A hexagonal macrocycle consisting of 18 phenylene units (hyperbenzene) was synthesized on a Cu(111) surface in ultrahigh vacuum by Ullmann coupling of six 4,4''-dibromo-m-terphenyl molecules. The large diameter of 21.3 Å and the ability to assemble in arrays makes hyperbenzene an interesting candidate for a nanotrough that could enclose metallic, semiconducting, or molecular quantum dots.
The formation, structure, and dynamics of planar organometallic macrocycles (meta-terphenyl-Cu)n and zigzag-shaped one-dimensional organometallic polymers on a Cu(111) surface were studied with scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). Vapor deposition of 4,4″-dibromo-meta-terphenyl (DMTP) onto Cu(111) at 300 K leads to C-Br bond scission and formation of C-Cu-C bonds, which connect neighboring meta-terphenyl fragments such that room-temperature stable macrocycles and zigzag chains are formed. The chains self-assemble to form islands, which are elongated in the direction of the chains. If DMTP is deposited onto Cu(111) held at 440 K, the island size is drastically increased (>200 × 200 nm(2)). STM sequences show the formation of ordered structures through reversible scission and reformation of the C-Cu-C bonds. The cyclic organometallic species such as the hexamer (meta-terphenyl-Cu)6 may represent intermediates in the surface-confined Ullmann synthesis of hydrocarbon macrocycles such as the recently discovered hyperbenzene.
The
selective temperature-controlled surface-assisted synthesis
of covalent, organometallic, and halogen-bonded nanomeshes based on
a 3,5,3″,5″-tetrabromo-para-terphenyl
(TBrTP) precursor was studied with scanning tunneling microscopy (STM)
and X-ray photoelectron spectroscopy (STM) in ultrahigh vacuum. Vapor
deposition of TBrTP onto Cu(111) at 90 K leads to a highly ordered
organic monolayer stabilized by Br···Br and Br···H
intermolecular bonds between the intact T-type assembled TBrTP molecules,
as confirmed by density functional theory (DFT) calculations. Annealing
the monolayer to 300 K results in C–Br bond scission and the
formation of C–Cu–C bonds, which link adjacent para-terphenyl fragments such that stable organometallic
frameworks are formed. Pore sizes correlate with the number of enclosed
adatoms (most likely Br atoms), which presumably play a size-determining
role during the process of the pore formation. Larger islands of the
organometallic framework are obtained by deposition of TBrTP onto
the copper surface held at 460 K. A further increase in sample temperature
to 570 K during deposition gives rise to the formation of covalent
organic frameworks with pores of tetragonal and trigonal symmetry.
The covalent nanostructures are not completely planar, but contain
phenylene units which are tilted relative to the surface plane, most
likely due to steric hindrance between the C–H bonds inside
the pores. Comparison of the three different bonding regimes reveals
that the degree of long-range order correlates inversely with the
strength of the bonds between the building blocks.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.