions have generally been connected with explosive or supernova nucleosynthesis. 

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