Michael J. Bojdys

Ionothermal Synthesis of Crystalline, Condensed, Graphitic Carbon Nitride

Herein we report the synthesis of a crystalline graphitic carbon nitride, or g-C(3)N(4), obtained from the temperature-induced condensation of dicyandiamide (NH(2)C(=NH)NHCN) by using a salt melt of lithium chloride and potassium chloride as the solvent. The proposed crystal structure of this g-C(3)N(4) species is based on sheets of hexagonally arranged s-heptazine (C(6)N(7)) units that are held together by covalent bonds between C and N atoms which are stacked in a graphitic, staggered fashion, as corroborated by powder X-ray diffractometry and high-resolution transmission electron microscopy.

Porous, Fluorescent, Covalent Triazine-Based Frameworks Via Room-Temperature and Microwave-Assisted Synthesis

Porous, fluorescent, covalent triazine-based frameworks (CTFs) are obtained in an unprecedentedly mild reaction, opening up a scalable pathway for molecular building blocks previously thought incompatible with this chemistry. Choice of monomers and synthetic conditions determines the optical properties and nano-scale ordering of these highly microporous materials with BET surface areas exceeding 1100 m(2) g(-1) and exceptional CO(2) capacities (up to 4.17 mmol g(-1)).

Rational Extension of the Family of Layered, Covalent, Triazine‐Based Frameworks with Regular Porosity

2010 WILEY-VCH Verlag Gmb Porous solids are an important class of materials in sorption and chromatography applications and more recently they have also become relevant for applications in catalysis (as active catalyst or support) and storage (gas storage in microporous, batteries). Controlled construction of such extended porous frameworks from suitable molecular building blocks paves the way for establishing a connection betweenmolecular and solid properties in a well-defined, pre-ordered chemical environment. Rational synthesis of extended arrays of organicmatter in bulk, in solution, in crystals, and in thin films has always been a paramount goal in chemistry. The classical synthetic tools to obtain long-range regularity are, however, limited to non-covalent interactions, in contrast to the structurally more random character of covalent polymerization reactions. The most challenging hurdle in the synthesis of extended, yet precisely defined 2D and 3D structures based on covalent chemistry is widely believed to be the requirement that the reaction linking individual organic constituents should be reversible, allowing the scaffold to arrange to the thermodynamic, well-ordered product rather than the kinetic, amorphous structure. Reports by Yaghi et al. have shown that two kinds of condensation reactions yielding planar, six-membered boroxine rings (B3O3) and five-membered BO2C2 rings meet this criterion and thus can be utilized as covalent linkers between organic units to generate 2D and 3D covalent organic frameworks (COFs). Successful synthesis of COF materials from light, non-metallic, molecular building blocks is appealing for applications such as gas storage and catalysis – in particular because they hold the promise of being completely inert with respect to water, unlike many (metal organic) frameworks known from literature. Additionally, the large number of inexpensive organic compounds offers modularity, in which desirable features such as surface functionalization and tunable pore sizes can conceptually be easily achieved. Previously, we showed that the polytrimerization reaction of 1,4-dicyanobenzene in zinc chloride is an alternative way towards covalently linked, covalent, triazine-based frameworks (CTF-1). Although other porous, organic networks based on the triazine linker have been synthesized since, CTF-1 remained unique in particular because it not only exhibited permanent microand mesoporosity but also crystallinity. In the following, we shall report on a secondmember in the class of covalent, triazine-based frameworks (termed CTF-2), which was obtained from the ionothermal condensation of 2,6-naphthalenedinitrile (Fig. 1). This find should corroborate our previous assertion that the triazine ring (C3N3) is a fruitful and modular linking-unit in the synthesis of extended and ordered layered frameworks. In planning the synthesis, we drew on our previous experiences with the cyclotrimerization of dinitrile compounds in a zinc chloride salt melt, and we chose 2,6-naphthalenedicarbonitrile, because of its rigidity and its relative chemical stability resulting from its extended aromatic p-system. The later trait was of special significance, since the reaction conditions involve both elevated temperatures ( 400 8C) and the partaking of a catalytically active species, opening up potential pathways to many undesired decomposition and condensation reactions. One such pathway of aromatic nitrile decomposition involves C H bond cleavage, but also the oxidative halogenation of the aromatic unit in the presence of a metal halide. Homolytic cleavage of the carbon nitrile bond at temperatures above 400 8C and the associated depletion of nitrogen content within the structure were observed previously for a set of studied model compounds in this type of reaction. The framework CTF-2 was synthesized heating zinc chloride and 2,6-naphthalenedicarbonitrile in a quartz glass ampoule at 400 8C for 40 h. The set-up in a closed system was chosen since the monomer starts to sublimate at temperatures around 220 8C. The typical yields of this reaction are in the range of 80–85%, suggesting that some of the side reactions outlined above do occur. In the FTIR spectrum we see that the intensity of the carbonitrile band at 2225 cm 1 decreases significantly after 20 h and diminishes further following the course of the reaction, while bands at 1535 and 1315 cm , indicative of aromatic C N stretching and breathing modes in the triazine unit, appear (c.f. Supporting Information). The C solid-state NMR (CP/MAS) experiment performed on CTF-2 further confirmed the presence of sp carbons from the triazine unit ( 169 ppm) and the naphthalene (133, 128 ppm) as well as sp carbons from unreacted carbonitriles (110 ppm), which are most likely situated at the terminal edges of the condensed material (Supporting Information). Elemental analysis revealed a molecular ratio of C36.0H18.8N5.4, which is close to the theoretical composition of a perfectly condensed, infinite framework, namely C36H18N6. The washing procedure outlined in the experimental section left a

