Inter-centroid Distance Research Articles

6,7-Diphenyl-5-thia-7-aza-spiro-[2.6]nonan-8-one 5,5-dioxide.

The racemic mixture of the title compound, C19H19NO3S, crystallizes in space group P with two homochiral mol-ecules in each asymmetric unit. The seven-membered ring in both mol-ecules is in a pucker-chair conformation. The extended structure exhibits C-H⋯O hydrogen bonds, of which two connect crystallographically independent mol-ecules to generate a chain propagating along the b-axis direction. One C-H grouping of the cyclo-propyl ring is in close contact with the phenyl ring of the neighboring independent mol-ecule in C-H⋯π type inter-actions with carbon atom-ring-centroid distances of 3.544 (5) and 3.596 (4) Å. Other inter-actions are of the parallel-reciprocal type, with the chiral carbon atom of one mol-ecule donating a proton to an oxygen atom of the sulfone group of a symmetry-related mol-ecule and vice-versa. Symmetry-related mol-ecular pairs also exhibit T-type inter-actions between aromatic rings with inter-planar angles of 74.2 (2) and 69.2 (2)° and inter-centroid distances of 4.965 (4) and 5.114 (4) Å.

Polymorphic structures of 3-phenyl-1H-1,3-benzo-diazol-2(3H)-one.

The polymorphic structures (I and II) of 3-phenyl-1H-1,3-benzo-diazol-2(3H)-one, C13H10N2O, acquired from pentane diffusion into the solution in THF, are reported. The structures show negligible differences in bond distances and angles, but the C-N-C-C torsion angles between the backbone and the phenyl substituent, 123.02 (15)° for I and 137.18 (11)° for II, are different. Compound I features a stronger C=O⋯H-N hydrogen bond than that in II, while the structure of II exhibits a stronger π-π inter-action than in I, as confirmed by the shorter inter-centroid distance [3.3257 (8) Å in II in comparison to 3.6862 (7) Å in I]. Overall, the supra-molecular inter-actions of I and II are distinct, presumably originating from the variation in the dihedral angle.

ANALYSIS OF THE CRYSTAL STRUCTURE AND ENERGY FRAMEWORKS OF 5-ACETIL-1,3-DIMETHYL BARBITURIC ACID

C8H9N2O4 was prepared via acetylation of 1,3-dimethyl barbituric acid. The atomic and crystalline structures were determined using single crystal analysis (X-ray). It is a member of the monoclinic system P 21/c group of space with a = 8.6056 (3) Å, b = 9.1602 (3) Å, c = 11.9601 (4) Å, β = 109.410 (3)°, Z = 4 and V = 889.22 (5) Å3. π–π interactions between circles of nearby molecules with intercentroid distances of 3.4300 (11) aid in the stability of the structure by keeping the crystals in place. The Hirshfeld surface (HS) analysis of the crystal structure reveals that the H... O/O... H (45.9%) and H... H (32.9%) interactions contribute the most to crystal packing. The most essential interactions in crystal packing are hydrogen bonding and van der Waals interactions. According to the dispersion, electrostatic and overall energy frameworks, the contribution of dispersion energy dominates the stability.

Synthesis, crystal structure and Hirshfeld surface analysis of dimethyl 3-(3-bromo-phen-yl)-6-methyl-7-oxo-3,5,6,7-tetra-hydro-pyrazolo-[1,2-a]pyrazole-1,2-di-carboxyl-ate.

The title compound, C17H17BrN2O5, resulted from the 1,3-dipolar cyclo-addition reaction between dimethyl acetyl-enedi-carboxyl-ate and (3-bromo-benzyl-idene)-4-methyl-5-oxopyrazolidin-2-ium-1-ide in CHCl3. The dihedral angle between the pyrazole rings (all atoms) is 32.91 (10)°; the oxo-pyrazole ring displays an envelope conformation whereas the other pyrazole ring adopts a twisted conformation. The bromo-phenyl ring subtends a dihedral angle of 88.95 (9)° with the mean plane of its attached pyrazole ring. In the crystal, the mol-ecules are linked by C-H⋯O hydrogen bonds and aromatic π-π inter-actions with an inter-centroid distance of 3.8369 (10) Å. The Hirshfeld surface analysis and fingerprint plots reveal that the mol-ecular packing is governed by H⋯H (37.1%), O⋯H/H⋯O (31.3%), Br⋯H/H⋯Br (13.5%) and C⋯H/H⋯C (10.6%) contacts. The energy framework indicates that dispersion energy is the major contributor to the mol-ecular packing.

