C6H5.N2.C6H5

from The Collaborative International Dictionary of English v.0.48

Azobenzene \Az`o*ben"zene\, n. [Azo- + benzene.] (Chem.)
   A substance ({C6H5.N2.C6H5}) derived from nitrobenzene,
   forming orange red crystals which are easily fusible.
   [1913 Webster]