Tetranitro blue tetrazolium chloride

[Cl-].COC1=CC (=CC=C1N1N=C (N=[N+]1C1=CC=C (C=C1) N (=O) =O) C1=CC=C (C=C1) N (=O) =O) C1=CC=C (N2N=C (N=[N+]2C2=CC=C (C=C2) N (=O) =O) C2=CC=C (C=C2) N (=O) =O) C (OC) =C1