Cu^II-Azide Polynuclear Complexes of Three Different Building Clusters with the Same Schiff-Base Ligand: Synthesis, Structures, Magnetic Behavior, and Density Functional Theory Studies

Three copper-azido complexes [Cu₄(N₃)₈(L¹)₂­(MeOH)₂]_<i>n</i> (<b>1</b>), [Cu₄(N₃)₈(L¹)₂] (<b>2</b>), and [Cu₅(N₃)₁₀(L¹)₂]_<i>n</i> (<b>3</b>) [L¹ is the imine resulting from the condensation of pyridine-2-carboxaldehyde with 2-(2-pyridyl)­ethylamine] have been synthesized using lower molar equivalents of the Schiff base ligand with Cu­(NO₃)₂·3H₂O and an excess of NaN₃. Single crystal X-ray structures show that the basic unit of the complexes <b>1</b> and <b>2</b> contains Cu^II₄ building blocks; however, they have distinct basic and overall structures due to a small change in the bridging mode of the peripheral pair of copper atoms in the linear tetranuclear structures. Interestingly, these changes are the result of changing the solvent system (MeOH/H₂O to EtOH/H₂O) used for the synthesis, without changing the proportions of the components (metal to ligand ratio 2:1). Using even lower proportions of the ligand, another unique complex was isolated with Cu^II₅ building units, forming a two-dimensional complex (<b>3</b>). Magnetic susceptibility measurements over a wide range of temperature exhibit the presence of both antiferromagnetic (very weak) and ferromagnetic exchanges within the tetranuclear unit structures. Density functional theory calculations (using B3LYP functional, and two different basis sets) have been performed on the complexes <b>1</b> and <b>2</b> to provide a qualitative theoretical interpretation of their overall magnetic behavior

Cu^II-Azide Polynuclear Complexes of Three Different Building Clusters with the Same Schiff-Base Ligand: Synthesis, Structures, Magnetic Behavior, and Density Functional Theory Studies

Three copper-azido complexes [Cu₄(N₃)₈(L¹)₂­(MeOH)₂]_<i>n</i> (<b>1</b>), [Cu₄(N₃)₈(L¹)₂] (<b>2</b>), and [Cu₅(N₃)₁₀(L¹)₂]_<i>n</i> (<b>3</b>) [L¹ is the imine resulting from the condensation of pyridine-2-carboxaldehyde with 2-(2-pyridyl)­ethylamine] have been synthesized using lower molar equivalents of the Schiff base ligand with Cu­(NO₃)₂·3H₂O and an excess of NaN₃. Single crystal X-ray structures show that the basic unit of the complexes <b>1</b> and <b>2</b> contains Cu^II₄ building blocks; however, they have distinct basic and overall structures due to a small change in the bridging mode of the peripheral pair of copper atoms in the linear tetranuclear structures. Interestingly, these changes are the result of changing the solvent system (MeOH/H₂O to EtOH/H₂O) used for the synthesis, without changing the proportions of the components (metal to ligand ratio 2:1). Using even lower proportions of the ligand, another unique complex was isolated with Cu^II₅ building units, forming a two-dimensional complex (<b>3</b>). Magnetic susceptibility measurements over a wide range of temperature exhibit the presence of both antiferromagnetic (very weak) and ferromagnetic exchanges within the tetranuclear unit structures. Density functional theory calculations (using B3LYP functional, and two different basis sets) have been performed on the complexes <b>1</b> and <b>2</b> to provide a qualitative theoretical interpretation of their overall magnetic behavior

