The Transition Elements and Their Coordination Compounds
Fe: in steel
Cr: in automobile parts
Au, Ag: jewelry
W: light bulb filament
Pt: auto catalytic converters
Zr: nuclear-reactor liners
Nitrinol (Ni and Ti used in stents)
And many more
Transition elements make up the d orbitals (we will cover here)
Inner transition metals make up the d and f orbitals
The transition elements (d block) and inner transition elements (f block) in the
Writing Electron Configurations of Transition Metal Atoms and Ions
Write condensed electron configurations for the following: (a) Zr; (b) V3+ (c) Mo3+.
(Assume that elements in higher periods behave like those in Period 4.)
Note that the general configuration is [noble gas] ns2(n - 1)dx. Recall that in ions the ns
electrons are lost first.
(a) Zr is the second element in the 4d series: [Kr] 5s24d2.
(b) V is the third element in the 3d series: [Ar] 4s23d3. In forming V3+, three electrons
are lost (two 4s and one 3d), so V3+ is a d2 ion: [Ar] 3d2
(c) Mo lies below Cr in Group 6B(6), so we expect the same exception as for Cr. Thus,
Mo is [Kr] 5s14d5. In forming the ion, Mo loses the one 5s and two of the 4d electrons,
so Mo3+ is a d3 ion: [Kr] 4d3
Horizontal trends in key atomic properties of the Period 4 elements
• Atomic size decreases overall across a period. The d electrons fill inner orbitals ,
so they shield outer electrons from the increasing nuclear charge very efficiently
and the outer 4s electrons are not pulled closer.
• Electronegativity usually increases across a period but the transition metals
exhibit a relatively small change in electrinegativity.
• IE1 increase relatively little because the inner 3d electrons shield efficiently and
the outer 4s electron experiences only a slightly higher effective nuclear charge.
Vertical trends in key properties within the transition elements
• Exhibit more than one
• Ionic bonding is more prevalent for the lower oxidation states and covalent
bonding is more prevalent for the higher oxidation states.
At room temperature TiCl2 is an ionic solid and TiCl4 is a molecular liquid
• In high oxidation states atoms have higher charge densities ⇒ polarize electron
clouds of non-metals ⇒ covalent bonding
• The oxides become less basic as the oxidation state increases
TiO is a weak base in water and TiO2 is amphoteric.
Color and Magnetism of Compounds
Colors of representative compounds of the Period 4 transition
sodium nickel(II) nitrate
potassium zinc sulfate
titanium oxide ferricyanide heptahydrate
scandium manganese(II) copper(II)
oxide chloride sulfate
vanadyl sulfate tetrahydrate cobalt(II) pentahydrate
• Most main group ionic compounds are colorless because the metal ion has a
filled outer level;
On the contrary,
• Electrons in particular filled d-sublevels can absorb visible wavelengths and
move to slightly higher energy d-orbitals. Therefore, many transition metal
compounds have striking colors. Exceptions occur when d orbitals are empty
or filled. Zn2+: [Ar] 3d10 and Sc3+ or Ti4+ [Ar] 3d0
Formation of Coordination Compounds
These are species consisting of a central metal cation (transition metal or main group
metal) that is bonded to molecules and or anions called ligands. In order to maintain
neutrality in the coordination compound, the complex ion is typically associated with
other ions, called counterions.
Metals ions are Lewis acids, because they accept electrons from Lewis bases. When
metal cations combine with Lewis bases, the resulting species is called a complex ion,
and the base is called a ligand.
Components of a Coordination Compound
Structures of Complex Ions:
Coordination Numbers, Geometries, and Ligands
Coordination Number (CN) - the number of ligand atoms that are bonded directly to
the central metal ion. The coordination number is specific for a given metal ion in a
particular oxidation state and compound ( 6 is the most common, 2 and 4 are often
Geometry - the geometry (shape) of a complex ion depends on the coordination number
and nature of the metal ion.
Donor atoms per ligand - molecules and/or anions with one or more donor atoms that
each donate a lone pair of electrons to the metal ion to form a covalent bond.
Types of Ligands and Their Names
Rules for writing formulas for the
1. The cation is written before the anion.
2. The charge of the cation(s) is balanced by
the charge of the anion(s).
3. For the complex ion, neutral ligands are
written before anionic ligands, and the
formula for the whole ion is placed in
Rules for naming complexes
1. The cation is named before the anion.
2. Within the complex ion, the ligands are named, in alphabetical order, before the
3. Neutral ligands generally have the molecule name, but there are a few exceptions
(Table 22.6). Anionic ligands drop the -ide and add -o after the root name.
4. A numerical prefix indicates the number of ligands of a particular type.
5. The oxidation state of the central metal ion is given by a Roman numeral (in
parentheses) only if the metal ion can have more than one state.
6. If the complex ion is an anion, we drop the ending of the metal name and add -ate.
a) What is the systematic name of Na3[AlF6]?
The complex ion is [AlF6]3-.
Six (hexa-) F- ions (fluoro) as ligands - hexafluoro
Aluminum is the central metal atom - aluminate
Aluminum has only the +3 ion, so we do not need Roman numerals.
∴ sodium hexafluoroaluminate
b) What is the systematic name of [Co(en)2Cl2]NO3?
