2Lewis Acid - Lewis Base Chemistry Lewis Acid : e- acceptor(metals are good e- acceptor)Lewis Base : e- donor(Ligands with lone pair electrons)Ligands, atoms or cluster of atoms with lone pair electrons available to donateComplexing Agent: H2O, NH3, Cl- CN-
3Metal possesses open orbitals to accept e- pair. M with empty d- orbitalsLigand with e- pairCombine to form LA-LB (Compound)In general, the complex is more stable than the separated compound.Complex - Metal ion bonded to a number of ligandsMMMMM
4Complex - Metal- Ligand compounds [MLn] i.e., [Ag(NH3)2]+ or [Co(NH3)6] Cl3[ ] denotes atoms bonded to each other through covalent bonds. These atoms are contained in the coordination sphere.Coordinated sphere is the directly bonded to each other.Counter ions are outside bracket, and are not part of the coordinate sphere.A coordinated compound behaves like an electrolyte in water: the complex ion and counter separates from each other. But the complex ion behaves like a polyatomic ion: the ligands and central metal ion remain attached.
5Coordination NumberCN - Number of ligand atoms bonded directly to the central metal ion.Specific for given metal ion in particular Oxidation #.i.e., [Co(NH3)6]+ CN = 6 Ligand # = 6[Ag(NH3)2]+ CN = 2 Ligand # = 2[Co(en)3]+ CN = 6 Ligand # = 3Geometry of Complex is related to CN.CN = 2 Linear CN= 4 Tetrahedral (d10)Sq Planar (d8)CN = 5 Trigonal bipyramidalSquare PyramideCN = 6 Octahedral
7Ligands Consider [Ag(NH3)2]+ Ligand (contains the donor atom, directly bonded to metal):NH3 - ligand occupy one site in coordinate sphere (monodentate)examples (Monodentate)N3- , X-, CN- , OH-, NH3 , pyridine, H2OPolydentate ligand - known as chelating agents - ligand which has several donor sites that can multi-bond (coordinate) metal simultaneously (chelates)i.e. en, oxalate, 1.10 phenanthroline, carbonate, bipyridine[EDTA]4- or (ethylenediaminetetraacetate), phenylpyridine
8Ligands Example of Typical mono-, bi- and poly dentate Ligands Name of Neutral and Anionic Ligands:Neutral: AnionicAqua H2O Fluoro Fl-Amine NH3 Chloro Cl-Nitrosyl NO Bromo Br-Carbonyl CO Iodo I-Hydroxo OH-Cyano CN-
9Chelates en ethylenediamine (shown) - two toothed ligand: Chelating Ligands have two or more donor atoms that simultaneously coordinate to a single metal ion.Polydentate - (Many toothed - ligand)Chelating agent (Claw)Sequestering agent - sequester - to set apart or separateen ethylenediamine (shown) - two toothed ligand:i.e., [Co(en)3]3+ [Pt(en)2]2+EDTA ethylenediaminetetraacetate(picture) hexadentateEDTA is the antidote forheavy metal poisoning
10Chelating agents in Living system Seven of 24 elements necessary for life, based on ability to formed complexesV, Cr, Mn, Fe, Co, Cu, ZnFe - hemoglobin, chlorophyll (Mg)Co - Vitamin B
11Chelating effectA complex containing chelate ligands is more stable than that from a monodentate ligand.Kf, larger for chelating complex.Ni(H2O) NH3 Ni(NH3) H2O kf = 4•108Ni(H2O) en Ni(en) H2O kf = 2•1018Driven by Entropy:Note that in the above reaction, the entropy increases via the increase of number of moles in the overall reaction. In reaction (1) there are 7 moles of reactant changing to seven moles of product but in reaction (2) there are 4 moles of reactant changing to 7 moles of product, Kf is much larger for reaction (2).
13NomenclatureCation - Anion: Salts: name cation before anions i.e., [Co(HN3)5Cl]Br2, we name [Co(HN3)5Cl] complex ion before bromides counter ions .Complex: Within complex ion, the ligands are named in alphabetical order before the metal i.e., tetraaminechlorocobalt(II), note that tetra is an indication of the number of NH3 group, and not considered in the alphabetizing of the ligand.Ligand: Anionic ligands end in -o and neutral ligands are name based on their molecular name (excepts are aqua H2O, amine: NH3)Greek prefixes are used to indicate number of ligands, di-, tri-, tetra-, penta-, hexa-. Exception occurs when ligand already has Greek prefix in its name, The prefixes bis-, tris-, tetrakis-, pentakis, & hexakis. are used instead.i.e., Ir(bpy)3 trisbipyridineiridium (III) bipyridine already has bi in its name.If the complex is an anion, then its name ends with suffix -ate.Further more, oxidation state of the metal is given in roman numerals in parenthesis at the end of the name.
14Nomenclature Rules: 1. The cation is written before the anion. 2. The charge of the cation(s) is balanced by the charge of the anion(s).3. For the complex ion, neutral ligands are written before anionic ligands (negative charge), and the whole ion is placed in brackets.Procedure Outline:1. The cation is named before the anion.2. Within the complex ion, the ligands are named, in alphabetical order.3. Neutral ligands generally have the molecule name.Anionic ligands drop the -ide and add -o after the root name.4. Numerical prefixes denote the number of a particular ligand.5. Oxidation state of metal ion is in Roman numeral in parenthesis.6. For anionic complex, the end of the metal name is replaced by -ate.
15Example: Naming from Formula Name from formulaa) K3[Au(CN)4]Potassium Tetracyanoaurate(I)d) K[Co(C2O4)2(NH3)2]Potassium diaminedioxaloCobaltate(I)f) [Cr(en)2F2]NO3Bis(ethylenediamine)difluorochromium(III) nitrateNaming anionic metalsIron: Ferrate Copper: CuprateLead: Plumbate Silver: ArgentateGold: Aurate Tin: Stannate
16Example: Formula from Name Name from formulaa) Hexaamminechromium(III) nitrate[Cr(NH3)4] (NO3)3d) dichlorobis(ethylenediamine)platinum(IV) bromide[PtCl2(en)2]Br2f) bis(ethylenediamine)zinc(II) tetraiodomercurate(II)[Zn(en)2][HgI4]More anionic metalsOsmium: Osmate Cobalt: CobaltateAmtimony: Antimonate Rhenium: RhenatePlatinum: Platinate Rhodium: Rhodate
17Geometry Coordinate Number (CN): Number of donor atoms bonded to metal 2- coordinate - linear4 - coordinate tetrahedral and square planarML4 , Pt(II) is always CN = 46- octahedralML6, Cr(III) and Co(III) CN = 6CN influence bySize of metal ionSmall metal /large ligand - Low coordinate numberSurrounding ligandLarge metal / small ligand - High coordination numberi.e., FeF63- and FeCl4- only