Complexes, metal

Metal complexes of phenols are important in nature and useful in the laboratory. The metals involved usually include iron, aluminum and magnesium. In nature the flavonoids account for most red, blue, and violet -and to some extent yellow - colors. The majority of yellow colors are the result of the presence of carotenoids and aurones. 

Several structures are capable of forming metal complexes o-dihydroxy phenols (2.16), 3-hydroxychromones (2.17), 5-hydroxychromones (2.18), and o-hydroxycarbonyls (2.19). 

The overall structure of the molecule determines the reactivity of the molecule with the metal, and the presence of the metal ion will impact the chemical properties of the complex. The degree to which the chemical 

Metal complexes are used for compound identification. They can shift or change absorption spectra, change the Rf of compounds in thin layer chromatography, and change visual colors used in chromatography. 

Metal Complexes - On stirring two equivalents of [(trpn) Co (H20)2] [trpn = tris(aminopropyl)amine] with the disodium salt of AMP in water for six 

With one equivalent of [(trpn) Co (H20)2] +, a complex is formed with AMP in which both emionic oxygens are coordinated to cobalt addition of the second equivalent is thought to form (234) transiently, with subsequent expulsion of adenosine affording the observed products. By heating at neutral pH in the presence of Mn2+ ions at temperatures above 50° C, ATP can be used to phosphorylate the hydroxy groups of serine and tyrosine non-enzymatically. Calcium ions can substitute for Mn + ions, albeit less effectively, but Mg + ions are ineffective. The reaction can be used to prepare radiolabelled phosphoserine - or phosphotyrosine-containing peptides. 

A correction has been published - to the structure of a 4, 7-diphenyl-l, 10-phenanthroline-derived ligand in a ruthenium (II) complex described in last year s Report [see structure (193) in ref. 132]. The amendment, involving positional substitution on the phenyl rings, in no way compromises the essential results reported. A series of mixed-ligand complexes of Ru(II), in which the ligands used were 2, 2 -bipyridyl, 1, 10-phenanthroline, 4, 7-diphenyl-l, 10-phenanthroline, 

5-nitro-l, 10-phenanthroline, 4, 5-diazafluoren-9-one, and 9,10-phenanthrene-quinonediimine, has been prepared and the isotherms and spectroscopic characteristics of binding to DNA were measured. 59 All except ruthenium 

Ions of the d metals participate in bioiogicai eiectron transfer (Chapter 8), the binding and transport of O2, and the mechanisms of action of many enzymes. To understand the biochemical function of d metal atoms, we need to develop a theory for the formation of bonds between them and biological molecules. 

In Chapter 9 we saw that the d-metal ions typically have an incomplete shell of d electrons. These electrons play a special role in d-metal complexes, giving rise to their biochemical activity, their colors, and their magnetic properties. There are two approaches one, crystal field theory, is a simple approach that accounts for the general structures of complexes the other, ligand field theory, is an adaptation of MO theory and is much more powerful. 

Strategy Determine the electronic configuration of the Fe + ion according to the rules described in Section 9.11. Then apply the building-up principle to the two sets of d orbitals, allowing the maximum number of unpaired electrons to be the dominant factor in high-spin complexes, but not in low-spin 

Crystcd-field theory has a major deficiency it attempts to ascribe the bonding of the complex to Coulombic interactions between d electrons localized on a central meted ion md electron pciirs localized in orbiteds confined to the ligands. However, we know from our discussion of MO theory that molecular orbitals spread over both meted atoms md Hgeuids. Ligemd-field theory develops this point of view in terms of moleculeu orbitals. It proceeds in three steps  

Interactions between metal ion orbitals and ligand 7t orbitals can either decrease or increase Aq. To see how this is so, consider the bonding schemes in Fig. 10.45. If a ligand it orbital and a nonbonding t2g orbital of the metal ion have similar energies, when they interact a Hkely outcome is shown in Fig. 10.45a. If the ligand n orbital suppfies two electrons and the t2g orbital supplies one, then the result is a decrease in Aq. On the other hand, if the metal tjg and ligand 7t orbitals have 

Mixed Metal Complexes. In contrast to the reaction producing [Fe5C(CO)j4 ] discussed above, treatment of Fe2(CO)g with [(jr-Cp)Mo(CO)3] at room temperature in THF yields [(7r-Cp)2Mo2Fe2(CO),Q] , for which structure (17) is suggested on the basis of i.r. data. The analogous tungsten compound has also been isolated, but no hydrides were isolated upon acidification.  

