3D printing of functional materials with spatial control of structure and composition is useful for many applications and increases design space. Here, a microextrusion-based method, known as direct ink writing (DIW), is harnessed to further advance 3D complexity by tuning dual-cure ink formulations via varying fillers and filler concentrations. In these inks, low-molecular-weight minor acrylate components enable printing of complex shapes by rapid UV curing during printing while the major heat-cured urethane components provide elastomeric properties when forming a urethane-grafted acrylate polymer (UGAP). The printing process itself displays exquisite control of structure and composition as well as robustness to inks exhibiting a wide range of yield stresses (between 11.5 and 8042 Pa) while still maintaining necessary shape retention during printing. By incorporating micro- or nanosized solid fillers in the inks, an expansive range of both structural and mechanical properties are achievable. Additionally, by modulating the ratio of resin and solid fillers, various combinations of print-mold and pore-forming steps can be employed to expand the design space. The power and versatility of these process permutations are demonstrated by producing a broad range of complex components with controlled properties and performance for applications such as soft robotics.

Elastomeric Ink Chemistries Novel urethane elastomeric ink chemistries for direct-ink-write printing with on-demand and post-print tunability are presented in article number 2100700 by Eric V. Bukovsky and colleagues. Realizing tunable and dynamic mechanical properties via multiple design routes in a single print for advanced material applications such as soft robotics.

Heterocyclic energetic polymers can bridge the gap between inert and detonable energetic materials.

The X-ray and DFT-optimized structures of the electron acceptor 2,3,6,7,9,10-anthra-cene(CF3)(6) (ANTH-6-1) and the 1/2 donor/acceptor co-crystal pyrene/(ANTH-6-1)(2) are reported. These structures, along with extensive DFT calculations on various conformations of ANTH-6-1 and 9,10-ANTH(CF3)(2), suggest that the degree of bending of the aromatic core in ANTH-6-1 and the DFT-predicted energies of ANTH-6-1 and 9,10-ANTH(CF3)(2) are strongly correlated with the relative eclipsed vs. staggered conformations of the CF3 groups attached to the central C(sp(2)) carbon atoms (C9 and C10). Other literature X-ray and DFT-optimized structures of anthracene and pentacene derivatives with n-C8F17 and/or CF3 substituents on the central C(sp(2)) atoms are analyzed and show (i) that the eclipsed vs. staggered correlation with the degree of bending of the aromatic cores may be a general phenomenon and (ii) that molecules of this type are probably more stable when the acene core is bent than when it is planar. DFT predicted modest changes in the electron affinities of ANTH, 9,10-ANTH(CF3)(2), and ANTH-6-1 as the aromatic cores are bent and the relative eclipsed vs. staggered conformations of the central CF3 groups are changed are also reported. This is the first time that DFT calculations have shown that uniform changes in the conformations of CF3 groups may affect the EAs of some CF3-substituted aromatic molecules. In addition, the tendency of CF3 substituents to exhibit 2-, 3-, and 4-fold rotational disorder in a variety of molecules, and to affect the degree of planarity and electronic properties of PAH(CF3)(n) derivatives, are briefly reviewed (PAH = polycyclic aromatic hydrocarbon).

Transit through the carbon liquid phase has significant consequences for the subsequent formation of solid nanocarbon detonation products. We report dynamic measurements of liquid carbon condensation and solidification into nano-onions over ∽200 ns by analysis of time-resolved, small-angle X-ray scattering data acquired during detonation of a hydrogen-free explosive, DNTF (3,4-bis(3-nitrofurazan-4-yl)furoxan). Further, thermochemical modeling predicts a direct liquid to solid graphite phase transition for DNTF products ~200 ns post-detonation. Solid detonation products were collected and characterized by high-resolution electron microscopy to confirm the abundance of carbon nano-onions with an average diameter of ∽10 nm, matching the dynamic measurements. We analyze other carbon-rich explosives by similar methods to systematically explore different regions of the carbon phase diagram traversed during detonation. Our results suggest a potential pathway to the efficient production of carbon nano-onions, while offering insight into the phase transformation kinetics of liquid carbon under extreme pressures and temperatures.

