Transition Metal Complexes

Transition metal complexes.

Purpose: The objective is to investigate reactions between transition metal ions and electrically charged ion and neutral molecules.

Introduction. Chemical bond (From Wikipedia, the free encyclopedia): In chemistry, a chemical bond is the force, which holds together atoms in molecules or crystals.

All chemical bonding arises from the energetically favourable (that is, low-energy) interaction between electrons on different atoms. The types of bonding are distinguished by the extent to which electron density is:  Localized - ionic bonding: electrons are mainly associated with individual atoms

 Delocalized - covalent bonding the electron density distributions within bonds are not assigned to individual atoms, but are instead delocalized across the molecule.

Unlike pure ionic bonds, covalent bonds may have directed anisotropic properties.

Complex compound: In chemistry, a complex is a structure composed of a central metal atom or ion, generally a cation, surrounded by a number of negatively charged ions or neutral molecules possessing lone pairs. A complex may also be called a coordination compound or metal complex.

The ions or molecules surrounding the metal are called ligands. A ligand that is bound to a metal ion is said to be coordinated with the ion.

Simple ligands like water or chlorine form only one link with the central atom and are said to be monodentate.

The process of binding to the metal ion with more than one coordination site per ligand is called chelation. Compounds that bind avidly to form complexes are thus called chelating agents.

Some ligands are capable of forming multiple links to the same metal atom, and are described as bidentate, tridentate etc.

Typically, the chemistry of complexes is dominated by interactions between s and p orbitals of the ligands and the d (or f) orbitals of the metal ions. Because of this, the simple octet bonding theory fails in the case of complexes.

Ligander Metaller Cl- Chloro- Cu Cuprum Br- Bromo- Ag Argentum I- Iodo- Au Aurum CN- Cyano- Hg Mercurum OH- Hydroxo- Fe Ferrum 2- S2O3 Thiosulfato- Pb Plumbum

H2O Aquo-

NH3 Ammin-

Chemicals. Equipment. . 0.2 M CuSO4 5H2O Beakers, 100 mL . 0.2 M Ni(NO3)2 2H2O Test tubes 0.2 M CoCl2 Magnetic stirrer 0.2 M FeCl3 0.2 M KSCN Conc. NH3 Conc. HCl 1 w/o Dimethylglyoxim (DMG)

Preparations. All preparations are made in either 100 mL beakers, or in test tubes. First, add a suitable amount of the first solution to the beaker/test tube. Slowly add the second solution, drop by drop and observed the changes. Compare the reactions and the chemical reactions below.

1 Copper (Cu)

. CuSO4 5H2O(s)

NH3 2+ HCl Cu(OH)2(aq) Cu(H2O)4 (aq) Cu(H2O)2Cl2(aq) HCl NH3

2+ 2- Cu(NH3)4 (aq) CuCl4 (aq)

+ - Electron configuration: NH3(aq) + H2O(l) <=> NH4 (aq) + OH (aq)

2+ - Cu: Cu (aq) + 2OH (aq) => Cu(OH)2(s)

Name and coordination number (CN):

. CuSO4 5H2O Cu(OH)2 2+ Cu(H2O)4 CN = 2+ Cu(NH3)4 CN = 2- CuCl4 CN =

Cu(H2O)2Cl2 Diaquo-dichlorokobber(II) CN = Diaquokobber(II)chlorid Kobber(II)chloriddihydrat

Comments:

Cu(OH)2 has been used as a blue pigment (solid color) in paint. It is unstable and convert to black CuO through: Cu(OH)2 => CuO + H2O.

2+ Addition of NH3(aq) to transition metal solutions has been used as an analytical tool for determination of Cu (dark blue color). The method cannot be used in solutions containing Co2+ (why ?). The method has been 2+ used for determination of Cu after reaction between Cu and Br2 (1g kemi).

