Chromium Group Metals

The chromium group metal complexes containing hydrogen atoms in the p position are very unstable. The lowest oxidation state which the chromium group complexes (Table 4.15) possess in their compounds containing gM—C bonds equals +2. As the... 

Table 4.15. Properties of G-Carbyl Complexes of Chromium Group Metals...

These reactions occur quite readily [reaction (5.143)]. The carbonyl groups much more easily undergo substitution reactions in 18e carbyne complexes of chromium group metals than in M(CO)6 ... 

Almost all stable olefin complexes of the chromium group metals are derivatives of carbonyl and cyclopentadienyl compounds (Table 6.13). Most of the metal alkene compounds may be classified as one of the following groups ... 

The tendency for oxidation of arene complexes of chromium group metals M(arene)2 decreases in the series W Mo>Cr. The chromium compounds are conveniently oxidized to the Cr(arene) cations by air in the presence of water. 

Electroplated Metals and Alloys. The metals electroplated on a commercial scale from specially formulated aqueous solutions iaclude cadmium, chromium, cobalt, copper, gold, iadium, iron, lead, nickel, platinum-group metals, silver, tin, and ziac. Although it is possible to electroplate some metals, such as aluminum, from nonaqueous solutions as well as some from molten salt baths, these processes appear to have achieved Httie commercial significance. 

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. 

Interaction of metals with cyclopropenylidene to form stable complexes has been widely studied340 in the last two decades since the first reported synthesis of pentacarbonyl(2,3-diphenylcyclopropenylidene)chromium (see belowy4. Two groups of cyclopropenylidene metal derivatives may be distinguished neutral cyclopropenylidene complexes represented by two resonance forms, and the cationic cyclopropenylium transition metal complexes of groups 6 (Cr, Mo, W), 7 (Mn), 8 (Fe) and 10 (Pd, Pt), whereas the latter cationic cr-complexes are derived from both main group metals (Li, Mg) and group 10 (Pd, Pt) transition metals. 

Many of the transition elements exhibit more than one valence state, resulting from the possible removal of successive electrons from the inner partially filled d subshell. These d electrons may be removed singly or in groups thus the various oxidation states of an element may differ by one unit or hy more than one unit. As examples, the important oxidation states of vanadium are +3, +4, and +5 those for chromium are +2, + 3, and +6 and those for manganese are +2, +3, +4, +6, and +7. Among families of transition metals, the higher valence states become the more stable near the bottom of each family for example, in the chromium group the stability of the +6 states decreases in the order ... 

The reaction is carried out by thermal decomposition of fluoroformates at temperatures in the range of 300-500 C in the presence of a catalyst. Suitable catalysts are platinum gauze. " V dluminum oxide, or platinum group metal impregnated alumina, where platinum shows the best results. Moreover iron, sled or oxides and halides of chromium. 

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