The structure of [(7r-Cp)RhFe3(CO)j J (see Vol. 1, p. 156) has been presented in detail. The reaction of (CO)3Fe(p-CO)(p-PPh2)Ni(Tc-Cp) with the acetylenes R C = CR yields complexes of the type (18), two isomers of each complex being obtained for unsymmetrically substituted acetylenes.  

However. [Ph3PAuFe(CO)j(NO)L] (L = PPhj or AsPhEt ), like [PhjPAu-ColCOlgPPhj], do not undergo dissociation.  

The clearance of DTPA metal complexes by the glomeruli is primarily dependent of the ligand. Thus, other metal complexes may also be useful for GFR measurements. For example, colored metal complexes that are exclusively excreted 

Solubility depends on the nature of the IL and on solvation or complex formation. Most metal ions display preferential partitioning into water in IL aqueous systems and are hence less soluble in the IL than in water. 

Simple metal compounds are poorly soluble in non-coordinating ILs, but the solubility of metal ions in an IL can be increased by addition of lipophilic ligands. LLowever, enhancement of lipophilicity also increases the tendency for the metal complex to leach into less polar organic phases. 

ILs have also been used as inert additives to stabilize transition metal catalysts during evaporative workup of reactions in organic solvent systems [35,36]. The non- 

Ideally, to ensure the complete removal of the metal ions from the aqueous phase, the complexant and the metal complex should remain in the hydrophobic phase. Thus, the challenges for separations include the identification of extractants that quantitatively partition into the IL phase and can still readily complex target metal ions, and also the identification of conditions under which specific metal ion species can be selectively extracted from aqueous streams containing inorganic complexing ions. 

Waste reduction methods of specific interest to PC board manufacture are discussed below 11.1.3 SOURCE REDUCTION 11.1.3.1 Metal Complexes 

Ferrous sulfate is a commonly used reducing agent for chelated waste streams that provides an illustration of the above problem. Although it is effective in removing process metals from complexes, the iron in the ferrous sulfate precipitates out along with the process metal. Since ferrous sulfate is typically added in sufficient quantity to raise the iron/process metal ratio to 8 1, considerable extra sludge is generated (Couture 1984). 

One strategy for avoiding the sludge problem is to use non-chelate process solutions wherever feasible. Non-chelate alkaline cleaners are available, as are non-chelate etchants 

Switching an operation to use of non-chelate process baths is not without problems. One problem is the need for continuous filtration of those baths through 1 to 5 micron filters to control the buildup of solids. Typical filter system costs range from 400 to 1000 per tank (USEPA 1989). 

Cations, particularly those with charge number z 1, are considerably smaller than the parent neutral atoms, and so the electric potential (oc z/r) at cation surfaces is high. Consequently, the electron cloud of a neighboring molecule or anion becomes displaced toward a cation, and, if there is an unused pair (lone pair) of electrons in the valence shell of the molecule or anion, it may actually become involved in a sort of covalent bond with the cation, using empty valence-shell orbitals on the cation.  

Such a bond, in which the donor molecule (or anion) provides both bonding electrons and the acceptor cation provides the empty orbital, is called a coordinate or dative bond. The resulting aggregation is called a complex. Actually, any molecule with an empty orbital in its valence shell, such as the gas boron trifluoride, can in principle act as an electron pair acceptor, and indeed BF3 reacts with ammonia (which has a lone pair, NHs) to form a complex H3N — BFs. Our concern here, however, is with metal cations, and these usually form complexes with from 2 to 12 donor molecules at once, depending on the sizes and electronic structures of the cation and donor molecules. The bound donor molecules are called ligands (from the Latin ligare, to bind), and the acceptor and donor species may be regarded as Lewis acids and Lewis bases, respectively. 

