Synthesis and structure of a new hybrid vanadium arsenate: [VO<Subscript>2</Subscript>(phen)]<Subscript>2</Subscript>(H<Subscript>2</Subscript>AsO<Subscript>4</Subscript>)⋅H<Subscript>3</Subscript>O

A new hybrid vanadium arsenate [VO₂(phen)]₂(H₂AsO₄)H₃O 1 (phen = 1,10-phenanthroline) was synthesized under hydrothermal reaction conditions and structurally characterized by single-crystal X-ray diffraction, thermogravimetric analysis (TGA), IR and elemental analyses. Crystal data for 1: monoclinic, P2₁/n, a = 9.175(2) Å, b = 18.638(5) Å, c = 14.482(4) Å, = 102.333(3), V = 2419(1) ų, Z = 4. Compound 1 is composed of discrete tricyclic (VO₂)₂(H₂AsO₄) cluster decorated with two phen ligands. The discrete arsenic–vanadium clusters are extended into three-dimensional supramolecular arrays via – stacking interactions of phen groups.     

1,4-Di-[2-phenyl-1-diazenyl]perhydro-1,4-diazepine: X-ray crystal structure

1,4-Di-[2-phenyl-1-diazenyl]perhydro-1,4-diazepine (1) has been synthesized by reaction of benzenediazonium chloride with homopiperazine (perhydro-1,4-diazepine). The crystal structure of 1 has been determined by single crystal X-ray diffraction analysis. The bis-triazene (1) adopts an extended conformation which precludes any close intramolecular interaction of the phenyl rings. The heterocyclic seven-membered ring adopts a chair conformation, with the triazene side chains occupying alternate axial and equatorial positions consistent with cis-geometry. Internal torsion angles of the seven-membered ring have been measured. The crystal packing is determined by short contacts between C=H groups of phenyl rings and nitrogens of triazene moieties and by van der Waals interactions, with no evidence for intermolecular – interactions. This work establishes the structure of the product of diazonium coupling with homopiperazine as 1,4-di[(E)-2-phenyl-1-diazenyl]perhydro-1,4-diazepine. Crystal data: 1 C₁₇H₂₀N₆, monoclinic, space group P2₁/n, a = 9.1838(5) Å, b = 12.1095(6) Å, c = 15.0081(8) Å, = 101.320(2), V = 1636.6(2) Å,³ for Z = 4.     

Molecular structure of 1-phenyl-1-dimethylamino-4,4-bis(trimethylsilyl)-2-aza-3λ3-phosphabutadiene-1,3

The crystal and molecular structure of 1-phenyl-1-dimethylamino-4,4-bis(trimethylsilyl)-2-aza-3³-phosphabutadiene-1,3, Me₂N(Ph)C=N—P=C(SiMe₃)₂ (1), has been determined. Crystal data: triclinic, P1¯, a = 8.975(4), b = 10.001(5), c = 12.440(6) Å, = 79.04(4), = 77.98(4), = 73.07(4)°, V = 1034.7 ų, Z = 2, and D _c = 1.08 g cm^–3. The main geometrical parameters of 1 as well as ab initio (HF/6-31+G**) calculations of the model systems show no clear evidence of high efficiency of the (C=N)— (P=C) conjugation.     

Synthesis, crystal structure, and thermal property of a novel supramolecular assembly: (NH4)2(C8H10N4O2)4 [H4V10O28]·2H2O, constructed from decavanadate and caffeine

A novel 3D supramolecular assembly constructed from decavanadate and caffeine building blocks, (NH₄)₂(C₈H₁₀N₄O₂)₄[H₄V₁₀O₂₈]·2H₂O (1), has been synthesized in aqueous solution and characterized by elemental analysis, IR, ¹H NMR, ⁵¹V NMR, TG-DTA, and single crystal X-Ray diffraction. The compound 1 crystallizes in monoclinic system, space groupP2 ₁/n, a = 15.801(1) Å, b = 12.914(1) Å, c = 15.913(2) Å, = 113.55°,V = 2976.4 (5)ų, Z = 2, R = 0.0498 with 6818 reflections. Water molecules, ammonium ions, and caffeine act as cement linking the polyanions into 1D chain along the c-axis by hydrogen bonding. In compound 1, extensive hydrogen-bond contacts and strong – interactions lead to an ordered 3D supramolecular framework. TG-DTA curves indicate that the weight loss of the complex can be divided into three stages.     

