Presentation on theme: "Complexes of metal ions and nomenclature for inorganic compounds ammonia ligands blue = nitrogen donor atom white = hydrogen atom Cobalt(III) ion [Co(NH."— Presentation transcript:
Complexes of metal ions and nomenclature for inorganic compounds ammonia ligands blue = nitrogen donor atom white = hydrogen atom Cobalt(III) ion [Co(NH 3 ) 6 ] 3+
Complexes of metal ions. Prior to the work of Werner on coordination complexes, formulated at the time as CoCl 3.6NH 3, for example, there was no understanding of why the six ammonia molecules were so strongly bound in this compound. Werner showed that the ammonia molecules were in fact chemically bound to the cobalt, and that the three Cl - ions were present only to act as counter-ions to the 3+ charge on the [Co(NH 3 ) 6 ] 3+ cation. Alfred Werner ( ) Nobel prize 1913 for his work on Coordination compounds
[Co(NH 3 ) 6 ] 3+ [Co(NH 3 ) 5 Cl] 2+ [Co(NH 3 ) 3 Cl 3 ] Werner proposed that Co(III) (trivalent cobalt) had a coordination number of six, which could be satisfied by six ammonias in a, five ammonias and a Cl - in b, and three ammonias and three Cl - in c. His theory explained why conductivity showed that in solution a was a 3+ cation, b was a 2+ cation, and c was neutral. The molecules or ions coordinated to the Co(III) are called ligands, from the Latin ligare meaning to join. The coordination geometry of the Co(III) is octahedral, which means that the six ligands are placed around the Co(III) at the corners of an octahedron. (a) (b) (c)
Some complexes of metal ions: Cobalt water molecule 2+ nickel cyanide ion 2+2- nickel ammonia [Co(H 2 O) 6 ] 2+ [Ni(NH 3 ) 6 ] 2+ [Ni(CN) 4 ] 2- A complex is written such that everything inside the square brackets is a ligand chemically bonded to the metal ion. Everything outside the brackets is a counter-ion or something simply present in the crystal lattice. Thus, we might have [Co(H 2 O) 6 ](NO 3 ) 2 where the NO 3 - ions are counter-ions. Hexaaquacobalt(II) hexamminenickel(II) tetracyanonickelate(II) C N O N
Formal Oxidation State: The formal oxidation state of metal ions in their complexes is determined by ascribing formal charges to all ligands which correspond to those they possess as the free molecules or ions: Neutral: NH 3, H 2 O, CO, PH 3, (CH 3 ) 2 S Anionic: OH -, F -, Cl -, Br -, I -, CN -, SCN - Cationic: NO +
Identifying which are ligands: In the formula for a complex, everything inside the square brackets (blue in formula below) is coordinated to the metal ion, everything outside (red) is a counterion or a lattice molecule. When the name of a complex is written, all the ligands that are coordinated to the metal ion come before it, while counter-ions come after the name of the metal: [Co(NH 3 ) 4 Cl 2 ]Cl is: tetramminedichlorocobalt(III)chloride ligands bonded to metal ion counterion
Naming of ligands in complexes: Neutral ligands: When naming a complex, the ligands are indicated by names as follows: Neutral ligands: NH 3 = ammine H 2 O = aqua CO =carbonyl The number of each type of ligand present is indicated by the Latin prefixes di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, and deca-: [Co(NH 3 ) 6 ]Cl 3 =hexamminecobalt(III) chloride [La(H 2 O) 9 ](NO 3 ) 3 =nona-aqua lanthanum(III) nitrate K 2 [Ti(CO) 6 ] =potassium hexacarbonyl titanate(-II)
Anionic ligands: To indicate that they are anions, ligands in complexes are given an o ending: fluoro, chloro, bromo, iodo, hydroxo, cyano, sulfato, nitro, etc. If the overall charge on the complex is negative, the metal ion is given an ate ending to indicate this: K 3 [Fe(CN) 6 ]=potassium hexacyanoferrate(III) or potassium hexacyanoiron(III) K 4 [Fe(CN) 6 ]=potassium hexacyanoferrate(II) Na 3 [AlF 6 ]=sodium hexafluoroaluminate(III) [Co(NH 3 ) 3 F 3 ]=triamminetrifluorocobalt(III) Naming of ligands in complexes: anionic ligands:
Nomenclature of complexes: Cations, including complex cations, come first, anions, including complex anions come second: [Co(NH 3 ) 6 ]Cl 3 = hexammine cobalt(III) chloride, Na 3 [CrCl 6 ] = sodium hexachlorochromate(III), [Ni(H 2 O) 6 ]Cl 2 = hexaaquanickel(II) chloride K 3 [Rh(CN) 6 ]= potassium hexacyanorhodate(III) [Co(NH 3 ) 6 ][Co(CN) 6 ] = hexamminecobalt(III) hexacyanocobaltate(III)
Naming more complex ligands: Many ligands are more complex and have more than one donor atom, such as en (ethylenediamine), bipy (2,2-bipyridyl) and acac (acetyacetonate) below: Where more complex ligands are present, one indicates the number of these present with prefixes bis-, tris-, tetrakis, pentakis, or hexakis, followed by the name of the ligand in parentheses. Thus, [Co(en) 3 ]Cl 3 is tris(ethylenediamine)cobalt(III) chloride.
