1. A method of generating a magnetic resonance image of a human or non-human animal body, comprising the steps of administering into the body of a subject in need of magnetic resonance imaging a compound of formula II, and generating a magnetic resonance image; wherein a compound represented by formula II is: wherein R represents independently for each occurrence H or alkyl; Y represents independently for each occurrence —C(O)— or —S(O)—; n represents independently for each occurrence 1, 2, 3, or 4; M is a metal atom; and X represents independently for each occurrence wherein s is 1, 2, 3 or 4.