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Part 2.8: Coordination Chemistry 1 Slide 2 Outline Coordination Complexes History Ligands Isomers Inorganic Bonding Crystal Field Theory Ligand Field Theory Orbital Diagrams Ligand Field Jahn-Teller Distortion Bioinorganic Chemistry 2 Slide 3 Ancient times through Alchemy: Descriptive chemistry, techniques, minerals (Cu compounds), glasses, glazes, gunpowder 17th Century Mineral acids (HCl, HNO 3, H 2 SO 4 ), salts and their reactions, acid and bases Quantitative work became important, molar mass, gases, volumes 1869: The periodic table Late 1800s: Chemical Industry Isolate, refine, purify metals and compounds 1896: Discovery of Radioactivity Atomic structure, quantum mechanics, nuclear chemistry (through early 20th century) History of Inorganic Chemistry 3 Slide 4 Inorganic History Side Note Friedrich Whler (1828) Potassium CyananteAmmonium Sulfate Ammonium Cyanante Urea I can no longer, so to speak, hold my chemical water and must tell you that I can make urea without needing a kidney. Whler in a letter to Berzelius Slide 5 20th Century Coordination chemistry, organometallic chemistry WWII & Military projects: Manhattan project, jet fuels (boron compounds) 1950s Crystal field theory, ligand field theory, molecular orbital theory 1955 Organometallic catalysis of organic reaction (polymerization of ethylene) History of Inorganic Chemistry 5 Slide 6 Metal Coordination Complexes Coordination complexes or coordination compounds- consists of a central atom, which is usually metallic, and a surrounding array of bound molecules or ions, that are in turn known as ligands or complexing agents. Stable in light and air. Accidentally discovered while trying to make a red dye (1705). Prussian blue Iron-hexacyanoferrate First synthetic blue dye. Known for centuries. 6 Slide 7 Prussian blue Iron-hexacyanoferrate Metal Coordination Complexes The Great Wave off Kanagawa Starry Night Structure of coordination complexes not understood until 1907. 7 Slide 8 Metal Coordination Complexes Ligands are ions or neutral molecules that bond to a central metal atom or ion. Denticity refers to the number of donor groups in a single ligand that bind to a central atom in a coordination complex. Ligand biting the metal. M = transition metal L = ligand Monodentate (one tooth) Bidentate (two teeth) Polydentate (many teeth) 8 Slide 9 Monodentate Ligands 9 Slide 10 Bidentate Ligands 10 Slide 11 Polydentate Ligands 11 Slide 12 EDTA ethylenediaminetetraacetate Ligands that bind to more than one site are called chelating agents. M = Mn(II), Cu(II), Fe(III), Pb (II) and Co(III) Added to foods to prevent catalytic oxidation In cleaning solutions (reduce water hardness) Chelation therapy for Hg and Pb poisoning Analytical titrations 12 Slide 13 Coordination Complex Isomers The same connectivities but different spatial arrangements. Different connectivities (same formula). 13 Slide 14 Coordination Isomers Same formula different bonding to the metal. [Cr(NH 3 ) 5 SO 4 ]Br and [Cr(NH 3 ) 5 Br]SO 4 Co + (NH 3 ) 5 + Cl + Br [Co(NH 3 ) 6 ] 3+ and [Cr(CN) 6 ] 3- ) [Cr(NH 3 ) 6 ] 3+ and [Co(CN) 6 ] 3- Cr + (NH 3 ) 5 + SO 4 + Br Co + Cr + (NH 3 ) 6 + (CN) 6 14 Slide 15 Linkage Isomers Composition of the complex is the same, but the point of attachment of the ligands differs. FormulaName NO 2 - nitrito (via O) NO 2 - nitro (via N) 15 Slide 16 Linkage Isomers The compounds have different properties and colors. Linear vs. bent nitrosyl N or S bond thiocyanate M-NCS M-SCN 16 Slide 17 Geometric Isomers In geometric isomers, the ligands have different spatial arrangements about the metal ion. Square planar complexes like [MX 2 Y 2 ]. Example: [Pt(NH 3 ) 2 Cl 2 ]. Octahedral complexes like [MX 4 Y 2 ]. Example: [Pt(NH 3 ) 4 Cl 2 ]. 