Phosphorus-based ligand effects on the structure and radical scavenging ability of molecular nanoparticles of CeO.

Two new Ce/O clusters, (pyH)[CeO(OH)(OPPh)(NO)] (1) and [CeO(OH)(OPPh)(OCBu)] (2), have been prepared that contain P-based ligands for the first time. They were obtained from the reaction of (NH)[Ce(NO)], PhPOH or PhPOH, and BuCOH in a 2 : 1 : 2 molar ratio in pyridine/MeOH (10 : 1 mL). Both compounds contain a {CeO(OH)} face-capped octahedral core, with 1 containing an additional four Ce on the outside to give a supertetrahedral Ce topology; the {CeO} unit is the smallest recognizable fragment of the fluorite structure of CeO. The HO˙ radical scavenging activities of 1 and 2 were measured by UV/vis spectral monitoring of methylene blue oxidation by HO˙ radicals in the presence and absence of the Ce/O clusters, and the results compared with those for larger Ce and Ce molecular nanoparticles of CeO prepared in previous work. 1 and 2 are both very poor HO˙ radical scavengers compared with Ce and Ce, a result that is consistent with reports in the literature that PO ions inhibit the radical scavenging ability of traditional CeO nanoparticles and putatively assigned to PO binding to the surface.