K. SAHU and R. KUMAR SAHU, “Tetranuclear Metal Chelates of Nickel(II) with 1,2,5,6-Tetraphenyl-3,4-diaza-1,6-dihydroxyimino-2, 4-hexadiene”., ajc, vol. 8, no. 2, pp. 229–231, Jun. 2010.