Abstract. Soft metal-organic grafting of periodic mesoporous silica (PMS) has recently been demonstrated to give gadolinium-loaded nanostructured hybrid materials with interesting 1 H relaxometric properties. Here, the sterically demanding alkoxide and aryloxide complexes, [Ln(OCH 2 CMe 3 ) 3 ] 4 and Ln(OC 6 H 3 tBu 2 -2,6) 3 (Ln = La, Gd), respectively, were grafted onto PMS materials MCM-41, SBA-15, and SBA-1. Support materials with distinct topology and pore diameters were utilized in order to direct the metal precursors towards the PMSs internal or external surfaces. All hybrid materials were examined by N 2 physisorption, Diffuse Reflectance Infrared Fourier Transform (DRIFT) and solid-state NMR spectroscopy, as well as elemental