1 research outputs found
Noncovalent Grafting of Molecular Complexes to Solid Supports by Counterion Confinement
Grafting molecular complexes on solid supports is a facile
strategy
to synthesize advanced materials. Here, we present a general and simple
method for noncovalent grafting on charge-neutral surfaces. Our method
is based on the generic principle of counterion confinement in surface
micropores. We demonstrate the power of this approach using a set
of three platinum complexes: Pt1 (Pt1L4(BF4)2, L = p-picoline), Pt2 (Pt2L4(BF4)4, L = 2,6-bis(pyridine-3-ylethynyl)pyridine),
and Pt12 (Pt12L24(BF4)24, L = 4,4′-(5-methoxy-1,3-phenylene)dipyridine).
These complexes share the same counterion (BF4–) but differ vastly in their size, charge, and structure. Imaging
of the grafted materials by aberration-corrected high-angle annular
dark-field scanning transmission electron microscopy (AC-HAADF-STEM)
and energy-dispersive X-ray (EDX) showed that our method results in
a homogeneous distribution of both complexes and counterions. Nitrogen
sorption studies indicated a decrease in the available surface area
and micropore volume, providing evidence for counterion confinement
in the surface micropores. Following the adsorption of the complexes
over time showed that this is a two-step process: fast surface adsorption
by van der Waals forces was followed by migration over the surface
and surface binding by counterion confinement. Regarding the binding
of the complexes to the support, we found that the surface–adsorbate
binding constant (KS) increases quadratically
with the number of anions per complex up to KS = 1.6 × 106 M–1 equaling
ΔG°ads = −35 kJ mol–1 for the surface binding of Pt12. Overall, our method has two important advantages: first, it is
general, as you can anchor different complexes (with different charges,
counterions, and/or sizes); second, it promotes the distribution of
the complexes on the support surface, creating well-distributed sites
that can be used in various applications across several areas of chemistry