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(共101张PPT)
Chapter 22
Coordination Chemistry
Coordination Chemistry
22
22.1 Coordination Compounds
Properties of Transition Metals
Ligands
Nomenclature of Coordination Compounds
22.2 Structure of Coordination Compounds
22.3 Bonding in Coordination Compounds: Crystal Field Theory
Crystal Field Splitting in Octahedral Complexes
Color
Magnetic Properties
Tetrahedral and Square-Planar Complexes
22.4 Reactions of Coordination Compounds
22.5 Applications of Coordination Compounds
Coordination Compounds
22.1
Coordination compounds contain coordinate covalent bonds formed by the reactions of metal ions with groups of anions or polar molecules.
A coordinate covalent bond is a covalent bond in which one of the atoms donates both of the electrons that constitute the bond.
Ammonia,
a Lewis base
Boron trifluoride
a Lewis acid
empty unhybridized 2pz orbital
A coordinate covalent bond
Coordination Compounds
Coordination compounds may consist of a complex ion and one or more counter ions.
K2[PtCl6]
The compound consists of the complex ion PtCl62– and two K+ counter ions.
Some coordination compounds do not contain complex ions.
Coordination Compounds
Most of the metals in coordination compounds are transition metals.
Coordination Compounds
Properties of transition metals include:
incompletely filled d subshells
react to form ions with incompletely filled d subshell
distinctive colors
paramagnetism
catalytic activity
tendency to form complex ions
exhibit variable oxidation state
Coordination Compounds
Coordination Compounds
Coordination Compounds
Coordination Compounds
The molecules or ions that surround the metal in a complex ion are called ligands.
Ligands must contain at least one unshared pair of valence electrons.
The atom in the ligand directly bonded to the metal atom is called the donor atom.
Coordination Compounds
Coordination Compounds
The coordination number in a coordination compound refers to the number of donor atoms surrounding the central metal atom in a complex ion.
Coordination Compounds
Bidentate and polydentate ligands are also called chelating agents
Coordination Compounds
Bidentate and polydentate ligands are also called chelating agents
Worked Example 22.1
Strategy Identify the components of each compound, and use known oxidation states and charges to determine the oxidation state of the metal.
Determine the oxidation state of the central metal atom in each of the following compounds: (a) [Ru(NH3)5(H2O)]Cl2, (b) [Cr(NH3)6](NO3)3, and (c) Fe(CO)5.
Solution (a) [Ru(NH3)5(H2O)]Cl2 consists of a complex ion (the part of the formula enclosed in a square brackets) and two Cl- counter ions. Because the overall charge on the compound is zero, the complex ion is [Ru(NH3)5(H2O)]2+. There are six ligands: five ammonia molecules and one water molecule. Each molecule has a zero charge (i.e., each ligand is neutral), so the charge on the metal is equal to the overall charge on the complex ion. Ru has an oxidation state of +2.
(b) [Cr(NH3)6](NO3)3 consists of a complex ion and three NO3- ions, making the complex ion [Cr(NH3)6]3+. Each of the six ammonia molecule ligands is neutral (i.e., each has a zero charge), making the charge on the metal equal to the
overall charge on the complex ion. Cr has an oxidation state of +3.
Worked Example 22.1 (cont.)
Solution (c) Fe(CO)5 does not contain a complex ion. The ligands are CO molecules, which has a zero charge, so the central metal also has a zero charge. Fe has an oxidation state of 0.
Think About It To solve a problem like this, you must be able to recognize the common polyatomic ions and you must know the charges.
Coordination Compounds
Nomenclature of Coordination Compounds
The cation is named before the anion, as in other ionic compounds.
Within a complex ion, the ligands are named first, in alphabetical order; the metal ion is named last.
The names of anionic ligands end with the letter o, whereas neutral ligands are usually called by the names of the molecules.
When two or more of the same ligand are present use Greek prefixes di, tri, tetra, penta and hexa, to specify their number.
The oxidation number of the metal is indicated in Roman numerals immediately following the name of the metal.
The names of anions end in –ate.
Multiplicity
Monodentate
mono => 1
di => 2
tri => 3
tetra => 4
penta => 5
hexa => 6
Bi- or tri- dentate
bis => 2
tris => 3
tetrakis => 4
Coordination Compounds
Coordination Compounds
Worked Example 22.2
Strategy For each compound, name the cation first and the anion second. Refer to Tables 22.4 and 22.5 for the names of ligands and anions containing metal atoms.