Analysis of structural conformation and supramolecular self-assembly of novel oxalate-bridged tetranuclear Cu(II) complex by combined crystallographic and computational studies

The heteroleptic tetranuclear copper(II) complex, [Cu(II)4(µ2-Cl)3 -(µ1-Cl)3 (µ- C2O4- κ 4 O1, O2: O1 ′, O2′) - (µ1-1-4-dioxane) - (terpy-κ3 N, N′, N″)]; have been synthesized and its crystal structure was solved using single crystal X-ray diffraction method under ambient conditions. Each Cu(II) ion is in a highly distorted square-pyramidal coordination environment in the title complex. In the crystal, the complex molecules are linked by C—H…Cl and C—H…O hydrogen bonds, forming propagating chains along the [110] direction. This complex exhibits a π-π interaction resulting from an overlap between pyridine rings of molecules A and B [intercentroid distance = 3.921(9)Å, 3. 813(9)Å and 3.724(9)Å] leading to the formation of a supramolecular framework. A detailed analysis of Hirshfeld surfaces and fingerprint plots show that van der Waals interactions constitute a further significant contribution to the intermolecular interactions, with H…H contacts accounting for 33.1% of the surface. In addition, the geometrical optimization of the tetranuclear Cu(II) complex was done by electronic structure method using density functional theory (DFT) to identify the active sites and to explore the chemically reactive parameters of the molecule and the HOMO-LUMO energy gap (0.5916 eV). QTAIM and the NCI index model analyses the vital role of distinct non-covalent interactions in the establishment of a unique structural topology. Furthermore, AChE/BChE and tyrosinase activity methods have been used to estimate the in vitro anti-Alzheimer effect of the synthesized complex, which has shown a potent AChE/BChE inhibition.

Synthesis of a new vanadium complex (V), hexa [4-methylimidazolium] decavanadate trihydrate (C4H7N2)6V10O28·3H2O: Physico-chemical and biological characterizations

Currently we observe the emergence of different infectious diseases, whose remedies are not available. On the other hand, an increasing number of potential applications for polyoxometalates in human medicine have been reported in the literature. In the present study, we have synthesized an hexa [4-methylimidazolium] decavanadate trihydrate, (C4H7N2)6V10O28·3H2O for an eventual therapeutic application. The structure of this compound has been characterized by: crystal X-ray diffraction, Infrared (IR) spectroscopy and Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray Analysis (EDX). Single-crystal analysis indicates that the formula unit is composed of one decavanadate [V10O28]6- anion, six 4-methylimidazolium [C4H7N2]+ cations and three water molecules. The cohesion is provided by NH⋯O, OH⋯O hydrogen bonds, and Van der Waals interactions leads to a three-dimensional structure. In the crystal, organic cations are linked by π-π interactions (inter-centroid distance = 3.693 Å). The Hirshfeld surface (HS) and their relative two-dimensional fingerprint plots (2D-FP) reveal that the structure is dominated by O…H/H…O (40.9%) and H…H (29.1%) contacts. Analysis of hepatic enzymes activities, lipid profile and liver histologic examination, showed that high doses of (C4H7N2)6V10O28·3H2O are safe when injected into mice, suggesting that it could be used as a potential therapeutic molecule.

The crystal structure, Hirshfeld surface analysis and energy frameworks of 2-[2-(meth-oxy-carbon-yl)-3,6-bis-(meth-oxy-meth-oxy)phen-yl]acetic acid.

