Engineering Hydrogen-Bonded Hexagonal Networks Built from Flexible 1,3,5-Trisubstituted Derivatives of Benzene

2,4-Diamino-1,3,5-triazinyl (DAT) groups are known to form N–H···N hydrogen bonds according to reliable patterns of self-association. In compounds <b>3a</b>–<b>c</b>, three DAT groups are attached to trigonally substituted phenyl cores via identical flexible arms. Crystallization of compounds <b>3a</b>–<b>c</b> produces robust networks in which each molecule is linked to its immediate neighbors by a total of 10–12 hydrogen bonds. In compound <b>3a</b>, the DAT groups are designed to lie close to the plane of the phenyl core, thereby giving hydrogen-bonded sheets built from hexameric rosettes. In contrast, the more highly substituted phenyl cores of analogues <b>3b</b> and <b>3c</b> favor conformations in which the DAT groups are no longer coplanar, leading predictably to the formation of three-dimensional networks. In general, the nominally trigonal topologies of compounds <b>3a</b>–<b>c</b> favor structures in which hexagonal networks are prominent, so they behave like trimesic acid despite their greater complexity and flexibility. The structures of all crystals incorporate open networks with significant fractions of volume accessible to guests (32–60%). Despite their flexibility, compounds <b>3a</b>–<b>c</b> appear to be unable to assume conformations that pack efficiently and simultaneously allow the DAT groups to engage in normal hydrogen bonding

Using Systematic Comparisons of 2D and 3D Structures To Reveal Principles of Molecular Organization. Tetraesters of Linear Bisisophthalic Acids

Linear bisisophthalic acids <b>1</b> and <b>2</b> and analogous structures are known to be adsorbed on graphite to give nanopatterns that are programmed by the concerted effects of topology and hydrogen bonding. For comparison, we have now studied the corresponding tetraesters <b>3</b>–<b>7</b>, which have similar topologies and affinities for graphite but cannot form strong intermolecular interactions. As a result, they fail to crystallize in 2D and 3D according to consistent patterns. The sharply contrasting behavior of the tetraacids and tetraesters provides compelling evidence for the hypothesis that molecular organization is best controlled in both 2D and 3D by using topology and strong directional interactions in tandem to control the relative orientation of neighbors. When topology and dominant intermolecular interactions are in harmony, then organization can be expected to follow reliable patterns within a related series of compounds, and structures in 2D and 3D can be designed to show high levels of homology

Using Systematic Comparisons of 2D and 3D Structures To Reveal Principles of Molecular Organization. Tetraesters of Linear Bisisophthalic Acids

Linear bisisophthalic acids <b>1</b> and <b>2</b> and analogous structures are known to be adsorbed on graphite to give nanopatterns that are programmed by the concerted effects of topology and hydrogen bonding. For comparison, we have now studied the corresponding tetraesters <b>3</b>–<b>7</b>, which have similar topologies and affinities for graphite but cannot form strong intermolecular interactions. As a result, they fail to crystallize in 2D and 3D according to consistent patterns. The sharply contrasting behavior of the tetraacids and tetraesters provides compelling evidence for the hypothesis that molecular organization is best controlled in both 2D and 3D by using topology and strong directional interactions in tandem to control the relative orientation of neighbors. When topology and dominant intermolecular interactions are in harmony, then organization can be expected to follow reliable patterns within a related series of compounds, and structures in 2D and 3D can be designed to show high levels of homology

Using Systematic Comparisons of 2D and 3D Structures To Reveal Principles of Molecular Organization. Tetraesters of Linear Bisisophthalic Acids

Linear bisisophthalic acids <b>1</b> and <b>2</b> and analogous structures are known to be adsorbed on graphite to give nanopatterns that are programmed by the concerted effects of topology and hydrogen bonding. For comparison, we have now studied the corresponding tetraesters <b>3</b>–<b>7</b>, which have similar topologies and affinities for graphite but cannot form strong intermolecular interactions. As a result, they fail to crystallize in 2D and 3D according to consistent patterns. The sharply contrasting behavior of the tetraacids and tetraesters provides compelling evidence for the hypothesis that molecular organization is best controlled in both 2D and 3D by using topology and strong directional interactions in tandem to control the relative orientation of neighbors. When topology and dominant intermolecular interactions are in harmony, then organization can be expected to follow reliable patterns within a related series of compounds, and structures in 2D and 3D can be designed to show high levels of homology