Supramolecular structure of tetrakis-μ-(4-chloro-3-nitrobenzoato)-bis(methanol)dicopper(II)

The title compound, [Cu₂(II)(4-Cl-3-NO₂–C₆H₃CO₂)₄(CH₃OH)₂] or [Cu₂(4-chloro-3-nitrobenzoate)₄(MeOH)₂] has been prepared and its structure determined using X-ray crystallography. The complex crystallizes in the triclinic space group P-1 with a = 9.6887(9)Å, b = 10.6448(9)Å, c = 11.4194(10)Å, = 108.094(2), = 110.682(2), = 105.055(2), V = 952.691(15)ų, and Z = 1. The structure consists of centrosymmetric dimers in which the Cu(II) atoms display a square pyramidal CuO₅ coordination, with four carboxylate O atoms in the basal plane [CuO 1.951(2)–1.968(2)Å] and the methanol O atoms in the apical position [CuO 2.170(2)Å]. The Cu atoms are 2.614(1)Å apart and are bridged by four benzoate groups. The discrete dimers are extended into 1D chains that result from hydrogen bonding between the coordinated methanol on one Cu(II) dimer and the nitro substituent on an adjacent Cu(II) dimer. The chains are interdigited and held by – stacking interactions forming 3D supramolecular array.     

Self-assemblies of Ni(II) with phenanthroline and maleate anions: [Ni(H2O)3(phen)L] ⋅ H2O (1) and [Ni(H2O)2(phen)L] ⋅ 2H2O (2) with H2L = maleic acid

The complex [Ni(H₂O)₃(phen)(C₄H₂O₄)] H₂O (1), which was obtained by reaction of phenanthroline, Ni(NO₃)₂ 6H₂O, and maleic acid in CH₃OH/H₂O at pH = 7.05, crystallized in the monoclinic space group P2₁ (no. 4) with cell dimensions: a = 9.350(1) Å, b = 7.631(1) Å, c = 12.821(1) Å, = 106.25(1), and D _calc = 1.607 g/cm³ for Z = 2. The Ni atoms are each octahe drally coordinated by one chelating phen ligand, three H₂O molecules and one monodentate maleato ligand to form [Ni(H₂O)₃(phen)(C₄H₂O₄)] complex molecules with d(Ni–O) = 2.038–2.090 Å, d(Ni–N) = 2.066, 2.089 Å. The formed complex molecules are, via the intermolecular hydrogen bonds, assembled into columnar 1D chains. Interdigitation of the chelating phen ligands of the neighboring chains leads to 2D layers and the crystal H₂O molecules are hydrogen bonded to the oxygen atoms of the maleate not coordinated to the Ni atom. However, reaction of NiCO₃, phen, and maleic acid in CH₃OH/H₂O at pH = 6.33 afforded [Ni(H₂O)₂(phen)(C₄H₂O₄)] 2H₂O (2), which crystallized in the triclinic space group (no. 2) with cell dimensions: a = 7.971(1) Å, b = 8.237(1) Å, c = 13.304(1) Å, = 81.005(6)°, = 87.877(8)°, = 78.322(8)°, and D _calc = 1.671 g/cm³ for Z = 2. The Ni atoms are each octahedrally coordinated by two N atoms of one phen ligand and four O atoms of two H₂O molecules and two bis–monodentate maleato ligands with d(Ni–O) = 2.041–2.120 Å and d(Ni–N) = 2.095 Å. The Ni atoms are bridged by the maleato ligands to generate 1D ¹ [Ni(H₂O)₂(phen)(C₄H₂O₄)_2/2] chains along [100]. The supramolecular assemblies of the 1D chains via – stacking inter- actions result in thick 2D layers parallel to (001), between which the noncoordinating H₂O molecules are sandwiched. The paramagnetic [Ni(H₂O)₂(phen)(C₄H₂O₄)_2/2] 2H₂O (2) obeys the Curie–Weiss law _m(T-) = 1.139cm³ mol^–1 K with the Weiss constant = –0.95 K.     

