Metals chromium subgroup

What place do the chromium subgroup elements occupy in the electrochemical series of the metals How do they react with acids and with alkalies Write the equations of the relevant reactions. 

The 7t-(C6)M system is also present in the complexes of cycloheptatriene (C7Hg), when this olefin is bonded to transition metals requiring six it electrons, such as the metals of the chromium subgroup 27) (Table XIX). It should be noted that in its complexes with the iron carbonyls, this ligand is bonded as a 7r-(C4)M system. It was ascertained through chemical and spectroscopic evidence that the third olefinic bond was not participating in coordination to the metal 48) (Table XV). 

The first metal-olefin complex was reported in 1827 by Zeise, but, until a few years ago, only palladium(II), platinum(Il), copper(I), silver(I), and mercury(II) were known to form such complexes (67, 188) and the nature of the bonding was not satisfactorily explained until 1951. However, recent work has shown that complexes of unsaturated hydrocarbons with metals of the vanadium, chromium, manganese, iron, and cobalt subgroups can be prepared when the metals are stabilized in a low-valent state by ligands such as carbon monoxide and the cyclopentadienyl anion. The wide variety of hydrocarbons which form complexes includes olefins, conjugated and nonconjugated polyolefins, cyclic polyolefins, and acetylenes. 

The ease with which olefins form complexes with metals naturally led to investigation of acetylenes as ligands but until recent years only a few ill-defined, unstable acetylene complexes of copper and silver were known. Now complexes of acetylenes with metals of the chromium, manganese, iron, cobalt, nickel, and copper subgroups are known. These complexes fall naturally into two classes—those in which the structure of the acetylene is essentially retained and those in which the acetylene is changed into another ligand during complex formation. Complexes of the first class are discussed here and the second class is discussed in Section VI. 

The cited reference discusses the further detailed and necessary separations within each of the specified subgroups titanium (1.1), alkaline earth (1.3), metal amine (1.4), sulfide (2.1), aluminum (2.4), chromium (2.5), lead (2.6), arsenic (2.7), halogen (3.3), phosphorus (3.5), sulfur and fluorine (3.6). 

Systems Fe-Cr-Nb and Co-Cr-Nb at 1000°C (in Russian), Paper No. 4988-80 deposited at VINITI, Moscow (1980) (Phase Diagram, Experimental, ), as quoted by [1988Kal] [1981Abr] Abram yan, A.Kh., Investigation of Interaction of Iron Subgroup Metals with Chromium and... 

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