Near‐stoichiometric O 2 binding on metal centers in Co(salen) nanoparticles

Co(salen) [cobaltous bis(salicylaldehyde)ethylenediamine] complexes are well‐known O 2 carriers in solution. In the solid phase, these complexes exhibit some O 2 binding but detailed studies have been complicated because few of the known polymorphs of Co(salen) actually bind O 2 . The O 2 binding results for nanoparticulate Co(salen) are presented in this study. Rod‐shaped Co(salen) nanoparticles, roughly 100 nm in diameter, were recrystallized by spraying a methylene chloride solution of commercially obtained Co(salen) into supercritical carbon dioxide. Temperature‐programmed desorption, thermogravimetric analysis, and a Rubotherm magnetic suspension balance measurements reveal a reversible O 2 uptake of ∼1.51 mmol/(g nanoparticles) at 25°C, consistent with a binding stoichiometry involving a bridging peroxo unit between two Co centers. In contrast, no measurable O 2 uptake was observed with the commercial Co(salen). These results clearly show the potential for bottom‐up design of nanoparticulate metal complexes for enhanced O 2 storage and other applications. © 2009 American Institute of Chemical Engineers AIChE J, 2009