[Co(en)2Cl2] X
chem 407
Data from Gmelin, Handbuch der Anorganische Chemie, vol. 58B p. 235 ff.
IR data from Baldwin, J. Chem. Soc. 1960, p 4369
edited October 22, 2000
file is called Coen_data.htm
The generic formula above refers to various salts with the same complex cation. The anion, X, can be varied; it was Cl- in our procedure. These salts can generally be prepared and isolated as crystalline materials.
Baldwin: (sections quoted from the paper)
Abstract
The infrared spectra of some ethylenediamine complexes of tervalent cobalt have been measured in the region 500-4000 cm-1. Assignment of the bands arising from the vibrations of the amino-group has been made by observing the shifts resulting on deuteration. A study of the region 850-900 cm-1 provides a means for differentiation of cis- and trans- isomers of bisethylenediamine complexes.
{remarks: we generally expect proton vibrations to shift to lower frequencies by about a factor of two or the square root of two on deuteration. Vibrations involving the C-C and C-N bonds will not be significantly changed. This allows one to begin sorting out the various spectral lines. We do not expect to see vibrations corresponding to the N-Co bonds.}
Experimental:
The spectra were recorded on a [Grubb-Parson G.S. 2A double beam] spectrometer. Solid samples in Nujol (B.P. Grade) mulls were examined between rock salt [NaCl] plates.
Deuterated Compounds:
In alkaline solution, the hydrogen atoms atached to the donor nitrogen atoms... undergo exchange with the solvent.... Deuterated trans-dichlorobis ethylenediamine cobalt(III) salts were prepared from trans- [Co(en)2Cl2]Cl. The protonated chloride was dissolved in 99.80% D2O (1M with respect to hydroxide), and the mixture left overnight. Excess of concentrated hydrochloric acid was added, and the mixture heated to dryness on a water bath. The resulting green crystals were dried at 110oC. A sample of the deuterated chloride as taken for infrared analysis.
IR Spectra
In metal amine (ammonia) complexes the four principal regions of absorption are
- ~3300 (NH stretching modes)
- ~1600 the asymmetric distortion
- ~1300 (the symmetric distortion)
- ~800 (the NH3 rocking mode)
| cis-
| IR Peaks |
|
|
|
|
|
|
|
| 3460sh
| 3425s
| 3274sh
| 3266m
| 3195s
| 3096m |
|
|
|
| 1634s
| 1587sh
| 1565s
| 1541sh |
|
|
|
|
|
| 1305m
| 1299sh
| 1285m
| 1272sh
| 1212s
| 1200s |
|
|
|
| 1163m
| 1134s
| 1117s
| 1111sh
| 1098m
| 1064sh
| 1058s
| 1010sh
| 999sh
|
| 900m
| 876m
| 788s
| 770s
| 714m
| 549s
| 433s |
|
|
|
|
|
|
|
|
|
|
|
|
| s=strong
| m=medium
| w=weak
| sh= shoulder
| v=very
| d= diffuse |
|
|
|
In the ethylenediamine complexes, the main N-H stretching region occurs between 3300-3077 cm-1. The bands shift on deuteration to 2400-2200 cm-1.
The bands at about 1600 cm-1 may be assigned to the NH2 bending vibration; on deuteration these shift to the region of 1180-1150 cm-1.
The remaining three sets of bands show smaller isotope shifts and can be assigned to vibrations of the NH2 group as a unit, viz., wagging, twisting, and rocking modes respectively.
...
Other bands which are unaffected by deuteration and may be assigned to vibrations of the CH2 group, appear in the regions around 1460, 1300, 1050 and 900 cm-1.
| trans- |
|
|
|
|
|
|
|
|
| 3274m
| 3250s
| 3165m
| 3125sh
| 3077s |
|
|
|
|
| 1591s |
|
|
|
|
|
|
|
|
| 1309m
| 1290w
| 1271s
| 1206s |
|
|
|
|
|
| 1120vs
| 1100vs
| 1053vs
| 1004vs
| 994vs |
|
|
|
|
| 888m
| 808s
| 754m
| 587vs |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Polarimetry and Optical Rotation
formula:
alpha = alphao x length x conc /100
alpha is the angle of rotation of polarized light
- alphao is the specific rotation, a constant for a given species (at specified temperature)
- a value of 164o is given for one isomer of this compound
- length is in decimeter
- conc. in grams of solute per 100 ml of solution
a 10 cm tube with 2g/100 ml would give rotation of 3.2o
return to Chem 407 home page