Abstract In this study selected bidentate (L 2) and tridentate (L 3) ligands were coordinated to the Re(I) or Tc(I) core [M(CO) 2(NO)] 2+ resulting in complexes of the general formula fac-[MX(L 2)(CO) 2(NO)] and fac-[M(L 3)(CO) 2(NO)] (M = Re or Tc; X = Br or Cl). The complexes were obtained directly from the reaction of [M(CO) 2(NO)] 2+ with the ligand or indirectly by first reacting the ligand with [M(CO) 3] + and subsequent nitrosylation with [NO][BF 4] or [NO][HSO 4]. Most of the reactions were performed with cold rhenium on a macroscopic level before the conditions were adapted to the n.c.a. level with technetium ( 99mTc). Chloride, bromide and nitrate were used as monodentate ligands, picolinic acid (PIC) as a bidentate ligand and histidine (HIS), iminodiacetic acid (IDA) and nitrilotriacetic acid (NTA) as tridentate ligands. We synthesised and describe the dinuclear complex [ReCl(μ-Cl)(CO) 2(NO)] 2 and the mononuclear complexes [NEt 4][ReCl 3(CO) 2(NO)], [NEt 4][ReBr 3(CO) 2(NO)], [ReBr(PIC)(CO) 2(NO)], [NMe 4][Re(NO 3) 3(CO) 2(NO)], [Re(HIS)(CO) 2(NO)][BF 4], [ 99Tc(HIS)(CO) 2(NO)][BF 4], [ 99mTc(IDA)(CO) 2 (NO)] and [ 99mTc(NTA)(CO) 2(NO)]. The chemical and physical characteristics of the Re and Tc–dicarbonyl–nitrosyl complexes differ significantly from those of the corresponding tricarbonyl compounds.