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We report on the adsorption and self-metalation of a prototypic tetrapyrrole compound, the free-base porphine (2H-P), on the Cu(111) surface. Our multitechnique study combines scanning tunneling microscopy (STM) results with near-edge X-ray absorption fine-structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) data whose interpretation is supported by density functional theory calculations. In the first layer in contact with the copper substrate the molecules adsorb coplanar with the surface as shown by angle-resolved NEXAFS measurements. The quenching of the first resonance in the magic angle spectra of both carbon and nitrogen regions indicates a substantial electron transfer from the substrate to the LUMO of the molecule. The stepwise annealing of a bilayer of 2H-P molecules sequentially transforms the XP and NEXAFS signatures of the nitrogen regions into those indicative of the coordinated nitrogen species of the metalated copper porphine (Cu-P), i.e., we observe a temperature-induced self-metalation of the system. Pre- and post-metalation species are clearly discriminable by STM, corroborating the spectroscopic results. Similar to the free-base porphine, the Cu-P adsorbs flat in the first layer without distortion of the macrocycle. Additionally, the electron transfer from the copper surface to the molecule is preserved upon metalation. This behavior contrasts the self-metalation of tetraphenylporphyrin (2H-TPP) on Cu(111), where both the molecular conformation and the interaction with the substrate are strongly affected by the metalation process. [ABSTRACT FROM AUTHOR]

Kagome lattices have attracted much attention due the very interesting properties they can exhibit, both from the electronic and the magnetic points of view, although much of the experimental studies have been reported on 3D metals or 2D nanosheets. In the past few years, on‐surface synthesis has allowed the fabrication of strictly monolayer 2D metal‐organic networks, many of them containing transition metals. In this paper we report the fabrication and the study of the electronic and magnetic properties of a monolayer 2D metal‐organic network where the nodes are lanthanide atoms forming a kagome lattice. [ABSTRACT FROM AUTHOR]

Efficient catalytic water splitting demands advanced catalysts to improve the slow kinetics of the oxygen evolution reaction (OER). Earth-abundant transition metal oxides show promising OER activity in alkaline media. However, most experimental information available is either from post-mortem studies or in-situ space-averaged X-ray techniques in the micrometer range. Therefore, the composition of the active centers under operando conditions is still under debate. In this work, we combine nanoscopic and spectroscopic measurements on the hydroxylation of molecular beam epitaxy (MBE)-prepared Ni and NiFe oxides nanoislands with operando local investigations of Ni and NiFe hydroxide electrocatalysts under OER conditions to reveal the nature of the active centers in 2D OER catalysts. Our results reveal that Fe doping increases the active surface area by island fragmentation, and boosts the intrinsic activity by creating optimized active centers consisting of both Ni and Fe atoms. In addition, our findings show that operando characterization at the nanoscale is crucial to reveal the dynamic nature of the interface of 2D catalysts under reaction conditions., (© 2025 Wiley‐VCH GmbH.)

The synthesis of porphyrinoid-based low-dimensional polymers has recently attracted considerable interest in view of their intriguing electronic, optical, and catalytic properties. Here, this is introduced by the surface-assisted synthesis of two carbaporphyrinoid-based polymers of increasing dimensionality under ultrahigh-vacuum conditions. The structural and electronic characterization of the resulting polymers has been performed by scanning tunneling and non-contact atomic force microscopies, complemented by theoretical modeling. First, a carbon-carbon coupling between dicarbahemiporphyrazine precursors is achieved by thermal activation of their isopropyl substituents via a [3+3] cycloaromatization, giving rise to one-dimensional (1D) polymers. Second, the same precursor is functionalized with chlorine atoms to complement the [3+3] cycloaromatization with orthogonal dehalogenation and homocoupling, affording two-dimensional (2D) molecular nanostructures. In addition, both low-dimensional free-base porphyrinoid-based polymers are exposed to an atomic flux of cobalt atoms, giving rise to cobalt-metalated macrocycles, with the metal atoms coordinated only to the two pyrrolic nitrogens, in contrast to the typical four-fold coordination that occurs inside tetrapyrroles. This on-surface protocol renders atomically precise covalently-linked porphyrinoid polymers and provides promising model systems toward the exploration of low-coordinated metals with utility in diverse technological areas., (© 2024 Wiley‐VCH GmbH.)

π-Electron magnetic compounds on surfaces have emerged as a powerful platform to interrogate spin interactions at the atomic scale, with great potential in spintronics and quantum technologies. A key challenge is organizing these compounds over large length scales, while elucidating their resulting magnetic properties. Herein, we offer a relevant contribution toward this objective, which consists of using on-surface synthesis coupled with coordination chemistry to promote the self-assembly of π-electron magnetic porphyrin species. A porphyrin precursor equipped with carbonitrile moieties in a trans arrangement was prepared by solution synthesis and deposited on Au(111)/mica. Depending on the specific growth protocol, surface-promoted reactions led to the transformation of the precursor into non-magnetic Au-CN coordinated porphyrin monomers, covalent porphyrin dimers, and one-dimensional porphyrin polymers (based on porphyrin monomers or covalent porphyrin dimers), as revealed by scanning probe microscopy studies combined with theoretical calculations. Interestingly, the scanning tunneling microscopy tip could convert such closed-shell porphyrin units into open-shell species by the removal of some peripheral hydrogen atoms. The magnetic features (i.e., singlet or triplet ground state) of the porphyrin units comprising the polymers were investigated for polymers of different lengths. No magnetic exchange coupling between adjacent units was observed, suggesting protection of the magnetic entities., (© 2024 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Realization of topological quantum states in carbon nanostructures has recently emerged as a promising platform for hosting highly coherent and controllable quantum dot spin qubits. However, their adjustable manipulation remains elusive. Here, we report the atomically accurate control of the hybridization level of topologically protected quantum edge states emerging from topological interfaces in bottom-up-fabricated π-conjugated polymers. Our investigation employed a combination of low-temperature scanning tunneling microscopy and spectroscopy, along with high-resolution atomic force microscopy, to effectively modify the hybridization level of neighboring edge states by the selective dehydrogenation reaction of molecular units in a pentacene-based polymer and demonstrate their reversible character. Density functional theory, tight binding, and complete active space calculations for the Hubbard model were employed to support our findings, revealing that the extent of orbital overlap between the topological edge states can be finely tuned based on the geometry and electronic bandgap of the interconnecting region. These results demonstrate the utility of topological edge states as components for designing complex quantum arrangements for advanced electronic devices.

