Presentation on theme: "Metal Complexes -- Chapter 24"— Presentation transcript:
1 Metal Complexes -- Chapter 24 Metal Complex -- consists of a set of ligands that are bonded to a central metal ion by coordinate covalent bonds.e.g. Cu L --> [CuL4]2+ ( L = NH3, H2O, etc)Ligands are Lewis Bases and can be:monodentate -- one donor atome.g. H2O, NH3, Cl–, OH–, etc.bidentate -- two donor atomse.g. ethylenediamine, NH2–CH2–CH2–NH2 “en”
2 Polydentate ligands = EDTA4– polydentate -- more than two donor atoms e.g. EDTA -- ethylenediaminetetraacetic acid(6 donor atoms)= EDTA4–
3 Chelate EffectChelate effect -- complexes with bi- or polydentate ligands are more stable than those with similar monodentate ligandse.g. [Ni(en)3]3+ is more stable than [Ni(NH3)6]3+Know Table 24.2!
4 Writing Formulas of Complex Ions Metal ion first, then ligands. Charge outside brackets.total charge = sum of metal ion + ligandse.g. metal ion ligand complexCu2+ H2O [Cu(H2O)]2+Co3+ NH3 [Co(NH3)6]3+Fe3+ CN– [Fe(CN)6]3–
5 Nomenclature 1. Name the ligands, put in alphabetical order. 2. Add prefixes for ligands that appear more than once.3. Name the metalCationic complex; metal nameAnionic complex; metal prefix + ate4. Add oxidation state in roman numerals5. As separate word, write “ion” if not neutral, or list counterions (positive first, negative second).Examples:Complex Name[Ni(CN)4]2– tetracyanonickelate(II) ion[CoCl6]3– hexachlorocobaltate(III) ion[CoCl2(NH3)4]+ tetraaminedichlorocobalt(III) ionNa3[Co(NO2)6] sodium hexanitrocobaltate(III)[CrCl2(en)2]2SO4 dichlorobis(ethylenediamine)chromium(III) sulfate
6 Coordination Number and Structure Coordination # -- number of donor atoms attached to the metal center(a) Two-Coordinate Complexes -- linear structuresRare except for Ag+e.g. [Ag(NH3)2]+ and [Ag(CN)2]–(b) Four-Coordinate Complexes -- two structural typesTetrahedral structures -- common for ions with filled d subshells, e.g. Zn2+ as in [Zn(OH)4]2–
7 More Coordination Number and Structure (b) Four-Coordinate Complexes -- two structural typessquare planar structures -- common for d8 metal ions (Ni2+, Pd2+, Pt2+) and for Cu2+e.g.(c) Six-Coordinate Complexes -- the most common!“always” octahedral structures, e.g.
8 Sample Problem1. Give the name or formula, as required. Draw the structure of each complex.a) [AgI2]–b) [Co(en)3]3+c) cis-dichlorobis(ethylenediamine)cobalt(III) chlorided) sodium tetracyanonickelate(II)
9 Answer 1. a) diiodoargentate(I) ion [I—Ag—I]– b) tris(ethylenediamine)cobalt(III) ionc) cis-[CoCl2(en)2]Clc) Na2[Ni(CN)4]
12 Stereoisomers of Coordination Complexes (a) Geometrical Isomerscistransfacmer(b) EnantiomersThree common ways to get enantiomers:--chiral ligand--tetrahedral complex with 4 different groups--octahedral complexes with chelating ligands (and no mirror plane)
13 Sample QuestionsDraw a clear, 3-dimensional structure of the geometrical isomer of Co(en)(NH3)2Cl2 that is optically active. (define any abbreviations)Excess silver nitrate is added to a solution containing mol of [Co(NH3)4Cl2]Cl. How many g of AgCl (FW = 143.3) will precipitate?
14 Sample QuestionsDraw a clear, 3-dimensional structure of the geometrical isomer of Co(en)(NH3)2Cl2 that is optically active. (define any abbreviations)Excess silver nitrate is added to a solution containing mol of [Co(NH3)4Cl2]Cl. How many g of AgCl (FW = 143.3) will precipitate?7.48 g
15 Crystal Field Theory (Bonding in Transition Metal Complexes) Metal complexes are usually highly colored and are often paramagnetic -- such facts can be explained by a “d-orbital splitting diagram”egdz2dx2-y2energyD = crystal field splitting energyt2gdxydxzdyzd orbitals of the metal ion inan octahedral field of ligandsd orbitals of the free metal ion
16 Shape and Directionality of the d Orbitals egDt2g
17 Crystal Field Strength The size of D depends on…The nature of the ligand (ligand-metal bond strength!)“spectrochemical series” -- D decreases:CN– > NO2– > en > NH3 > H2O > OH– > F– > Cl– > Br–“strong field ligands” “weak field ligands”The oxidation state of the metal (charge!)D is greater for M3+ than for M2+The row of the metal in the periodic table (size!)for a given ligand and oxidation state of the metal, D increases going down in a groupe.g. D is greater in Ru(NH3)63+ than in Fe(NH3)63+Colors of metal complexes are due to electronic transition between the t2g and eg energy levels
18 d Orbital Splitting Diagrams for Octahedral Complexes egdx2dx2–y2egdx2dx2–y2large D“low spin”small D“high spin”t2gt2gdxydxzdyzdxydxzdyzFe(H2O)62+Fe(CN)64–
19 High Spin vs. Low SpinCN– is a stronger field ligand than is H2O which leads to a greater D value (i.e. a greater d orbital splitting)As a result,Fe(H2O)62+ is a “high spin” complex and is paramagnetic (4 unpaired electrons)while,Fe(CN)64– is a “low spin” complex and is diamagnetic (no unpaired electrons)The CN– complex with the larger D value absorbs light of higher energy (i.e. higher frequency but shorter wavelength)OMIT … d orbital splitting diagrams for other geometries (i.e. tetrahedral and square planar)
20 Sample QuestionsA complex [CoA6]3+ is red. The complex [CoB6]3+ is green.a) Which ligand, A or B, produces the larger crystal field splitting D?b) If the two ligands are ammonia and water, which is A and which is B?c) Draw the d orbital diagram of either complex, assuming it is “high spin.” How many unpaired electrons will it have?Give the order of increase of D in the following sets:a) Cr(NH3)63+, CrCl63–, Cr(CN)63–b) Co(H2O)62+, Co(H2O)63+, Rh(H2O)63+
21 Sample QuestionsA complex [CoA6]3+ is red. The complex [CoB6]3+ is green.a) Which ligand, A or B, produces the larger crystal field splitting D?b) If the two ligands are ammonia and water, which is A and which is B?c) Draw the d orbital diagram of either complex, assuming it is “high spin.” How many unpaired electrons will it have?a) Ab) A = NH3, B = H2Oc) 4 unpaired electronsGive the order of increase of D in the following sets:a) Cr(NH3)63+, CrCl63–, Cr(CN)63–b) Co(H2O)62+, Co(H2O)63+, Rh(H2O)63+a) Cr(CN)63– > Cr(NH3) > CrCl63–b) Rh(H2O) > Co(H2O) > Co(H2O)62+dz2dx2-y2egdxydxzdyzt2g