Chapter 23 Transition Metals and Coordination Chemistry … · 2017-11-13 · 2011-11-25 7 Ferromagnetism(강자기성) • In ferromagnetic substances,,p the unpaired spins influence

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Chapter 23

Lecture Presentation

Chapter 23

Transition Metals and Coordination

Chemistry전이금속과배위화학(전이금속과배위화학)

John D. BookstaverSt. Charles Community College

Cottleville, MO© 2012 Pearson Education, Inc.

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Minerals(광물)• Most metals,

including transition gmetals, are found in solid inorganic compounds known as minerals.

• Minerals are named by common, not chemical, names.

© 2012 Pearson Education, Inc.

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Atomic Radii(원자반경)

As one goes from left gto right across a row, we see a decrease, then an increase in the radius of transition metals.


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Atomic Radii• On the one hand,

increasing effective gnuclear charge tends to make atoms smaller.

• On the other hand, the strongest (and, therefore, shortest) metallic bonds are found in the center of the transition metals.


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Traits of Transition Metals

• Because most transition metals havetransition metals have only partially occupied d subshells, the metals and/or their compounds often– Have more than oneHave more than one

oxidation state.


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Traits of Transition Metals• Because most

transition metals havetransition metals have only partially occupied d subshells, the metals and/or their compounds often– Have more than one

oxidation state,– Are pigmented.


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Ni2+, Co2+,Zn2+

Traits of Transition Metals• Because most

transition metals have only partially occupied d subshells, the metals and/or their compounds often– Have more than one

id ioxidation state,– Are pigmented,– Have magnetic

properties.


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Paramagnetism(상자기성)

• Paramagnetism, as you g yrecall from Chapter 9, results from an atom having unpaired electrons.

• Such atoms, then, show attraction to a magnet placed close by.


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Ferromagnetism(강자기성)• In ferromagnetic

substances, the unpaired , pspins influence each other to align in the same direction, thereby exhibiting strong attractions to an external

fmagnetic field.• Such species are

permanent magnets.


Antiferromagnetism(반강자성)

• Antiferromagnetic b t hsubstances have

unpaired spins on adjacent atoms that align in opposing directions.

• These magnetic• These magnetic fields tend to cancel each other.


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Ferrimagnetism(준강자성)

• Ferrimagnetic substances have spins that align opposite each other, but the spins are not equal, so there is a net magnetic field.E l NiM O• Examples are NiMnO3, Y3Fe5O12, and Fe3O4.


Complexes(착물)

• Commonly, transition metals can have molecules or ions that bond to them.

• These give rise to complex ions (착이온)or coordinationor coordination compounds (배위화합물).


[Co(NH3)4Cl2]+

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Ligands(리간드)

The molecules or ions that bind to the central metal are called ligands (from the Latin ligare, meaning “to bind”).


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Coordination(배위)

One of the properties that has led to theOne of the properties that has led to the fascination with complexes and transition metals is the wide range of stunning (근사한) colors found in them.


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Werner Theory (Werner 이론)

The Swiss chemist Alfred Werner deduced that there was a difference between the oxidation number of a metal and the number of ligands it took on, which he called the coordination number(배위수).


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Werner Theory

Thus, although the first two complexes in the t bl b h h 3 hl i i th fi ttable above each have 3 chlorines, in the first all three serve as anions, while in the second one of the chlorines is tightly bound to the cobalt and the other two are counterions.


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The Metal–Ligand Bond(금속-리간드결합)• The reaction between a metal and a ligand is a

reaction between a Lewis acid (the metal) and Lewis base (the ligand)base (the ligand).

• The new complex has distinct physical and chemical properties.

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Coordination Numbers(배위수)

• The coordination number of a metal depends upon the size of the metal and the size of the ligands.

• While iron(III) can bind t 6 fl id itto 6 fluorides, it can only accommodate 4 of the larger chlorides.


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Common Ligands

The table above contains some ligands commonly found in complexes.

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Common Ligands

Monodentate ligands coordinate to one site on the metal, bidentate to two, and so forth.

Common Ligands

Bi− and polydentate ligands are also called chelating agents(킬레이트시약).


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[Co(EDTA]-착이온

Chelates in Biological Systems

• There are many ytransition metals that are vital to human life.

• Several of these are bound to chelating agents.


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Chelates in Biological Systems

• For instance, the iron in hemoglobin carries O2 and CO2through the blood.

• Carbon monoxide and cyanide are poisonous because pthey will bind more tightly to the iron than will oxygen.


Nomenclature in Coordination Chemistry (배위화학에서의명명법)

1. In naming complexes that are salts, the name of the cation is given before the name of the anion.


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Nomenclature in Coordination Chemistry

2 I i l i l l2. In naming complex ions or molecules, the ligands are named before the metal. Ligands are listed in alphabetical order, regardless of their charges.


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3. The names of anionic ligands end in the letter o but electrically neutral ligandsletter o, but electrically neutral ligands ordinarily bear the name of the molecules.

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4. Greek prefixes (di-, tri-, tetra-, etc.) are used to indicate the number of each kind of ligand when more than one is present. If the ligand contains a Greek prefix or is polydentate, the prefixes bis-, tris-, t t ki t d d th li dtetrakis-, etc. are used and the ligand name is placed in parentheses.


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5. If the complex is an anion, its name ends pin -ate.

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


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Isomers (이성질체)

• Isomers have the same molecular formula but a different arrangement of atoms.

• There are two main subgroupings: structural isomers and stereoisomers.

Linkage Isomers (결합이성질체)In linkage isomers the ligand is bound to the metal by a different atom.

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Coordination Sphere Isomers(배위권이성질체)

• Coordination sphere isomers differ in what ligands are bound to the metal and which fall outside the coordination sphere.

• For example, CrCl3(H2O)6 exists as[Cr(H O) ]Cl– [Cr(H2O)6]Cl3,

– [Cr(H2O)5Cl]Cl2 H2O, or– [Cr(H2O)4Cl2]Cl 2H2O.


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Geometric Isomers (기하이성질체)

[Pt(NH3)2Cl2]

I t i i th li d h• In geometric isomers, the ligands have a different spatial relationship.

• In the complexes above, the chlorines can be adjacent to each other (cis) or opposite each other (trans).

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Optical Isomers (광학이성질체)Optical isomers, or enantiomers, are non-superimposable mirror images of one another.

Color

• The complex [Ti(H2O)6]3+

at the left appearsat the left appears red-violet because those are the wavelengths of visible light not absorbed by the complex.

• Many complexes areMany complexes are pigmented because they absorb in the visible part of the spectrum.

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Crystal-Field Theory (결정장이론)

• As was mentioned earlier, ligands are Lewis bases that are attracted to a Lewis acid (the metal).

• But d electrons on the metal would repel the ligand.


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Crystal-Field Theory• Therefore, the d orbitals on a metal in a complex

would not be degenerate.• Those that point toward ligands would be higher p g g

in energy than those that do not.

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Crystal-Field Theory

The energy gap between d orbitals often gy g pcorresponds to the energy in a photon of visible light.


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The stronger the crystal-field strength of the ligand, the larger the energy gap between d orbitals, and the shorter the wavelength of light absorbed by the complex.

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The spectrochemical series(분광화학적계열)The spectrochemical series(분광화학적계열)ranks ligands in order of their ability to increase the energy gap between d orbitals.


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고스핀 저스핀

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Tetrahedral

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Documents

Chapter 23 Transition Metals and Coordination Chemistry … · 2017-11-13 · 2011-11-25 7 Ferromagnetism(강자기성) • In ferromagnetic substances,,p the unpaired spins influence