A ligand of a formula (I):X represents a single bond, methylene, 1,1-cyclobutylene, 1,1-cyclopentylene or 1,1-cyclohexylene each of A1, A2and A3represents hydrogen, a C1~C3alkyl group, a C1~C3phenylalkyl group, a C1~C3methoxyphenylalkyl group, diphenylmethyl or a C1~C3isothiocyanato phenylalkyl group and R represents an aromatic ring, which may be chelated with a copper ion. The present invention also provides a metal complex for preparing a MRI contrast agent for detecting the heavy metal ions.一種如下式(I)所示之配位化合物:X表示單鍵、伸甲基、1,1-伸環丁基、1,1-伸環戊基或1,1-伸環己基;A1、A2及A3各自表示氫、C1~C3之烷基、C1~C3之苯烷基、C1~C3之甲氧基苯烷基、二苯甲基或C1~C3之異硫氰苯烷基;及R表示可與銅離子產生螯合之芳香環基。本發明另提供一種金屬錯合物,此金屬錯合物可用於製備一種供偵測生物體內之重金屬離子之磁振造影對比劑。
