Cis
-dioxo-metal complex ( NH,CHZCHZNHZ 12.s [ Md!i W6Y)Oz-(oc&O)2] 1 was obtained by the reaction of tetra-butyl ammonium hexamolybdotungstate with 1.2-dihydroxybenzene in the mixed solvent of CH3OH. CH3CN and ethylenediamine, and characterized by X-ray diffraction, UV-vis and EPR analysis. Compared with its analogous complexes (NH~CHZCHZ-02(Oc6)40)2] 3, the results show that tungsten(\l) is less ac- tive in redox than molybdenum(VI) and that the change of the valence induced by substitution of W( VI) for Mo( V ) in [ M02-(Oc6&0),]'does not iduence the coordination geometry of the complex anion in which the metal center exhibits distorted octahedral coordination with cis-dioxo catechol. The responses to EPR of complexes 1 and 2 are active but complex 3 is silent, and the UV-vis spectra exhibited by the three complexes are obvious different because of the different electronic configuration between the central Mo(V) and W(V1) ions in the complexes. It is noteworthy that complexes 1 and 2 have the similar EPR signal to flavoenzyme , suggesting that the three complexes have the m e coordination geometry feature with the co-factor of flavoenzyme . N H ~) , [ M O ( ~) O ~( O C ~H ~O ) ~I 2 and (NH,CH&H~NHZ)~[ W""-Keywords dihydroxybenzene, EPR, UV-vis , octahedral coordination cis -dioxo-molybdo ( V ) tungsten