There are two ligands, chlorine and ethylenediamine - dichloro, [bis(ethylenediamine)]
The complex is the cation and we have to use Roman numerals for the cobalt oxidation
state since it has more than one - (III)
The anion, nitrate, is named last.
∴ dichlorobis(ethylenediamine)cobalt(III) nitrate
c) What is the formula of tetraamminebromochloroplatinum(IV) chloride?
4 NH3, Br − , Cl − , Pt4+ Cl −
d) What is the formula of hexaamminecobalt(III) tetrachloro-ferrate(III)?
6 NH3 Co3+ 4Cl − Fe3+
chelate with one two three
Notice how the ligand “grabs” the metal from two sides like a claw
Typical CN for some common ions
M+ CN M2+ CN M3+ CN
+ + 2+ 2+ 2+ 2+ 2+ 3+ 3+ 3+
Cu , Au 2,4 Co ,Ni , Cu ,Zn Mn 4,6 Sc , Cr , Co 6
Ag+ 2 Fe2+ 6 Au3+ 4
Isomers (same chemical formula but different properties)
Coordination isomers occur when the composition of the complex ion changes but not
that of the compound
[Pt(NH3)4Cl2](NO2)2 and [Pt(NH3)4 (NO2)2]Cl2
Linkage isomers occur when the composition of the complex ions remains the same but
the attachment of the ligand donor atom changes
Geometric isomers (also called cis-trans and sometimes diastereomers) occur when
atoms or groups of atoms are arranged differently in space relative to the central metal
Optical isomers (also called enantiomers) occur when a molecule and its mirror image
cannot be superimposed.
Determining the Type of Stereoisomerism
PROBLEM: Draw all stereoisomers for each of the following and state the type
(b) [Cr(en)3]3+ (en = H2NCH2CH2 NH2)
PLAN: Determine the geometry around each metal ion and the nature of
the ligands. Place the ligands in as many different positions as
possible. Look for cis-trans and optical isomers.
SOLUTION: (a) Pt(II) forms a square planar complex and there are two pair
of monodentate ligands - NH3 and Br.
These are geometric isomers;
they are not optical isomers
since they are superimposable
on their mirror images.
(b) Ethylenediamine is a bidentate ligand. Cr3+ has a coordination number of 6 and an
Since all of the ligands are identical, there will be no geometric isomerism possible
The mirror images are non-
superimposable and are therefore,
Application of VB Theory to Complex Ions
Hybrid orbitals and bonding in the octahedral [Cr(NH3)6]3+ ion
Hybrid orbitals and bonding in the square planar [Ni(CN)4]2- ion
Hybrid orbitals and bonding in the tetrahedral [Zn(OH)4]2- ion
What is color?
White light: EM radiation consisting of all λ’s in the visible range.
Objects appear colored in white light b/c they absorb certain λ’s and transmit (reflect)
The transmitted light enters the eye, hits the retina and the brain perceives a color.
• If an object absorbs all λ’s ⇒ black
• If an object reflects all λ’s ⇒ white
• If an object absorbs all λ’s except for green , the reflected (transmitted) green
enters brain and it is interpreted as green.
• If an object absorbs only red (complementary of green) the remaining mixture
of reflected (transmitted) λ’s is entered the brain and it is interpreted as green.
Overview of d orbitals
Splitting of d-orbital energies by an octahedral field of ligands
∆ is the splitting energy
The effect of the ligand on splitting energy
The color of [Ti(H2O)6]3+
Effects of the metal oxidation state and of ligand identity on color
[Cr(NH3)6]3+ [Cr(NH3)5Cl ]2+
• For a given ligand, the color depends on the oxidation state of the metal ion.
• For a given metal ion, the color depends on the ligand.
The spectrochemical series
Ranking Crystal Field Splitting Energies for
Complex Ions of a Given Metal
PROBLEM: Rank the ions [Ti(H2O)6]3+, [Ti(NH3)6]3+, and [Ti(CN)6]3- in terms of
the relative value of ∆ and of the energy of visible light absorbed.
PLAN: The oxidation state of Ti is +3 in all of the complexes so we are
looking at the crystal field strength of the ligands. The stronger the
ligand, the greater the splitting, and the higher the energy of the
SOLUTION: The ligand field strength is CN- > NH3 > H2O, so the relative
size of ∆ and energy of light absorbed is
[Ti(CN)6]3- > [Ti(NH3)6]3+ > [Ti(H2O)6]3+
High-spin and low-spin complex ions of Mn2+
Identifying Complex Ions as High Spin or Low Spin
PROBLEM: Iron (II) forms an essential complex in hemoglobin. For each of the
two octahedral complex ions [Fe(H2O)6] and [Fe(CN)6] , draw an
orbital splitting diagram, predict the number of unpaired electrons,
and identify the ion as low or high spin.
PLAN: The electron configuration of Fe2+ gives us information that the iron
has 6d electrons. The two ligands have different field strengths.
Draw the orbital box diagrams, splitting the d orbitals into eg and
t2g. Add the electrons noting that a weak-field ligand gives the
maximum number of unpaired electrons and a high-spin complex
PE [Fe(H2O)6]2+ --
4 unpaired e eg
eg no unpaired e
Orbital occupancy for high-spin
and low-spin complexes of d4
through d7 metal ions
Splitting of d-orbital energies by a tetrahedral
field of ligands
Splitting of d-orbital energies by a square
planar field of ligands