219220Alfred Werner 1866-1919 - Father of Inorganic Stereochemistry and Coordination Chemistry - Nobel Prize in 1913 - Introduced a Revolutionary Theory of “Metal-Centered Coordination Chemistry” - Saved inorganic chemistry from fading into oblivion in 1893 others such as Blomstrand and Jorgensen thought metal compounds formed chains! M-X-NH3-NH3-NH3-X, etc.,221222Wernerian Chemistry (main discoveries) Structural Isomers Ionization Isomers These isomers result from the interchange of ions inside and outside the coordination sphere. For example, the red violet [Co(NH3)5Br]SO4 and the red [Co(NH3)5SO4]Br are ionization isomers. [Co(NH3)5Br]SO4 [Co(NH3)5SO4]Br Bromopentaamminecobalt(III) sulfate Sulfatopentaaminecobalt(III) bromide Optical Isomers Optical isomers of cis-dibromo-cis-diammine-cis-diaquacobalt(III) ion223The cis-dibromo-cis-diammine-cis-diaquacobalt(III) geometric isomer exists in two forms that bear the same relationship to each other as left and right handed isomers. They are non-superimposable mirror images of each other and are called optical isomers or enantiomers. Optical isomers have identical physical and chemical properties except that they interact with polarized light in different ways. Coordination Isomers Coordination isomerism can occur in compounds containing both complex cations and complex anions. Such isomers involve exchange of ligands between cation and anion, i.e., between coordination spheres [Pt(NH3)4][PtCl6] [Pt(NH3)4Cl2][PtCl4] tetraammineplatinum(II) trans-dichlorotetraammine hexachloroplatinate(IV) platinum(IV) tetrachloroplatinate(II)224 Linkage Isomers Certain ligands can bind to a metal ion in more than one way. Examples of such ligands are cyano, -CN-, and isocyano, -NC-; nitro, -NO2-, and nitrite, -ONO-. The donor atoms are on the left in these representations. Examples of linkage isomers are given below. [Co(NH3)5ONO]Cl2 [Co(NH3)5NO2]Cl2 nitritopentaamminecobalt(III) nitropentaamminecobalt(III) chloride chloride red, decomposes in acids yellow, stable in acids225Geometrical Isomers These are stereoisomers that are not optical isomers (see p. 806) but are geometrical isomers or positions isomers. Cis-trans isomerism is one kind of geometrical isomerism. Cis means “adjacent to” and trans means “on the opposite side of”. Cis- and trans-dichlorodiammineplatinum(II) are shown below. often different physical properties cis trans pale yellow dark yellow In the cis complex, the chloro groups are closer to each other (on the same side of the square) then they are in the trans complex. the amine groups are also closer together in the cis complex.226Other Isomers Hydration isomerism and ionization isomerism are quite similar. In some crystalline complexes, water can occur in more than one way, inside and outside the coordination sphere. For example, solutions of the three hydrate isomers given below yield three, two, and one mole of silver chloride precipitate, respectively, per mole of complex when treated with excess silver nitrate. [Cr(OH2)6]Cl3 [Cr(OH2)5Cl]Cl2·H2O [Cr(OH2)4Cl2]Cl·2H2O hexaaquacobalt(III) chloropentaaqua trans-dichlorotetraaqua chloride cobalt(III) cobalt(III) chloride hydrate chloride dihydrate violet blue-green green Definitions Coordination Complex- The defining characteristic of a coordination compounds or “complex” is that a metal ion is surrounded by atoms or molecules (either neutral or ionic) in a particular geometry.227Furthermore, these ions and molecules are capable of existing independently of each other. M2+ + 6 L → Outline of Coordination Chemistry 1. Alfred Werner father of coordination chemistry 2. Metal is at the center of a group of ligands → called a complex 3. Structural Isomers (realized by Werner) a. Ionization Isomers b. Optical Isomers c. Coordination Isomers d. Linkage Isomers e. Geometrical Isomers f. Hydrate Isomers This cation can exist in solution2284. Geometries coordination numbers 2, 3, 4, 5, 6, > 6 5. Ligands a. donor type/names b. number of donor sites c. chelate effect 6. Nomenclature a. abbreviations b. rules 7. Reactivity Patterns a. octahedral complexes b. square planar complexes c. associative (A) versus dissociative (D) substitution d. solution stabilities thermodynamic versus kinetic stability 8. Electron Transfer Reactions “inner-sphere” versus “outer-sphere” mechanisms 9. Stereochemical non-rigidity “fluxional” behavior interconversion of geometries229 Ligand Any molecule or ion that has at least one electron pair that can be donated to a metal atom or ion. Lewis Bases Ligands (in organic chem. → nucleophiles) Lewis Acids Metal Ions (in organic chemistry → electrophiles) Classifications of Ligands 1. type of bonding they engage in π-donation, σ-donation, π-accepting 2. number of electrons that they donate 3. number of bonds they make to a metal ion through different atoms230Discussion of Ligands 1. Classical σ-donors these form bonds by donating an e- to a σ-bond e.g :NH3 :PR3 :R- (alkyl) 2. Non-classical π-donors and π-acceptors π-donors :X- halides can form π-bonds π-acceptor C≡O carbon monoxide can accept electrons into any empty π* symmetry molecular orbital Types of Ligands monodentate bidentate tridentate tetradentate literally “one-toothed”, “two-toothed”, etc. The “denticity” of a ligand refers to how many total donor sites for binding to a metal231Monodentate NH3, RNH2, amines H2O, OH-, ROH, R2O, R2CO, R2SO R3PO, PR3, X- (Note, some can bridge as well) e.g. or or232Bidentate carboxylate sulfate acetylacetonate (general class is β-diketones) ethylenediamine H2 (en) anti-conformer gauche would give a conformer bridge between would two metals chelate bridging versus chelating for a bidentate L-L ligand233 Bis(diphenylphosphino)ethane also called “dppe” for short dppe can chelate and bridge or 2,2’-bipyridine 1,10-phenanthroline terpyridine (or bpy) (phen) (terpy) Bidentate Tridentate (forms meridonal isomers) Ph2 Ph2 phenyl groups two