In the title compound, C14H18O8, (I), the meth-oxy-carbonyl [-C(=O)OCH3] and the acetic acid [-CH2C(=O)OH] groups are inclined to the benzene ring by 79.24 (11) and 76.71 (13)°, respectively, and are normal to each other with a dihedral angle of 90.00 (13)°. In the crystal, mol-ecules are linked by a pair of O-H⋯O hydrogen bonds forming the familiar acetic acid inversion dimer. The dimers are linked by two C-H⋯O hydrogen bonds and an offset π-π inter-action [inter-centroid distance = 3.6405 (14) Å], forming layers lying parallel to the (10) plane. The layers are linked by a third C-H⋯O hydrogen bond and a C-H⋯π inter-action to form a supra-molecular framework.

Crystal structures and Hirshfeld surface analyses of 6,8-dimeth-oxy-3-methyl-1H-isochromen-1-one and 5-bromo-6,8-dimeth-oxy-3-methyl-1H-isochromen-1-one chloro-form monosolvate.

In the mol-ecule of 6,8-dimeth-oxy-3-methyl-1H-isochromen-1-one, C12H12O4, (I), the two meth-oxy groups are directed anti with respect to each other. In the mol-ecule of the brom-inated derivative, 5-bromo-6,8-dimeth-oxy-3-methyl-1H-isochromen-1-one, that crystallized as a chloro-form monosolvate, C12H11BrO4·CHCl3, (II·CHCl3 ), the meth-oxy groups are directed syn to each other. In the crystal of I, mol-ecules are linked by bifurcated C-H⋯O hydrogen bonds, forming chains along the c-axis direction. The chains are linked by C-H⋯π inter-actions, forming a supra-molecular framework. In the crystal of II·CHCl3 , mol-ecules are linked by C-H⋯O hydrogen bonds forming 21 helices parallel to the b-axis direction. The chloro-form solvate mol-ecules are linked to the helices by C-H⋯O(carbon-yl) hydrogen bonds. The helices stack up the c-axis direction and are linked by offset π-π inter-actions [inter-centroid distance = 3.517 (3) Å], forming layers parallel to the (100) plane. Compound II·CHCl3 was refined as a two-component twin. Two chlorine atoms of the chloro-form solvate are disordered over two positions and were refined with a fixed occupancy ratio of 0.5:0.5.

High-Resolution Episcopic Imaging for Visualization of Dermal Arteries and Nerves of the Auricular Cymba Conchae in Humans

Therapeutic applications of auricular vagus nerve stimulation (VNS) have drawn recent attention. Since the targeted stimulation process and parameters depend on the electrode–tissue interaction, the lack of structural anatomical information on innervation and vascularization of the auricle restrain the current optimization of stimulation paradigms. For the first time, we employed high-resolution episcopic imaging (HREM) to generate histologic volume data from donated human cadaver ears. Optimal parameters for specimen preparation were evaluated. Anatomical 3D vascular and nerve structures were reconstructed in one sample of an auricular cymba conchae (CC). The feasibility of HREM to visualize anatomical structures was assessed in that diameters, occupied areas, volumes, and mutual distances between auricular arteries, nerves, and veins were registered. The selected region of CC (3 × 5.5 mm) showed in its cross-sections 21.7 ± 2.7 (mean ± standard deviation) arteries and 14.66 ± 2.74 nerve fibers. Identified nerve diameters were 33.66 ± 21.71 μm, and arteries had diameters in the range of 71.58 ± 80.70 μm. The respective occupied area showed a share of, on average, 2.71% and 0.3% for arteries and nerves, respectively, and similar volume occupancy for arteries and nerves. Inter-centroid minimum distance between arteries and nerves was 274 ± 222 μm. The density of vessels and nerves around a point within CC on a given grid was assessed, showing that 50% of all vessels and nerves were found in a radial distance of 1.6–1.8 mm from any of these points, which is strategically relevant when using stimulation needles in the auricle for excitation of nerves. HREM seems suitable for anatomical studies of the human ear. A 3D model of CC was established in the micrometer scale, which forms the basis for future optimization of the auricular VNS. Obviously, the presented single cadaver study needs to be validated by additional anatomical data on the innervation and vascularization of the auricle.

