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Unit 6: Transition Metals and Coordination Chemistry

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    • 6.1: Introduction to Coordination Chemistry
      Complexes or coordination compounds are molecules that posess a metal center that is bound to ligands (atoms, ions, or molecules that donate electrons to the metal). These complexes can be neutral or charged. When the complex is charged, it is stabilized by neighboring counter-ions.
    • 6.2: What is a Complex Ion?
      This page explains the terms complex ion and ligand, and looks at the bonding between the ligands and the central metal ion. It discusses various sorts of ligand (including some quite complicated ones), and describes what is meant by coordination number.
    • 6.3: Coordination Numbers and Geometry
      The total number of points of attachment to the central element is termed the coordination number and this can vary from 2 to as many as 16, but is usually 6. In simple terms, the coordination number of a complex is influenced by the relative sizes of the metal ion and the ligands and by electronic factors, such as charge which is dependent on the electronic configuration of the metal ion.
    • 6.4: Isomers
      Isomers are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical isomers, etc. (see chart below). There are two main forms of isomerism: structural isomerism and stereoisomerism (spatial isomerism).
    • 6.5: Nomenclature of Coordination Complexes
      There are well-established rules for both naming and writing the formulae of coordination compounds. The purpose of these rules is to facilitate clear and precise communication among chemists.
    • 6.6: Ligands
      Ligands are classified based on whether they bind to the metal center through a single site on the ligand or whether they bind at multiple sites. Ligands that bind through only a single site are called monodentate from the Latin word for tooth; in contrast, those which bind through multiple sites are called chelating.
    • 6.7: Electronic Configurations
      To be able to use Crystal Field Theory (CFT) successfully, it is essential that you can determine the electronic configuration of the central metal ion in any complex. This requires being able to recognise all the entities making up the complex and knowing whether the ligands are neutral or anionic, so that you can determine the oxidation number of the metal ion.
    • 6.8: Bonding Theories
      Coordination complexes caused great fascination among chemists during the nineteenth century, although it wasn’t until the century’s end that Alfred Werner determined the fundamental principles of their structure. A fuller understanding of their structures was developed over the first half of the twentieth century. This understanding developed in stages, with newer theories and models building on previous ones rather than replacing them completely.
    • 6.9: Crystal Field Theory
      One of the most striking characteristics of transition-metal complexes is the wide range of colors they exhibit. In this section, we describe crystal field theory (CFT), a bonding model that explains many important properties of transition-metal complexes, including their colors, magnetism, structures, stability, and reactivity. The central assumption of CFT is that metal–ligand interactions are purely electrostatic in nature.
    • 6.10: Factors Affecting Electronic Structure
      The magnitude of the crystal field splitting energy, Δo, dictates whether a complex with four, five, six, or seven d electrons is high spin or low spin, which affects its magnetic properties, structure, and reactivity. Large values of Δo (i.e., Δo > P) yield a low-spin complex, whereas small values of Δo (i.e., Δo < P) produce a high-spin complex. As we noted, the magnitude of Δo depends on three factors: the charge on the metal ion, the principal quantum number of the metal (and thus its locati
    • 6.11: Crystal Field Stabilization Energy
      A parameter called the crystal field stabilization energy (CFSE) was developed to assess the energy difference between the metal ion in an octahedral coordination geometry and a spherical field. To determine CFSE, we simply add up the energy of all the electrons relative to the energy level of electrons in the spherical field, in units of \(\Delta_o\).
    • 6.12: Colors of Coordination Complexes
      The color for a coordination complex can be predicted using the Crystal Field Theory (CFT). Knowing the color can have a number of useful applications, such as the creation of pigments for dyes in the textile industry. The tendency for coordination complexes to display such a wide array of colors is merely coincidental; their absorption energies happen to fall within range of the visible light spectrum.
    • 6.13: Complex-Ion Equilibria
      In general, chemical equilibrium is reached when the forward reaction rate is equal to the reverse reaction rate and can be described using an equilibrium constant, K. Complex ion equilibria are no exception to this and have their own unique equilibrium constant. This formation constant, Kf , describes the formation of a complex ion from its central ion and attached ligands. This constant may be caled a stability constant or association constant.
    • 6.14: The Chelate Effect
      Ligands like chloride, water, and ammonia are said to be monodentate (one-toothed, from the Greek mono, meaning “one,” and the Latin dent-, meaning “tooth”): they are attached to the metal via only a single atom. Ligands can, however, be bidentate (two-toothed, from the Greek di, meaning “two”), tridentate (three-toothed, from the Greek tri, meaning “three”), or, in general, polydentate (many-toothed, from the Greek poly, meaning “many”), indicating that they are attached to the metal at two, th
    • 6.16: Hard and Soft Acids and Bases
      The thermodynamic stability of a metal complex depends greatly on the properties of the ligand and the metal ion and on the type of bonding. Metal–ligand interaction is an example of a Lewis acid–base interaction. Lewis bases can be divided into two categories: hard bases contain small, relatively nonpolarizable donor atoms (such as N, O, and F), and soft bases contain larger, relatively polarizable donor atoms (such as P, S, and Cl).
    • 6.17: Complex Ion Chemistry
      An introduction to the complex ions formed by transition and other metals. Includes bonding, shapes and names, and a simple look at the origin of color. Looks in detail at various ligand exchange reactions and the chemistry of common hexaaqua ions.
    • 6.18: Crystal Field Theory
      One of the most striking characteristics of transition-metal complexes is the wide range of colors they exhibit. Crystal field theory (CFT) is a bonding model that explains many important properties of transition-metal complexes, including their colors, magnetism, structures, stability, and reactivity. The central assumption of CFT is that metal–ligand interactions are purely electrostatic in nature.

    Unit 6: Transition Metals and Coordination Chemistry is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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