The crystal structure of 4-methyl-4′,5′-dihydropyrrolocoumarin (MDPC) has been determined by X-ray diffraction. The crystal, C₁₂H₁₁NO₂, belongs to space group P2₁/c with cell dimensions of a = 7.539(2)Å, b = 19.230(2)Å, c = 6.9395(9)Å, β = 103.89(1)°. The final R value is 0.036. The methylene bridge in the indoline moiety makes the amino moiety more pyramidal than simple N-alkylation.

View full abstract

The crystal structure properties of [SiH₂Mes₂] (Mes = 2,4,6-trimethylphenyl) are: monoclinic, space group C2/c with a = 13.221(6), b = 9.076(2), c = 13.448(5)Å, Z = 4, R1 = 0.054 and wR2 = 0.129 with 1727 reflections (I > 2σ(I)). The coordination geometry about Si is approximately tetrahedral with a C-Si-C angle of 114.14(11)°. There is π-π stacking interaction between the parallel aromatic rings.

View full abstract

The crystal structure of N-(4-methylbenzothiazole-2-yl)-1-(4-trifluoromethylphenyl)-O,O-dipropyl-α-aminophosphonate was determined by X-ray analysis. The compound crystallizes in the monoclinic system, space group P2₁/c, with unitcell parameters of a = 9.0204(13), b = 25.289(4), c = 10.8869(15)Å, and β = 104.159(2)°. The crystal structure was solved by direct methods and refined by full-matrix least squares to final values of R = 0.0524 and Rw = 0.1357 with 2879 reflections (I>2σ(I)). The dihedral angle between the planes of benzothiazole and benzene is 71.75°.

View full abstract

The crystal structure of N,N′-diethyl-N,N′-[[4,4′-dihydroxy-1,1′-binaphthalene]-3,3′-diyl]bisbenzamide was determined. This compound was synthesized from a reaction between N-ethyl-2-naphthylamine and benzoylperoxide. The torsion angle between the two-ring system (C5-C4-C24-C25) is 129.0(2)°. The length of the inter-ring C4-C24 bond is 1.488(3)Å. The amide bonds in the ethylbenzamide groups have cis stereochemistry.

View full abstract

The title compound, [4-(OCH₃)C₆H₄CH₂NH₃]₄H₂P₃O₁₀H₄P₃O₁₀, crystallizes in the monoclinic space group C2/c with a = 13.647(3)Å, b = 12.266(2)Å, c = 27.792(4)Å, β = 93.20(1)°, Z = 4 and V = 4645(1). The atomic arrangement of the title compound can be described as a layer-type organization. Layers built by H₂P₃O₁₀^3- and H₄P₃O₁₀^- anions are parallel to the (a, b) planes. The organic molecules are linked through their -NH₃ groups to some external oxygen atoms of the triphosphoric layers via N-H…O bonds.

View full abstract

The crystal of the title compound, C₁₀H₂₂N₄·H₂SO₄, belongs to space group Pn with the cell dimensions a = 7.131(4), b = 12.969(6), c = 8.068(4)Å, and β = 110.32(3)°. The final R value is 0.063. The azocane ring adopts a boat-chair conformation. In a molecule, the N atom of the azocane ring and one of the N atoms of the guanidine group are bridged by a sulfate ion through a hydrogen bond. Hence, the ethylguanidine group takes a folded conformation. The ethylguanidine occupies an equatorial position of the ring.

View full abstract

The crystal structure of [(H₅O₂)(pydaH)₂][Gd(pydc)₃]·2(H₂O), (pyda·H = 2,6-diaminopyridinum), (pydc = 2,6-pyridinedicarboxylate), has been determined by the X-ray diffraction method. This ionic complex crystallizes in the monoclinic system, space group P2/n, with two molecules per unit cell. The unit cell dimensions are a = 9.641(4), b = 10.653(5), c = 17.696(9)Å, β = 95.649(13)°, V = 1808.5(14)ų. The final R value is 0.0493 for 3177 measured reflections. The organic salt of a complex anion is formed between gadolinium(III) and three deprotonated [pydc·H₂]ligand moieties. The gadolinium atom is at the center of a distorted tricaped trigonal prismatic donor-atom geometry. The geometry of the ligands and that of the primary coordination sphere is very similar to that of the analogous anionic tris(ligand)-rare earth complexes of the [pydc]^2- dianion.

