Four isostructural heptanuclear clusters [LnIr(6)(ppy)(12)(bpp)(2)(bppH)(4)](CF3SO3) center dot xH(2)O (Ir(6)Ln, Ln= Eu, Tb, Er, Yb) are reported, where the lanthanide ions are six-coordinated by the phosphonate oxygen donors from six [Ir (ppy)(2)(bpp)] (ppy(-) = 2-phenylpyridine, bpp(2-) = 2-pyridylphosphonate) chromophores. All show phosphorescence originating from the IrIII moieties. For compounds Ir6Er and Ir6Yb, field-induced slow magnetization relaxation is also observed, thus providing the first examples of Ir-Er or Ir-Yb complexes showing bifunctional phosphorescence and field-induced single ion magnet behaviors.