The design of novel low-dimensional carbon materials is at the forefront of modern chemistry. Recently, on-surface covalent synthesis has emerged as a powerful strategy to synthesize previously precluded compounds and polymers. Here, we report a scanning probe microscopy study, complemented by theoretical calculations, on the sequential skeletal rearrangement of sumanene-based precursors into a coronene-based organometallic network by stepwise intra- and inter-molecular reactions on Au(111). Interestingly, upon higher annealing, the formed organometallic networks evolve into two-dimensional coronene-based covalently linked patches through intermolecular homocoupling reactions. A new reaction mechanism is proposed based on the role of C-Au-C motifs to promote two stepwise carbon-carbon couplings to form cyclobutadiene bridges. Our results pave avenues for the conversion of molecular precursors on surfaces, affording the design of unexplored two-dimensional organometallic and covalent materials., (© 2024 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The design of innovative carbon-based nanostructures stands at the forefront of both chemistry and materials science. In this context, π-conjugated compounds are of great interest due to their impact in a variety of fields, including optoelectronics, spintronics, energy storage, sensing and catalysis. Despite extensive research efforts, substantial knowledge gaps persist in the synthesis and characterization of new π-conjugated compounds with potential implications for science and technology. On-surface synthesis has emerged as a powerful discipline to overcome limitations associated with conventional solution chemistry methods, offering advanced tools to characterize the resulting nanomaterials. This review specifically highlights recent achievements in the utilization of molecular precursors incorporating carbon geminal (gem)-polyhalides as functional groups to guide the formation of π-conjugated 0D species, as well as 1D, quasi-1D π-conjugated polymers, and 2D nanoarchitectures. By delving into reaction pathways, novel structural designs, and the electronic, magnetic, and topological features of the resulting products, the review provides fundamental insights for a new generation of π-conjugated materials., (© 2024 Wiley‐VCH GmbH.)

The synthesis of lanthanide-based organometallic sandwich compounds is very appealing regarding their potential for single-molecule magnetism. Here, it is exploited by on-surface synthesis to design unprecedented lanthanide-directed organometallic sandwich complexes on Au(111). The reported compounds consist of Dy or Er atoms sandwiched between partially deprotonated hexahydroxybenzene molecules, thus introducing a distinct family of homoleptic organometallic sandwiches based on six-membered ring ligands. Their structural, electronic, and magnetic properties are investigated by scanning tunneling microscopy and spectroscopy, X-ray absorption spectroscopy, X-ray linear and circular magnetic dichroism, and X-ray photoelectron spectroscopy, complemented by density functional theory-based calculations. Both lanthanide complexes self-assemble in close-packed islands featuring a hexagonal lattice. It is unveiled that, despite exhibiting analogous self-assembly, the erbium-based species is magnetically isotropic, whereas the dysprosium-based compound features an in-plane magnetization., (© 2024 The Authors. Advanced Science published by Wiley‐VCH GmbH.)

Antiferromagnetic spintronics is a rapidly emerging field with the potential to revolutionize the way information is stored and processed. One of the key challenges in this field is the development of novel 2D antiferromagnetic materials. In this paper, the first on-surface synthesis of a Co-directed metal-organic network is reported in which the Co atoms are strongly antiferromagnetically coupled, while featuring a perpendicular magnetic anisotropy. This material is a promising candidate for future antiferromagnetic spintronic devices, as it combines the advantages of 2D and metal-organic chemistry with strong antiferromagnetic order and perpendicular magnetic anisotropy., (© 2023 The Authors. Small published by Wiley‐VCH GmbH.)

