The title complex is formed in a quantitative yield in diluted solutions and the kinetics of its template synthesis and its acidic decomposition were photometricaly studied. The effective synthesis rate constants were determined as the pseudo-first-order rate constants with respect to the concentration of Fe2+ ions. The orders with respect to those of nioxime, CH3B(OH)2 and H+ ions are equal to 3, 1 and –1, respectively. The plausible pathway of its assembly includes a reversible formation of the protonated pseudooctahedral iron(II) tris-nioximate, followed by its monodeprotonation and addition of CH3B(OH)2. Thus obtained pseudooctahedral intermediate undergoes a rate-determining stage of double cyclization with elimination of two molecules of water and structural rearrangement as well, thus giving the trigonal-prismatic iron(II) semiclathrochelate monocation. The latter complex easily undergoes a cross-linking with CH3B(OH)2, resulted in elimination of H+ ion and in formation of the title clathrochelate. Its acidic decomposition rate constants were also obtained as the pseudo-first-order rate constants, but with respect to the concentration of this complex. This rate substantially increases with increase in activity of H+ ions and decreases in the presence of CH3B(OH)2.