W0258
New Metal Carboxylates Prepared at Room Temperature and
under Hydrothermal Conditions. G. Díaz de Delgado, M.
Gutiérrez, L. León, J. Contreras, J.M. Delgado. Laboratorio de
Cristalografía, Dept. de Química, Facultad de Ciencias, Univ. de
Los Andes, Mérida, 5101, Venezuela.
Hydrothermal routes of synthesis have proven useful in the
preparation of new open-framework compounds. Even when these synthetic routes do
not lead to materials with porosity appropriate for technological applications,
the fact that the structures obtained may be different from the ones prepared at
room temperature is still of interest. This certainly provides a better
understanding of the systems under investigation. Experiments carried out in our
laboratory indicate, for example, that the same crystalline phase is obtained
for Ca fumarate at room temperature and under hydrothermal conditions. However,
Ba-mesaconate is an interesting case. Slow evaporation at room temperature
produces tetraaquomesaconatebarium (II),
Ba(C5H4O4)(OH2)4]n
a 2-D coordination polymer (P21/n, a = 8.8930(10), b =
7.4780(10), c = 16.582(2)Å, β = 105.130(10)°). However,
under autogeneous pressure a triclinic P-1 phase is obtained, with unit cell
parameters, a = 7.338(2) Å, b = 10.484(4), c =
11.616(4), α = 78.24(2)°, β = 98.61(2)°, γ =
104.64(2)°, V=841.9(5)Å3. In this structure, layers of
Ba-mesaconate units parallel to the ab plane are connected through
fumarate ligands which result from partial decomposition of some of the
mesaconate ligands. The details of this and other structures will be
presented.
This work was supported by FONACIT-Venezuela through grant
LAB-97000821.