R33Fe14-xAlx+yB25-yC34 (R = La or Ce; x <= 0.9; y <= 0.2) and R33Fe13-xAlxB18C34 (R = Ce or Pr; x < 0.1) were synthesized from reactions of iron with boron, carbon, and aluminum in R-T eutectic fluxes (T = Fe, Co, or Ni). These phases crystallize in the cubic space group Im<(3)over bar>m (a = 14.617(1) angstrom, Z = 2, R-1 = 0.0155 for Ce33Fe13.1Al11B24.8C34, and a = 14.246(8) angstrom, Z = 2, R-1 = 0.0142 for R33Fe13B18C34 ). Their structures can be described as body-centered cubic arrays of large Fe-13 or Fe, clusters which are capped by borocarbide chains and surrounded by rare earth cations. The magnetic behavior of the cerium-containing analogs is complicated by the possibility of two valence states for cerium and possible presence of magnetic moments on the iron sites. Temperature-dependent magnetic susceptibility measurements and Mossbauer data show that the boron-centered Fe-14 clusters in Ce33Fe14-xAlx+yB25-yC34 are not magnetic. X-ray photoelectron spectroscopy data. indicate that the cerium is trivalent at room temperature, but the temperature dependence of the resistivity and the magnetic susceptibility data suggest Ce3+/4+ valence fluctuation beginning at 120 K. Bond length analysis and XPS studies of Ce33Fe13B18C34 indicate the cerium in this phase is tetravalent, and the observed magnetic ordering at T-c = 180 K is due to magnetic, moments on the Fen clusters.