View full abstract

A copper(II) complex with 8-hydroxyquinoline-2-carboxylic acid was synthesized and its crystal structure was determined by X-ray crystallography. 8-Hydroxyquinoline-2-carboxylic acid acted as a dibasic tridentate ligand to form a neutral mononuclear complex with a distorted square-pyramidal geometry with two water molecules.

View full abstract

The crsytal structure of 2-methoxy-6-(pyrazin-2-yl iminomethyl)phenol, C₁₂H₁₁N₃O₂, was determined by X-ray diffraction at room temperature. The compound crystallizes in the monoclinic system, and space group P2₁/c, with the following unit-cell dimensions: a = 6.8996(5)Å, b = 8.8565(8)Å, c = 8.3586(16)Å, β = 100.798(6)°. The structure was refined by a full-matrix least-squares procedure on F² to final R = 0.0524 using 770 reflections with I ≥ 2 σ (I).

View full abstract

The title compound, C₁₃H₁₆N₂O₂, consists of a planar benzoxazolone ring system and a piperidine ring. Crystals of the title compound are twinned and the structure could be solved with satisfactory results. It crsytallizes in the triclinic P1 space group. The unit-cell parameters at 293 K are a = 6.608(5), b = 9.092(5), c = 11.075(5)Å, α = 105.714(5)°, β = 98.929(5)°, γ = 106.017(5)°, V = 596.3(6)ų, D_x = 1.294 g/cm³, Z = 2. In the crystal structure, there are intermolecular C-H…O hydrogen contacts.

View full abstract

The crystal structure of C₁₀H₁₀N₄S, was determined by X-ray diffraction at low temperature (100 K). The compound crystallizes in monoclinic P2₁/c; a = 8.006(5)Å, b = 15.363(5)Å, c = 8.936(5)Å, β = 104.441(5)°. The molecular structure is non-planar. The crystal packing is stabilized by N-H…N and C-H…S type hydrogen bonds.

View full abstract

Optically pure 2-benzylsuccinic acid is obtained by optical resolution of the racemates with the chiral host 1-phenylethylamine. The structure of the salt complex between (S)-2-benzylsuccinic acid and (R)-1-phenylethylamine was first elucidated by X-ray analysis, indicating that the hydrogen bonds are formed between the acetate anions and the protonated amino group. The intermolecular hydrogen bond links the salt complex into a quasi-two-dimentional net-like structure.

View full abstract

The crystal structure of methyl 4-hydroxy-3-nitro-2-(4-nitrophenyl)-5-(1,1,1-triphenyl-λ⁵-phosphanylidene)-1,3-cyclopentadiene-1-carboxylate was determined by crystallographic methods. The crystal, C₃₁H₂₃N₂O₇P, belongs to space group P2₁/n with cell dimensions of a = 11.0660(6), b = 21.1793(12), c = 11.7339(6)Å, β = 100.1860(10)°, V = 2706.7(3)ų, Z = 4, D_cal = 1.390 Mg/m³, T = 120(2)K. The crystal structure was solved by direct methods and refined by full-matrix least squares to final values of R1 = 0.0559 and wR2 = 0.1122 with 4470 reflections (I > 2σ(I)). There is an intramolecular-hydrogen bond between the O(2) atom of the nitro group and the hydrogen of the OH group.

View full abstract

The title compound, C₂₇H₂₈O₄, consisting of three O-benzyl modieties and one glucal modiety, belongs to the space group P2₁ with cell parameters a = 12.0729(5), b = 4.7002(2), c = 19.6720(8)Å and β = 90.989(4)°. The glucal moiety has a twist-boat conformation.

View full abstract

In the title compound, C₁₆H₁₄N₂O₂, the dihedral angles between pyrrole and benzene rings are 1.66(9) and 83.25(8)°. Intermolecular N-H…N and C-H…O hydrogen bonds stabilize the crystal structure by causing the formation of a supramolecular architecture. It belongs to the space group P2₁/c with cell parameters a = 10.220(3), b = 13.812(4), c = 10.420(3)Å, β = 110.771(4)°.

