Lecture_1_LigandField

Lecture_1_LigandField - Chem 310 Lecture Module 1...

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Chem 310 Lecture Module 1 Coordination Complexes and Ligand Field Theory
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ransition metals ( ements); center part of the periodic table Transition metals ( d elements); center part of the periodic table group 3 4 5 6 7 8 9 10 11 12 Sc Ti V Cr Mn Fe Co Ni Cu Zn Y Zr Nb Mo Tc Ru Rh Pd Ag Cd La Hf Ta W Re Os Ir Pt Au Hg Electron configuration: n s 2 (n-1) d g-2 , with n = main quantum number, g = group number Examples: Ti, 4 s 2 3 d 2 ; W, 6 s 2 5 d 4 ; Ir, 6 s 2 5 d 7 . [Formation of cations: remove s electrons first, e.g., Ti 3+ , 3 d 1 4 s 0 . ] Exceptions: Cu, 4 s 1 3 d 10 ; Mo, 5 s 1 4 d 5 . Because of tendency towards half and full shells.
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d orbitals:
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Werner theory Observations, four complexes of cobalt(III)chloride with ammonia F ormula color name i) CoCl 3 . 6NH 3 yellow Lateo complex ii) CoCl 3 . 5NH 3 purple Purpureo complex iii) CoCl 3 . 4NH 3 green Praseo complex iv) CoCl 3 . 4NH 3 violet Violeo complex Reactions with AgNO 3 (AgCl is ppt’d and then measured) i) CoCl 3 . 6NH 3 +A g + --> 3 AgCl ) CoCl . NH g + AgCl ii) CoCl 3 5NH 3 + Ag --> 2 AgCl iii) CoCl 3 . 4NH 3 g + --> 1 AgCl iv) CoCl 3 . 4NH 3 g + --> 1 AgCl Werner noted that chlorine atoms may behave as ions or like Cl in chloroethane As ammonia molecules are removed, they are replaced by Cl Æ covalently bound. Thus, the coordination number is always six (here, that is). ew formulation of these four salts: (see also conductivity, pp 389 of text): New formulation of these four salts: (see also conductivity, pp 389 of text): [Co(NH 3 ) 6 ]Cl 3 , [Co(NH 3 ) 5 Cl]Cl 2 , [Co(NH 3 ) 4 Cl 2 ]Cl, and [Co(NH 3 ) 4 Cl 2 ]Cl. Conclusion: Oxidation state and coordination number are important.
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Possible coordination isomers Formula planar trigonal prismatic octahedral experimental MA 5 B 1 1 1 1 MA 4 B 2 3 3 2 2 MA 3 B 3 3 3 2 2 Formula planar tetrahedral experimental A MA 3 B 1 1 1 MA 2 B 2 2 1 1 - 2
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Nomenclature 1) Complexes are written in brackets []. 2) In the formula, M comes first, then anionic ligands, followed by neutral ligands. ) In the name ligands come first then central atom M 3) In the name, ligands come first, then central atom M. 4) The M oxidation number is added in parentheses (II). 5) In anionic complexes, -ate is added to the name of M. ) - is added to anionic ligands. 6) o is added to anionic ligands. 7) Ligands are sorted in alphabetical order. 8) Prefixes mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa- are used to indicate the multitude of L. 9) Bridging ligands are indicated with μ -. Examples: [Fe(CN) 6 ] 4- : Hexacyanoferrate(II) [Re 2 Cl 8 ] 2- : Octachlorodirhenate(III) [CoCl 2 (NH 3 ) 4 ] + : Tetraamminedichlorocobalt(III)
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onding in Coordination Compounds Bonding in Coordination Compounds a) Valence bond (VB) theory, Linus Pauling (1930s) b) Crystal field (CF) theory (Bethe, 1929; van Vleck, 1935) ligand field (LF) theory b) C ys e d (C ) eo y ( e e, 9 9; v V ec , 9 ) gde d ( ) e o y (1950s) c) Molecular orbital (MO) theory a) Valence bond theory M+ n L ML n metal (ion) ligand Lewis acid - Lewis base I.e, acid/base complex with coordinate covalent (dative) bonds odel uses the idea of hybridization of the and alence orbitals of M: Model uses the idea of hybridization of the s , p , and d valence orbitals of M:
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Hybrid geometry bond angle(s) sp
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This note was uploaded on 02/28/2011 for the course CHEM 310 taught by Professor Nazar during the Fall '09 term at Waterloo.

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Lecture_1_LigandField - Chem 310 Lecture Module 1...

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