Synthesis of a Coordination Compound

Transcription

1 Synthesis of a Coordination Compound synthesize a coordination compound Cu(NH 3 ) 4 SO 4 H 2 O and investigate the nature of coordination compounds and complexes through examination of color changes

2 Coordination Complexes (Complex Ions) central metal ion surrounded by & bonded to a number of ions (ex. Cl - ) or polar molecules (ex. NH 3 ) called ligands ligands are Lewis bases metals are Lewis acids

3 donor atoms/coordinate covalent bonds Donor atom must have one or more lone pair ligands like NH 3, H 2 O, Cl -, have only one donor atom ligands like CO, NO 2-, SCN -, CN - have two donor atoms (but can only bond with one or the other) Example - only a single N donor atom In each NH 3

4 Some ligands bind through multiple donor atoms - bidentate ligands EDTA is hexacoordinate

5 Coordination compounds - Complex ion(s) with charge balancing ions to generate neutral compound

6 Synthesis Procedure weigh out 7.00 grams of the CuSO 4 5H 2 O, place it in a 125 ml Erlenmeyer flask, and dissolve it in 15.0 ml of water Convert Cu(H 2 O) 4 2+ (aq) into Cu(NH 3 ) 4 2+ (aq) by adding a 2x excess of the required stoichiometric equivalent of NH 3 [conc. NH 3(aq) is 28% m/m with d = 0.90 gcm -3 giving a conc. = 14.8 M] WORK IN THE HOOD conc. NH 3(aq) should not be used on an open lab bench

7 Synthesis Procedure Note: a light blue ppt. may form upon initial addition of the conc. NH 3 this is not the desired product... What could it be? Dissolve ALL of this light blue ppt. prior to moving to the subsequent step. This should happen with stirring (with no heat)... A little bit more conc. NH 3 can be added to encourage dissolution of the ppt.

8 Isolation of the Product The product is a combination of the tetraammine copper (II) complex ion, a sulfate ion, and a single water of hydration: Cu(NH 3 ) 4 2+ (aq) + SO 4 2- (aq) + H 2 O Add ~15.0 ml of CH 3 OH to lower the solubility of the product (why does this work?). Cool the solution in an ice bath for about 10 min. stirring occasionally. A new dark royal blue solid should appear. Vacuum filter -

9 Isolation of the Product Vacuum filter - Set up a suction filter and collect the solid Rinse Erlenmeyer flask with three separate 2 ml washes of methanol pouring each through the solid on the filter Allow the solid to drip dry thoroughly and lay the filter paper out on a paper towel so your compound can air dry. Turn it frequently to promote drying...you will need to weigh it later in the lab period.

10 d-orbitals (ex. 3d) axial orientation

11 Interaction of ligand(s) with metal orbitals example: octahedral

12 number of ligands and arrangement affect metal d-orbitals differently

13 strength of ligands affect metal d- orbitals more (or less)

14 strength of ligands affect metal d- orbitals more (or less)

15 Changing central metal or the ligands results in a color change

16 The Effect of Ligand Field Strength on Light Absorption Recall the concepts of complimentary colors used in prior experiments A pink solution is likely absorbing in the green region Recall the relative energies of ROYGBIV Violet light is high E Red light is low E

17 The Effect of Ligand Field Strength on Light Absorption Cu 2+ observations made during the synthesis Record the color you observed for CuSO 4 5H 2 O (s) and for Cu(H 2 O) 4 2+ (aq). Also, record the color of light that is most likely being absorbed by the solution Record the color you observed for Cu(NH 3 ) 4 2+ (aq). Also, record the color of light that is most likely being absorbed by the solution.

18 The Effect of Ligand Field Strength on Light Absorption (Co 2+ ) Obtain several grains of CoCl 2 6H 2 O (s) in a small test tube and record the color of the crystals. record the color of light that is most likely being absorbed. Dissolve the solid in ~3 ml of extra dry methanol and record the color of the solution. record the color of light that is most likely being absorbed. Now add about ~5 ml of distilled water and record the color of the solution. record the color of light that is most likely being absorbed.

19 The Effect of Ligand Field Strength on Light Absorption (Fe 3+ ) Obtain about 3 ml of the 0.10 M FeCl 3 solution and record the color. record the color of light that is most likely being absorbed by the solution. Now add about 1 ml of the 0.10 M thiocyanate (SCN - ) solution and record the color. record the color of light that is most likely being absorbed by the solution.