b)

Carbon-13 pulse sequence for paramagnetic cobaltocene with composite pulse decoupling

4. Acquisition

Time requirement: 20 min

Sample: ca. 80 mg cobaltocene in 1 ml [D₆]benzene. The preparation of the sample for this experiment is somewhat more elaborate: commercially available cobaltocene is freshly sublimed at 10⁻² torr / 80°C and afterwards transfered into an NMR tube under strict exclusion of oxygen. This is best performed using an NMR working cross found in many organometallic laboratories or in a glove box. Over sodium-potassium alloy previously dried and O₂-free, [D₆]benzene is condensed in vacuo into the NMR tube. Finally the NMR tube is sealed in vacuo. DO NOT USE ARGON as a protecting gas, since this is easily condensed in the NMR tube which subsequently will explode violently.

For the proton experiment a load standard ¹H NMR parameters. You have to set:

td	64 k
sw	110 ppm
o1	25 ppm to lower frequencies from TMS signal
p1	45° ¹H transmitter pulse
d1	100 ms
transmitter attenuation	[3 dB]
ns	8

For the ¹³C experiment b load standard ¹³C NMR parameters. You have to set:

td	64 k
sw	990 ppm
o1	400 ppm to higher frequencies from TMS signal
o2	on resonance of the previously determined ¹H NMR frequency of the cobaltocene signal
p1	45° ¹³C transmitter pulse
d1	100 ms
ns	2048