Synthesis and crystal structure of bis(2,2′-bipyridyl)mononitritozinc(II) perchlorate. An example of a six-coordinate cis-octahedral ZnN4O2 chromophore

The crystal structure of bis(2,2-bipyridyl)mononitritozinc(II) perchlorate, [Zn(bipy)₂ (ONO)][ClO₄] (1) has been determined. The complex is monoclinic, with a = 10.9195(4) Å, b = 12.2320(5) Å, c = 16.5477(8) Å, = 105.6150(10), P2₁/n space group, with final R1 = 0.0657 and wR2 = 0.1630. The complex involves a [Zn(bipy)₂ (ONO)]⁺ cation and a [ClO₄]^– anion. The ZnN₄O₂ chromophore is six-coordinate, with a cis-distortion of the two oxygens of the nitrite, O(1) and O(2), at distances 2.216(5) and 2.197(5) Å from the zinc (Zn– O _mean = 2.206(5) Å, O = 0.019(5) Å) and two out of plane Zn–N bonds, Zn–N(2) and Zn–N(3), at 2.129(4) and 2.135(4) Å (Zn–n _mean/out = 2.132(4) Å, n _2,3 = 0.006(4) Å). The two inplane nitrogens, N(1) and N(4), at distances Zn–N(1) = 2.090(4) and Zn–N(4) = 2.085(4) Å (Zn–n _mean/in = 2.087(4) Å, n _1,4 = 0.005(4) Å) are greater than 2.0 Å, but slightly shorter than the axial bonds. The inplane angles ₁, ₂, and ₃ in 1 have values 150.33(18), 108.98(17), and 99.73(18) respectively. The stereochemistry is cis-distorted octahedral, with an ₃ = 99.37(18), which is lower than ₃ = 103.4(1) observed in [Zn(bipy)₂(ONO)][NO₃] (5). Comparison with the corresponding [Cu(bipy)₂(ONO)][Y] complexes suggested that the cis-distortion of the CuN₄O₂ chromophore in the copper(II) series does not originate in the Jahn–Teller or pseudo-Jahn–Teller effect.     

Crystal structures of a series of 3,7-bis-(arylazo)-1,3,5,7-tetraazabicyclo[3.3.1]nonanes

The crystal and molecular structure of a series of 3,7-bis(arylazo)-1,3,5,7-tetraazabicyclo[3.3.1] nonanes (1a–d) have been determined by single crystal X-ray diffraction analysis. All four compounds have the same feature, that the tetraazabicyclononane unit assumes a cage-like structure with the aryltriazene moieties lying parallel to one another so that the aryl rings are held together by – stacking. Crystal data: 1a C₁₇H₁₈N₁₀O₄, triclinic, space group P – 1, a = 9.8899(10), b = 13.0845(13), c = 16.458(2) Å, = 94.095(2)°, = 107.004(2)°, = 111.027(2)°, V = 1863.5(3) ų and Z = 4; 1b, C₁₉H₁₈F₆N₈, orthorhombic, space group Pbca, a = 15.3210(8), b = 10.9512(6), c = 24.5698(13) Å, V = 4122.4(4) ų and Z = 8; 1c C₁₉H₁₈N₁₀, monoclinic, space group P2₁/n a = 6.3742(6), b = 13.7343(13), c = 21.542(2)Å, = 97.738(2)°, V = 1868.8(3) ų, and Z = 4; 1d, C₁₉H₁₈N₁₀, monoclinic, space group P2₁/c, a = 18.205(2), b = 17.398(2), c = 12.784(12) Å, = 109.480(2)°, V = 3818.0(6) ų, and Z = 8.     

Synthesis, crystal structures, and properties of copper complexes with tripodal ligands and azide anion

Two new Cu^II complexes, (CuL¹N₃)ClO₄ (1) and (CuL²N₃)ClO₄ (2), have been synthesized and characterized in the presence of NaN₃, where L¹ = tris[2-(6-methylpyridyl)methyl]amine and L² = tris[(3,5-dimethylpyrazol-l-yl)methyl]amine, and their crystal structures have been determined by X-ray diffraction methods. Compound 1 crystallizes in the triclinic space group P–1, with a = 8.258(2) Å, b = 11.481(2) Å, c = 14.158(3) Å, = 72.30(3)°, = 79.05(3)°, = 86.08(3)°, V = 1255.4(5) ų. Compound 2 crystallizes in the monoclinic space group C2/c, with a = 26.752(2) Å, b = 10.561(2) Å, c = 21.059(4) Å, = 120.51(3)°, V = 5126(3) ų. In both compounds, each Cu^II center is in a distorted trigonal–bipyramidal coordinated environment with four nitrogen atoms from the tripodal ligand and one nitrogen atom from the azide group. The coordination geometry around Cu^II center of 1 is axially compressed trigonal bipyramid, while that of 2 is an axially elongated trigonal bipyramid. The coordinated azide group is in the axial site in both complexes. A quasi-dimeric structure of 1 has been formed in the unit cell through hydrogen bonding. The electronic spectra of two complexes in solution have been further studied by UV–vis technique, and the coordination properties have been discussed.     