View full abstract

The title compounds, (2S,3S)-tartranilic acid and its novel 3-naphtyl substituted derivative, were synthesized, and the crystal structures were determined. The molecules have a common twisted structure consisting of a propanoic moiety, which is essentially identical to those of the previous tartaric acids and its monoamide. In the crystal structures, the hydrogen bonds form an infinity planar network for tartranilic acid, and an infinity helical network for the 3-naphtyl derivative.

View full abstract

The X-ray structure of endo-N-(4-methylphenyl)-3-(4-bromobenzoyl)-1-methyl-1,2,3,10b-tetrahydropyrrolo[2,1-a]phthalazine-1,2-dicarboximide 4, a cycloadduct obtained from the 1,3-dipolar cycloaddition reaction between phthalazinium phenacylide 2 and the non-symmetrical cyclic olefin 2-methyl-1-(4-methylphenyl)maleimide 3, is described. Compound 4 crystallizes in the monoclinic space group P2₁/c with unit cell parameters a = 9.6294(1)Å, b = 11.7731(2)Å, c = 20.9911(4)Å, β = 100.350(1)° and Z = 4. From the stereochemistry of 4, it was possible to conclude that the cycloaddition is both endo- and regioselective, and that the N-ylide 2 takes part in the reaction in the anti form.

View full abstract

The structure of the title compound, [Zn(C₅₆H₄₄N₄O₄)], was confirmed by low-temperature single-crystal analysis. The crystal system belongs to monoclinic with space group of P2₁/n. The crystal structure reveals that the Zn^II center adopts a square-planar coordination geometry and the molecules are stacked with a separation of 11.056(3)Å between the neighboring Zn centers along the crystallographic b-axis.

View full abstract

Single crystals of a novel cyclotetraphosphate, [p-ClC₆H₄NH₃]₄P₄O₁₂, have been synthesised and characterized by X-ray diffraction. This hybrid compound crystallizes in the monoclinic system, space group P2₁/a, with cell dimensions of a = 7.582(1), b = 31.280(9), c = 8.052(1)Å, β = 117.320(1)°. Its structure is built by P₄O₁₂^4- ring anions and p-chloroanilinium cations. The packing of these entities leads to thick layers around the planes y = 0 and y = 1/2, maintained by electronic interactions and hydrogen bonds.

View full abstract

The structure of a new organotin(IV) complex with formula [4-NH₃C₆H_4-NO₂]⁺₂[Sn(CH₃)₂Cl₄]^2- is reported. This crystal belongs to space group P2₁/c with cell dimensions a = 7.8026(4)Å, b = 20.8627(11)Å, c = 6.8990(4)Å, β = 111.4560(10)°; the final R value is 0.0291. This compound exists as a three-dimensional polymer produced by intermolecular N-H…Cl and N-H…O hydrogen bonds. Also, weak C-H…O and C-H…Cl hydrogen bonds were observed in the crystal lattice.

View full abstract

A proton-transfer compound, (EDGH₂)(pydc)·3H₂O, was synthesized from the reaction of 2,6-pyridinedicarboxylic acid, pydcH₂, and ethylenediguanidine, EDG. The crystal structure was determined by single-crystal X-ray diffraction. This compound crystallized in the space group P1 of the triclinic system and contained two molecules per unit-cell. The unitcell parameters were: a = 7.798(1)Å, b = 10.806(2)Å, c = 10.829(2)Å, with α = 102.462(2)°, β = 104.433(2)°, and γ = 96.094(2)°. The final R value was 0.0573 for 3484 measured reflections.

View full abstract

The title compound C₁₅H₁₅N₃O₂ was synthesized and the structure was investigated by X-ray crystallography. It crystallizes in the orthorhombic space group Pna2₁ with cell parameters a = 8.943(7)Å, b = 5.674(5)Å, c = 26.380(2)Å and Z = 4. The final residual factor is 0.0388. The intermolecular hydrogen bonds of the type N-H…O were observed in the structure.

View full abstract

The single-crystal structure of 1,5-dimethylbenzodiazepin-2,4-dione (C₁₁H₁₂N₂O₂) was determined at room temperature. The compound is orthorhombic, P_nma with Z = 4; the molecule is symmetrical to the mirror. The unit cell dimensions are: a = 8.144(2)Å, b = 13.315(2)Å, c = 8.996(2)Å and V = 975.5(4)ų. The R value is 0.043 for 781 observed reflections.