Electron-Rich Triphenylamine-Based Sensors for Picric Acid Detection

This paper demonstrates the role of solvent in selectivity and sensitivity of a series of electron-rich compounds for the detection of trace amounts of picric acid. Two new electron-rich fluorescent esters (<b>6</b>, <b>7</b>) containing a triphenylamine backbone as well as their analogous carboxylic acids (<b>8</b>, <b>9</b>) have been synthesized and characterized. Fluorescent triphenylamine coupled with an ethynyl moiety constitutes π-electron-rich selective and sensitive probes for electron-deficient picric acid (PA). In solution, the high sensitivity of all the sensors toward PA can be attributed to a combined effect of the ground-state charge-transfer complex formation and resonance energy transfer between the sensor and analyte. The acids <b>8</b> and <b>9</b> also showed enhanced sensitivity for nitroaromatics in the solid state, and their enhanced sensitivity could be attributed to exciton migration due to close proximity of the neighboring acid molecules, as evident from the X-ray diffraction study. The compounds were found to be quite sensitive for the detection of trace amount of nitroaromatics in solution, solid, and contact mode

Sunlight-Induced Covalent Marriage of Two Triply Interlocked Pd₆ Cages and Their Facile Thermal Separation

A template-free triply interlocked Pd₆ cage (<b>2</b>) was synthesized by two-component self-assembly of <i>cis</i>-blocked 90° acceptor <i>cis-</i>(tmen)­Pd­(NO₃)₂ (<b>M</b>) and 1,3,5-tris­((<i>E</i>)-2-(pyridin-3-yl)­vinyl)­benzene (<b>L</b>). Assembly <b>2</b> was characterized by ¹H NMR and ESI-MS, and the structure was confirmed by X-ray crystallography, which revealed a parallel conformation of the olefin double bonds belonging to the adjacent cages in the solid state at a distance of 3.656 Å, thereby indicating the feasibility of [2+2] photochemical reaction. Two adjacent interlocked cages were covalently married together by intermolecular [2+2] cycloaddition in a single crystal-to-single crystal fashion upon exposure to sunlight/UV irradiation. Most surprisingly, the covalently married pair was easily separated thermally in aqueous medium under mild reaction conditions

Electron-Rich Triphenylamine-Based Sensors for Picric Acid Detection

This paper demonstrates the role of solvent in selectivity and sensitivity of a series of electron-rich compounds for the detection of trace amounts of picric acid. Two new electron-rich fluorescent esters (<b>6</b>, <b>7</b>) containing a triphenylamine backbone as well as their analogous carboxylic acids (<b>8</b>, <b>9</b>) have been synthesized and characterized. Fluorescent triphenylamine coupled with an ethynyl moiety constitutes π-electron-rich selective and sensitive probes for electron-deficient picric acid (PA). In solution, the high sensitivity of all the sensors toward PA can be attributed to a combined effect of the ground-state charge-transfer complex formation and resonance energy transfer between the sensor and analyte. The acids <b>8</b> and <b>9</b> also showed enhanced sensitivity for nitroaromatics in the solid state, and their enhanced sensitivity could be attributed to exciton migration due to close proximity of the neighboring acid molecules, as evident from the X-ray diffraction study. The compounds were found to be quite sensitive for the detection of trace amount of nitroaromatics in solution, solid, and contact mode

Image Comparison Based On Local Pixel Clustering

Image comparison is a fundamental step for monitoring images and has wide applications in many disciplines of sciences, including satellite imaging, medical research, quality control and so forth. This problem, however, is complicated because (i) the observed images often contain noise, (ii) the image intensity functions are discontinuous and have spatial structures. In the literature, a vast majority of the methods are intensity-based. However, such an approach is often questionable in real life situations where small changes in the background may not indicate an actual meaningful change in the images as long as the boundaries of the image objects remain the same. In this article, we propose a flexible and effective image comparison method based on local pixel clustering and construct a test statistic based on the Variation of Information metric. This is a feature based image comparison technique where edges or the jump points are considered as the primary features. Numerical examples and statistical properties show that the proposed image comparison method performs well in various real life scenarios.</p

