From Sequential to One-Pot Synthesis of Dipyrrin Based Grid-Type Mixed Metal–Organic Frameworks

Both sequential and one-pot strategies
for the preparation of a
series of grid-type mixed metal–organic frameworks (MM′MOFs)
based on dipyrrin ligands appended with either a pyridyl or a phenyl-imidazolyl
moiety have been investigated. For the stepwise approach, the differentiation
between the two coordination sites (nature, charge, and denticity)
was exploited for the synthesis of a family of five discrete Zn­(II),
Cu­(II), and Pd­(II) complexes. Acting as metallatectons, these construction
building blocks lead to the formation of a series of MM′MOFs
upon self-assembly with CdCl2. In these rhombic grid-type
architectures, four consecutive metallatectons are bridged by Cd­(II)
cations adopting an octahedral coordination geometry with the chloride
anions occupying apical positions, thus behaving as square nodes.
The shape of the rhombus grids as well as the way they are packed
(stacking or interpenetration) in the crystalline phase are controlled
by the nature of metallatectons and the solvent molecules present
in the crystals. Consequently, the heterometallic assemblies display
different accessible voids, although they are built on layers with
the same connectivity. More interestingly, as demonstrated by X-ray
diffraction on both single crystals and microcrystalline powders,
the same MM′MOFs were obtained by a one-pot strategy through
direct combinations of dipyrrin derivatives with the corresponding
metal salts. This one-pot approach is efficient and more convenient
than the sequential alternative, since the isolation, purification,
and characterization of the, sometimes insoluble, metallatectons are
not required.