Coordination complexes and transition metals in action
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Coordination Complexes and Transition Metals in Action. Al 2 O 3 crystal with traces of Cr 3+ (ruby). Spring and summer – chlorophyll and xanthophyll. Fall – xanthophyll colors dominate. Plants and Animals. chlorophyll. heme. Colors of Chromium. Cr(NO 3 ) 3. CrCl 3. K 2 CrO 4.

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Coordination Complexes and Transition Metals in Action

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Coordination complexes and transition metals in action

Coordination Complexes and Transition Metals in Action

Al2O3 crystal with traces of Cr3+ (ruby)

Spring and summer –

chlorophyll and xanthophyll

Fall –

xanthophyll colors dominate


Plants and animals

Plants and Animals

chlorophyll

heme


Colors of chromium

Colors of Chromium

Cr(NO3)3

CrCl3

K2CrO4

K2Cr2O7

Cr3+

Cr6+


Coordination compound and complex

Coordination Compound and Complex

Coordination Compound is [Co(NH3)6]Cl3

[Co(NH3)6]Cl3 [Co(NH3)6]3+ + 3 Cl-

Coordination Complex is [Co(NH3)6]3+


Components of complex coordination sphere

Metal ion – usually transition metals with empty valence orbitals

Specifically empty d orbitals

Act as Lewis acid (electron pair acceptor)

Ligand – complexing agent bound to (surrounding) the metal ion (Lewis base)

Normally ligands are anions or polar molecules

Anion (CN-)

Polar molecule (NH3)

Donor atom

Components of Complex (Coordination Sphere)

[Co(NH3)6]3+


Characteristics of complex coordination sphere

Metal ion

Oxidation number

Co = ?

Ligand

Charge on ligand

NH3 = ?

Characteristics of Complex (Coordination Sphere)

Charge of Complex – sum of charges on the central metal ion and the surrounding ligands

What is the charge of the complex?

[Co(NH3)6]Cl3

Coordination number – The number of donor atoms attached to the metal.


Example problem

Example Problem

  • Indicate the coordination number of the metal and the oxidation number of the metal in each of the following complexes:

    Na2[CdCl4][Co(NH3)4Cl2]Cl

    K2[MoOCl4][Zn(en)2]Br2


Types of ligands

Types of Ligands

  • Monodentate ligand NH3, H2O, Cl-

  • Bidentate ligandethylenediamine (en)

  • Polydentate ligand ethylenediaminetetraacetate ion (EDTA)4-


Chelating agent

Chelating Agent

  • Polydentate ligands (including bidentate) are called chelating agents because they appear to grasp the metal between donor atoms


Example ligands

Example Ligands

What kind of ligands are these examples?


Chelate effect

Chelate Effect

  • Chelating agents form more stable complexes with metal ions than monodentate ligands

    Ni2+(aq) + 6NH3(aq) [Ni(NH3)6]2+(aq) Kf = 4 x 108

    Ni2+(aq) + 3 en (aq) [Ni(en)3]2+(aq) Kf = 2 x 1018

    Sequestering agents – because the chelating agents can be used to remove or separate ions

    removal of ions from hard water

    removal of trace metals from food

    removal of heavy metal ions from blood


Geometry of complex

Geometry of Complex

  • Common coordination # of 4

square planar

Transition metal ions with 8 d electrons

Tetrahedral

Most common


Geometry of complex1

Geometry of Complex

  • Coordination # 6

Octahedral


Effect of ligand on coordination number

Effect of Ligand on Coordination Number

  • The larger the size of the ligand, the fewer ligands that can get close enough to bind to the central metal.

    [FeF6]3-[FeCl4]-

  • Ligands which provide negative charge to the complex reduce the coordination number.

    [Ni(NH3)6]2+[Ni(CN)4]2-


Metal complexes

Metal Complexes

  • Distinct chemical properties different from the metals and ligands from which they were formed.

    • Different colors

    • Different electrochemical properties

    • Different solubility properties


Nomenclature

Nomenclature

  • In naming salts, the name of the cation is given before the name of the anion.

