The coordination-restricted ortho -site C–H bond activation and dehydrogenative homocoupling of 4,4′-(1,3-phenylene)dipyridine (1,3-BPyB) and 4,4′-(1,4-phenylene)dipyridine (1,4-BPyB) on different metal surfaces were studied by a combination of scanning tunneling microscopy, noncontact atomic force microscopy, and density functional theory calculations. The coupling products on Cu(111) exhibited certain configurations subject to the spatial restriction of robust two-fold Cu–N coordination bonds. Compared to the V-shaped 1,3-BPyB, the straight backbone of 1,4-BPyB helped to further reduce the variety of reactive products. By utilizing the three-fold coordination of Fe atoms with 1,4-BPyB molecules on Au(111), a large-scale network containing single products was constructed. Our results offer a promising protocol for controllable on-surface synthesis with the aid of robust coordination interactions.

Realization of the Kagome antiferromagnetic (KAF) lattice is of high interest because the geometric frustration in the Kagome lattice is expected to give rise to highly degenerated ground states that may host exotic phases such as quantum spin liquid. Here we demonstrate the design and synthesis of a single-layer two-dimensional metal−organic framework (2D-MOF) containing a Kagome lattice of Fe(II) ions assembled on a Au(111) surface. First-principles calculations reveal that the Fe(II) ions are at a high spin state of S = 2 and are coupled antiferromagnetically with nearest-neighboring exchange J 1 = 5.8 meV. The ground state comprises various degenerated spin configurations including the well-known q = 0 and q = √3 × √3 phases. Remarkably, we observe a spin excitation at 6 meV using tunneling spectroscopy. This work points out a feasible route toward realizing spin 1 / 2 KAF, a candidate quantum spin liquid system, by replacing Fe(II) by Cu(II) in the same structure.

Fractals are found in nature and play important roles in biological functions. However, it is challenging to controllably prepare biomolecule fractals. In this study, a series of Sierpinśki triangles with global organizational chirality is successfully constructed by the coassembly of L-tryptophan and 1,3-bi(4-pyridyl)benzene molecules on Ag(111). The chirality is switched when replacing L-tryptophan by D-tryptophan. The fractal structures are characterized by low-temperature scanning tunneling microscopy at the single-molecule level. Density functional theory calculations reveal that intermolecular hydrogen bonds stabilize the Sierpinśki triangles.

The study of lanthanide (Ln)-transition-metal (TM) heterometallic clusters which play key roles in various high-tech applications is a rapid growing field of research. Despite the achievement of numerous Ln-TM cluster compounds comprising one Ln atom, the synthesis of Ln-TM clusters containing multiple Ln atoms remains challenging. Here, we present the preparation and self-assembly of a series of Au-bridged heterometallic clusters containing multiple cerium (Ce) atoms via on-surface coordination. By employing different pyridine and nitrile ligands, the ordered coordination assemblies of clusters containing 2, 3 and 4 Ce atoms bridged by Au adatoms are achieved on Au(111) and Au(100), as revealed by scanning tunneling microscopy. Density functional theory calculations uncover the indispensable role of the bridging Au adatoms in constructing the multi-Ce-containing clusters by connecting the Ce atoms via unsupported Ce-Au bonds. These findings demonstrate on-surface coordination as an efficient strategy for preparation and organization of the multi-Ln-containing heterometallic clusters.

Tuning the spin-dependent electron transport through molecules is of fundamental importance in single-molecule spintronics. Here, the transport properties of iron phthalocyanine on Au(111) was investigated by a combination of scanning tunneling microscopy and density functional theory calculations. Using high-resolution scanning tunneling spectroscopy performed at 0.5 K, a Kondo resonance was observed on FePc. After removing its eight outermost hydrogen atoms, the spectroscopic feature changed into a double-step structure, which reflected inelastic transitions of molecular spin states. The density functional theory calculations revealed that the coupling between Fe and Au(111) became much weaker after cutting the hydrogen atoms. This explained the change of the spin-related fingerprints in the differential spectra.