Colors of complex ions

The Color of Complex Ions and Crystal Field Strength... 

P = parent ion detected in mass spectrum. Color of complex p-y, pale yellow o, orange o-b, orange-brown c, colorless w, white d-g, deep-green b-g, blue-green r-b, red-brown d-p, dark-purple 1, lemon r, red g, green. H NMR data are available on all the compounds and P NMR on all the Pt-phosphine complexes 231). 

Soluble compounds of the complex ion [Co(NH3)3]3+ have a maximum absorption of visible light at 437 nm. (a) What is the value of A for this complex ion express the answer in cm-1. (b) What is the color of this ion in solution (c) How many unpaired electrons would you expect this ion to have if it is considered low-spin, and how many if it is considered high-spin ... 

There are two topics that are somewhat related to the material in this chapter. One of them is frequently referred to in questions, while the second only rarely pops up. The first deals with the colors of various substances at least one multiple-choice question usually refers to it. The second topic is the formation of complexes, like the ones mentioned in the previous section, but it goes a bit beyond the subject as it is addressed here. Occasionally a question about the nomenclature of complex ions appears, so we ll address that here (for lack of a better place to put it). 

Since chelation is merely a special type of complex formation, many effects due to chelation are analogous to effects due to simple complexing. The color of an ion may deepen, fade, or change upon chelation a precipate may dissolve when a chelating agent is added the stability of an oxidation state of the metal ion may be appreciably altered or the pH of a solution of a chelating agent in water may drop when a metal... 

Although the localized electron model can account in a general way for metal-ligand bonds, it is rarely used today because it cannot predict important properties of complex ions, such as magnetism and color. Thus we will not pursue the model any further. 

The main reason that the localized electron model cannot fully account for the properties of complex ions is that in its simplest form it gives no information about how the energies of the d orbitals are affected by complex ion formation. This is critical because, as we will see, the color and magnetism of complex ions result from changes in the energies of the metal ion d orbitals caused by the metal-ligand interactions. 

The hydrolysis of ferric salts is so common that the color of ferric ion, Fe(H20)g+ + , is usually masked by that of the hydroxide complexes. Ferric ion is nearly colorless it eems to have a very pale violet color, seen in crystals of ferric alum, KFe(SO )o I2H.2O, and ferric nitrate, Fe(N03)3 9H20, and in ferric solutions strongly acidified with nitric or perchloric acid. Solutions of ferric salts ordinarily have the characteristic yellow to brown color of the hydroxide coniplexe Fe(H20)50H + + and Fe(H20)4(OH)o+, or even the red-brown color of colloidal particles of hydrated ferric hydroxide. 

An example of the effect of temperature on an endothermic reaction is illustrated in Figure 12. The following equation describes an equilibrium that involves the two colored cobalt complex ions. 

Benedict s reagent contains an alkaline solution of cupric ion (Cu ) complexed with citrate anion. A positive test is detected by the disappearance of the blue color of cupric ion and the formation of a red precipitate. The red precipitate is CU2O which forms when cupric ion is reduced to cuprous (Cu ). 

It is this splitting of the 3d orbital energies (symbolized by A) that explains the color and magnetism of complex ions of the first-row transition metal ions. For example, in an octahedral complex of Co " (a metal ion with six 3d electrons), there are two possible ways to place the electrons in the split 3d orbitals (Fig. 19.23). If the splitting produced by the ligands is very large. 

A model [22] of how heparin acts specifically in many biological systems in modifying activities of complex ions may be provided by the metachromatic effect on dyes referred to earlier. The dye. Azure A, shows maximum light absorption at 610 nm. This is decreased when heparin is added, and a new absorption band at 505 mu develops. Heparins and heparinoids are able to produce this color change at very low concentrations and under conditions unfavorable to other metachromatic inducing substances. However, little attention has been paid to the numerous experimental observations reported on metachromasia with heparin and heparinoids, of practical importance to those using this color reaction in studies on heparin and mast cells. In... 

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