Some cobalt(III) complexes of more complex ligands: tris(ethylenediamine) tris(2,2-bipyridyl)tris(acetylacetonato) cobalt(III)chloride cobalt(III) nitratecobalt(III)
NOMENCLATURE 1.1 Formulas of Simple Ionic substances. For ionic compounds, the cation (more electropositive element) should always be first. (KCl, Na 2 S). If several cations are present, they should be listed in alphabetical order, followed by anions in alphabetical order (LiMgClF 2 ). An exception is the proton, which is always listed last in the sequence of cations, (RbHF 2 ).
Nomenclature (contd.) 1.2. Sequence of atoms in formulas of polyatomic ions and molecules: For polyatomic species with a central atom, these are generally listed first followed by the attached atoms in alphabetical order (SO 4 2-, CCl 2 H 2, PCl 3 O, SO 3, -CF 3, -SCN). An exception is the linear thiocyanate group (-SCN), where the atoms are placed in the order in which they occur in the thiocyanate ion: - S=C=N
Formulas and Names of Common substances. AcidName Name of anion HNO 3 Nitric acidnitrate H 3 PO 4 Phosphoric acidphosphate H 2 SO 4 Sulfuric acidsulfate HClO 4 Perchloric acidperchlorate HClO 3 Chloric acidchlorate HClO 2 Chlorous acidchlorite HClOHypochlorous acidhypochlorite HClHydrochloric acidchloride
Chemical Names Names of the Elements: These originated with Berzelius (1813) who developed the system that the symbol for an element was the first letter of its name, e.g., F, O, N, C, B. If there was more than one element whose name started with the same letter, then a second, lower-case letter, was added, which was usually the second letter of the name of the element. e.g. C for carbon, but Ca, Cd, Ce, Cf, Cl, Cm, Co, Cr, Cs, Cu. B for Boron, but Ba, Be, Bi, Bk, Br, and so on.
Names of metallic elements you should know (pretty much all of them): H hydrogen LiBe lithiumberyllium NaMg sodiummagnesium KCaScTiV potassiumcalciumscandiumtitaniumvanadium RbSrYZrNb rubidiumstrontiumyttriumzirconiumniobiuim CsBaLaHfTa cesiumbariumlanthanumhafniumtantalum
Names of metallic elements you should know (continued): Cr MnFe CoNi Cu Zn chromium manganese iron cobaltnickel copper zinc Mo TcRu RhPd Ag Cd molybdenum technetium ruthenium rhodium palladium silver cadmium W ReOs IrPt Au Hg tungsten rheniumosmium iridiumplatinum gold mercury Lanthanides: LaCe….Gd…….Lu lanthanumceriumgadoliniumlutetium Actinides: AcTh….U Np PuAm actiniumthoriumuranium neptunium plutoniumamericium
Geometrical Isomerism cis-diamminedichloro trans-diamminedichloro- platinum(II) platinum(II) chloride Pt ammonia Pt Geometrical isomers can exist with two identical ligands placed next to each (cis) or at 180º to each other (trans). Again, Werners theory could explain how two different complexes corresponding to [(NH 3 ) 2 Cl 2 Pt] could exist.
Cis and trans isomerism of octahedral complexes: trans-[Co(NH 3 ) 4 Cl 2 ] + cis-[Co(NH 3 ) 4 Cl 2 ] + (green) (violet) An important aspect of Werners theory was that it could explain how two compounds of identical formula, i.e. [Co(NH 3 ) 4 Cl 2 ]Cl, could exist as two entirely different forms, which we now know to be the cis and trans forms above. green = Cl
fac (facial) and mer (meridional) geometrical isomers of the [Co(NH 3 ) 3 Cl 3 ] complex mer fac mer-[Co(NH 3 )Cl 3 ] fac-[Co(NH 3 )Cl 3 ]
Optical isomerism: Λ (lambda) form Δ (delta) form The tris(ethylenediamine)cobalt(III) complex exists as optical isomers. the Δ and Λ forms, which are non-superimposable mirror images of each other. This will be discussed further under group theory. mirror plane