2,4,6-Triphenyl-N-{(3E)-3-[(2,4,6-tri-phenyl-phen-yl)imino]-butan-2-yl-idene}aniline.

The title compound, C52H40N2, is disposed about a centre of inversion and the conformation about the imine bond [1.268 (3) Å] is E. The terminal benzene ring is approximately perpendicular to the central 1,4-di-aza-butadiene mean plane, forming a dihedral angle of 81.2 (3)°. Weak C-H⋯π and π-π [inter-centroid distance = 4.021 (5) Å] inter-actions help to consolidate the packing.

2-[(2,4,6-Tri-methyl-benzene)-sulfon-yl]phthalazin-1(2H)-one: crystal structure, Hirshfeld surface analysis and computational study.

The X-ray crystal structure of the title phthalazin-1-one derivative, C17H16N2O3S {systematic name: 2-[(2,4,6-tri-methyl-benzene)-sulfon-yl]-1,2-di-hydro-phthalazin-1-one}, features a tetra-hedral sulfoxide-S atom, connected to phthalazin-1-one and mesityl residues. The dihedral angle [83.26 (4)°] between the organic substituents is consistent with the mol-ecule having the shape of the letter V. In the crystal, phthalazinone-C6-C-H⋯O(sulfoxide) and π(phthalazinone-N2C4)-π(phthalazinone-C6) stacking [inter-centroid distance = 3.5474 (9) Å] contacts lead to a linear supra-molecular tape along the a-axis direction; tapes assemble without directional inter-actions between them. The analysis of the calculated Hirshfeld surfaces confirm the importance of the C-H⋯O and π-stacking inter-actions but, also H⋯H and C-H⋯C contacts. The calculation of the inter-action energies indicate the importance of dispersion terms with the greatest energies calculated for the C-H⋯O and π-stacking inter-actions.

Crystal structures and Hirshfeld surface analyses of two new tetra-kis-substituted pyrazines and a degredation product.

The two new tetra-kis-substituted pyrazines, 1,1',1'',1'''-(pyrazine-2,3,5,6-tetra-yl) tetra-kis-(N,N-di-methyl-methanamine), C16H32N6, (I) and N,N',N'',N'''-[pyrazine-2,3,5,6-tetra-yltetra-kis-(methyl-ene)]tetra-kis-(N-methyl-aniline), C36H40N6, (II), both crystallize with half a mol-ecule in the asymmetric unit; the whole mol-ecules are generated by inversion symmetry. There are weak intra-molecular C-H⋯N hydrogen bonds present in both mol-ecules and in (II) the pendant N-methyl-aniline rings are linked by a C-H⋯π inter-action. The degredation product, N,N'-[(6-phenyl-6,7-di-hydro-5H-pyrrolo-[3,4-b]pyrazine-2,3-di-yl)bis(methyl-ene)]bis-(N-methyl-aniline), C28H29N5, (III), was obtained several times by reacting (II) with different metal salts. Here, the 6-phenyl ring is almost coplanar with the planar pyrrolo-[3,4-b]pyrazine unit (r.m.s. deviation = 0.029 Å), with a dihedral angle of 4.41 (10)° between them. The two N-meth-yl-aniline rings are inclined to the planar pyrrolo-[3,4-b]pyrazine unit by 88.26 (10) and 89.71 (10)°, and to each other by 72.56 (13)°. There are also weak intra-molecular C-H⋯N hydrogen bonds present involving the pyrazine ring and the two N-methyl-aniline groups. In the crystal of (I), there are no significant inter-molecular contacts present, while in (II) mol-ecules are linked by a pair of C-H⋯π inter-actions, forming chains along the c-axis direction. In the crystal of (III), mol-ecules are linked by two pairs of C-H⋯π inter-actions, forming inversion dimers, which in turn are linked by offset π-π inter-actions [inter-centroid distance = 3.8492 (19) Å], forming ribbons along the b-axis direction.