    [Mo(NH3)3Br3]NO3

Cation

Anion = nitrate


Nomenclature1

Nomenclature

  • Within a complex ion or molecule the ligands are named before the metal. Ligands are listed in alphabetical order, regardless of charge on the ligand. Prefixes that give the number of ligands are not considered part of the ligand name in determining alphabetical order.

    [Mo(NH3)3Br3]NO3

Ammonia, bromide, molybdenum


Nomenclature2

Nomenclature

  • The names of the anionic ligands end in the letter o, whereas neutral ones ordinarily bear the name of the molecules.

    [Mo(NH3)3Br3]NO3

Example ligand names

NH3 – ammine

CO – carbonyl

NO - nitrosyl

H2O – aqua

CN- – cyano

en - ethylenediammine

Ammine, bromo, molybdenum


Nomenclature3

Nomenclature

  • Greek prefixes (di, tri, tetra, penta, hexa) are used to indicate the number of each kind of ligand when more than one is present.

    [Mo(NH3)3Br3]NO3

    If the ligand itself contains a prefix, then these prefixes are used for the ligand name (bis-, tris-, tetrakis-, pentakis-, etc.).

    [Ru(bipy)3]Cl3

triamminetribromomolybdenum

tris-bipyridineruthenium


Nomenclature4

Nomenclature

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

    K3[V(C2O4)3]

cation = potassium

anion = trioxalatevanadate


Nomenclature5

Nomenclature

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

    [Mo(NH3)3Br3]NO3

    [Ru(bipy)3]Cl3

    K3[V(C2O4)3]

triamminetribromomolybdenum(IV) nitrate

tris-bipyridineruthenium(III) chloride

Potassium trioxalatevanadate(III)


Isomers

Isomers

Hydrate isomer

Ionization isomer


Coordination complexes and transition metals in action

Structural Isomerismhave the same numbers and kinds of atoms, but differ in the bonds that are present.

Ionization isomer – exchange of ligand with an anion or neutral molecule [CoBr(NH3)5]SO4 and [CoSO4(NH3)5] Br

Hydrate isomer – the exchange of H2O molecule with another ligand [CrBr(H2O)6]Cl3 and [CrClBr(H2O)5]Cl2*H2O

Coordination isomers- differ due to the exchange of one or more ligands between a cationic complex and an anionic complex [Cr(NH3)6][Fe(CN)6]

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

Linkage isomers- contain the same ligand coordinated to the metal through different donor atoms[Pd(NH3)3SCN]+ and [Pd(NH3)3NCS]+


Linkage isomerism

Linkage Isomerism

Nitro

Nitrito


Stereoisomerism

Stereoisomerism

Geometric isomers have the same number and kinds of bonds, but differ in the relative positions of the ligands.

Optical isomers rotate the plane of polarized light in opposite directions.


Geometric isomers

Geometric Isomers


Geometric isomers1

Geometric Isomers


Optical isomers

Optical Isomers

Rotate the plane of polarized light in opposite directions.

Levrorotatory – rotate left

Dextrorotatory – rotate right


Optical isomers1

Optical Isomers

Chiral molecules have mirror-image structures that cannot be superimposed.

Only chiral molecules are optically active.

Enantiomers are chiral molecules of each other.

Racemic Mixture occurs when equal amounts of each enantiomer are mixed. When this happens, the optical activity of each is canceled by the other.


Enantiomers

Enantiomers


Properties of coordination complexes

Properties of Coordination Complexes

  • Color– Many coordination complexes exhibit a wide variety of colors, that depend on the metal, its oxidation state, and the ligands present.

    • The observed colors result from the absorption of light in the visible region by the complexes.

Color Exhibited

Colorless

Partially filled d orbital

Totally filled or empty d orbital (d0 and d10)


Color exhibited or colorless

Color Exhibited

[Cr(NH3)6]3+

[Fe(SO4)(H2O)4]

Colorless

[Cd(NH3)4](NO3)2

Na[AlCl4]

Color Exhibited or Colorless


Color of complexes

Color of Complexes


Crystal field theory

Crystal Field Theory

Crystal field theory assumes electrostatic interactions between the negative or neutral ligands and the positive metal ion lower the energy of the system.

