Philip Dutton University of Windsor, Canada N9B 3P4 Prentice-Hall © 2002 General Chemistry Principles and Modern Applications Petrucci Harwood Herring 8 th Edition Chapter 25: Complex Ions and Coordination Compounds

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 2 of 55 Contents 25-1Werners Theory of Coordination Compounds: An Overview 25-2Ligands 25-3Nomenclature 25-4Isomerism 25-5Bonding in Complex Ions: Crystal Field Theory 25-6Magnetic Properties of Coordination Compounds and Crystal Field Theory 25-7Color and the Colors of Complexes

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 3 of 55 Contents 25-8Aspects of Complex-Ion Equilibria 25-9Acid-Base Reactions of Complex Ions 25-10Nomenclature 25-11Applications of Coordination Chemistry Focus On Colors in Gemstones

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 4 of Werners Theory of Coordination Compounds: An Overview Compounds made up of simpler compounds are called coordination compounds. CoCl 3 and NH 3. –CoCl 3 · (NH 3 ) 6 and CoCl 3 · (NH 3 ) 5. –Differing reactivity with AgNO 3.

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 5 of 55 Werners Theory [Co(NH 3 ) 6 ]Cl 3 [Co(NH 3 ) 6 ] Cl - [CoCl(NH 3 ) 5 ]Cl 2 [CoCl(NH 3 ) 5 ] Cl - Two types of valence or bonding capacity. –Primary valence. Based on the number of e - an atom loses in forming the ion. –Secondary valence. Responsible for the bonding of other groups, called ligands, to the central metal atom.

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 6 of 55 Coordination Number

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 7 of 55 Example 25-1 Relating the Formula of a Complex to the Coordination Number and Oxidation State of the Central Metal. What are the coordination number and oxidation state of Co in the complex ion [CoCl(NO 2 )(NH 3 ) 4 ] + ? Solution: The complex has as ligands 1 Cl, 1 NO 2, 4 NH 3. The coordination number is 6.

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 8 of 55 Example 25-1 Charge on the metal ion:

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 9 of Ligands Ligands are Lewis bases. –Donate electron pairs to metals (which are Lewis acids). Monodentate ligands. –Use one pair of electrons to form one point of attachment to the metal ion. Bidentate ligands. –Use two pairs of electrons to form two points of attachment to the metal ion. Tridentate, tetradentate…..polydentate

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 10 of 55 Table 25.2 Some Common Monodentate Ligands.

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 11 of 55 Table 25.3 Some Common Polydentate Ligands (Chelating Agents)

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 12 of 55 Ethylene Diamine

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 13 of Nomenclature In names and formulas of coordination compounds, cations come first, followed by anions. Anions as ligands are named by using the ending –o. –Normally – ide endings change to –o. – ite endings change to –ito. – ate endings change to –ato. Neutral molecules as ligands generally carried the unmodified name.

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 14 of 55 Nomenclature The number of ligands of a given type is given by a prefix. Mono, di, tri, tetra, penta, hexa… –If the ligand name is a composite name itself Place it in brackets and precede it with a prefix: –Bis, tris, tetrakis, pentakis...

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 15 of 55 Nomenclature Name the ligands first, in alphabetical order, followed by the name of the metal centre. –Prefixes are ignored in alphabetical order decisions. The oxidation state of the metal centre is given by a Roman numeral. If the complex is an anion the ending –ate is attached to the name of the metal.

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 16 of 55 Nomenclature When writing the formula the chemical symbol of the metal is written first, followed by the formulas of anions, –in alphabetical order. and then formulas of neutral molecules, –in alphabetical order.

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 17 of Isomerism Isomers. –Differ in their structure and properties. Structural isomers. –Differ in basic structure. Stereoisomers. –Same number and type of ligands with the same mode of attachement. –Differ in the way the ligands occupy space around the metal ion.

