1. Metal Complexes -- Chapter 24
Metal Complex -- consists of a set of ligands that are bonded to a central metal ion by coordinate covalent bonds.
e.g. Cu L --> [CuL4]2+ ( L = NH3, H2O, etc)
Ligands are Lewis Bases and can be:
monodentate -- one donor atom
e.g. H2O, NH3, Cl–, OH–, etc.
bidentate -- two donor atoms
e.g. ethylenediamine, NH2–CH2–CH2–NH2 “en”

2. Polydentate ligands = EDTA4– polydentate -- more than two donor atoms
e.g. EDTA -- ethylenediaminetetraacetic acid
(6 donor atoms)
= EDTA4–

3. Chelate Effect
Chelate effect -- complexes with bi- or polydentate ligands are more stable than those with similar monodentate ligands
e.g. [Ni(en)3]3+ is more stable than [Ni(NH3)6]3+
Know Table 24.2!

4. Writing Formulas of Complex Ions
Metal ion first, then ligands. Charge outside brackets.
total charge = sum of metal ion + ligands
e.g. metal ion ligand complex
Cu2+ H2O [Cu(H2O)]2+
Co3+ NH3 [Co(NH3)6]3+
Fe3+ CN– [Fe(CN)6]3–

5. Nomenclature 1. Name the ligands, put in alphabetical order.
2. Add prefixes for ligands that appear more than once.
3. Name the metal
Cationic complex; metal name
Anionic complex; metal prefix + ate
4. Add oxidation state in roman numerals
5. As separate word, write “ion” if not neutral, or list counterions (positive first, negative second).
Examples:
Complex Name
[Ni(CN)4]2– tetracyanonickelate(II) ion
[CoCl6]3– hexachlorocobaltate(III) ion
[CoCl2(NH3)4]+ tetraaminedichlorocobalt(III) ion
Na3[Co(NO2)6] sodium hexanitrocobaltate(III)
[CrCl2(en)2]2SO4 dichlorobis(ethylenediamine)chromium(III) sulfate

6. Coordination Number and Structure
Coordination # -- number of donor atoms attached to the metal center
(a) Two-Coordinate Complexes -- linear structures
Rare except for Ag+
e.g. [Ag(NH3)2]+ and [Ag(CN)2]–
(b) Four-Coordinate Complexes -- two structural types
Tetrahedral structures -- common for ions with filled d subshells, e.g. Zn2+ as in [Zn(OH)4]2–

7. More Coordination Number and Structure
(b) Four-Coordinate Complexes -- two structural types
square planar structures -- common for d8 metal ions (Ni2+, Pd2+, Pt2+) and for Cu2+
e.g.
(c) Six-Coordinate Complexes -- the most common!
“always” octahedral structures, e.g.

8. Sample Problem
1. Give the name or formula, as required. Draw the structure of each complex.
a) [AgI2]–
b) [Co(en)3]3+
c) cis-dichlorobis(ethylenediamine)cobalt(III) chloride
d) sodium tetracyanonickelate(II)

9. Structural Isomers of Coordination Complexes
Linkage isomers
Coordination isomers
pentaamminenitrocobalt(II) ion
pentaamminenitritocobalt(II) ion
pentaamminechlorocobalt(II) bromide
pentaamminebromocobalt(II) chloride

10. Isomerism; Overview

11. Stereoisomers of Coordination Complexes
(a) Geometrical Isomers
cis
trans
fac
mer
(b) Enantiomers
Three common ways to get enantiomers:
--chiral ligand
--tetrahedral complex with 4 different groups
--octahedral complexes with chelating ligands (and no mirror plane)

12. Sample Questions
Draw a clear, 3-dimensional structure of the geometrical isomer of Co(en)(NH3)2Cl2 that is optically active. (define any abbreviations)
Excess silver nitrate is added to a solution containing mol of [Co(NH3)4Cl2]Cl. How many g of AgCl (FW = 143.3) will precipitate?

13. Sample Questions
Draw a clear, 3-dimensional structure of the geometrical isomer of Co(en)(NH3)2Cl2 that is optically active. (define any abbreviations)
Excess silver nitrate is added to a solution containing mol of [Co(NH3)4Cl2]Cl. How many g of AgCl (FW = 143.3) will precipitate?
7.48 g

14. Crystal Field Theory (Bonding in Transition Metal Complexes)
Metal complexes are usually highly colored and are often paramagnetic -- such facts can be explained by a “d-orbital splitting diagram” eg
dz2
dx2-y2
energy
D = crystal field splitting energy
t2g
dxy
dxz
dyz
d orbitals of the metal ion in
an octahedral field of ligands
d orbitals of the free metal ion

15. Shape and Directionality of the d Orbitalseg D
t2g

16. Crystal Field Strength
The size of D depends on…
The nature of the ligand (ligand-metal bond strength!)
“spectrochemical series” -- D decreases:
CN– > NO2– > en > NH3 > H2O > OH– > F– > Cl– > Br–
“strong field ligands” “weak field ligands”
The oxidation state of the metal (charge!)
D is greater for M3+ than for M2+
The row of the metal in the periodic table (size!)
for a given ligand and oxidation state of the metal, D increases going down in a group
e.g. D is greater in Ru(NH3)63+ than in Fe(NH3)63+
Colors of metal complexes are due to electronic transition between the t2g and eg energy levels

17. d Orbital Splitting Diagrams for Octahedral Complexeseg
dx2
dx2–y2 eg
dx2
dx2–y2
large D
“low spin”
small D
“high spin”
t2g
t2g
dxy
dxz
dyz
dxy
dxz
dyz
Fe(H2O)62+
Fe(CN)64–

18. High Spin vs. Low Spin
CN– is a stronger field ligand than is H2O which leads to a greater D value (i.e. a greater d orbital splitting)
As a result,
Fe(H2O)62+ is a “high spin” complex and is paramagnetic (4 unpaired electrons)
while,
Fe(CN)64– is a “low spin” complex and is diamagnetic (no unpaired electrons)
The CN– complex with the larger D value absorbs light of higher energy (i.e. higher frequency but shorter wavelength)
OMIT … d orbital splitting diagrams for other geometries (i.e. tetrahedral and square planar)

19. Sample Questions
A complex [CoA6]3+ is red. The complex [CoB6]3+ is green.
a) Which ligand, A or B, produces the larger crystal field splitting D?
b) If the two ligands are ammonia and water, which is A and which is B?
c) Draw the d orbital diagram of either complex, assuming it is “high spin.” How many unpaired electrons will it have?
Give the order of increase of D in the following sets:
a) Cr(NH3)63+, CrCl63–, Cr(CN)63–
b) Co(H2O)62+, Co(H2O)63+, Rh(H2O)63+