Organic, complexes with metals

Some organic complexes with metals may lower solubility and decrease the bioavailability of metals. 

Finding the End Point with a Visual Indicator Most indicators for complexation titrations are organic dyes that form stable complexes with metal ions. These dyes are known as metallochromic indicators. To function as an indicator for an EDTA titration, the metal-indicator complex must possess a color different from that of the uncomplexed indicator. Furthermore, the formation constant for the metal-indicator complex must be less favorable than that for the metal-EDTA complex. 

The regularity of micellar extraction of large grope of organic reagents and their complexes with metal ions was investigated. 

Precipitation is often applied to the removal of most metals from wastewater including zinc, cadmium, chromium, copper, fluoride, lead, manganese, and mercury. Also, certain anionic species can be removed by precipitation, such as phosphate, sulfate, and fluoride. Note that in some cases, organic compounds may form organometallic complexes with metals, which could inhibit precipitation. Cyanide and other ions in the wastewater may also complex with metals, making treatment by precipitation less efficient. A cutaway view of a rapid sand filter that is most often used in a municipal treatment plant is illustrated in Figure 4. The design features of this filter have been relied upon for more than 60 years in municipal applications. 

One important factor to consider in the preparation of the organic phase is the presence of inhibitors in the monomers. Some formulae call for the removal of inhibitors, primarily TCB, from the monomers. The TCB inhibitor forms highly colored complexes with metallic salts rendering the final product colored. Styrene has about 50 ppm of TCB. DVB, being more reactive, contains about 1000 ppm of TCB. There are several options for the removal of inhibitors. Columns packed with DOWEX MSA-1 or DOWEX 11 ion-exchange resins (Dow Chemical Company) can be used. White drierite or activated alumina also works well. 

Structures of organic complexes with alkali metal ions. M. R. Truter, Struct. Bonding (Berlin), 1973,16, 71-111 (107). 

The cyclopentadienide ion, C H , is a common organic anion that forms very stable complexes with metal cations. The anion is derived by removing a proton from cyclopentadiene, QH, with strong base. The molecule has a five-memhered ring of carbon atoms, with four carbon atoms attached to only one proton and one carbon atom bonded to two. Draw the Lewis... 

Tributsch H (1982) Photoelectrochemical Energy Conversion Involving Transition Metal d-States and Intercalation of Layer Compounds. 49 127-175 Truter MR (1973) Structures of Organic Complexes with Alkali Metal Ions. 16 71-111 Tytko KH, Mehmke J, Kurad D (1999) Bond Length-Bond Valence Relationships, With Particular Reference to Polyoxometalate Chemistry. 93 1-64 Tytko KH (1999) A Bond Model for Polyoxometalate Ions Composed of M06 Octahedra (MOk Polyhedra with k > 4). 93 65-124... 

Metal deactivators—Organic compounds capable of forming coordination complexes with metals are known to be useful in inhibiting metal-activated oxidation. These compounds have multiple coordination sites and are capable of forming cyclic strucmres, which cage the pro-oxidant metal ions. EDTA and its various salts are examples of this type of metal chelating compounds. 

Truter, M. R. Structures of Organic Complexes with Alkali Metal Ions. Vol. 16, pp. 71-111. 

The Debye temperature is usually high for metallic systems and low for metal-organic complexes. For metals with simple cubic lattices, for which the model was developed, is found in the range from 300 K to well above 10 K. The other extreme may be found for iron in proteins, which may yield d as low as 100-200 K. Figure 2.5a demonstrates how sharply/(T) drops with temperature for such systems. Since the intensity of a Mossbauer spectrum is proportional to the... 

Certain physical or chemical characteristics of the wastestream may limit the application of precipitation. For example, some organic compounds (as well as cyanide or other ions) may form organometallic complexes with metals, decreasing the precipitation potential. 

McEldowney (2000) reported that 65% of Cd2+ was associated with the cell walls of Pseudomonas fluorescens, while 33% was present in the cytoplasm, and 2% was bound to extracellular polymeric substances (EPS) excreted by the bacteria. EPS include polyssacharides, proteins and siderophores. Organic matter, derived from dead microbes, can also form extracellular complexes with metals. 

As a result of microbial formation of metal-organic complexes with fulvic acids in soils of Tropical Rain Forest ecosystems, the surface and sub-surface runoff waters are enriched in some heavy metals like manganese and copper. A similar tendency has been shown for boron, strontium and fluorine. 

A safe method for decomposing complexes of various organic ligands with metal perchlorates prior to analysis involves heating them with ammonium chloride, but... 

Known as crown ethers because of their crown-like shape, these ethers contain cavities that are ideal for forming complexes with metal ions. It is this property that allows ordinary salts to dissolve in organic solvents. For example, potassium permanganate is usually insoluble in benzene, but readily dissolves in benzene if [18]-crown-6 ether is added. This solution is useful because it allows oxidation with potassium permanganate to be carried out in organic solvents. The potassium ion (shown in green) is just the right size to fit into the cavity in the crown ether. 

Metal-Organic Complexes with Organic Adduct Formers, Type MA B ... 

Several other explanations have been put advanced to explain retention hysteresis, including (1) surface precipitation of metallic cations whose hydroxides, phosphates, or carbonates are sparingly soluble (2) chemical reactions with solid surfaces, including organic surfaces, which form complexes with metallic cations and (3) incorporation into the subsurface organic matter through chemical reactions and biochemical transformation. For the case described by Fig. 5.9 or explanations (1) and (2), the contaminant release always exhibits a hysteresis... 

Organic isocyanides (C=N-R) are versatile ligands in transition metal complex chemistry. As compared with their pseudo-isoelectronic cousin, C=0, they are stronger o-donors [1], As a result, isocyanides form more stable complexes with metals in relatively high oxidation states (e.g., +2 and +3) than CO. In contrast, they have a lower ir-accepting ability than CO and therefore form less stable complexes with metals in low oxidation states (e.g., -1 and -2). Nevertheless, they form a broad range of metal complexes, and various aspects of their syntheses, structures and bonding have been reviewed [1-7]. 

Extraction can be nsed for separation or isolation of the analyte from the sample matrix or vice versa as well as a preconcentration method. Extraction of metal ions is based on the reaction of weak organic acids with metal ions that give nncharged complexes that are highly solnble in organic solvents as ethers, hydrocarbons, ketones and polychlorinated species (generally chloroform and carbon tetrachloride). The efficacy of the extraction is mainly dependent on the extent to which solntes distribnte themselves between two immiscible solvents. The amonnts of analyte can be determined spectrophotometrically as well as with other available analytical methods. 

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