Robust 2D Coordination Networks from a Two-Step Assembly Process with Predesigned Silver Cyclic Dimers and Hexamethylenetetramine

A two-step self-assembly methodology
has been used to obtain 2D
coordination polymers with an egg-crate structure of trigonal symmetry
and space group R3̅m. The
polymers have the molecular formula [Ag3(L1)3(hmt)]­X3 (L1 = bis­(pyrazol-1-yl)­(pyridin-4-yl)­methane;
hmt = hexamethylenetetramine; X = BF4, ClO4,
PF6). In the first step, the previously reported box-like
cyclic dimers [Ag L1]2X2, in which
the ligands L1 are in a head-to-tail disposition, were
obtained and these were subsequently reacted with the base hexamethylenetetramine
to form Ag–N­(hmt) bonds. The dimers act as linear connectors
and the bases as triconnected nodes to give slightly undulating hexagons
that form honeycomb sheets. The sheets follow an ABCABC stacking arrangement
along [001] so that between them two types of large cavities arise
which are occupied by disordered solvent, e.g., DMF inherited from
synthesis. The anions, which participate in the formation of the cavities,
interact with the sheets through hydrogen bonds. The polymers can
be activated by removing the solvents without collapsing, which enabled
an evaluation of these materials for use as gas adsorption, anion
exchange, and proton capture systems.