transition metal chemistry and coordination compounds · chromium manganese iron ... a coordination...

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Transition Metal Chemistry and Coordination Compounds

1Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Properties of the Transition Metals

All transition metals are metals, whereas main-group elements in each period change from metal to nonmetal.

Many transition metal compounds are colored and paramagnetic, whereas most main-group ionic compounds p g , g p pare colorless and diamagnetic.

The properties of transition metal compounds are related to the electron configuration of the metal ion.

The Transition MetalsThe Transition Metals

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Notice that Zn, Cd and AgAre not included

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Writing Electron Configurations of Transition Metal Atoms and Ions

PROBLEM: 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.)

PLAN: We locate the element in the periodic table and count its position in the respective transition series. These elements are in Periods 4 and 5 so the general electron configuration isin Periods 4 and 5, so the general electron configuration is [noble gas]ns2(n – 1)dx. For the ions, we call that ns electrons are lost first.

SOLUTION:

(a) Zr is the second element in the 4d series:

[Kr]5s24d2

(b) V is the third element in the 3d series, so its configuration is [Ar]4s23d3. When it forms V3+, it loses the two 4s e- first, then one of the 3d e-:

[Ar]3d2

(c) Mo lies below Cr in group 6B(6), so we expect the same ti f C Th fi ti f M i th fexception as for Cr. The configuration for Mo is therefore

[Kr]5s14d5. Formation of the Mo3+ ion occurs by loss of the single 5s electron followed by two 4d electrons:

[Kr]4d3

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Aqueous oxoanions of transition elements.

Mn2+ MnO42− MnO4

−+2 +6 +7

The highest oxidation state for Mn equals its group number.

VO43− Cr2O7

2− MnO4−

+5 +6 +7

Transition metal ions are often highly colored.

Oxidation States of the 1st Row Transition Metals(most stable oxidation numbers are shown in red)

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Ionization Energies for the 1st Row Transition Metals

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Scandium Titanium Vanadium

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Chromium Manganese Iron

Cobalt Nickel Copper

Colors of representative compounds of the Period 4 transition metals.

titanium(IV) oxide sodium chromatepotassium

ferricyanidenickel(II) nitrate

hexahydratezinc sulfate

heptahydrate

scandium oxide vanadyl sulfate dihydrate

manganese(II) chloride

tetrahydrate

cobalt(II) chloride

hexahydrate

copper(II) sulfate pentahydrate

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Coordination Compounds

A coordination compound typically consists of a complex ion and a counter ion.

A complex ion contains a central _______cation bonded to one or more molecules or ions.

The molecules or ions that surround the metal in a complex ion are called

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metal in a complex ion are called _______________________has at least one unshared pair of valence electrons

H

O

H

• •

H

N

HH• •

••Cl• •

••

-••C O••


The atom in a ligand that is bound directly to the metal atom is the donor atom.

H

O

H

• •

H

N

HH

The number of donor atoms surrounding the central metal atom in a complex ion is the coordination number

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in a complex ion is the coordination number.

Ligands with:

one donor atom ____________

two donor atoms ____________

three or more donor atoms ____________

H2O, NH3, Cl-

ethylenediamine

EDTA

Some Common Ligands in Coordination CompoundsSome Common Ligands in Coordination Compounds

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H2N CH2 CH2 NH2• • • •

bidentate ligand

[Co(en)3]2+

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or

Chelates

Bidentate and polydentate ligands give rise to rings in the complex ion.

A complex ion containing this type of structure is called a chelate because the ligand seems to grab the metal ion like claws.

EDTA has six donor atoms and forms very stable complexes with metal ions.

polydentate ligand(EDTA)

[PbEDTA]2-

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Bidentate and polydentate ligands are called _____________agents

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ChelatesChelates

Copyright 1999, PRENTICE HALL 22

ChelatesChelates


Fe++

ChelatesChelatesMetals and Chelates in Living SystemsMetals and Chelates in Living Systems


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ChelatesChelatesMetals and Chelates in Living SystemsMetals and Chelates in Living Systems


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Oxidation NumbersOxidation Numbers

What are the oxidation numbers of the metals in K[Au(OH)4] and [Cr(NH3)6](NO3)3 ?

OH- has charge of -1 NO3- has charge of -1

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OH has charge of 1

K+ has charge of +1

? Au + 1 + 4x(-1) = 0

Au = +3

3 g

NH3 has no charge

? Cr + 6x(0) + 3x(-1) = 0

Cr = +3

Oxidation NumbersOxidation Numbers

Determine the oxidation numbers of the metals in

K3[Fe(CN)6]

[Ru(NH3)5 (H2O]Cl2

[Fe(CO) ]

Fe = ______

Ru = ______

Fe =

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[Fe(CO)5] Fe = _______

Naming Coordination CompoundsSix Rules

The cation is named before the anion.

