Investigations on the structure of dimethyl sulfoxide and acetone in aqueous solution

Aqueous solutions of dimethyl sulfoxide (DMSO) and acetone have been investigated using neutron diffraction augmented with isotopic substitution and empirical potential structure refinement computer simulations. Each solute has been measured at two concentrations-1:20 and 1:2 solute:water mole ratios. At both concentrations for each solute, the tetrahedral hydrogen bonding network of water is largely unperturbed, though the total water molecule coordination number is reduced in the higher 1:2 concentrations. With higher concentrations of acetone, water tends to segregate into clusters, while in higher concentrations of DMSO the present study reconfirms that the structure of the liquid is dominated by DMSO-water interactions. This result may have implications for the highly nonideal behavior observed in the thermodynamic functions for 1:2 DMSO-water solutions.     

Double-bridge bonding of aluminium and hydrogen in the crystal structure of gamma-AlH3

Aluminum trihydride (alane) is one of the most promising among the prospective solid hydrogen-storage materials, with a high gravimetric and volumetric density of hydrogen. In the present work, the alane, crystallizing in the gamma-AlH3 polymorphic modification, was synthesized and then structurally characterized by means of synchrotron X-ray powder diffraction. This study revealed that gamma-AlH3 crystallizes with an orthorhombic unit cell (space group Pnnm, a = 5.3806(1) A, b = 7.3555(2) A, c = 5.77509(5) A). The crystal structure of gamma-AlH3 contains two types of AlH6 octahedra as the building blocks. The Al-H bond distances in the structure vary in the range of 1.66-1.79 A. A prominent feature of the crystal structure is the formation of the bifurcated double-bridge bonds, Al-2H-Al, in addition to the normal bridge bonds, Al-H-Al. This former feature has not been previously reported for Al-containing hydrides so far. The geometry of the double-bridge bond shows formation of short Al-Al (2.606 A) and Al-H (1.68-1.70 A) bonds compared to the Al-Al distances in Al metal (2.86 A) and Al-H distances for Al atoms involved in the formation of normal bridge bonds (1.769-1.784 A). The crystal structure of gamma-AlH3 contains large cavities between the AlH6 octahedra. As a consequence, the density is 11% less than for alpha-AlH3.     

Iridium(III) Complexes Bearing Pyrene‐Functionalized 1,10‐Phenanthroline Ligands as Highly Efficient Sensitizers for Triplet–Triplet Annihilation Upconversion

“Chemistry‐on‐the‐complex” synthetic methods have allowed the selective addition of 1‐ethynylpyrene appendages to the 3‐, 5‐, 3,8‐ and 5,6‐positions of Ir^III‐coordinated 1,10‐phenanthroline via Sonogashira cross‐coupling. The resulting suite of complexes has given rise to the first rationalization of their absorption and emission properties as a function of the number and position of the pyrene moieties. Strong absorption in the visible region (e.g. 3,8‐substituted Ir‐3 : λ_abs=481 nm, ?=52 400 m ^?1 cm^?1) and long‐lived triplet excited states (e.g. 5‐substituted Ir‐2 : τ_T=367.7 μs) were observed for the complexes in deaerated CH₂Cl₂. On testing the series as triplet sensitizers for triplet–triplet annihilation upconversion, those Ir^III complexes bearing pyrenyl appendages at the 3‐ and 3,8‐positions ( Ir‐1 , Ir‐3 ) were found to give optimal upconversion quantum yields (30.2 % and 31.6 % respectively).     