Write the names of the following coordination compounds: (a) [Co(NH3)4Cl2]Cl and (b) K3[Fe(CN)6].
Solution (a) The cation is a complex ion containing four ammonia molecules and two chloride ions. The counter ion is chloride (Cl-), so the charge on the complex cation +1, making the oxidation state of cobalt +3.
The compound is named tetraamminedichlorocobalt(III) chloride.
(b) The cation is K+, and the anion is a complex ion containing six cyanide ions. The charge on the complex ion is 3, making the oxidation state of iron +3.
The compound is named potassium hexacyanoferrate(III).
Think About It When the anion is a complex ion, its name must end in –ate, followed by the metal’s oxidation state in Roman numerals. Also, do not use prefixes to denote numbers of counter ions.
Worked Example 22.3
Strategy If you can’t remember them yet, refer to Tables 22.4 and 22.5 for the names of ligands and anions containing metal atoms.
Write formulas for the following compounds: (a) pentaamminechlorocobalt(III) chloride and (b) dichlorobis(ethylenediamine)platinum(IV) nitrate.
Solution (a) There are six ligands: five NH3 molecules and one Cl- ion. The oxidation state of cobalt is +3, making the overall charge on the complex ion +2. Therefore, there are two chloride ions as counter ions.
The formula is [Co(NH3)5Cl]Cl2.
(b) There are four ligands: two bidentate ethylenediamines and two Cl- ions. The oxidation state of platinum is +4, making the overall charge on the complex ion +2. Therefore, there are two nitrate ions as counter ions.
The formula is [Pt(en)2Cl2](NO3)2.
Think About It Although ligands are alphabetized in a compound’s name, they do not necessarily appear in alphabetical order in the compound’s formula.
配位化合物中文命名法
配离子的命名
配离子命名顺序：1、配体，2、中心离子，中间加一“合”字，配体的数目用汉字写在配体的前面，中心离子的氧化数用罗马字写在中心离子名称的后面，并加括弧；
[Co(NH3)6]3+ 六氨合钴(III)离子
若有两种或以上配体时，先写阴离子，再写中性分子，中间加圆点“ ”分开。若阴离子不止一种时，则先写简单的，再写复杂的，最后写有机酸根离子；
[CoCl(SCN)(en)2]+ 一氯 硫氰酸根 二（乙二胺）合钴（III）离子
当中性分子不止一种时，则按配原子元素符号顺序排列；
[Co(NH3)5H2O]3+ 五氨 水合钴（III）离子
含配阳离子配合物的命名
1、外界阴离子，2、配体，3、中心离子， 1，2 之间加一“化”字或不加字
没有外界的配合物
可不必标明中心离子的氧化态
含配阴离子配合物的命名
1、配体，2、中心离子，3、外界的金属离子。 2，3 之间加一“酸”字
The geometry of a coordination compound plays a significant role in determining its properties.
Structure of Coordination Compounds
22.2
Coordination Number Structure
2 Linear
4 Tetrahedral or square planar
6 Octahedral
Compounds that differ in the arrangement of ligands around the central atom are known as stereoisomers.
Stereoisomers have different chemical and physical properties.
Structure of Coordination Compounds
Stereoisomers may exhibit two types of stereoisomerism: geometric and optical.
Geometrical isomers are stereoisomers that cannot be interconverted without breaking chemical bonds. Geometric isomers come in pairs.
Structure of Coordination Compounds
Stereoisomers may exhibit two types of stereoisomerism: geometric and optical.
Structure of Coordination Compounds
Optical isomers are nonsuperimposable mirror images.
Stereoisomers may exhibit two types of stereoisomerism: geometric and optical.
Structure of Coordination Compounds
Optical isomers are nonsuperimposable mirror images.
Structure of Coordination Compounds
Optical isomers – nonsuperimposable mirror images
Termed chiral
Rotate polarized light in different directions
Rotation to the right – dextrorotatory (d isomer)
Rotation to the left – levorotatory (l isomer)
Enantiomers – a pair of d and l isomers
Racemic mixture – equimolar mixture of two enantiomers
Net rotation of polarized light is zero
Structure of Coordination Compounds
Structure of Coordination Compounds
Valence Bond Theory
Bonding in Coordination Compounds:
Crystal Field Theory
Crystal field theory explains the bonding in complex ions purely in terms of electrostatic forces.
