Polyamine ligands (L) have excellent binding characteristics for the formation of fac-Tc-99m(CO)(3)-based radiopharmaceuticals. Normally, these L are elaborated so as to leave pendant groups designed to impart useful biodistribution characteristics to the fac-[Tc-99m(CO)(3)L] imaging agent. Our goal is to lay a foundation for understanding the features of the bound elaborated ligands by using the fac-[Re(CO)(3)L]-analogue approach with the minimal prototypical ligands, diethylenetriamine (dien) or simple dien-related derivatives. Treatment of the fac-[Re(CO)(3)(H2O)(3)](+) cation with such triamine (NNN) ligands afforded fac-[Re(CO)(3)L](+) complexes. Ligand variations included having a central amine thioether donor, thus allowing X-ray crystallographic and NMR spectroscopic comparisons of fac-[Re(CO)(3)L](+) complexes with NNN and NSN ligands. fac-[Re(CO)(3)L](+) complexes with two terminal exo-NH groups exhibit unusually far upfield exo-NH NMR signals in DMSO-d(6). Upon the addition of Cl-, these exo-NH signals move downfield, while the signals of any endo-NH or central NH groups move very little. This behavior is attributed to the formation of 1:1 ion pairs having selective Cl-hydrogen bonding to both exo-NH groups. Base addition to a DMSO-d(6) solution. of meso-exo-[Re(CO)(3)(N,N',N ''-Me(3)dien)]PF6 led to isomerization of only one NHMe group, producing the chiral isomer. The meso isomer did not form. The [Re(CO)(3)(N,N,N',N '',N ''-pentamethyidiethylenetriamine)]trif late center dot[Re(CO)(3)(mu(3)-OH)](4)center dot 3.35H(2)O crystal, the first structure with a fac-[Re(CO)(3)L] complex cocrystallized with this well-known cluster, provided parameters for a bulky NNN ligand and also reveals CO-CO interlocking intermolecular interactions that could stabilize the crystal.