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In the title compound, C22H13ClN2, the quinoxaline ring system is close to planar [maximum deviation = 0.061 (2) Å]. The phenyl ring at the 2-position and the phenyl ring of the phenyl­ethynyl substituent make dihedral angles of 49.32 (7) and 11.99 (7) °, respectively, with the quinoxaline mean plane. The two phenyl rings are inclined to one another by 61.27 (9)°. In the crystal, mol­ecules are linked by C—H⋯π and π–π inter­actions [centroid–centroid distances = 3.6210 (12) and 3.8091 (12) Å].

In the solid state, the title compound, C22H10N2S, forms centrosymmetric dimers by pairs of non-classical C—H⋯S hydrogen bonds linking approximately coplanar mol­ecules. The benzene ring involved in this inter­action makes a dihedral angle of only 7.21 (16)° with the thio­phene ring, while the other benzene ring is twisted somewhat out of the plane, with a dihedral angle of 39.58 (9)°. The hydrogen-bonded dimers stack on top of each other with an inter­planar spacing of 3.44 Å. C—H⋯N hydrogen bonds link together stacks that run in approximately perpendicular directions. Each mol­ecule thus inter­acts with 12 adjacent mol­ecules, five of them approaching closer than the sum of the van der Waals radii for the relevant atoms. Optimization of the inter-stack contacts contributes to the non-planarity of the mol­ecule.

In the centrosymmetric title compound, C64H62N4, the two phenyl­ethynyl groups lie at diagonal meso positions. The 24-membered porphyrin has in-plane distortion with respect to the mean plane of the macrocycle and two intra-ring bifurcated N—H⋯(N,N) hydrogen bonds occur. The dihedral angles between the phenyl rings in the phenyl­ethynyl group and the 3,5-bis­(tert-but­yl)phenyl group with respect to the mean plane of the porphyrin are 17.2 (2) and 59.2 (3)°. The tert-butyl groups are disordered over two sets of sites in a 0.661 (13):0.339 (13) ratio.

The title compound, C26H22O4, is a derivative of 1,4-bis­(phenyl­ethyn­yl)benzene substituted by four meth­oxy groups at the terminal benzene rings. The asymmetric unit consists of two half-molecules; one centrosymmetric molecule is planar but the other is non-planar, with dihedral angles of 67.7 (1)° between the central benzene ring and the terminal benzene rings. In the crystal structure, mol­ecules form a zigzag mol­ecular network due to π–π [the inter­planar and centroid–centroid distances between the benzene rings are 3.50 (1) and 3.57 (1) Å, respectively] and C—H⋯π inter­actions (2.75 Å). Introduction of the four meth­oxy groups results in the supra­molecular architecture.

The title compound, C26H22O4, is a derivative of 1,4-bis­(phenyl­ethyn­yl)benzene substituted by four meth­oxy groups on the terminal benzene rings. The mol­ecule is almost planar with an r.m.s. deviation of 0.266 Å. The dihedral angles between the two terminal benzene rings and the central benzene ring are 7.96 (6) and 13.32 (7)°. In the crystal structure, mol­ecules aggregate via C—H⋯O inter­actions, forming mol­ecular tapes along the a axis, which aggregate to form a herring-bone structure.

The structure of the title compound, C6H6O3, has been redetermined at low temperature [room-temperature structure: Maartmann-Moe (1965 ▶). Acta Cryst. 19, 155–157]. The mol­ecule is planar with approximate D 3h point symmetry, yet it crystallizes in the chiral ortho­rhom­bic space group P212121 with a three-dimensional hydrogen-bonding network containing infinite O—H⋯O—H⋯O—H chains.

The tellurium atom in the title bis-ethynyl telluride, Te(C9H7)2 or C18H14Te, is located on a crystallographic twofold axis, the C—Te—C angle being 92.23 (15)°. The dihedral angle between the rings is 87.27 (7)°. In the crystal structure, mol­ecules are connected in chains parallel to the b axis and mediated by C—H⋯π inter­actions.

