Chemistry 401

Ligands

Usually ligands are Lewis bases (nonmetals, either anions or neutrals with lone pairs) but this is not required.

The ligand could be another metal complex to give a multimetal compound

Re₂Cl₈^2– (D_4h)

(quadruple metal-metal bond)

Traditional ligands have N, O, halide, S, P as the binding site (all have lone pairs)

Binding of C to metals is also well known - this is organometallic chemistry

Ligands may have multiple binding sites:

monodentate : one binding site NH₃, Cl^–, H₂O, CN^–

ambidentate : two available binding sites but only one can be used CN^–, SCN^–

This gives the possibility of linkage isomerization : M-SCN differs from M-NCS

bidentate : two binding sites and both used

ethylenediamine (en), oxalate (ox), 2,2'-bipyridine (bipy), acetylacetonate (acac), phenanthrene (phen)

chelation : ligand plus metal form a ring system; requires a multidentate ligand

tridentate : three binding sites used

H₂NCH₂CH₂NHCH₂CH₂NH₂ (dien)

quadridentate : four binding sites

porphyrin

polydentate : many binding sites

EDTA^4– (^–O₂CCH₂)₂–NCH₂CH₂N– (CH₂CO₂^–)₂

binds strongly to nearly all metals; used to treat heavy metal poisoning

Nomenclature of transition metal complexes

Cationic and Neutral complexes:

1) ligands are listed in alphabetical order using systematic name except:

a) if the ligand name ends in -ide, -ate, or ite, drop the final e and and add an o

b) others : O^2– oxo; OH^– hydroxo; CN^– cyano; O₂^2– peroxo; NH₃ ammine; H₂O aqua; NO nitrosyl; CO carbonyl; F^– fluoro; Cl^– chloro; Br^– bromo; I^– iodo

2) the number of times a ligand appears is prefixed to the ligand using

StoichiometryPrefixAlternateuse the alternate when the preferred prefix gives ambiguity

 

2bibis

 

3tritris

 

4tetratetrakis

 

5pentapentakis

 

6hexahexakis

 

3) structural information prefixes ligands, and can be for each ligand if necessary

cis-; trans-; fac-; mer-; μ- (ligand bridges two metals);

η^x– (x = number of C bonded to metal in an organic ligand)

4) metal is last followed by parentheses with the formal oxidation state in roman numerals

5) if cationic, counterion is the second word

Examples

Co(NH₃)₆Cl₃

hexaamminecobalt(III) chloride

[Co(NH₃)₅Cl]Cl₂

pentaamminechlorocobalt(III) chloride

[Co(NH₃)₄Cl₂]Cl

cis-tetraamminebichlorocobalt(III) chloride

trans-tetraamminebichlorocobalt(III) chloride

[Co(NH₃)₃Cl₃]

fac-triamminetrichlorocobalt(III)

mer-triamminetrichlorocobalt(III)

CuCl₂(CH₃NH₂)₂

cis-bichlorobis(methylamine)copper(II)

Ni(CO)₄

tetracarbonylnickel(0)

PtCl₂(CH₂=CH₂)

bichloro-η²-etheneplatinum(II)

(C₅H₅)₂Fe

bis(η⁵-cyclopentadienyl)iron(II) [more commonly known as ferrocene]

Br₂Pt-(S(CH₃)₂)₂-PtBr₂

bis(μ-dimethylsulfido)bis(dibromoplatinum(II))

Anions:

1) counterion is first word

2) use cationic rules except add -ate to the end of the metal before the oxidation state info sometimes can use the Latin root

Examples

K₂[OsCl₅N]

potassium pentachloronitridoosmate(VI)

Na₃[Ag(S₂O₃)₂]

sodium bis(thiosulfato)argentate(I)

Na₂[Fe(CN)₅NO]

sodium pentacyanonitrosylferrate(III)