Guest-Switchable Multi-Step Spin Transitions in an Amine-Functionalized Metal-Organic Framework.

Materials with hysteretic multi-step spin-crossover (SCO) have potential application in high-order data storage. Here, an unprecedented hysteretic four-step SCO behavior with the sequence of LS↔HS0.25 LS0.75 ↔HS0.5 LS0.5 ↔ HS0.75 LS0.25 ↔HS is found in a three-dimensional (3D) Hofmann-type metal-organic framework (MOF), which is evidenced by magnetic, differential scanning calorimetry, and crystal data. Further experiments involving guest exchange leads to the first reversible modulation of four-, two-, and one-stepped SCO behaviors, which provides a new strategy for developing multi-step SCO materials.

Two-Step Spin-Crossover with Three Inequivalent FeII Sites in a Two-Dimensional Hofmann-Type Coordination Polymer.

An unprecedented two-step spin-crossover behavior with the sequence of γHS =1↔γHS =3/4↔γHS =1/4 was observed in two-dimensional Hofmann type coordination polymer [Fe(isoq)2 {Ag(CN)2 }2 ] (isoq=isoquinoline), which resulted from three crystallographically inequivalent FeII sites with distinct transition temperatures.

Anion complexation with cyanobenzoyl substituted first and second generation tripodal amide receptors: crystal structure and solution studies.

Anion complexation properties of two new tripodal amide receptors have been extensively studied here. Two tripodal receptors have been synthesized from the reaction of cyanobenzoyl acid chloride with two tri-amine building blocks such as (i) tris(2-aminoethyl)amine and (ii) tris(2-(4-aminophenoxy)ethyl)amine, which resulted in the first (L1) and second (L2) generation tripodal amides respectively. A detailed comparison of their coordination behavior with anions is also described by crystallographic and solution state experiments. The crystal structure demonstrates various types of spatial orientations of tripodal arms in two receptors and concomitantly interacts with anions distinctively. Intramolecular H-bonding between amide N­H and CO prevents opening of the receptor cavity in the crystal, which leads to a locked conformation of L1 having C(3v) symmetry and makes amide hydrogen unavailable for the anion which results in side cleft anion binding. However, in L2 we conveniently shift the anion binding sites to a distant position which increases cavity size as well as rules out any intramolecular H-bonding between amide N­H and CO. The crystal structure shows a different orientation of the arms in L2; it adopts a quasi-planar arrangement with C(2v) symmetry. In the crystal structure two arms are pointed in the same direction and while extending the contact the third arm is H-bonded with the apical N-atom through a ­CN group, making a pseudo capsular cavity where the anion interacts. Most importantly spatial reorientation of the receptor L2 from a C(2v) symmetry to a folded conformation with a C(3v) symmetry was observed only in the presence of an octahedral SiF6(2-) anion and forms a sandwich type complex. Receptors L1 and L2 are explored for their solution state anion binding abilities. The substantial changes in chemical shifts were observed for the amide (-NH) and aromatic hydrogen (-CH) (especially for F(-)), indicating the role of these hydrogens in anion binding. The anion interacts with receptor L2 more strongly than L1 as confirmed by 1H NMR titration upon monitoring the -NH signal.

An aggregation-induced emission (AIE) active probe renders Al(III) sensing and tracking of subsequent interaction with DNA.

An aggregation-induced emission (AIE) active probe (L) displayed TURN-ON fluorescence response toward Al(3+) under physiological conditions and in HeLa cells. The L-Al(3+) ensemble could subsequently facilitate tracking of interaction with DNA in solution.

Fluorescence Turn on Sensor for Sulfate Ion in Aqueous Medium Using Tripodal-Cu(2+) Ensemble.

We report the selective recognition of sulfate anion in aqueous medium at biological pH 7.2 over the other interfering anions based on naphthoic acid bearing tripodal ligand by applying fluorescence turn off -on mechanism. The carboxylic acid groups in the ligand enhance the solubility in water and enable it to form complex with copper salt. Thus formed L-Cu2+ ensemble quench the fluorescence of the parent ligand and in turn recognize sulfate anion via revival of fluorescence intensity. The 1:2 stoichiometry was confirmed by ESI mass spectral data and Job's plot. The average binding constant was found to be 6.2×10(8) M(-2).