Complexes Complexes Compounds in which a metal atom

Complexes

Complexes Compounds in which a metal atom or ion is surrounded by a number of oppositely charged ions or by neutral molecules. All possessing lone pairs of electrons which are available for donation to vacant orbitals of the metal atom or ion.

Structure 1. [Hexaammineplatinum(IV)] chloride [Pt(NH 3)6]Cl 4 central ion coordination number ligand complex cation

2. Potassium hexachloroplatinate(IV) K 2[Pt. Cl 6] central ion coordination number ligand complex anion

3. Iron(O)pentacarbonyl [Fe(CO)5] central atom coordination number ligand complex molecule

Central ions, atoms: Transition metals Alkaline earth metals Alkaline metals Coordination numbers: Number of ligands in the first coordination sphere

Complexes with various coordination numbers Coordination Complex number 2 [Ag(NH 3)2]+, [Cu. Cl 2]3 4 5 6 7 8 [Hg. I 3][Zn(NH 3)4]2+, [Ni(CN)4]2[Ni(CN)5]3 -, Fe(CO)5 [Cr(H 2 O)6]3+, [Fe(CN)6]3[Zr. F 7]3[Mo(CN)8]4 -

Geometry: linear (2) tetrahedral (4) square planar (4) octahedral (6)

Monodentate Ligands Cations: H 2 N-NH 3+ Anions: F-, Cl-, OH-, CN-, NO 3 -, NO 2 Neutral molecules: H 2 O, NH 3, CO

Water Carbon monoxide Ammonia Thiocyanate ion Chloride ion Cyanide ion Hydroxide ion

Polydentate Ligands Ethylenediamine (en) Glycinate ion (gly-) Oxalate ion Ethylenediaminetetraacetate ion (EDTA 4 -)

Chelates Bi- or polydentate ligands Men+n+ Me Me

Nomenclature: IUPAC 1. Cation preceeds anions 2. Ligands preceed central ions or atoms 3. Anion ligands: -o ending (hydroxo, chloro, cyano…) 4. Cations, neutral molecules: unchanged Exception(!): aqua, ammine, carbonyl, nitrosyl 5. Complex anions: -ate ending 6. Oxidation state: Roman numbers

Dissociation of complexes Conductance* Number of ions Number of chloride ions [Pt(NH 3)6]Cl 4 523 5 4 [Pt(NH 3)5 Cl]Cl 3 404 4 3 [Pt(NH 3)4 Cl 2]Cl 2 228 3 2 [Pt(NH 3)3 Cl 3]Cl 97 2 1 [Pt(NH 3)2 Cl 4] 0 0 0 K[Pt(NH 3)Cl 5] 108 2 0 K 2[Pt. Cl 6] 256 3 0 Formula *Molar conductance: cm 2/ ·mól, 0, 001 M, 25°C

Stability constant, formation Properties of metal complex differ from metal ion! 1. 2. 3. 4. Colour changing Solubility Ligand reactions Number of particles, dissociation Formation constant: Kstab (stability constant) Pl. : Ag+ + 2 NH 3 K= [Ag(NH 3)2]+ [Ag+][NH 3]2 Dissociation constant: Kd = = 1, 7·107 1 [Kstab]

Izomerism Isomers Constitutional isomers Linkage isomers Ionization isomers Stereoisomers Diastereoisomers Enantiomers

Cr. Cl 3·6 H 2 O [Cr(H 2 O)6]Cl 3 [Cr(H 2 O)4 Cl 2]Cl·2 H 2 O [Cr(H 2 O)5 Cl]Cl 2·H 2 O

cis trans NH 3 Cl Co NH 3 Cl NH 3 [dichloro-tetraammine-cobalt(III)] ion

Cl Cl Cl en Cl Co Co en en [dichloro-bis(etylenediammine)cobalt(III)] ion en = etylenediammine en

Bonding in complexes: • Valence Bond Theory • Crystal Field Theory