• As in ionic compounds

• + or - Charge on complex ion doesn’t affect this rule

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g p

• Ni(CO)4 =

• nickel tetracarbonyl

• K3[Fe(CN)6] =

• potassium hexacyanoferrate

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Naming Coordination Compounds

Within a complex ion, the ligands are named first in alphabetical order and the metal atom is named last.

• K3[Fe(CN)6] =

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3[ ( )6] _______________________________

• [Cr(NH3)3(H2O)]Cl3 = ___________________________


The names of anionic ligands end with the letter o.

• Neutral ligands are usually called by the

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usually called by the name of the molecule. The exceptions are

• H2O (aqua), CO (carbonyl), and NH3

(ammine).

From Chang, Table 22.4

• K3[Fe(CN)6] =

• potassium hexacyano___________________

• Na2[NiCl4] =

sodium tetrachloro

Naming Coordination CompoundsSome examples

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• sodium tetrachloro_____________________

• Na[PtCl3(NH3)] =

• sodium amminetrichloroplatinate (II)

• Note that the Greek prefixes mono-, di,- tri-, etc. do not affect alphabetization of the ligands

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• When several ligands of a particular kind are present, the Greek prefixes di-, tri-, tetra-, penta-, and hexa- are used to indicate the number. If the ligand already contains a Greek prefix, use the prefixes bis, tris, and tetrakis to indicate the number.

2 bis 6 hexakis3 t i 7 h t ki

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3 tris 7 heptakis4 tetrakis 8 octakis5 pentakis 9 ennea

•[Co(en)3]SO4 = tris(ethylenediamine)cobalt(II) sulfate

• is the same as tris(H2NCH2CH2NH2)cobalt(II) sulfate

•and as tris(en)cobalt(II) sulfate

Examples of Some Ligands Containing Prefixes

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• The oxidation number of the metal is written in Roman numerals following the name of the metal.

What is the systematic name of [Cr(H2O)4Cl2]Cl ?

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____________________________________

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If the complex is an anion, its name ends in –ate.

[Z (OH) ]2

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e.g., [Zn(OH)4]2-

tetrahydroxozincate(II)

Structure of Coordination Compounds

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2

4

6

_____________________

_____________or ____________

_________________________

Coordination number Structure

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CUBIC CLOSEST-PACKED (CCP) - Way in which atoms (considered as hard spheres) pack together to fill space. In cubic closest-packing, there are three alternating hexagonal layers, a, b, and c, offset from one another so that the spheres in one layer sit in the small triangular depressions of neighboring layers. Each sphere is touched by 12 neighbors, 6 in the same layer, 3 in the layer above, and 3 in the layer below.

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Notice that in NaCl, each Cl ionis also surrounded by 6 Na ionsin octahedral coordination. So,again, the 1/6 of a positivecharge from each Na reachesthe Cl ion and thus the Cl ion

6*1/6 1 i i h

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sees 6*1/6 = 1 positive charge,which exactly balances the -1charge on the Cl.


___________isomers are compounds that are made up of the same types and numbers of atoms bonded together in the same sequence but with different spatial arrangements.

_______________ isomers are stereoisomers that cannot be interconverted without breaking a chemical bond.

42cis-[Pt(NH3)2Cl2] trans-[Pt(NH3)2Cl2]

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cis

trans

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_____-[Co(NH3)4Cl2] ________-[Co(NH3)4Cl2]

Are these additional geometric isomers of [Co(NH3)4Cl2]?

IsomerismIsomerismStereoisomerismStereoisomerism


Structure of Coordination CompoundsOptical isomers are nonsuperimposable mirror images.

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cis-[Co(en)2Cl2] trans-[Co(en)2Cl2]

optical isomers

chiral

not optical isomers

achiral

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Chiral molecules are optically active.

Rotate the plane of polarized light.

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Polarimeter

Geometric (cis-trans) isomerism.

The cis and trans isomers of [Pt(NH ) Cl ]

In the cis isomer, identical ligands are adjacent to each other, while in the trans isomer they are across from each other.

The cis and trans isomers of [Pt(NH3)2Cl2].

The cis isomer (cisplatin) is an antitumor agent while the transisomer has no antitumor effect.

Geometric (cis-trans) isomerism.

The cis and trans isomers of [Co(NH3)4Cl2]+. Note the placement of the Cl- ligands (green spheres).

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Optical isomerism in an octahedral complex ion.

Structure I and its mirror image, structure II, are optical isomers of cis-[Co(en)2Cl2]+.

Optical isomerism in an octahedral complex ion.

The trans isomer of [Co(en)2Cl2]+ does not have optical isomers. Structure I can be superimposed on its mirror image, structure II.

