Chemistry
Transition Metal Ions in Aqueous Solution
Transition metal ions in aqueous solution refer to the behavior of transition metal ions when they are dissolved in water. These ions can form complex ions with water molecules, leading to the formation of coordination complexes. The presence of transition metal ions in aqueous solution can affect the color, reactivity, and other properties of the solution.
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eBook - PDFMetallic Systems
A Quantum Chemist's Perspective
- Thomas C. Allison, Orkid Coskuner, Carlos A. Gonzalez(Authors)
- 2011(Publication Date)
- CRC Press(Publisher)
107 © 2011 by Taylor & Francis Group, LLC 4 Aqueous Solutions of Metal Ions Orkid Coskuner and Thomas C. Allison* 4.1 INTRODUCTION Metal. ions. play. crucial. roles. in. diverse. areas. such. as. medicine,. nanotechnology,. catalysis,.environmental.sciences,.and.geochemistry . .For.example,.the.chemistry.of. metal.ions.with.biomolecules.and.organic.compounds.is.extremely.important.for.a. wide. range. of. medicinal. and. environmental. processes. that. depend. on. metal. ions. as. active. participants. [1–3] . . Organic. complexes. that. coordinate. to. metal. ions. are. becoming. increasingly. prevalent. as. therapeutic. agents. for. treating. a. wide. variety. of.metabolic.disorders.and.diseases . .For.instance,.cisplatin.has.been.shown.to.be. toxic.to.cancer.cells.(see.Chapter.1.for.a.more.detailed.discussion.of.cisplatin).and. the.platinum-based.compound.known.as.“ trans , trans , trans -Pt(N 3 ) 2 (OH) 2 (NH 3 )(py)”. has.been.shown.to.be.highly.toxic.and.less.stable.than.cisplatin . .It.is.between.13.and. 80.times.more.toxic.to.cancer.cells.than.cisplatin.and.kills.cancer.cells.via.a.differ-ent.mechanism.so.it.can.also.kill.cisplatin-resistant.cancer.cells . .When.we.consider. that.most.biological.processes.occur.in.solution.and.that.the.human.body.consists.of. ∼ 60%.water,.the.role.of.the.aqueous.solution.environment.on.the.structure–function. relationships.of.metal.ion–based.organometallic.drugs.cannot.be.ignored . In.environmental.sciences,.understanding.the.interactions.of.metal.ions.that.are. toxic.to.plants.and.organisms.and.that.are.constituents.of.natural.and.wastewaters. * . Contribution.of.the.National.Institute.of.Standards.and.Technology . CONTENTS 4.1 . Introduction. .................................................................................................. 107 4.2 . Methods. ........................................................................................................
eBook - PDF- Robert P. Mason(Author)
- 2013(Publication Date)
- Wiley-Blackwell(Publisher)
The bonds of these metals are more “covalent” in nature, and these metals have a larger tendency to form complexes. 3.2 Bonding, electronic configuration, and complex formation Metal(loid)s do not exist merely as charged ions in solution because water is a polar liquid. Molecules of water associate themselves around the ion in a fashion to neutralize the charge of the ion [2]. This is the case for any charged ion in aqueous solution and the interaction can be conceptualized as shown in Fig. 3.3. The area immediately around the central ion is termed the primary solvation (hydration) shell and this refers to the region where the water molecules are directly interacting with the central ion. This interaction can occur through the formation of a chemical bond, or involve a weaker interaction. The strength of this interaction varies considerably for the metal(loid)s of interest here. Most tran-sition metal ions in solution are surrounded by six water r = Q/V. At steady state, when there is no longer a concen-tration change in the system [1]: dC /dt k C k C rC rC A f A b B AO A = -+ + -= 0 (3.36) and dC /dt k C k C rC rC B f A b B BO B = -+ -= 0 (3.37) and, as C C C C A B AO BO + = + (3.38) Then it can be shown that: C rC k rC C / k k r A AO b AO BO f b = + + + + ( ( )) ( ) (3.39) and C rC k rC C / k k r B BO b AO BO f b = + + + + ( ( )) ( ) (3.40) and C /C rC k C C / rC k C C B A BO f AO BO AO b AO BO = + + + + ( ( )) ( ( )) (3.41) We can deduce from this expression that when r is relatively small, the values of the other expressions will be substan-tially greater and: C C k /k B A f b / ~ (3.42) Similarly, if the concentrations of C A0 and C B0 are small compared to those in the system, then rC A0 and rC B0 may be small compared to the other expressions and the assumption of the steady state will also be valid, being essentially equiva-lent to the equilibrium condition.