View full abstract

The single crystals of N-protected NO₂S₂ macrocycles with tosyl (I) and Boc (II) groups were prepared and their crystal structures were analyzed. Compound I exhibits a folded and twisted conformation due to intramolecular H-bondings as well as the π-π stacking interaction. In contrast, compound II is fully stretched because of the exo-orientation of two sulfur donors to the cavity.

View full abstract

The title complex with a tetradentate ligand, 2,2′-[2,3-naphthylenebis(oxy)]-bis(N,N-diisopropyl(acetamide)), was prepared and its crystal structure was determined by X-ray crystallography. The crystal reveals that complex [Y(NO₃)₃(L)] is a mononuclear complex. The Y atom is ten-coordinated by four O atoms from a tetradentate ligand and three nitrate anions in a distorted bicapped dodecahedron.

View full abstract

The crystal structure of the title compound was determined by the X-ray diffraction method. The crystal system is triclinic, space group P1 with Z = 2. The unit-cell parameters are: a = 7.4417(8)Å, b = 10.7676(12)Å, c = 11.3576(13)Å, with α = 108.599(2)°, β = 91.892(2)° and γ = 92.532(2)°. The final R value is 0.0561 for 3165 reflections measured. The geometry for the complex ion corresponds to the characteristic “three-legged piano stool” configuration.

View full abstract

The reaction of TiCl₂(Cp)₂ in methanol (Cp = cyclopentadienyl) with LH₂, (pydaH₂)(pydc) (pyda = 2,6-pyridinediamine, pydcH₂ = 2,6-pyridinedicarboxylic acid) in water, which is ion-pairing, led to the formation of a Ti(IV) complex, [Ti(Cp)₂(pydc)]. The crystal and molecular structure of complex was determined by X-ray diffraction. This complex crystallized in the crystal system of tetragonal with the space group P4₃2₁2 and four molecules per unit cell. The unit cell parameters at 153 K were a = 7.840(1)Å, c = 22.590(5)Å, and V = 1388.4(4)ų. The R value was 0.0247 for 1454 measured reflections. Each titanium atom is coordinated by two cyclopentadienyl rings and three atoms (two oxygen atoms and one nitrogen atom) from 2,6-pyridinedicarboxylate group, respectively. Therefore, coordination number of Ti(IV) is five.

View full abstract

The title compound, C₄₀H₃₄N₄S₄, crystallizes in the monoclinic system, space group C2/c. The cell parameters are a = 29.888(3)Å, b = 5.1829(5)Å, c = 22.511(2)Å, β = 93.686(5)°, V = 3479.9(5)ų, and Z = 4. The final R value is 0.056. The molecule, half of which is crystallographically independent, is almost planar and has a transoid-configuration.

View full abstract

The title compound, C₁₇H₂₇NO₄, is an antihypertensive and antiangina agent. The crystal belongs to space group Cc with the cell dimensions a = 5.721(3), b = 27.25(1), c = 10.782(6)Å and β = 101.57(4)°. The final R value is 0.063. The cyclohexene ring adopts a half-chair conformation and two hydroxyl groups occupy axial and equatorial positions. The 3-amino-2-hydroxypropoxy group takes a fully extended conformation.

View full abstract

The title compound, C₂₄H₃₃FO₆, is a glucocorticoid. The crystal belongs to space group C2 with the cell dimensions a = 30.575(2), b = 9.3616(9), c = 17.012(5)Å and β = 120.67(4)°. The final R value is 0.049. There are two crystallographically independent flurandrenolide molecules. The cyclohexenone rings in both molecules adopt different half-chair conformations. The dioxolane rings in both molecules take different puckered forms. The other corresponding rings in both molecules take essentially similar conformations.

View full abstract

The crystal of the title compound, C₁₉H₁₉NS·C₄H₄O₄, belongs to space group Pbca with cell dimensions of a = 17.0132(4), b = 9.3344(2), c = 26.1413(4)Å. The final R value is 0.073. The thioxanthene ring takes a butterfly conformation with the dihedral angle between the two phenyl rings being 50.4(1)°. The piperidine ring takes a slightly deformed-chair conformation.

View full abstract

The crystal of the title compound, C₉H₁₂N₄O₃, belongs to space group P2₁ with cell dimensions a = 4.522(1), b = 12.615(2), c = 9.093(2)Å, and β = 104.79(2)°. The final R value is 0.055. The bond lengths in the purine ring are significantly different from those of the corresponding bonds in theophylline. The hydroxyethyl group adopts a gauche conformation.

