UHV Deposition and Characterization of a Mononuclear Iron(III) \u3b2-diketonate Complex on Au(111)

The adsorption of the sterically hindered \u3b2-diketonate complex Fe(dpm)3, where Hdpm = dipivaloylmethane, on Au(111) was investigated by ultraviolet photoelectron spectroscopy (UPS) and scanning tunnelling microscopy (STM). The high volatility of the molecule limited the growth of the film to a few monolayers. While UPS evidenced the presence of the \u3b2-diketonate ligands on the surface, the integrity of the molecule on the surface could not be assessed. The low temperature STM images were more informative and at submonolayer coverage they showed the presence of regular domains characterized by a flat morphology and height of 480.3 nm. Along with these domains, tetra-lobed features adsorbed on the kinks of the herringbone were also observed. DFT-simulated images of the pristine molecule and its possible decomposition products allowed to assess the partial fragmentation of Fe(dpm)3 upon adsorption on the Au(111) surface. Structural features with intact molecules were only observed for the saturation coverage. An ex situ prepared thick film of the complex was also investigated by X-ray magnetic circular dichroism (XMCD) and features typical of high-spin iron(III) in octahedral environment were observed

Unraveling the mechanism of the one-pot synthesis of exchange coupled Co-based nano-heterostructures with a high energy product

The development of reproducible protocols to synthesize hard/soft nano-heterostructures (NHSs) with tailored magnetic properties is a crucial step to define their potential application in a variety of technological areas. Thermal decomposition has proved to be an effective tool to prepare such systems, but it has been scarcely used so far for the synthesis of Co-based metal/ferrite NHSs, despite their intriguing physical properties. We found a new approach to prepare this kind of nanomaterial based on a simple one-pot thermal decomposition reaction of metal-oleate precursors in the high boiling solvent docosane. The obtained NHSs are characterized by the coexistence of Co metal and Co doped magnetite and are highly stable in an air atmosphere, thanks to the passivation of the metal with a very thin oxide layer. The investigation of the influence of the metal precursor composition (a mixed iron–cobalt oleate), of the ligands (oleic acid and sodium oleate) and of the reaction time on the chemical and structural characteristics of the final product, allowed us to rationalize the reaction pathway and to determine the role of each parameter. In particular, the use of sodium oleate is crucial to obtain a metal phase in the NHSs. In such a way, the one-pot approach proposed here allows the fine control of the synthesis, leading to the formation of stable, high performant, metal/ferrite NHSs with tailored magnetic properties. For instance, the room temperature maximum energy product was increased up to 19 kJ m−3 by tuning the Co content in the metal precursor.This work was supported by EU-H2020 AMPHIBIAN Project (no. 720853) and by European Union's Horizon 2020 research and innovation programme under grant agreement no. 823717-ESTEEM3.Peer reviewe

Structure, magnetic properties and thermal sublimation of fluorinated Fe4 Single-Molecule Magnets

Fluorinated tetrairon(III) Single-Molecule Magnets (SMMs) [Fe4(L1)2(dpmF6)6] (1dpmF6), [Fe4(L2)2(dpmF6)6] (2dpmF6), and [Fe4(L2)2(pta)6] (2pta) were assembled combining the tripodal ligands H3L1 = 2-hydroxymethyl-2-phenylpropane-1,3-diol and H3L2 = S-5-hydroxy-4,4-bis(hydroxymethyl)pentyl ethanethioate with fluorinated β-diketones analogues of dipivaloylmethane (Hdpm), namely 1,1,1-trifluoro-2,6,6-trimethyl-2-(trifluoromethyl)heptane-3,5-dione (HdpmF6) and pivaloyltrifluoroacetone (Hpta). The new compounds, along with [Fe4(L1)2(dpm)6] (1dpm) and [Fe4(L1)2(pta)6] (1pta), were designed in order to investigate the effect of fluorination degree on processability by thermal sublimation. The two different functional groups on the tripodal ligands, i.e. C6H5 in H3L1 and (CH2)3SAc in H3L2, are suitable for promoting physisorption and chemisorption on surfaces, respectively. Direct current magnetic data are typical for the metal-centred triangular topology of Fe4 complexes, with antiferromagnetic nearest-neighbour coupling constants in the range 16–18 cm−1 and an S = 5 ground spin state. Alternating current susceptibility measurements showed that slow magnetic relaxation persists in fluorinated compounds. When heated in high vacuum (10−7 mbar), 2dpmF6 and 2pta undergo thermal decomposition before subliming, while 1dpmF6 was found to sublimate at 497 ± 5 K in the same conditions, being the third sublimable SMM of this family after 1pta (440 ± 5 K) and 1dpm (500 ± 10 K)

Thermal and light-induced spin transition in a nanometric film of a new high-vacuum processable spin crossover complex

Spin crossover complexes are among the most studied classes of molecular switches and have attracted considerable attention for their potential technological use as active units in new multifunctional devices. A fundamental step towards a practical implementation is their effective processability into thin films. Crucially, the physical property of technological interest shown by these materials in the bulk phase has to be retained once they are deposited on a solid surface. These conditions are not easily satisfied by most of the intrinsically fragile coordination compounds, either because the material processing methods can compromise their molecular structure, or the interaction between the molecule and the surface can induce drastic changes in the resulting properties. Herein, we report the identification of a novel high-vacuum processable spin-crossover complex, [Fe(qnal)2] (qnal = quinoline-naphthaldehyde), and the preparation of a 50 nm sublimated film of this molecular switch on gold. X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) were used to investigate the composition and the temperature- and light-induced spin-crossover of the deposited material, providing full evidence of the capability of this molecular system to be efficiently processed into nanometric films with retention of its switchable magnetic properties.Initiative d'excellence de l'Université de BordeauxMOLSPIN COS

Valence electronic structure of sublimated Fe4 single-molecule magnets: An experimental and theoretical characterization

The valence electronic structures of two single-molecule magnets (SMMs), [Fe4(L)2(dpm)6] and [Fe4(L)2(pta)6], (Hdpm = dipivaloylmethane, Hpta = pivaloyltrifluoroacetone, L3- = Ph\u2013C(CH2O)33-), are investigated by means of ultraviolet photoemission spectroscopy (UPS) and ab initio calculations. The experimental UPS spectra of both compounds are analysed and compared with the total density of states (TDOS) computed with the hybrid functional PBE0. The substitution of half of the methyl groups in [Fe4(L)2(dpm)6] with fluorine atoms in [Fe4(L)2(pta)6] unexpectedly affects the spectrum shape in the Fermi region, thus becoming a useful fingerprint of the two SMMs. Moreover, a computational protocol at DFT + U level of theory is assessed on both compounds, which is in good agreement with the experimental spectroscopic and magnetic data. The basis for the future modelling of the adsorption of Fe4 clusters on surfaces is established