Sixteen novel derivatives of 1,1,1-tris (salicylaldiminomethyl)ethane have been synthesized for the purpose of encapsulating Tc-99m(IV) ions and generating new Tc-99m radiopharmaceuticals. Two methods for the preparation of the Tc-99g(IV) analog complexes are presented; one utilizes SnCl2 reduction on (TcO4-)-Tc-99g and the other a direct substitution route starting with [(TcCl6)-Tc-99g](2-). Free ligands (H(3)L) are characterized by melting points, H-1 NMR, C-13 NMR, mass spectroscopy, TLC, and/or elemental analyses. [(99g)TcL](+) complexes are characterized by FAB-ms, UV-VIS, IR and/or CV. An X-ray structural analysis was performed on a crystal of [M(6,6'-[[2-[[((4-Methoxy-2-hydroxyphenyl)methylene)-amino]methyl]-2-methyl-1,3-propanediyl]bis(nitrilomethylidyne)]-bis-3-methoxyphenol)] tetraphenylborate, where M represents a 1/3 isomorphous mixture of Tc-99g/Sn as determined by SEM. The metal coordination site is 6-coordinate, composed of N3O3 donor atoms, and intermediate between octahedral and trigonal prismatic geometry. The [(99m)TcL](+) complexes were prepared in a stannous environment; equivalence of the Tc-99m and Tc-99g complexes is demonstrated by HPLC techniques. The [SnL](+) complex was prepared for comparison purposes. An unusual ligand oxidation occurs for one series of ligands in which in situ amine -->imine conversion is observed during the complexation reaction in reducing media. Guinea pig, rat, dog, and human metabolism studies are reported for selected [(99m)TcL](+) complexes, the myocardial uptake of which approaches 2% of the injected dose.