A study of tris(imido) complexes is reported in which X-ray crystallography and molecular orbital calculations are used to probe the bonding in heavily pi-loaded transition metal complexes. In this work we focus on Tc-tris(imido) complexes of the form TcX(NR)(3). The bonding in tris(imido) complexes is very sensitive to the nature of the X group. The Tc-N-imido-H angle and Tc-N-imido bond length are not sensitive enough to X to use in probing the bonding in these complexes. Also, there is no correlation between these two metric parameters. The metric parameter which is the best gauge for changes in electronic structure of the complex is the X-Tc-N-imido angle. Subtle variations in X-Tc-N-imido as a function of X are accurately reproduced by calculations for an entire series of X ligands from hard ligands to soft metal electrophiles to three-coordinate complexes in which no X ligand is present. Analysis of the trends in X-Tc-N-imido as a function of the acid-base properties of X lead to the conclusion that the X ligand exerts its influence on the bonding through the sigma framework. The solid-state structures of ReI(NAr)(3) and TcMe(NAr)(3) (Ar = 2,6-diisopropylphenyl) were investigated by X-ray crystallography : ReI(NAr)(3), orthorhombic, Fdd2, a = 36.874(10) Angstrom, b = 39.297(11) Angstrom, c = 10.506(2) Angstrom, V = 15,223(7) Angstrom(3), Z = 16; TcMe(NAr)(3), orthorhombic, Fdd2, a = 37.007(14) Angstrom, b = 40.287(13) Angstrom, c = 10.607(2) Angstrom, V = 15,813(9) Angstrom(3), Z = 16.