lecture 11 - 1 [Co(NH 3 ) 5 Cl]Cl 2 K 3 [Fe(CN) 6 ]...

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Unformatted text preview: 1 [Co(NH 3 ) 5 Cl]Cl 2 K 3 [Fe(CN) 6 ] Transition-Metal Complexes are extremely colorful! What is the origin of this color? green green/blue blue purple Emperical Evidence for Ligand's Influence on Properties [Ni(H 2 O) 6 ] +2 [Ni(en)(H 2 O) 4 ] +2 [Ni(en) 2 (H 2 O) 2 ] +2 [Ni(en) 3 ] +2 What s responsible for these colors?. Metal complex history Alfred Werner postulated the existence of a symmetric shell of water ligands around nickel ions in 1893 the coordination theory of metal complexes 3 How to explain the structure of metal complexes Crystal field (CF) theory Hans Bethe (1928 University of Tubingen) Termaufspaltung in Kristallen (Splitting of Terms in Crystals) Ligand field (LF) theory John Van Vleck (1932 Harvard University) The Theory of the Variations in Paramagnetic Anisotropy among Different Salts of the Iron Group 4 How to explain the structure of metal complexes In the 1950s, new formulations of molecular orbital theory, such as those weve been studying, revitalized CF and LF theory. Leslie Orgel (1952 -- Cambridge University), The effects of crystal fields on the properties of transition-metal ions 5 C r y s t a l F i e l d T h e o r y The The relationship relationship between colors between colors and complex and complex metal ions metal ions 400 500 600 800 Crystal Field Model A purely ionic model for transition metal complexes. Ligands are considered as point charge. Predicts the pattern of splitting of d-orbitals. Used to rationalize spectroscopic and magnetic properties. d-orbitals: look attentively along the axis Linear combination of d z 2-d x 2 and d z 2-d y 2 d 2z 2- x 2- y 2 Octahedral Field We assume an octahedral array of negative charges placed around the metal ion (which is positive). The ligand and orbitals lie on the same axes as negative charges. Therefore, there is a large, unfavorable interaction between ligand (-) and these orbitals. These orbitals form the degenerate high energy pair of energy levels. The d xy , d yz , and d xz orbitals bisect the negative charges. Therefore, there is a smaller repulsion between ligand and metal for these orbitals. These orbitals form the degenerate low energy set of energy levels. d x 2-y 2 d z 2 d xy d xz d yz In Octahedral Field In Tetrahedral Field Magnitude of Oxidation state of the metal ion Number of ligands and geometry Nature of the ligand [Ru(H 2 O) 6 ] 2+ 19800 cm-1 [Ru(H 2 O) 6 ] 3+ 28600 cm-1 I- <S 2- <SCN- <Cl- <NO 3- <N 3- <F- <OH- <C 2 O 4 2- <H 2 O<..CN- <CO t < o t = 4/9 o Crystal Field Splitting Energy (CFSE) In Octahedral field, configuration is:...
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lecture 11 - 1 [Co(NH 3 ) 5 Cl]Cl 2 K 3 [Fe(CN) 6 ]...

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