Derivatives of azobarbituric acid or salts or complexes thereof

A compound which, in the form of its free acid corresponds in one of its tautomeric structures to the formula ##STR25## in which L=O or NR.sub.7,

• L.sub.1 =O or NR.sub.7,
• with the proviso that only one of L and L.sub.1 can at the same time be NR.sub.7,
• one of M or M.sub.1 =O and the other is O, NR.sub.7, CN or ##STR26## R.sub.6 represents hydrogen, alkyl, cycloalkyl, aryl or aralkyl and R.sub.7 represents hydrogen, cyano, alkyl cycloalkyl, aryl, aralkyl or acyl which acyl is (C.sub.1 -C.sub.6 -alkyl)carbonyl, phenylcarbonyl, C.sub.1 -C.sub.6 -alkylsulphonyl, phenylsulphonyl, carbamoyl, carbamoyl substituted by C.sub.1 -C.sub.6 -alkyl, phenyl or naphtyl, sulphamoyl, sulphamoyl substituted by C.sub.1 -C.sub.6 -alkyl, pheny or naphthyl, said alkyl radical being unsubstituted or substituted by halogen, --OH, --CN, --NH.sub.2 or C.sub.1 -C.sub.6 -alkoxy, and said phenyl and naphthyl radicals being unsubstituted or substituted by halogen, --OH, C.sub.1 -C.sub.6 -alkyl, C.sub.1 -C.sub.6 -alkoxy, --NH.sub.2, NO.sub.2 or CN,
• R.sub.1, R.sub.2, R.sub.3 and R.sub.4 represent hydrogen, alkyl, cycloalkyl, aryl or aralkyl or salts or complexes of mono-, di-, tri and tetra-anions of said compound, said salts and complexes containing a metal selected from the group consisting of Li, Cs, Mg, Cd, Co, Al, Cr, Sn, Na K, Ca, Sr, Ba, Zn, Fe, Ni, Cu, Mn and Pb with the exception of azobarbituric acid and its salts and complexes.