Solid compound Color Ionized Cl Formulation as Complex 

The green and violet tetraammines have the same chemical composition, that is, they axe isomers and are the only two isomers with this composition. Werner realized that this was possible only if the six ligands were deployed about the cobalt (III) center in an octahedral arrangement (cf. octahedral coordination in solids. Sections 4.3 and 4.4) for example, a flat hexagonal complex Co(NH3)4Cl2 would have three isomers, like ortho-, meta-, and para-disubstituted benzenes. Werner correctly identified the green compound as the trans isomer (chloro ligands on opposite sides of the octahedron) and the violet as cis (same side), as in Fig. 13.1. 

In the same way, the existence of two isomers, yellow and orange, of Pt(NH3)2Cl2 showed that these complexes are square planar, rather than tetrahedral (Fig. 13.2) the yellow one has no electric dipole moment and therefore is the trans isomer, whereas the orange does and is cis. A tetrahedral Pt(NH3)2Cl2 would have just one isomer (with a dipole moment). Four-coordinate complexes of platinum(II), palladium(II), and gold(III) are virtually always square planar, but tetrahedral complexes such as the purple 

The step from eonfigurations to states is conceptually less simple than for organic molecules beeause, as mentioned above, coordination compounds may have high symmetry (i.e., degenerate MOs) and open-shell ground configurations (i.e., partially occupied HOMOs). 

In conclusion, metal complexes tend to have more complex and specihc Jab-lonski diagrams than organic molecules. Points to be noticed are (1) spin multiplicity other than singlet and triplet can occur, but for each electronic conhguration the state with highest multiplicity remains the lowest one (2) excited states can 

In the following, in order to discuss some general concept of molecular photochemistry we will make use of a generic Jablonski diagram based on singlet and triplet states. 

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Ultrasonic absorption is used in the investigation of fast reactions in solution. If a system is at equilibrium and the equilibrium is disturbed in a very short time (of the order of 10"seconds) then it takes a finite time for the system to recover its equilibrium condition. This is called a relaxation process. When a system in solution is caused to relax using ultrasonics, the relaxation lime of the equilibrium can be related to the attenuation of the sound wave. Relaxation times of 10" to 10 seconds have been measured using this method and the rates of formation of many mono-, di-and tripositive metal complexes with a range of anions have been determined. 

Wight C A and Armentrout P B 1993 Laser photoionization probes of ligand-binding effects in multiphoton dissociation of gas-phase transition-metal complexes ACS Symposium Series 530 61-74... 

Benedetti M, Biscarini P and Brillante A, The effect of pressure on circular dichroism spectra of chiral transition metal complexes Physica B 265 1... 

To see physically the problem of motion of wavepackets in a non-diagonal diabatic potential, we plot in figure B3.4.17 a set of two adiabatic potentials and their diabatic counterparts for a ID problem, for example, vibrations in a diatom (as in metal-metal complexes). As figure B3.4.17 shows, if a wavepacket is started away from the crossing point, it would slide towards this crossing point (where where it would... 

A. (The gas phase estimate is about 100 picoseconds for A at 1 atm pressure.) This suggests tliat tire great majority of fast bimolecular processes, e.g., ionic associations, acid-base reactions, metal complexations and ligand-enzyme binding reactions, as well as many slower reactions that are rate limited by a transition state barrier can be conveniently studied with fast transient metliods. 

Magnetic circular dicliroism (MCD) is independent of, and thus complementary to, the natural CD associated with chirality of nuclear stmcture or solvation. Closely related to the Zeeman effect, MCD is most often associated with orbital and spin degeneracies in cliromophores. Chemical applications are thus typically found in systems where a chromophore of high symmetry is present metal complexes, poriihyrins and other aromatics, and haem proteins are... 

Chen P and Meyer T J 1998 Medium effects on charge transfer in metal complexes Chem. Rev. 98 1439-78... 

INORGANIC COMPLEXES. The cis-trans isomerization of a planar square form of a rt transition metal complex (e.g., of Pt " ) is known to be photochemically allowed and themrally forbidden [94]. It was found experimentally [95] to be an inhamolecular process, namely, to proceed without any bond-breaking step. Calculations show that the ground and the excited state touch along the reaction coordinate (see Fig. 12 in [96]). Although conical intersections were not mentioned in these papers, the present model appears to apply to these systems. 

