Realization of long-range magnetic order in surface-supported two-dimensional systems has been challenging, mainly due to the competition between fundamental magnetic interactions as the short-range Kondo effect and spin-stabilizing magnetic exchange interactions. Spin-bearing molecules on conducting substrates represent a rich platform to investigate the interplay of these fundamental magnetic interactions. Here we demonstrate the direct observation of long-range ferrimagnetic order emerging in a two-dimensional supramolecular Kondo lattice. The lattice consists of paramagnetic hexadeca-fluorinated iron phthalocyanine (FeFPc) and manganese phthalocyanine (MnPc) molecules co-assembled into a checkerboard pattern on single-crystalline Au(111) substrates. Remarkably, the remanent magnetic moments are oriented in the out-of-plane direction with significant contribution from orbital moments. First-principles calculations reveal that the FeFPc-MnPc antiferromagnetic nearest-neighbour coupling is mediated by the Ruderman–Kittel–Kasuya–Yosida exchange interaction via the Au substrate electronic states. Our findings suggest the use of molecular frameworks to engineer novel low-dimensional magnetically ordered materials and their application in molecular quantum devices.

The presence of an oxygen reconstruction on the Cu(001) surface results in the self-metalation of 5,10,15,20-tetraphenylporphyrin (2HTPP) below room temperature (at ~285 K), in contrast to 2HTPP on the bare Cu(001) substrate, where a temperature of ~450 K is required. This study demonstrates the decisive impact of a surface reconstruction on the redox reaction in the solvent-free ultra-high vacuum environment.

A bottom-up approach is introduced to fabricate two-dimensional self-assembled layers of molecular spin-systems containing Mn and Fe ions arranged in a chessboard lattice. We demonstrate that the Mn and Fe spin states can be reversibly operated by their selective response to coordination/decoordination of volatile ligands like ammonia (NH3).

The controlled manipulation of spin states in atoms/molecules is of profound interest towards the design of future spin-based devices. [1,2] A prominent example of how spin states are modified (S = 2$S = 0) can be found in natures Fe II porphyrin moiety within hemoglobin and its coordination with the O 2 ligand.[3] Recently, we have implemented this concept in a synthetic on-surface arrangement using metallo-porphyrins adsorbed on ferromagnetic surfaces. By axial coordination with an external NO ligand the induced magnetic moment in the (S = 1/2) Co II porphyrin has been switched-off. [4] These experiments depend on a characteristic property of paramagnetic metallo-porphyrins as well as phthalocyanines: their interfacial chemical interaction with the ferromagnetic surface ligand induces a magnetic moment stable up to room temperature. [4,5] Axial coordination can also be used to control the magnetic anisotropy [6] as well as the strength and sign of the exchange interaction.[4b]Controlling on-surface/interface spin systems [4, 5j,k, 6, 7] is a prerequisite for applications in organic spintronics [1] which makes this research field increasingly popular. Recently, we combined chemically directed self-assembly and coordination chemistry to obtain selectively switchable, highly ordered supramolecular 2D spin arrays.[5j] Concerning chemical control of the magnetic moment, only off-switching [4, 5j] and spintuning, [4b, 5k] that is, switching spin-on!spin-off and spin-on! spin-on' (a modified spin state) have been established. So far this set of on-surface chemical spin operations was incomplete since the spin-off!spin-on case was missing. Generally, switching the spin in organometallic complexes by external ligands to the on-state is more difficult to achieve than switching to the off-state, since chemical bonding has to overcome the spin-pairing energy. An additional complication arises from the possibility that the surface can modify the spin states before as well as after the axial ligation.[4b] This can also lead to spin-quenching on the surface. [4b, 8] Here we report on the first demonstration of an on-surface chemical spin onswitch, for Ni II porphyrins (S = 0) adsorbed on a ferromagnetic (FM) Co substrate, by the diamagnetic (S = 0) external NH 3 ligand. A schematic representation of this spin on-switch (S = 0$S = 1) is shown in Figure 1 a.To study this effect, Ni II tetraphenylporphyrin (NiTPP; see Figure 1 a) molecules were thermally sublimed in ultrahigh vacuum onto clean Co thin films on Cu(001) single crystals. [4, 5e,f,j] For a description of the methods see the Supporting Information.In scanning tunneling microscopy (STM) experiments (Figure 1 b), we consistently find the molecules adsorbed in a random fashion on Co and Ni substrates, [4, 5f] in contrast to self-assembly of NiTPP on Au and Ag substrates.[9a] Most of the NiTPP molecules on the Co surface can be recognized as rectangular shapes-the so-called saddle-shape conformation [9b] (Figure 1 c), whereas a minority of the molecules is obse...

