A new polymorph of 2,6‐diaminopyridine

2,6‐Diaminopyridine (26‐DAP, C₅H₇N₃) is a common intermediate in the synthesis of aromatic azo chromophores, which are widespread in the dyes and pigments industry. Sublimation of commercial 26‐DAP powder yielded a new polymorph, denoted Form II, which grew as colorless orthorhombic needles. Recrystallization from acetone or toluene also yielded Form II as the major phase. Thermal analysis shows that Form II is a less stable polymorph and it converts upon heating at 335 K to the previously reported Form I.     

2,2’-二(4-羟基苯基)丙烷与四丁基铵包合物([(n-C4H9)4N]＋• [(C15H15O2)2H]－)的两种同质异晶体

合成了2,2’-二(4-羟基苯基)丙烷为主体分子的四丁基铵包合物, [(n-C4H9)4N]＋•[(C15H15O2)2H]－, 并通过单晶Ｘ射线衍射法对其进行了晶体结构测定, 发现该包合物的晶体存在两种同质异晶体. 结果表明, 晶型1属单斜晶系, C2/c空间群, 晶胞参数a＝2.8199(2) nm, b＝0.92730(8) nm, c＝2.1450(3) nm, β＝130.050(1)°, Z＝4, R1＝0.0771, wR2＝0.2452; 晶型2属三斜晶系, P`1空间群, 晶胞参数a＝1.0895(1) nm, b＝1.2331(2) nm, c＝1.7244(2) nm, α＝108.137(2)°, β＝94.458(2)°, γ＝100.172(2)°, Z＝2, R1＝0.0697, wR2＝0.2176. 晶型1中2,2’-二(4-羟基苯基)丙烷阴离子的氢键链构成管道式主体晶格, 正四丁基铵阳离子被包合在这些管道中; 晶型2中2个独立的2,2’-二(4-羟基苯基)丙烷阴离子分别形成氢键主体层, 它们交替排列并与夹在其间的正四丁基铵阳离子形成类三明治层状包合物.     

A new crystalline form of αβ‐d‐lactose prepared by oven drying a concentrated aqueous solution of d‐lactose

A new crystalline form of αβ‐d ‐lactose (C₁₂H₂₂O₁₁) has been prepared by the rapid drying of an approximately 40% w/v syrup of d ‐lactose. Initially identified from its novel powder X‐ray diffraction pattern, the monoclinic crystal structure was solved from a microcrystal recovered from the generally polycrystalline mixed‐phase residue obtained at the end of the drying step. This is the second crystalline form of αβ‐d ‐lactose to be identified and it has a high degree of structural three‐dimensional similarity to the previously identified triclinic form.     

New solvents for cellulose: Hydrazine/thiocyanate salt system

The hydrazine/thiocyanate system was found to be an excellent solvent for cellulose. The solubility and solution properties were investigated. Even at room temperature, the combinations of hydrazine and lithium, sodium, and potassium thiocyanate had high dissolution power for cellulose, up to an 18% (w/w) maximum, unrelated to the polymorph, whereas a combination with ammonium thiocyanate exhibited a solubility difference among celluloses I, II, and III. The effect of the temperature cycling of the system for the rapid dissolution of cellulose was investigated thermodynamically. In these systems, a high concentration of salts was necessary to effect the cellulose dissolution; this suggested that an undissociated salt–solvent complex played an important role in the cellulose dissolution as implied by electroconductivity measurements of the hydrazine/salt system. Gel and liquid‐crystal formation was observed in all systems above 4 and 6% (w/w) cellulose concentrations, respectively. The values of both critical concentrations were quite similar to those observed in the ammonia/ammonium thiocyanate system studied earlier in our laboratories. The gelation temperature was between approximately 10 and 50 °C, depending on the salt and cellulose concentration. The dependence of the cellulose solubility on the degree of polymerization was also examined. It is suggested that these solvent systems have great potential for the fiber and film formation of cellulose. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 601–611, 2002; DOI 10.1002/pola.10135     

Ferrocenecarboxylic anhydride: identification of a new polymorph

A new monoclinic polymorph of ferrocenecarboxylic anhydride, [Fe₂(C₅H₅)₂(C₁₂H₈O₃)], was obtained. Three molecules are present in the asymmetric unit, two of them being nearly identical (r.m.s. deviation = 0.11 Å), with the Fe atoms on the same side of the anhydride functional group. In the third molecule, the two Fe atoms are located at opposite sides of the functional group (ferrocene–ferrocene pseudo‐torsion angle = 146.2°), a very unsual feature in metallocene anhydrides. A network of weak intermolecular hydrogen bonds was also disclosed.     

