Electronic configuration of the 3d transition elements

Sc Ti V Cr Mn Fe Co Ni Cu Zn

4s 2 2 2 1 2 2 2 2 1 23d 1 2 3 5 5 6 7 8 10 10

Electronic configuration of the Lanthanides

La Ce Pr Nd Sm Eu Gd Tb Yb Lu Hf

6s 2 2 2 2 2 2 2 2 2 25d 1 1 0 0 0 1 0 0 1 24f 0 1 3 6 7 7 9 14 14 14

204

Pm

205

2 010

Dy Ho

2 011

2 012

Er Tm

2 013

Definition:

A complex or coordination compound is a compound in which an atom (called “central atom”) is bound to more groups (called “ligands”) than expected with respect to its charge and position in the periodic table.

The number of ligands around a central atom is called the “coordination number”.

Rules for naming complexes

first in the names of a complex the ligands are named in alphabetic order of the first character (there is no distinction between anionic and other ligands)

followed by the name of the central atom

the number of ligands is indicated by greek numerals: mono, di, tri, tetra, penta, hexa, hepta, octa, nona, deca

if necessary bis, tris, tetrakis, pentakis etc. may be used

for the central atom the following rules are used:in a neutral or cationic complex the name of the metal is used followed by an information on its oxidation statein an anionic complex the name of the metal is used plus an suffix -ate for some metals the latin name has to be used: -plumbate, -ferrate, -argentate, -cuprate, aurate etc.

The names of the ligands are used with an suffix -o if the ligand is an anion

-chloro, -hydroxo, -thio, -oxo, -nitrato, carbonato etc.

For neutral or cationic ligands the name of the ligand is used and sometimes included in round brackets. In some cases special names have to been used: aqua (H2O), ammine (NH3), carbonyl (CO), nitrosyl(NO)

Examples: Potassiumtetrafluorooxochromate

Tris(ethylendiamin)cobalt(III)sulfate

Tetrakis(trifluorphosphin)nickel(0)

Tetraammincopper(II)chloride

Rules for writing formula of complexes

•complexes are enclosed in square brackets

•first the name of the central atom is given

•followed by first the anionic ligand and then the neutral ligands; within each group they are alphabetically ordered according to the first character of their formula

Examples: [PtCl2(C2H4)(NH3)]K2[PdCl4][Co(en)3]Cl3

L

L

L

L

LLZ

L

L L

L

L

L

Z

L

L

L

L

L

LZ

L

L

L

LL

L

Z

Possible arrangements of 6 ligands L around a central atom Z

L

L

X

X

LLZ L

X

L

X

LLZ

Possible arrangements of the ligands in an octahedral complex of composition [ZL4X2]

LL

L X

X

L

Z

L

L L

X

L

X

Z

L

L X

L

L

X

Z

Possible arrangements of the ligands in a trigonal prismatic complex of composition [ZL4X2]

Possible arrangements of the ligands in a hexagonal planar complex of composition [ZL4X2]

L

L

X

L

L

XZ

L

L

X

X

L

LZ

L

L

X

L

X

LZ

L

L

X

XL

L

Z

L

L

X

LL

X

Z

L

X

X

LL

L

Z

Possible arrangements of the ligands in a trigonal antiprismatic complex of composition [ZL4X2]

Examples:

[Co(NO2)6]3- [PtCl6]2- [Ag(NH3)4]+

Co3+ 24 e- Pt4+ 74 e- Ag+ 46 e-

6NO2- 12 e- 6Cl- 12 e- 4NH3 8 e-

36 e- 86 e- 54 e-

but

[Cr(NH3)6]3+ [Ni(NH3)6]2+ [CoCl4]2-

Cr3+ 21 e- Ni2+ 26 e- Co2+ 25 e-

6NH3 12 e- 6NH3 12 e- 4Cl- 8 e-

33 e- 38 e- 33 e-

Many elements form complexes which do not obey the EAN rule.

