Chapter 23: The Transition Elements and Their Coordination Compounds

23.1 An Overview of Transition Element Properties

23.2 The Inner Transition Elements

23.3 Highlights of Selected Transition Metals

23.4 Coordination Compounds

23.5 Theoretical Basis for the Bonding and Properties of Complexes

Fig. 23.1

Orbital Occupancy of the Period 4 Metals–I

Element Partial Orbital Diagram Unpaired Electrons

Sc 1

Ti 2

V 3

Cr 6

Mn 5

4s 3d 4p

Table 23.1 (p. 1003)

Orbital Occupancy of the Period 4 Metals–II

Element Partial Orbital Diagram Unpaired Electrons

Fe 4

Co 3

Ni 2

Cu 1

Zn 0

4s 3d 4p

Table 23.1 (p. 1003)

Fig. 23.3

Fig. 23.4

Aqueous Oxoanions of V, Cr, and Mn in their Highest Oxidation States

Fig 23.5

Oxidation States and d-Orbital Occupancy of the Period 4 Transition Metals

3B 4B 5B 6B 7B 8B 8B 8B 1B 2BOxidation (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) State Sc Ti V Cr Mn Fe Co Ni Cu Zn

0 0 0 0 0 0 0 0 0 0 0 (d1) (d2) (d3) (d5) (d5) (d6) (d7) (d 8) (d10) (d10)+1 +1 +1 +1 +1 +1 +1 (d3) (d5) (d5) (d7) (d8) (d10)+2 +2 +2 +2 +2 +2 +2 +2 +2 +2 (d2) (d3) (d4) (d5) (d6) (d7) (d8) (d9) (d10)+3 +3 +3 +3 +3 +3 +3 +3 +3 +3 (d0) (d1) (d2) (d3) (d4) (d5) (d6) (d7) (d8)+4 +4 +4 +4 +4 +4 +4 +4 (d0) (d1) (d2) (d3) (d4 ) (d5) (d6)+5 +5 +5 +5 +5 (d0) (d1) (d2) (d4)+6 +6 +6 +6 (d0) (d1) (d2)+7 +7 (d0)

Table 23.2

(p. 1006)

Standard Electrode Potentials of Period 4 M2+ Ions

Half-Reaction E0 (V)

Ti2+(aq) + 2 e- Ti(s) -1.63

V2+(aq) + 2 e- V(s) -1.19

Cr2+(aq) + 2 e- Cr(s) -0.91

Mn2+(aq) + 2 e- Mn(s) -1.18

Fe2+(aq) + 2 e- Fe(s) -0.44

Co2+(aq) + 2 e- Co(s) -0.28

Ni2+(aq) + 2 e- Ni(s) -0.25

Cu2+(aq) + 2 e- Cu(s) 0.34

Zn2+(aq) + 2 e- Zn(s) -0.76

Table 23.3 (p. 1007)

Colors of Representative Compounds of the Period 4 Transition Metals

b

a c

d

e

f

g

h

i

j

a = Scandium oxideb = Titanium(IV) oxidec = Vanadyl sulfate dihydrated = Sodium chromatee = Manganese(II) chloride tetrahydrate

f = Potassium ferricyanideg = Cobalt(II) chloride hexahydrateh = Nickel(II) nitrate hexahydratei = Copper(II) sulfate pentahydrate j = Zinc sulfate heptahydrate

Fig. 23.6

(p. 1012)

Coordination Compounds: ComplexesCoordination Compounds: Complexes• Lewis acids are electron pair acceptors.

• Coordination compounds are metal compounds formed by Lewis acid-base interactions.

• Complexes: Have a metal ion (can be zero oxidation state) bonded to a number of ligands. Complex ions are charged. Example, [Ag(NH3)2]+.

• Ligands are Lewis bases.

• Coordination number: the number of ligands attached to the metal.

Coordination Numbers and GeometryCoordination Numbers and Geometry• The most common coordination numbers are 4 and 6.• Some metal ions have a constant coordination number

(e.g. Cr3+ and Co3+ have a coordination number of 6).• The size of the ligand affects the coordination number

(e.g. [FeF6]3- forms but only [FeCl4]- is stable).

• The amount of charge transferred from ligand to metal affects coordination number (e.g. [Ni(NH3)6]2+ is stable but only [Ni(CN)4]2- is stable).

• Four coordinate complexes are either tetrahedral or square planar (commonly seen for d 8 metal ions).

• Six coordinate complexes are octahedral.

Fig. 23.9(Square brackets enclose the metal ion and ligands.)

(p. 1017)

LigandsLigands• Monodentate ligands bind through one donor atom

only.– Therefore they occupy only one coordination site.

• Polydentate ligands (or chelating agents) bind through more than one donor atom per ligand.– Example, ethylenediamine (en), H2NCH2CH2NH2.

• The octahedral [Co(en)3]3+ is a typical en complex.

• Chelate effect: More stable complexes are formed with chelating agents than with the equivalent number of monodentate ligands.

(p. 1018)

NomenclatureNomenclature• Rules:

– For salts, name the cation before the anion. Example in [Co(NH3)5Cl]Cl2 we name [Co(NH3)5Cl]2+ before Cl-.

– Within a complex ion, the ligands are named (in alphabetical order) before the metal. Example [Co(NH3)5Cl]2+ is tetraamminechlorocobalt(II). Note the tetra portion is an indication of the number of NH3 groups and is therefore not considered in the alphabetizing of the ligands.

– Anionic ligands end in -o and neutral ligands are simply the name of the molecule. Exceptions: H2O (aqua) and NH3 (ammine).

NomenclatureNomenclature• Rules:

– Greek prefixes are used to indicate number of ligands (di-, tri-, tetra-, penta-, and hexa-). Exception: if the ligand name has a Greek prefix already. Then enclose the ligand name in parentheses and use bis-, tris-, tetrakis-, pentakis-, and hexakis.

• Example [Co(en)3]Cl3 is tris(ethylenediamine)cobalt(III) chloride.

– If the complex is an anion, the name ends in -ate.– Oxidation state of the metal is given in Roman

numerals in parenthesis at the end of the complex name.

Names of Some Neutral and Anionic Ligands

Name Formula

A. Neutral Aqua H2O Ammine NH3

Carbonyl CO Nitrosyl NO

B. Anionic Fluoro F -

Chloro Cl-

Bromo Br-

Iodo I-

Hydroxo OH-

Cyano CN-

Table 23.8 (p. 1019)

Names of Some Metal Ions in Complex Anions

Metal Name in Anion

Iron Ferrate

Copper Cuprate

Lead Plumbate

Silver Argentate

Gold Aurate

Tin Stannate

Table 23.9 (p. 1019)

Some Coordination Compounds of Cobalt Studied by Werner

Werner’s Data*Traditional Total Free Modern Charge ofFormula Ions Cl- Formula Complex Ion

CoCl3 6 NH3 4 3 [Co(NH3)6]Cl3 3+

CoCl3 5 NH3 3 2 [Co(NH3)5Cl]Cl2 2+

CoCl3 4 NH3 2 1 [Co(NH3)4Cl2]Cl 1+

CoCl3 3 NH3 0 0 [Co(NH3)3Cl3] ---

.

.

.

.

Table 23.10 (p. 1020)