17 Slide 18 Geometric Isomers Octahedral complexes with the formula [MX 3 Y 3 ] can be fac (facial) or mer (meridional). In geometric isomers, the ligands have different spatial arrangements about the metal ion. 18 Slide 19 Optical Isomers Optical isomers are compounds with non-superimposable mirror images (chiral molecules). C 1, C n, and D n also T, O, and I Chiral molecules lack an improper axis of rotation (S n ), a center of symmetry (i) or a mirror plane ()! Common for octahedral complexes with three bidentate ligands. 19 Slide 20 Optical Isomers Can be viewed like a propeller with three blades. 20 Slide 21 Optical Isomers Co(en) 2 Cl 2 Not Optically active Optically active 21 Slide 22 Outline Coordination Complexes History Ligands Isomers Inorganic Bonding Crystal Field Theory Ligand Field Theory Orbital Diagrams Ligand Field Jahn-Teller Distortion Bioinorganic Chemistry 22 Slide 23 Organic Bonding 1857- Kekule proposes the correct structure of benzene. 1856- Couper proposed that atoms joined to each other like modern-day Tinkertoys. Oxalic acidEthanol 23 Slide 24 Inorganic Complexes Late 1800s- Blomstrand and Jorgenson Co 3+, 4 x NH 3, 3 x Cl Their rules Charge on the metal ion determined the number of bonds - Co 3+ = 3 bonds Similar bonding concepts to organics NH 3 can form chains like -CH 2 - Only Cl - attached to an NH 3 could dissociate Did not explain isomers. 24 Slide 25 Inorganic Complexes 1893- Werners Theory Co 3+, 6 x NH 3, 3 x Cl His rules Metals interact with 6 ligands in octahedral geometry to form complex ions -Primary/inner coordination sphere: bound to metal -Secondary/outer coordination sphere: balance charge Blomstrand StructureWerner Structure 25 Slide 26 Werners Theory Explains multiple complexes of the same sets of ligands in different numbers [Co(NH 3 ) 6 ]Cl 3 [Co(NH 3 ) 5 Cl]Cl 2 [Co(NH 3 ) 4 Cl 2 ]Cl [Co(NH 3 ) 3 Cl 3 ] Different numbers of ions are produced due to outer sphere dissociation Explains multiple complexes with exact same formula = isomers Werner Complexes 26 Slide 27 Werners Other Contributions Werner Complexes Coordination Number = Most first row transition elements prefer 6 ligands. Pt 2+ prefers 4 ligands. CoA 4 B 2 only has two isomers. Not trigonal prismatic because trigonal antiprimatic because they would give 3 isomers. Octahedral because it only has two possible isomers. PtA 2 B 2 only has two isomers so it must be square planar. Tetrahedral would have only 1 isomer. Water completes the Inner Sphere coordination in aqueous solutions: NiCl 2 + H 2 O [Ni(H 2 O) 6 ]Cl 2 27 Slide 28 Werners Other Contributions Werner Complexes In 1914, Werner resolved hexol, into optical isomers, overthrowing the theory that only carbon compounds could possess chirality. 28 Slide 29 Werner Complexes Werner was awarded the Nobel Prize in 1913 (only inorg. up until 1973) 29 Slide 30 Coordination Complexes Shortcomings of Werners Theory Does not explain the nature of bonding withing the coordination sphere. Does not account for the preference between 4- and 6- coordination. Does not account for square planar vs tetrahedral. Crystal Field TheoryLigand Field Theory 30 Slide 31 Crystal Field Theory Electrostatic approach to bonding. First Applied to ionic crystalline substances. Assumptions: 1)Metal ion at the center. 