The design of pore properties utilizing flexible motifs and functional groups is of importance to obtain porous coordination polymers with desirable functions. We have prepared a 3D pillared-layer coordination polymer, {[Cd(2)(pzdc)(2)L(H(2)O)(2)].5(H(2)O).(CH(3)CH(2)OH)}(n) (1, H(2)pzdc = 2,3-pyrazinedicarboxylic acid; L = 2,5-bis(2-hydroxyethoxy)-1,4-bis(4-pyridyl)benzene) showing (i) a rotatable pillar bearing ethylene glycol side chains acting as a molecular gate with locking/unlocking interactions triggered by guest inclusion between the side chains, (ii) framework flexibility with slippage of the layers, and (iii) coordinatively unsaturated metal centers as guest accessible sites through the removal of the water coligands. The framework clearly shows reversible single-crystal-to-single-crystal transformations in response to the removal and rebinding of guest molecules, the observation of these processes has provided fundamental clues to the understanding of the sorption profiles. The X-ray structures indicate that the 3D host framework is retained during the transformations, involving mainly rotation of the pillars and slippage of the layers. The structure of dried form 2, [Cd(2)(pzdc)(2)L](n), has no void volume and no water coligands. Interestingly, the adsorption isotherm of water for 2 at 298 K exhibits three distinct steps coinciding with the framework functions. Compound 2 favors the uptake of CO(2) (195 K) over N(2) (77 K) and O(2) (77 K). Above all, we report on a molecular gate with a rotational module exhibiting a locking/unlocking system which accounts for gate-opening type sorption profiles.

A new synthetic approach to prepare flexible porous coordination polymers (PCPs) by the use of soft secondary building units (SBUs) which can undergo multiple reversible metal-ligand bonds breaking is reported. We have prepared a zinc paddle-wheel-based two-fold interpenetrated PCP, {[Zn(2)(tp)(2)(L(2))]·2.5DMF·0.5water}(n) (2a, H(2)tp = terephthanlic acid; L(2) = 2,3-difluoro-1,4-bis(4-pyridyl)benzene), showing dynamic structural transformations upon the removal and rebinding of guest molecules. The X-ray structures at different degrees of desolvation indicate the highly flexible nature of the framework. The framework deformations involve slippage of the layers and movement of the two interpenetrated frameworks with respect to each other. Interestingly, the coordination geometry of a zinc paddle-wheel unit (one of the popular SBUs) is considerably changed by bond breaking between zinc and oxygen atoms during the drying process. Two zinc atoms in the dried form 2d reside in a distorted tetrahedral geometry. Compound 2d has no void volume and favors the uptake of O(2) over Ar and N(2) at 77 K. The O(2) and Ar adsorption isotherms of 2d show gate-opening-type adsorption behaviors corroborating the structure determination. The CO(2) adsorption isotherm at 195 K exhibits multiple steps originating from the flexibility of the framework. The structural transformations of the zinc clusters in the framework upon sorption of guest molecules are also characterized by Raman spectroscopy in which the characteristic bands corresponding to ν(sym)(COO(-)) vibration were used.

A heterogeneous “naked‐eye” colorimetric and spectrophotometric cation sensor, SNT‐1, was prepared by immobilization of the azo‐coupled macrocyclic receptor 1 on a silica nanotube (SNT) via sol–gel reaction. The optical sensing ability of SNT‐1 was studied by addition of metal ions such as Ag+, Co2+, Cd2+, Pb2+, Zn2+, Fe3+, Cu2+, and Hg2+ (all as nitrates) in water. Upon the addition of Hg2+ in suspension SNT‐1 resulted in a color change from yellow to violet. This is novel rare example for chromogenic sensing of a specific metal ion by inorganic nanotubes. On the other hand, no significant changes in color were observed in the parallel experiments with Co2+, Cd2+, Pb2+, Zn2+, Fe3+, Cu2+, and Ag+. These findings confirm that SNT‐1 can be useful as chemosensors for selective detection of Hg2+ over a range of metal ions. More interestingly, after addition of NO3– and ClO4– SNT‐1 was observed to change color from yellow to violet and pink, respectively. However, no color changes were observed upon addition of Cl–, Br–, I–, SCN–, or SO42–. Furthermore, the extraction ability of SNT‐1 was also estimated by measuring the amount of Hg2+ adsorbed by ion chromatography, showing that 95 % of the Hg2+ ion is extracted by SNT‐1. This suggests that SNT‐1 is potentially useful as a stationary phase for the separation of Hg2+ in liquid chromatography. In order to extend the above performance to a portable chemosensor kit, SNT‐1 was coated as a thin film of 50 μm thickness onto a glass substrate. The supported SNT‐1 also changed from yellow to violet when dipped into Hg2+ solution. On the other hand, no significant change in color was observed in other metal‐ion solutions. The results imply that the supported SNT‐1 is applicable as a portable colorimetric sensor for detection of Hg2+ in the field.