Temperature, Cooling Rate, and Additive-Controlled Supramolecular Isomerism in Four Pb(II) Coordination Polymers with an in Situ Ligand Transformation Reaction

Solvothermal reactions of Pb­(Ac)₂ with a new flexible 1,3-bis­(4-pyridyl-3-cyano)­propane (1, BPCP) ligand under different synthesis conditions via an in situ ligand transformation reaction produced three true coordination polymorphs, namely, [PbL^2–]_n (for 2 and 3) and [Pb₃L^2–₃]_n (4), as well as their polymorphic framework [(Pb₂L^2–)·2H₂O]_n (5) (H₂L = 1,3-bis­(4-pyridyl-3-carboxyl)­propane). These compounds were characterized by elemental analysis, IR, TG, PXRD, and single-crystal X-ray diffraction. In these compounds, the L^2–ligand exhibits different coordination conformations and modes tuned by different synthesis conditions, including reaction temperature, cooling rate, and additive, and constructs various architectures by bridging a variety of building units. Polymorphs 2 and 3 display a 3D framework with 1D channels built up from dinuclear ringlike [Pb₂L^2–₂] units and dinuclear semi-ring-like [Pb₂L^2–] units, respectively. Polymorph 4 also features a 3D architecture constructed from dinuclear ringlike [Pb₂L^2–₂] units interlinked by the L^2– ligand. Interestingly, the framework of 4 is big enough to allow the other net to penetrate to form a 2-fold interpenetrating framework with a trinodal (3,6,10)-connected topology with a point symbol of (4³)­(4⁴·6¹⁰·8)­(4⁸·6²⁴·8⁹·10⁴). For 5, there exists two kinds of dinuclear ringlike [Pb₂L^2–₂] units. These [Pb₂L^2–₂] units are interconnected by Pb atoms to afford a 2D undulant network that is further connected by the hydrogen-bonding interactions and weak interactions to afford a 3D supramolecular network. In addition, the photoluminescence properties of 1–5 and the H₂L ligand in the solid state at room temperature were also investigated.