eBook - PDFChemistry
An Atoms First Approach
- Steven Zumdahl, Susan Zumdahl, Donald J. DeCoste, , Steven Zumdahl, Steven Zumdahl, Susan Zumdahl, Donald J. DeCoste(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
20.1 The Transition Metals: A Survey General Properties Electron Configurations Oxidation States and Ionization Energies Standard Reduction Potentials The 4d and 5d Transition Series 20.2 The First-Row Transition Metals 20.3 Coordination Compounds Coordination Number Ligands Nomenclature 20.4 Isomerism Structural Isomerism Stereoisomerism 20.5 Bonding in Complex Ions: The Localized Electron Model 20.6 The Crystal Field Model Octahedral Complexes Other Coordination Geometries 20.7 The Biological Importance of Coordination Complexes 20.8 Metallurgy and Iron and Steel Production Hydrometallurgy The Metallurgy of Iron Production of Steel Heat Treatment of Steel Transition Metals and Coordination Chemistry CHAPTER 20 The chrome plated winged mercury on the hood of a classic automobile. (Christian Delbert/Shutterstock.com) 796 Copyright 2021 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. T ransition metals have many uses in our society. Iron is used for steel; copper for electrical wiring and water pipes; titanium for paint; silver for photographic paper; manganese, chromium, vanadium, and cobalt as additives to steel; platinum for industrial and automotive catalysts; and so on. One indication of the importance of transition metals is the great concern shown by the U.S. government for continuing the supply of these elements. In recent years the United States has been a net importer of about 60 “strategic and critical” minerals, including cobalt, manganese, platinum, palladium, and chromium.
eBook - PDF- Allan Blackman, Steven E. Bottle, Siegbert Schmid, Mauro Mocerino, Uta Wille(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
Despite this, [Co(NH 3 ) 6 ] 3+ can be recovered unchanged after several days in 1.0 mol L -1 H 3 O + , meaning that the NH 3 ligands cannot easily exchange with H 2 O. We say that [Co(NH 3 ) 6 ] 3+ is inert to ligand substitution and, therefore, is an example of a thermodynamically unstable, but kinetically inert, transition metal complex. Most first-row transition metal complexes are labile, but complexes containing metals with a d 3 or d 6 electron configuration are often inert, with Cr(III) and Co(III) being the classic examples of inert metal centres. It is important, therefore, that you are careful when using the word ‘stable’, and that you realise that thermodynamic stability and kinetic stability are entirely separate concepts. Electrochemical aspects of transition metal complexes Electrochemistry provides another convenient method of quantifying the thermodynamic stability of transition metal complexes. As we saw in the chapter on oxidation and reduction, the reduction potentials of simple aqueous transition metal ions span a wide range of values and, therefore, electrochemical behaviour. Thus, the Ag + (aq) ion is moderately oxidising (E o Ag + ∕Ag = +0.80 V) while the Cr 3+ (aq) ion shows negligible oxidising ability (E o Cr 3+ ∕Cr = -0.74 V). However, coordination of ligands to aqueous transition metal ions can result in the formation of complexes having very different electrochemical behaviours from those of the parent aqueous transition metal ions. The classic example of this is provided by the Co 3+ (aq) (or [Co(OH 2 ) 6 ] 3+ ) ion. Under standard conditions in aqueous solution, this ion is extremely strongly oxidising (E o Co 3+ ∕Co 2+ = +1.9 V), and as a result is generally stable only under ice-cold acidic conditions.
eBook - PDF- Young, William Vining, Roberta Day, Beatrice Botch(Authors)
- 2017(Publication Date)
- Cengage Learning EMEA(Publisher)
● First and second ionization energy values for the transition metals are generally much smaller than third ionization energies due to the similar valence electron configura-tions of these elements (24.1c). ● Most transition metals have at least two oxidation states (24.1c). 24.2 Isolation from Metal Ores ● Metals can be classified by the kinds of ores they form. Most transition metals are litho-philes, chalcophiles, or siderophiles (24.2a). ● Metals are extracted from ores by a number of different methods that include elec-trolysis, reaction with a reducing agent such as carbon (coke), and roasting (24.2b). 24.3 Coordination Compounds: Structure and Isomerism ● Coordination compounds typically consist of a metal, some ligands, and counterions (if needed) (24.3a). ● Ligands are classified by the number of attachments they form to a metal (24.3a). ● Coordination compounds and complex ions vary in their coordination number, the number and type of species inside and outside the coordination sphere, and the types of ligands attached to the metal (24.3a). ● Coordination compounds are named by a standard set of rules (24.3b). ● The chelate effect explains why coordination compounds containing chelating ligands are more thermodynamically stable than similar compounds containing only monoden-tate ligands (24.3c). ● Octahedral and square planar coordination compounds exhibit a variety of structural isomers (linkage isomers and ionization isomers) and stereoisomers (geometric iso-mers and optical isomers) (24.3d). Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-300 Unit 24 The Transition Metals 801 24.4 Coordination Compounds: Bonding and Spectroscopy ● Crystal field theory explains why the d orbitals in a coordination compound are not equal in energy (24.4a).
