Methods are provided for the generation of nanostructures suitable for use in magnetic resonance imaging where the nanostructures have at least one dimension of about 2 nm or less. In particular, the methods comprise the selective use of incubation temperatures that result in the controlled removal of ligands from metallic cores to which they are attached, allowing the metallic cores or the precursor moieties to unite to form nanostructures of defined and predictable shapes, but having at least one dimension significantly less that at least one other dimension. Accordingly, the nanostructures of the disclosure may be ultrathin sheets, rods, whiskers and the like, or even structures that are thin and porous resembling rice grains. The temperatures useful in the methods of the disclosure are less than 300° C. and allow for progressive elevation of the incubation temperature. The methods are especially advantageous for synthesizing nanoparticles that may be administered to an animal or human subject for imaging with magnetic resonance. Accordingly, the nanostructures of the disclosure comprise a metallic core, most typically, but not necessarily limited to, a ferrite moiety that can be a ferrous or ferric ion alone or in combination with other metallic elements. However, the methods of the disclosure are also suitable for generating nanostructures with non-ferrous cores such as magnesium or manganese cores.