In the structure of the title compound, [CoCl2(C9H16N2Si)2], the CoII atom is located on an inversion center in a slightly distorted tetra­hedral environment formed by two chloride ions and the pyridine N atoms of two chelating 6-methyl-2-[(trimethyl­silyl)amino]pyridine ligands. The dihedral angle between the planes of the pyridine rings is 80.06 (5)°. Cohesion within the crystal structure is accomplished by N—H⋯Cl hydrogen bonds.

The mol­ecular structure of the title compound, [Fe(C5H5)(C13H4F5)], consists of a ferrocenyl group and a 2,3,4,5,6-penta­fluoro­benzene group linked through an ethyne spacer. The crystal packing is dominated by inter­molecular C—H⋯F hydrogen bonds, C—F⋯π inter­actions between the penta­fluoro­benzene groups [F⋯centroid distances = 3.882 (2) and 3.884 (2) Å] and π–π inter­actions between the penta­fluoro­benzene and cyclo­penta­dienyl rings [centroid–centroid distance = 3.741 (1) Å].

The asymmetric unit of the title compound, C26H16F6O2, contains one half of the mol­ecule situated on an inversion centre. In the rod-like mol­ecule, the two terminal benzene rings form a dihedral angle of 71.9 (1)° with the central benzene ring. The trifluoro­methyl group is rotationally disordered over two orientations in a 0.53 (1):0.47 (1) ratio. The crystal packing exhibits no classical inter­molecular inter­actions.

The title compound, C18H23N2Si+·Cl−·H2O, was synthesized from 1-[(trimethyl­sil­yl)meth­yl]benzimidazole and benzyl chloride in dimethyl­formamide. The benzimidazole ring system is approximately planar, with a maximum deviation of 0.022 (2) Å, and makes an angle of 74.80 (12)° with the phenyl ring. The crystal packing is stabilized by O—H⋯Cl, C—H⋯Cl, C—H⋯O and C—H⋯π inter­actions between symmetry-related mol­ecules together with π–π stacking inter­actions between the imidazolium and benzene rings [centroid–centroid distance = 3.5690 (15) Å] and between the benzene rings [centroid–centroid distance = 3.7223 (14) Å].

The mol­ecular structure of the title compound, trans-[Cu(C2H)Cl(C26H24P2)2], consists of an RuII cation, located on an inversion centre, in an octa­hedral environment defined by two chelating phosphines, one acetyl­ide and one chloride ligand. The –C CH and the chlorine ligands are disordered over two equivalent positions (0.5 occupancy each). The coordination geometry is distorted octa­hedral, with the –C CH fragment and the Cl ligand in trans positions. The four P atoms occupy the equatorial plane of the octa­hedron and the chloride and acetyl­ide ligands the axial positions.

The crystal structure of a previously unreported polymorph (form II) of 2,4-dinitro­phenyl­hydrazine (DNPH), C6H6N4O4, was determined at 90 K. The first polymorph (form I) is described in the monoclinic space group P21/c [Okabe et al. (1993 ▶). Acta Cryst. C49, 1678–1680; Wardell et al. (2006 ▶). Acta Cryst. C62, o318–320], whereas form II is in the monoclinic space group Cc. The mol­ecular structures in forms I and II are closely similar, with the nitro groups at the 2- and 4-positions being almost coplanar with the benzene ring [dihedral angles of 3.54 (1) and 3.38 (1)°, respectively in II]. However, their packing arrangements are completely different. Form I exhibits a herringbone packing motif, whereas form II displays a coplanar chain structure. Each chain in form II is connected to adjacent chains by the inter­molecular inter­action between hydrazine NH2 and 2-nitro groups, forming a sheet normal to (101). The sheet is stabilized by N—H⋯π inter­actions.

