Polydentate Ligands & Polydentate Ligands & Nomenclature Nomenclature

Chapter 24 – Lecture 2Chapter 24 – Lecture 2

Chemistry 123Spring 2008

Dr. Woodward

Chelating (Polydentate) Chelating (Polydentate) LigandsLigands

PorphyrinsPorphyrins

Porphine Porphine (C(C2020HH1414NN44))

Myoglobin & Myoglobin & HemoglobinHemoglobin

ChlorophyllChlorophyll

Rules for Naming Coordination Rules for Naming Coordination CompoundsCompounds

1. For ionic compounds the cation comes before the anion.2. For the complex ion part (within brackets) the ligands are

listed in alphabetical order before the metal.3. Anionic ligands end in the letter o, neutral ligands retain

their names (NH3 = ammine, H2O = aqua).ClCl−− = chloro = chloro BrBr−− = bromo = bromo I I−− = iodo = iodoOHOH−− = hydroxo = hydroxo CNCN−− = cyano = cyano O O2−2− = oxo = oxo

4. Greek prefixes are used to indicate the number of ligands (different prefixes are used if the ligand itself has one of these prefixes).

2 = di 3 = tri 4 = tetra 5 = penta 6 = hexa 2 = di 3 = tri 4 = tetra 5 = penta 6 = hexa 2 = bis 3 = tris 4 = tetrakis (alternate prefixes)2 = bis 3 = tris 4 = tetrakis (alternate prefixes)

5. If the complex ion has a negative charge it ends in ate.6. The oxidation number of the metal is given in parentheses

in roman numerals.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

250 300 350 400 450 500 550 600 650 700wavelength (nm)

abso

rban

ce (C

rO42-

)

0

1

2

3

4

5

abso

rban

ce (S

rCrO

4, Pb

CrO

4)

dilute CrO42-

solution

SrCrO4 PbCrO4

conc. CrO4

2-

solution

Color: CrOColor: CrO44-- & Chromate & Chromate

SaltsSalts

SrCrO4 behaves much like a concentrated CrO42- solution. Sr2+ ions have

little effect on the electronic absorption, whereas Pb2+ ions shift the absorption edge to lower energy (longer wavelengths).