Chapter 21 Transition Metals and Coordination Chemistry...show great similarities within a given period as well as within a given vertical group. Key reason: last electrons added are inner electrons (d’s, f’s). Inner d and f electrons cannot participate as easily in bonding as can the valence s and p electrons.

Figure 21.1 The Position of the Transition Elements on the Periodic Table

Complex Ions...species where the transition metal ion is surrounded by a certain number of ligands (Lewis bases). Co(NH 3 ) 6 3+ Pt(NH 3 ) 3 Br + Most compounds are colored, because the transition metal ion in the complex ion can absorb visible light of specific wavelengths. Many compounds are paramagnetic.

Electron Configurations For the first row transition metals 3d orbitals begin to fill after the 4s orbital is complete. Sc:[Ar]4s 2 3d 1, Ti: [Ar]4s 2 3d 2, V: [Ar]4s 2 3d 3, Cr: [Ar]4s 2 3d 4 (expected), [Ar]4s 1 3d 5 (actual). Chromium configuration occurs because the energies of the 3d and 4s orbital are very similar for the first row transition elements. Cu: [Ar]4s 2 3d 9 (expected) but the actual is [Ar]4s 1 3d 10. The energy of the 3d orbitals in transition metal ions is significantly less that of the 4s orbital.

Oxidation States and Ionization Energies The transition metals can form a variety of ions by losing one or more electrons. For the first five metals the maximum possible oxidation state corresponds to the loss of all the 4s and 3d electrons. Toward the right end of the period, maximum oxidation state are not observed, in fact 2+ ions are the most common because the 3d orbitals become lower in energy as the nuclear charge increases, and the electrons become increasingly difficult to remove.

Figure 21.2 Plots of the First (Red Dots) and Third (Blue Dots) Ionization Energies for the First-Row Transition Metals

The 4d and 5d Transition Series There is a decrease in size going from left to right for each of the series. There is an increase in radius in going from the 3d to the 4d metals but 4d and 5d metals are remarkably similar in size. This phenomenon is the result of lanthanide contraction. In the lanthanide series electrons are filling the 4f orbitals. The 4f orbitals are buried in the interior of these atoms, the increasing nuclear charge causes the radii of the lanthanide elements to decrease significantly going from left to right.

Figure 21.3 Atomic Radii of the 3d, 4d, and 5d Transition Series

A Coordination Compound... typically consists of a complex ion (transition metal ion with its attached ligand) and counter ions (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 Secondary valence: refers to the ability of a metal ion to bind to Lewis base (ligand) to form complex ions. This is known as coordination number (# of bonds formed between the metal ion and the ligands) Primary valence: refers to the ability of the metal ion to form ionic bonds with oppositely charged ions which is also known as oxidation state.

Figure 21.5 The Ligand Arrangements for Coordination Numbers 2, 4, and 6

A Ligand... a neutral molecule or ion having a lone electron pair (Lewis base) that can be used to form a bond to a metal ion (Lewis acid). Coordinate covalent bond: metal-ligand bond formed because of the interaction of Lewis base and Lewis acid. Monodentate ligand: one bond to metal ion Polydentate ligand (chelates): can form more than two bonds to a metal ion

Naming Coordination Compounds [Co(NH 3 ) 5 Cl]Cl 2 1.Cation is named before the anion. “chloride” goes last 2.Ligands are named before the metal ion. ammine, chlorine named before cobalt 3.For ligand, an “o” is added to the root name of an anion (fluoro, bromo). For neutral ligands the name of the molecule is used, with exceptions. ammine, chloro 4.The prefixes mono-, di-, tri-, etc., are used to denote the number of simple ligands. penta ammine

Naming Coordination Compounds [Co(NH 3 ) 5 Cl]Cl 2 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 7.If the complex ion has a negative charge, the suffix “ate” is added to the name of the metal. pentaamminechlorocobalt (III) chloride

Isomerism When two or more species have the same formula but different properties, they are said to be isomers. The arrangements of the atoms differ, and this leads to different properties. Structural isomerism: where the isomers contain the same atoms but one or more bonds differ. Stereoisomerism: all the bonds are the same but the spatial arrangements of the atoms are different.

Figure 21.8 Some Classes of Isomers

Structure Isomerism Coordination isomerism: The composition of the complex ion varies. [Cr(NH 3 ) 5 SO 4 ]Br and [Cr(NH 3 ) 5 Br]SO 4 Linkage isomerism: Same complex ion structure but point of attachment of at least one of the ligands differs. [Co(NH 3 ) 4 (NO 2 )Cl]Cl [Co(NH 3 ) 4 (ONO)Cl]Cl

Figure 21.9 Bonding of NO 2 -

Stereoisomerism Stereoisomers have the same bonds but different spatial arrangements of the atoms. Geometrical isomerism (cis-trans): Atoms or groups of atoms can assume different positions around a rigid ring. Pt(NH 3 ) 2 Cl 2 Optical isomerism: the isomers have opposite effects on plane-polarized light. Dextrorotatory (d): that rotates the plane of light to the right. Levorotatory (l): that rotates the plane of light to the left.

Figure (a) The cis isomer, (b) trans isomer

Figure Typical cis-trans compounds of cobalt

Figure Unpolarized Light Consists of Waves Vibrating in Many Different Planes

Figure The Rotation of the Plane of Polarized Light by an Optically Active Substance

Figure A Human Hand Exhibits a Nonsuperimposable Mirror Image

Figure Isomers of I and II of Co(en) 3 3+ are Mirror Images That Cannot Be Superimposed

Figure The Optical Isomers of Co(en) 2 CI 2 +

The Localized Electron Model A complex ion with a coordination number of 6 will have an octahedral arrangement of ligands and complexes with two ligands will be linear. Complex ions with a coordination number of 4 can be either tetrahedral or square planar. The interaction of a metal ion and a ligand can be viewed as a Lewis acid-base reaction with the ligand donating a lone pair of electrons to an empty orbital of the metal ion to form a coordinate covalent bond.

Figure Hybrid Orbitals on Co 3+

Figure The Hybrid Orbitals Required for Tetrahedral, Square Planar, and Linear Complex Ions

Crystal Field Model... focuses on the energies of the d orbitals. Assumptions 1.Ligands are negative point charges. 2.Metal-ligand bonding is entirely ionic. Strong-field (low-spin): large splitting of d orbitals Weak-field (high-spin): small splitting of d orbitals Spectrochemical series: CN - >NO 2 - >en>NH 3 >H 2 O>OH - >F - >Cl - >Br - >I - strong-fieldweak-field

Figure An Octahedral Arrangement of Point-Charge Ligands and the Orientation of the 3d Orbitals

Figure The Energies of the 3d Orbitals for a Metal Ion in an Octahedral Complex

Figure The Visible Spectrum

Figure Violet Light

Figure The d Orbitals in a Tetrahedral Arrangement of Point Charges

Figure The Crystal Field Diagrams for Octahedral and Tetrahedral Complexes

Figure The Heme Complex

Figure Chlorophyll

Figure Myoglobin

Figure Hemoglobin

Metallurgy The process of separating a metal from its ore and preparing it for use is known as metallurgy. The steps in this process are: –Mining –Pretreatment –Reduction to the free metal –Purification of the metal (refining) –Alloying

Figure The Blast Furnace Used in the Production of Iron