Solids showing unusual and unexpected properties are the key toward the development of new advanced functional materials. Here, we describe two different types of Zn(II) complexes obtained from three different derivatives of 4-styrylpyridine under the same experimental conditions: [Zn 3 (cin) 6 (2F-4spy) 2 •Zn 2 (cin) 4 (2F-4spy) 2 ] (1), [Zn 2 (cin) 4 (4spy) 2 ] (2), and [Zn 2 (cin) 4 (3F-4spy) 2 ] (3), where cin = cinnamate, 2F-4spy = 2-fluoro-4′styrylpyridine and 3F-4spy = 3-fluoro-4′-styrylpyridine. Of these 1 is a photostable inorganic cocrystal comprising a trinuclear Zn(II) complex and a paddlewheel Zn(II) complex, whereas 2 and 3 are photoreactive Zn(II) complexes with paddlewheel structure. The neighboring olefin bonds in the styrylpyridine ligands in 2 and 3 are aligned in a head-to-tail manner, but not the olefin bonds in the cinnamate ligands. The distance between the pairs of olefin bonds are 4.348(2) Å in 2 and 4.045(2) Å in 3. However, they not only undergo solid state photochemical [2 + 2] cycloaddition reaction under UV light but also show the photosalient behavior during the photoreaction. An overall increase in the percentage cell volume of 11.93% and 10.13% for 2 and 3, respectively, during the photoreaction appears to indicate a significant anisotropic expansion is responsible for the photosalient effect.

Although a plethora of metal complexes have been characterized, those having multifunctional properties are very rare. This article reports three isotypical complexes, namely [Cu(benzoate)L 2], where L = 4-styrylpyridine (4spy) (1), 2′-fluoro-4-styrylpyridine (2F-4spy) (2) and 3′-fluoro-4-styrylpyridine (3F-4spy) (3), which show photosalient behavior (photoinduced crystal mobility) while they undergo [2+2] cycloaddition. These crystals also exhibit anisotropic thermal expansion when heated from room temperature to 200°C. The overall thermal expansion of the crystals is impressive, with the largest volumetric thermal expansion coefficients for 1, 2 and 3 of 241.8, 233.1 and 285.7 × 10−6 K−1, respectively, values that are comparable to only a handful of other reported materials known to undergo colossal thermal expansion. As a result of the expansion, their single crystals occasionally move by rolling. Altogether, these materials exhibit unusual and hitherto untapped solid-state properties.

In this review, we provide an elaborate overview of the state-of-the-art synthesis, design, properties and applications of cyclodextrin metal-organic frameworks (CD-MOFs), CD-MOF hybrids and materials derived from CD-MOFs.

Reaction of bpy (bpy = 4,4'-bipyridine) with Pb(OAc)·3HO in DMF (DMF = dimethylformamide) afforded a metal-organic framework (MOF), [Pb(μ-bpy)(μ-OCCH)(μ-OCCH)]·HO (1). Reaction of bpy with Pb(OCCF) in a methanol and chloroform mixture furnished another MOF, [Pb(μ-bpy)(μ-OCCF)]·/CHCl (2). However, the reaction of bpy with Pb(OAc)·3HO in the presence of trifluoroacetic acid in a similar reaction condition yielded a hydrogen-bonded zwitter-ionic complex of Pb(II), [Pb(bpy-H)(OCCF)] (3). All compounds have been characterized by single crystal X-ray crystallography, FT-IR, and H NMR spectroscopies. Compound 1 forms four heptacoordinated Pb(II) joined by (OCCH)-O- linkages, resulting in a 3D noninterpenetrated MOF net with a four-connected uninodal sra (SrAl) topology. However, in 2, tetra-connected Pb(OCCF) cluster units are linked further through eight bpy ligands to furnish a doubly interpenetrated MOF with a new topology but having the very similar connectivity of 1, whereas 3 forms a zigzag hydrogen-bonded chain structure. The variation of carboxylate anions, pH of the reaction medium, and the ratio of the reactants profoundly affected the final topological structure of the compounds synthesized. The solid-state photoluminescence of 1-3 was investigated at room temperature. Interestingly 1, 2, and 3 achieved close to white light emission when excited at 329, 376, and 330 nm, respectively. The systematic understanding of the photophysical properties of analogous Pb-based compounds may open new perspectives for developing single-phase white-light-emitting materials using Pb(II) based MOFs.