Grafting Single Molecule Magnets on Gold Nanoparticles

Abstract

The chemical synthesis and characterization of the first hybrid material composed by gold nanoparticles and single molecule magnets (SMMs) are described. Gold nanoparticles are functionalized via ligand exchange using a tetrairon(III) SMM containing two 1,2-dithiolane end groups. The grafting is evidenced by the shift of the plasmon resonance peak recorded with a UV–vis spectrometer, by the suppression of nuclear magnetic resonance signals, by X-ray photoemission spectroscopy peaks, and by transmission electron microscopy images. The latter evidence the formation of aggregates of nanoparticles as a consequence of the cross-linking ability of Fe4 through the two 1,2-dithiolane rings located on opposite sides of the metal core. The presence of intact Fe4 molecules is directly proven by synchrotron-based X-ray absorption spectroscopy and X-ray magnetic circular dichroism spectroscopy, while a detailed magnetic characterization, obtained using electron paramagnetic resonance and alternating-current susceptibility, confirms the persistence of SMM behavior in this new hybrid nanostructure

Adding Remnant Magnetization and Anisotropic Exchange to Propeller‐like Single‐Molecule Magnets through Chemical Design

“…Best simulations21 of the spectra were obtained by using S =13/2, D =−0.318(4) cm −1 , E <0.006 cm −1 , g x,y =2.010(5) and g z =2.040(5), while no evident effect of the presence of the axial fourth‐order term could be found. It is evident that a residual contribution from traces of Fe 4 is present, clearly witnessed by a parallel transition at 1 kOe 7. 22 Notwithstanding this impurity, the obtained values confirm the easy axis nature and the very small rhombicity of the Fe 3 V system, in agreement with the close‐to‐axial symmetry of the molecule.…”

“…[5] In particular, homometallic iron(III) derivatives, despite the weak anisotropy introduced by high-spin d 5 ions, have led to the first observation of magnetic hysteresis from SMMs deposited on a conducting substrate such as a flat gold surface [6] or gold nanoparticles. [7] However, as the blocking of the magnetization in such molecules occurs below 1 K, experiments on tetrairon(III) systems are extremely demanding. Moreover, fast relaxation in zero field owing to tunneling of the magnetic moment prevents the observation of a significant remnant magnetization in randomly oriented samples.…”

“…Such systems attracted much attention because they exhibit a relatively large spin in the ground state even in the presence of antiferromagnetic interactions 5. In particular, homometallic iron(III) derivatives, despite the weak anisotropy introduced by high‐spin d 5 ions, have led to the first observation of magnetic hysteresis from SMMs deposited on a conducting substrate such as a flat gold surface6 or gold nanoparticles 7. However, as the blocking of the magnetization in such molecules occurs below 1 K, experiments on tetrairon(III) systems are extremely demanding.…”

Diamondoid Structure in a Metal–Organic Framework of Fe4 Single‐Molecule Magnets

“…To obtain independent information on magnetic anisotropy, we also recorded W‐band EPR spectra on microcrystalline powder of 2 at 40 K (Figure ). The spectrum shows the typical features observed in several Fe 4 compounds measured at this frequency . Of particular relevance for the determination of the axial zfs parameter D is the low‐field transition, assigned to the M S =−4→ M S =−3 resonance .…”

Proof of Principle: Immobilisation of Robust CuII3TbIII‐Macrocycles on Small, Suitably Pre‐functionalised Gold Nanoparticles

“…Moreover, characterising the magnetic properties of an SMM on a surface usually requires highly sensitive synchrotron‐based techniques because of the tiny quantities of sample present in a mono‐ or even multi‐layer. However, some of us reported that appropriately functionalised Fe 4 SMMs could be immobilised on monodisperse Au nanoparticles (NPs), and that the resulting hybrid material could be characterised by standard SQUID (superconducting quantum interference device) methods . Murugesu and co‐workers instead attached Dy 2 SMMs to “naked” gold NPs of a wide range of sizes (generated by laser ablation), then studied them by standard methods, revealing a more pronounced change in the magnetisation dynamics …”