Iron, complexes with diazotized 3-aminobenzenesulfonic acid coupled with diazotized 2-amino-5-nitrobenzenesulfonic acid, diazotized 2-[(4-aminophenyl)amino]-5-nitrobenzenesulfonic acid and 4-[(2-hydroxy-3,5-dinitrophenyl) azo]-1,3-benzenediol, sodium salt