The incorporation of non-benzenoid motifs in graphene nanostructures significantly impacts their properties, making them attractive for applications in carbon-based electronics. However, understanding how specific non-benzenoid structures influence their properties remains limited, and further investigations are needed to fully comprehend their implications. Here, we report an on-surface synthetic strategy toward fabricating non-benzenoid nanographenes containing different combinations of pentagonal and heptagonal rings. Their structure and electronic properties were investigated via scanning tunneling microscopy and spectroscopy, complemented by computational investigations. After thermal activation of the precursor P on the Au(111) surface, we detected two major nanographene products. Nanographene A a-a embeds two azulene units formed through oxidative ring-closure of methyl substituents, while A a-s contains one azulene unit and one Stone-Wales defect, formed by the combination of oxidative ring-closure and skeletal ring-rearrangement reactions. A a-a exhibits an antiferromagnetic ground state with the highest magnetic exchange coupling reported up to date for a non-benzenoid containing nanographene, coexisting with side-products with closed shell configurations resulted from the combination of ring-closure and ring-rearragement reactions (B a-a , B a-s , B s-a and B s-s ). Our results provide insights into the single gold atom assisted synthesis of novel NGs containing non-benzenoid motifs and their tailored electronic/magnetic properties., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Non-benzenoid non-alternant nanographenes (NGs) have attracted increasing attention on account of their distinct electronic and structural features in comparison to their isomeric benzenoid counterparts. In this work, we present a series of unprecedented azulene-embedded NGs on Au(111) during the attempted synthesis of cyclohepta[def]fluorene-based high-spin non-Kekulé structure. Comprehensive scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM) evidence the structures and conformations of these unexpected products. The dynamics of the precursor bearing 9-(2,6-dimethylphenyl)anthracene and dihydro-dibenzo-cyclohepta[def]fluorene units and its reaction products on the surface are analyzed by density functional theory (DFT) and molecular dynamics (MD) simulations. Our study sheds light on the fundamental understanding of precursor design for the fabrication of π-extended non-benzenoid NGs on a metal surface., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Despite their great potential as molecular building blocks for organic synthesis, tetrabromo- p -quinodimethanes (TBQs) are a relatively unknown family of compounds. Herein, we showcase a series of five derivatives incorporating two tetrabromo-anthraquinodimethane (TBAQ) units linked by π-conjugated spacers of different nature and length. The resulting dimers TBQ1-5 are fully characterised by means of thorough spectroscopic measurements and theoretical calculations. Interestingly, owing to the steric hindrance imposed by the four bulky bromine atoms, the TBAQ fragments adopt a characteristically warped geometry, somehow resemblant of a butterfly, and the novel dimers show a complex NMR pattern with signal splittings. To ascertain whether dynamic processes regarding fluxional inversion of the butterfly configurations are involved, first-principles calculations assessing the interconversion energy barriers are performed. Three possible stereoisomers are predicted involving two diastereomers, thus accounting for the observed NMR spectra. The rotational freedom of the TBAQ units around the π-conjugated linker influences the structural and electronic properties of TBQ1-5 and modulates the electronic communication between the terminal TBAQ moieties. The role of the linker on the electronic properties is investigated by Raman and UV-vis spectroscopies, theoretical calculations and UV-vis measurements at low temperature. TBQ1-5 are of interest as less-explored structural building precursors for a variety of scientific areas. Finally, the sublimation, self-assembly and reactivity on Au(111) of TBQ3 is assessed., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

The synthesis of two-dimensional metal-organic networks (2D-MOCNs) on solid substrates is a rapidly growing field of research due to their potential applications in gas sensing, catalysis, energy storage, spintronics, and quantum information. In addition, the possibility of using lanthanides as coordination nodes makes them a very straightforward alternative to create an ordered array of magnetic atoms on a surface, thus paving the way for their use in information storage at the single-atom level. This feature article reviews the strategies to design two-dimensional periodic nanoarchitectures comprising lanthanide atoms in ultra-high vacuum (UHV) environment, focusing on lanthanide-directed 2D-MOCNs on metal surfaces and decoupling substrates. The characterization of their structure, electronic, and magnetic properties is also discussed, including the use of state-of-the-art scanning probe microscopies and photoelectron spectroscopies, complemented by density functional theory calculations and multiplet simulations.

The design of a well-ordered arrangement of atoms on a solid surface has long been sought due to the envisioned applications in many different fields. On-surface synthesis of metal-organic networks is one of the most promising fabrication techniques. Hierarchical growth, which involves coordinative schemes with weaker interactions, favours the formation of extended areas with the desired complex structure. However, the control of such hierarchical growth is in its infancy, particularly for lanthanide-based architectures. Here the hierarchical growth of a Dy-based supramolecular nanoarchitecture on Au(111) is described. Such an assembly is based on a first hierarchical level of metallo-supramolecular motifs, which in a second level of hierarchy self-assemble through directional hydrogen bonds, giving rise to a periodic two-dimensional supramolecular porous network. Notably, the size of the metal-organic based tecton of the first level of hierarchy can be tailored by modifying the metal-ligand stoichiometric ratio., (© 2023 Wiley-VCH GmbH.)

The coordination of lanthanides atoms in two-dimensional surface-confined metal-organic networks is a promising path to achieve an ordered array of single atom magnets. These networks are highly versatile with plenty of combinations of molecular linkers and metallic atoms. Notably, with an appropriate choice of molecules and lanthanide atoms it should be feasible to tailor the orientation and intensity of the magnetic anisotropy. However, up to now only tilted and almost in-plane easy axis of magnetizations were reported in lanthanide-based architectures. Here we introduce an Er-directed two-dimensional metallosupramolecular network on Cu(111) featuring strong out-of-plane magnetic anisotropy. Our results will contribute to pave avenues for the use of lanthanides in potential applications in nanomagnetism and spintronics.

