[en] Chemical effects associated with the sup(59)Co(n,γ)sup(60m,g)Co and sup(59)Co(γ,n)sup(58m,g)Co reactions, together with the isomeric transition of sup(58m)Co, were studied in tris(β-diketonato)-cobalt(III) complexes. It was further confirmed in the systems of the Co(acac)sub(3) or Co(bzac)sub(3) mixed with Al(bzac)sub(3) that thermal annealing of the recoil sup(60)Co atoms is highly affected by the steric configuration of the matrix complexes. (author)