Synthesis of Salts of 1,2,5,6- and 1,4,5,8-Naphthalenetetramine

1,2,5,6-Naphthalenetetramine (<b>1a</b>), its 1,4,5,8-isomer (<b>2a</b>), and their salts are valuable precursors for synthesizing nitrogen-containing arenes and other targets of interest. We describe how salts of tetramines <b>1a</b> and <b>2a</b> can be made from simple protected derivatives of 1,5-naphthalenediamine (<b>2d</b>) by sequences of regioselective dinitration, deprotection, and reduction. Various shortcomings of previously reported syntheses of tetramines <b>1a</b> and <b>2a</b> can thereby be avoided. In addition, we report structural studies that may help clarify the mechanism of nitration and resolve an earlier controversy about the regioselectivity observed in nitrations of derivatives of 1,5-naphthalenediamine (<b>2d</b>)

Molecular Organization of 2,1,3-Benzothiadiazoles in the Solid State

Derivatives of 2,1,3-benzothiadiazole (<b>1</b>) are widely used in many areas of science and are particularly valuable as components of active layers in various thin-film optoelectronic devices. Even more effective benzothiadiazoles are likely to result if a deeper understanding of their preferred patterns of molecular association can be acquired. To provide new insight, we have analyzed the structures of compounds in which multiple benzothiadiazole units are attached to well-defined planar and nonplanar molecular cores. Our results show that molecular organization can be controlled in complex structures by using directional S···N bonding of benzothiadiazole units and other characteristic interactions. Moreover, the observed structures are distinctly different from those of analogous arenes. Replacing benzene rings in arenes by thiadiazoles thereby provides a strategy for making new compounds with extended systems of π-conjugation and unique patterns of molecular organization, including the ability to co-crystallize with the fullerenes C₆₀ and C₇₀

Molecular Networks Created by Charge-Assisted Hydrogen Bonding in Phosphonate, Phosphate, and Sulfonate Salts of Bis(amidines)

Two bis­(amidines), 2,2′-bi-2-imidazoline (BI) and fluoflavin (FF), were treated with phosphonic, phosphoric, and sulfonic acids in an effort to produce crystalline salts composed of ions linked by networks of charge-assisted hydrogen bonds. As intended, mixing bis­(amidine) BI with 1,4-benzenediphosphonic acid and 1,3,5-benzenetriphosphonic acid yielded crystals of phosphonate salts of dication H₂BI⁺². Structural analyses showed that such salts tend to incorporate tapes composed of alternating dications and anions linked by multiple charge-assisted N–H···O hydrogen bonds of type R₂²(9) and R₂¹(7). Typically, the ionic tapes are further connected to form sheets or other assemblies by additional O–H···O hydrogen bonds involving phosphonate anions. An analogous reaction of the more weakly basic bis­(amidine) FF with 1,4-benzenedisulfonic acid yielded only a sulfonate salt of monocation HFF⁺; however, diprotonation could be achieved by phosphoric acid to produce a crystalline salt built from stacks of H₂FF⁺² dications linked to phosphate anions by charge-assisted N–H···O hydrogen bonds of type R₂²(8). Together, these results demonstrate that acids with multiple PO­(OH)₂ and SO₂OH groups can react with bis­(amidines) to produce salts with structural features resulting predictably from the geometry of the ions and their ability to engage in multiple charge-assisted hydrogen bonds according to standard patterns

Recycling Indium Tin Oxide (ITO) Electrodes Used in Thin-Film Devices with Adjacent Hole-Transport Layers of Metal Oxides

Many thin-film optoelectronic devices use electrodes made of tin-doped indium oxide (ITO), which is acceptably conductive, as well as virtually transparent and colorless. Regrettably, indium is an uncommon element and its price continues to rise, so it is increasingly important to recover ITO electrodes from devices that are no longer needed. Previous work has shown that simple sonication in neutral water can separate intact ITO electrodes from other components in typical devices, in which the active components and ITO are separated by an ionic buffer layer of poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS). Sonication in water appears to be effective because it favors selective penetration and dissolution of PEDOT:PSS, thereby freeing the underlying ITO electrode. However, PEDOT:PSS is being replaced in emerging devices by the use of various metal oxides as hole-transport materials. We have now found that ITO electrodes in these new devices can be recycled by sonication in dilute aqueous base. The layers of ITO undergo only minor changes in composition and morphology, and the recovered electrodes can be reused many times to fabricate new devices without loss of performance

A Green Approach to Organic Thin-Film Electronic Devices: Recycling Electrodes Composed of Indium Tin Oxide (ITO)

Organic thin-film optoelectronic devices, unlike inorganic analogues, offer the attractive prospect of large, flexible, and inexpensive arrays made by simple procedures such as roll-to-roll printing. In current organic thin-film devices, layers of tin-doped indium oxide (ITO) are widely used as electrodes. Motivated by the increasing price of indium and the high cost of ITO-coated substrates, we have examined ways to recover and recycle ITO substrates in typical devices by environmentally benign methods. A process using only water yields recovered ITO substrates that can be reused at least 10 times to prepare new devices without loss of efficiency