Surface reactions of 2,5-diethynyl-1,4-bis(phenylethynyl)benzene on Ag(111), Ag(110), and Ag(100) were systematically explored and scrutinized by scanning tunneling microscopy, molecular mechanics simulations, and density functional theory calculations. On Ag(111), Glaser coupling reaction became dominant, yielding one-dimensional molecular wires formed by covalent bonds. On Ag(110) and Ag(100), however, the terminal alkynes reacted with surface metal atoms, leading to one-dimensional organometallic nanostructures. Detailed experimental and theoretical analyses revealed that such a lattice dependence of the terminal alkyne reaction at surfaces originated from the matching degree between the periodicities of the produced molecular wires and the substrate lattice structures.

The activation of C-H bonds in terminal alkynyl groups at room temperature was achieved in the reaction of 2,5-diethynyl-1,4-bis(4-bromophenylethynyl)benzene on Ag(111). Scanning tunneling microscopy studies showed the formation of organometallic species, whose stabilization was confirmed by density functional theory calculations, at room temperature as the product of C-H bond activation. The partial conversion of organometallic structures into covalent products of the homocoupling between the terminal alkynes was achieved by further annealing the sample at 420 K. Detached Br adatoms were suggested to play a key role in promoting the C-H bond activation. This proposal was supported by the theoretical study based on a simplified model of the system, showing the weakening of the C-H bond in the alkynyl group by an approaching Br atom. The results provide a new strategy for on-surface C-H bond activation under mild conditions, which register great potential applications in on-surface synthesis and bottom-up preparation of functional nanomaterials.

Coupled spin-crossover complexes in supramolecular systems feature rich spin phases that can exhibit collective behaviors. Here, we report on a molecular-level exploration of the spin phase and collective spin-crossover dynamics in metallo-supramolecular chains. Using scanning tunneling microscopy, spectroscopy, and density functional theory calculations, we identify an antiferroelastic phase in the metal−organic chains, where the Ni atoms coordinated by deprotonated tetrahydroxybenzene linkers on Au(111) are at a low-spin (S = 0) or a high-spin (S = 1) state alternately along the chains. We demonstrate that the spin phase is stabilized by the combined effects of intrachain interactions and substrate commensurability. The stability of the antiferroelastic structure drives the collective spin-state switching of multiple Ni atoms in the same chain in response to electron/hole tunneling to a Ni atom via a domino-like magnetostructural relaxation process. These results provide insights into the magnetostructural dynamics of the supramolecular structures, offering a route toward their spintronic manipulations.