title: Pandas Set element of a new column as a list (iterable) raise ValueError: setting an array element with a sequence
body: <p>I want to, at the same time, create a new column in a pandas dataframe and set its first value to a list.</p>
  <p>I want to transform this dataframe</p>
  <pre><code>df = pd.DataFrame.from_dict({'a':[1,2],'b':[3,4]})
  
     a  b  
  0  1  3
  1  2  4
  </code></pre>
  <p>into this one</p>
  <pre><code>   a  b   c
  0  1  3 [2,3]
  1  2  4 NaN
  </code></pre>
  <p>I tried :</p>
  <pre><code>df.loc[0, 'c'] = [2,3]
  
  df.loc[0, 'c'] = np.array([2,3])
  
  df.loc[0, 'c'] = [[2,3]]
  
  df.at[0,'c'] = [2,3]
  
  df.at[0,'d'] = [[2,3]]
  </code></pre>
  <p>It does not work.</p>
  <p>How should I proceed?</p>