Sample Problem Determining the Type of Stereoisomerism

PROBLEM: Draw stereoisomers for each of the following and state the type of isomerism:

(a) [Pt(NH3)2Br2] (square planar) (b) [Cr(en)3]3+ (en = H2NCH2CH2NH2)

PLAN: We determine the geometry around each metal ion and the nature of the ligands. If there are different ligands that can be placed in different positions relative to each other geometricplaced in different positions relative to each other, geometric (cis-trans) isomerism occurs. Then we see whether the mirror image of an isomer is superimposable on the original. If it is not, optical isomerism also occurs.

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Sample Problem

SOLUTION:

(a) The square planar Pt(II) complex has two different types of monodentate ligands. Each pair of ligands can be next to each other or across from each other. Thus geometric isomerism occurs.

These are geometric isomers; they do not have optical isomers since each compound is superimposable on its mirror image.

Sample Problem

(b) Ethylenediamine (en) is a bidentate ligand. The Cr3+ ion has a coordination number of 6 and an octahedral geometry, like Co3+. The three bidentate ligands are identical, so there is no geometric isomerism. However, the complex ion has a nonsuperimposable mirror image. Thus optical isomerismoccurs.

N

mirror

N

CrN

N N

N

N

N

CrN

NN

N

N

N

rotate

not the same as

CrN

NN

N

N

N

Bonding in Coordination CompoundsValence Bond Theory

• bonding takes place when the filled atomic orbital on the _______ overlaps an empty atomic orbital on the __________ ion

• explain geometries well, but doesn’t explain __________________________properties

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Bonding in Coordination CompoundsCrystal Field Theory

• bonds form due to the attraction of the electrons on the ligand for the charge on the metal cation

• electrons on the ligands repel electrons in the unhybridized d orbitals of the metal iony

• the result is the energies of orbitals the d sublevel are split

• the difference in energy depends the complex and kinds of ligands– crystal field splitting energy– strong field splitting and weak field splitting

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Splitting of d Orbital Energies due to Ligands in a Octahedral Complex

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Bonding in Coordination Compounds

d-orbital orientation relative to x, y, and z axes

58All equal in energy in the absence of ligands!

Strong and Weak Field Splitting

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Isolated

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Isolatedtransition metal

atomBonded

transition metalatom

Crystal field splitting () is the energy difference between two sets of d orbitals in a metal atom when ligands are present

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E = h

Complex Ion Color

• the observed color is the complimentary color of the one that is absorbed

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Complex Ion Color and Crystal Field Strength

• the colors of complex ions are due to electronic transitions between the split dsublevel orbitals

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• the wavelength of maximum absorbance can be used to determine the size of the energy gap between the split d sublevel orbitals

Ephoton = h = hc/ =

The absorption maximum for the complex ion [Co(NH3)6]3+

occurs at 470 nm. What is the color of the complex and what is the crystal field splitting in kJ/mol?

Absorbs blue, will appear orange.

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= hhc=

(6.63 x 10-34 J s) x (3.00 x 108 m s-1)

470 x 10-9 m= = 4.23 x 10-19 J

(kJ/mol) = 4.23 x 10-19 J/atom x 6.022 x 1023 atoms/mol

= 255 kJ/mol

Ligand and Crystal Field Strength

• the strength of the crystal field depends in large part on the ligands– strong field ligands include: CN─ > NO2

─ > en > NH3

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strong field ligands include: CN NO2 en NH3

– weak field ligands include H2O > OH─ > F─ > Cl─ > Br─ > I─

• crystal field strength increases as the charge on the metal cation increases

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The Spectrochemical Series

The complexes of cobalt (III) show the shift in color due to the ligand. (a) CN–, (b) NO2

–, (c) phen, (d) en, (e) NH3, (f) gly, (g) H2O, (h) ox2–, (i) CO3

2–.

Bonding in Octahedral Coordination Compounds

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I- < Br- < Cl- < OH- < F- < H2O < NH3 < en < CN- < CO

Spectrochemical Series

Strong field ligandsLarge

Weak field ligandsSmall

Paramagnetic and Diamagnetic Properties

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weak ligand field strong ligand field

Obeys Hund’s rule

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Bonding in Octahedral Coordination Compounds

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weak ligand fieldhigh spin

strong ligand fieldlow spin

maximum stability,higher E cost

less stability,lower E cost

Orbital Diagrams for High Spin and Low Spin

Octahedral Complexes

Nature makes compromisesNature makes compromises

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Octahedral Complexes

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Crystal Field splitting in a Square Planar Complex

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Crystal Field splitting in a Tetrahedral Complex

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Chemistry In Action: Coordination Compounds in Living Systems

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transition metal chemistry and coordination compounds · chromium manganese iron ... a coordination...

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