Lecture 24

Lecture 24 - Coordina(on Complex • Transi'on metals...

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Unformatted text preview: Coordina(on Complex • Transi'on metals form coordina'on compounds (or complexes) • Composi'on of coordina'on compounds:  at least one complex ion  a central metal ion is bonded to ligands (molecules or anions)  complex ion is associated with a counter ion • All ligands have ac've lone pairs of electrons in their outer energy levels that are used form coordinate bonds with the metal • Other metals also form complex ions. However, transi'on metals form a very wide range of complex ions. Figure 22.7 models Components of a coordina(on compound. wedge diagrams chemical formulas Structures of Complex Ions: Coordina(on Numbers, Geometries, and Ligands • Coordina(on Number  ­ the number of ligand atoms that are bonded directly to the central metal ion. The coordina'on number is specific for a given metal ion in a par'cular oxida'on state and compound. • Geometry  ­ the geometry (shape) of a complex ion depends on the coordina'on number and nature of the metal ion. • Donor atoms per ligand  ­ molecules and/or anions with one or more donor atoms that each donate a lone pair of electrons to the metal ion to form a covalent bond. Formulas and Names of Coordina(on Compounds Rules for wri'ng formulas: 1. The ca'on is wriIen before the anion. 2.  The charge of the ca'on(s) is balanced by the charge of the anion(s). 3.  For the complex ion, neutral ligands are wriIen before anionic ligands, and the formula for the whole ion is placed in brackets. Formulas and Names of Coordina(on Compounds con'nued Rules for naming complexes: 1. The ca'on is named before the anion. 2.  Within the complex ion, the ligands are named, in alphabe'cal order, before the metal ion. 3.  Neutral ligands generally have the molecule name, but there are a few excep'ons (Table 22.6). Anionic ligands drop the  ­ide and add  ­o aQer the root name. 4.  A numerical prefix indicates the number of ligands of a par'cular type. 5.  The oxida'on state of the central metal ion is given by a Roman numeral (in parentheses) only if the metal ion can have more than one state. 6.  If the complex ion is an anion, we drop the ending of the metal name and add  ­ate. Sample Problem 22.2 PROBLEM: Wri(ng Names and Formulas of Coordina(on Compounds (a) What is the systema'c name of Na3[AlF6]? (b) What is the systema'c name of [Co(en)2Cl2]NO3? (c) What is the formula of tetraamminebromochloropla'num(IV) chloride? (d) What is the formula of hexaamminecobalt(III) tetrachloro ­ferrate (III)? Use the rules presented in Slide 22 ­18 and 22 ­19, and refer to Tables 22.6 and 22.7. SOLUTION: (a) The complex ion is [AlF6]3 ­. PLAN: Six (hexa ­) F ­ ions (fluoro) as ligands  ­ hexafluoro Aluminum is the central metal atom  ­ aluminate Aluminum has only the +3 ion, so we do not need Roman numerals. sodium hexafluoroaluminate Sample Problem 22.2 con(nued Wri(ng Names and Formulas of Coordina(on Compounds (b) There are two ligands, chlorine and ethylenediamine  ­ dichloro, [bis(ethylenediamine)] The complex is the ca'on and we have to use Roman numerals for the cobalt oxida'on state since it has more than one  ­ (III) The anion, nitrate, is named last. dichlorobis(ethylenediamine)cobalt(III) nitrate (c) 4 NH3 Br ­ Cl ­ Pt4+ Cl ­ tetraamminebromochloropla'nate(IV) chloride [Pt(NH3)4BrCl]Cl2 (d) 6 NH3 Co3+ 4 Cl ­ Fe3+ hexaamminecobalt(III) tetrachloroferrate(III) [Co(NH3)6][FeCl4]3 Figure 22.8 Important types of isomerism in coordina(on compounds. • Coordina(on isomers– Composi'on of the complex ion changes but the composi'on of the compound remains the same • Linkage isomers– composi'on of the complex ion remains the same but but the ligand donor atom changes. • Geometric isomers– arrangements of the ligands vary in space. • Op(cal isomers– when a molecule and its mirror image cannot be superimposed. Figure 22.9 Figure 22.10 Geometric (cis ­trans) isomerism. Figure 22.11 Op(cal isomerism in an octahedral complex ion. Sample Problem 22.3 PROBLEM: Determining the Type of Stereoisomerism Draw all stereoisomers for each of the following and state the type of isomerism: SOLUTION: : PLAN: : (a) [Pt(NH3)2Br2] (b) [Cr(en)3]3+ (en = H2NCH2CH2 NH2) Determine the geometry around each metal ion and the nature of the ligands. Place the ligands in as many different posi'ons as possible. Look for cis ­trans and op'cal isomers. (a) Pt(II) forms a square planar complex and there are two pair of monodentate ligands  ­ NH3 and Br. These are geometric isomers; they are not op'cal isomers since they are superimposable on their mirror images. Sample Problem 22.3 Determining the Type of Stereoisomerism con(nued (b) Ethylenediamine is a bidentate ligand. Cr3+ has a coordina'on number of 6 and an octahedral geometry. Since all of the ligands are iden'cal, there will be no geometric isomerism possible. The mirror images are nonsuperimposable and are therefore, op<cal isomers. Figure 22.12 Hybrid orbitals and bonding in the octahedral [Cr(NH3)6]3+ ion. Figure 22.13 Hybrid orbitals and bonding in the square planar [Ni(CN)4]2 ­ ion. Figure 22.14 Hybrid orbitals and bonding in the tetrahedral [Zn(OH)4]2 ­ ion. ...
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This note was uploaded on 02/18/2012 for the course CHEM 6C taught by Professor Hoeger during the Spring '08 term at UCSD.

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