A New Bridging Chelating Ligand for Crystal Engineering: Synthesis, Polymorphism, and Two Modes of Assembly of 1,4-Bis(3-phenyl-1,3-propanedion)benzene with Metal Cations Resulting in Either Discrete or Polymeric Complexes

This work introduces a new ligand (H2L, PhCOCH2COPhCOCH2COPh) bearing two β-diketonate
functions separated by a phenylene ring. The free ligand was synthesized and isolated in two polymorphic
modifications. The ligand exhibits a preference for one of two basic conformational types where β-diketonate functions
are approximately coplanar and directed either on opposite sides (trans) or on the same side ∼60° to each other
(cis). In the free form, the ligand exists as 100% enol; in the solid state, it adopts a trans conformation. In a one-dimensional (1D) coordination polymer [ZnPy2L]n*nPy, the ligand adopts the trans conformation and chelates to
two zinc(II) centers bridging them at 11.3 Å. In three of the crystals studied, another structure was observed with
an ideal formula [M3Py6L3]*5(CHCl3). In this case, the ligand adopts a cis conformation and chelates to two metal
centers bridging them at 10.7 Å, to produce a trinuclear macrocyclic species. In the crystal, these triangles pack to
create channels that accommodate chloroform as a guest. The specific crystals studied had the following overall
compositions:  [Co3Py6L3]*4.84(CHCl3), [Co3Py6L3]*4.11(CHCl3), and [Ni3Py6L3]*4.68(CHCl3). The architecture
displays flexibility and zeolite-like behavior.

本工作报道了一种新型配体（H₂L，PhCOCH₂COPhCOCH₂COPh），其带有两个被亚苯基环（phenylene ring）分隔的β-二酮酸酯（β-diketonate）官能团。该游离配体经合成并分离得到两种多晶型变体。该配体倾向于两种基本构象类型之一：其中β-二酮酸酯官能团大致共面，且分别朝向两侧（反式，trans）或以约60°夹角朝向同侧（顺式，cis）。游离态下，该配体以100%烯醇式存在；固态下则采取反式构象。在一维（1D）配位聚合物（coordination polymer）[ZnPy₂L]ₙ·nPy中，该配体采取反式构象，螯合于两个锌(II)中心之间，两中心间距为11.3 Å。在所研究的三类晶体中，还观测到另一种结构，其理想分子式为[M₃Py₆L₃]·5(CHCl₃)。在此结构中，配体采取顺式构象，螯合于两个金属中心之间，两中心间距为10.7 Å，由此形成三核大环物种（trinuclear macrocyclic species）。晶体中，这类三角形单元堆积形成孔道，以容纳作为客体的三氯甲烷。所研究的特定晶体的整体组成如下：[Co₃Py₆L₃]·4.84(CHCl₃)、[Co₃Py₆L₃]·4.11(CHCl₃)以及[Ni₃Py₆L₃]·4.68(CHCl₃)。该体系架构展现出柔性与类沸石行为（zeolite-like behavior）。