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 18 of 55 Examples of Isomerism Ionization Isomerism [CrSO 4 (NH 3 ) 5 ]Cl[CrCl(NH 3 ) 5 ]SO 4 pentaaminsulfatochromium(III) chloride pentaaminchlorochromium(III) sulfate Coordination Isomerism [Co(NH 3 ) 6 ][CrCN 6 ] hexaaminecobalt(III) hexacyanochromate(III) [Cr(NH 3 ) 6 ][CoCN 6 ] hexaaminechromium(III) hexacyanocobaltate(III)

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 19 of 55 Linkage Isomerism

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 20 of 55 Geometric Isomerism

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 21 of 55 Geometric Isomerism

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 22 of 55 Optical Isomerism

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 23 of 55 Optical Isomerism

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 24 of 55 Mirror Images

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 25 of 55 Optical Activity dextrorotatory d- levorotatory l-

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 26 of Bonding in Complex Ions: Crystal Field Theory Consider bonding in a complex to be an electrostatic attraction between a positively charged nucleus and the electrons of the ligands. –Electrons on metal atom repel electrons on ligands. –Focus particularly on the d-electrons on the metal ion.

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 27 of 55 Octahedral Complex and d-Orbital Energies

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 28 of 55 Electron Configuration in d-Orbitals Hunds rule Δ > P low spin d 4 Δ < P high spin d 4 pairing energy considerations Δ P

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 29 of 55 Spectrochemical Series CN - > NO 2 - > en > py NH 3 > EDTA 4- > SCN - > H 2 O > ONO - > ox 2- > OH - > F - > SCN - > Cl - > Br - > I - Large Δ Strong field ligands Small Δ Weak field ligands

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 30 of 55 Weak and Strong Field Ligands Two d 6 complexes:

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 31 of 55 Energy Effects in a d 10 System

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 32 of 55 Tetrahedral Crystal Field

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 33 of 55 Square Planar Crystal Field

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 34 of Magnetic Properties of Coordination Compounds and Crystal Field Theory. Paramagnetism illustrated:

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 35 of 55 Example 25-4 Using the Spectrochemical Series to Predict Magnetic Properties. How many unpaired electrons would you expect to find in the octahedral complex [Fe(CN) 6 ] 3- ? Solution: Fe [Ar]3d 6 4s 2 Fe 3+ [Ar]3d 5

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 36 of 55 Example 25-5 Using the Crystal Field theory to Predict the Structure of a Complex from Its Magnetic Properties. The complex ion [Ni(CN 4 )] 2- is diamagnetic. Use ideas from the crystal field theory to speculate on its probably structure. Solution: Coordination is 4 so octahedral complex is not possible. Complex must be tetrahedral or square planar. Draw the energy level diagrams and fill the orbitals with e -. Consider the magnetic properties.

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 37 of 55 Example 25-5 Tetrahedral:Square planar:

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 38 of Color and the Colors of Complexes Primary colors: –Red (R), green (G) and blue (B). Secondary colors: –Produced by mixing primary colors. Complementary colors: –Secondary colors are complementary to primary. –Cyan (C), yellow (Y) and magenta (M) –Adding a color and its complementary color produces white.

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 39 of 55 Color and the Colors of Complexes

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 40 of 55

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 41 of 55 Effect of Ligands on the Colors of Coordination Compounds

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 42 of 55 Table 25.5 Some Coordination Compounds of Cr 3+ and Their Colors

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 43 of Aspects of Complex-Ion Equilibria K f = [[Zn(NH 3 ) 4 ] 2+ ] [Zn 2+ ][NH 3 ] 4 = Zn 2+ (aq) + 4 NH 3 (aq) [Zn(NH 3 ) 4 ] 2+ (aq) [Zn(H 2 O) 4 ] 2+ (aq) + NH 3 (aq) [Zn(H 2 O) 3 (NH 3 )] 2+ (aq) + H 2 O(aq) K1=K1= [[Zn(H 2 O) 3 (NH 3 )] 2+ ] [[Zn(H 2 O) 4 ] 2+ ][NH 3 ] = 1 = Displacement is stepwise from the hydrated ion: Step 1:

