\left( \begin{array}{cccc}
1 & 0 & 0 & 1 \\
0 & 0 & 0 & 1 \end{array} \right)\ i \left( \begin{array}{cccc}
1 & 0 & 0 & 0\\
0 & 0 & 0 & 0 \end{array} \right)\