eBook - PDFThe Chemistry of the Metallic Elements
The Commonwealth and International Library: Intermediate Chemistry Division
- David J. Steele, J. E. Spice(Authors)
- 2017(Publication Date)
- Pergamon(Publisher)
The complete sequence is shown below. Cr(NH 3 ) 6 + + + ) Cr(NH 3 ) 5 (Br) + + ^Cationic Cr(NH 3 ) 4 (Br) 2 + J Cr(NH 3 ) 3 (Br) 3 Neutral Cr(NH 3 ) 2 (Br) 4 ] (Cr(NH 3 )(Br) 5 --)* [Anionic Cr(Br) 6 -- J * The existence of this is uncertain. r~ , i H,N '3 N> S | / N H 3 H 3 N< /N NH, The Transition Elements: their General Chemistry 93 It will be appreciated that the electronic configuration round the central metal atom remains the same throughout the above changes, for the bonding on to that atom involves the donation of a pair of electrons from each ammonia or molecule or bromide ion; the substitution of bromide for ammonia simply changes the charge of the ion. Ions or molecules attached to a central transition metal atom, e.g. NH 3 and Br mentioned above, are called ligands. A ligand so common that its presence is often ignored is the water molecule. Reactions involving aqueous solutions of metal salts are often discussed in terms of ionic species such as Cu + + , Fe + + , Fe + + + , etc.; it must be remembered that they are co-ordination compounds in which the ligands are water molecules. They are called aquo-complexes; two examples are shown below, the aquo-complex of copper con-tains four water molecules in the plane of the copper atom; that of ferrous iron has six aquo-ligands arranged octahedrally. H 2 0 H 2 0 V ^ H 0-Cu 2 ij) K o 0 H.,0 Fe* + • H ? 0 **' i H *° H 2 0 Reactions in solution in which co-ordination complexes are formed result from the replacement of water molecules by other ligands. For example, the well-known reaction between cupric salts and ammonia solution may be represented thus: excess NH 4 OH Cu(H 2 0)t + T Cu(NH 3 )t + +4H 2 0. tetrammine cupric ion It will be observed that such a reaction involves a series of reactions in each one of which one water molecule is replaced in turn by an ammonia molecule; the above equation thus only represents the final result of a sequence of four reactions.
eBook - PDF- Edward J. Neth, Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson(Authors)
- 2019(Publication Date)
- Openstax(Publisher)
This figure shows, from left to right, solutions containing [M(H 2 O) 6 ] n+ ions with M = Sc 3+ (d 0 ), Cr 3+ (d 3 ), Co 2+ (d 7 ), Ni 2+ (d 8 ), Cu 2+ (d 9 ), and Zn 2+ (d 10 ). (credit: Sahar Atwa) Remember that in most main group element compounds, the valence electrons of the isolated atoms combine to form chemical bonds that satisfy the octet rule. For instance, the four valence electrons of carbon overlap with electrons from four hydrogen atoms to form CH 4 . The one valence electron leaves sodium and adds to the seven valence electrons of chlorine to form the ionic formula unit NaCl ( Figure 19.13). Transition metals do not normally bond in this fashion. They primarily form coordinate covalent bonds, a form of the Lewis acid-base interaction in which both of the electrons in the bond are contributed by a donor (Lewis base) to an electron acceptor (Lewis acid). The Lewis acid in coordination complexes, often called a central metal ion (or atom), is often a transition metal or inner transition metal, although main group elements can also form coordination compounds. The Lewis base donors, called ligands, can be a wide variety of chemicals—atoms, molecules, or ions. The only requirement is that they have one or more electron pairs, which can be donated to the central metal. Most often, this involves a donor atom with a lone pair of electrons that can form a coordinate bond to the metal. FIGURE 19.13 (a) Covalent bonds involve the sharing of electrons, and ionic bonds involve the transferring of electrons associated with each bonding atom, as indicated by the colored electrons. (b) However, coordinate covalent bonds involve electrons from a Lewis base being donated to a metal center. The lone pairs from six water molecules form bonds to the scandium ion to form an octahedral complex. (Only the donated pairs are shown.) The coordination sphere consists of the central metal ion or atom plus its attached ligands.
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