Iron Group Metals

Reed et al. (12) and Masuda et al. (56) have elucidated the structures of five-coordinate iron(III) complexes Fe(tpp)C104 (Fig. 3) and Fe(oep)-C104 by X-ray crystallography. In both complexes, the perchlorate is linked to the metal ion through one of the oxygen atoms at the apical site of the square pyramid. The Fe—O distance is slightly shorter in 

Reaction of ferrous and ferric perchlorates with pyzNO (L) in EtOH-teof yields complexes of the formulas FeL3(ClC 4)2 (red) and FeL ClO (straw yellow), respectively (48,49). The ferrous complex, on exposure to moisture, adds on a molecule of water, turning orange. The resulting aquo complex shows IR bands characteristic of coordinated perchlorate (Table III). A number of Fe(II) and Fe(IH) complexes, containing donor molecules like mmpp, puHNO, phzNO, phzNC 2, quxNO, quxNC 2, and adH, have been proposed to involve unidentately or bidentately coordinated perchlorates (21, 35, 39-41, 53). 

Christian and Roper (57) have isolated white crystals of a six-coordinate ruthenium(II) complex, fmns-RuH(C0)(p-tNC)(Ph3P)20C103 by treating the corresponding chloro complex with AgC104 in EtOH. The coordinated perchlorate can be readily displaced by CO or Ph3P. 

---

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. 

The magnetic criterion is particularly valuable because it provides a basis for differentiating sharply between essentially ionic and essentially electron-pair bonds Experimental data have as yet been obtained for only a few of the interesting compounds, but these indicate that oxides and fluorides of most metals are ionic. Electron-pair bonds are formed by most of the transition elements with sulfur, selenium, tellurium, phosphorus, arsenic and antimony, as in the sulfide minerals (pyrite, molybdenite, skutterudite, etc.). The halogens other than fluorine form electron-pair bonds with metals of the palladium and platinum groups and sometimes, but not always, with iron-group metals. 

The oxygen reactions occur at potentials where most metal surfaces are covered by adsorbed or phase oxide layers. This is particularly true for oxygen evolution, which occurs at potentials of 1.5 to 2.2 V (RHE). At these potentials many metals either dissolve or are completely oxidized. In acidic solutions, oxygen evolution can be realized at electrodes of the platinum group metals, the lead dioxide, and the oxides of certain other metals. In alkaline solutions, electrodes of iron group metals can also be used (at these potentials, their surfaces are practically completely oxidized). 

Many types of oxide layers have a certain, not very high electrical conductivity of up to 10 to 10 S/cm. Conduction may be cationic (by ions) or anionic (by or OH ions), or of the mixed ionic and electronic type. Often, charge transport occurs by a semiconductor hole-type mechanism, hence, oxides with ionic and ionic-hole conduction are distinguished (in the same sense as p-type and n-type conduction in the case of semiconductors, but here with anions or cations instead of the electrons, and the corresponding ionic vacancies instead of the electron holes). Electronic conduction is found for the oxide layers on iron group metals and on chromium. 

Anodic passivation can be observed easily and clearly with iron group metals and alloys as shown in Fig. 11-10. In principal, anodic passivation occurs with most metals. For instance, even with noble metals such as platinum, which is resistant to anodic dissolution in sulfuric acid solutions, a bare metal surface is realized in the active state and a superficial thin oxide film is formed in the passive state. For less noble metals of which the affinity for the oxide formation is high, the active state is not observed because the metal surface is alwa covered with an oxide film. 

Perchlorate ion complexes, 28 255-299 with cobalt group metals, 28 265-268 coordination types, 28 256-260 with copper group metals, 28 273-283 with early transition metals, 28 260-263 electronic spectra. 28 258-259 ESR spectra, 28 260 infrared and Raman spectra, 28 257-258 with iron group metals, 28 263-265 with lanthanides, 28 260-265, 287-288 magnetic susceptibility, 28 260 molar conductivities, 28 260 with nickel group metals. 28 268-273 X-ray crystal structure analysis, 28 256-257... 

In the last 10 years, the electrodeposition of the new Zn-Me alloys and ternary alloys was studied. The influence of plating conditions and different additives for deposition of alloys of Zn with iron group metals was studied in detail. 

The electrodeposition of zinc and iron group metal alloys (Zn-Co, Zn-Ni, Zn-Fe) on Cu electrode was also studied in methanol bath [443]. 

Iron-Group Metals. SWNTs were first discovered by using the iron-group metals (Fe, Co, and Ni) as catalysts. When iron alone is used as a catalyst, a CH.,/Ar mixture must be used as buffer to produce SWNTs (8). However, the yield of SWNTs from iron alone is very low. 

The diameter of the SWNTs is typically 1.8-2.1 nm, thicker than the SWNTs produced from the iron-group metals (Fe, Co, Ni). On the other hand, a typical length of the tubes obtained from rare-earth catalysts is shorter (30 to 100 nm) than those obtained from the iron-group metals ( 1 (jliti). 

Mixtures of the Iron-Group Metals. It was first reported by Seraphin et al. (50) that a binary mixture of Fi and Ni yielded more abundant SWNTs than Fe or Ni alone catalyst. Saito et al. (51) showed that a mixture of Fe and Ni with the ratio of 1 1 (by weight) gave the highest yield of SWNTs, and deviation from the 1 to 1 composition reduced the yield. Approximately 10% of all the carbon in the raw soot (both the chamber and cathode soot) was incorporated into SWNTs at the highest yield. Diameters of SWNTs produced from Fe/Ni range from 0.9 to 1.4 nm, and the mode diameter is located in 1.1-1.2 nm. 

A Co/Ni alloy is the next active catalyst among the binary combinations within the iron-group metals in the arc discharge method (51). Laser vaporization of metal/ carbon composite in argon atmosphere at high temperature (1200°C) can also produce SWNTs (41). Guo et al. (41) reported that the Co/Ni alloy was the most effectual, with a yield of 50-90% in the laser ablation method. 

A discussion of other properties of hexahydrated ions and other complexes of the iron-group metals, including paramagnetic resonance and spin-orbit coupling constants evaluated from absorption spectra, has led to the conclusion that in both bipositive and tripositive metal-ion complexes the metal atom is close to electric neutrality.64... 

Rapid development of this area followed the discovery of routes to these complexes, either by ready conversion of terminal alkynes to vinylidene complexes in reactions with manganese, rhenium, and the iron-group metal complexes (11-14) or by protonation or alkylation of some metal Recent work has demonstrated the importance of vinylidene complexes in the metabolism of some chlorinated hydrocarbons (DDT) using iron porphyrin-based enzymes (15). Interconversions of alkyne and vinylidene ligands occur readily on multimetal centers. Several reactions involving organometallic reagents may proceed via intermediate vinylidene complexes. 

Iron-group metal Product, % 180°C. Middle oil above 180°C. ... 

Soneda Y., Duclaux L., Beguin F. Synthesis of high quality multi-walled carbon nanotubes from the decomposition of acetylene on iron-group metal catalysts supported on MgO. Carbon, 2002, 40(6), 965-969. 

A. R. Kudinov, M. I. Rybinskaya, Yu. T. Struchkov, A. I. Yanovskii, and P. V. Petrovskii, Synthesis of the First 30-Electron Triple-Decker Complexes of the Iron Group Metals with Cyclopentadienyl Ligands. X-Ray Structure of [(/ -C5H5)Ru (p,jy-C5Me5)Ru(jy-C5Me5)]PF6, J. Organomet. Chem. 336, 187-197 (1987). 

---