A solution, solid-state, and computational study is reported of polycyclic aromatic hydrocarbon PAH/PAH(CF3 )n donor/acceptor (D/A) charge-transfer complexes that involve six PAH(CF3 )n acceptors with known gas-phase electron affinities that range from 2.11(2) to 2.805(15) eV and four PAH donors, including seven CT co-crystal X-ray structures that exhibit hexagonal arrays of mixed π-stacks with 1/1, 1/2, or 2/1 D/A stoichiometries (PAH=anthracene, azulene, coronene, perylene, pyrene, triphenylene; n=5, 6). These are the first D/A CT complexes with PAH(CF3 )n acceptors to be studied in detail. The nine D/A combinations were chosen to allow several structural and electronic comparisons to be made, providing new insights about controlling D/A interactions and the structures of CT co-crystals. The comparisons include, among others, CT complexes of the same PAH(CF3 )n acceptor with four PAH donors and CT complexes of the same donor with four PAH(CF3 )n acceptors. All nine CT complexes exhibit charge-transfer bands in solution with λmax between 467 and 600 nm. A plot of E(λmax ) versus [IE(donor)-EA(acceptor)] for the nine CT complexes studied is linear with a slope of 0.72±0.03 eV eV-1 . This plot is the first of its kind for CT complexes with structurally related donors and acceptors for which precise experimental gas-phase IEs and EAs are known. It demonstrates that conclusions based on the common assumption that the slope of a CT E(λmax ) versus [IE-EA] plot is unity may be incorrect in at least some cases and should be reconsidered.

Multiple variations of the reaction conditions reported in 1964 for the diamination of K2B12H12 (potassium dodecahydro-closo-dodecaborate(2-)) with hydroxylamine-O-sulfonic acid were studied to improve the isolated yields of the three isomers of B12H10(NH3)(2). Screening the sets of reaction conditions without completely working up each of the reaction mixtures, and therefore without the lengthy separation and isolation of the individual B12H10(NH3)(2) isomers for each reaction mixture, was possible by recording H-1-N-15 HSQC NMR spectra of the crude reaction mixtures. The H-1-dimension of these spectra exhibited narrow, baseline separated resonances for 1,2-, 1,7- and 1.12-B12H10(NH3)(2) and for the B12H11(NH3)(-) intermediate, allowing their relative concentrations to be determined to the nearest percent. The best synthetic conditions resulted in 9, 25, and 6% isolated yields of 1,2-, 1,7- and 1.12-B12H10(NH3)(2), respectively. The decafluoro derivatives 1,2-, 1,7-, and 1,12-B12F10(NH3)(2) were prepared for the first time by direct fluorination of the B12H10(NH3)2 isomers, either individually or as a mixture subsequently separated by column chromatography similar to the separation and purification of the B12H10(NH3)(2) isomers. The structures of 1,7-B12F10(NH2)(2)center dot 4CH(3)CONH(2), 1,12-B12F10(NH2)(2)center dot 6CH(3)CONH(2), 1,2-B12H10(NH2)(2)center dot 1.5CH(3)CO(2)CH(2)CH(3), 1,7-B12H10(NH2)(2)center dot 1.23H(2)O, 1,12-B12H10(NH2)(2)center dot 2CH(3)CN, and solvent-free 1,12-B12H10(NH2)(2) were determined by single-crystal X-ray diffraction.

Metal powders are commonly added to explosive formulations to modify the blast behavior. Although detonation velocity is typically reduced compared to the neat explosive, the metal provides other benefits. Aluminum is a common additive to increase the overall energy output and high-density metals can be useful for enhancing momentum transfer to a target. Typically, metal powder is homogeneously distributed throughout the material; in this study, controlled distributions of metal powder in explosive formulations were investigated. The powder structures were printed using powder bed printing and the porous structures were filled with explosives to create bulk explosive composites. In all cases, the overall ratio between metal and explosive was maintained, but the powder distribution was varied. Samples utilizing uniform distributions to represent typical materials, discrete pockets of metal powder, and controlled, graded powder distributions were created. Detonation experiments were performed to evaluate the influence of metal powder design on the output pressure/time and the overall impulse.

Additive manufacturing (AM) has recently shown great promise as a means to tailor a wide range of material properties, both quasi-static and dynamic. An example of controlling the dynamic behavior is to tailor the chemical energy release rate in composite energetic materials such as thermites - which are a subset of pyrotechnics that use a metal fuel and a metal oxide as an oxidizer. Since these materials are most hazardous once finely mixed, the approach taken here is to formulate the fuel and oxidizer separately such that they can be mixed on-the-fly. Herein, the development, formulation, and characterization of two respective aqueous 3D printable inks consisting of Al and CuO are discussed. The rheological properties and ability of the material to span gaps are characterized. To demonstrate that the materials could be mixed and sustain a reaction, the inks are fed into a static mixing nozzle and extruded into a high-aspect ratio test strip. Upon drying, the material can be ignited and sustain a propagation through the part. These results present a facile, and safe, way to AM thermite which can be used for more detailed follow on studies looking at the role of architecture on the reactivity.