2)Ligands are treated as point charges. 3)Bonding occurs through M+ and L- electrostatic attraction. 4)Bonding is purely ionic. 5)M and L electrons repel each other. 6)d orbital degeneracy is broken as ligands approach. 31 Slide 32 Crystal Field Theory 32 Slide 33 Octahedral Splitting E M d-orbitals align along the octahedral axis will be affected the most. d z2 d x2-y2 d xy d yz d xz 33 Slide 34 d x2-y2 d z2 d xz d xy d yz Tetrahedral SplittingTetrahedral 34 Slide 35 Other Geometries 35 Slide 36 Other Geometries 36 Slide 37 Crystal Field Theory Merits of crystal field theory: 1)Can be used to predict the most favorable geometry for the complex. 2)Can account for why some complexes are tetrahedral and others square planar. 3)Usefull in interpreting magnetic properties. 4)The colors of many transition metal complexes can be rationalized. Limitations of crystal field theory: 1)Becomes less accurate as delocalization increases (more covalent character). 2)Point charge does not accurately represent complexes. 3)Does not account for pi bonding interactions. 4)Does not account for the relative strengths of the ligands. 37 Slide 38 Ligand Field Theory Application of molecular orbital theory to transition metal complexes. Ligands are not point charges. Takes into account bonding. Can be used to explain spectrochemical series. Better than valence-bond model or crystal field theory at explaining experimental data. 38 Slide 39 Outline Coordination Complexes History Ligands Isomers Inorganic Bonding Crystal Field Theory Ligand Field Theory Orbital Diagrams Ligand Field Jahn-Teller Distortion Bioinorganic Chemistry 39 Slide 40 Coordination Complexes History Ligands Isomers Inorganic Bonding Crystal Field Theory Ligand Field Theory Orbital Diagrams Ligand Field Jahn-Teller Distortion Bioinorganic Chemistry Outline Octahedral bonding bonding -Ligand Field Strength Square Planar bonding bonding Tetrahedral Organometallics 40 Slide 41 Octahedral Only MOs 1.Assign a point group 2.Choose basis function 3.Apply operations -if the basis stays the same = +1 -if the basis is reversed = -1 -if it is a more complicated change = 0 4.Generate a reducible representation H s orbitals OhOh Fs 6 0 0 2 in-between H 2 0 0 04 2 through H-M-H 41 Slide 42 Octahedral Only MOs 1.Assign a point group 2.Choose basis function 3.Apply operations -if the basis stays the same = +1 -if the basis is reversed = -1 -if it is a more complicated change = 0 4.Generate a reducible representation 5.Reduce to irreducible representation 6.Combine orbitals by their symmetry 7.Fill MOs with e - 8.Generate SALCs of peripheral atoms 9.Draw peripheral atoms SALC with central atom orbital to generate bonding/antibonding MOs. H s orbitals OhOh 42 Slide 43 Octahedral Only MOs 5.Reduce to irreducible representation Hs 6 0 0 2 2 0 0 04 2 Hs : A 1g + T 1u + E g 43 Slide 44 Octahedral Only MOs 5.Irreducible reps for M orbitals s d p 44 Slide 45 T 1u EgEg Octahedral Only MOs 6.Combine the orbital's by their symmetry M 6 x H A 1g T 1u 4s 4p EgEg T 1u A 1g EgEg T 2g 3d E g,T 2g A 1g oo 45 Slide 46 Octahedral Only MOs 6.Combine the orbital's by their symmetry M L EgEg EgEg