A computational modeling of the formation of bis-Cr(III) biscyclam shows that the thermodynamically favored isomer is that with a trans,trans ' geometry. Experimentally, only the kinetically favored cis,cis ' isomer is observed. Calculations suggest that the presence of the second macrocycle in the biscyclam ligand is sufficient to limit cis --> trans isomerization, trapping the complex in a metastable conformation. The cis,trans ' complex is illustrated. [GRAPHICS]