The title compound, C16H6N6, is a polymorph of the previously reported structure [Kozlov & Goldberg (2008 ▶). Acta Cryst. C64, o498–o501]. Unlike the previously reported monoclinic polymorph (space group P21/c, Z = 8), the title compound reveals ortho­rhom­bic symmetry (space group Pnma, Z = 4). The mol­ecule shows crystallographic mirror symmetry, while the previously reported structure exhibits two independent mol­ecules per asymmetric unit. In the title compound, adjacent mol­ecules are essentially parallel along the c axis and tend to be vertical along the b axis with dihedral angles of 72.02 (6)°. However, in the reported polymorph, the entire crystal structure shows an anti­parallel arrangement of adjacent columns related by inversion centers and the two independent mol­ecules are nearly parallel with a dihedral angle of 2.48 (6)°.

The transamination reaction of (2-pyridylmeth­yl)(triiso­propyl­silyl)amine with bis­{bis­(trimethyl­silyl)amido}zinc(II) yields the colorless title solvate, [Zn(C15H27N2Si)2]·0.5C7H8·0.25C4H8O. The title compound was crystallized from toluene and tetra­hydro­furan. There are two independent mol­ecules in the asymmetric unit. In each mol­ecule, the Zn atom is tetra­hedrally coordinated by four N atoms. The two mol­ecules differ in the orientation of the isopropyl groups. The mol­ecules show large N—Zn—N angles [143.0 (2) and 145.7 (2)° between the amide groups].

The title compound, C6H5NO3, crystallizes in the triclinic system with six independent mol­ecules in the asymmetric unit. In a previous study, the structure of the title compound was determined in the monoclinic P21/n space group at 100 K [Valerga et al. (2009 ▶). Acta Cryst. E65, o1979]. All six independent mol­ecules display an E configuration about the C=C double bond, with the dihedral angles between the planes of the furan rings and the nitro­alkenyl groups ranging from 0.61 (7) to 5.03 (7)°. The crystal structure is stabilized by inter­molecular C—H⋯O hydrogen-bonding inter­actions.

The crystal structure of the title compound, [Fe(C4H6)(CO)3], was previously reported by Mills & Robinson [Acta Cryst. (1963) ▶, 16, 758–761]. The compound crystallizes in the centrosymmetric space goup Pnma with the complex located on a mirror plane. The redetermination of this structure at 100 K yielded almost equilibrated C—C bond lengths within the butadiene ligand according to a metal-to-ligand bonding–back-bonding mechanism. The C—C bond lengths presented herein are significantly shorter than those reported earlier. The H-atom positions that have not been reported so far were located by difference Fourier maps. The positional parameters of all H atoms and individual U iso values were refined freely.

The title compound, C13H9N3O5, prepared as a solid derivative of 3-nitro­analine via reaction with 4-nitro­benzoyl chloride, crystallizes in a chiral space group. The mol­ecule is non-planar with a dihedral angle of 26.1 (1)° between the two benzene rings. Both nitro groups are twisted slightly out of the plane of their corresponding benzene rings, making dihedral angles of 10.7 (4) and 13.5 (4)°. The mol­ecules are stacked along the a axis with benzene ring centroid–centroid distances of 3.8878 (6) Å. In the crystal, inter­molecular benzene C—H⋯O inter­actions involving one nitro group and the carbonyl group link the mol­ecules, forming chains along [001]. An additional set of aromatic C—H⋯O inter­actions with the second nitro group form chains along [101], connecting adjacent chains to create layers perpendicular to the b axis.

The title compound, [Fe(C8H5)(C22H16P)(C3H9P)3], was synthesized by the addition of phenyl­ethine to a solution of the parent methyl iron complex Fe(CH3){P(C6H5)2(C10H6)}(PMe3)3 at 213 K, accompanied by evolution of methane. The coordination around the iron center can be described as slightly distorted octa­hedral [Fe—P 2.2485 (12)–2.2902 (12) Å; Fe—C 1.918 (5), 2.015 (4) Å], with a meridional arrangement of the trimethyl­phosphine ligands and the introduced terminal alkinyl-ligand trans to the P(Ph)2-anchoring group.

