Ligand which has one of the general structures A, B or C: where R 1, R 2, R 3, R 4, in each case independently of one another, are selected from: -H, -(C 1 -C 12)-alkyl, X and Y, in each case independently of one another, can be O or N, if X is O, n = 1, if Y is O, m = 1, if X is N, n = 1 or 2, if Y is N, m = 1 or 2, V and W, in each case independently of one another, are selected from: - H, -(C 1 -C 12)-alkyl, -(C 1 -C 12)-heteroalkyl, -(C 4 -C 20)-aryl, -(C 4 -C 20)-aryl-(C 1 -C 12)-alkyl, -(C 4 -C 20)-aryl-O-(C 1 -C 12)-alkyl, -(C 1 -C 12)-alkyl-(C 4 -C 20)-aryl, -(C 4 -C 20)-aryl-COO-(C 1 -C 12)-alkyl, -(C 4 -C 20)-aryl-CONH-(C 1 -C 12)-alkyl, - (C 4 -C 20)-aryl-CON[(C 1 -C 12)-alkyl] 2, - (C 4 -C 20)-heteroaryl, - (C 4 -C 20)-heteroaryl-(C 1 -C 12)-alkyl, -(C 3 -C 12)-cycloalkyl, - (C 3 -C 12)-cycloalkyl-(C 1 -C 12)-alkyl, -(C 3 -C 12)-heterocycloalkyl, -(C 3 -C 12)-heterocycloalkyl-(C 1 -C 12)-alkyl, -CO-(C 1 -C 12)-alkyl, -CO-(C 4 -C 20)-aryl, -CO-(C 4 -C 20)-heteroalkyl, -(C4-C 20)-aryl-CO-(C 1 -C 12)-alkyl, -(C 4 -C 20)-aryl-CO-(C 4 -C 20)-aryl, Z is selected from: - (C 1 -C 14)-alkyl-, -(C 4 -C 20)-aryl-, -(C 4 -C 20)-aryl-(C 1 -C 12)-alkyl-, -(C 1 -C 14)-heteroalkyl-, -(C 4 -C 20)-heteroaryl-, - CO-(C 4 -C 14)-heteroaryl-, -CO-(C 4 -C 20)-aryl-, -(C 3 -C 12)-cycloalkyl-, -(C 3 -C 12)-heterocycloalkyl-, -(C 4 -C 20)-aryl-CO-(C 4 -C 20)-aryl-, -(C 1 -C 14)-alkyl-O-(C 1 -C 14)-alkyl-, where the specified alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl and heteroaryl groups are optionally mono- or polysubstituted. R 1, R 2, R 3, R 4, in each case independently of one another, are selected from: -H, -(C 1 -C 12)-alkyl, X and Y, in each case independently of one another, can be O or N, if X is O, n = 1, if Y is O, m = 1, if X is N, n = 1 or 2, if Y is N, m = 1 or 2, V and W, in each case independently of one another, are selected from: - H, -(C 1 -C 12)-alkyl, -(C 1 -C 12)-heteroalkyl, -(C 4 -C 20)-aryl, -(C 4 -C 20)-aryl-(C 1 -C 12)-alkyl, -(C 4 -C 20)-aryl-O-(C 1 -C 12)-alkyl, -(C 1 -C 12)-alkyl-(C 4 -C 20)-aryl, -(C 4 -C 20)-aryl-COO-(C 1 -C 12)-alkyl, -(C 4 -C 20)-aryl-CONH-(C 1 -C 12)-alkyl, - (C 4 -C 20)-aryl-CON[(C 1 -C 12)-alkyl] 2, - (C 4 -C 20)-heteroaryl, - (C 4 -C 20)-heteroaryl-(C 1 -C 12)-alkyl, -(C 3 -C 12)-cycloalkyl, - (C 3 -C 12)-cycloalkyl-(C 1 -C 12)-alkyl, -(C 3 -C 12)-heterocycloalkyl, -(C 3 -C 12)-heterocycloalkyl-(C 1 -C 12)-alkyl, -CO-(C 1 -C 12)-alkyl, -CO-(C 4 -C 20)-aryl, -CO-(C 4 -C 20)-heteroalkyl, -(C4-C 20)-aryl-CO-(C 1 -C 12)-alkyl, -(C 4 -C 20)-aryl-CO-(C 4 -C 20)-aryl, - H, -(C 1 -C 12)-alkyl, -(C 1 -C 12)-heteroalkyl, -(C 4 -C 20)-aryl, -(C 4 -C 20)-aryl-(C 1 -C 12)-alkyl, -(C 4 -C 20)-aryl-O-(C 1 -C 12)-alkyl, -(C 1 -C 12)-alkyl-(C 4 -C 20)-aryl, -(C 4 -C 20)-aryl-COO-(C 1 -C 12)-alkyl, -(C 4 -C 20)-aryl-CONH-(C 1 -C 12)-alkyl, - (C 4 -C 20)-aryl-CON[(C 1 -C 12)-alkyl] 2, - (C 4 -C 20)-heteroaryl, - (C 4 -C 20)-heteroaryl-(C 1 -C 12)-alkyl, -(C 3 -C 12)-cycloalkyl, - (C 3 -C 12)-cycloalkyl-(C 1 -C 12)-alkyl, -(C 3 -C 12)-heterocycloalkyl, -(C 3 -C 12)-heterocycloalkyl-(C 1 -C 12)-alkyl, -CO-(C 1 -C 12)-alkyl, -CO-(C 4 -C 20)-aryl, -CO-(C 4 -C 20)-heteroalkyl, -(C4-C 20)-aryl-CO-(C 1 -C 12)-alkyl, -(C 4 -C 20)-aryl-CO-(C 4 -C 20)-aryl, Z is selected from: - (C 1 -C 14)-alkyl-, -(C 4 -C 20)-aryl-, -(C 4 -C 20)-aryl-(C 1 -C 12)-alkyl-, -(C 1 -C 14)-heteroalkyl-, -(C 4 -C 20)-heteroaryl-, - CO-(C 4 -C 14)-heteroaryl-, -CO-(C 4 -C 20)-aryl-, -(C 3 -C 12)-cycloalkyl-, -(C 3 -C 12)-heterocycloalkyl-, -(C 4 -C 20)-aryl-CO-(C 4 -C 20)-aryl-, -(C 1 -C 14)-alkyl-O-(C 1 -C 14)-alkyl-, - (C 1 -C 14)-alkyl-, -(C 4 -C 20)-aryl-, -(C 4 -C 20)-aryl-(C 1 -C 12)-alkyl-, -(C 1 -C 14)-heteroalkyl-, -(C 4 -C 20)-heteroaryl-, - CO-(C 4 -C 14)-heteroaryl-, -CO-(C 4 -C 20)-aryl-, -(C 3 -C 12)-cycloalkyl-, -(C 3 -C 12)-heterocycloalkyl-, -(C 4 -C 20)-aryl-CO-(C 4 -C 20)-aryl-, -(C 1 -C 14)-alkyl-O-(C 1 -C 14)-alkyl-,