The design of open-shell carbon-based nanomaterials is at the vanguard of materials science, steered by their beneficial magnetic properties like weaker spin-orbit coupling than that of transition metal atoms and larger spin delocalization, which are of potential relevance for future spintronics and quantum technologies. A key parameter in magnetic materials is the magnetic exchange coupling (MEC) between unpaired spins, which should be large enough to allow device operation at practical temperatures. In this work, we theoretically and experimentally explore three distinct families of nanographenes (NGs) ( A , B , and C ) featuring majority zigzag peripheries. Through many-body calculations, we identify a transition from a closed-shell ground state to an open-shell ground state upon an increase of the molecular size. Our predictions indicate that the largest MEC for open-shell NGs occurs in proximity to the transition between closed-shell and open-shell states. Such predictions are corroborated by the on-surface syntheses and structural, electronic, and magnetic characterizations of three NGs ( A[3,5] , B[4,5] , and C[4,3] ), which are the smallest open-shell systems in their respective chemical families and are thus located the closest to the transition boundary. Notably, two of the NGs ( B[4,5] and C[4,3] ) feature record values of MEC (close to 200 meV) measured on the Au(111) surface. Our strategy for maximizing the MEC provides perspectives for designing carbon nanomaterials with robust magnetic ground states.

Nanocars are carbon-based single-molecules with a precise design that facilitates their atomic-scale control on a surface. The rational design of these molecules is important in atomic and molecular-scale manipulation to advance the development of molecular machines, as well as for a better understanding of self-assembly, diffusion and desorption processes. Here, we introduce the molecular design and construction of a collection of minimalistic nanocars. They feature an anthracene chassis and four benzene derivatives as wheels. After sublimation and adsorption on an Au(111) surface, we show controlled and fast manipulation of the nanocars along the surface using the tip of a scanning tunneling microscope (STM). The mechanism behind the successful displacement is the induced dipole created over the nanocar by the STM tip. We utilized carbon monoxide functionalized tips both to avoid decomposition and accidentally picking the nanocars up during the manipulation. This strategy allowed thousands of maneuvers to successfully win the Nanocar Race II championship., (© 2022 Wiley-VCH GmbH.)

The design of antiferromagnetic nanomaterials preserving large orbital magnetic moments is important to protect their functionalities against magnetic perturbations. Here, we exploit an archetype H 6 HOTP species for conductive metal-organic frameworks to design a Co-HOTP one-atom-thick metal-organic architecture on a Au(111) surface. Our multidisciplinary scanning probe microscopy, X-ray absorption spectroscopy, X-ray linear dichroism, and X-ray magnetic circular dichroism study, combined with density functional theory simulations, reveals the formation of a unique network design based on threefold Co +2 coordination with deprotonated ligands, which displays a large orbital magnetic moment with an orbital to effective spin moment ratio of 0.8, an in-plane easy axis of magnetization, and large magnetic anisotropy. Our simulations suggest an antiferromagnetic ground state, which is compatible with the experimental findings. Such a Co-HOTP metal-organic network exemplifies how on-surface chemistry can enable the design of field-robust antiferromagnetic materials.

The synthesis of novel polymeric materials with porphyrinoid compounds as key components of the repeating units attracts widespread interest from several scientific fields in view of their extraordinary variety of functional properties with potential applications in a wide range of highly significant technologies. The vast majority of such polymers present a closed-shell ground state, and, only recently, as the result of improved synthetic strategies, the engineering of open-shell porphyrinoid polymers with spin delocalization along the conjugation length has been achieved. Here, we present a combined strategy toward the fabrication of one-dimensional porphyrinoid-based polymers homocoupled via surface-catalyzed [3 + 3] cycloaromatization of isopropyl substituents on Au(111). Scanning tunneling microscopy and noncontact atomic force microscopy describe the thermal-activated intra- and intermolecular oxidative ring closure reactions as well as the controlled tip-induced hydrogen dissociation from the porphyrinoid units. In addition, scanning tunneling spectroscopy measurements, complemented by computational investigations, reveal the open-shell character, that is, the antiferromagnetic singlet ground state ( S = 0) of the formed polymers, characterized by singlet-triplet inelastic excitations observed between spins of adjacent porphyrinoid units. Our approach sheds light on the crucial relevance of the π-conjugation in the correlations between spins, while expanding the on-surface synthesis toolbox and opening avenues toward the synthesis of innovative functional nanomaterials with prospects in carbon-based spintronics.

On-surface synthesis has recently emerged as a powerful strategy to design conjugated polymers previously precluded in conventional solution chemistry. Here, an N-containing pentacene-based precursor (tetraazapentacene) is ex-professo synthesized endowed with terminal dibromomethylene (:CBr 2 ) groups to steer homocoupling via dehalogenation on metallic supports. Combined scanning probe microscopy investigations complemented by theoretical calculations reveal how the substrate selection drives different reaction mechanisms. On Ag(111) the dissociation of bromine atoms at room temperature triggers the homocoupling of tetraazapentacene units together with the binding of silver adatoms to the nitrogen atoms of the monomers giving rise to a N-containing conjugated coordination polymer (P1). Subsequently, P1 undergoes ladderization at 200 °C, affording a pyrrolopyrrole-bridged conjugated polymer (P2). On Au(111) the formation of the intermediate polymer P1 is not observed and, instead, after annealing at 100 °C, the conjugated ladder polymer P2 is obtained, revealing the crucial role of metal adatoms on Ag(111) as compared to Au(111). Finally, on Ag(100) the loss of :CBr2 groups affords the formation of tetraazapentacene monomers, which coexist with polymer P1. Our results contribute to introduce protocols for the synthesis of N-containing conjugated polymers, illustrating the selective role of the metallic support in the underlying reaction mechanisms., (© 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.)