ABSTRACT:The formation of on-surface coordination polymers is controlled by the interplay of chemical reactivity and structure of the building blocks, as well as by the orientating role of the substrate registry. Beyond the pre-determined patterns of structural assembly, the chemical reactivity of the reactants involved may provide alternative pathways in their aggregation. Organic molecules, which are transformed in a surface reaction, may be subsequently trapped via coordination of homo-or heterometal adatoms, which may also play a role in the molecular transformation itself. The amino-functionalized perylene derivative, 4,9-diaminoperylene-quinone-3,10-diimine (DPDI), undergoes specific levels of dehydrogenation (-1 H 2 or -3 H 2 ) depending on the nature of the present adatoms (Fe, Co, Ni or Cu, respectively). In this way, the molecule is converted to an endo-or an exo-ligand, possessing a concave or convex arrangement of ligating atoms, which is decisive for the formation of either 1D or 2D coordination polymers.

Condensation processes are of key importance in nature and play a fundamental role in chemistry and physics. Owing to size effects at the nanoscale, it is conceptually desired to experimentally probe the dependence of condensate structure on the number of constituents one by one. Here we present an approach to study a condensation process atom-by-atom with the scanning tunnelling microscope, which provides a direct real-space access with atomic precision to the aggregates formed in atomically defined ‘quantum boxes’. Our analysis reveals the subtle interplay of competing directional and nondirectional interactions in the emergence of structure and provides unprecedented input for the structural comparison with quantum mechanical models. This approach focuses on—but is not limited to—the model case of xenon condensation and goes significantly beyond the well-established statistical size analysis of clusters in atomic or molecular beams by mass spectrometry.

A 2D array of electronically coupled quantum boxes is fabricated by means of on-surface self-assembly assuring ultimate precision of each box. The quantum states embedded in the boxes are configured by adsorbates, whose occupancy is controlled with atomic precision. The electronic interbox coupling can be maintained or significantly reduced by proper arrangement of empty and filled boxes.

The controlled manipulation of spin states in atoms/molecules is of profound interest towards the design of future spin-based devices. [1,2] A prominent example of how spin states are modified (S = 2$S = 0) can be found in nature s Fe II porphyrin moiety within hemoglobin and its coordination with the O 2 ligand. [3] Recently, we have implemented this concept in a synthetic on-surface arrangement using metallo-porphyrins adsorbed on ferromagnetic surfaces. By axial coordination with an external NO ligand the induced magnetic moment in the (S = 1/2) Co II porphyrin has been switched-off. [4] These experiments depend on a characteristic property of paramagnetic metallo-porphyrins as well as phthalocyanines: their interfacial chemical interaction with the ferromagnetic surface ligand induces a magnetic moment stable up to room temperature. [4,5] Axial coordination can also be used to control the magnetic anisotropy [6] as well as the strength and sign of the exchange interaction. [4b] Controlling on-surface/interface spin systems [4, 5j,k, 6, 7] is a prerequisite for applications in organic spintronics [1] which makes this research field increasingly popular. Recently, we combined chemically directed self-assembly and coordination chemistry to obtain selectively switchable, highly ordered supramolecular 2D spin arrays. [5j] Concerning chemical control of the magnetic moment, only off-switching [4, 5j] and spintuning, [4b, 5k] that is, switching spin-on!spin-off and spin-on! spin-on' (a modified spin state) have been established. So far this set of on-surface chemical spin operations was incomplete since the spin-off!spin-on case was missing. Generally, switching the spin in organometallic complexes by external ligands to the on-state is more difficult to achieve than switching to the off-state, since chemical bonding has to overcome the spin-pairing energy. An additional complication arises from the possibility that the surface can modify the spin states before as well as after the axial ligation. [4b] This can also lead to spin-quenching on the surface. [4b, 8] Here we report on the first demonstration of an on-surface chemical spin onswitch, for Ni II porphyrins (S = 0) adsorbed on a ferromagnetic (FM) Co substrate, by the diamagnetic (S = 0) external NH 3 ligand. A schematic representation of this spin on-switch (S = 0$S = 1) is shown in Figure 1 a.To study this effect, Ni II tetraphenylporphyrin (NiTPP; see Figure 1 a) molecules were thermally sublimed in ultrahigh vacuum onto clean Co thin films on Cu(001) single crystals. [4, 5e,f,j] For a description of the methods see the Supporting Information.In scanning tunneling microscopy (STM) experiments (Figure 1 b), we consistently find the molecules adsorbed in a random fashion on Co and Ni substrates, [4, 5f] in contrast to self-assembly of NiTPP on Au and Ag substrates. [9a] Most of the NiTPP molecules on the Co surface can be recognized as rectangular shapes-the so-called saddle-shape conformation [9b] (Figure 1 c), whereas a minority of the molec...