Coordination Compounds
Coordination compounds are molecules that consist of a central metal atom or ion bonded to surrounding molecules or ions, known as ligands. These ligands donate electron pairs to the metal, forming coordinate covalent bonds. Coordination compounds often exhibit unique properties and are widely used in fields such as catalysis, medicine, and materials science.
5 Key excerpts on "Coordination Compounds"
eBook - ePubBiermann's Handbook of Pulp and Paper
Volume 2: Paper and Board Making
- Pratima Bajpai(Author)
- 2018(Publication Date)
- Elsevier(Publisher)
...The distinction is arbitrary but has historical precedence. More information and detail on this important subject may be found in advanced inorganic chemistry textbooks. Coordinate chemistry explains the behavior of alum (which is central to many aspects of wet end chemistry) in aqueous solutions. Aluminum ions will be used to demonstrate some aspects of coordinate chemistry. Also, many size press formulations contain zirconium compounds or synthetic polymers containing carboxylated polymers that are “set” with metal ions. Applications of coordinate chemistry will undoubtedly receive much wider recognition in the future by the pulp and paper industry. The first explanation of the actual nature of complexes is credited to the classic 1906 work of Werner, for which Werner received the Nobel Prize in 1913. Werner showed that neutral compounds were bound directly to metal atoms in many complexes. Thus CuCl 2 ·6NH 3 is correctly written as Cu(NH 3) 6 Cl 2. In general, coordination complexes are formed upon the reaction of Lewis acids, compounds which accept electron pairs, with Lewis bases, compounds which donate electron pairs, to form the complex. Acid–base reactions involving proton transfers are examples of coordinate chemistry reactions. The reaction of H + and OH − to form the product H 2 O proceeds as H + + :OH − → H:OH, where the electron pair is shared in the product. Lewis greatly expanded the class of acid–base reactions over that of the Bronsted–Lowry theory by making electron pairs of central importance rather than the proton. Many other reactions besides acid–base reactions are included as well. One classic example is the reaction of the two gases BF 3 and NH 3 to form the complex H 3 N:BF 3, which is a white solid. Ligands The term ligand denotes the species donating the electron pair(s). Ligands are Lewis bases. In the previous chemical equation, the ligand was NH 3...
eBook - ePub- Jeffrey Gaffney, Nancy Marley(Authors)
- 2017(Publication Date)
- Elsevier(Publisher)
...Examples include the metal cations such as Cu + 2, Co + 3, Fe + 2, and Fe + 3, the hydrogen ion (H +), protonated compounds such as NH 4 +, H 3 O +, and also CH 3 +, a species very important to organic chemistry and will be discussed in Chapter 13. Metal cations have two properties that allow them to act as Lewis acids: (1) their positive charge attracts electrons and (2) they have at least one empty orbital that can accept an electron pair. When a metal cation (Lewis acid) reacts with a species containing a lone pair of electrons (Lewis base), a coordination complex is formed. A coordination complex is a product of a Lewis acid-base reaction in which neutral molecules or anions bond to a central metal cation by coordinate covalent bonds. The molecules or anions that bond to the central metal cation are called ligands, from the Latin meaning “to tie or bind.” When a metal salt is dissolved in water, it ionizes to release the metal cations. Because the metal cations are electron-deficient, they react with water molecules (an electron pair donor) to form coordinate covalent bonds. These metal-water coordination complexes contain the central metal ion with water as the ligands. They are the predominant species in aqueous solutions of many metal salts, such as metal nitrates, sulfates, and perchlorates. They have the general stoichiometry of [M(H 2 O) n ] z +, where M is the metal cation with a charge of z +. Since the coordination complex carries a net charge, it is called a complex ion. The properties of these metal-water coordination complexes are important in many aspects of environmental, biological, and industrial chemistry. The most common of the metal-water coordination complexes are those where the metal cation is bonded to six water molecules with the formulas [M(H 2 O) 6 ] 2 + and [M(H 2 O) 6 ] 3 + (Fig. 5.4). This makes the molecular geometry of the complex ion octahedral, as described in Section 3.7...
