Dual emissions and thermochromic luminescences of isomorphic chiral twofold interpenetrated 3-D nets built from I1O2 type hybrid inorganic-organic frameworks of [NH2(CH3)2]3[Pb2X3(BDC)2] (X = Br, I)

© 2018 The Royal Society of Chemistry. Two pairs of MOF-based hybrid enantiomorphs, [NH2(CH3)2]3[Pb2X3(BDC)2] (H2BDC = 1,4-benzenedicarboxylic acid, X = Br or I), have been synthesized using the solvothermal reaction and then manually separated, which are labeled as 1a/1b (X = Br) and 2a/2b (X = I). The isomorphic 1a and 2a crystallize in tetragonal space group P43212, and the isomorphic 1b and 2b in the enantiomorphic space group P41212. Twofold interpenetrated three-dimensional (3-D) networks were built from two sets of equivalent I1O2 type hybrid inorganic-organic frameworks in 1a/1b and 2a/2b. Each I1O2 type hybrid inorganic-organic framework constructs by the inorganic pentagonal bipyramid-shape PbX3O4 (X = Br or I) polyhedral chains along the c-axis, which are further connected though bridged BDC2- ligands in the directions perpendicular to the c-axis. Hybrids 1a/1b and 2a/2b have been characterized by elemental analysis (C, H and N elements), thermogravimetric and powder X-ray diffraction techniques, and UV-visible absorption spectroscopy in the solid state. These hybrids show dual emissions at ambient conditions, which arise from the π-π∗ electron transition within the aromatic rings in the BDC2- ligands and the electron transition in the inorganic polyhedral semiconducting chains, as well as thermochromic luminescence behavior from 10 to 300 K owing to two emission bands displaying different responses to the temperature change.