Using adenine and metal ions to form secondary building
units (SBUs),
further connected by a highly symmetrical multicarboxylic linker to
construct an amino-modified porous framework with high porosity, is
an effective strategy. By regulating the deprotonation and hydrolysis
capacity of the synthesized solvent, it is possible to obtain different
charged frameworks. In this work, two stable anionic/neutral MOFs,
(Et2NH2)[Zn3(TCPE)(adenine)2CH3COO]·DEF·3H2O (1)
and [Zn3.5(adenine)(TCPE)1.5(DMA)(H2O)0.5]·2DMA·2H2O (2),
have been synthesized based on zinc-adeninate building units and symmetric
tetrakis(4-carboxyphenyl)ethylene (H4TCPE) in N,N-diethylformamide (DEF) and N,N-dimethylacetamide (DMA) reaction systems, respectively. 1 is an anionic framework based on 1D rod zinc-adeninate SBU,
containing 1D rectangular (14.3 × 6.3 Å2) and
square (14.3 × 14.3 Å2) channels. While 2 is a neutral framework built from isolated zinc-adeninate
SBU, it contains hexagonal cages with a dimension of 5.5 Å in
the structure. Both of them have high porosity (61.6% for 1 and 46.3% for 2) and high stability in a wide range
of pH. 1 and 2 show high C2H2 adsorption capacity at 298 K (48.1 and 70.1 cm3 g–1, respectively) and selective capacity for
C2H2/CO2 mixtures, which was confirmed
by the breakthrough experiments. Furthermore, the interaction between
the frameworks and gas molecules has also been explained by theoretical
calculation. This work provides a good example of the design and regulation
of porous structures for adsorption and separation functions.