EgEg T 2g 3d E g,T 2g oo 46 Slide 47 Octahedral Only MOs 6.Combine the orbital's by their symmetry EgEg EgEg EgEg T2gT2g E g,T 2g oo EgEg EgEg EgEg T2gT2g oo Weak donor Weak Lewis base Weaker bonding interaction Weak Field Smaller o M L M L Stronger donor Strong Lewis base Stronger bonding interaction Strong Field Larger o 47 Slide 48 Octahedral Only MOs 6.Combine the orbital's by their symmetry o : I - < Br - < Cl - < F - Stronger Lewis base = Larger o Smaller ligands = Larger o 48 EgEg EgEg EgEg T2gT2g E g,T 2g oo EgEg EgEg EgEg T2gT2g oo M L M L Slide 49 Octahedral Only MOs 6.Combine the orbital's by their symmetry M 6 x H AgAg T 1u 4s 4p EgEg T 1u A 1g EgEg EgEg T 2g 3d E g,T 2g T 1u A 1g T 1u oo 49 Slide 50 4.Fill MOs with e - 5.Generate SALCs of peripheral atoms 6.Draw peripheral atoms SALC with central atom orbital to generate bonding/antibonding MOs. 50 Slide 51 Octahedral Only MOs AgAg T 1u 4s 4p EgEg T 1u A 1g EgEg EgEg T 2g 3d E g,T 2g T 1u A 1g T 1u Hs : A 1g + T 1u + E g s obitals p obitals p : A 1g + T 1u + E g What about p orbitals? M L 51 Slide 52 Octahedral + MOs 52 Slide 53 1.Assign a point group 2.Choose basis function ( bonds) 3.Apply operations -if the basis stays the same = +1 -if the basis is reversed = -1 -if it is a more complicated change = 0 4.Generate a reducible representation 5.Reduce to irreducible representation orbitals OhOh LL 12 0 0 0 in-between L -4 0 0 00 0 through L-M-L Octahedral + MOs L = T 1g + T 2g + T 1u + T 2u 53 Slide 54 6.Combine the orbital's by their symmetry M L AgAg T 1u 4s 4p EgEg T 1u A 1g EgEg EgEg T 2g 3d E g,T 2g T 1u A 1g T 1u Octahedral + MOs orbitals L = T 1g + T 2g + T 1u + T 2u orbitals T 2g T 1g T 1u T 2u 54 Slide 55 6.Combine the orbital's by their symmetry M L AgAg T 1u 4s 4p EgEg T 1u A 1g EgEg 3d E g,T 2g EgEg T 2g T 1u A 1g T 1u Octahedral + MOs orbitals orbitals T 2g T 1g T 1u T 2u 55 Slide 56 6.Combine the orbital's by their symmetry M-L EgEg T 2g Octahedral + MOs T 2g filled donor base donates to M T 2g EgEg EgEg oo oo oo empty acceptor acid accepts from M 56 Slide 57 Strong Field Weak Field oo oo Ligand Field Strength Filled donor base Donates to M Empty acceptor acid Accepts from M t 2g egeg egeg Weak donor Weak Lewis base Weaker bonding interaction Stronger donor Strong Lewis base Stronger bonding interaction bonding bonding 57 Slide 58 Pure donating ligands: en > NH 3 donating ligands: : H 2 O > F > RCO 2 > OH > Cl > Br > I accepting ligands: : CO, CN -, > phenanthroline > NO 2 - > NCS - Ligand Field Strength oo oo t 2g egeg egeg The Spectrochemical Series CO, CN - > phen > NO 2 - > en > NH 3 > NCS - > H 2 O > F - > RCO 2 - > OH - > Cl - > Br - > I - Note: increases with increasing formal charge on the metal ion increases on going down the periodic table (larger metal) 58 Slide 59 Ligand Field Strength oo oo t 2g egeg egeg The Spectrochemical Series CO, CN - > phen > NO 2 - > en > NH 3 > NCS - > H 2 O > F - > RCO 2 - > OH - > Cl - > Br - > I - Larger Smaller Why do we care? Predict/Tune/Understand the: 1.Photophysical properties of metal coordination complexes. 2.Magnetic properties of metal coordination complexes. 3.And others. 59 Slide 60 Increasing The Spectrochemical Series CO, CN - > phen > NO 2 - > en > NH 3 > NCS - > H 2 O > F - > RCO 2 - > OH - > Cl - > Br - > I - Larger Smaller Photophysical Properties 60 Slide 61 d1d1 d2d2 d3d3 d4d4 Strong fieldWeak fieldStrong fieldWeak field Magnetic Properties 61 Slide 62 Pairing Energy, The pairing energy, , is made up of two parts. 