Crystal structure of 751-1751-1751-1751-2751-2751-2

The title compound crystallizes in the centrosymmetric triclinic space group (No. 2) witha=10.818(1)Å,b=10.876(1)Å,c=11.072(2)Å, =98.74(1)°, =98.83(1)°, =96.61(1)°,V=125906(3)ų andZ=2. Interatomic distances include Fe–P=2.243(2)Å, Fe–CO=1.771(6)–1.781(5)Å, Fe–C(C₅H₅)=2.074(6)–2.103(5)Å and P–F=1.511(6)–1.571(4)Å.     

Crystal structures of two 1,2-bis-(1-aryl-3-methyltriazene-3-yl-)ethanes with aryl substituents of opposite polarity

The crystal and molecular structure of 1,2-bis-{1-(2-cyanophenyl)-3-methyltriazen-3-yl-}ethane (1) and 1,2-bis-{1-(2-methoxyphenyl)-3-methyltriazen-3-yl-}ethane (2) have been determined by single crystal X-ray diffraction analysis. Bis-triazene (1) exists as the staggered conformation in the solid state, with an anti-anti configuration around the N2–N3 bond of the triazene units, whereas 2 assumes a gauche conformation with the syn-syn configuration in the triazene units. Crystal data: 1 C₁₈H₁₈N₈, triclinic, space group P –1, a = 6.108(2), b = 8.118(3), c = 9.600(4)Å, = 101.37(7)°, = 96.47(7)°, = 102.71(5)°, V = 449.1(3)ų, Z = 2; 2 C₁₈H₂₄N₆O₂, monoclinic, space group P 2₁/n, a = 13.119(5), b = 7.745(2), c = 19.201(2)Å, = 96.47(7)°, V = 1910.3(9)ų, Z = 4.     

Synthesis and structure of [(nitrito-O,O′) bis(di-2-pyridylamine)copper(II)] nitrite

The synthesis and molecular structure of the title compound, [(nitrito-O,O) (dpa)₂Cu(II)] (NO₂), 1, is reported. Compound 1 crystallized in the orthorhombic space group Pccn with a = 11.397(5) Å, b = 12.256(6) Å, c = 14.876(8) Å, and V = 2077.9(17) ų with Z = 4. The distorted octahedral copper(II) cations are linked through a hydrogen-bonded polymer network. The polymer network is formed through the amine N–H of the cations and hydrogen bonded to the N–HO nitrite anions.     

Crystal structures of the new diphosphates,K2NiP2O7 and K6Sr2Ni5(P2O7)5

Crystalline K₂NiP₂O₇ (I): monoclinic, P2₁,a=9.230(2),b=17.540(8),c=8.319(9)Å, =91.44(2)°,Z=8,d _calc=3.067 g cm^–3, MoK =0.71069Å,R/R _w=6.5/9.4%, is characterized by the existence of face sharing NiO₆ octahedra with Ni–Ni separation of 2.827 Å (Ni–O; 1.93(2)–2.17(2)Å). K⁺ is seen in sites of seven, six, and fivefold coordination (K–O, averages; 2.83(2), 2.81(2), and 2.77(2)Å, respectively) P₂O₇ ^4– groups are observed in semieclipsed conformation. K₆Sr₂Ni₅(P₂O₇)₅ (II) crystallizes in monoclinic space group P2₁/c;a=11.038(7),b=9.533(13),c=7.438(2)Å, =100.13(4)°,D _calc=3.309 g cm^–3,Z=2,R/R _w=6.4/8.1%. Nickel atoms are distributed on planes parallel to the crystallographic (100) plane at =0 and =0.5. On the planes, =0, Ni²⁺ ions form successive linked trimers of edge sharing NiO₆ octahedra (Ni–Ni, 3.018(1), 3.008(1)Å; Ni–O, av 2.07(2)Å). The intermediate planes (=0.5) contain isolated and six coordinate Ni²⁺ ions (Ni–O av. 2.09(2)Å). Seven-coordinate potassium ions (K–O, av. 2.74(2)Å) are located on intermediate planes at =0.25 and 0.75. P₂O₇ ^4– groups are found in eclipsed conformation. Strontium atoms are located between nickel and potassium planes and are surrounded by seven oxygen atoms (Sr–O, av. 2.586(2)Å).     

