Abstract: STUDY OF TECHNETIUM CHEMISTRY ⅨSTABILITY OF THE STRUCTURE AND VALENCE OF THE BRAIN IMAGINGS BELONGING TO THE ANALOGUES OF 99Tcm(Ⅴ)OBATMeng Zhaoxing Lin Haojing Liu Boli(Department of Chemistry,Beijing Normal University,Beijing 100875)ABSTRACTThe transformation process of valence of the brain imagings belonging to the analogues of Tc（Ⅴ）OBAT is studied with the improved CNDO/2 method. It has been proposed that ion X for coordination balance probably exists after the complexation of N2S2 derivatives with the TcO3＋core. Then symmetrical 99Tcmcomplex with one positive charge may be formed due to the prior decomplexation of X in solution. Immediately,it will automatically transform to the unsymmetrical and relatively more stable neutral 99Tcmcomplex.Therefore,the process of transformation results,in the fact that only one coordinating nitrogen atom retains a proton.The concept of decreasing percent of bond order is suggested as an indicator of retention property of the proton linked to the coordinating nitrogen atom in the process of coordination.The essential factor of different retention propery of the protons between two coordinating nitrogen atoms of 99Tcm(Ⅴ)ON2S2　complexes and that of 99Tcm(Ⅴ) complexes is well explained.The results may give some theoretical informations for designing the structure of 99Tcmcomplex with different valences.Key words 99Tcm(Ⅴ) core 99Tcm(Ⅴ)≡N core Decreasing percent of bond order 99Tcmcomplex