Nomenclature & Coordination Chem

Lewis 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 donate Complexing Agent: H2O, NH3, Cl- CN-

Metal possesses open orbitals to accept e- pair. M with empty d- orbitals Ligand with e- pair Combine to form LA-LB (Compound) In general, the complex is more stable than the separated compound. Complex - Metal ion bonded to a number of ligands M M M M M

Complex - 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.

Coordination Number CN - 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 # = 3 Geometry of Complex is related to CN. CN = 2 Linear CN= 4 Tetrahedral (d10) Sq Planar (d8) CN = 5 Trigonal bipyramidal Square Pyramide CN = 6 Octahedral

Coordinated Complexes and Coordination Number Coord Shape Example Number 2 Linear [CuCl2]-, [Ag(NH3)2]+, [AuCl2]- 4 Square Planar [Ni(CN)4] 2-, [PdCl4]2- [Pt(NH3)4] 2+, [Cu(NH3)4] 2+ 4 Tetrahedral [Cu(CN)4] 3-, [Zn(NH3)4]2+ [CdCl4] 2-, [MnCl4] 2- 6 Octahedral [Cu(H2O)6] 3+, [V(CN)6] 4-, [Cu(NH3)4Cl2] +, [Co(en)3] 3+

Ligands 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, H2O Polydentate 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

Ligands Example of Typical mono-, bi- and poly dentate Ligands Name of Neutral and Anionic Ligands: Neutral: Anionic Aqua H2O Fluoro Fl- Amine NH3 Chloro Cl- Nitrosyl NO Bromo Br- Carbonyl CO Iodo I- Hydroxo OH- Cyano CN-

Chelates 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 separate en ethylenediamine (shown) - two toothed ligand: i.e., [Co(en)3]3+ [Pt(en)2]2+ EDTA ethylenediaminetetraacetate (picture) hexadentate EDTA is the antidote for heavy metal poisoning

Chelating agents in Living system Seven of 24 elements necessary for life, based on ability to formed complexes V, Cr, Mn, Fe, Co, Cu, Zn Fe - hemoglobin, chlorophyll (Mg) Co - Vitamin B

Chelating effect A complex containing chelate ligands is more stable than that from a monodentate ligand. Kf, larger for chelating complex. Ni(H2O)62+ + 6NH3  Ni(NH3)6 + 6H2O kf = 4•108 Ni(H2O)62+ + 3en  Ni(en)3 + 6H2O kf = 2•1018 Driven 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).

Biological Coordinating Complexes Chlorophyll Oxymyoglobin Ferrichrome

Nomenclature Cation - 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.

Nomenclature 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.

Example: Naming from Formula Name from formula a) K3[Au(CN)4] Potassium Tetracyanoaurate(I) d) K[Co(C2O4)2(NH3)2] Potassium diaminedioxaloCobaltate(I) f) [Cr(en)2F2]NO3 Bis(ethylenediamine)difluorochromium(III) nitrate Naming anionic metals Iron: Ferrate Copper: Cuprate Lead: Plumbate Silver: Argentate Gold: Aurate Tin: Stannate

Example: Formula from Name Name from formula a) Hexaamminechromium(III) nitrate [Cr(NH3)4] (NO3)3 d) dichlorobis(ethylenediamine)platinum(IV) bromide [PtCl2(en)2]Br2 f) bis(ethylenediamine)zinc(II) tetraiodomercurate(II) [Zn(en)2][HgI4] More anionic metals Osmium: Osmate Cobalt: Cobaltate Amtimony: Antimonate Rhenium: Rhenate Platinum: Platinate Rhodium: Rhodate

Geometry Coordinate Number (CN): Number of donor atoms bonded to metal 2- coordinate - linear 4 - coordinate tetrahedral and square planar ML4 , Pt(II) is always CN = 4 6- octahedral ML6, Cr(III) and Co(III) CN = 6 CN influence by Size of metal ion Small metal /large ligand - Low coordinate number Surrounding ligand Large metal / small ligand - High coordination number i.e., FeF63- and FeCl4- only