Attraction between the metal ion (atom) and the ligands
22.3
Repulsion between the lone pairs on the ligands and the electrons in the d orbitals of the metal.
In the absence of ligands, the d orbitals are degenerate.
Bonding in Coordination Compounds: Crystal Field Theory
In the presence of ligands, electrons in d orbitals experience different levels of repulsion for the ligand lone pairs.
As a result (depending on the geometry) some d orbitals attain higher energy and others lower energy.
The five d-orbitals in an octahedral field of ligands
Bonding in Coordination Compounds: Crystal Field Theory
In an octahedral complex:
The electrons in the d orbitals located along the coordinate axes experience stronger repulsions and increase in energy.
The electrons in the d orbitals 45o from the coordinate axes experience weaker repulsions and decrease in energy.
The energy difference between the two sets of orbitals is the crystal field splitting (Δ).
depends on the nature of metal and ligands
determines color and magnetic properties
Bonding in Coordination Compounds
Spherical Field
transition metal
atom
Bonded
transition metal
atom
Crystal field splitting ( D) is the energy difference between two sets of d orbitals in a metal atom when ligands are present
Bonding in Coordination Compounds: Crystal Field Theory
Color
As with reflected light, transmitted light of selected wavelengths is responsible for color.
The color of observed light is the complementary color to the light absorbed.
Bonding in Coordination Compounds: Crystal Field Theory
The process of photoabsorption:
An absorption spectrum of [Ti(H2O)6]3+
The energy of the incoming photon is equal to the crystal field splitting.
Bonding in Coordination Compounds: Crystal Field Theory
Spectroscopic measurements of D allow an ordering of ligands ability to split the d orbitals called a spectrochemical series.
strong field ligand
weak field ligand
increasing
small D
large D
The spectrochemical series
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.
I- < Cl- < F- < OH- < H2O < SCN- < NH3 < en < NO2- < CN- < CO
WEAKER FIELD
STRONGER FIELD
LARGER D
SMALLER D
LONGER
SHORTER
Back-bonding 反馈键
Bonding in Coordination Compounds: Crystal Field Theory
Magnetic Properties
The magnitude of the crystal field splitting also determines the magnetic properties of a complex ion.
The electron configuration of the ion is a balance between:
The energy to promote an electron to a higher energy d orbital
Stability gained by maximum number of unpaired spins
Bonding in Coordination Compounds: Crystal Field Theory
Worked Example 22.3
Strategy The magnetic properties of a complex ion depend on the strength of the ligands. Strong-field ligands, which cause a high degree of splitting among the d orbital energy levels, result in low-spin complexes. Weak-field ligands, which cause only a small degree of splitting among the d orbital energy levels, result in high-spin complexes.
Predict the number of unpaired spins in the [Cr(en)3]2+ ion.
Solution The electron configuration of Cr2+ is [Ar]3d4; and en is a strong-field ligand. Because en is a strong-field ligand, we expect [Cr(en)3]2+ to be a low-spin complex. According to Figure 22.18, all four electrons will be placed in the lower-energy d orbitals (dxy, dyz, and dxz) and there will be a total of two unpaired spins.
Think About It It is easy to draw the wrong conclusion regarding high- and low-spin complexes. Remember that the term high spin refers to the number of spins (unpaired electrons), not to the energy levels of the d orbitals. The greater the energy gap between the lower-energy and higher-energy d orbitals, the greater the chance that the complex will be low spin.
