copyright © houghton mifflin company. all rights reserved. 20a–1 alfred werner 1913 nobel prize...

Copyright © Houghton Mifflin Company. All rights reserved. 20a–1

Alfred Werner

1913 Nobel Prize in Chemistry

Theory of the structure of coordination compounds


Werner'sCoordination Theory

• primary valence => ion charge• secondary valence => coordination

number• inner sphere => ligands bonded

directly to metal ion• outer sphere => next sheath of ions

or molecules


Terminology

coordinate covalent bond - covalent bond formed by one atom donated both electrons of shared pair; Lewis acid-base reaction

ligand - electron pair donor; Lewis base

coordination number - number of electrons pairs accepted by central metal atom


Coordinate Covalent Bond

H N

H

H

+ H+ H N

H

H

H

+

or H N

H

H

H

+


Some Common Ligand


More Ligands

Some important aspects of transition metal ions:

1. The valence electrons are in d orbitals2. The d orbitals do not have large radial extension3. The d orbitals are therefore mostly nonbonding in complexes of transition metal ions4. For these reasons, the effects of redox changes are substantially smaller for transition metals than for main group elements


Molecular model: The CO(NH3)63+ ion


Aqueous solutions containing metal ions


Coordination Compounds: Structure and Nomenclature

Coordination Number => 2, 4 & 6 most common

CN Shape

2 linear

4 tetrahedral

4 square planar

6 octahedral


Figure 20.6: Ligand arrangements for coordination numbers 2, 4, and 6


Coordination Number 2


Multiplicity

Monodentate

mono => 1

di => 2

tri => 3

tetra => 4

penta => 5

hexa => 6

Bi- or tri- dentate

bis => 2

tris => 3

tetrakis => 4


Figure 20.7: Bidentate ligand ethylene-diamine can bond to the metal ion through the lone pair on each nitrogen atom, thus forming two coordinate covalent bonds.


Figure 20.8: The coordination of EDTA with a 2+ metal ion.

Names1. In naming the entire complex, the name of the cation is given first and the anion second (just as for sodium chloride), no matter whether the cation or the anion is the complex species.

2. In the complex ion, the name of the ligand or ligands precedes that of the central metal atom. (This procedure is reversed from writing formulae.)

3. Ligand names generally end with 'o' if the ligand is negative ('chlorido' for Cl-, 'cyanido' for CN-, 'hydrido' for H-) and unmodified if the ligand is neutral ('methanamine' for MeNH2). Special ligand names are 'aqua' for water, 'ammine' for ammonia, 'carbonyl' for CO, 'nitrosyl' for NO.


4. A Greek prefix (mono, di, tri, tetra, penta, hexa, etc.) indicates the number of each ligand (mono is usually omitted for a single ligand of a given type). If the name of the ligand itself contains the terms mono, di, tri, eg triphenylphosphine, then the ligand name is enclosed in parentheses and its number is given with the alternate prefixes bis, tris, tetrakis instead. For example, NiCl2(PPh3)2 is named dichloridobis(triphenylphosphane)nickel(II).

Again, one would use diammine, for (NH3)2, but bis(methylamine), for (NH2Me)2, to make a distinction from dimethylamine. (Note that this ambiguity does not arise if the preferred IUPAC name, methanamine, is used instead of methylamine). There is no elision of vowels or use of a hyphen, e.g. in tetraammine and similar names. Some texts suggest that if a ligand is "complicated" then use the bis, tris multipliers. What constitutes "complicated" is not spelled out however, so a simpler approach is to use them if the name of the ligand is three or more syllables long!


5. A Roman numeral or a zero in parentheses is used to indicate the oxidation state of the central metal atom.

6. If the complex ion is negative, the name of the metal ends in 'ATE' for example, ferrate, cuprate, nickelate, cobaltate etc.

7. If more than one ligand is present in the species, then the ligands are named in alphabetical order regardless of the number of each. For example, NH3 (ammine) would be considered an 'a' ligand and come before Cl- (chlorido). (This is where the 1971 rules differed from the 1959 rules. Some texts still say that ligands are named in the order: neutral then anionic). Examples:[Co(en)3]Cl3 [Co(NH3)3(NO2)3] K2[CoCl4] note that it is not necessary to enclose the halogens in brackets


Nomenclature

Neutral molecule

[Ru(NH3)4(HSO3)2]

bis(bisulfite)tetraamineruthenium(II)


Nomenclature

Anionic coordination sphere

K3[Fe(CN)6]

potassium hexacyanoferrate(III)


Nomenclature

Cationic coordination sphere

[Cu(NH3)4]SO4

tetraaminecopper(II) sulfate


Nomenclature

Cationic coordination sphere & Anionic coordination sphere

[Ti(H2O)6][CoCl6]

hexaaquatitanium(III)

hexachlorocobaltate(III)


Coordination Isomers

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

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

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