Transition metals colour

Flowever, transition metal complexes do absorb in the visible region, giving them a characteristic colour. Flow can this happen if the transitions are forbidden The answer is that interaction may occur between the motion of the electrons and vibrational motions so that some vibronic transitions are allowed (see Section 7.3.4.2b). 

Zincon disodium salt (o-[l-(2-bydroxy-5-sulfo)-3-pbenyl-5-formazono]-benzoic acid di-Na salt) [135-52-4, 56484-13-0] M 484.4, m -250-260 (dec). Zincon soln is prepared by dissolving 0.13g of the powder in aqueous N NaOH (2mL diluted to lOOmL with H2O). This gives a deep red colour which is stable for one week. It is a good reagent for zinc ions but also forms stable complexes with transition metal ions. [UV-VIS Bush and Yoe Anal Chem 26 1345 1954 Hunter and Roberts J Chem Soc 820 1941 Platte and Marcy Anal Chem 31 1226 1959] The free acid has been recrystd from dilute H2SO4. [Fichter and Scheiss Chem Ber 33 751 1900.]... 

In 1826 J. J. Berzelius found that acidification of solutions containing both molybdate and phosphate produced a yellow crystalline precipitate. This was the first example of a heteropolyanion and it actually contains the phos-phomolybdate ion, [PMoi204o] , which can be used in the quantitative estimation of phosphate. Since its discovery a host of other heteropolyanions have been prepared, mostly with molybdenum and tungsten but with more than 50 different heteroatoms, which include many non-metals and most transition metals — often in more than one oxidation state. Unless the heteroatom contributes to the colour, the heteropoly-molybdates and -tungstates are generally of varying shades of yellow. The free acids and the salts of small cations are extremely soluble in water but the salts of large cations such as Cs, Ba" and Pb" are usually insoluble. The solid salts are noticeably more stable thermally than are the salts of isopolyanions. Heteropoly compounds have been applied extensively as catalysts in the petrochemicals industry, as precipitants for numerous dyes with which they form lakes and, in the case of the Mo compounds, as flame retardants. 

Colour - A striking feature of transition-metal compounds is their colour. Whether it is the pale blue or pink hues of copper(ii) sulfate and cobalt(ii) chloride, or the intense purple of potassium permanganate, these colours tend to be associated most commonly with transition-metal compounds. It is rare for compounds of main group metals to be highly coloured. 

There are a number of particular technical advantages associated with the formation of coloured metal complexes. Commonly, the transition metal complexes of a coloured organic ligand exhibit lightfastness which is significantly better than that of the free ligand. An explanation that has been offered for this effect is that coordination with a transition metal ion... 

Among the potential impurities in ionic liquids water, halide ions and organic starting material are of great importance for transition metal chemistry while the colour of an ionic liquid is not a critical parameter in most applications. 

Group 1 superoxides are coloured compounds, which is unusual for group 1 compounds not containing a transition metal ion. The trend in oxide formation is the result of the increasing size of the metal cations as the group is descended. 

In the modern world, we are accustomed to taking the chemical stability of glass very much for granted - we rely on the durability of glass for so many things, such as windows and (until the widespread availability of plastics) bottles, as well as its use in the chemical laboratory as an extremely inert and unreactive container. In addition to its apparent inertness, glass has a number of other beneficial properties, such as its transparency or the ability to take on virtually any colour as the result of the addition of a small amount of transition metals. 

Transition metal Modern raw material Colouring ion Colour in tetrahedral coordination (network former) Colour in octahedral coordination (network modifier)... 

The colour of the transition metal ions, which is one of their major characteristics, arises directly from the interaction between the outer orbital electrons of the transition metal and the electric field created by the presence of the co-ordinating ligands. The theory of this is called ligand field theory, and is well covered in most basic textbooks on inorganic chemistry (e.g., Cotton and Wilkinson, 1976). Ligand field theory is an extremely powerful tool, which... 

Clearly then, in glasses coloured by metal ions, the co-ordination chemistry of the transition metal ion has a major influence on the colour. The other major influence is the oxidation state of the metal ion, since variable valency is another characteristic of the transition metals. All other things being equal, for example, iron in the Fe11 form will give a pale blue colour, whereas Fem gives... 

It is clear that the colour of a glass is the result of a complex interplay between the co-ordination of the transition metal ions, the redox reactions between the various ions present and the redox potential in the furnace. The traditional archaeological view that colour can be simply related to the presence of various colouring agents can only be regarded as a very crude guide. 

Thus, transitions such as 2p -> Is, 3p -> Is, 3d -> 2p are allowed, whereas 2s - Is, 3d-> Is, 3d -> 3d are strictly forbidden. As discussed in Chapter 5, however, transitions within the J-orbitals (so-called d-d band transitions) do occur, and are important in the consideration of the colour developed by transition metals in solution. Other forbidden transitions also occur. 

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