Synthesis and magnetic properties of decamethylsamarocene composites of mesoporous niobium oxide

Abstract

Mesoporous niobium oxide with a pore size of 22 A was treated with excess decamethylsamarocene THF complex in THF to give a new mesoporous niobium oxide composite with a mixed oxidation state organosamarium phase in the pores. XRD and nitrogen adsorption studies confirmed that the mesostructure was retained on reduction of the framework, showing the decrease in surface area and pore volume expected as a result of occlusion of the pores by the organosamarium phase. Elemental analysis suggested that the structural integrity of the sandwich complex was largely retained upon intercalation, with a small amount of decomposition by loss of ligand. XPS studies confirmed the presence of the decamethylsamarocene THF complex and its corresponding cation. The Nb 3d region of the XPS spectrum exhibited 5/2, 3/2 emissions at a lower binding energy than the unreduced oxide, consistent with reduction to a state between Nb(V) and Nb(IV). The EPR spectrum showed a broad resonance at g = 2.00, indicative of free electrons in the walls of the mesoporous framework. Plots of magnetization versus temperature and magnetization versus field demonstrated that the material was paramagnetic, with a small contribution from a superparamagnetic phase, although no blocking temperature was observed. There was also evidence for spin glass behavior at low temperature, a phenomenon that is common in reduced samples of mesoporous transition metal oxides.