Cobalt (Co):

CoCl2(s)

NH3 2+ 2+ HCl 2- Co(NH3)6 (aq) Co(H2O)6 (aq) CoCl4 (aq)

Electron configuration: NH3 has one lone pair: NH3 H O has two lone pairs: 2 H O Co: (One or two may participate) 2

Co2+: Cl- is negatively charged: Cl-

2 Name and coordination number (CN):

CoCl2 CN = 2+ Co(H2O)6 CN = 2+ Co(NH3)6 CN = 2- CoCl4 CN =

Comments:

The color change is used analytically. Some cobalt compounds are blue in the dry state. When exposed to 2+ moisture (H2O), the aqous Co(H2O)6 ions are formed and the color changes to red.

Nickel (Ni)

. Ni(NO3)2 2H2O(s)

NH3 2+ 2+ HCl 2- Ni(NH3)6 (aq) Ni(H2O)6 (aq) NiCl4 (aq)

CN- DMG

2- 2+ Ni(CN)4 (aq) Ni(DMG)2 (s)

Electron configuration: H3C N OH H H Ni: C O O C Ni2+: H C N N CH H3C N OH 3 3 2+ Ni3+: Ni DMG = DiMethylGlyoxim H3C N N CH3 O O H H

Chelat: ”Two or more groups from the same molecule form bonds in such a way as to form a closed ring”.

Bidentat = may bond to the same metalion with 2 bonds (tridentat, tetradentat etc.). Name and coordination number (CN):

. Ni(NO3)2 2H2O 2+ Ni(H2O)6 CN = 2+ Ni(NH3)6 CN = 2- NiCl4 CN = 2- Ni(CN)4 CN = 2+ Ni(DMG)2 Bis(dimethylglyoimato)nikkel(II)ion CN =

Comments:

The red color associated with the Bis(dimethylglyoimato)nikkel(II)ion is used as an analytical tool for determination of trace amounts of Ni (se Frk. Hansens Smykkeskrin).

3 Iron (Fe)

FeCl3(s)

NH3 2+ 2+ 2+ HCl - Fe(H2O)5(OH) (s) + Fe(H2O)4(OH)2 (s) + ..... Fe(OH)3(s) Fe(H2O)6 (aq) FeCl4 (aq)

- 3- Fe(SCN)3(aq) + Fe(SCN)4 (aq) + ..... + Fe(SCN)6 (aq)

Electron configuration: Sure ioner:

3+ 2+ + Fe: Fe(H2O)6 + H2O <=> Fe(H2O)5(OH) + H3O

Fe2+: SCN- = thiocyanato-

Name and coordination number (CN):

FeCl3 2+ Fe(H2O)6 CN = Fe(OH)3 2+ Fe(H2O)4(OH)2 CN = 2- Fe(H2O)2(OH)4 CN = 3+ Fe(SCN)6 CN = 2- FeCl4 CN =

Fe 2+ and Fe 3+ .

+ 4- K4Fe(CN)6(aq) <=> 4K + Fe(CN)6 (aq) Name: Kaliumhexacyanoferrat(II) (Gult blodludsalt)

+ 3- K3Fe(CN)6(aq) <=> 3K + Fe(CN)6 (aq) Name: Kaliumhexacyanoferrat(III) (Rødt blodludsalt )

2+ 3+ Fe(II) Fe(III)(CN)6 Fe 3- Fe 4- Fe(CN)6 Fe(CN)6 Fe(III) Fe(II)(CN)6

Fe(II)[Fe(III)(CN)6] : Jern(II)ferricyanid [Turnbull’s blue]

Fe(III)[Fe(II)(CN)6] : Jern(III)ferrocyanid [Prussian blue]

Comments:

Rust is a serious problem i northern Europe. Damages worth approx. £109 pr. year were estimated in the United Kingdom in the mid-nineties.

Fe[Fe(CN)6] is a powerful blue pigment, discovered in 1704 by Diesbach in Berlin, and produced commercially in Paris since 1724. It is named Prussian blue, Paris blue, Berliner blue, Iron blue, Milori blue, depending on who made it and where. It was the first synthetic lightfast and wheather resistant blue pigment since the secret of the manufacture of aegyptian blue was lost around 500 ad.