1)Coulombic repulsion energy caused by having two electrons in same orbital. Destabilizing energy contribution of c for each doubly occupied orbital. High Energy 2)Exchange stabilizing energy for each pair of electrons having the same spin and same energy. Stabilizing contribution of e for each pair having same spin and same energy. Medium Energy Hund's Rules Less repulsion Less p + screening Low EnergyMedium Energy 62 Slide 63 Side note: Exchange Energy, e Excitation Internal Conversion Fluorescence Non-radiative decay Intersystem Crossing Phosphorescence S0S0 S1S1 S2S2 E T1T1 Ground State (S 0 ) Singlet Excited State (S 1 ) Triplet Excited State (T 1 ) E ST e 2J e 63 Slide 64 Pairing Energy, The pairing energy, , is made up of two parts. 1)Coulombic repulsion energy caused by having two electrons in same orbital. Destabilizing energy contribution of c for each doubly occupied orbital. High Energy 2)Exchange stabilizing energy for each pair of electrons having the same spin and same energy. Stabilizing contribution of e for each pair having same spin and same energy. Medium Energy Hund's Rules = sum of all c and e interactions Less repulsion Less p + screening Low EnergyMedium Energy High Energy Low Energy 64 Slide 65 d4d4 Strong field = Low spin (2 unpaired) Weak field = High spin (4 unpaired) < o > o When the 4 th electron will either go into the higher energy e g orbital at an energy cost of 0 or be paired at an energy cost of , the pairing energy. vs. o oo oo 65 Slide 66 1 u.e.5 u.e. d5d5 0 u.e.4 u.e. d6d6 1 u.e.3 u.e. d7d7 2 u.e. d8d8 1 u.e. d9d9 0 u.e. d 10 Magnetic Properties 66 Slide 67 Magnetic Properties The Spectrochemical Series CO, CN - > phen > NO 2 - > en > NH 3 > NCS - > H 2 O > F - > RCO 2 - > OH - > Cl - > Br - > I - Larger Smaller High Spin Low Spin Diamagnetic- all electrons paired. Paramagnetic- unpaired electrons. 67 Slide 68 Pure donating ligands: en > NH 3 donating ligands: : H 2 O > F > RCO 2 > OH > Cl > Br > I accepting ligands: : CO, CN -, > phenanthroline > NO 2 - > NCS - Ligand Field Strength oo oo t 2g egeg egeg 68 The Spectrochemical Series CO, CN - > phen > NO 2 - > en > NH 3 > NCS - > H 2 O > F - > RCO 2 - > OH - > Cl - > Br - > I - Larger Smaller Slide 69 Coordination Complexes History Ligands Isomers Inorganic Bonding Crystal Field Theory Ligand Field Theory Orbital Diagrams Ligand Field Jahn-Teller Distortion Bioinorganic Chemistry Outline Octahedral bonding bonding -Ligand Field Strength Square Planar bonding bonding Tetrahedral Organometallics 69 Slide 70 Square Planar 70 Slide 71 Square Planar MOs p orbitals of L D 4h Use a local coordinate system on each ligand with: y pointing in towards the metal. (p y = bonding) z being perpendicular to the molecular plane. (p z = bonding) x lying in the molecular plane. (p x = || bonding) 1.Assign a point group 2.Choose basis function (p orbitals of L) orbitals (p y ) orbitals (p x,z ) 71 Slide 72 Square Planar MOs p orbitals of L D 4h orbitals (p y ) 1.Assign a point group 2.Choose basis function (p orbitals of L) 3.Apply operations -if the basis stays the same = +1 -if the basis is reversed = -1 -if it is a more complicated change = 0 (py) : A 1g + B 1g + E u 72 Slide 73 Square Planar MOs p orbitals of L D 4h orbitals (p y ) 1.Assign a point group 2.Choose basis function (orbitals) 3.Apply