The synthesis of long n-peri-acenes (n-PAs) is challenging as a result of their inherent open-shell radical character, which arises from the presence of parallel zigzag edges beyond a certain n value. They are considered as π-electron model systems to study magnetism in graphene nanostructures; being potential candidates in the fabrication of optoelectronic and spintronic devices. Here, we report the on-surface formation of the largest pristine member of the n-PA family, i.e. peri-heptacene (n=7, 7-PA), obtained on an Au(111) substrate under ultra-high vacuum conditions. Our high-resolution scanning tunneling microscopy investigations, complemented by theoretical simulations, provide insight into the chemical structure of this previously elusive compound. In addition, scanning tunneling spectroscopy reveals the antiferromagnetic open-shell singlet ground state of 7-PA, exhibiting singlet-triplet spin-flip inelastic excitations with an effective exchange coupling (J eff ) of 49 meV., (© 2022 Wiley-VCH GmbH.)

The design of lanthanide multinuclear networks is an emerging field of research due to the potential of such materials for nanomagnetism, spintronics, and quantum information. Therefore, controlling their electronic and magnetic properties is of paramount importance to tailor the envisioned functionalities. In this work, a multidisciplinary study is presented combining scanning tunneling microscopy, scanning tunneling spectroscopy, X-ray absorption spectroscopy, X-ray linear dichroism, X-ray magnetic circular dichroism, density functional theory, and multiplet calculations, about the supramolecular assembly, electronic and magnetic properties of periodic dinuclear 2D networks based on lanthanide-pyridyl interactions on Au(111). Er- and Dy-directed assemblies feature identical structural architectures stabilized by metal-organic coordination. Notably, despite exhibiting the same +3 oxidation state, there is a shift of the energy level alignment of the unoccupied molecular orbitals between Er- and Dy-directed networks. In addition, there is a reorientation of the easy axis of magnetization and an increment of the magnetic anisotropy when the metallic center is changed from Er to Dy. Thus, the results show that it is feasible to tune the energy level alignment and magnetic anisotropy of a lanthanide-based metal-organic architecture by metal exchange, while preserving the network design., (© 2022 The Authors. Small published by Wiley-VCH GmbH.)

The combination of a reducible transition metal oxide and a noble metal such as Pt often leads to active low-temperature catalysts for the preferential oxidation of CO in excess H 2 gas (PROX reaction). While CO oxidation has been investigated for such systems in model studies, the added influence of hydrogen gas, representative of PROX, remains less explored. Herein, we use ambient pressure scanning tunneling microscopy and ambient pressure X-ray photoelectron spectroscopy on a CoO x /Pt(111) planar model catalyst to analyze the active phase and the adsorbed species at the CoO x /Pt(111) interface under atmospheres of CO and O 2 with a varying partial pressure of H 2 gas. By following the evolution of the Co oxidation state as the catalyst is brought to a reaction temperature of above 150 °C, we determine that the active state is characterized by the transformation from planar CoO with Co in the 2+ state to a mixed Co 2+ /Co 3+ phase at the temperature where CO 2 production is first observed. Furthermore, our spectroscopy observations of the surface species suggest a reaction pathway for CO oxidation, proceeding from CO exclusively adsorbed on Co 2+ sites reacting with the lattice O from the oxide. Under steady state CO oxidation conditions (CO/O 2 ), the mixed oxide phase is replenished from oxygen incorporating into cobalt oxide nanoislands. In CO/O 2 /H 2 , however, the onset of the active Co 2+ /Co 3+ phase formation is surprisingly sensitive to the H 2 pressure, which we explain by the formation of several possible hydroxylated intermediate phases that expose both Co 2+ and Co 3+ . This variation, however, has no influence on the temperature where CO oxidation is observed. Our study points to the general importance of a dynamic reducibility window of cobalt oxide, which is influenced by hydroxylation, and the bonding strength of CO to the reduced oxide phase as important parameters for the activity of the system.

First-row transition metal oxides are promising materials for catalyzing the oxygen evolution reaction. Surface sensitive techniques provide a unique perspective allowing the study of the structure, adsorption sites, and reactivity of catalysts at the atomic scale, which furnishes rationalization and improves the design of highly efficient catalytic materials. Here, a scanning probe microscopy study complemented by density functional theory on the structural and electronic properties of CoO nanoislands grown on Au(111) is reported. Two distinct phases are observed: The most extended displays a Moiré pattern (α-region), while the less abundant is 1Co:1Au coincidental (β-region). As a result of the surface registry, in the β-region the oxide adlayer is compressed by 9%, increasing the unoccupied local density of states and enhancing the selective water adsorption at low temperature through a cobalt inversion mechanism. Tip-induced voltage pulses irreversibly transform α- into β-regions, thus opening avenues to modify the structure and reactivity of transition metal oxides by external stimuli like electric fields., (© 2022 Wiley-VCH GmbH.)

The synthesis of nanographenes (NGs) with open-shell ground states have recently attained increasing attention in view of their interesting physicochemical properties and great prospects in manifold applications as suitable materials within the rising field of carbon-based magnetism. A potential route to induce magnetism in NGs is the introduction of structural defects, for instance non-benzenoid rings, in their honeycomb lattice. Here, we report the on-surface synthesis of three open-shell non-benzenoid NGs ( A 1 , A 2 and A 3 ) on the Au(111) surface. A 1 and A 2 contain two five- and one seven-membered rings within their benzenoid backbone, while A 3 incorporates one five-membered ring. Their structures and electronic properties have been investigated by means of scanning tunneling microscopy, noncontact atomic force microscopy and scanning tunneling spectroscopy complemented with theoretical calculations. Our results provide access to open-shell NGs with a combination of non-benzenoid topologies previously precluded by conventional synthetic procedures.

