Spin Transition in a Chainlike Supramolecular Iron(II) Complex

A one-dimensional supramolecular head-to-tail N+−H···N-type hydrogen-bonded chain of the complex [FeII(L)2H](ClO4)3·MeOH [L = 4‘-(4‘ ‘‘-pyridyl)-1,2‘:6‘1‘ ‘-bis(pyrazolyl)pyridine] exhibits a reversible, thermally driven spin transition at 286 K with a hysteresis loop of ca. 2 K

Spin Transition in a Chainlike Supramolecular Iron(II) Complex

A one-dimensional supramolecular head-to-tail N+−H···N-type hydrogen-bonded chain of the complex [FeII(L)2H](ClO4)3·MeOH [L = 4‘-(4‘ ‘‘-pyridyl)-1,2‘:6‘1‘ ‘-bis(pyrazolyl)pyridine] exhibits a reversible, thermally driven spin transition at 286 K with a hysteresis loop of ca. 2 K

Highly Adaptable Two-Dimensional Metal–Organic Coordination Networks on Metal Surfaces

The formation of extended two-dimensional metal–organic coordination networks (2D-MOCNs) showing high adaptability to surface step edges and structural defects is revealed by scanning tunneling microscopy. Rod-like 4,4′-di-(1,4-buta-1,3-diynyl)-benzoic acid (BDBA) and iron atoms assemble into extended 2D-MOCNs on Au(111) and Ag(100) surfaces. Independent from the chosen substrate and its surface symmetry the MOCN grows continuously over multiple surface terraces through mutual in-phase structure adaptation of network domains at step edges as well as on terraces. The adaptability of the MOCNs is mainly ascribed to the high degree of conformational flexibility of the butadiynyl functionality of the ligand. Despite their flexibility, the MOCNs exhibit considerable robustness against annealing at high temperatures. The findings show that mesoscale self-assembled functional architectures with a high degree of substrate error tolerance can be realized with metal coordination networks

Functionalization of Open Two-Dimensional Metal–Organic Templates through the Selective Incorporation of Metal Atoms

Surface-confined molecular networks can serve as templates to steer the adsorption and organization of secondary ligands, metal atoms, and clusters. Here, the incorporation of Ni atoms and clusters into open two-dimensional robust metal–organic templates self-assembled from butadiyne dibenzoic acid molecules and Fe atoms on Au(111) and Ag(100) surfaces is investigated by scanning tunneling microscopy. The metal substrate plays a crucial role in the interaction of Ni atoms with the metal–organic host networks. On Ag(100) the metal–organic template steers the growth of Ni clusters underneath the network pattern near the central butadiyne moiety. In contrast, on Au(111) Ni interacts preferentially with the benzene rings forming size-limited clusters inside the network cavities. Thereby, on both surfaces Ni clusters consisting of a few atoms with both high areal density and thermal stability up to 450 K are realized. The Ni-functionalized networks enable the coordination of additional molecules into the open structures demonstrating the utilization of selective interactions for the assembly of multicomponent architectures at different organizational stages

CO₂ Binding and Induced Structural Collapse of a Surface-Supported Metal–Organic Network

Extensive efforts have been directed toward identifying catalytic material composites for efficiently transforming CO2 into valuable chemicals. Within this longstanding scientific challenge, the investigation of model systems is of particular interest to gain fundamental insight into the relevant processes and to synergistically advance materials functionalities. Inspired by the ubiquitous presence of metal–organic active sites in the conversion of CO2, we study here the interaction of CO2 with a two-dimensional metal–organic network synthesized directly on a metal surface as a model system for this class of compounds. The impact of individual CO2 molecules is analyzed using scanning tunneling microscopy supported by density functional theory calculations. Dosage of CO2 gas to the thermally robust Fe-carboxylate coordination structure at low temperatures (100 K) leads to a series of substantial rearrangements of the coordination motif, accompanied by a collapse of the entire network structure. Several binding sites of weak and moderate strengths are identified for CO2 near the iron nodes leading to a moderate structural weakening of the existing coordination bonds in the adapted models with no indication of CO2 dissociation. The observations suggest a concerted reaction pathway involving both CO2 and ligand molecules starting at irregular coordination sites that may eventually lead to the collapse of the entire network structure. The electronic properties of the Fe atoms in the carboxylate environment are determinant for the response of the network toward CO2, which depends critically on the local coordination environment. The results highlight that finely tuned metal–organic complexes and networks at surfaces present promising features to activate and transform CO2

Expanding the Coordination Cage: A Ruthenium(II)−Polypyridine Complex Exhibiting High Quantum Yields under Ambient Conditions

A mononuclear ruthenium(II) polypyridyl complex with an enlarged terpyridyl coordination cage was synthesized by the formal introduction of a carbon bridge between the coordinating pyridine rings. Structurally, the ruthenium(II) complex shows an almost perfect octahedral N6 coordination around the central RuII metal ion. The investigation of the photophysical properties reveals a triplet metal-to-ligand charge transfer emission with an unprecedented quantum yield of 13% and a lifetime of 1.36 μs at room temperature and in the presence of air oxygen. An exceptional small energy gap between light absorption and light emission, or Stokes shift, was detected. Additionally, time-dependent density functional theory calculations were carried out in order to characterize the ground state and both the singlet and triplet excited states. The exceptional properties of the new compound open the perspective of exploiting terpyridyl-like ruthenium complexes in photochemical devices under ambient conditions

Molecular Orbital Gates for Plasmon Excitation

Future combinations of plasmonics with nanometer-sized electronic circuits require strategies to control the electrical excitation of plasmons at the length scale of individual molecules. A unique tool to study the electrical plasmon excitation with ultimate resolution is scanning tunneling microscopy (STM). Inelastic tunnel processes generate plasmons in the tunnel gap that partially radiate into the far field where they are detectable as photons. Here we employ STM to study individual tris-(phenylpyridine)-iridium complexes on a C₆₀ monolayer, and investigate the influence of their electronic structure on the plasmon excitation between the Ag(111) substrate and an Ag-covered Au tip. We demonstrate that the highest occupied molecular orbital serves as a spatially and energetically confined nanogate for plasmon excitation. This opens the way for using molecular tunnel junctions as electrically controlled plasmon sources

Dynamic Control of Plasmon Generation by an Individual Quantum System

Controlling light on the nanoscale in a similar way as electric currents has the potential to revolutionize the exchange and processing of information. Although light can be guided on this scale by coupling it to plasmons, that is, collective electron oscillations in metals, their local electronic control remains a challenge. Here, we demonstrate that an individual quantum system is able to dynamically gate the electrical plasmon generation. Using a single molecule in a double tunnel barrier between two electrodes we show that this gating can be exploited to monitor fast changes of the quantum system itself and to realize a single-molecule plasmon-generating field-effect transistor operable in the gigahertz range. This opens new avenues toward atomic scale quantum interfaces bridging nanoelectronics and nanophotonics