Eight M(H2O) n(Z) salt hydrates were characterized by single-crystal X-ray diffraction (Z2- = B12F122-): M = Ca, Sr, n = 7; M = Mg, Co, Ni, Zn, n = 6; M = Ba, n = 4, 5. Weak O-H···F hydrogen bonding between the M(H2O) n2+ cations and Z2- resulted in room-temperature Fourier transform infrared (FTIR) spectra having sharp ν(OH) bands, with full widths at half max of 10-30 cm-1, which are much more narrow than ν(OH) bands in room temperature FTIR spectra of most salt hydrates. Clearly resolved νasym(OH/OD) and νsym(OH/OD) bands with Δν(OH) as small as 17 cm-1 and Δν(OD) as small as 11 cm-1 were observed (Δν(OX) = νasym(OX) - νsym(OX)). The isomorphic hexahydrates ( R3̅) have two fac-(H2O)3 sets of H2O ligands and nearly octahedral coordination spheres. They exhibited four resolvable ν(OH) bands, one νasym(OH)/νsym(OH) pair for H2O ligands with longer O(H)···F distances and one νasym(OH)/νsym(OH) pair for H2O ligands with shorter O(H)···F distances. The ν(OH) bands for the three H2O molecules with shorter, slightly stronger O(H)···F hydrogen bonds were broader, more intense, and red-shifted by ca. 25 cm-1 relative to the bands for the three other H2O molecules, the first time that such small differences in relatively weak O(H)···F hydrogen bonds in the same crystalline hexahydrate have resulted in observable IR spectroscopic differences at room temperature. For the first time room temperature ν(OH) values for salt hexahydrates showed the monotonic progression Mg2+ > Co2+ > Ni2+ > Zn2+, essentially the same progression as the p Ka values for these metal ions in aqueous solution. A further manifestation of the weak O-H···F hydrogen bonding in these hydrates is the latent porosity exhibited by Ba(H2O)5,8(Z), Sr(H2O) n,m(Z), and Ca(H2O)4,6(Z). Finally, the H2O/D2O exchange reaction Co(D2O)6(Z) → Co(H2O)6(Z) was ca. 50% complete in 1 h at 50 °C in N2/17 Torr H2O( g).

The interdigitated and layered structures of the tetraalkylferrocenium salts [DEC][CB11H12], [DEC](2)[B12F12], [DEC][BF4], [DEC][PF6], and [DEC][ClO3] were determined by single-crystal X-ray diffraction (DEC+ = 1,1 ',3,3 '-tetrakis(2-methyl-2-nonyl)ferrocenium(1+)). The structures of the salts of the two smaller anions were similar to the previously published oxoanion structures of [DEC][XOn-](XOn- = NO3-, ClO4-, and ReO4-), with layers of trigonal-pyramidal ClO3- or tetrahedral BF4- anions stuffed between layers of interdigitated ferrocenium ions. The DEC+ cations in structures with the more highly charged and/or larger anions B12F122-, CB11H12-, and PF6- are also layered but the interdigitation is not as regular and not as complete as in the structures with relatively small 1- anions. Other differences and similarities of the eight [DEC](n)[X] structures (n = 1, 2) are discussed. (C) 2018 Elsevier B.V. All rights reserved.

The compound (SiEt3)(2)(B12F12) was generated in hexane by reacting SiHEt3 with (CPh3)(2)(B12F12) in a 2:1 mol ratio. A small crop of crystals of the very reactive compound (SiEt3)(2)(B12F12) suitable for diffraction was isolated and its structure was determined by X-ray crystallography (Pbca, a = 16.67(1) angstrom, b = 17.77(1) angstrom, c = 18.53(1) angstrom). Two SiR3+ cation-like moieties are weakly bonded to F atoms on opposite sides of the B12F322- anion. The Si-F distances are 1.832(2) and 1.842(2) angstrom. The B-F(Si) distances, at 1.459(5) and 1.464(5) angstrom, are 0.087-0.109 angstrom (i.e., 17-21 sigma) longer than the other ten B-F distances. This is the first time that statistically significant B-F bond lengthening due to coordination of B12F122- to a cation has been observed.