The atomically precise control over the size, shape and structure of nanographenes (NGs) or the introduction of heteroatom dopants into their sp 2 -carbon lattice confer them valuable electronic, optical and magnetic properties. Herein, we report on the design and synthesis of a hexabenzocoronene derivative embedded with graphitic nitrogen in its honeycomb lattice, achieved via on-surface assisted cyclodehydrogenation on the Au(111) surface. Combined scanning tunnelling microscopy/spectroscopy and non-contact atomic force microscopy investigations unveil the chemical and electronic structures of the obtained dicationic NG. Kelvin probe force microscopy measurements reveal a considerable variation of the local contact potential difference toward lower values with respect to the gold surface, indicative of its positive net charge. Altogether, we introduce the concept of cationic nitrogen doping of NGs on surfaces, opening new avenues for the design of novel carbon nanostructures., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Quantum phase transitions (QPTs) driven by quantum fluctuations are transitions between distinct quantum phases of matter. At present, they are poorly understood and not readily controlled. Here, scanning tunneling microscopy (STM) and noncontact atomic force microscopy (nc-AFM) are used to explore atomic scale control over quantum phase transitions between two different topological quantum states of a well-defined π-conjugated polymer. The phase transition is driven by a pseudo Jahn-Teller effect that is activated above a certain polymer chain length. In addition, theoretical calculations indicate the presence of long-lasting coherent fluctuations between the polymer's two quantum phases near the phase transition, at finite temperature. This work thus presents a new way of exploring atomic-scale control over QPTs and indicates that emerging quantum criticality in the vicinity of a QPT can give rise to new states of organic matter., (© 2021 Wiley-VCH GmbH.)

Taming the magnetic anisotropy of lanthanides through coordination environments is crucial to take advantage of the lanthanides properties in thermally robust nanomaterials. In this work, the electronic and magnetic properties of Dy-carboxylate metal-organic networks on Cu(111) based on an eightfold coordination between Dy and ditopic linkers are inspected. This surface science study based on scanning probe microscopy and X-ray magnetic circular dichroism, complemented with density functional theory and multiplet calculations, reveals that the magnetic anisotropy landscape of the system is complex. Surface-supported metal-organic coordination is able to induce a change in the orientation of the easy magnetization axis of the Dy coordinative centers as compared to isolated Dy atoms and Dy clusters, and significantly increases the magnetic anisotropy. Surprisingly, Dy atoms coordinated in the metallosupramolecular networks display a nearly in-plane easy magnetization axis despite the out-of-plane symmetry axis of the coordinative molecular lattice. Multiplet calculations highlight the decisive role of the metal-organic coordination, revealing that the tilted orientation is the result of a very delicate balance between the interaction of Dy with O atoms and the precise geometry of the crystal field. This study opens new avenues to tailor the magnetic anisotropy and magnetic moments of lanthanide elements on surfaces., (© 2021 The Authors. Small published by Wiley-VCH GmbH.)

The design of organometallic complexes is at the heart of modern organic chemistry and catalysis. Recently, on-surface synthesis has emerged as a disruptive paradigm to design previously precluded compounds and nanomaterials. Despite these advances, the field of organometallic chemistry on surfaces is still at its infancy. Here, we introduce a protocol to activate the inner diacetylene moieties of a molecular precursor by copper surface adatoms affording the formation of unprecedented organocopper metallacycles on Cu(111). The chemical structure of the resulting complexes is characterized by scanning probe microscopy and X-ray photoelectron spectroscopy, being complemented by density functional theory calculations and scanning probe microscopy simulations. Our results pave avenues to the engineering of organometallic compounds and steer the development of polyyne chemistry on surfaces., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A new compound (1) formed by two antiparallelly disposed tetracyano thienoquinoidal units has been synthesized and studied by electrochemistry, UV/Vis-NIR, IR, EPR, and transient spectroscopy. Self-assembly of 1 on a Au(111) surface has been investigated by scanning tunneling microscopy. Experiments have been rationalized by quantum chemical calculations. 1 exhibits a unique charge distribution in its anionic form, with a gradient of charge yielding a neat molecular in-plane electric dipole momentum, which transforms out-of-plane after surface deposition due to twisted→folded conformational change and to partial charge transfer from Au(111). Intermolecular van der Waals interactions and antiparallel trapezoidal shape fitting lead to the formation of an optimal dense on Au(111) two-dimensional assembly of 1., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Among the plethora of polycyclic structures that have emerged in recent years, indenofluorenes comprise a unique class of compounds due to their potential in organic electronic systems such as OLEDs, OFETs, and OPVCs. However, the synthesis of fully conjugated indenofluorenes without bulky groups on the apical carbons under standard chemistry conditions is not easily accessible. In this regard, on-surface synthesis has appeared as a newly developing field of research, which exploits the use of well-defined solid surfaces as confinement templates to initiate and develop chemical reactions. Here, we demonstrate the successful fabrication of indeno[1,2-b]fluorene π-conjugated polymers linked via cumulene-like connections on well-defined metallic surfaces under ultra-high vacuum conditions. The structure and electronic properties of the formed polymers have been precisely characterized by scanning tunneling microscopy, noncontact atomic force microscopy and scanning tunneling spectroscopy, complemented by computational investigations.