Syntheses and crystal structures of a new pyrazine dicarboxamide ligand, N 2,N 3-bis-(quinolin-8-yl)pyrazine-2,3-dicarboxamide, and of a copper perchlorate binuclear complex.

The title pyrazine dicarboxamide ligand, N 2,N 3-bis-(quinolin-8-yl)pyrazine-2,3-dicarboxamide (H2L1), C24H16N6O2, has a twisted conformation with the outer quinoline groups being inclined to the central pyrazine ring by 9.00 (6) and 78.67 (5)°, and by 79.94 (4)° to each other. In the crystal, molecules are linked by C-H⋯O hydrogen bonds, forming layers parallel to the (10) plane, which are in turn linked by offset π-π inter-actions [inter-centroid distances 3.4779 (9) and 3.6526 (8) Å], forming a supra-molecular three-dimensional structure. Reaction of the ligand H2L1 with Cu(ClO4)2 in aceto-nitrile leads to the formation of the binuclear complex, [μ-(3-{hy-droxy[(quinolin-8-yl)imino]-meth-yl}pyrazin-2-yl)[(quinolin-8-yl)imino]-methano-lato]bis-[diaceto-nitrile-copper(II)] tris-(per-chlor-ate) aceto-nitrile disolvate, [Cu2(C24H15N6O2)(CH3CN)4](ClO4)3·2CH3CN or [Cu2(HL1-)(CH3CN)4](ClO4)3·2CH3CN (I). In the cation of complex I, the ligand coordinates to the copper(II) atoms in a bis-tridentate fashion. A resonance-assisted O-H⋯O hydrogen bond is present in the ligand; the position of this H atom was located in a difference-Fourier map. Both copper(II) atoms are fivefold coordinate, being ligated by three N atoms of the ligand and by the N atoms of two aceto-nitrile mol-ecules. The first copper atom has a perfect square-pyramidal geometry while the second copper atom has a distorted shape. In the crystal, the cation and perchlorate anions are linked by a number of C-H⋯O hydrogen bonds, forming a supra-molecular three-dimensional structure.

The crystal structure of the triclinic polymorph of 1,4-bis-([2,2':6',2''-terpyridin]-4'-yl)benzene.

The title triclinic polymorph (Form I) of 1,4-bis-([2,2':6',2''-terpyridin]-4'-yl)benzene, C36H24N6, was formed in the presence of the Lewis acid yttrium trichloride in an attempt to obtain a coordination compound. The crystal structure of the ortho-rhom-bic polymorph (Form II), has been described previously [Fernandes et al. (2010 ▸). Acta Cryst. E66, o3241-o3242]. The asymmetric unit of Form I consists of half a mol-ecule, the whole mol-ecule being generated by inversion symmetry with the central benzene ring being located about a crystallographic centre of symmetry. The side pyridine rings of the 2,2':6',2''-terpyridine (terpy) unit are rotated slightly with respect to the central pyridine ring, with dihedral angles of 8.91 (8) and 10.41 (8)°. Opposite central pyridine rings are coplanar by symmetry, and the angle between them and the central benzene ring is 49.98 (8)°. The N atoms of the pyridine rings inside the terpy entities, N⋯N⋯N, lie in trans-trans positions. In the crystal, mol-ecules are linked by C-H⋯π and offset π-π inter-actions [inter-centroid distances are 3.6421 (16) and 3.7813 (16) Å], forming a three-dimensional structure.

Crystal structure and Hirshfeld surface analysis of 2-(4-nitro-phen-yl)-2-oxoethyl 2-chloro-benzoate.