A new, easily scalable reactor for trifluoromethylation of carbon-rich thermally stable substrates has been designed, built, and tested in this work. This reactor can withstand temperatures up to 520 degrees C and pressures up to 10(6) Torr (20,000 psi). Several proof-of-concept experiments with polycyclic aromatic hydrocarbons and fullerenes were performed and the results: product distributions, percent conversion of the starting material to useful products, etc., were compared to other synthetic methods. The results of the trifluoromethylation of fullerenes, C-60 and C-70, were shown to produce predominantly thermodynamically stable compounds, S-6-C-60(CF3)(12), C-1-C-70(CF3)(10), and C-s-C-70(CF3)(8), and thus the new reactor can be considered a viable, safe, and economical tool to target the production of these compounds.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The synthesis of high-purity Na2B12F12 and the crystal structures of Na2(B12F12) (5 K neutron powder diffraction (NPD)), Na2(H2O)4(B12F12) (120 K single-crystal X-ray diffraction (SC-XRD)), Na2(B12Cl12) (5 and 295 K NPD), and Na2(H2O)6(B12Cl12) (100 K SC-XRD) are reported. The compound Na2(H2O)4(B12F12) contains {[(Na(μ-H2O)2Na(μ-H2O)2)]2+}∞ infinite chains; the compound Na2(H2O)6(B12Cl12) contains discrete [(H2O)2Na(μ-H2O)2Na(H2O)2]2+ cations with OH···O hydrogen bonds linking the terminal H2O ligands. The structures of the two hydrates and the previously published structure of Na2(H2O)4(B12H12) are analyzed with respect to the relative coordinating ability of B12F122-, B12H122-, and B12Cl122- toward Na+ ions in the solid state (i.e., the relative ability of these anions to satisfy the valence of Na+). All three hydrated structures have distorted octahedral NaX2(H2O)4 coordination spheres (X = F, H, Cl). The sums of the four Na-O bond valence contributions are 71, 75, and 89% of the total bond valences for the X = F, H, and Cl hydrated compounds, respectively, demonstrating that the relative coordinating ability by this criterion is B12Cl122- ≪ B12H122- < B12F122-. Differential scanning calorimetry experiments demonstrate that Na2(B12F12) undergoes a reversible, presumably order-disorder, phase transition at ca. 560 K (287 °C), between the 529 and 730 K transition temperatures previously reported for Na2(B12H12) and Na2(B12Cl12), respectively. Thermogravimetric analysis demonstrates that Na2(H2O)4(B12F12) and Na2(H2O)6(B12Cl12) undergo partial dehydration at 25 °C to Na2(H2O)2(B12F12) and Na2(H2O)2(B12Cl12) in ca. 30 min and 2 h, respectively, and essentially complete dehydration to Na2(B12F12) and Na2(B12Cl12) within minutes at 150 and 75 °C, respectively (the remaining trace amounts of H2O, if any, were not quantified). The changes in structure upon dehydration and the different vapor pressures of H2O needed to fully hydrate the respective Na2(B12X12) compounds provide additional evidence that B12Cl122- is more weakly coordinating than B12F122- to Na+ in the solid state. Taken together, the results suggest that the anhydrous, halogenated closo-borane compounds Na2(B12F12) and Na2(B12Cl12), in appropriately modified forms, may be viable component materials for fast-ion-conducting solid electrolytes in future energy-storage devices.

Structures of the alkali-metal hydrates Li2(H2O)4Z, LiK(H2O)4Z, Na2(H2O)3Z, and Rb2(H2O)2Z, unit cell parameters for Rb2Z and Rb2(H2O)2Z, and the density functional theory (DFT)-optimized structures of K2Z, K2(H2O)2Z, Rb2Z, Rb2(H2O)2Z, Cs2Z, and Cs2(H2O)Z are reported (Z2- = B12F122-) and compared with previously reported X-ray structures of Na2(H2O)0,4Z, K2(H2O)0,2,4Z, and Cs2(H2O)Z. Unusually rapid room-temperature hydration/dehydration cycles of several M2Z/M2(H2O)nZ salt hydrate pairs, which were studied by isothermal gravimetry, are also reported. Finely ground samples of K2Z, Rb2Z, and Cs2Z, which are not microporous, exhibited latent porosity by undergoing hydration at 24-25 °C in the presence of 18 Torr of H2O(g) to K2(H2O)2Z, Rb2(H2O)2Z, and Cs2(H2O)Z in 18, 40, and 16 min, respectively. These hydrates were dehydrated at 24-25 °C in dry N2 to the original anhydrous M2Z compounds in 61, 25, and 76 min, respectively (the exact times varied from sample to sample depending on the particle size). The hydrate Na2(H2O)2Z also exhibited latent porosity by undergoing multiple 90 min cycles of hydration to Na2(H2O)3Z and dehydration back to Na2(H2O)2Z at 23 °C. For the K2Z, Rb2Z, and Cs2Z transformations, the maximum rate of hydration (rhmax) decreased, and the absolute value of the maximum rate of dehydration (rdmax) increased, as T increased. For K2Z ↔ K2(H2O)2Z hydration/dehydration cycles with the same sample, the ratio rhmax/rdmax decreased 26 times over 8.6 °C, from 3.7 at 23.4 °C to 0.14 at 32.0 °C. For Rb2Z ↔ Rb2(H2O)2Z cycles, rhmax/rdmax decreased from 0.88 at 23 °C to 0.23 at 27 °C. For Cs2Z ↔ Cs2(H2O)Z cycles, rhmax/rdmax decreased 20 times over 8 °C, from 6.7 at 24 °C to 0.34 at 32 °C. In addition, the reversible substitution of D2O for H2O in fully hydrated Rb2(H2O)2Z in the presence of N2/16 Torr of D2O(g) was complete in only 60 min at 23 °C.