Transition Metals &
Coordination Compounds
Gemstones
 The colors of rubies and emeralds are
both due to the presence of Cr+3 ions –
the difference lies in the crystal
hosting the ion
 In rubies, some Al+3 ions in the Al2O3
are replaced by Cr+3 ions.
 In emeralds, some Al+3 ions in the
Be3Al2(SiO3)6 are replaced by Cr+3
ions.
Electron Configuration
 For 1st & 2nd transition series = ns2 (n−1)dx
 Fe = [Ar]4s23d6; Zr = [Kr]5s24d2
 For 3rd transition series = ns2 (n−2)f14 (n−1)dx
 Re = [Xe] 6s2 4f14 5d5
 Some individuals deviate from the general pattern
by “promoting” one or more s electrons into the
underlying d to complete the subshell
 Form ions by losing the ns electrons first, then the
(n – 1)d
Lewis Acids & Bases
 Section 15.11
 G.N. Lewis – noticed that acid-base chemistry always





involves an electron pair.
BH3 + NH3  H3B:NH3
Acid = electron pair acceptor
Base = electron pair donor
Greatly expands what we view as an “acid”
LEP #1
Complexes
 An ion like [Ag(NH3)2]+1, are called complex ions as well as
coordination compounds.
 The molecules or ions that bond to the metal are known as
ligands.
 The coordination sphere is the metal and the total number
of ligands bonded to it.
 The complex is a neutral charge salt, which may contain
additional cations or anions not bonded to the metal.
Complexes
 [Cu(NH3)4] SO4
 The complex ion charge is _____.
 The charge of Copper is _____.
 Coordination number is the number of lone pairs
donated to the metal.
 Coordination numbers of 2, 4, and 6 are most
common.
Complexes
Molecular Geometry
Chelates
 Ligands are sometimes
referred to as chelates (Greek
= claw).
 Most are monodentate (one
“toothed”) like NH3, Cl-, CN-,
etc.
 A few are bidentate (two
“toothed”) like
ethylenediamine and the
oxalate ion.
 A few are polydentate like
EDTA.
Chelates
 The formation of complexes favors the products as




seen in Chapter 17.
Ni+2(aq) + 6 NH3(aq)  Ni(NH3)6+2 ; Kf = 4 E8
Ni+2(aq) + 3 en(aq)  Ni(en)3+2(aq) ; Kf = 2 E18
The larger K for the bidentate ligand is known as the
chelating effect.
Uses of EDTA and the EDTA challenge.
Metals in Living Systems
 Nine metals important to life – V, Cr, Mn, Fe, Co, Ni,




Cu, Zn, and Mo – owe their roles to their ability to
form complexes with ligands.
The role of iron in hemeglobin is a perfect example.
In hemeglobin, the iron is bonded to four N atoms in a
molecule called porphoryn.
The fifth site is bonded to the protein (globin).
This leaves one position empty in the octahedral
geometry.
Metals in Living Systems
Porphine molecule
Nomenclature
 Complexes are named using a systematic method.
 Rules:
1.
2.
3.
4.
Cation named first, then anion
Name of the complex is always one word, name of ligands come first
and in alphabetical order
Name of ligands include prefixes if more than one Anionic ligands
get an –o suffix
Name of metal also includes oxidation number in ( ). If complex is
an anion, metal name ends in –ate. Ex) Vandium = Vanadate,
Ferrum = Ferrate
Note: Some metals use old Latin names!
Nomenclature
LEP #2, #3
Isomers
 Isomers are
compounds with the
same formula but
either atoms are in a
different order
(structural) or atoms
are in a different
spatial arrangement
(stereoisomers).
Structural Isomers
 A linkage isomer occurs
when a ligand can bond
through a different atom.
 NO2- can bond through
the N (NO2-) or the O
(ONO-).
 Another one is SCN-.
Structural Isomers
 A coordination sphere isomer occurs when the ligands
bonded to the metal are exchanged for ones outside of
the coordination sphere.
 For example, the formula CrCl36H2O has several
forms.
 [Cr(H2O)6] Cl3 is purple
 [Cr(H2O)5Cl] Cl2H2O is green
Stereoisomers
 A geometric isomer
occurs when the spatial
orientation of a complex
can be changed. These
are referred to as cis-trans
isomers.
 Example is the square
planar geometry of
PtCl2(NH3)2.
Stereoisomers
 Can also produce cis-trans for octahedral complexes if
general formula is: MX4Y2.
 Example is Co(NH3)4Cl2+.
Stereoisomers
 A second type of geometric isomerism can occur if the
general formula is MX3Y3 called fac-mer (short for
facial and meridian).
 An example is Co(NH3)3Cl3.
Stereoisomers
 An optical isomer occurs when the mirror image of the
complex is non-superimposable.
 The pair of isomers are called enantiomers.
Stereoisomers
 In complexes, the only way to get optical isomerism is
with a 6-coordinate system and two or three bidentate
ligands.
 Most of the chemical and physical properties of any
enantiomer pair are identical.
 However, towards other optically active molecules only
one might react.
Stereoisomers
 If the two mirror image complex ions can be
separated, then they can be tested with plane
polarized light.
Color
 Some ions are highly colored.
 Cu+2 = blue
 Ni+2 = green
 Co+2 = pink
 Some ions are not colored.
 Zn+2
 Ba+2
 Al+3
Color

Color depends on two factors:
1.
2.

_______________
_______________
Compounds must absorb some visible light to
have a color.
Color
 A compound’s color can be due
to:
 either it absorbs all
wavelengths but that color
 OR, it absorbs one color
exclusively
 For the second choice, the
color is then the
complimentary color.
Spectrum for Ti(H2O)6+3
Color Wheel
 The color wheel shows
the complimentary
colors.
 Those that are opposite
are complimentary.
Spectrum of
+2
Ni
Electron Configurations
 In period 4, the d orbitals start with Sc.
 Sc: [Ar] 4s2 3d1
 Orbital diagram – shows how each of the d orbitals are
filled.
 Example) Fe: [Ar] 4s2 3d6
 Will see many metal ions, so that means you have to
remove some of the electrons.
 Co+3
Magnetism
 Unpaired electrons = paramagnetic
 Paired electrons = diamagnetic
 Zn(Cl4)-2 = diamagnetic
 CoF6-3 = paramagnetic
 Co(CN)6-3 = diamagnetic
 ???
Crystal Field Theory (CFT)
 As the ligand donates its electron pair to form the
bond, it interacts with the metal’s d orbitals.
 Not all the d orbitals are affected in the same way.
 This splits the d orbitals into different levels.
d orbitals
d orbitals
CFT
CFT
CFT
High and Low Spin
 Normally, electrons fill the d orbitals one at a time
WITH parallel spins.
 Octahedral complexes
 Small D = fill each level first before pairing
 Large D = fill the lower level completely before moving
to upper level
 only matters for d4 to d7 configurations
High and Low Spin
 [CoF6]-3
 [Co(CN)6]-3
 They are
different!
Spectrochemical Series
 Ranks the ligands from weak to strong field.
Cl- < F- < H2O < NH3 < en < NO2- < CN
increasing D

Tetrahedral and Square Planar
 D is always small for tetrahedral complexes so these are
always high spin.
 D is always large for square planar complexes so these
are always low spin.
Tetrahedral and Square Planar
 Ni+2 can be
either
 d8
 [NiCl4]-2
 [Ni(CN4)]-2
Measuring Delta
 D = hc / l
 Remember, though, if a compound is red, then it
absorbs green.
 Use wavelength in green part of the spectrum!