A highly stable pillared and double-walled zinc(II) metal-organic framework with regular nanochannels displays single-crystal to single-crystal transformation upon desolvation and a large quantity of iodine uptake, controlled release, and electrical conductivity elevation due to synergy between the iodine guests and the host framework.

{[Cu6(pybz)8(OH)2]·I5(–)·I7(–)}n (1), obtained hydrothermally by using iodine molecules as a versatile precursor template, consists of a cationic framework with two types of zigzag channels, which segregate I5(–) and I7(–) anions. The framework exhibits the first observed bipillared-bilayer structure featuring both interdigitation and interpenetration. 1 displays high framework stability in both acidic (HCl) and alkaline (NaOH) solutions. 1 slowly releases iodine in dry methanol to give [Cu6(pybz)8(OH)2](I–)2·3.5CH3OH (1′) and partially recovers iodine from cyclohexane to form [Cu6(pybz)8(OH)2](I–)2·xI2 (1″). Differences of up to 100 times in electrical conductivity and of 4 times in nonlinear optical activity (NLO) have been measured between 1 and 1′. This compound is one of few displaying multifunctionality, electrical conductivity, NLO, and crystal–crystal stability upon release and recovery of iodine. It is also unique in the iodine release from polyiodide anions in a metal–organic framework.

Four coordination polymers Ni(quin-6-c) 2 (1), Zn 2 (quin-6-c) 4 (2), Co 2 (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" 6 5 .8 topology, crystallizes in the acentric orthorhombic space group Pna2 1 and displays powder SHG intensity ca. 460 times in comparing with that of R-quartz. The [Zn(µ 2 -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.

The NiII atom in the title compound, [Ni(C12H8NO2)2(H2O)4], exists in an all-trans octa­hedral coordination environment. The 3-(4-pyrid­yl)benzoate ligand binds to Ni atom through the pyridyl N atom; the pyridine and benzene rings are oriented at a dihedral angle of 26.27 (10)°. Adjacent complexes are linked by O—H⋯O hydrogen bonds, forming a three-dimensional network. The metal atom lies on a special position of 2 site symmetry in the crystal structure.