The Power of Molecular Chemistry in Nanoscale Materials Research
George Christou
Department of Chemistry, University of Florida, Gainesville, FL 32611, USA
Molecular chemistry brings many powerful advantages to the study of nanoscale materials of various kinds, and this area of ‘molecular nanoscience’ is therefore a rapidly growing field. The advantages include truly monodisperse (single-size) products and a monolayer shell of organic ligands that imparts solubility and crystallinity, allowing structural characterization of molecular crystals to atomic resolution by X-ray crystallography. The ligands can usually also be modified as desired, allowing tuning of redox properties and atom/isotope labelling (2H, 19F, etc.) for studies in the solid state and solution, such as NMR spectroscopy.
In the molecular nanomagnetism arena, these advantages have been absolutely crucial in the study of single-molecule magnets (SMMs), molecules that function as individual nanomagnets. They have greatly assisted the synthesis and study of numerous SMMs, and led to discovery of new quantum physics phenomena important to new 21st century technologies, such as quantum tunneling of the magnetization vector and quantum superposition/entanglement states. Giant (~4 nm) SMMs have also bridged the gap between the ‘top-down’ world of traditional magnetic nanoparticles and the ‘bottom-up’ world of molecular nanomagnets. We have also developed controlled ways to form supramolecular [Mn3]n oligomers of 2 or more linked Mn3 SMMs to study the resulting quantum properties introduced by the weak inter-SMM exchange coupling, such as exchange-biased QTM and quantum superposition states, including in solution for the first time.
More recently still, we have extended our molecular approach to the bottom-up synthesis of nanoscale pieces of important metal oxides, targeting molecular clusters whose metal-oxo core has the same structure as the bulk material, and which are thus ligand-stabilized fragments of the bulk materials – what we have named “molecular nanoparticles”. To date, we have been concentrating on CeO2, whose importance as a catalyst spans a wide range from industry to medicine, and the AMnO3 manganites (A = lanthanide or main group metal) with the perovskite structure, which include many ferromagnets, ferroelectrics and multiferroics important to various new applications.
A selection of these materials and studies will be described.