Complex Formation Do Now: What is a coordinate bond? What is a covalent bond? What does Fe3+(aq) mean?

What is a Complex? Some definitions ... Ligand ion/ molecule with a lone pair that forms co-ordinate bond with a metal Complex metal ion with ligands co-ordinately bonded to it Co-ordination number number of co-ordinate bonds from ligand(s) to metal ions Remind pupils of co-ordinate bonds – covalent bond where one atom donates BOTH electrons Make it clear that Lewis acids and Lewis bases are NOT the same as Bronsted-Lowry acids and Bases (opposite way around and involve

Formation of complex Transition metals have a smaller radii than non-transition metals Due to the smaller radii, they can attract electron-rich species more strongly e.g. water molecules The water molecules are attracted to the TM ions strongly so they form a specific number of bonds

Complexes A complex is an ion or molecule with a central atom or ion surrounded by ligands joined by co-ordinate bonds so that the number of ligands exceeds the oxidation state of the central atom. e.g., [Cu(H2O)6]2+

Complexes It is a well known fact that copper(II) sulphate is not a blue solid! Anhydrous copper(II) sulphate is a white solid but becomes blue in solution because of the formation of this complex. Cu2+ + 6H2O  [Cu(H2O)6] 2+ white(s) blue(aq) Demo CuSO4 anhydrous and hydrated

Ligands These can be: Negative ions: Cl-, OH-, CN- Uncharged molecules that have one or more lone pairs of e-: NH3, H2O

Complexes 6 4 The co-ordination number of the complex is the number of co-ordinate bonds attached to the central atom or ion. [Cr(NH3)6]3+ co-ord no. = [CuCl4]2- co-ord no. = 6 4

Naming Complexes

Naming Complexes Formulas give us a lot of info ... [Cu(H2O)6]2+ [CuCl4]2- Brackets: () = ligands comprising more than 1 element (H2O, NH3, OH-, CN-). NOT needed if ligand is ion formed from 1 element. [] = to enclose the complex. Overall charge on the outside. Name also gives a lot of info ... [Cu(H2O)6]2+ Overall charge = +2, central Cu ion, 6 water molecules as ligands, Cu ox state = +2 [CuCl4]2- Overall charge = -2, central Cu ion, 4 chloride ions as ligands, Cu ox state = +2

Naming Complexes Name gives info on ... Number of each type of ligand The identity of each ligand The identity of the central metal ion and its oxidation state

Naming Complexes Number of ligands Prefix 2 Di 3 Tri 4 Tetra 5 Penta 6 1. Number of each type of ligand Number of ligands Prefix 2 Di 3 Tri 4 Tetra 5 Penta 6 hexa

Naming Complexes Ligand Name in complex Water Aqua Ammonia Ammine 2. The identity of each ligand Ligand Name in complex Water Aqua Ammonia Ammine Chloride Chloro Hydroxide Hydroxo cyanide Cyano Ammine is with 2 “m” – not to be confused with “amine” Also Diammine and diamine

Name in anionic complex Naming Complexes 3. The identity of the central metal ion and its oxidation state Name changes depending on whether complex is positively or negatively charged. POSITVELY Charged: Metal has normal name and ox state in brackets e.g., [Cu(H2O)6]2+ hexaaquacopper(II) ion (Cu in ox state +2) NEGATIVELY Charged: Ox state still in brackets. Add suffix “-ate” to end of metal e.g., [CuCl4]2- tetrachlorocuprate(II) ion(Cu in ox state +2) Metal Name in anionic complex Chromium Chromate cobalt Cobaltate Copper Cuprate Iron Ferrate Manganese Manganate Nickel Nickelate Silver Argenate Vanadium Vanadate Aluminium is not a TM, but included here for completeness

Examples [Ag(NH3)2]+ [Co(NH3)6]2+ [Co(H2O)6]2+ [CuCl4]2- [AgCl2]- Diamminesilver(I) Hexaamminecobalt(II) Hexaaquacobalt(II) Tetrachlorocuprate(II) Dichloroargenate(I)

Naming Complexes If 2 or more different ligands are present – name in alphabetical order (of the ligand, not the number prefix) [Cu(H2O)5(OH)2]+ Pentaaquadihydroxocopper(II) [Cu(H2O)2(NH3)4]2+ Tetraamminediaquacopper(II)

Notes on naming ... 1. Oxidation state NOT charge: The number in brackets in the name is the oxidation state of the central TM ion, NOT the charge on the complex. [Cu(H2O)6]2+Hexaaquacopper(II) [CuCl4]2-Tetrachlorocuprate(II) 2. When writing formula, put the central metal ion first, then the ligands: They are written in alphabetical order of first symbol in their formula (not written names) E.g., tetraaquadichlorochromium(III) [CrCl2(H2O)4]+ and not [Cr(H2O)4Cl2]+ 3. As An aside ... IUPAC Says When writing formula, write the ligand so that its donor atom symbol is nearest to the central metal ion: So H2O Should be written as (OH2) BUT to avoid confusion, we will use H2O A Level textbooks and exam papers use the non-IUPAC Convention, athough technically incorrect

Quick Check ... Name the following: [Fe(H2O)6]2+ [Cr(NH3)6]3+ [Ag(CN)2]- [MnCl4]2- [Fe(H2O)4(OH)2]+ Write the formula of the following: Diaquasilver(I) Hexaaquavanadium(III) Tetracyanonickelate(II) Tetrachloroferrate(II) Diaquatetrahydroxoaluminate(III)

Quick Check ... Name the following: [Fe(H2O)6]2+ hexaaquairon(II) [Cr(NH3)6]3+ hexaamminechromium(III) [Ag(CN)2]- dicyanoargenate(I) [MnCl4]2- tetrachloromanganate(II) [Fe(H2O)4(OH)2]+ tetraaquadihydroxoiron(III) Write the formula of the following: Diaquasilver(I) [Ag(H2O)2]+ Hexaaquavanadium(III) [V(H2O)6]3+ Tetracyanonickelate(II) [Ni(CN)4]2- Tetrachloroferrate(II) [FeCl4]2- Diaquatetrahydroxoaluminate(III) [Al(H2O)2(OH)4]-