152c20new

Chapter 20Chapter 20

Transition Metals and Coordination Chemistry

COORDINATION COMPOUNDSCOORDINATION COMPOUNDS

-- Lewis Acid - Base reactions:

Base – electron pair donor

Acid - electron pair acceptor

-- Coordinate covalent bonds

-- ligands, Lewis bases

-- Complex ions called “Metal Complexes”

ALFRED WERNER’SALFRED WERNER’SCOORDINATION THEORYCOORDINATION THEORY

-- Oxidation number of central atom

-- Coordination number

-- Coordination sphere (containing metal ion)

- anions

- cations

- neutral

-- Geometry

- look at hybridization shapes

-- Ligands

Formulas and Name of Some Common LigandsFormulas and Name of Some Common LigandsFormula NameH2O aquaNH3 ammineCO carbonylNO nitrosylH2NC2H4NH2 ethylenediamineOH- hydroxoO2- oxoF- fluoroCl- chloroBr- bromoI- iodoCN- cyano-NCS- isothiocyanato*-SCN- thiocyanato*SO4

2- sulfatoSO3

2- sulfitoNO3

- nitrato*-NO2

- nitro*-ONO- nitrito*CO3

2- carbonate*In these ligands two forms are known; they differ in the atom that donates the electron pair to the metal ion.

Various coordination geometries

Nomenclature of Coordination CompoundsNomenclature of Coordination Compounds1.The cation is named first in ionic compounds, then the anion.2.Nonionic compounds are given a one-word name.3.The following rules pertain to the names of ligands. a. The ligands are named first and the central atom last.

b. Ligands are named in alphabetical order by their root name.c. Neutral ligands are named the same as the molecule, except for a few such as

H2O (aqua) and NH3 (ammine), which have special names.d. Anionic ligands are named by adding –o to the stem of the usual name, such as chloro for Cl- and sulfato for SO4

2-. e. The name of each ligand is preceded by a Latin prefix (di-, tri- tetra-, penta, hexa- etc.) if more than one of that ligand Is bonded to the cetnral atom. For example, the ligands in PtCl4

2- are named tetrachloro, and the ligands in Co(NH3)4Cl2

+ are named tetraamminedichloro. If the ligand is polydentate, as in ethylenediamine, the number of ligands

bonded to the central atom is indicated by the corresponding Greek prefixes (bis-, tris-, tetrakis-, pentakis-, hexakis-, etc.). For example, the ligands in Co(en)3

3+ are named trisethylenediamine. A Greek prefix is also used when a Latin prefix forms a part of the name of the ligand, as in triethylamine, N(CH3)3. In this case, the ligand name is enclosed in parentheses. For example, the ligands in [Co(N(CH3)3)4]2+ are named tetrakis(triethylamine).

4, For a cationic complex ion or a nonionic compound, the central atom is given its ordinary name followed by its oxidation number n Roman numerals, enclosed in parentheses. For example, [Cr(H2O)5Cl]2+ is named pentaaquachlorochromium(III) ion, and [Cr(NH3)3Cl3] is name triamminetrichlorochromium (III).

5. For anionic complex ions, the suffix –ate is added to the name of the central atom, followed by the oxidation number in Roman numerals, enclosed in parentheses. For example, [Cr(CN)6]3- is name hexacyanochromate (III) ion.

Name the following complex ions.

a. Ru(NH3)5Cl2+

b. Fe(CN)64-

c. Mn(NH2CH2CH2NH2)32+

d. Co(NH3)5NO22+

Name the following coordination compounds.

a. [Co(NH3)6]Cl2

b. [Co(H2O)6]I3

c. K2 [PtCl4]

d. K4[PtCl6]

Give the formulas for the following.a. Hexakispyridinecobalt(III)chlorideb. Pentaammineiodochromium(III) iodidec. Trisethylenediamminenickel(II)bromided. Potassium tetracyanonickelate(II)e. Tetraamminedichloroplatinum(IV)

tetrachloroplatinate(II)Draw geometrical isomers of each of the following complex ions.

a. [CO(C2O4)2(H2O2]-

b. [Pt(NH3)4I2]2+

c. [Ir(NH3)3Cl3]d. [Cr(en(NH3)2I2]+

Amino acids can act as ligand toward transition metal ions. The simplest amino acid is glycine (NH2CH2CO2H). Draw a structure of the glycinate anion (NH2CH2CO2

-) acting as a bidentate ligand. Draw the structure isomers of the square planar complex Cu(NH2CH2CO2)2.

