NEW MATERIAL: A compd. of formula I [X is an anion; Y is a vicinal dioxime (salt) of formula II (R1, R2 are each H, a halogen, alkyl, aryl, amino, etc.); Z is a boron deriv. of formula B-R3 (R3 is hydroxy, an alkyl, alkenyl, aryl, etc.)].

EXAMPLE: Rhenium-chloride-tris(cyclohexanediondioxime)butylboron complex.

USE: A radiotherapeutic agent to malignant tumors. etc.

PROCESS: The compd. of the formula I is obtd. by charging, for example, formula ReCl3(CH3CN)(PPh3)2 (Ph is phenyl),cyclohexanediondioxime and butyl boric acid into a reaction vessel, flushing the same with gaseous nitrogen, adding CH2Cl2 thereto, subjecting the mixture to heating and refluxing to effect reaction, then distilling away the solvent, adding acetonitrile to the reaction product to dissolve the product, refining the product with column chromatography and evaporating the eluted component to dryness.