View full abstract

The title compound, [Zn₂(CH₃COO)₄(C₆H₆N₂O)₂]·2H₂O, crystallized in the triclinic space group P1, with cell parameters a = 10.918(2)Å, b = 10.894(2)Å, c = 8.2112(9)Å, α = 88.22(1)°, β = 92.89(1)°, γ = 42.443(7)Å and Z = 1. The acetato ligands serve to bridge the two Zn(II) centres, while nicotinamide behaves as a monodentate ligand. Coordination of the metal centre to nicotinamide occurs through the lone pair residing on the pyridine ring nitrogen. Crystalline water participates in hydrogen bonding to the O atom of nicotinamide. The geometry around Zn(II) is a distorted square pyramidal form in nature.

View full abstract

Solid-state photoirradiation of 2-pyrone-5-carboxylic acid afforded a single anti-head-to-tail [2 + 2]dimer at the position of C5-C6 double bonds in the 2-pyrone ring.

View full abstract

The hydrothermal synthesis and crystal structure of a new organic hydrogen-monophosphate, [N₂C₉H₂₂]·[HPO₄]·4H₂O, are presented. The cell is tetragonal, space group I4₁/amd, with a = 20.403(1)Å, c = 15.462(2)Å, V = 6436.2(9)ų, and Z = 16. The structure, determined from single-crystal X-ray diffraction data, was refined to R = 0.076 for 889 reflections (I ≥ 2σ(I)). It is built up from disordered [HPO₄] tetrahedra associated into dimers and hydrogen bonded to water molecules and diprotonated amines.

View full abstract

The reaction between Ni(Pic)₂·6H₂O (Pic=picrate anions) and N,N,N′,N′-tetrakis[(2-benzimidazolyl)methyl]-1,2-ethane-diamine (EDTB) in DMF resulted in a mononuclear nickel(II) complex, [Ni(EDTB)](Pic)₂·4DMF. Crystallographic studies show that the Ni(II) ion is octahedrally coordinated to four benzimidazole imine nitrogen atoms and two amine nitrogen atoms in EDTB.

View full abstract

The crystal structures of the title compounds, L-(R)-cysteine-D-(R)-mandelic acid, (I), and L-(R)-cysteine-L-(S)-mandelic acid, (II), have been determined. The structures show a common fashion in molecular recognition in hydrophilic layers, except for the arrangement of phenyl rings against mercapto groups. Crystallographic and physicochemical experiments have clarified the entropic and enthalpic advantage of (II) than (I). It plays a key role in the optical separation of mandelic acid with chiral L-cysteine.

View full abstract

The title compound was synthesized and its crystal structure was determined by an X-ray method. The crystal belongs to the monoclinic system, space group C2/c, cell parameters: a = 32.276(7)Å, b = 9.3186(19)Å, c = 21.188(4)Å, β = 123.69(3)°. V = 5302.4(18)ų, Z = 8, D_x = 1.224 Mg/m³. The π-π stacking interactions play important roles in the solid-state packing of the title compound.

View full abstract

The crystal structure of the title compound, C₇H₇N₂S⁺·ClO₄^-, contains cations and anions linked by N-H…O hydrogen bonds that form ribbons of alternating edge-fused R⁴₄(12) and R⁴₄(16) rings running along the b axis.

View full abstract

The title compound, (1-adamantylmetyl)trimethyl-ammonium iodide (AdMeNMe3I), was synthesized, and its structure was investigated by X-ray crystallography. It was crystallized in the monoclinic space group P2₁/n with the following cell parameters: a = 7.573(2)Å, b = 13.935(3)Å, c = 14.1095(18)Å, β = 99.792(15)°, and Z = 4. The final residual factor was 0.0984. The compound exhibited a warped cavity of the adamantyl group due to an interaction with a quaternary ammonium group.

View full abstract

The title compound, [C₂₀H₂₂N₁₀S₂Ni], crystallizes in the triclinic space group P1 with cell parameters a = 10.9319(9)Å, b = 12.0083(9)Å, c = 13.4978(11)Å, α = 87.057(7)°, β = 85.841(7)°, γ = 63.820(6)°, V = 1585.6(2)ų, Z = 2. The structure was refined to a final R value of 0.0498 for 4798 reflections [I > 2σ(I)]. The nickel atom is in a regular octahedral environment by four nitrogen atoms and two sulfur atoms.