The interest in exploiting the unique properties of lanthanides has led to the recent design of two-dimensional coordination networks incorporating f-block elements on metallic surfaces. In order to take this field to the next step of progression, it is necessary to electronically decouple these two-dimensional architectures from the metallic surface underneath. As a first step in this direction, we report the formation of dysprosium-directed metal-organic networks employing three-fold ligands as molecular linkers equipped with terminal carbonitrile functional groups on weakly interacting substrates such as Au(111) and graphene/Ir(111). We observe on both substrates identical quasi-hexagonal Dy-carbonitrile coordination networks based on majority five-fold nodes. Our findings provide perspectives for the formation of lanthanide coordination networks on graphene and related sp 2 materials grown on metals.

Polycyclic aromatic hydrocarbons (PAHs) are a family of organic compounds comprising two or more fused aromatic rings which feature manifold applications in modern technology. Among these species, those presenting an open-shell magnetic ground state are of particular interest for organic electronic, spintronic, and non-linear optics and energy storage devices. Within PAHs, special attention has been devoted in recent years to the synthesis and study of the acene and fused acene (periacene) families, steered by their decreasing HOMO-LUMO gap with length and predicted open-shell character above some size. However, an experimental fingerprint of such magnetic ground state has remained elusive. Here, we report on the in-depth electronic characterization of isolated peripentacene molecules on a Au(111) surface. Scanning tunnelling spectroscopy, complemented by computational investigations, reveals an antiferromagnetic singlet ground state, characterized by singlet-triplet inelastic excitations with an experimental effective exchange coupling ( J eff ) of 40.5 meV. Our results deepen the fundamental understanding of organic compounds with magnetic ground states, featuring perspectives in carbon-based spintronic devices.

On-surface synthesis has recently become an essential approach toward the formation of carbon-based nanostructures. Special emphasis is set on the synthesis of π-conjugated polymers taking into consideration their relevance and potential in organic electronics, optoelectronics and spintronics. Here, we report the on-surface synthesis of conjugated ladder polymers consisting of pentacene units doubly-linked via ethynylene-like bonds on the Au(111) surface under ultra-high vacuum conditions. To this aim, we have sublimed pentacene-like precursors equipped with four :CBr 2 functional groups to steer the desired reaction upon annealing on the surface. The atomically precise structure of the obtained polymers has been unambiguously characterized via low-temperature scanning tunneling microscopy and non-contact atomic force microscopy. In addition, scanning tunneling spectroscopy complemented with density-functional theory calculations reveal the narrow bandgap of the polymer. Our results provide potential for the synthesis of π-conjugated polymers with prospects in functional carbon-based nanomaterials that exploit multiple connections between molecular backbones.

We report on the synthesis and characterization of atomically precise one-dimensional diradical peripentacene polymers on a Au(111) surface. By means of high-resolution scanning probe microscopy complemented by theoretical simulations, we provide evidence of their magnetic properties, which arise from the presence of two unpaired spins at their termini. Additionally, we probe a transition of their magnetic properties related to the length of the polymer. Peripentacene dimers exhibit an antiferromagnetic (S=0) singlet ground state. They are characterized by singlet-triplet spin-flip inelastic excitations with an effective exchange coupling (J eff ) of 2.5 meV, whereas trimers and longer peripentacene polymers reveal a paramagnetic nature and feature Kondo fingerprints at each terminus due to the unpaired spin. Our work provides access to the precise fabrication of polymers featuring diradical character which are potentially useful in carbon-based optoelectronics and spintronics., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

The development of synthetic strategies to engineer π-conjugated polymers is of paramount importance in modern chemistry and materials science. Here we introduce a synthetic protocol based on the search for specific vibrational modes through an appropriate tailoring of the π-conjugation of the precursors, in order to increase the attempt frequency of a chemical reaction. First, we design a 1D π-conjugated polymer on Au(111), which is based on bisanthene monomers linked by cumulene bridges that tune specific vibrational modes. In a second step, upon further annealing, such vibrational modes steer the twofold cyclization reaction between adjacent bisanthene moieties, which gives rise to a long pentalene-bridged conjugated ladder polymer featuring a low bandgap. In addition, high resolution atomic force microscopy allows us to identify by atomistic insights the resonance form of the polymer, thus confirming the validity of the Glidewell and Lloyd´s rules for aromaticity. This on-surface synthetic strategy may stimulate exploiting previously precluded reactions towards π-conjugated polymers with specific structures and properties.