The title compound, C15H10ClNO5, is relatively planar with the two aromatic rings being inclined to each other by 3.56 (11)°. The central -C(=O)-C-O-C(=O)- bridge is slightly twisted, with a C-C-O-C torsion angle of 164.95 (16)°. In the crystal, mol-ecules are linked by C-H⋯O and C-H⋯Cl hydrogen bonds, forming layers parallel to the (101) plane. The layers are linked by a further C-H⋯O hydrogen bond, forming a three-dimensional supra-molecular structure. There are a number of offset π-π inter-actions present between the layers [inter-centroid distances vary from 3.8264 (15) to 3.9775 (14) Å]. Hirshfeld surface analyses, the d norm surfaces, electrostatic potential and two-dimensional fingerprint plots were examined to verify the contributions of the different inter-molecular contacts within the supra-molecular structure. The shape-index surface shows that two sides of the mol-ecule are involved in the same contacts with neighbouring mol-ecules, and the curvedness plot shows flat surface patches that are characteristic of planar stacking.

Bis[2-(4,5-diphenyl-1H-imidazol-2-yl)-4-nitrophenolato]copper(II) dihydrate: crystal structure and Hirshfeld surface analysis.

The crystal and mol-ecular structures of the title CuII complex, isolated as a dihydrate, [Cu(C21H14N3O3)2]·2H2O, reveals a highly distorted coordination geometry inter-mediate between square-planar and tetra-hedral defined by an N2O2 donor set derived from two mono-anionic bidentate ligands. Furthermore, each six-membered chelate ring adopts an envelope conformation with the Cu atom being the flap. In the crystal, imidazolyl-amine-N-H⋯O(water), water-O-H⋯O(coordinated, nitro and water), phenyl-C-H⋯O(nitro) and π(imidazol-yl)-π(nitro-benzene) [inter-centroid distances = 3.7452 (14) and 3.6647 (13) Å] contacts link the components into a supra-molecular layer lying parallel to (101). The connections between layers forming a three-dimensional architecture are of the types nitro-benzene-C-H⋯O(nitro) and phenyl-C-H⋯π(phen-yl). The distorted coordination geometry for the CuII atom is highlighted in an analysis of the Hirshfeld surface calculated for the metal centre alone. The significance of the inter-molecular contacts is also revealed in a study of the calculated Hirshfeld surfaces; the dominant contacts in the crystal are H⋯H (41.0%), O⋯H/H⋯O (27.1%) and C⋯H/H⋯C (19.6%).

Crystal structure of catena-poly[[gold(I)-μ-cyanido-[di-aqua-bis-(2-phenyl-pyrazine)-iron(II)]-μ-cyanido] dicyanidogold(I)

In the title polymeric complex, {[Fe(CN)2(C10H8N2)2(H2O)2][Au(CN)2]} n , the FeII ion, which is located on a twofold rotation axis, has a slightly distorted FeN4O2 octa-hedral geometry. It is coordinated by two phenyl-pyrazine mol-ecules, two water mol-ecules and two di-cyano-aurate anions, the Au atom also being located on a second twofold rotation axis. In the crystal, the coordinated di-cyano-aurate anions bridge the FeII ions to form polymeric chains propagating along the b-axis direction. In the crystal, the chains are linked by Owater-H⋯Ndi-cyano-aurate anions hydrogen bonds and aurophillic inter-actions [Au⋯Au = 3.5661 (3) Å], forming layers parallel to the bc plane. The layers are linked by offset π-π stacking inter-actions [inter-centroid distance = 3.643 (3) Å], forming a supra-molecular metal-organic framework.

Crystal structures of two new isocoumarin derivatives: 8-amino-6-methyl-3,4-diphenyl-1H-isochromen-1-one and 8-amino-3,4-diethyl-6-methyl-1H-isochromen-1-one.

