Patent ID: 7173061

Claim:
A compound of formula (I): or a salt thereof, wherein either: (i) R is hydrogen and R 2 is the group â€”OCR 4 R 5 [B]-[A] wherein R 4 and R 5 are independently selected from hydrogen and C 1-6 alkyl, [A] is a chelate, and [B] is a linking group and is preferably â€”C(O)NR 6 â€” wherein R 6 is hydrogen or C 1-6 alkyl; or (ii) R is the group and one of R 1 and R 2 is the group â€”OCR 4 R 5 [B]-[A] as defined above; and the other is the group â€”(O) n â€”C 1-6 alkyl-NR 7 R 8 wherein n is 0 or 1, and R 7 and R 8 are independently selected from hydrogen and C 1-6 alkyl; and R 3 is halo, preferably chloro.