[Display omitted] A series of "2 + 1" mixed ligand tricarbonyl complexes of the general formula fac -[Re/99mTc/186Re(CO) 3 (DDTC)(L)] containing diethyldithiocarbamate (DDTC) as a monoanionic bidentate ligand and a series of monodentate ligands L was synthesized, characterized and evaluated. The impact of ligand L on the radiochemical yield (RCY) and biodistribution of the final compounds was also investigated. DDTC and the appropriate L ligand [cyclohexyl isocyanide (cisc), tert -butyl isocyanide (tbi), triphenylphosphine (PPh 3), methyldiphenylphosphine (PPh 2 Me), triphenylarsine (AsPh 3), imidazole (im), and 4-aminopyridine (4AP)] readily reacted in equimolar amounts with the [Et 4 N] 2 [Re(CO) 3 Br 3 ] precursor to afford fac -[Re(CO) 3 (DDTC)(cisc)], Re1 , fac -[Re(CO) 3 (DDTC)(tbi)], Re2 , fac -[Re(CO) 3 (DDTC)(PPh 3)], Re3 , fac -[Re(CO) 3 (DDTC)(PPh 2 Me)], Re4 , fac -[Re(CO) 3 (DDTC)(AsPh 3)], Re5 , fac -[Re(CO) 3 (DDTC)(im)], Re6 and fac -[Re(CO) 3 (DDTC)(4AP)], Re7 , complexes in high yields (>80%). All Re complexes were fully characterized by IR, NMR, and in addition Re4 , Re5 , and Re7 with X-ray crystallography. Analogous reactions as performed with Re were subsequently explored on the 99mTc and 186Re-tracer levels using the corresponding fac -[99mTc/186Re(CO) 3 (H 2 O) 3 ]+ precursor. Complexes 99mTc1 – 99mTc5 , 186Re1 and 186Re3 were obtained in high radiochemical yield (>91%), while the complexes 99mTc6 , 99mTc7 and 186Re7 formed with radiochemical yields of 55%, 28%, and 75%, respectively. The 99mTc and 186Re-complexes were characterized by comparative HPLC analysis using the analogous Re complexes. During histidine and cysteine challenge experiments at 37 °C through 6 h, complexes 99mTc1 – 99mTc5 remained > 92% stable, while complexes 99mTc6 and 99mTc7 remained only 8% stable through 3 h. Similar studies for 186Re-complexes showed that 186Re1 and 186Re3 remained > 95% stable for up to 48 h, while 186Re7 had decreased to 7% after 3 h. LogD 7.4 data of 99mTc1 – 99mTc5 , 186Re1 , and 186Re3 complexes, which ranged from 2.59 to 3.39, suggested high lipophilicity. Biodistribution studies in healthy Swiss albino mice showed hepatobiliary excretion for 99mTc1 , 99mTc2 , and 99mTc4 , fast blood clearance for 99mTc4 , while high liver uptake and retention for 99mTc3 and 99mTc5 were measured. Moreover, 99mTc2 showed high accumulation in the lungs with sustained retention (52.80% ID/g at 4 h p.i.) and significant brain uptake at 2 min p.i. (1.89% ID/g). The study showed the great influence of monodentate ligand in the synthesis and biodistribution of the mixed ligand complexes. [ABSTRACT FROM AUTHOR]