quiz11key - and a water molecule Since the nitrogen ligands...

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CHEMISTRY 131 Quiz #11 Friday, April 28, 2006 Name: _____________________________________ 1. What is the difference between an inner sphere ligand and an outer sphere ligand? (3 points) An inner sphere ligand is directly coordinated to the metal; it is involved in a Lewis acid- base interaction with the metal. An outer sphere ligand is present simply to balance charge. It does not participate directly in an interaction with the metal. In a chemical formula indicating the composition of a complex, inner sphere ligands are written on the inside of square brackets with the metal, while outer sphere ligands are indicated outside the brackets. 2. Why is hemoglobin blue when it is deoxygenated, but red when it binds to oxygen? (5 points) When hemoglobin is deoxygenated, it contains an Fe ion that is coordinated to four nitrogen atoms from the porphyrin ring, a fifth nitrogen atom from a histidine side chain,
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Unformatted text preview: and a water molecule. Since the nitrogen ligands are σ-donors and the water molecule is a π-donor, the HOMO-LUMO gap ( ∆ o ) is fairly small, so that the complex absorbs orange light and appears blue. However, when oxygen binds, it displaces the water molecule from the sixth position around the Fe atom. O 2 is a weak π-acceptor, so that the ∆ o gap increases and the absorption shifts to higher energy (green), so that the color changes to red. 3. What is the d count of the metal in [Mo(gly) 2 (NH 3 ) 2 ]Cl? (2 points) Cl-is an outer sphere ligand and balances the charge of the actual complex, so that the complex is [Mo(gly) 2 (NH 3 ) 2 ] + . NH 3 is a neutral ligand, but gly (glycine) is negatively charged; thus, the Mo must be a +3 ion since the charge on the entire complex is +1. When Mo is neutral, it has a total of 6 valence electrons; so, Mo +3 must be a d 3 ion....
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