The chemical induced decay constant variations for some complex compounds of Tc-99 m were measured by means of a semidifferential approach, using the scintillation technique. The results areTheoretical estimations by means of atomic structure calculations show that Tc04~ should have the greatest decay constant among the compounds investigated, in accordance with the measured values, and that the decay constants of the octahedral complexes should follow the spectrochemical series, partly confirmed by the experiments.