A 99mTc complex which contains the moiety Tc═NR, Tc—N═NY or Tc(—N═NY)2, and as a synthetic organic ligand which confers biological target-seeking properties on the technetium complex, where: R is an aryl group, a substituted or unsubstituted alkyl group or the group —NR1R2; Y is an aryl group or a substituted or unsubstituted alkyl group; R1 and R2 are H, aryl groups or substituted or unsubstituted aliphatic or cyclic alkyl groups, and are the same or different provided that both are not hydrogen; where at least one of the R or Y groups comprises an aryl group which chelates the 99mTc.