A2 Chemistrytransition metal

complexes

a visual guide

Designed by Samuel Millar

VERSION 1

NOTES• Black text – CORE

KNOWLEDGE– Red text – EXCEPTIONS TO

THE PATTERNS

• Grey text – EXTENSION

The colour and formula are given for the complex formed by each ion with each • reagent, starting with the aqueous complex. In the case of NaOH and NH3, the hydroxide precipitate produced is given, followed by the complex formed (if any) when excess (“xs”) of the reagent is added.

The colours are named as CCEA wants them in the exam! The colour boxes hopefully give some indication of the actual shade.Most of the complexes involve six ligands and so are octahedral. However, chloride complexes take tetrahedral or square planar shapes.

Copper (II) and Cobalt (II)

• Cu2+

• blue soln[Cu(H2O)6]2+

• blue ppt[Cu(OH)2(H2O)4]insoluble in xs

• blue ppt[Cu(OH)2(H2O)4]soluble – deep blue soln[Cu(NH3)4(H2O)2]2+

• yellow-green soln[CuCl4]2-

• Co2+

• pink soln[Co(H2O)6]2+

• blue ppt[Co(OH)2(H2O)4]insoluble in xs

• blue ppt[Co(OH)2(H2O)4]soluble – yellow soln[Co(NH3)6]2+

• blue soln[CoCl4]2-

• ion

• aq

• NaOH

• NH3

• conc HCl

Iron (III) and Iron (II)• Fe2+

• green soln[Fe(H2O)6]2+

• green ppt*2

[Fe(OH)2(H2O)4]insoluble in xs

• green ppt*2

[Fe(OH)2(H2O)4]insoluble in xs

• Fe3+

• yellow/orange soln[Fe(H2O)6]3+ *1

• rust/brown ppt[Fe(OH)3(H2O)3]insoluble in xs

• rust/brown ppt[Fe(OH)3(H2O)3] insoluble in xs

• blood-red soln[Fe(SCN)(H2O)5]2-

• ion

• aq

• NaOH

• NH3

• SCN-

thiocyanate

*1[Fe(H2O)6]3+ is actually pale violet. The high charge density on the metal ion causes some deprotonation and the yellow-orange colour is actually due to [Fe(OH)(H2O)5]2+

*2NB: Iron (II) hydroxide slowly oxidises to iron (III) hydroxide, so a rust/brown colour is observed after some time.

Chromium (III) and Manganese (II)

• Cr3+

• green soln[Cr(H2O)6]3+

• green-blue ppt[Cr(OH)3(H2O)3]soluble – green soln[Cr(OH)6]3-

• green-blue ppt[Cr(OH)3(H2O)3]soluble – violet soln[Cr(NH3)6]3+

• Mn2+

• pink soln[Mn(H2O)6]2+

• white ppt*[Mn(OH)2(H2O)4]insoluble in xs

• white ppt*[Mn(OH)2(H2O)4] insoluble in xs

• ion

• aq

• NaOH

• NH3

*NB: Manganese (II) hydroxide slowly oxidises to manganese (III) oxide, so the white (off-white) precipitate slowly turns brown/black.

• Chromium (VI) CrO42- yellow soln

• Chromium (VII) Cr2O72- orange soln

• aq

• Chrome alum KCr(SO4)2 violet crystals

Nickel (II) and Vanadium• Ni2+

• green soln [Ni(H2O)6]2+

• green ppt [Ni(OH)2(H2O)4]insoluble in xs

• green ppt [Ni(OH)2(H2O)4]soluble – blue soln [Ni(NH3)6]2+

• yellow soln [NiCl4]2-

• blue soln [Ni(edta)]2-

• purple soln [Ni(en)3]2+

• ion

• aq

• NaOH

• NH3

• conc HCl

• edta

• en

• Vanadium (II) V2+ violet

• Vanadium (III) V3+ green

• Vanadium (IV) VO2+ blue

• Vanadium (III) VO2+ yellow• aq