Synthesis of picolinate-iron(III) compounds through an aqueous solution process

A novel picolinate-iron(III) compound, Fe(C6H4NO2)2(OH) (1), was synthesized from an aqueous solution of a picolinate-iron(II) complex. Compound 1 was obtained by a thermal treatment of the picolinate-iron complex aqueous solution, whose pH was adjusted to 3­7, containing more than twice molar picolinic acid (Hpa) to Fe at 353K for 72 h. When the iron aqueous solution in the presence of more than six times molar Hpa to Fe at pH 2­5 was heated, Fe(C6H4NO2)3·H2O (2) appeared. Millimeter-sized yellow-green single crystals of 2 could be obtained by the heat treatment of the picolinate-iron aqueous solution, whose pH was adjusted to 3, with Fe2+:Hpa = 1:10 at 373K for 72 h. Formation mechanism of 1 and 2 was also discussed through investigations of relationship between synthesis conditions and products. Our approach opens a promising new route for preparation of precursors for synthesis of high functional ceramics and development of new organic­inorganic hybrids.