Two-dimensional materials such as graphene, MXenes, or 2D transition-metal dichalcogenides have attracted much research attention due to ttheir unique properties. Two-dimensional black phosphorus (2D BP) or “phosphorene” sheets can be obtained by exfoliation of the layered bulk material. The properties of 2D BP could be tuned by functionalizing the surface of the layers, for example, with nanoparticles or molecular fragments. However, little is known about 2D BP functionalized with single metal atoms or low-nuclearity metal systems.

Matteo Vanni, Institute for the Chemistry of Organometallic Compounds (CNR-ICCOM), Sesto Fiorentino, Italy, and University of Siena, Italy, Maria Caporali, Gabriele Manca, Maurizio Peruzzini, CNR-ICCOM, and colleagues have prepared functionalized 2D BP with unusual discrete Pd₂ units. The team used a liquid-phase exfoliation of BP to prepare the 2D material. Then the 2D BP was suspended in dichloromethane (DCM) and reacted with the dimeric organometallic precursor [Pd(η³-C₃H₅)Cl]₂.

The team fully characterized the palladium-functionalized product using scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-angle annular dark-field imaging scanning transmission electron microscopy (HAADF-STEM), energy-dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and NMR spectroscopy, among other methods. They found that the product contains unprecedented interlayer Pd–Pd units that are sandwiched between stacked BP layers. According to the researchers, the phosphorus atoms stabilize the Pd₂ units, and thus, prevent the formation of nanoparticles.

• Interlayer Coordination of Pd–Pd Units in Exfoliated Black Phosphorus,
  Matteo Vanni, Marco Bellini, Silvia Borsacchi, Lucia Calucci, Maria Caporali, Stefano Caporali, Francesco d’Acapito, Marco Geppi, Andrea Giaccherini, Andrea Ienco, Gabriele Manca, Antonio Massimiliano Mio, Giuseppe Nicotra, Werner Oberhauser, Manuel Serrano-Ruiz, Martina Banchelli, Francesco Vizza, Maurizio Peruzzini,
  J. Am. Chem. Soc. 2021.
  https://doi.org/10.1021/jacs.1c01754