BAL is a chelating agent used in treating heavy-metal poisoning. It acts as a bidentate ligand. What types of linkage isomers are possible when Bal coordinates to a metal ion?

Geometrical Isomers of [Co(NH3)4Cl2]+

Geometrical isomers of [pt(NH3)2Cl2]

Mirror images of cis-[Co(en)2Cl2]+ and trans-[Co(en)2Cl2]+

COORDINATION COORDINATION COMPOUND REACTIONSCOMPOUND REACTIONS

Oxidation – ReductionOuter sphere: coordination sphere and ligands do not change.Inner sphere: one or more

coordination sphere changes.

Substitution Reactions (Displacement)

Ligand reactions

COORDINATE COVALENT COORDINATE COVALENT BONDS AND GEOMETRYBONDS AND GEOMETRY

Valence Bond Theoryversus

Crystal Field Theory

Valence Bond hybridization

Octahedral d2sp3

Tetrahedral sp3

Square planar dsp2

“low spin” and “high spin” complexes

The 6 ligands in an octahedral crystal field

Formation of d2sp3 orbitals

Draw the d-orbital splitting diagrams for the octahedral complex ions of each of the following.

a. Fe2+ (high and low spin)b. Fe3+ (high spin)c. Ni2+

d. Zn 2+

e. Co2+ (high and low spin)

How many unpaired electrons are in the following complex ions?

a. Ru(NH3)62+ (low-spin case)

b. Fe(CN)63- (low-spin case)

c. Ni(H2O)62+

d. V(en)33-

e. CoCl42-

The 4 ligands in a tetrahedral crystal field

Tetrahedral crystal field splitting energy

The d orbital energy level

diagram for an

octahedral complex

Free Coorbitals

The d energy

diagrams for square,

planar, and linear complexes

Spectra of emerald and ruby

Absorption and emission of light by Cr (III) complex ions

Spectrochemical Series of LigandsSpectrochemical Series of Ligands

Wavelength in nm Crystal Fieldof Peak in Spectrum Splitting Energy

Ligand of Co(NH3)4X* (nm) for Co(NH3)5X (kJ/mol)COCN- 440 272-NO2

- 458 261en-NC-

NH3 475 252-NCS- 496 241OH2 490 244C2O4

2-

-ONO- 491 244OH- 503 238-ONO2

- 500 239F- 510 235Cl- 533 224-SCN-

S2-

Br- 550 217I- 580 206*This wavelength is that at which there is a maximum absorption of light in the spectrum of the Cobalt(III) complex ion.

Pairing Energy

Large

Small

The complex ion NiCl42- has two unpaired

electrons, while Ni(CN)42- is diamagnetic.

Propose structures for these two complex ions.

Tetrahedral complexes of Co2+ are quite common. Use a d-orbital splitting diagram to rationalize the stability of Co2+ tetrahedral complex ions.

The compound Ni(H2O)6Cl2 is green, while Ni(NH3)6Cl2 is purple. Predict the predominant color of light absorbed by each compound. Which compound absorbs light with the shorter wavelength? Predict in which compound is greater and whether H2O or NH3 is a stronger field ligand. Do your conclusions agree with the spectrochemical series?

The complex ion Fe(CN)63- is paramagnetic with one

unpaired electron. The complex ion Fe(SCN)63- has

five unpaired electrons. Where does SCN- lie in the spectrochemical series relative to CN-?