View full abstract

Red single crystals of an iridium(III) complex, [(bpq)₂Ir(acac)] (bpq = 2-(p-biphenylyl)quinoline, acac = acetylacetone), were grown from sublimation, and determined using a CCD diffractometer. The R value is R₁ = 0.0227, and wR₂ = 0.0505. The iridium complex shows an approximately octahedral coordination geometry and has a stable sterical configuration. It is expected to be a good candidate for OLEDs.

View full abstract

The crystal structure of 5-(R)-menthyloxy-butyrolacto[3,4-b]-2(S)-6(R)-1-N-isopropylaziridine was determined by the X-ray diffraction method. This compound crystallizes in the orthorhombic system, space group P2₁2₁2₁. The unit cell dimensions are a = 6.4800(7), b = 8.4926(9), c = 33.030(3)Å, V = 1817.7(3)ų and Z = 4. The structure was refined to a final R value of 0.0444 for 2992 reflections (I > 2σ(I)). The results of X-ray single crystal analysis indicate that there are six chiral centers and one intermolecular C(2)-H(2)…N(1) hydrogen bond in the crystal of the title compound.

View full abstract

The title compound was synthesized following classical Hantzsch (dihydro) pyridine synthesis and characterized by the X-ray diffraction method. The compound crystallises in triclinic space group P1. A molecule of dimethylformamide (DMF) is retained with the compound during the crystallization process.

View full abstract

The compound 2-(4-bromophenyl)-3-(4-methylphenyl)-1,3-thiazolidin-4-one was synthesized. The compound crystallizes in the orthorhombic system with space group Pbca and the cell parameters are a = 12.364(1)Å, b = 13.179(3)Å, c = 18.653(4)Å, Z = 8, V = 3039(1)ų. The final residual factor is R1 = 0.066. The compound exhibits an intermolecular hydrogen bond of type C-H…Br.

View full abstract

The title compound was synthesized and the structure was investigated by X-ray methods. The compound crystallizes in monoclinic crystal class in the space group P2₁/c with cell parameters a = 5.893(6)Å, b = 31.781(3)Å, c = 8.341(8)Å, β = 94.256(5)°, Z = 4. The structure exhibits intermolecular hydrogen bonds of the type C-H…O.

View full abstract

The pyridoxylidene-taurineatocopper(II) complex [Cu(C₁₀H₁₃N₂O₅S)₂·H₂O] was synthesized by the reaction of the taurine pyridoxal Schiff base and copper acetate in a water-ethanol solution, and determined by an X-ray diffraction method. The complex crystallized in a monoclinic system with space group C2/c, and a = 23.908(5)Å, b = 7.7562(16)Å, c = 17.266(4)Å, β = 130.45(3)°. V = 2436.3(9)ų, Z = 4, D_x = 1.712 Mg/m³. The neighboring molecules in the complex are connected by three types of hydrogen bonds, obtaining a three-dimensional network supramolecular architecture.

View full abstract

The title compound, “3,3,6,6-tetramethyl-9-pyridyl-3,4,5,6-tetrahydroacridine-1,8(2H,5H)-dione” crystallized in an orthorhombic space group, Pbcn, with cell parameters a = 6.0581(5), b = 19.0837(16), c = 16.4145(14)Å, V = 1897.7(3)ų, D_x = 1.220 Mg/m³. The structure was refined to final R = 0.054 using 1826 observed reflections. The molecule occupies a two-fold axis passing through N1, C5, C6 and N2 atoms. The outer cyclohexane rings adopt a conformation intermediate between a half chair and a sofa. The crystal packing is stabilized by van der Waals interactions.

View full abstract

In the title compound, C₁₉H₁₇O₆Cl, the biphenyl twist angle is 45.4(2)°. All of the three ester groups attached to the phenyl ring are planar and make dihedral angles of 60.2(2), 70.0(2) and 15.3(2)°, respectively. The chlorine atom lies in the plane of the phenyl ring to which it is attached. C-H…O interactions contribute to both the molecular and crystal stability and C-H…Cl influences the packing.

View full abstract