The title compounds, 8-amino-6-methyl-3,4-diphenyl-1H-isochromen-1-one, C22H17NO2, (I), and 8-amino-3,4-diethyl-6-methyl-1H-isochromen-1-one, C14H17NO2, (II), are new isocoumarin derivatives in which the isochromene ring systems are planar. Compound II crystallizes with two independent mol-ecules (A and B) in the asymmetric unit. In I, the two phenyl rings are inclined to each other by 56.41 (7)° and to the mean plane of the 1H-isochromene ring system by 67.64 (6) and 44.92 (6)°. In both compounds, there is an intra-molecular N-H⋯O hydrogen bond present forming an S(6) ring motif. In the crystal of I, mol-ecules are linked by N-H⋯π inter-actions, forming chains along the b-axis direction. A C-H⋯π inter-action links the chains to form layers parallel to (100). The layers are then linked by a second C-H⋯π inter-action, forming a three-dimensional structure. In the crystal of II, the two independent mol-ecules (A and B) are linked by N-H⋯O hydrogen bonds, forming -A-B-A-B- chains along the [101] direction. The chains are linked into ribbons by C-H⋯π inter-actions involving inversion-related A mol-ecules. The latter are linked by offset π-π inter-actions [inter-centroid distances vary from 3.506 (1) to 3.870 (2) Å], forming a three-dimensional structure.

Crystal structure and DFT study of (E)-2-chloro-4-{[2-(2,4-di-nitro-phen-yl)hydrazin-1-yl-idene]meth-yl}phenol aceto-nitrile hemisolvate.

The title Schiff base compound, C13H9ClN4O5·0.5CH3CN, crystallizes as an aceto-nitrile hemisolvate; the solvent mol-ecule being located on a twofold rotation axis. The mol-ecule is nearly planar, with a dihedral angle between the two benzene rings of 3.7 (2)°. The configuration about the C=N bond is E, and there is an intra-molecular N-H⋯Onitro hydrogen bond present forming an S(6) ring motif. In the crystal, mol-ecules are linked by O-H⋯O and N-H⋯O hydrogen bonds, forming layers lying parallel to (10). The layers are linked by C-H⋯Cl hydrogen bonds, forming a supra-molecular framework. Within the framework there are offset π-π stacking inter-actions [inter-centroid distance = 3.833 (2) Å] present involving inversion-related mol-ecules. The DFT study shows that the HOMO and LUMO are localized in the plane extending from the phenol ring to the 2,4-di-nitro-benzene ring, and the HOMO-LUMO gap is found to be 0.13061 a.u.

The crystal structures of the ligand N-(quinolin-8-yl)pyrazine-2-carboxamide and of a tetra-nuclear copper(II) complex.

The title tridentate ligand, C14H10N4O, N-(quinolin-8-yl)pyrazine-2-carboxamide (HL1), crystallizes with three independent mol-ecules (A, B and C) in the asymmetric unit. All three mol-ecules are relatively planar (r.m.s. deviations are 0.068, 0.055 and 0.06 Å, respectively), with the NH H atom forming three-centered (bifurcated) intra-molecular N-H⋯N hydrogen bonds in each mol-ecule. There is also an intra-molecular C-H⋯O contact present in each mol-ecule, involving the benzene ring of the quinoline unit and the amide carboxamide O atom. In the crystal, the three mol-ecules stack in columns with the various mol-ecules being linked by offset π-π inter-actions [inter-centroid distances vary from 3.367 (5) to 3.589 (5) Å], forming layers parallel to the ab plane. The title complex, [Cu4(C42H44N8O16)]·2CH3OH, {hexa-μ-acetato-1:2κ2 O:O';2:3κ8 O:O';3:4κ2 O:O'-di-methanol-1κO,2κO-bis-[N-(quinolin-8-yl)pyrazine-2-carboxamide]-1κ3 N,N',N'';4κ3 N,N',N''-tetra-copper(II) methanol disolvate} (I), was obtained by the reaction of HL1 with Cu(CH3CO2)2. It consists of a tetra-nuclear complex with a central tetra-kis-(μ-acetato)-dicopper paddle-wheel moiety linked on either side via bridging acetato ions to a mononuclear copper(II)-(L1) complex; it crystallizes as a methanol disolvate. The complex possesses inversion symmetry, being located about a center of symmetry situated at the mid-point of the Cu⋯Cu bond of the paddle-wheel moiety. In the crystal, the complex mol-ecules are linked by O-H⋯O hydrogen bonds, forming chains along the [01] direction, which are linked by offset π-π inter-actions [inter-centroid distance = 3.7367 (11) Å] and C-H⋯O hydrogen bonds, leading to the formation of a supra-molecular framework.