operations 4.Generate a reducible representation 5.Reduce to irreducible representation 6.Combine orbitals by their symmetry (py) : A 1g + B 1g + E u 73 Slide 74 74 Square Planar MOs 5.Irreducible reps for M orbitals s d p Slide 75 Square Planar MOs 75 Slide 76 Bonding in Square Planar MOs orbitals of L D 4h orbitals (p x,z ) 76 Slide 77 Bonding in Square Planar MOs 77 Slide 78 Complete Square Planar MOs 78 Slide 79 Coordination Complexes History Ligands Isomers Inorganic Bonding Crystal Field Theory Ligand Field Theory Orbital Diagrams Ligand Field Jahn-Teller Distortion Bioinorganic Chemistry Outline Octahedral bonding bonding -Ligand Field Strength Square Planar bonding bonding Tetrahedral Organometallics 79 Slide 80 Only T d MOs 80 4 1 00 2 : A 1 + T 2 Slide 81 Only T d SALC 11 22 33 44 81 : A 1 + T 2 Slide 82 Only T d MOs 82 Slide 83 Coordination Complexes History Ligands Isomers Inorganic Bonding Crystal Field Theory Ligand Field Theory Orbital Diagrams Ligand Field Jahn-Teller Distortion Bioinorganic Chemistry Outline Octahedral bonding bonding -Ligand Field Strength Square Planar bonding bonding Tetrahedral Organometallics 83 Slide 84 Organometallic Chemistry Organometallic compound- a complex with direct metal-carbon bonds. Zeises salt- the first organometallic compound Isolated in 1825 (by William Zeise) Structure confirmed in 1838. 84 Slide 85 -bonding Ligands 85 Slide 86 History of Ferrocene Pauson and Kealy (1951 ) orange solid of "remarkable stability" FeCl 3 + Fulvalene Nature 1951, 168, 1039 - 1040 G. Wilkinson, M. Rosenblum, M. C. Whiting, R. B. Woodward Journal of the American Chemical Society 1952, 74, 2125 2126. Wilkinson and Fischer (1952) E. O. Fischer, W. Pfab Zeitschrift fr Naturforschung B 1952, 7, 377379. 86 Slide 87 The first sandwich complex. Fuel additives-anitknocking agents. Electrochemical standard. Some derivatives show anti-cancer activity. Small rotation barrier (~ 4 kJmol 1 ) and ground state structures of ferrocene can be D 5d or D 5h. Ferrocene D 5d D 5h D5D5 What about the bonding? 87 Slide 88 MOs of Cyclopentadienyl C5H5-C5H5- D 5h Decomposition/Reduction Formula 88 Slide 89 MOs of Cyclopentadienyl Generate SALC Energy increases as the # of nodes increases. 89 Slide 90 MOs of Ferrocene C5H5-C5H5- D 5h Fe(C 5 H 5 ) 2 D 5d 90 Slide 91 Decomposition/Reduction Formula MOs of Ferrocene Fe(C 5 H 5 ) 2 D 5d 91 Slide 92 Generate SALC MOs of Ferrocene From the equation Assemble 2 x C 5 H 5 - 92 Slide 93 MOs of Ferrocene 2 x 93 Slide 94 MOs of Ferrocene 94 Slide 95 MOs of Ferrocene D 5h D 5d A2A2 E 1 E2E2 E2E2 E 2g E 2u E 2g E 2u E 1g E 1u E 1g E 1u A 2u A 1g 95 Slide 96 MOs of Ferrocene 96 Slide 97 MOs of Ferrocene 97 Slide 98 MOs of Ferrocene 98 Slide 99 MOs of Ferrocene 99 Slide 100 MOs of Ferrocene 100 Slide 101 Outline Coordination Complexes History Ligands Isomers Inorganic Bonding Crystal Field Theory Ligand Field theory Orbital Diagrams Ligand Field Jahn-Teller Distortion Bioinorganic Chemistry 101 Slide 102 Jahn-Teller Distortion Jahn-Teller theorem: there cannot be unequal occupation of orbitals with identical energy Molecules will distort to eliminate the degeneracy! E Distortion d3d3 1 u.e. d9d9 equal occupation unequal occupation 102 Slide 103 egeg t 2g E d xz dx2-y2dx2-y2 d yz d xy dz2dz2 Jahn-Teller Distortion [Cu(H 2 O) 6 ] 2+ 2.45 2.00 103 Slide 104 Jahn-Teller Distortion 104 Slide 105 Jahn-Teller Distortion 105 