Abstracts Book - IMRC 2018

• SA6-O003
LIGAND-CONTROLLED MAGNETISM OF MONOLAYER-PROTECTED
GOLD NANOCLUSTERS
Mikhail Agrachev 1 , Sabrina Antonello 1 , Tiziano Dainese 1 , Marco Ruzzi 1 , Alfonso Venzo 2 , Alfonso
Zoleo 1 , Flavio Maran 1
1
Università degli Studi di Padova, Chemistry Department, Italy. 2 CNR, Chemistry Department,
Italy.
While bulk gold is widely known to be a diamagnetic material, several studies
showed that, by going to the nanoscale, a magnetic moment can appear.
However, the magnetic behaviour of gold nanoparticles is often not
reproducible and the origin of this behavior is still not fully understood. We used
a molecular approach to shed light on gold nanomagnetism, by using atomically
precise monolayer-protected gold clusters (MPCs) of controlled charge state. In
particular, we used Au25(SR)18 (SR = thiolated ligand) which shows distinct
molecular properties and is paramagnetic in its stable neutral form. Specifically,
we focused on the influence of ligands on the magnetic properties of this cluster.
By using a combined EPR/ENDOR/NMR/MD approach we showed that ligands
have a remarkable effect on the spin density distribution of isolated clusters (in
solution). This demonstrates that, to accurately describe the magnetic
properties of these systems, ligands must be necessarily taken into account. This
is in contrast with the common opinion that the magnetic moment is located
only in the metal core. The effect of the ligands is even more dramatic in the
solid state: we showed by EPR measurements and DFT calculations that, by
changing the length and type of the ligands, we can modulate the intercluster
exchange interactions and switch from ferromagnetism to antiferromagnetism.
Different magnetic orderings are associated to different crystallographic
orderings, as revealed by XRD: ferromagnetism is observed for 3D network
structures, while the formation of 1D polymeric chains of clusters gives rise to
antiferromagnetic couplings. In our opinion, these findings are of considerable
importance for possible applications in the fields of spintronics and magnetic
memories. Additionally, we investigated the properties of clusters supported on
TiO2 nanoparticles, in view of possible photocatalytic applications.
Keywords: gold nanoclusters, magnetism, EPR
Presenting authors email: mikhail.agrachev@studenti.unipd.it