The detailed theory of bonding in transition metal complexes is beyond the scope of this book, but further references will be made to the effects of the energy splitting in the d orbitals in Chapter 13. 

The modeling of inorganic compounds in general is gaining more and more interest [25-28]. The authors of MOMEC addressed this in a monograph describing how molecular modeling techniques can be applied to metal complexes and how the results can be interpreted [29]. The current force field parameter set is available on the author s web site. 

DFT calculations offer a good compromise between speed and accuracy. They are well suited for problem molecules such as transition metal complexes. This feature has revolutionized computational inorganic chemistry. DFT often underestimates activation energies and many functionals reproduce hydrogen bonds poorly. Weak van der Waals interactions (dispersion) are not reproduced by DFT a weakness that is shared with current semi-empirical MO techniques. 

V S, C M Kelly and C R Landis 1991. SHAPES Empirical Force-Field - New Treatment of igular Potentials and Its Application to Square-Planar Transition-Metal Complexes. Journal of American Chemical Society 113 1-12. 

Rappe A K, K S Colwell and C J Casewit 1993. Application of a Universal Force Field to Metal Complexes. Inorganic Chemistry 32 3438-3450. 

The absorbance table at X for each of the metal complexes constitutes a matrix with rows of absorbances, at one wavelength, of Mo, Ti, and V complexes, in that order. Each column comprises absorbances for one metal complex at 330, 410, and 460 nm, in that order ... 

Martell, A. E. Hancock, R. D. Metal Complexes in Aqueous Solution, Plenum Press New York, 1996... 

For transition metal complexes, techniques derived from a crystal-field theory or ligand-field theory description of the molecules have been created. These tend to be more often qualitative than quantitative. 

A common disadvantage of many template reactions is that it is often difficult to remove the metal ion. Such syntheses are therefore in situ syntheses of metal complexes and can only occasionally be used for the synthesis of the metal-free ligands. 

The direct connection of rings A and D at C l cannot be achieved by enamine or sul> fide couplings. This reaction has been carried out in almost quantitative yield by electrocyclic reactions of A/D Secocorrinoid metal complexes and constitutes a magnificent application of the Woodward-Hoffmann rules. First an antarafacial hydrogen shift from C-19 to C-1 is induced by light (sigmatropic 18-electron rearrangement), and second, a conrotatory thermally allowed cyclization of the mesoionic 16 rc-electron intermediate occurs. Only the A -trans-isomer is formed (A. Eschenmoser, 1974 A. Pfaltz, 1977). 

Khan, M. M. T. 1974, Homogeneous Catalysis by Metal Complexes, Vol. II, Activation of Alkenes and Alkynes, Academic Press New York - London... 

Pd-cataly2ed reactions of butadiene are different from those catalyzed by other transition metal complexes. Unlike Ni(0) catalysts, neither the well known cyclodimerization nor cyclotrimerization to form COD or CDT[1,2] takes place with Pd(0) catalysts. Pd(0) complexes catalyze two important reactions of conjugated dienes[3,4]. The first type is linear dimerization. The most characteristic and useful reaction of butadiene catalyzed by Pd(0) is dimerization with incorporation of nucleophiles. The bis-rr-allylpalladium complex 3 is believed to be an intermediate of 1,3,7-octatriene (7j and telomers 5 and 6[5,6]. The complex 3 is the resonance form of 2,5-divinylpalladacyclopentane (1) and pallada-3,7-cyclononadiene (2) formed by the oxidative cyclization of butadiene. The second reaction characteristic of Pd is the co-cyclization of butadiene with C = 0 bonds of aldehydes[7-9] and CO jlO] and C = N bonds of Schiff bases[ll] and isocyanate[12] to form the six-membered heterocyclic compounds 9 with two vinyl groups. The cyclization is explained by the insertion of these unsaturated bonds into the complex 1 to generate 8 and its reductive elimination to give 9. 

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