The EAN rule is helpful for organometallic compounds and carbonyl complexes, which obey in most cases this rule:

[Cr(CO)6] [Fe(CO)5] [Ni(CO)4]

Cr 24 e- Fe 26 e- Ni 28 e-

6CO 12 e- 5CO 10 e- 4CO 8 e-

36 e- 36 e- 36 e-

metals with odd numbers of electrons form dimers or are reduced

or oxidized

[Mn(CO)6]+

[Mn(CO)5]- [Mn(CO)5] [Mn2(CO)10]

[Co(CO)4]- [Co(CO)4] [Co2(CO)8]

[Co(CO)5]+

dimerization

dimerization

oxidation

oxidation

unknown

unknown

reduction

reduction

Similarly the formation of olefin complexes and metallocenes may be explained by the EAN rule:

olefines donate 2 electrons /double bondethylene 2butadiene 4benzene 6cyclopentadienyl radical 5

[Fe(C5H5)2] [Mn(CO)5C2H4]+ [Cr(C6H6)2] Fe 26 Mn+ 24 Cr 24 2 C5H5· 10 5 CO 10 2 C6H6 12 36 C2H4 2 36 36

Bonding in co-ordination compounds

• effective atomic number (EAN) rule based on the octet theory of Lewis this is the first attempt to account for the bonding in complexes

The formation of a complex was described as an acid - base reaction according to Lewis

The sum of the electrons on the central atom (Lewis acid) including those donated from the ligands (Lewis base) should be equal to the number of elctrons on a noble gas

Bonding in coordination compounds

• valence bond theory Linus Pauling made the first successful application of bonding theory to coordination compounds closely related to hybridization and geometry of non complex compounds the structures of complexes may be rationalized by the following hybrid orbitals: d2sp3 octahedral dsp3 trigonal bipyramid dsp2 square planar sp3 tetrahedral

Crystal field theory

d- electrons in an octahedral field of ligands

octahedron tetrahedron distorted tetrahedron

tetrahedron cube

tetragonal pyramid trigonal bipyramid

octahedron square bipyramid square

UV/VIS spectra of three chromium(III) complexes: a) [Cr(en)3]3+

b) [Cr(ox)3]3-

c) [CrF6]3-

look for the shift of the two

absorption peaks 1 and 2 to

lower frequencies.

a)

b)

c)

Spectrochemical series

phosph: 4-methyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane

Jahn-Teller splitting

compressed elongatedoctahedron (along the z-axis)

Isomerism in co-ordination compounds

if two or more molecules or ions have the same molecular formula but the atoms are arranged differently we call them isomers. The structures of isomers are not superimposable.Isomers have different physical and/or chemical properties.

We distiguish between

•structural isomers which contain the same number and kind of atoms, but the connectivity between the atoms is different and

•Stereoisomers which contain both the same number and kind of atoms and the same connectivity between the atoms but the spatial arrangement of the atoms is different

Structural isomers

• Ionization isomerism complex salts which show ionization isomerism are composed in such a way that a ligand and a counter ion change their places

[CoCl(NH3)5]SO4 [CoSO4(NH3)5]Cl

Structural isomers

• hydrate isomerism this a special case of the ionization isomerism. Here water molecules are present as ligand in one case and as water of crystallzation in the second case

[Cr(H2O)6]Cl3

[CrCl(H2O)5]Cl2.H2O

[CrCl2(H2O)6]Cl.2H2O

Structural isomers

• Co-ordination isomerism if in a complex salt both anion and cation are complexes there can be an exchange of ligands between cation and anion

[Co(NH3)6] [Cr(CN)6]

[Cr(NH3)6] [Co(CN)6]

Structural isomers

• Linkage isomerism if a ligand containes more than one atom with a free electron pair, the ligand may be bound to the central atom via the different atoms.

C NS

C N bonding via C cyano-bonding via N isocyano-

bonding via S thiocyanato-bonding via N isothiocyanato-

NO O

bonding via N nitro-bonding via O nitrito-

Stereoisomers can be divided in two groups:

• Enatiomers, i.e. stereoisomers that have a non-superimposable mirror image

• Diastereoisomers, i.e. all stereoisomers that are not enantiomers

Diastereoisomers

• cis - trans isomerism if a square planar or an octahedral complex containes two ligands of the same type, they can be arranged so that the angle L - Z - L is 90° (cis) or 180° (trans)

Co

Cl

Cl

CoCl

ClNH3

NH3PtCl

Cl Cl

ClPt NH3

NH3

cis trans cis trans

square planar octahedral

Diastereoisomers

• fac - mer isomerism if an octahedral complex containes three ligands of the same type they can be arranged such that they all are in a cis position (fac) or that two of them are in a trans position (mer)

Co

Cl

ClCl

CoCl

Cl

Cl

fac(ial) mer(idional)

Enantiomers

• stereoisomers that have a non-superimposable mirror image are called enantiomers

CoCl

ClCo

Cl

Cl

mirror plane

mirror plane

Co

Cl

Cl

Co

Cl

Cl

The corresponding trans complex is not an enantiomer

If a molecule or complex is either

asymmetric, i.e. has no symmetry at all, ordissymmetric, i.e. has no center of inversion or mirror plane or other Sn,

it is called chiral.