亚微米级ε型CL-20的制备、表征与性能

采用超临界气体抗溶剂(gas anti-solvent, GAS)技术制备了平均粒径为721.9 nm的亚微米级ε型六硝基六氮杂异伍兹烷(CL-20),应用傅立叶变换红外光谱(Fourier translation infrared spectrum, FT-IR),对亚微米级CL-20的晶型进行了鉴别,并进行了小隔板试验、撞击感度和爆发点测试.研究结果表明,细化后的亚微米级ε型CL-20冲击波感度的隔板厚度降低了58.6%,撞击感度的特性落高提高了84.1%,而爆发点保持不变.     

A novel superhard boron nitride polymorph with monoclinic symmetry

In this work, a new superhard material named Pm BN is proposed. The structural properties, stability, mechanical properties, mechanical anisotropy properties, and electronic properties of Pm BN are studied in this work. Pm BN is dynamically and mechanically stable, the relative enthalpy of Pm BN is greater than that of c-BN, and in this respect, and it is more favorable than that of T-B₃N₃, T-B₇N₇, tP24 BN, Imm2 BN, NiAs BN, and rocksalt BN. The Young's modulus, bulk modulus, and shear modulus of Pm BN are 327 GPa, 331 GPa, and 738 GPa, respectively, and according to Chen's model, Pm BN is a novel superhard material. Compared with its original structure, the mechanical anisotropy of Young's modulus of Pm BN is larger than that of C14 carbon. Finally, the calculations of the electronic energy band structure show that Pm BN is a semiconductor material with not only a wide band gap but also an indirect band gap.     

Polymorph Separation by Ordered Patterning

We herein address the problem of polymorph selection by introducing a general and straightforward concept based on their ordering. We demonstrated the concept by the ordered patterning of four compounds capable of forming different polymorphs when deposited on technologically relevant surfaces. Our approach exploits the fact that, when the growth of a crystalline material is confined within sufficiently small cavities, only one of the possible polymorphs is generated. We verify our method by utilizing several model compounds to fabricate micrometric “logic patterns” in which each of the printed pixels is easily identifiable as comprising only one polymorph and can be individually accessed for further operations.     

Backbone flexibility on conjugated polymer's crystallization behavior and thin film mechanical stability

Extensive efforts have been made to develop flexible electronics with conjugated polymers that are intrinsically stretchable and soft. We recently systematically investigated the influence of conjugation break spacers (CBS) on the thermomechanical properties of a series n-type naphthalene diimide-based conjugated polymer and found that CBS can significantly reduce chain rigidity, melting point, as well as glass transition temperature. In the current work, we further examined the influence of CBS on the crystallization behaviors of PNDI-C3 to C6, including isothermal crystallization kinetics, crystal polymorphism and subsequently time-dependent modulus, in a holistic approach using differential scanning calorimetry, X-ray scattering, polarized optical microscopy, atomic force microscopy, and pseudo-free-standing tensile test. Results demonstrate that increasing the length of CBS increases the crystallization half-time by 1 order of magnitude from PNDI-C3 to PNDI-C6 from approximately 10³ to 10⁴ s. The crystallization rate shows a bimodal dependence on the temperature due to the presence of different polymorphs. In addition, crystallization significantly affects the mechanical response, a stiffening in the modulus of nearly three times is observed for PNDI-C5 when annealed at room temperature for 12 h. Crystallization kinetic is also influenced by molecular weight (MW). Higher MW PNDI-C3 crystallizes slower. In addition, an odd–even effect was observed below 50°C, odd-number PNDI-Cxs (C3 and C5) crystallize slower than the adjacent even-numbered PNDI-Cxs (C4 and C6). Our work provides an insight to design flexible electronics by systematically tuning the mechanical properties through control of polymer crystallization by tuning backbone rigidity.     

马来酰肼多形态的太赫兹光谱研究

分子的多形态(多晶型)是指化学组成相同但存在不止一种晶体形式的物质.这些多形态广泛存在于自然界中,其中药物的多形态尤其普遍.这些药物多形态虽然具有相同的化学分子组成,但其理化性质却存在差异,最终会导致药物作用功能的不同.近年来,随着太赫兹(THz)辐射源的产生方式成为一种常规技术后,太赫兹时域光谱技术(THz-TDS)...