Chapter 21 Transition Metals and Coordination Chemistry

Section 21.1 The Transition Metals: A Survey Return to TOC Copyright © Cengage Learning. All rights reserved 2 The Position of the Transition Elements on the Periodic Table

Section 21.1 The Transition Metals: A Survey Return to TOC Copyright © Cengage Learning. All rights reserved 3 Forming Ionic Compounds More than one oxidation state is often found. Cations are often complex ions – species where the transition metal ion is surrounded by a certain number of ligands (Lewis bases).

Section 21.1 The Transition Metals: A Survey Return to TOC Copyright © Cengage Learning. All rights reserved 4 The Complex Ion Co(NH 3 ) 6 3+

Section 21.1 The Transition Metals: A Survey Return to TOC Copyright © Cengage Learning. All rights reserved 5 Ionic Compounds with Transition Metals Most compounds are colored because the transition metal ion in the complex ion can absorb visible light of specific wavelengths. Many compounds are paramagnetic. –is a form of magnetism whereby the substance is only attracted when in the presence of an induced magnetic field.

Section 21.1 The Transition Metals: A Survey Return to TOC Copyright © Cengage Learning. All rights reserved 6 Electron Configurations Example  V: [Ar]4s 2 3d 3 Exceptions: Cr and Cu  Cr: [Ar]4s 1 3d 5  Cu: [Ar]4s 1 3d 10

Section 21.1 The Transition Metals: A Survey Return to TOC Copyright © Cengage Learning. All rights reserved 7 Electron Configurations First-row transition metal ions do not have 4s electrons.  Energy of the 3d orbitals is less than that of the 4s orbital. Ti: [Ar]4s 2 3d 2 Ti 3+ : [Ar]3d 1

Section 21.1 The Transition Metals: A Survey Return to TOC Lanthanide Contraction Electrons fill the 4f orbitals 4f orbitals are buried in the interior of the atom As electrons are added to the buried 4f, the atomic size does not increase The atomic radii decreases due to increase nuclear charge Notice similar radii for 4d and 5d elements (green & red) Copyright © Cengage Learning. All rights reserved 8

Section 21.3 The MoleCoordination Compounds Return to TOC Copyright © Cengage Learning. All rights reserved 9 A Coordination Compound Typically consists of a complex ion and counterions (anions or cations as needed to produce a neutral compound): [Co(NH 3 ) 5 Cl]Cl 2 [Fe(en) 2 (NO 2 ) 2 ] 2 SO 4 K 3 Fe(CN) 6

Section 21.3 The MoleCoordination Compounds Return to TOC Copyright © Cengage Learning. All rights reserved 10 Coordination Number Number of bonds formed between the metal ion and the ligands in the complex ion.  6 and 4 (most common)  2 and 8 (least common)

Section 21.3 The MoleCoordination Compounds Return to TOC Copyright © Cengage Learning. All rights reserved 11 Ligands Neutral molecule or ion having a lone electron pair that can be used to form a bond to a metal ion.  Monodentate ligand – one bond to a metal ion  Bidentate ligand (chelate) – two bonds to a metal ion  Polydentate ligand – more than two bonds to a metal ion

Section 21.3 The MoleCoordination Compounds Return to TOC Copyright © Cengage Learning. All rights reserved 12 [Co(NH 3 ) 5 Cl] 2- AND / OR

Section 21.3 The MoleCoordination Compounds Return to TOC Copyright © Cengage Learning. All rights reserved 13 Coordinate Covalent Bond Bond resulting from the interaction between a Lewis acid (the metal ion) and a Lewis base (the ligand). [Co(NH 3 ) 5 Cl]Cl 2

Section 21.3 The MoleCoordination Compounds Return to TOC Copyright © Cengage Learning. All rights reserved 14 Rules for Naming Coordination Compounds 1.Cation is named before the anion. “chloride” goes last (the counterion) 2.Ligands are named before the metal ion. ammonia (ammine) and chlorine (chloro) named before cobalt [Co(NH 3 ) 5 Cl]Cl 2

Section 21.3 The MoleCoordination Compounds Return to TOC Copyright © Cengage Learning. All rights reserved 15 Rules for Naming Coordination Compounds 3.For negatively charged ligands, an “o” is added to the root name of an anion (such as fluoro, bromo, chloro, etc.). 4.The prefixes mono-, di-, tri-, etc., are used to denote the number of simple ligands. pentaammine [Co(NH 3 ) 5 Cl]Cl 2

Section 21.3 The MoleCoordination Compounds Return to TOC Copyright © Cengage Learning. All rights reserved 16 Rules for Naming Coordination Compounds 5.The oxidation state of the central metal ion is designated by a Roman numeral: cobalt (III) 6.When more than one type of ligand is present, they are named alphabetically: pentaamminechloro [Co(NH 3 ) 5 Cl]Cl 2

Section 21.3 The MoleCoordination Compounds Return to TOC Copyright © Cengage Learning. All rights reserved 17 Rules for Naming Coordination Compounds 7.If the complex ion has a negative charge, the suffix “ate” is added to the name of the metal. The correct name is: pentaamminechlorocobalt(III) chloride [Co(NH 3 ) 5 Cl]Cl 2

Section 21.3 The MoleCoordination Compounds Return to TOC Copyright © Cengage Learning. All rights reserved 18 Exercise Name the following coordination compounds. a)[Co(H 2 O) 6 ]Br 3 b)Na 2 [PtCl 4 ] hexaaquacobalt(III) bromide sodiumtetrachloro-platinate(II)

Section 21.5 Bonding in Complex Ions: The Localized Electron Model Return to TOC Copyright © Cengage Learning. All rights reserved 19 Bonding in Complex Ions 1.The VSEPR model for predicting structure generally does not work for complex ions.  However, assume a complex ion with a coordination number of 6 will have an octahedral arrangement of ligands.  And, assume complexes with two ligands will be linear.  But, complexes with a coordination number of 4 can be either tetrahedral or square planar.

Section 21.6 The Crystal Field Model Return to TOC Copyright © Cengage Learning. All rights reserved 20 Complex Ion Colors When a substance absorbs certain wavelengths of light in the visible region, the color of the substance is determined by the wavelengths of visible light that remain.  Substance exhibits the color complementary to those absorbed.