Cuprate(4-), [.mu.-[7-[[4-chloro-6-[[6-[(3-chloro-2-hydroxy- 5-sulfophenyl)azo]-5-hydroxy-7-sulfo-2-naphthalenyl]amino]-1 ,3,5-triazi n-2-yl]amino]-4-hydroxy-3-[(2-hydroxy-5-sulfophen yl)azo]-2-naphth