Structurally characterized hetero-oligopolyphenylenes: synthetic advances toward next-generation heterosuperbenzenes

The successful Diels-Alder [2+4] cycloaddition of dipyrimidyl acetylene and suitably substituted 2,3,4,5-tetraarylcyclopenta-2,4-dien-1-ones (3-7) generates a series of selectively functionalized hexaarylbenzenes. Each has two pairs of peripheral functional groups (R' and R=tert-butyl 8 and R=methyl 9, methoxy 10, bromo 11, triisopropylsilylethynyl 12) and four ortho-imine nitrogen atoms. The dibromo derivative 11 is a useful precursor for the formation of a mono ethynyl 13 and diethynyl 14 substituted polyphenylene. Changing the dienophile to di(2-thienyl)acetylene gives an S-heteroatom polyphenylene 15. The compounds were fully characterized by using (1)H, (13)C and a range of 2 D NMR spectroscopic techniques, elemental analysis, and mass spectrometry. Oxidative cyclodehydrogenation of dimethoxy hexaphenylbenzene 10 by using iron(III) chloride results in the formation of a spirocyclic dienone 16, which in a separate reaction undergoes dienone/phenol rearrangement to give the first 4-fused-ring, N-heterosuperbenzene (HSB) 17. Six single crystal molecular structures reveal the commonality of unidirectional twisting of the external aromatic rings in these heteroatom polyphenylenes. The twist angles and any H-bonding or interdigitation in these structures are discussed.     

Extending the nitrogen-heterosuperbenzene family: the spectroscopic, redox, and photophysical properties of "half-cyclized" N-1/2HSB and Its Ru(II) complex

Oxidative cyclodehydrogenation is an important process in the formation of the new graphene, N-(1)/(2)HSB 2. This heteropolyaromatic results from the FeCl(3)-catalyzed oxidative cyclodehydrogenation of 1,2-dipyrimidyl-3,4,5,6-tetra-(4-tert-butylphenyl)benzene. Three new C-C bonds are formed that lock the two pyrimidines in a molecular platform comprising eight fused aromatic rings flanked by two remaining "uncyclized" phenyl rings. Mechanistically intriguing is the fact that N-HSB 1, the product of six C-C bond fusions, is co-synthesized with its "half-cyclized" daughter in this reaction. 1 and 2 have the same bidentate N-atom arrangement. This facilitates formation of the heteroleptic Ru(II) complexes, [Ru(bpy)(2)(2)](PF(6))(2) 4 and [Ru(bpy)(2)(1)](PF(6))(2) 3, which differ in the size and planarity of their aromatic ligands. The new ligand 2 and its complex 4 are characterized by (1)H NMR, IR, ESI-MS, and accurate mass methods. 2 exhibits photophysical properties that are consistent with a reduction of the pi/pi framework, a concomitant increase in the energy of the LUMO, and a blue-shift of the solvent-dependent fluorescence (lambda(em) = 474 nm, phi(F) = 0.55, toluene) as compared to its parent. Complex 4 absorbs throughout the visible region and borders on near-IR emitter character, exhibiting a slightly blue-shifted (3)MLCT emission (868 nm, CH(3)CN) as compared to that of [Ru(bpy)(2)(1)](PF(6))(2) 3 (880 nm, CH(3)CN). Electrochemical analyses permit further elucidation of the intermolecular interactions of 3 and 4. These and the concentration and temperature-dependent NMR spectra of 4 confirm it to be nonaggregating, a direct result of the two uncyclized and rotatable phenyl rings in 2.     

Role of thermodynamics in the shape transformation of embedded metal nanoparticles induced by swift heavy-ion irradiation

Swift heavy-ion irradiation of elemental metal nanoparticles (NPs) embedded in amorphous SiO(2) induces a spherical to rodlike shape transformation with the direction of NP elongation aligned to that of the incident ion. Large, once-spherical NPs become progressively more rodlike while small NPs below a critical diameter do not elongate but dissolve in the matrix. We examine this shape transformation for ten metals under a common irradiation condition to achieve mechanistic insight into the transformation process. Subtle differences are apparent including the saturation of the elongated NP width at a minimum sustainable, metal-specific value. Elongated NPs of lesser width are unstable and subject to vaporization. Furthermore, we demonstrate the elongation process is governed by the formation of a molten ion-track in amorphous SiO(2) such that upon saturation the elongated NP width never exceeds the molten ion-track diameter.