Triazine‐Based Graphitic Carbon Nitride: a Two‐Dimensional Semiconductor

Graphitic carbon nitride has been predicted to be structurally analogous to carbon-only graphite, yet with an inherent bandgap. We have grown, for the first time, macroscopically large crystalline thin films of triazine-based, graphitic carbon nitride (TGCN) using an ionothermal, interfacial reaction starting with the abundant monomer dicyandiamide. The films consist of stacked, two-dimensional (2D) crystals between a few and several hundreds of atomic layers in thickness. Scanning force and transmission electron microscopy show long-range, in-plane order, while optical spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculations corroborate a direct bandgap between 1.6 and 2.0 eV. Thus TGCN is of interest for electronic devices, such as field-effect transistors and light-emitting diodes.

Tuning of gallery heights in a crystalline 2D carbon nitride network

Poly(triazine imide)—a 2D layered network—can be obtained as an intercalation compound with halides from the ionothermal condensation of dicyandiamide in a eutectic salt melt. The gallery height of the intercalated material can be tuned via the composition of the eutectic melt and by post-synthetic modification. Here, we report the synthesis of poly(triazine imide) with intercalated bromide ions (PTI/Br) from a lithium bromide and potassium bromide salt melt. PTI/Br has a hexagonal unit-cell (P63cm (no. 185); a = 8.500390(68) A, c = 7.04483(17) A) that contains two layers of imide-bridged triazine (C3N3) units stacked in an AB-fashion as corroborated by solid-state NMR, FTIR spectroscopy and high-resolution TEM. By comparison with a recently reported material PTI/Li+Cl−, prepared from a LiCl/KCl eutectic, the layer-stacking distance in the analogous bromide material was expanded from 3.38 A to 3.52 A – an exceptionally large spacing for an aromatic, discotic system (cf. graphite 3.35 A). Subsequent treatment of PTI/Br with concentrated ammonium fluoride yields poly(triazine imide) with intercalated fluoride ions (PTI/F) (P63/m (no. 176); a = 8.4212(4) A, c = 6.6381(5) A) as a statistical phase mix with PTI/Br. Fluoride intercalation leads to a contraction of the gallery height to 3.32 A, demonstrating that the gallery height is synthetically tuneable in these materials.