Crystal and molecular structure of bis[(1,2-dihapto-3,5-dimethyl-pyrazolido)-π-allylpalladium(II)]

The crystal and molecular structure of bis[(1,2-dihapto-3,5-dimethylpyrazolido)--allylpalladium(II)], C₁₆H₂₄N₄Pd₂, has been determined by X-ray diffraction techniques. The crystals are monoclinic,P2₁/c (No. 14), witha = 8.752(1),b = 18.932(2),c = 11.780(3) Å, and = 109.78(1) °. The observed crystal density (1.746 g cm^–3) agrees well with that calculated on the basis of four molecules per unit cell (1.754 g cm^–3). The structure has been refined by full-matrix least-squares techniques to a finalR ₁ value of 0.045 (R ₂ = 0.056) for 2974 unique reflections withI _net7 counts sec^–1. The Pd₂N₄ ring is in a boat conformation in which the two palladium atoms are 1.113 and 1.064 Å out of the plane defined by the four nitrogen atoms. The Pd-C bond distances to the terminal atoms of the -allyl groups (2.12 Å) are longer than those to the central carbon atoms (2.06 Å). The molecule possesses approximatemm2 (C _2v ) symmetry.     

Methyl 4-((E)-2-{3-[(3-{ (E)-2-[4-(methoxycarbonyl)phenyl]- 1-diazenyl}-5,5-dimethylhexahydro-1-pyrimidinyl)methyl]-5,5-dimethylhexahydro-1-pyrimidinyl-1-diazenyl) benzoate. X-ray crystal structure

Methyl 4-((E)-2-{3-[(3-{(E)-2-[4-(methoxycarbonyl)phenyl]-1-diazenyl}-5, 5-dimethyl hexahydro-1-pyrimidinyl)methyl]-5, 5- dimethylhexahydro-1- pyrimidinyl}-1- diazenyl) benzoate (1) has been synthesized by reaction of a mixture of formaldehyde and 2,2-dimethyl-1,3-propanediamine with p-methoxycarbonylbenzenediazonium chloride. The crystal structure of 1 has been determined by single crystal X-ray diffraction analysis. The crystals of 1 displayed problems of disorder; the asymmetric unit is built up by two independent molecules, which display disorder within a methoxycarbonyl group. The two independent molecules in the asymmetric unit are very similar, differing only slightly about the mutual orientation of the aryltriazenyl groups. With respect to the N–C–N bridge between the hexahydropyrimidinyl rings, the two equivalent fragments containing the triazene moieties are in a cis orientation. The N–N single bonds, in the range 1.319(4)–1.348(4) Å, and the N=N double bonds, in the range 1.255(5)–1.275(4) Å, indicate significant conjugations within the triazene moieties. All the hexahydropyrimidine six-membered rings adopt a chair conformation as shown by their puckering parameters. The crystal packing is determined only by simple van der Waals interactions. The crystal structure of 1 is compared with the previously reported structure of the unbranched hexahydropyrimidine analogue 2. Crystal data: 1 C29H40N8O4, triclinic, space group P-1, a = 13.9652(2), b = 14.2908(3), c = 16.6129(4) Å, = 97.279(1), = 90.872(1), = 107.385(1), V = 3133.6(1) ų, for Z = 4.     

The synthesis and structural characterization of silyl-substituted fluorenes

Three silyl-substituted fluorenes have been prepared by direct synthetic methods and structurally characterized by X-ray diffraction. The three silyl-substituted fluorenes studied were 9-trimethylsilylfluorene (1), 9-(tert-butyldimethyl)silylfluorene (2), and 2,7-di-tert-butyl-9-trimethylsilylfluorene (3). Complex 1 is orthorhombic, P2₁2₁2₁, a = 6.2681(14) Å, b = 14.329(3) Å, c = 15.231(4) Å, Z = 4. Complex 2 is monoclinic, P2₁/c, a = 12.1953(10) Å, b = 6.9977(6) Å, c = 19.6536(17) Å, = 93.818(2), Z = 4. Complex 3 is monoclinic, P2₁/c, a = 11.9954(9) Å, b = 9.8978(7) Å, c = 18.5464(13) Å, = 92.456(2), Z = 4. The long carbon–silicon bonds effectively remove any significant intramolecular interactions as little distortion is exhibited around the sp ³-carbon atom and the fluorenyl backbone demonstrates near planarity. The bulky silicon substituents also prevent intermolecular interactions, as only a few close contacts less than 4.0 Å exist in all three solid state structures.     

