A series of 32 heterometallic ionic complexes CeNi 6 (Ala) 12 (Ln x Ce 1 – x )(NO 3 ) 3 (OH) 3 (H 2 O) (Ln = Tb, Ho, Er, Tm, Yb, Lu) have been synthesized and characterized by XRD and IPC-MS. The dependence of the degree of substitution of lanthanides in the anionic position on the nature of Ln 3+ and precipitation conditions has been determined. The processes occurring during the formation of the complexes have been studied by UV-Vis, diffuse reflectance electronic spectroscopy, and ICP-MS. Based on these data, a model of equilibria in the system was proposed to explain the increase in the degree of substitution of Ln in the anionic position in the lanthanide series and with a decrease in the concentration of Ce and Ln in the solution from which precipitation is performed.