Abstract:
Two new homochiral metal–organic frameworks of Cd(II), [{Cd2(L-glu)2(bpe)3(H2O)}·2H2O] (1) and
[{Cd3(L-glu)2(bpe)3(H2O)}·2NO3·H2O] (2) (where, L-glu = L-glutamate dianion, and bpe = 1,2-bis(4-
pyridyl)ethylene) have been synthesized solvothermally by employing two different temperatures.
Single crystal X-ray diffraction studies revealed that both 1 and 2 are homochiral and possess a 3D
pillar-layered framework structure having 4,8- and 8,10-connected binodal nets with vertex symbols
of {3^2.4.5^3}{3^4.4^6.5^10.6^8} and {3^11.4^28.5^5.6}2{3^8.4^18.5.6}, respectively. Interestingly,
solvothermal synthesis carried out at 100 °C resulted in a 3D framework, 1 which features large rectangular 1D channels with a dimension of ∼10.38 × 4.44 Å2 decorated with pendant –NH2 groups.
Whereas, increasing the temperature of the reaction to 120 °C led to a non-porous highly connected
3D framework, 2 in which the –NH2 group of the L-glu ligand is coordinated to a Cd(II) node. Gas (N2,
CO2, H2 and Ar) uptake studies on the dehydrated framework of 1 revealed excellent selectivity for
CO2 over other gases at 273 K with a high isosteric heat of adsorption (Qst) value of 40.8 kJ mol−1
. The
high selectivity for CO2 gas has been attributed to the stronger interaction of CO2 with the basic
–NH2 functionalized pore surface of compound 1. Furthermore, 1 acts as a very good recyclable catalyst for the carbon–carbon bond forming reactions, such as the Knoevenagel condensation and Henry
reaction of benzaldehydes. Moreover, the catalyst can be easily separated from the reaction mixture
and reused in four consecutive cycles without significant loss of catalytic activity and structural
rigidity
