The one subject of the invention is the compounds of general formula (I), their isomers, their physiologically acceptable salts and/or Mn(II), Fe(II), Fe(III), Co(II) and Ni(II) complexes. The other subject of the invention is the application of the above compounds. The compounds of general formula (I): wherein —NRR1 group may refer to: a) —NRR1 with N atom in the ring means a ring of 4 to 7, that in certain cases may contain another heteroatom, and in specific cases the ring may be replaced with an aryl group (of 5 to 7 carbon atoms) substituted with —COOH, —OH, —OCH3, —NO2, —NH2, —NCS, —NHS-activated ester, aryl (of 5 to 7 carbon atoms), or nitro-, amino- or isothiocyanate group, or b) in the —NRR1 group R means a H atom, alkyl, aryl, nitroaryl, aminoaryl or isothiocyanate-aryl group (of 1 to 6 carbon atoms) and R4 is a H atom, alkyl (of 1 to 6 carbon atoms) or —(CH2)n—COOH group, whereas n=1 to 10 integer, or c) —NRR1 group is one of the following groups: (formula II) whereas R2 is a H atom, carboxyl- or alkyl-carbonyl group (of 1 to 4 carbon atoms); (formula III) and R2 is a H atom or alkyl or aryl group (of 1 to 6 carbon atoms), and X means independently from one another H atom, —CH3, —COOH, —OH, —OCH3, alkoxy- (of 2 to 6 carbon atoms), —NO2, —NH2, —NCS, —NHS-activated ester, alkyl (of 2 to 12 carbon atoms) or aryl (of 5 to 7 carbon atoms) group, in certain cases the latter may be substituted with hydroxyl, hydroxyalkyl (of 1 to 6 carbon atoms), nitro, amino or isothiocyanate group.