Cobalt (Ii) Oxygen

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Cobalt(II) Oxygen adduct complex
Inorganic 461 lab
2-29-2012

Abstract
This experiment uses Co(salen) as a model compound illustrating the uptake of oxygen in hemoglobin. SalenH2 was prepared as the intermediate, and reacted with hydrated cobalt to prepare Co(salen). Using Co(salen) the oxygen up-take was tested. The synthesis of SalenH2 produced 0.65 g. The percent yield of salenH2 was 116% on the filter paper and 105% after transferring salenH2 to a vial. The melting point of salenH2, was 128 oC. The color of salenH2 was yellow. This was all expected from salenH2. The synthesis of Co(salen) produced 0.232 g. The percent yield of Co(salen) was 88.22% on the filter paper and 86.1 % after transferring the Co(salen) to a vial. Co(salen) was red, the active form of Co(salen). The melting point of Co(salen) was138oC. Co(salen) was able to absorb 6.83x10-5mol of O2 Why? What chemistry is taking place?

Introduction
Heme proteins have been studied for years by scientists. Heme proteins contain a transition metal that can coordinate molecular oxygen. Examples of this can be found in myoglobin, hemoglobin proteins, copper containing hemocyanian and vanadium containing hemovanadin, these are all Essential for life. Myoglobin contains a porphyrin ring with an iron center .a proximal histidine group was attached directly to the iron center, and a distal histidine group on the opposite face, not bonded to the iron. In hemeoglobin, an iron held in a porphyrin ring. The porphyrin ring consists of four pyrrole molecules cyclically linked together, by methene bridges, with the iron ion bound in the center.[2] The iron ion, which was the site of oxygen binding, coordinates with the four nitrogens in the center of the ring, which all lie in one plane. The iron bounds strongly to the globular protein via the imidazole ring of the histidine residue below the porphyrin ring. A sixth position can reversibly bind oxygen by a coordinate covalent bond, completing the octahedral group of six ligands

Cobalt (II) complex of N,N’-bis(salicyaldehyde)ethylendiimine, (salenH2) was extensively studied. Salen chelating ligand belongs in a special class of ligands known as Schiff’s bases. This ligands contains 2 atoms (O,N) as the donor sites. Co(II)-salen was a four-coordinate complex that readily adds ligands to become five or six-coordinate complexes.[1] In the solid state, Co(II)-salen can exist in two different forms: complexes A, the active species, appears as a dark red and will absorbs oxygen. Complexes B, the inactive, appears as a brown color and does not interacts with oxygen (fig 1). Both complexes are comprised of two monomers which were linked together by hydrogen bonds, coordinate bonds, or covalent bonds, known as dimeric complex. Co(salen) will form as adduct with a peroxo-bridged oxygen, by absorbing oxygen from DMSO. The overall reaction for this experiment follows: ethylenediamine + 2 salicylaldehydesalenH2(rxn1)

salenH2 + Co2+ Co(II)salen

fig 1
Materials:
Salicylaldehyde was provided from Fisher scientific, the purity was unknown. The ethylenediamine was purchased from Aldridge, with 99 % purity. Cobalt(II) acetate tetrahydrate was purchased from fisher scientific. Ethanol was also purchased from fisher scientific, with a 90% purity. The nitrogen gas was supplied from Rockford industry supply. Both steps of this reaction were performed under nitrogen gas, and room pressure. Methods

Preparation of N,N’-Bis(salicyladehyde)ethlediimine
In a 10-mLErlenmeyer flask, 5-mL of 95 % ethanol and a magnetic stir bar was added. The Erlenmeyer flask was placed on top of a sand bath. Once the ethanol started to boil, 450 μL of salicyladehyde was added. Than 140 μL of ethylenediamine was added to the mixture. The solution was stirred for 3 minutes. Then the Erlenmeyer flask was placed into an ice bath. The yellow crystals was suction filtrated in a Hirsh funnel. The product, salenH2 was washed with 2 drops of ethanol....
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