Make a new Data frame by filtering an old Data frame

Question

I want to make a dataset such that it has all unique ['contentId']

I used the following code:

l = df2['contentId']
l = list(set(l))
print(l)
print(len(l))

df2_row = df2.loc(df2['contentId'].isin(l))
df2_row.head()

But is gives an error: Output

What do I do?