The incorporation of pillars in 2D solids allows the preparation
of 3D porous materials with tailored cavity size and
shape. In this sense, planar coordination polymers based on
tetracyanometallates, T[M(CN)4] with T = Mn, Fe, Co, Ni,
Cu, Zn, Cd; M = Ni, Pd, Pt, appear as an ideal prototype of
2D solids to be considered. The metal centers at their surface
contain available coordination sites which can be used as anchoring
positions for the ligands to be used as pillars. Under
certain preparative conditions, a fraction of the available metal
coordination sites could be maintained free of ligands to allow
their interaction with the guest molecule within the cavities.
Such possibility provides an ideal system of porous 3D solids
for studies related with the hydrogen storage in nanocavities;
in fact, two studies in that sense has already been reported
[1, 2]. All the studies related with the hydrogen storage in
porous solids are carried out under cryogenic conditions, usually
at 77 K. For some cyanometallates negative thermal expansion
behavior has been reported [3], which could be interpreted
as evidence of charge redistribution within the T-N-CM-
C-N-T chain on the temperature change, particularly under
cryogenic conditions. This suggests that in 2D pillared solids
low temperature structural transformation could be present,
particularly for pillars of certain flexibility and where the electronic
structure of layers and pillars remains strongly coupled.
Such possibility is explored in this contribution. As prototype
of pillared 2D solids T[Ni(CN)4].2pyz, with pyz = Pyrazine
were used