Splitting of d-orbital energies by a tetrahedral field and a square planar field of ligands
tetrahedral
square planar
Bonding in Coordination Compounds: Crystal Field Theory
Tetrahedral and square planar complexes
Proximity of the ligands to d orbitals changes with the geometry of the complex
d electrons in orbitals more closely associated with the lone pairs of ligand electrons attain higher energies
Splitting patterns reflect this repulsion
Tetrahedral field
Bonding in Coordination Compounds: Crystal Field Theory
Tetrahedral and square planar complexes
Proximity of the ligands to d orbitals changes with the geometry of the complex
d electrons in orbitals more closely associated with the lone pairs of ligand electrons attain higher energies
Splitting patterns reflect
this repulsion
Square planar field
t = 4/9 o
MO
Electronic Spectra
Lambert-Beer Law
Relaxation of Selection Rules
Octahedral complexes: centrosymmetric
Laporte rule relaxed by vibronic coupling
Tetrahedral complexes: non-centrosymmetric
Laporte rule relaxed by orbital mixing
Selection Rules
Spin Selection Rule
DS = 0
There must be no change in spin multiplicity during an electronic transition
Laporte Selection Rule
D l = ± 1
There must be a change in parity during an electronic transition
d5 complexes: vibronic coupling and Spin-orbit coupling
Selection Rules
Transition e complexes
Spin forbidden 10-3 – 1 Many d5 Oh cxs
Laporte forbidden [Mn(OH2)6]2+
Spin allowed
Laporte forbidden 1 – 10 Many Oh cxs
[Ni(OH2)6]2+
10 – 100 Some square planar cxs
[PdCl4]2-
100 – 1000 6-coordinate complexes of low symmetry, many square planar cxs particularly with organic ligands
Spin allowed 102 – 103 Some MLCT bands in cxs with unsaturated ligands
Laporte allowed
102 – 104 Acentric complexes with ligands such as acac, or with P donor atoms
103 – 106 Many CT bands, transitions in organic species
CHARGE-TRANSFER SPECTRA
Jahn Teller Effects
For a non-linear molecule that is in an electronically degenerate state, distortion must occur to lower the symmetry, remove the degeneracy, and lower the energy.
Jahn-Teller effects do not predict which distortion will occur other than that the center of symmetry will remain.
The distortion by the unsymmetrical distribution of electrons in eg orbital is stronger than that of t2g.
Jahn-Teller Theorem
If the ground electronic configuration of a nonlinear molecule is degenerate, the molecule will distort so as to remove a degeneracy and achieve a lower energy.
e.g. Octahedral Cu(II) complexes (d9) Two degenerate ground electronic configurations:
d8 d9 d10
Degenerate No Yes No
configuration
J-T distortion No Yes No
The geometry of some six-coordinated
Cu(II) complexes is tetragonal instead of octahedral.
Solid-state structure of [Cu(NH3)6]2+
Elongation of the two axial bonds leads to stabilization of z2 and destabilization of x2-y2.
Overall, the tetragonal geometry is more stable than the octahedral analogue by (2 1 – 1) or 0.5 1
N.B. Distortion by either elongation or compression of the axial bonds will remove the degeneracy and results in stabilization
J-T theorem cannot predict which way it will take
Tetragonal geometry for 6-coordinated Cu(II) complexes
Broadening of absorption band for [Ti(H2O)6]3+ (splitting into two peaks)
Small K5 and K6 for [CuL6]
e.g. Cu2+(aq) + xs NH3(aq) → deep blue soln
Reactions of Coordination Compounds
22.4
Complex ions undergo ligand exchange (or substitution) reactions in solution.
Example: Exchange of NH3 with H2O
Rates of exchange reactions vary widely
Reactions of Coordination Compounds
Exchange reactions are characterized by:
Thermodynamic stability – measured by Kf
Large Kf values indicate stability
Small Kf values indicate instability
Kinetic lability – tendency to react
Labile complexes undergo rapid exchange
Inert complexes undergo slow exchange
Thermodynmically stable complexes can be labile or inert
Applications of Coordination Compounds
22.5
Metallurgy – extraction by complex formation
Chelation therapy – removal of toxins by chelation
Chemotherapy – use of complexes to inhibit the growth of cancer cells
Applications of Coordination Compounds
Chemical analysis – used in both qualitative and quantitative analysis
Example: dimethylgloxime (DMG) in nickel analysis
Applications of Coordination Compounds
Detergents
Chelating agents (tripolyphosphates) to complex divalent ions associated with water hardness
Environmental impact – eutrophication from phosphates
Sequestrants (Example: EDTA)
Agents to complex metal ions that catalyze oxidation reactions in foods
Key Concepts
22
Coordination Compounds
Properties of Transition Metals
Ligands
Nomenclature of Coordination Compounds
Structure of Coordination Compounds
Bonding in Coordination Compounds: Crystal Field Theory
Crystal Field Splitting in Octahedral Complexes
Color
Magnetic Properties
Tetrahedral and Square-Planar Complexes
Reactions of Coordination Compounds
Applications of Coordination Compounds

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