Time-resolved X-ray (Tr-XAS) and optical transient absorption (OTA) spectroscopy on the pico-microsecond timescale coupled with density functional theory calculations are applied to study the light-induced spin crossover processes of a Fe-based macrocyclic complex in solution. Tr-XAS analysis after light illumination shows the formation of a seven-coordinated high-spin quintet metastable state, which relaxes to a six-coordinated high-spin configuration before decaying to the ground state. Kinetic analysis of the macrocyclic complex reveals an unprecedented long-lived decay lifetime of approximately 42.6 μs. Comparative studies with a non-macrocyclic counterpart illustrate a significantly shortened approximately 568-fold decay lifetime of about 75 ns, and highlight the importance of the ligand arrangement in stabilizing the reactivity of the excited state. Lastly, OTA analysis shows the seven-coordinated high-spin state to be formed within approximately 6.2 ps. These findings provide a complete understanding of the spin crossover reaction and relaxation pathways of the macrocyclic complex, and reveal the importance of a flexible coordination environment for their rational design., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We report a low-temperature scanning tunneling microscopy investigation of the in-situ growth of gadolinium phthalocyaninato complexes by combined deposition of free-base phthalocyanines and gadolinium atoms on a smooth Ag(111) substrate. A careful control of the stoichiometry allows the expression of a multilevel structurecomposed of irregularly distributed Gd x-1 (Pc) x complexes, x=2-5, thus paving new avenues for surface-confined columnar growth., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Engineering low-band-gap π-conjugated polymers is a growing area in basic and applied research. The main synthetic challenge lies in the solubility of the starting materials, which precludes advancements in the field. Here, we report an on-surface synthesis protocol to overcome such difficulties and produce poly(p-anthracene ethynylene) molecular wires on Au(111). To this aim, a quinoid anthracene precursor with =CBr 2 moieties is deposited and annealed to 400 K, resulting in anthracene-based polymers. High-resolution nc-AFM measurements confirm the nature of the ethynylene-bridge bond between the anthracene moieties. Theoretical simulations illustrate the mechanism of the chemical reaction, highlighting three major steps: dehalogenation, diffusion of surface-stabilized carbenes, and homocoupling, which enables the formation of an ethynylene bridge. Our results introduce a novel chemical protocol to design π-conjugated polymers based on oligoacene precursors and pave new avenues for advancing the emerging field of on-surface synthesis., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Metallo-supramolecular engineering on surfaces provides a powerful strategy toward low-dimensional coordination architectures with prospects for several application fields. To date, most efforts have relied on transition metal centers, and only recently did we pioneer lanthanide-directed assembly. Coordination spheres and motifs with rare-earth elements generally display distinct properties and structural features. The size of the cations and shielding role of the 4f orbitals induces high coordination numbers, frequently entailing flexible coordination geometries. Following Pearson's hard and soft acid-base theory, lanthanide cations are hard Lewis acids and thus feature strong affinity for nitrile, terpyridine, and carboxylate donor moieties. The prevailing oxidation state is +3, although in certain compounds stable +2 or +4 cations occur. The chemistry of rare-earth elements is currently receiving widespread attention, as they are key ingredients for established and emerging 21st century science and technology with relevance for energy conversion, sensing, catalysis, magnetism, photonics, telecommunications, superconductivity, biomedicine, and quantum engineering. In this Account, we review recent advances toward the design of interfacial supramolecular nanoarchitectures incorporating lanthanide centers. We apply controlled ultrahigh vacuum conditions whereby atomistically clean substrates are prepared and exposed to ultrapure atomic and molecular beams of the chosen sublimable constituents. We focus on direct molecular-level investigations and in situ assembly operative close to equilibrium conditions. Our scanning probe microscopy techniques provide atomistic insights regarding the formation, stability, and manipulability of metal-organic compounds and networks. In order to gain deeper insights into the experimental findings, complementary computational analysis of bond characteristics, electronic properties, and coordination motifs has been performed for several case studies. Exemplary elements under consideration include cerium, gadolinium, dysprosium, and europium. By the use of ditopic molecular linkers equipped with carbonitrile moieties, adaptive coordination spheres are unveiled, yielding vertices with two- to sixfold symmetry. The respective coordination nodes underlie the expression of complex networks, such as semiregular Archimedean tessellations for cerium- or gadolinium-directed assemblies and random-tiling quasicrystalline characteristics for europium. Tunability via constituent stoichiometry regulation is revealed for bimolecular arrangements embedding europium centers, simultaneously connecting to carbonitrile and terypyridine ligands. Ditopic carboxylate linkers yield robust reticular networks based on a lateral coordination number of 8 for either gadolinium or dysprosium complexation, featuring a prevalent ionic nature of the coordination bond. Orthogonal insertion protocols give rise to d-f reticular architectures exploiting macrocyclic tetradentate cobalt complexation and peripheral carbonitrile-gadolinium coordination, respectively. Furthermore, lanthanides may afford metalation of adsorbed free-base tetrapyrrole species and can be engaged for interfacial synthesis of sandwich compounds, thus providing prospects for columnar design of coordination architectures. Finally, direct manipulation experiments achieved lateral displacement of single supramolecules and molecular rotation of sandwich or other molecular units. These findings evidence prospects for advancing molecular machinery components. The presented accomplishements herald further advancements in metallo-supramolecular design on surfaces, with versatile nanosystems and architectures emanating from the flexible coordination spheres. The embedding and systematic rationalization of lanthanide centers in tailored interfacial environments are keys to establishing relations between structure and physicochemical characteristics toward the generation of novel functionalities with technological significance.

We have measured STM movies to study the diffusion of individual vacancies in a self-assembled layer of a tetrathiafulvalene derivative (exTTF) on Au(111) at room temperature. The diffusion is anisotropic, being faster along the compact direction of the molecular lattice. A detailed analysis of the anisotropic displacement distribution of the single vacancies shows that the relative abundance of double jumps (that is, the collective motion of molecular dimers) with respect to single jumps is rather large, the number of double jumps being more than 20% of the diffusion events. We conjecture that the relative abundances of long jumps might be related to the strength of the intermolecular bonding and the misfit of the molecular overlayer with the substrate lattice.