Molecular Packing Variation of Crimpled 2D Layers and 3D Uncommon 6⁵.8 Topology: Effect of Ligand on the Construction of Metal−Quinoline-6-carboxylate Polymers

Four coordination polymers Ni(quin-6-c)2 (1), Zn2(quin-6-c)4 (2), Co2(quin-6-c)4 (3), and Zn(OH)(quin-6-c) (4) (quin-6-c = quinoline-6-carboxylate) have been synthesized by methods of hydrothermal reaction and their crystal structures determined. In the compound 1, quin-6-c ligands act as ditopic linkers bound to Ni atoms, resulting in the formation of an unusually wavelike 2D (4,4) net. The adjacent layers are stacked offset with respect to each other, in an ABAB fashion. Compounds 2 and 3 are isostructural and feature a unique 2D molecular network composed of crimpled double-line ribbons. The 2D layers stack in a rare, interesting ABCD pattern along the crystallographic c axis. Compound 4 forms a novel 3D framework based on uncommon “new” 65.8 topology, crystallizes in the acentric orthorhombic space group Pna21 and displays powder SHG intensity ca. 460 times in comparing with that of α-quartz. The [Zn(μ2-OH)]n helical chains connected to each other through unsymmetrical quin-6-c ligands in 4 have ensured its acentricity and SHG-activity. A discussion of the crystal structures, as well as the coordination properties of quin-6-c ligands upon different geometries of the central ions, is provided.