Exfoliation of Crystalline 2D Carbon Nitride: Thin Sheets, Scrolls and Bundles via Mechanical and Chemical Routes

The carbon nitride poly(triazine imide) with intercalated bromide ions is a layered, graphitic material of 2D covalently bonded molecular sheets with an exceptionally large gallery height of 3.52 Å due to the intercalated bromide anions. The material can be cleaved both mechanically and chemically into thin sheets and scrolls analogous to the carbon-only systems graphite and graphene.

Geomimetics for green polymer synthesis: highly ordered polyimides via hydrothermal techniques

Inspired by geological ore formation processes, we apply one-step hydrothermal (HT) polymerization to the toughest existing high-performance polymer, poly(p-phenyl pyromellitimide) (PPPI). We obtain highly-ordered and fully imidized PPPI as crystalline flakes and flowers on the micrometer scale. In contrast to classical 2-step procedures that require long reaction times and toxic solvents and catalysts, HT polymerization allows for full conversion in only 1 h at 200 °C, in nothing but hot water. Investigation of the crystal growth mechanism via scanning electron microscopy (SEM) suggests that PPPI aggregates form via a dissolution–polymerization–crystallization process, which is uniquely facilitated by the reaction conditions in the HT regime. A conventionally prefabricated polyimide did not recrystallize hydrothermally, indicating that the HT polymerization and crystallization occur simultaneously. The obtained material shows excellent crystallinity and remarkable thermal stability (600 °C under N2) that stem from a combination of a strong, covalent polymer backbone and interchain hydrogen bonding.

Anionic silicate organic frameworks constructed from hexacoordinate silicon centres

Crystalline frameworks composed of hexacoordinate silicon species have thus far only been observed in a few high pressure silicate phases. By implementing reversible Si–O chemistry for the crystallization of covalent organic frameworks, we demonstrate the simple one-pot synthesis of silicate organic frameworks based on octahedral dianionic SiO6 building units. Clear evidence of the hexacoordinate environment around the silicon atoms is given by 29Si nuclear magnetic resonance analysis. Characterization by high-resolution powder X-ray diffraction, density functional theory calculation and analysis of the pair-distribution function showed that those anionic frameworks—M2[Si(C16H10O4)1.5], where M = Li, Na, K and C16H10O4 is 9,10-dimethylanthracene-2,3,6,7-tetraolate—crystallize as two-dimensional hexagonal layers stabilized in a fully eclipsed stacking arrangement with pronounced disorder in the stacking direction. Permanent microporosity with high surface area (up to 1,276 m2 g−1) was evidenced by gas-sorption measurements. The negatively charged backbone balanced with extra-framework cations and the permanent microporosity are characteristics that are shared with zeolites. Hexacoordinate silicon is seen often in molecular compounds, but very rarely in crystalline silicate materials. Now, reversible Si–O chemistry has been used to assemble octahedral dianionic SiO6 building units and anthracene derivatives into crystalline microporous silicate organic frameworks that share characteristics of both covalent organic frameworks and inorganic zeolites.

Bulk and Adsorbed Monolayer Phase Behavior of Binary Mixtures of Undecanoic Acid and Undecylamine: Catanionic Monolayers

Differential scanning calorimetry (DSC) and X-ray powder diffraction (PXRD) have been used to determine the phase behavior of the binary mixtures of undecanoic acid (A) and undecylamine (B) in the bulk. In addition, we report DSC data that indicates very similar behavior for the solid monolayers of these materials adsorbed on the surface of graphite. The two species are found to form a series of stoichiometric complexes of the type AB, A(2)B, and A(3)B on the acid rich side of the phase diagram. Interestingly, no similar series of complexes is evident on the amine rich side. As a result of this complexation, the solid monolayers of the binary mixtures exhibit a very pronounced enhancement in stability relative to the pure adsorbates.

Carbon nitride frameworks and dense crystalline polymorphs

We used ab initio random structure searching (AIRSS) to investigate polymorphism in