Chapter 20 Transition Metals and Coordination Chemistry COORDINATION COMPOUNDS -- Lewis Acid - Base reactions: Base – electron pair donor Acid - electron pair acceptor -- Coordinate covalent bonds -- ligands, Lewis bases -- Complex ions called “Metal Complexes” ALFRED WERNER’S COORDINATION THEORY -- Oxidation number of central atom -- Coordination number -- Coordination sphere (containing metal ion) - anions - cations - neutral -- Geometry - look at hybridization shapes -- Ligands Formulas and Name of Some Common Ligands Formula Name H2O aqua NH3 ammine CO carbonyl NO nitrosyl H2NC2H4NH2 ethylenediamine OH- hydroxo O2- oxo F- fluoro Cl- chloro Br- bromo I- iodo CN- cyano -NCS- isothiocyanato* -SCN- thiocyanato* SO42- sulfato SO32- sulfito NO3- nitrato* -NO2- nitro* -ONO- nitrito* CO32- carbonate *In these ligands two forms are known; they differ in the atom that donates the electron pair to the metal ion. Various coordination geometries Nomenclature of Coordination Compounds 1.The cation is named first in ionic compounds, then the anion. 2.Nonionic compounds are given a one-word name. 3.The following rules pertain to the names of ligands. a. The ligands are named first and the central atom last. b. Ligands are named in alphabetical order by their root name. c. Neutral ligands are named the same as the molecule, except for a few such as H2O (aqua) and NH3 (ammine), which have special names. d. Anionic ligands are named by adding –o to the stem of the usual name, such as chloro for Cl- and sulfato for SO42-. e. The name of each ligand is preceded by a Latin prefix (di-, tri- tetra-, penta, hexa- etc.) if more than one of that ligand Is bonded to the cetnral atom. For example, the ligands in PtCl42- are named tetrachloro, and the ligands in Co(NH3)4Cl2+ are named tetraamminedichloro. If the ligand is polydentate, as in ethylenediamine, the number of ligands bonded to the central atom is indicated by the corresponding Greek prefixes (bis-, tris-, tetrakis-, pentakis-, hexakis-, etc.). For example, the ligands in Co(en)33+ are named trisethylenediamine. A Greek prefix is also used when a Latin prefix forms a part of the name of the ligand, as in triethylamine, N(CH3)3. In this case, the ligand name is enclosed in parentheses. For example, the ligands in [Co(N(CH3)3)4]2+ are named tetrakis(triethylamine). 4, For a cationic complex ion or a nonionic compound, the central atom is given its ordinary name followed by its oxidation number n Roman numerals, enclosed in parentheses. For example, [Cr(H2O)5Cl]2+ is named pentaaquachlorochromium(III) ion, and [Cr(NH3)3Cl3] is name triamminetrichlorochromium (III). 5. For anionic complex ions, the suffix –ate is added to the name of the central atom, followed by the oxidation number in Roman numerals, enclosed in parentheses. For example, [Cr(CN)6]3- is name hexacyanochromate (III) ion. Name the following complex ions. a. Ru(NH3)5Cl2+ b. Fe(CN)64- c. Mn(NH2CH2CH2NH2)32+ d. Co(NH3)5NO22+ Name the following coordination compounds. a. [Co(NH3)6]Cl2 b. [Co(H2O)6]I3 c. K2 [PtCl4] d. K4[PtCl6] Give the formulas for the following. a. Hexakispyridinecobalt(III)chloride b. Pentaammineiodochromium(III) iodide c. Trisethylenediamminenickel(II)bromide d. Potassium tetracyanonickelate(II) e. Tetraamminedichloroplatinum(IV) tetrachloroplatinate(II) Draw geometrical isomers of each of the following complex ions. a. [CO(C2O4)2(H2O2]- b. [Pt(NH3)4I2]2+ c. [Ir(NH3)3Cl3] d. [Cr(en(NH3)2I2]+ Amino acids can act as ligand toward transition metal ions. The simplest amino acid is glycine (NH2CH2CO2H). Draw a structure of the glycinate anion (NH2CH2CO2-) acting as a bidentate ligand. Draw the structure isomers of the square planar complex Cu(NH2CH2CO2)2. BAL is a chelating agent used in treating heavy- metal poisoning. It acts as a bidentate ligand. What types of linkage isomers are possible when Bal coordinates to a metal ion? Geometrical Isomers of [Co(NH3)4Cl2]+ Geometrical isomers of [pt(NH3)2Cl2] Mirror images of cis-[Co(en)2Cl2]+ and trans-[Co(en)2Cl2]+ COORDINATION COMPOUND REACTIONS Oxidation – Reduction Outer sphere: coordination sphere and ligands do not change. Inner sphere: one or more coordination sphere changes. Substitution Reactions (Displacement) Ligand reactions COORDINATE COVALENT BONDS AND GEOMETRY Valence Bond Theory versus Crystal Field Theory Valence Bond hybridization Octahedral d2sp3 Tetrahedral sp3 Square planar dsp2 “low spin” and “high spin” complexes The 6 ligands in an octahedral crystal field Formation of d2sp3 orbitals Draw the d-orbital splitting diagrams for the octahedral complex ions of each of the following. a. Fe2+ (high and low spin) b. Fe3+ (high spin) c. Ni2+ d. Zn 2+ e. Co2+ (high and low spin) How many unpaired electrons are in the following complex ions? a. Ru(NH3)62+ (low-spin case) b. Fe(CN)63- (low-spin case) c. Ni(H2O)62+ d. V(en)33- e. CoCl42- The 4 ligands in a tetrahedral crystal field Tetrahedral crystal field splitting energy The d orbital energy level diagram for an octahedral complex Free Co orbitals The d energy diagrams for square, planar, and linear complexes Spectra of emerald and ruby Absorption and emission of light by Cr (III) complex ions Spectrochemical Series of Ligands Wavelength in nm Crystal Field of Peak in Spectrum Splitting Energy Ligand of Co(NH3)4X* (nm) for Co(NH3)5X (kJ/mol) CO CN- 440 272 -NO2- 458 261 en -NC- Large NH3 475 252 -NCS- 496 241 OH2 490 244 Pairing C2O42- Energy -ONO- 491 244 OH - 503 238 -ONO2 - 500 239 - F Cl- 510 533 235 224 Small -SCN- S2- Br- 550 217 I - 580 206 *This wavelength is that at which there is a maximum absorption of light in the spectrum of the Cobalt(III) complex ion. The complex ion NiCl42- has two unpaired electrons, while Ni(CN)42- is diamagnetic. Propose structures for these two complex ions. Tetrahedral complexes of Co2+ are quite common. Use a d-orbital splitting diagram to rationalize the stability of Co2+ tetrahedral complex ions. The compound Ni(H2O)6Cl2 is green, while Ni(NH3)6Cl2 is purple. Predict the predominant color of light absorbed by each compound. Which compound absorbs light with the shorter wavelength? Predict in which compound is greater and whether H2O or NH3 is a stronger field ligand. Do your conclusions agree with the spectrochemical series? The complex ion Fe(CN)63- is paramagnetic with one unpaired electron. The complex ion Fe(SCN)63- has five unpaired electrons. Where does SCN- lie in the spectrochemical series relative to CN-?