Electronic Structure of Surface-supported Bis(phthalocyaninato) terbium(III) Single Molecular Magnets

Abstract

The electronic structure of isolated bis(phthalocyaninato) terbium(III) molecules, a novel single-molecular-magnet (SMM), supported on the Cu(111) surface has been characterized by density functional theory and scanning tunneling spectroscopy. These studies reveal that the interaction with the metal surface preserves both the molecular structure and the large spin magnetic moment of the metal center. The 4f electron states are not perturbed by the adsorption while a strong molecular/metal interaction can induce the suppression of the minor spin contribution delocalized over the molecular ligands. The calculations show that the inherent spin magnetic moment of the molecule is only weakly affected by the interaction with the surface and suggest that the SMM character might be preserved.The miniaturization of information storage devices drives the search for new nanoscale magnetic materials. Single molecular magnets (SMMs) formed by metal-organic complexes are very promising candidates as their large spin ground-state and large magnetic anisotropy are characteristics of each isolated molecule.1 Moreover, these systems provide a natural playground to explore magnetism at the nanoscale. Their future technological applications, such as quantum computing and high-density magnetic storage devices, are presently hampered by the difficulty of adsorbing SMMs onto surfaces and, quite importantly, by the lack of understanding on whether their magnetic properties are modified upon adsorption. In particular, the nonapplicability of conventional techniques, which allow an in-vacuum deposition, has so far hindered the systematic study of individual molecular magnets on surfaces. Solution-based deposition techniques including drop casting, 2,3 Langmuir-Blodgett, 4 microcontact printing, 5 covalent Au-S attaching, 6 and surface functionalization 7 have been successfully used to transfer molecules to surfaces but the magnetic properties of the adsorbed molecules have so far not been demonstrated. 3 This has tentatively been assigned to an induced local disorder caused by the used deposition techniques or by the coupling to the surface. 8 In this letter, we describe the structural, magnetic and electronic properties of a surface-supported SMM by combining scanning tunneling microscopy (STM) and spectroscopy (STS) with numerical simulations based on density functional theory (DFT). Topographic images and conductance maps of isolated SMM (namely bis(phthalocyaninato) terbium(III)) achieved at several energies confirm that the molecular structure is unchanged by the interaction with the surface. The Tb-4f electron states, which are responsible for the large magnetic moment of the molecular magnet, are little affected by molecular adsorption on the metal surface. Thus, it can be expected that the SMM character of the surface supported bis(phthalocyaninato) terbium(III) (abbreviated by TbPc2) molecules is preserved.TbPc2 molecules represent the first example of mononuclear metal complexes behaving as SMMs (i.e., showing large mag...

Real-space observation of spin-split molecular orbitals of adsorbed single-molecule magnets

“…The appearance of an eight-lobe structure is expected for both a neutral [TbPc2] 0 (with the ligand spin still present) as well as for a negatively charged [TbPc 2 ] − molecule (with the ligand spin quenched by the reduction with the additional electron) 16 . Therefore, spin-averaged measurements cannot distinguish between the charged and the neutral state of adsorbed TbPc 2 .…”

“…In neutral [TbPc 2 ] 0 , the highest occupied molecular orbital (HOMO), which is delocalized over both Pc rings 15 , is therefore just singly occupied. With spin-polarized scanning tunnelling microscopy (SP-STM), this ligand spin should be observable as follows: as the singly occupied molecular orbital of [TbPc 2 ] 0 is also the lowest unoccupied molecular orbital (LUMO) 16 , it should be visible both below as well as above the Fermi level. Because of the Pauli exclusion principle, these orbitals have opposite spin character (Fig.…”

Guided Molecular Assembly on a Locally Reactive 2D Material

“…This feature, which can also be discerned in Figure 1a, closely resembles the highest occupied π molecular orbital (π-HOMO) level of a Pc ligand as seen in DFT calculations of an isolated molecule. [19] STM images of weakly interacting Pc molecules on thin insulators [14,34] and the decoupled top Pc ligand of a double decker Pc molecule [35][36][37] also exhibit this same electronic structure.…”

Coadsorption of TbIII–Porphyrin Double-decker Single-molecule Magnets in a Porous Molecular Network: Toward Controlled Alignment of Single-molecule Magnets on a Carbon Surface

“…Because the surface-confined pores in the 2D porous molecular network are known to immobilize other molecules as guests, 13,14,19,2326 the surface periodicity and density of the SMM molecule can be controlled by its coadsorption in a porous molecular network. For this purpose, we chose alkoxylated dehydrobenzo [12]annulene (DBA) derivatives 2629 because these are reported to form porous networks at liquid/solid interfaces via alkyl chain interdigitation (van der Waals interactions) with adjacent molecules. One of the advantages of using DBA networks is their pore size tunability, according to which the pore diameter can be controlled from 1 to 7 nm (corner to corner distance) by the use of different alkyl chain lengths.…”