Stoichiometry complex

Nickel and palladium react with a number of olefins other than ethylene, to afford a wide range of binary complexes. With styrene (11), Ni atoms react at 77 K to form tris(styrene)Ni(0), a red-brown solid that decomposes at -20 °C. The ability of nickel atoms to coordinate three olefins with a bulky phenyl substituent illustrates that the steric and electronic effects (54,141) responsible for the stability of a tris (planar) coordination are not sufficiently great to preclude formation of a tris complex rather than a bis (olefin) species as the highest-stoichiometry complex. In contrast to the nickel-atom reaction, chromium atoms react (11) with styrene, to form both polystyrene and an intractable material in which chromium is bonded to polystyrene. It would be interesting to ascertain whether such a polymeric material might have any catal3dic activity, in view of the current interest in polymer-sup-ported catalysts (51). 

The term exciplex (excited complex) is used to describe an electronically excited molecular complex of definite stoichiometry. Complexes which fall into this broad classification include ... 

In recent years, the development of new concepts for the rational design of larger, more complex molecules has led to considerable progress in supramolecular chemistry to afford structures of a variety of symmetries, sizes, and stoichiometries. complexes have provided versatile molecular tectons in a plethora of such structures. 

Ozone oxidizes bis(terpyridine)iron(II) into the corresponding iron(III) complex, as well as the bipyridine and 1,10-phenanthroline complexes of iron(II). The first complex is more stable than the latter complexes in a sHghtly acidic medium. Judging from the molar absorptivity of the iron(II) complex (1.1 X 10" mol 1 cm and reaction stoichiometry (complex/Os = 2), this method may be as sensitive as the indigo method. 

In empirical formulas of inorganic compounds, electropositive elements are listed first [3]. The stoichiometry of the element symbols is indicated at the lower right-hand side by index numbers. If necessary, the charges of ions are placed at the top right-hand side next to the element symbol (e.g., S "). In ions of complexes, the central atom is specified before the ligands are listed in alphabetical order, the complex ion is set in square brackets (e.g., Na2[Sn(OH)+]). 

Techniques responding to the absolute amount of analyte are called total analysis techniques. Historically, most early analytical methods used total analysis techniques, hence they are often referred to as classical techniques. Mass, volume, and charge are the most common signals for total analysis techniques, and the corresponding techniques are gravimetry (Chapter 8), titrimetry (Chapter 9), and coulometry (Chapter 11). With a few exceptions, the signal in a total analysis technique results from one or more chemical reactions involving the analyte. These reactions may involve any combination of precipitation, acid-base, complexation, or redox chemistry. The stoichiometry of each reaction, however, must be known to solve equation 3.1 for the moles of analyte. 

This reaction occurs quickly and is of known stoichiometry. A titrant of SCN is easily prepared using KSCN. To indicate the titration s end point we add a small amount of Fe + to the solution containing the analyte. The formation of the red-colored Fe(SCN) + complex signals the end point. This is an example of a direct titration since the titrant reacts with the analyte. 

In an indirect analysis the analyte participates in one or more preliminary reactions that produce or consume acid or base. Despite the additional complexity, the stoichiometry between the analyte and the amount of acid or base produced or consumed may be established by applying the conservation principles outlined in Section 2C. Example 9.3 illustrates the application of an indirect analysis in which an acid is produced. 

The equivalence point of a complexation titration occurs when stoichiometri-cally equivalent amounts of analyte and titrant have reacted. For titrations involving metal ions and EDTA, the equivalence point occurs when Cm and Cedxa are equal and may be located visually by looking for the titration curve s inflection point. 

Quantitative Calculations The stoichiometry of complexation reactions is given by the conservation of electron pairs between the ligand, which is an electron-pair donor, and the metal, which is an electron-pair acceptor (see Section 2C) thus... 

This is simplified for titrations involving EDTA where the stoichiometry is always 1 1 regardless of how many electron pairs are involved in the formation of the metal-ligand complex. 

Molecular absorption, particularly in the UV/Vis range, has been used for a variety of different characterization studies, including determining the stoichiometry of metal-ligand complexes and determining equilibrium constants. Both of these examples are examined in this section. 

Mole-ratio plots used to determine the stoichiometry of a metal-ligand complexation reaction. 

Both the method of continuous variations and the mole-ratio method rely on an extrapolation of absorbance data collected under conditions in which a linear relationship exists between absorbance and the relative amounts of metal and ligand. When a metal-ligand complex is very weak, a plot of absorbance versus Ay or n-J m may be curved, making it impossible to determine the stoichiometry by extrapolation. In this case the slope ratio may be used. 

In this experiment the method of continuous variations is used to determine the stoichiometry and equilibrium constant for the organic complex of 3-aminopyridine with picric acid in CHCI3, and the inorganic complex of Fe +with salicylic acid. 

Data from the spectrophotometric titrations of Fe + with SCN , and of Cu + with EDTA are used to determine the stoichiometry of the resulting complexes using the method of continuous variations. 

Using this data, determine the stoichiometry of the metal-ligand complex. 

The shift in the voltammogram for a metal ion in the presence of a ligand may be used to determine both the metal-ligand complex s stoichiometry and its formation constant. To derive a relationship between the relevant variables we begin with two equations the Nernst equation for the reduction of O... 

Determine values for the stoichiometry of the complex and the formation constant of the complex. 

Graphical determination of the stoichiometry and formation constant for a complexation reaction. 

Determine the stoichiometry of the Pb-hydroxide complex and its formation constant. 

This experiment describes the use of FIA for determining the stoichiometry of the Fe +-o-phenanthroline complex using the method of continuous variations and the mole-ratio method. Directions are also provided for determining the stoichiometry of the oxidation of ascorbic acid by dichromate and for determining the rate constant for the reaction at different pH levels and different concentration ratios of the reactants. 

Fig. 1. The GP Ib-IX-V complex. The complex consists of seven transmembrane polypeptides denoted GP Iba (mol wt 145,000), GP IbP (mol wt 24,000), GPIX (mol wt 17,000) and GP V (mol wt 82,000), in a stoichiometry of 2 2 2 1. The hatched region represents the plasma membrane. The area above the hatched region represents the extracellular space that below represents the cytoplasm. The complex is a major attachment site between the plasma membrane and the cytoskeleton. Two molecules associated with the cytoplasmic domain are depicted a 14-3-3 dimer, which may mediate intracellular signaling, and actin-binding protein, which connects the complex to the cortical cytoskeleton and fixes its position and influences its function.

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