Due to the chirality it has a non-superimposable mirror image

Optical isomerism

• if the lifetimes of the two enantiomers of a chiral molecule are long enough to be separable they are called optical isomers

• pure enantiomers are optically active, they rotate the plane of polarized light in different directions. This is the only difference in the physical properties of the two enantiomers

Geometry of complexesThe main structural characteristics of complexes are their co-ordination numbers and their co-ordination polyhedra.

1. Co-ordination number 2

Complexes with co-ordination number 2 are rare. They are only formed by central atoms of the group Cu+, Ag+ and Au+.The complexes are linear. Bent geometries as they are found in three-atomic molecules like H2O have never been seen with complexes.

L Z L

2. Co-ordination number 3

Complexes with co-ordination number 3 are seldom. Examples are HgI3

-, [Pt(P{C6H5}3]3.

The complexes are trigonal planar, sometimes slightly deformed. There is no possibility for the formation of isomers in complexes of type [ZL2L’] or [ZLL’L’’]

Z

LLL

Z

L

LL

Some complexes of CN 3 have the form of a trigonal pyramid like NH3, OR3

+ or SR3+ due to a free electron

pair. They are said to be pseudo-tetrahedral as the free electron pair and the three ligands occupy the four corners of a tetrahedron.

3. Co-ordination number 4

For the co-ordination number 4 which is very common there are 4 different structures possible:

Z

LLL

L

LZ

LL

L

L

L

LL

Z

L LLL

Z

tetrahedral square planar bisphenoidal tetragonal pyramid

Examples:tetrahedral: [Al(OH)4]-, [Cd(CN)4]2-, [BF4]-

square planar: [PtCl4]2-, [Ni(diacetyldioxim)2], [AuF4]-

bisphenoidal: main group elements with a free electron pair like As or Sb [AsF4]- [SbCl4]-

there is the possibility that the bisphenoid becomes distorted towards a tetragonal pyramid when the electron pair needs more space

Sometimes there is a CN of 4 though the formula suggests CN 3for instance gaseous AlCl3 is dimeric built from two tetrahedra scharing one edge so that two chloro ligands are bridging and four are end standing

Or in the case of (AuCl3)2 the central atoms are square planar co-ordinated by 4 chloro ligands with 2 of them in bridging positions

Al

Au Au

Cl

ClCl

Cl

Cl Cl Cl

ClClCl

Al Cl

Cl

4. Co-ordination number 5

this co-ordination number is formed not very often. There are two different geometries possible:

L

L

LL

ZL

L LLL

Z

L

trigonal bipyramid tetragonal pyramid

In the trigonal bipyramid we can distinguish between equatorial and apical positions of the ligands

Examples:trigonal bipyramid: Fe(CO)5, [SnCl5]-

tetragonal pyramid: [VO(acetylacetonate)2]

5. Co-ordination number 6

of the possible co-ordination geometries (octahedron, trigonal prismatic, trigonal antiprismatic and hexagonal planar) only the octahedron and the trigonal antiprismatic co-ordination is observed in co-ordination compounds.

Very often the octahedra are not ideal as not all edges are equally long.This may be caused by an elongation or a compression along the 4 fold axisor by an elongation along the 3 fold axis leading to the trigonal antiprismatic polyhedron

L

L

L

L

LL

Z

C4 axis

C3 axis

A

A

LL

ZL

Slight deformations of the trigonal bipyramid in the indicated way lead to the formation of the tetragonal pyramid

This can lead to an exchange of the apical and equatorial positions of the ligands

A LAL

Z

L L

L

AA

ZL

6. Co-ordination number 7

3 different co-ordination polyhedra exist for CN 7. The energetic difference between them is low. Sometimes the co-ordination polyhedron changes when the cation changes

pentagonal bipyramid monocapped trigonal prism monocapped octahedron

LL

L L

L

L

Z LL

L

L

L

LL

Z

LL

L

L L

LLL

Examples:pentagonal bipyramid: [UO2F5]3-, [HfF7]3-

moncapped trigonal prism: [TaF7]3- monocapped octahedron: [IF6]-, [NbOF6]3-

7. Co-ordination number 8

4 different co-ordination polyhedra exist for CN 8. The energetic differences between them are low. They become lower with increasing CN.

Z Z

Z cube square antiprism dodecahedron hexagonal bipyramid

Z

Examples:cube: seldom, but [UF8]3- square antiprism: more stable than cube [TaF8]3- , [ReF8]3- dodecahedron: [Mo(CN)8]4- , [W(CN)8]4- hexagonal bipyramid: [UO2(acetylacetonate)3]-