Transition metal complexes covalently attached to inert supports are attracting widespread interest for applications in catalysis, molecular devices, and sensors. We have studied the consequences of covalent, attachment on ferroin ([Fe(phen-R)(3)](2+)) ligand exchange reactions. Mixtures of complexes comprising molecules with zero, one, two, or three tethers were reacted with excess Ni2+ in sol-gel silicate media. Statistical analysis of the reactivity data reveals that the stability of the complexes varies aperiodically as a function of the number of tethers.