The crystal structure of the title compound, [C(NH2)3]6[Mo7O24]·H2O, previously determined at room temperature in the monoclinic space group C2/c from Weissenberg techniques [Don & Weakley (1981 ▶). Acta Cryst. B37, 451–453], has been redetermined from low-temperature single-crystal data in the monoclinic space group P21/c. The asymmetric unit contains one hepta­molybdate anion, six guanidinium cations and one water mol­ecule of hydration. The anions and cations are linked by an extensive network of N—H⋯O hydrogen bonds.

The title Schiff base compound, C21H26N2O4, is a second triclinic polymorph of a previously reported room-temperature structure [Jia (2009 ▶). Acta Cryst. E65, o646]. Strong intra­molecular O—H⋯N hydrogen bonds generate S(6) ring motifs. Inter­molecular C—H⋯O inter­actions link neighbouring mol­ecules into dimers with an R 2 2(16) ring motif. The mean planes of the two benzene rings are almost perpendicular to each other, making a dihedral angle of 88.24 (5)°. An inter­esting feature of the crystal structure is the intermolecular short C⋯O [3.1878 (13) Å] contact which is shorter than the sum of the van der Waals radii of the relevant atoms. The crystal structure is further stabilized by inter­molecular C—H⋯π and π–π inter­actions [centroid–centroid distance = 3.7414 (6) Å]. The structure has a stereogenic centre but the space group is centrosymmetric, so the mol­ecule exists as a racemate.

The structure of ortho-vanillin, C8H8O3, has been revisited with modern methods and at low temperature (100 K). The previous structure [Iwasaki et al. (1976 ▶). Acta Cryst. B32, 1264–1266] is confirmed, but geometric precision is improved by an order of magnitude. The C atom of the meth­oxy group lies close to the benzene ring plane, which is the most common geometry for –OMe groups lying ortho to –OH groups on an aromatic ring. The crystal structure displays one intra­molecular O—H⋯O and three weak inter­molecular C—H⋯O hydrogen bonds.

The title compound, C15H22N2O3, was obtained as a by-product of oxidative cleavage of 1,3-dicyclo­hexyl-(3-oxo-2,3-dihydro­benzofuran-2-yl)imidazolidine-2,4-dione. Herein, we report the crystal structure of a second polymorph, which was obtained by crystallization from an ethanol solution at 253 K, instead of slow evaporation of the same solvent at room temperature. While the first polymorph [Talhi et al. (2011). Acta Cryst. E67, o3243] crystallized in the non-centrosymmetric space group P212121, this second polymorph crystallizes in the centrosymmetric space group P21/n. Compared to the first polymorph, in the crystal no C=O⋯C=O inter­actions were found (C⋯O inter­molecular distance longer than 3.15 Å) and instead, close packing of individual mol­ecular units is mediated by C—H⋯π and weak C—H⋯O inter­actions.

The 1,3-dioxin-4-one ring in the title compound, C16H16O3, is in a half-boat conformation with the quaternary O—C(CH3)2—O atom lying 0.546 (1) Å out of the plane defined by the remaining five atoms. The crystal structure is consolidated by C—H⋯O contacts that lead to supra­molecular layers.

In the title compound, [Co(C13H9)(C28H20)], the Co atom is sandwiched between cyclo­penta­dienyl and cyclo­butadienyl rings that are inclined at a dihedral angle of 2.6 (3)°. The four phenyl rings are tilted with respect to the cyclo­butadienyl plane so that the C4Ph4 unit constitutes a four-bladed propeller. The phenyl ring of the phenyl-alkyne substituent is inclined to the cyclo­penta­dienyl ring at an angle of 34.92 (18)°. The crystal structure is stabilized solely by C—H⋯π inter­actions which generate a three-dimensional network.