eBook - ePub- James F. Pankow(Author)
- 2019(Publication Date)
- CRC Press(Publisher)
...Part III Metal/Ligand Chemistry 10 Complexation of Metal Ions by Ligands 10.1 Introduction “Coordination chemistry” is the subdiscipline in chemistry concerned with the association of metal ions with species like OH –, Cl –, SO 4 2 −, NH 3, EDTA, and many others. In this context, species like OH – are referred to as “ligands”. As with “ligament”, the word “ligand” derives from the Latin verb ligare, “to bind”. Ligands are often negatively charged, but this is not always the case (cf., NH 3). The combined metal–ligand species is a “complex”. Cd 2 + + Cl − = CdCl + metal ion + ligand = complex K Cl1 = { CdCl + } { Cd 2+ } { Cl − }. (10.1) The subscript Cl followed by 1 (one) denotes addition of a first Cl − to the metal ion. A second Cl − be added, leading to a higher complex: CdCl + + Cl − = CdCl 2 o K Cl2 = { CdCl 2 o } { CdCl + } { Cl − }. (10.2) Before proceeding, we make two points. First, the specific value of a complexation constant such as K Cl1 will be different for Cd 2+ as compared to Fe 2+, and for Fe 2+ as compared to Fe 3+, etc. In complicated problems, metal-specific notation will be needed, as with K Cl1 Cd(II), K Cl1 Fe(II), and K Cl1 Fe(III), etc.; within this chapter we will consider one metal at a time. Second, in preceding chapters, we have considered Cl − to be a spectator ion. Here too, most of the chloride present in a solution remains as a spectator ion, even if trace metals like Cd and Au as in sea waters and brines can be mostly complexed with Cl − (Byrne, 2002); not much Cl − can be drawn into trace metals. H 2 O itself is an important ligand in aqueous solutions because it has two pairs of outer shell non-bonding electrons, either of which can be used to bind to a metal. In Chapter 3, it was discussed that aqueous H + is actually present in water as a mix of solvated species with the general formula H(H 2 O) n +, with n = 6 being an important example...
eBook - ePubBiochemistry
An Organic Chemistry Approach
- Michael B. Smith(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
...10 Carbon–Metal Bonds, Chelating Agents and Coordination Complexes When a metal is incorporated into a molecule with a metal–carbon bond, the resulting molecule is called an organometallic compound. In organic chemistry, organometallic compounds are used most often as nucleophilic reagents, effectively as carbanion surrogates. On general, organometallic reagents are reactive species and often used as reagents. In biology, metals are important at cofactors for the efficient activity of enzymes, and their ability to form multivalent compounds leads to the use of metals as chelating agents and their importance for the formation of coordination complexes. 10.1 Organometallics Carbon–metal bonds are important in many areas of organic chemistry. This section will briefly review simple examples. A carbon–boron bond and a carbon–mercury bond are important examples of a class of compounds known as organometallics (organic molecules that incorporate one or more metal atoms). As a practical matter, the type of metal can be divided into two categories, alkali metals (Li, Na, Mg) or transition metals (Cu, Pd, etc.). While some definitions of an organometallic compound are limited to compounds that contain a transition metal, the broader definition includes both types of metal. For convenience, the term organometallics in this book will include both alkali and transition metals. Carbon forms bonds to many metals to yield molecules that contain a C—M unit, where M is the metal. The more common metals include lithium, magnesium, and copper, and organometallic compounds based on those metals are introduced in this chapter. Other organometallic compounds will be introduced as they are required. 10.2 Organometallics in Organic Chemistry An important class of carbon nucleophiles is formed by the reaction of alkyl halides (R—X, where X = halogen) with alkali metals...
eBook - ePubCation Binding by Macrocycles
Complexation of Cationic Species by Crown Ethers
- Yoshihisa Inoue, George W. Gokel(Authors)
- 2018(Publication Date)
- Routledge(Publisher)
...17 Second-Sphere Coordination of Transition Metal Complexes by Crown Ethers J. FRASER STODDART AND RYSZARD ZARZYCKI * The University, Sheffield, United Kingdom 1 From Classical to Contemporary Chemistry 2 Recognition by Mesomolecules 3 The Concept of Second-Sphere Coordination 4 3nCn Crown Ethers as Second-Sphere Ligands 4.1 Adducts involving ammine ligands 4.2 Adducts involving aqua ligands 4.3 Adducts involving other ligands 5 DB 3nCn Crown Ethers as Second-Sphere Ligands 5.1 Adducts involving transition metal monoammine complexes 5.2 Adducts involving transition metal diammine complexes 6 Macrobicyclic and Macropolycyclic Crown Ethers as Second-Sphere Ligands 6.1 Macrobicyclic crown ether ligands 6.2 A macropolycyclic crown ether ligand 7 Simultaneous First- and Second-Sphere Coordination Ligands 8 Other Molecular Receptors as Second-Sphere Ligands 9 Third-Sphere Coordination Ligands? 10 Future Perspectives Acknowledgments References 1 FROM CLASSICAL TO CONTEMPORARY CHEMISTRY Classical chemistry is all about the primary forces responsible for chemical bonding. Linus Pauling [1], the grandfather of modern chemical bonding theory, first postulated that atoms are held together by either metallic (not discussed further here), ionic, or covalent bonds. Ionic bonding arises from electrostatic attractions (X + ⋯ Y −) between oppositely charged cations (X +) and anions (Y −), leading to solids that are comprised of lattices. Covalent bonding arises from the sharing (X—Y) of electrons by atoms (X and Y), leading to molecular compounds. Since molecular compounds can exist as liquids, or indeed even as solids (simple or lattice), at low pressures and temperatures, it follows that other forces must operate between the molecules in addition to the forces that exist within them. Otherwise all molecular compounds would be gases even down to temperatures approaching absolute zero...
