Complexes of metal ions and nomenclature for inorganic

compounds

ammonia ligands

blue = nitrogen donor atom

white =hydrogen atom

Cobalt(III) ion

[Co(NH3)6]3+

Complexes of metal ions.

Prior to the work of Werner on coordination complexes, formulated at the time as CoCl3.6NH3, for example, there was no understanding of why the six ammonia molecules were so strongly bound in this compound. Werner showed that the ammonia molecules were in fact chemically bound to the cobalt, and that the three Cl- ions were present only to act as counter-ions to the 3+ charge on the [Co(NH3)6]3+ cation.

Alfred Werner (1866-1919)

Nobel prize 1913 for his work on Coordination compounds

[Co(NH3)6]3+ [Co(NH3)5Cl]2+ [Co(NH3)3Cl3]

Werner proposed that Co(III) (trivalent cobalt) had a coordination number of six, which could be satisfied by six ammonias in ‘a’, five ammonias and a Cl- in ‘b’, and three ammonias and three Cl- in ‘c’. His theory explained why conductivity showed that in solution ‘a’ was a 3+ cation, ‘b’ was a 2+ cation, and ‘c’ was neutral. The molecules or ions coordinated to the Co(III) are called ligands, from the Latin ‘ligare’ meaning ‘to join’. The coordination geometry of the Co(III) is octahedral, which means that the six ligands are placed around the Co(III) at the corners of an octahedron.

(a) (b) (c)

Some complexes of metal ions:

Cobalt water molecule

2+

nickel

cyanide ion

2+ 2-

nickelammonia

[Co(H2O)6]2+ [Ni(NH3)6]2+ [Ni(CN)4]2-

A complex is written such that everything inside the square brackets isa ligand chemically bonded to the metal ion. Everything outside the brackets is a counter-ion or something simply present in the crystal lattice. Thus, wemight have [Co(H2O)6](NO3)2 where the NO3

- ions are counter-ions.

Hexaaquacobalt(II) hexamminenickel(II) tetracyanonickelate(II)

C N

O N

Formal Oxidation State:

The formal oxidation state of metal ions in their complexes is determined by ascribing formal charges to all ligands which correspond to those they possess as the free molecules or ions:

Neutral: NH3, H2O, CO, PH3, (CH3)2SAnionic: OH-, F-, Cl-, Br-, I-, CN-, SCN-

Cationic: NO+

Examples of oxidation states:

[Co(NH3)6]3+ = Co(III)hexamminecobalt(III)

K3[Fe(CN)6] = Fe(III)potassium hexacyanoferrate(III)

[Co(NH3)4Cl2]Cl = Co(III)tetrammiinedichlorocobalt(III) chloride

[FeNO(NH3)5]Cl3 = Fe(II)pentamminenitrosyliron(II) chloride

[Cr(CO)6] = Cr(0)hexacarbonylchromium(O)

K[V(CO)6] = V(-I)potassium hexacarbonylvanadate(-I)

[Mn(NO)3CO] = Mn(-III)trinitrosylcarbonylmanganese(-III)

Identifying which are ligands:

In the formula for a complex, everything inside the square brackets (blue in formula below) is coordinated to the metal ion, everything outside (red) is a counterion or a lattice molecule.

When the name of a complex is written, all the ligands that are coordinated to the metal ion come before it, while counter-ions come after the name of the metal:

[Co(NH3)4Cl2]Cl is:

tetramminedichlorocobalt(III)chloride

ligands bonded to metal ion counterion

Naming of ligands in complexes: Neutral ligands:

When naming a complex, the ligands are indicated by names as follows:

Neutral ligands: NH3 = ammineH2O = aquaCO = carbonyl

The number of each type of ligand present is indicated by the Latin prefixes di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, and deca-:

[Co(NH3)6]Cl3 = hexamminecobalt(III) chloride[La(H2O)9](NO3)3 = nona-aqua lanthanum(III)

nitrateK2[Ti(CO)6] = potassium hexacarbonyl

titanate(-II)

Anionic ligands: To indicate that they are anions, ligands in complexes are given an ‘o’ ending: fluoro, chloro, bromo, iodo, hydroxo, cyano, sulfato, nitro, etc. If the overall charge on the complex is negative, the metal ion is given an ‘ate’ ending to indicate this:

K3[Fe(CN)6] = potassium hexacyanoferrate(III)or potassium hexacyanoiron(III)

K4[Fe(CN)6] = potassium hexacyanoferrate(II)

Na3[AlF6] = sodium hexafluoroaluminate(III)

[Co(NH3)3F3] = triamminetrifluorocobalt(III)

Naming of ligands in complexes: anionic ligands:

Nomenclature of complexes:

Cations, including complex cations, come first, anions, including complex anions come second:

[Co(NH3)6]Cl3 = hexammine cobalt(III) chloride, Na3[CrCl6] = sodium hexachlorochromate(III), [Ni(H2O)6]Cl2 = hexaaquanickel(II) chloride

K3[Rh(CN)6] = potassium hexacyanorhodate(III)

[Co(NH3)6][Co(CN)6] = hexamminecobalt(III) hexacyanocobaltate(III)

Naming more complex ligands:

Many ligands are more complex and have more than one donor atom, such as en (ethylenediamine), bipy (2,2’-bipyridyl) and acac (acetyacetonate) below:

Where more complex ligands are present, one indicates the number of these present with prefixes bis-, tris-, tetrakis, pentakis, or hexakis, followed by the name of the ligand in parentheses. Thus, [Co(en)3]Cl3 is tris(ethylenediamine)cobalt(III) chloride.