Slide 106 Outline Coordination Complexes History Ligands Isomers Inorganic Bonding Crystal Field Theory Ligand Field theory Orbital Diagrams Ligand Field Jahn-Teller Distortion Bioinorganic Chemistry 106 Slide 107 Transition Metals in Biochemistry 107 Slide 108 Transport/storage proteins : Transferrin (Fe) Ferritin (Fe) Metallothionein (Zn) O 2 binding/transport:Myoglobin (Fe) Hemoglobin (Fe) Hemerythrin (Fe) Hemocyanin (Cu) Enzymes (catalysts) Hydrolases:Carbonic anhydrase (Zn) Carboxypeptidase (Zn) Oxido-Reductases: Alcohol dehydrogenase (Zn) Superoxide dismutase (Cu, Zn, Mn, Ni) Catalase, Peroxidase (Fe) Nitrogenase (Fe, Mo) Cytochrome oxidase (Fe, Cu) Hydrogenase (Fe, Ni) Isomerases: B 12 coenzymes (Co) Aconitase (Fe-S) Oxygenases: Cytochrome P450 (Fe) Nitric Oxide Synthases (Fe) Electron carriers:Cytochromes (Fe) Iron-sulfur (Fe) Blue copper proteins (Cu) Metals in Biochemistry Structural Skeletal roles via biomineralization Ca 2+, Mg 2+, P, O, C, Si, S, F as anions, e.g. PO 4 3 , CO 3 2 . Charge neutralization. Mg 2+, Ca 2+ to offset charge on DNA - phosphate anions Charge carriers: Na+, K +, Ca 2+ Transmembrane concentration gradients ("ion-pumps and channels") Trigger mechanisms in muscle contraction (Ca). Electrical impulses in nerves (Na, K) Heart rhythm (K). Hydrolytic Catalysts: Zn 2+, Mg 2+ Lewis acid/Lewis base Catalytic roles. Small labile metals. Redox Catalysts: Fe(II)/Fe(III)/Fe(IV), Cu(I)/Cu(II), Mn(II)/Mn(III)/(Mn(IV), Mo(IV)/Mo(V)/Mo(VI), Co(I)/Co(II)/Co(III) Transition metals with multiple oxidation states facilitate electron transfer - energy transfer. Biological ligands can stabilize metals in unusual oxidation states and fine tune redox potentials. Activators of small molecules. Transport and storage of O 2 (Fe, Cu) Fixation of nitrogen (Mo, Fe, V) Reduction of CO 2 (Ni, Fe) Organometallic Transformations. Cobalamins, B 12 coenzymes (Co), Aconitase (Fe-S) 108 Slide 109 Transition Metals in Biochemistry 109 Slide 110 Amino acid binding functionalities: -OH, -SH, -COOH, -NH, CONH 2 Biological Ligands 110 Slide 111 Biological Ligands 111 Slide 112 Bioinorganic Chemistry 112 Slide 113 Bioinorganic Examples Hemoglobin iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates. hemoglobin in the blood carries oxygen from the respiratory organs (lungs or gills) to the rest of the body. 113 Slide 114 Bioinorganic Examples Nitrogenase Reduction of N 2 to 2NH 3 + H 2 Fe 7 MoS 9 cluster Mechanism not fully known. Mo sometimes replaced by V or Fe. Inhibited by CO. 114 Slide 115 Bioinorganic Examples Iron Sulfur Clusters Mediate electron transport. Biological capacitors Fe(II) and Fe(III) Found in a variety of metalloproteins, such as the ferredoxins, hydrogenases, nitrogenase, cytochrome c reductase and others. Ferredoxin 115 Slide 116 Metal Ions and Life 116 Slide 117 Not Enough Metal Ions 117 Slide 118 Argyria or argyrosis: a condition caused by inappropriate exposure to chemical compounds of the element silver. Excess Metal Ions Colloidal Silver Paul Karason- Used silver to treat dermatitis, acid reflux and other issues. Food and Drug Administration (FDA) doesn't approve of colloidal silver as a medical treatment! 118 Slide 119 To Much Ag 119 Slide 120 Outline Coordination Complexes History Ligands Isomers Inorganic Bonding Crystal Field Theory Ligand Field theory Orbital Diagrams Ligand Field Jahn-Teller Distortion Bioinorganic Chemistry 120