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Soft metalorganic grafting of periodic mesoporous silica (PMS) materials is introduced as a method for obtaining nanostructured GdIII‐loaded silica particles with relatively high 1H relaxivity. The silylamide complex Gd[N(SiHMe2)2]3(THF)2 was grafted onto MCM‐41, SBA‐15, and SBA‐1, thereby providing PMSs of distinct symmetry as well as pore size and configuration. The materials were characterized by infrared spectroscopy, elemental analysis, powder X‐ray diffraction (PXRD), N2 physisorption, and scanning as well as transmission electron microscopy (SEM/TEM). Relaxivities up to 15.8 mM–1 s–1 were determined at high magnetic field strength (400 MHz). The nuclear magnetic resonance dispersion (NMRD) data of a calcined Gd[N(SiHMe2)2]3(THF)2@SBA‐1 material had a shape typical for slow‐tumbling systems, with a maximum at approximately 50 MHz. Temperature‐dependence studies of the relaxivity (r1) indicated that the grafted materials were characterized by an efficient water exchange. To maintain a high relaxivity, a low (1 wt.‐%) GdIII loading and a hydrophilic surface had to be provided. Varying the topology of the silica support only resulted in small variations in r1 of the hybrid materials.

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