Racemic and (+)-ethyl 2-acetamido-2-carboxy-5-oxohexanoate

Racemic ethyl 2-acetamido-2-carboxy-5-oxohexanoate has been isolated by single hydrolysis of the corresponding diethyl ester and resolved essentially quantitatively by diastereomeric salt formation with (–)-quinine. The (+)-isomer was retrieved from the less-soluble quininium salt. Racemate crystals, (plusmn;)-1, are monoclinic, space group P2₁/c, a = 7.609(4)Å, b = 16.731(7)Å, c = 10.746(5) Å, = 99.83(4)° enantiomeric crystals, (+)-1, are monoclinic, space group P2₁, a = 5.857(2)Å, b = 15.282(4)Å, c = 7.618(2)Å, = 95.62(2)°. Molecular packing is similar in the two structures; the enantiomer has a 0.7% higher volume per molecule and the lower fusion temperatures by 3°C. In both structures, carboxylic acids donate hydrogen bonds to the amide carbonyls of adjacent molecules without reciprocation. Amides form three-centered hydrogen bonds to carboxy oxygen of an intramolecular carboxylic acid group and to oxygen of a ketone carbonyl in an adjacent molecule.     

Structural characterization of Elisabatin B and Elisabatin C

X-ray structures of Elisabatin B (1) and Elisabatin C (2) have been determined. Crystal data for 1: Triclinic, P (No. 2), a = 7.528(2) Å, b = 9.404(2) Å, c = 11.414(2) Å, = 75.363(3)°, = 86.668(4)°, = 89.683(4)°, and Z = 2. Crystal data for 2: Monoclinic, P2₁/c (No. 14), a = 8.242(2) Å, b = 14.870(2) Å, c = 13.060(2) Å, = 101.458(3)°, and Z = 4. Both compounds are highly unsaturated leading to extended aromatic conjugation. They show different intermolecular O–HO hydrogen bonds, via which 1 forms dimers, and 2 zig-zag polymeric chains.     

Crystallographic characterization of N,N′-diarylformamidines bearing an alkoxy substituent at either the meta- or ortho-position

Crystal structures of four diphenylformamidines bearing phenyl substituents ortho-CH₃O (1), ortho-C₂H₅O (2), meta-CH₃O (3), and meta- ⁿ BuO (4) are reported. In each of the structures, formamidine exists as an unsymmetrical cyclic hydrogen bond dimer, and the geometry of the amidine unit is consistent with the localized C–N and C=N bonds. Interesting conformations due to the orientation of aryl groups were also observed. Crystal Data: 1, orthorhombic, Pbca, a = 11.297(1) Å, b = 15.092(1) Å, c = 16.380(2) Å, V = 2792.6(4) ų, Z = 8; 2, triclinic, P , a = 9.651(1) Å, b = 11.974(1) Å, c = 14.583(2) Å, = 101.789(2)°, = 99.320(2)°, = 99.048(2)°, V = 1595.9(3) ų, Z = 4; 3, orthorhombic, Pbca, a = 15.562(2) Å, b = 8.626(1) Å, c = 20.110(2) Å, V = 2699.4(5) ų, Z = 8; 4, monoclinic, P2₁/c, a = 14.525(2) Å, b = 15.534(2) Å, c = 8.818(1) Å, = 93.113(2)°, V = 1986.6(4) ų, Z = 4.     

Synthesis,thermal reactivity and structure of 1,2-bis(4-hydroxy-3-methoxyphenylethynyl)benzene

The crystal structure of the new enediyne 3 was determined by X-ray diffraction. 3 crystallizes in the orthorhombic space group Pbca (No. 61) with a = 12.7148(9) Å, b = 7.4872(8) Å, c = 38.890(4) Å, = = = 90 and Z = 8. The three-dimensional structure is characterized by an 8-membered cyclic array linking four molecules of 3 by hydrogen bonding between phenolic and methoxy groups. Furthermore, stabilization by –-stacking and CH s interactions is present. The important cd distance (between the two terminal acetylene carbons of the enediyne) which is relevant for the Bergman cyclization, was determined to 401 pm, being in good agreement with the high cyclization barrier ( G = 147.9 kJ mol^–1 at 220C) that was determined by differential scanning calorimetry (DSC).