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 44 of Aspects of Complex-Ion Equilibria [Zn(H 2 O) 3 (NH 3 )] 2+ (aq) + NH 3 (aq) [Zn(H 2 O) 2 (NH 3 ) 2 ] 2+ (aq) + H 2 O(aq) K 2 = [[Zn(H 2 O) 2 (NH 3 ) 2 ] 2+ ] [[Zn(H 2 O) 3 (NH 3 )] 2+ ][NH 3 ] = K = 2 = [[Zn(H 2 O) 2 (NH 3 ) 2 ] 2+ ] [[Zn(H 2 O) 4 ] 2+ ][NH 3 ] 2 = K 1 K 2 = Step 2: [Zn(H 2 O) 4 ] 2+ (aq) + 2 NH 3 (aq) [Zn(H 2 O) 2 (NH 3 ) 2 ] 2+ (aq) + 2 H 2 O(aq) Combining steps 1 and 2:

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 45 of 55 Aspects of Complex Ion Equilibria 4 = K 1 K 2 K 3 K 4 = K f

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 46 of Acid-Base Reactions of Complex Ions [Fe(H 2 O) 6 ] 3+ (aq) + H 2 O(aq) [Fe(H 2 O) 5 (OH)] 2+ (aq) + H 3 O + (aq) K a1 = [Fe(H 2 O) 5 (OH)] 2+ (aq) + H 2 O(aq) [Fe(H 2 O) 4 (OH) 2 ] 2+ (aq) + H 3 O + (aq) K a2 =

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 47 of Some Kinetic Considerations [Cu(H 2 O) 4 ] NH 3 [Cu(NH 3 ) 4 ] H 2 Ofast [Cu(H 2 O) 4 ] Cl - [Cu(Cl) 4 ] H 2 Ofast Water is said to be a labile ligand. Slow reactions (often monitored by color change) are caused by non-labile ligands.

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 48 of Applications of Coordination Chemistry Hydrates –Crystals are often hydrated. –Fixed number of water molecules per formula unit.

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 49 of 55 Stabilization of Oxidation States Co 3+ (aq) + e - Co 2+ (aq)E° = V 4 Co 3+ (aq) + 2 H 2 O(l) 4 Co 2+ (aq) + 4 H + + O 2 (g) But: E° cell = V [Co(NH 3 ) 6 ] 3+ (aq) + e - [Co(NH 3 ) 6 ] 2+ (aq)E° = V Co 3+ (aq) + NH 3 (aq) [Co(NH 3 ) 6 ] 2+ (aq) K f = and

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 50 of 55 Photography: Fixing a Photographic Film Black and white. –Finely divided emulsion of AgBr on modified cellulose. –Photons oxidize Br - to Br and reduce Ag + to Ag. Hydroquinone (C 6 H 4 (OH) 2 ) developer: –Reacts only at the latent image site where some Ag + is present and converts all Ag + to Ag. –Negative image. Fixer removes remaining AgBr. AgBr(s) + 2 S 2 O 3 2- (aq) [Ag(S 2 O 3 ) 2 ] 3- (aq) + Br - (aq) Print the negative

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 51 of 55 Sequestering Metal Cations tetrasodium EDTA

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 52 of 55 Sequestering Metal Cations Some Log values: 10.6 (Ca 2+ ), 18.3 (Pb 2+ ), 24.6 (Fe 3+ ).

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 53 of 55 Biological Applications chlorophyl aporphyrin

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 54 of 55 Focus On Colors in Gemstones Emerald 3BeO·Al 2 O 3 ·6SiO 2 + Cr 3+ in Al 3+ sites Ruby Al 2 O 3 + Cr 3+ in Al 3+ sites

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 55 of 55 Chapter 25 Questions Develop problem solving skills and base your strategy not on solutions to specific problems but on understanding. Choose a variety of problems from the text as examples. Practice good techniques and get coaching from people who have been here before.