Generating or even retaining slow magnetic relaxationin surfaceimmobilized single-molecule magnets (SMMs) from promising molecularprecursors remains a great challenge. Illustrative examples are organolanthanidecompounds that show promising SMM properties in molecular systems,though surface immobilization generally diminishes their magneticperformance. Here, we show how tailored Lewis acidic Al-(III) siteson a silica surface enable generation of a material with SMM characteristicsvia chemisorption of (Cp-ttt)(2)DyCl ((Cp-ttt)(-) = 1,2,4-tri-(tert-butyl)-cyclopentadienide).Detailed studies of this system and its diamagnetic Y analogue indicatethat the interaction of the metal chloride with surface Al sites resultsin a change of the coordination sphere around the metal center inducingfor the dysprosium-containing material slow magnetic relaxation upto 51 K with hysteresis up to 8 K and an effective energy barrier(U (eff)) of 449 cm(-1),the highest reported thus far for a supported SMM.