Two-Dimensional Nanosheets from Redox-Active Superatoms

We
describe a new approach to synthesize two-dimensional (2D) nanosheets
from the bottom-up. We functionalize redox-active superatoms with
groups that can direct their assembly into multidimensional solids.
We synthesized Co6Se8­[PEt2(4-C6H4COOH)]6 and found that it forms a
crystalline assembly. The solid-state structure is a three-dimensional
(3D) network in which the carboxylic acids form intercluster hydrogen
bonds. We modify the self-assembly by replacing the reversible hydrogen
bonds that hold the superatoms together with zinc carboxylate bonds
via the solvothermal reaction of Co6Se8­[PEt2(4-C6H4COOH)]6 with Zn­(NO3)2. We obtain two types of crystalline materials
using this approach: one is a 3D solid and the other consists of stacked
layers of 2D sheets. The dimensionality is controlled by subtle changes
in reaction conditions. These 2D sheets can be chemically
exfoliated, and the exfoliated, ultrathin 2D layers are soluble. After
they are deposited on a substrate, they can be imaged. We cast them
onto an electrode surface and show that they retain the redox activity
of the superatom building blocks due to the porosity in the sheets.