Three pentanuclear lanthanoid hydroxo clusters of composition [Ln(OH)(5)(abzm)(10)], where Ln = Eu, Tb, Ho and abzm = di(4-allyloxy)benzoylmethanide, have been prepared. The structures have been characterised by means of IR, Raman, elemental analyses and X-ray diffraction, showing a pyramidal square-based cluster core. The clusters (Tb and Ho) exhibit Curie-Weiss Law behaviour, displaying antiferromagnetic ordering at low temperatures. The emission properties of the Eu cluster demonstrate the abzm(-) ligand is an efficient antenna (lambda(ex) = 420 nm) only for the sensitisation of Eu luminescence in the visible range, via energy transfer to the D-5(0) state of the trivalent metal. The clusters have been reacted in the presence of methyl methacrylate and azobisisobutyronitrile to prepare reinforced polymers via radical polymerisation. The obtained materials exhibit swelling upon immersion into organic solvents up to approximate to 110 of their original size, in agreement with the presence of cluster-crosslinked polymeric chains. Also, no loss of transparency was observed in the preparation of the materials. The characteristic red emission of the Eu cluster in also retained in the polymeric material.