Electron-Rich Triphenylamine-Based Sensors for Picric Acid Detection

This paper demonstrates the role of solvent in selectivity and sensitivity of a series of electron-rich compounds for the detection of trace amounts of picric acid. Two new electron-rich fluorescent esters (<b>6</b>, <b>7</b>) containing a triphenylamine backbone as well as their analogous carboxylic acids (<b>8</b>, <b>9</b>) have been synthesized and characterized. Fluorescent triphenylamine coupled with an ethynyl moiety constitutes π-electron-rich selective and sensitive probes for electron-deficient picric acid (PA). In solution, the high sensitivity of all the sensors toward PA can be attributed to a combined effect of the ground-state charge-transfer complex formation and resonance energy transfer between the sensor and analyte. The acids <b>8</b> and <b>9</b> also showed enhanced sensitivity for nitroaromatics in the solid state, and their enhanced sensitivity could be attributed to exciton migration due to close proximity of the neighboring acid molecules, as evident from the X-ray diffraction study. The compounds were found to be quite sensitive for the detection of trace amount of nitroaromatics in solution, solid, and contact mode

Molecular Marriage through Partner Preferences in Covalent Cage Formation and Cage-to-Cage Transformation

Unprecedented self-sorting of three-dimensional purely organic cages driven by dynamic covalent bonds is described. Four different cages were first synthesized by condensation of two triamines and two dialdehydes separately. When a mixture of all the components was allowed to react, only two cages were formed, which suggests a high-fidelity self-recognition. The issue of the preference of one triamine for a particular dialdehyde was further probed by transforming a non-preferred combination to either of the two preferred combinations by reacting it with the appropriate triamine or dialdehyde

New Structural Topologies in a Series of 3d Metal Complexes with Isomeric Phenylenediacetates and 1,3,5-Tris(1-imidazolyl)benzene Ligand: Syntheses, Structures, and Magnetic and Luminescence Properties

In this article we present the syntheses, characterizations, magnetic and luminescence properties of five 3d-metal complexes, [Co­(tib)­(1,2-phda)]_<i>n</i>­·(H₂O)_<i>n</i> (<b>1</b>), [Co₃(tib)₂­(1,3-phda)₃­(H₂O)]_<i>n</i>­·(H₂O)_2<i>n</i> (<b>2</b>), [Co₅(tib)₃­(1,4-phda)₅­(H₂O)₃]_<i>n</i>­·(H₂O)_7<i>n</i> (<b>3</b>), [Zn₃(tib)₂­(1,3-phda)₃]_<i>n</i>­·(H₂O)_4<i>n</i> (<b>4</b>), and [Mn­(tib)₂­(H₂O)₂]_<i>n</i>­·(1,4-phdaH)_2<i>n</i>­·(H₂O)_4<i>n</i> (<b>5</b>), obtained from the use of isomeric phenylenediacetates (phda) and the neutral 1,3,5-tris­(1-imidazolyl)­benzene (tib) ligand. Single crystal X-ray structures showed that <b>1</b> constitutes 3,5-connected 2-nodal nets with a double-layered two-dimensional (2D) structure, while <b>2</b> forms an interpenetrated 2D network (3,4-connected 3-nodal net). Complex <b>3</b> has a complicated three-dimensional structure with 10-nodal 3,4,5-connected nets. Complex <b>4</b>, although it resembles <b>2</b> in stoichiometry and basic building structures, forms a very different overall 2D assembly. In complex <b>5</b> the dicarboxylic acid, upon losing only one of the acidic protons, does not take part in coordination; instead it forms a complicated hydrogen bonding network with water molecules. Magnetic susceptibility measurements over a wide range of temperatures revealed that the metal ions exchange very poorly through the tib ligand, but for the Co­(II) complexes the effects of nonquenched orbital contributions are prominent. The 3d¹⁰ metal complex <b>4</b> showed strong luminescence with λ_max = 415 nm (for λ_ex = 360 nm)

Molecular Marriage through Partner Preferences in Covalent Cage Formation and Cage-to-Cage Transformation

Unprecedented self-sorting of three-dimensional purely organic cages driven by dynamic covalent bonds is described. Four different cages were first synthesized by condensation of two triamines and two dialdehydes separately. When a mixture of all the components was allowed to react, only two cages were formed, which suggests a high-fidelity self-recognition. The issue of the preference of one triamine for a particular dialdehyde was further probed by transforming a non-preferred combination to either of the two preferred combinations by reacting it with the appropriate triamine or dialdehyde