  • Anionic ligands – electrostatic attraction

  • Neutral ligands – ion dipole


Lowered energy of metal ligand complex

Lowered Energy of Metal/Ligand Complex

Crystal Field – repulsive interaction between electrons in the ligands and the d orbital electrons in the metal


Consequence d electron repulsion

Consequence:d electron repulsion

Crystal Field

  • The negative ligands repel the electrons in the metal ion d orbitals.

  • The repulsion energy of d electrons depends on the orientation of the orbital, relative to the location of the negative ligands.


D orbitals

d Orbitals


D orbitals1

d Orbitals


Coordination complexes and transition metals in action

Octahedral complex


D orbital splitting

d orbital splitting

D = Energy gap – the energy necessary for an electron to move across the gap is similar to energy of a visible light photon

Explains why d0 or d10 transition elements do not show color


Spectrochemical series

Spectrochemical Series


Electron configurations

Electron Configurations

Co3+ a d6 ion


Electron configurations1

Electron Configurations

  • High spin

  • Low spin

Weak Field ligand

Spin pairing energy is the energy required to pair 2 electrons in orbital

Strong Field ligand


Properties of coordination complexes1

Properties of Coordination Complexes

  • Paramagnetism- a property due to unpaired electrons, is common among transition metal complexes.

    • Different complexes of the same metal ion, may have different numbers of unpaired electrons.

      Predict the magnetic properties of:

      [Fe(H2O)6]2+[Fe(CN)6]4-


Energy calculation

Energy Calculation

  • The complex [Ti(H2O)6]3+ absorbs light of wavelength 510 nm. What is the crystal field d orbital splitting energy (D) for the complex?


Metal and oxidation

Metal and Oxidation #

  • Color– Many coordination complexes exhibit a wide variety of colors, that depend on the metal, its oxidation state, and the ligands present.

    [Cr(H2O)6]3+[V(H2O)6]2+

The larger the charge on the metal ion involved in the complex, the more metal-ligand interaction. Therefore, D will be larger when the oxidation state of the metal is larger.


Increased interaction between metal and ligand increased crystal field

Increased Interaction Between Metal and Ligand: Increased Crystal Field

Crystal Field – repulsive interaction between electrons in the ligands and the d orbital electrons in the metal


Crystal field theory tetrahedral

Crystal Field Theory Tetrahedral

Tetrahedral complex always have high spin because D is small


Crystal field theory square planar

Crystal Field Theory Square Planar

Square planar complexes always have high spin because D is large


Tetrahedral and square planar

Tetrahedral and Square Planar

  • Draw the crystal field splitting diagrams for [Ni(CN)4]2- and [NiCl4]2- and predict the magnetic properties of each.


Electron configurations2

Electron Configurations

  • High spin

  • Low spin

Weak Field ligand

Spin pairing energy is the energy required to pair 2 electrons in orbital

Strong Field ligand


Energy calculation1

Energy Calculation

  • The complex [Ti(H2O)6]3+ absorbs light of wavelength 510 nm. What is the crystal field d orbital splitting energy (D) for the complex?

    c = lnE = hn

  • = c/l = E = (6.63 x 10-34 Js) (5.88 x 1014 s-1)

  • = 3.00 x 108 m/s______ E = 3.90 x 10-19 J

    (510 nm) ___1 m___ E = (3.90 x 10-19 J) _1 kJ_

    • 1 x 109 nm 1000 J

  • = 5.88 x 1014 s-1E = 3.90 x 10-22 kJ/photon

  • E = (3.90 x 10-22 __kJ__) (6.022 x 1023photons) = 235 _kJ_

    photon mole mole


  • Spectroscopy

    Spectroscopy


    Sources of electromagnetic radiation

    Sources of Electromagnetic Radiation


    Window material

    Window Material


    Wavelength selector

    Wavelength Selector


    Detectors

    Detectors


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