Structural flexibility and mobility of coordination polymers on Cu(111)

Area of Science:

• Surface science
• Materials science
• Nanotechnology

Background:

• Scanning tunneling microscopy (STM) enables atomic-level investigation of surface coordination polymers.
• Analyzing dynamic behavior of these polymers at low temperatures is challenging due to strong ligand adsorption.

Purpose of the Study:

• To design a novel ligand (2,7-dicyano-9,9-dimethyl-9H-fluorene, DCF) for studying coordination polymer mobility at low temperatures.
• To understand how ligand design influences polymer dynamics and surface interactions.

Main Methods:

• Utilized STM to observe DCF-copper (DCF-Cu) coordination polymers on a copper (Cu(111)) surface.
• Employed density functional theory (DFT) calculations to analyze structural transformations.

Main Results:

• Individual DCF ligands were tracked, revealing reduced interaction with the surface due to dimethyl groups.
• Branched polymer structures showed less mobility than linear or short polymers with free ends upon heating (4 K to 78 K).
• Observed polymer chain cleavage, recombination, and insertion, facilitated by flexible coordination angles.

Conclusions:

• The study demonstrates distinct mobility differences based on coordination polymer architecture.
• Ligand design, specifically the dimethyl group, is crucial for observing low-temperature dynamics.
• Findings provide direct experimental evidence for structure-dependent polymer motion in surface-based systems.