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, [PbL2–]n (for 2 and 3) and [Pb3L2–3]n (4), as well as their polymorphic framework [(Pb2L2–)·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 L2–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 [Pb2L2–2] units and dinuclear semi-ring-like [Pb2L2–] units, respectively. Polymorph 4 also features a 3D architecture constructed from dinuclear ringlike [Pb2L2–2] units interlinked by the L2– 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 [Pb2L2–2] units. These [Pb2L2–2] 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.