N N

H2N NH2

en bipy acac

O O-

H3C CH3

Some cobalt(III) complexes of more complex ligands:

NH2

Co

NH2

H2NH2N

H2N NH2

Co

N

N

N

N

N

N

CoO

O

O

O

O

O

CH3

H3C

H3C

CH3

CH3

CH3

.Cl3 .(NO3)3

tris(ethylenediamine) tris(2,2’-bipyridyl) tris(acetylacetonato)cobalt(III)chloride cobalt(III) nitrate cobalt(III)

NOMENCLATURE

1.1 Formulas of Simple Ionic substances.

For ionic compounds, the cation (more electropositive element) should always be first. (KCl, Na2S). If several cations are present, they should be listed in alphabetical order, followed by anions in alphabetical order (LiMgClF2). An exception is the proton, which is always listed last in the sequence of cations, (RbHF2).

Nomenclature (contd.)

1.2. Sequence of atoms in formulas of polyatomic ions and molecules:

For polyatomic species with a central atom, these are generally listed first followed by the attached atoms in alphabetical order (SO4

2-, CCl2H2, PCl3O, SO3, -CF3, -SCN). An exception is the linear thiocyanate group (-SCN), where the atoms are placed in the order in which they occur in the thiocyanate ion: -S=C=N

Formulas and Names of Common substances.

Acid Name Name of anion

HNO3Nitric acid nitrate

H3PO4 Phosphoric acid phosphate

H2SO4 Sulfuric acid sulfate

HClO4 Perchloric acid perchlorate

HClO3 Chloric acid chlorate

HClO2 Chlorous acid chlorite

HClOHypochlorous acid hypochlorite

HCl Hydrochloric acid chloride

Chemical Names

Names of the Elements: These originated with Berzelius (1813) who developed the system that the symbol for an element was the first letter of its name, e.g., F, O, N, C, B. If there was more than one element whose name started with the same letter, then a second, lower-case letter, was added, which was usually the second letter of the name of the element. e.g. C for carbon, but Ca, Cd, Ce, Cf, Cl, Cm, Co, Cr, Cs, Cu. B for Boron, but Ba, Be, Bi, Bk, Br, and so on.

Names of metallic elements you should know (pretty much all of them):

Hhydrogen

Li Belithium beryllium

Na Mgsodium magnesium

K Ca Sc Ti Vpotassium calcium scandium titanium vanadium

Rb Sr Y Zr Nbrubidium strontium yttrium zirconium niobiuim

Cs Ba La Hf Tacesium barium lanthanum hafnium tantalum

Names of metallic elements you should know (continued):

Cr Mn Fe Co Ni Cu Znchromium manganese iron cobalt nickel copper zinc

Mo Tc Ru Rh Pd Ag Cdmolybdenum technetium ruthenium rhodium palladium silver cadmium

W Re Os Ir Pt Au Hgtungsten rhenium osmium iridium platinum gold mercury

Lanthanides:La Ce …. Gd ……. Lulanthanum cerium gadolinium lutetium

Actinides:Ac Th …. U Np Pu Amactinium thorium uranium neptunium plutonium americium

Geometrical Isomerism

cis-diamminedichloro trans-diamminedichloro- platinum(II) platinum(II)

chloridePt

ammonia

Pt

Geometrical isomers can exist with two identical ligands placed next to each (cis) or at 180º to each other (trans). Again, Werner’stheory could explain how two different complexes correspondingto [(NH3)2Cl2Pt] could exist.

Cis and trans isomerism of octahedral complexes:

trans-[Co(NH3)4Cl2]+ cis-[Co(NH3)4Cl2]+

(green) (violet)

An important aspect of Werner’s theory was that it could explain howtwo compounds of identical formula, i.e. [Co(NH3)4Cl2]Cl, could existas two entirely different forms, which we now know to be the cis andtrans forms above.

green= Cl

fac (facial) and mer (meridional) geometrical isomers of the [Co(NH3)3Cl3] complex

mer fac mer-[Co(NH3)Cl3] fac-[Co(NH3)Cl3]

Optical isomerism:

Λ (lambda) form Δ (delta) form

The tris(ethylenediamine)cobalt(III) complex exists as optical isomers.the Δ and Λ forms, which are non-superimposable mirror images of each other. This will be discussed further under group theory.

mirror plane