Crystal structures of N-[4-(tri-fluoro-meth-yl)phen-yl]benzamide and N-(4-meth-oxy-phen-yl)benz-amide at 173†K: a study of the energetics of conformational changes due to crystal packing.

As a part of our study of the syntheses of aryl amides, the crystal structures of two benzamides were determined from single-crystal X-ray data at 173 K. Both crystal structures contain mol-ecular units as asymmetric units with no solvent in the unit cells. Crystal structure I, TFMP, is the result of the crystallization of N-[4-(tri-fluoro-meth-yl)phen-yl]benzamide, C14H10F3NO. Crystal structure II, MOP, is composed of N-(4-meth-oxy-phen-yl)benzamide, C14H13NO2, units. TFMP is triclinic, space group P , consisting of two mol-ecules in the unit cell related by the center of symmetry. MOP is monoclinic, space group P21/c, consisting of four mol-ecules in the unit cell. Both types of mol-ecules contain three planar regions; a phenyl ring, an amide planar region, and a para-substituted phenyl ring. The orientations of these planar regions within the asymmetric units are compared to their predicted orientations, in isolation, from DFT calculations. The aryl rings are tilted approximately 60° with respect to each other in both experimentally determined structures, as compared to 30° in the DFT results. These conformational changes result in more favorable environments for N-H⋯O hydrogen bonding and aryl ring π-stacking in the crystal structures. Inter-molecular inter-actions were examined by Hirshfeld surface analysis and qu-anti-fied by calculating mol-ecular inter-action energies. The results of this study demonstrate that both hydrogen bonding and dispersion are essential to the side-by-side stacking of mol-ecular units in these crystal structures. Weaker dispersion inter-actions along the axial directions of the mol-ecules reveal insight into the melting mechanisms of these crystals.

2,5-Dioxopyrrolidin-1-yl 2-methyl-prop-2-enoate.

In the title compound, C8H9NO4, the pyrrolidine ring (r.m.s. deviation 0.014 Å) is almost normal to the mean plane of the propenoate group (r.m.s deviation 0.028 Å), making a dihedral angle of 86.58 (4)°. In the crystal, mol-ecules are linked via pairs of weak C-H⋯O hydrogen bonds, forming inversion dimers which stack along the c axis.

High extinction coefficient Ru-sensitizers that promote hole transfer on nanocrystalline TiO2.

Two series of Ru(II) polypyridyl compounds with formulas [(bpy)2RuL](PF6)2 and [(deeb)2RuL](PF6)2, where bpy is 2,2'-bipyridine, deeb is 4,4'-diethylester-2,2'-bpy, and L is one of several substituted 9'-(1,3-dithiole-2-ylidene)-4',5'-diazafluorene ligands, were studied as potential photosensitizers for TiO2. These compounds possess notably high extinction coefficients (≥40,000 M(-1) cm(-1) @470 nm) which are shown by time-dependent density functional theory (TD-DFT) calculations to result from overlapping metal-to-ligand charge transfer (MLCT) and ligand-localized transitions. Low-temperature absorption and photoluminescence measurements were suggestive of a short-lived MLCT excited state. When adsorbed onto TiO2 thin films, both the free ligands (L) and their corresponding [(deeb)2RuL](2+) complexes exhibited rapid excited-state electron injection into TiO2; in the case of the complexes, this was followed by rapid (k>10(8) s(-1)) hole transfer from Ru(III) to the 1,3-dithiole ring of the L ligand. Observation of diffusion-limited reductive quenching of the [Ru(bpz)3](2+)* (bpz is 2,2'-bipyrazine) excited state by the L ligands in solution supported the occurrence of intramolecular hole transfer following electron injection by the TiO2-anchored complexes.

New dicarboxylic acid bipyridine ligand for ruthenium polypyridyl sensitization of TiO2.

An ambidentate dicarboxylic acid bipyridine ligand, (4,5-diazafluoren-9-ylidene) malonic acid (dfm), was synthesized for coordination to Ru(II) and mesoporous nanocrystalline (anatase) TiO(2) thin films. The dfm ligand provides a conjugated pathway from the pyridyl rings to the carbonyl carbons of the carboxylic acid groups. X-ray crystal structures of [Ru(bpy)(2)(dfm)]Cl(2) and the corresponding diethyl ester compound, [Ru(bpy)(2)(defm)](PF(6))(2), were obtained. The compounds displayed intense metal-to-ligand charge transfer (MLCT) absorption bands in the visible region (ε > 11,000 M(-1) cm(-1) for [Ru(bpy)(2)(dfm)](PF(6))(2) in acetonitrile). Significant room temperature photoluminescence, PL, was absent in CH(3)CN but was observed at 77 K in a 4:1 EtOH:MeOH (v:v) glass. Cyclic voltammetry measurements revealed quasi-reversible Ru(III/II) electrochemistry. Ligand reductions were quasi-reversible for the diethyl ester compound [Ru(bpy)(2)(defm)](2+), but were irreversible for [Ru(bpy)(2)(dfm)](2+). Both compounds were anchored to TiO(2) thin films by overnight reactions in CH(3)CN to yield saturation surface coverages of 3 × 10(-8) mol/cm(2). Attenuated total reflection infrared measurements revealed that the [Ru(bpy)(2)(dfm)](2+) compound was present in the deprotonated carboxylate form when anchored to the TiO(2) surface. The MLCT excited states of both compounds injected electrons into TiO(2) with quantum yields of 0.70 in 0.1 M LiClO(4) CH(3)CN. Micro- to milli-second charge recombination yielded ground state products. In regenerative solar cells with 0.5 M LiI/0.05 M I(2) in CH(3)CN, the Ru(bpy)(2)(dfm)/TiO(2) displayed incident photon-to-current efficiencies of 0.7 at the absorption maximum. Under the same conditions, the diethylester compound was found to rapidly desorb from the TiO(2) surface.

cis-3,3-Dimethyl-3,3a,4,5,6,6a-hexa-hydro-1H-cyclo-penta-[c]furan-1,6-dione.

The bicyclic mol-ecule of the title compound, C(9)H(12)O(3), contains two five-membered rings with different functional groups, viz. a ketone and an ester. Both rings assume an envelope conformation. The mean planes of these functional groups form a dihedral angle of 60.7 (1)°. The crystal structure exhibits weak inter-molecular C-H⋯O inter-actions, which link the mol-ecules into zigzag chains extended in the [010] direction. The unit cell contains a racemic mixture of enanti-omers.

2,4,6-Tris-(4-fluoro-phen-yl)-2-(1-pyrid-yl)-boroxine.

Crystals of the title compound, C(23)H(17)B(3)F(3)NO(3), were obtained unintentionally by slow evaporation of a chloro-form solution of the preformed boroxine-pyridine adduct. The mol-ecule contains three fluoro-substituted benzene rings, each bonded to one of the three B atoms of a six-membered boroxine ring. A pyridyl ring is also bound to one of the B atoms through a Lewis acid-base inter-action. The binding of the pyridyl substituent causes the otherwise planar boroxine ring to twist, resulting in a maximum torsion angle within the ring of 17.6 (2)°.