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 beta-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 beta-diketonate functions are approximately coplanar and directed either on opposite sides (trans) or on the same side similar to60degrees 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 Angstrom. 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 Angstrom, 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.