Synthesis and Crystal Structure of Nickel(II) Complex with 2,2′-Biimidazole and 4-Aminobenzoic Acid

Abstract  The Ni(II) complex, [Ni(H₂biim)₂(PABA)₂]Cl₂·2H₂O, H₂biim being 2,2′-biimidazole, PABA being 4-aminobenzoic acid has been synthesized and the crystal structure determined using X-ray crystallography. The complex crystallizes in triclinic system, space group P − 1 with unit cell parameters a = 8.3920(9) ?, b = 9.8436(11) ?, c = 9.8874(11) ?, α = 94.862(2)°, β = 109.142(2)°, γ = 90.992(2)°, V = 767.95(15) ?³ and Z = 1. The molecules of the complex in the crystal assemble by way of N–H⋯Cl, O–H⋯Cl, O–H⋯O hydrogen bonds as well as π–π stacking interactions to provide a two-dimensional supramolecular structure. Index Abstract  Synthesis and Crystal Structure of Nickel(II) Complex with 2,2′-Biimidazole and 4-Aminobenzoic Acid Yanping Li and Pin Yang* The molecules of the title complex [Ni(H₂biim)₂(PABA)₂]Cl₂·2H₂O in the crystal assemble by way of N–H⋯Cl, O–H⋯Cl, O–H⋯O hydrogen bonds as well as π–π stacking interactions to provide a two-dimensional supramolecular structure.      

An Efficient and Simple One-Pot Synthesis of Novel 2-Amino-5-aza-6-(dinitrilomethylene)-4,7,7-trimethylbicyclo[2.2.2]octane-1,3-dicarbo-nitrile and its Crystal Structure

Abstract  

The title compound was prepared by the reaction of 4-methyl-pent-3-en-2-one and malononitrile, at room temperature, in the presence of indium-triflate and triethylamine. The structure of the molecule was established by spectral analysis and X-ray diffraction studies. The compound crystallizes in the monoclinic space group C2/c with unit cell parameters: a = 14.269 (2), b = 10.141 (2), c = 19.743 (3) ?, β = 95.523(4)°, Z = 8. The crystal structure was solved by direct methods and refined to R = 0.0526 for 2,690 observed reflections. The isoquinuclidine rings adopt boat conformation. The molecules in the unit cell are arranged in layers. The crystal structure is stabilized by N–H⋯N interactions.     

Crystal Structure and Conformational Analysis of 4-[(<Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Dimethylamino)Benzylidene]-2-Phenyloxazole-5-One

Abstract  

Molecular and crystal structure of 4-[(p-N,N-dimethylamino)benzylidene]-2-phenyloxazol-5-one, C₁₈H₁₆N₂O₂, have been determined by single crystal X-ray diffraction study. The title compound is monoclinic, with a = 12.1704(23) ?, b = 3.9810(5) ?, c = 30.9603(56) ?, β = 101.176(15)°, Z = 4, D _x = 1.32 g/cm³, μ(Mo Kα) = 0.087 mm⁻¹, and space group is P12₁/c1. The structure was solved by direct methods and refined to a final R = 0.047 for 3166 reflections with I > 2σ(I). The crystal structure is stabilized by C–H⋯O and C–H⋯N type intra-molecular, C–H⋯O type inter-molecular interactions. To enlighten the flexibility and the geometric isomerism (E or Z) of the title compound, the selected torsion angle is varied from −180 to 180° in every 10° separately and molecular energy profile is calculated and analyzed.     

The Crystal and Molecular Structure of the Dinuclear Mo(VI) Species: [(cis-MoO2L)(μ-O)(cis-MoOL(OH2)]?·?CHCl3 where L?=?(S-benzyl 3-(2-Hydroxyphenyl)Methylenedithiocarbazate)

Abstract  The title dinuclear complex, [(cis-MoO₂L)(μ-O)(cis-MoOL(OH₂)], was characterized as a chloroform solvate. In this structure, one Mo atom features a cis-[MoO₂]²⁺ core to which is also bonded a dinegative, tridentate S-benzyl 3-(2-hydroxyphenyl)methylenedithiocarbazate ligand (= L), via sulfur-, oxygen-, and nitrogen-donors, and a water molecule completes the distorted octahedral coordination geometry. A similar NO₄S donor set is found for the other Mo atom but in this case, the water molecule is substituted by a bridging oxo atom derived from the first Mo species. Two dimers associate via cooperative O–H⋯O hydrogen bonds to form a supramolecular dimer which, in turn, are linked into supramolecular chains via O–H⋯N hydrogen bonding. The complex crystallizes in the triclinic space group P-1 with a = 10.4714(12) ?, b = 10.7627(14) ?, c = 16.708(2) ?, α = 87.916(7)°, β = 76.249(6)°, γ = 83.610(7)°, and Z = 2. Index Abstract  Dinuclear [(cis-MoO₂L)(μ-O)(cis-MoOL(OH₂)], characterized as a chloroform solvate, with octahedral Mo centers, are connected into supramolecular dimers via O–H⋯O hydrogen bonding which are connected via O–H⋯N hydrogen bonds into chains.      

Synthesis, Crystal Structure and Electrochemical Property of New Rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene)bis(azido)cobalt(III) Nitrate Methanol Solvate Complex

Abstract  

The new cobalt compound, [Co(C₁₆H₃₅N₁₀]⁺(NO₃)⁻·CH₃OH (1), have been synthesized and characterized. It’s structure and electrochemical property were investigated using single-crystal X-ray diffraction and cyclic voltammetry in solutions of dimethyl sulfoxide (DMSO) and methanol (CH₃OH). The X-ray diffraction analysis reveals that 1 crystallizes in the monoclinic space group P2₁/c with a = 9.8339 (10) ?, b = 16.4048 (17) ?, c = 15.3628 (16) ?, β = 104.96 (9)° and Z = 4. The complex 1 consists of one [Co(C₁₆H₃₅N₁₀)]⁺ cation, one NO₃ ⁻ anions and one solvent CH₃OH molecule. The metal center of complex 1 is six-coordinated, with the four nitrogens of the macrocycle defining an equatorial plane and two axially ligated [N₃]⁻ ions completing the cobalt coordination sphere. Moreover, hydrogen bonds of O–H⋯N, O–H⋯O and N–H⋯O and static force connect two components of the compound and maintain the crystal structure. Additionally, in situ spectro-electrochemical measurements support Co(III)/Co(II) reversible reduction processes with the observation of the corresponding spectral changes with the applied potentials E _app = −1.5 and 0.5 V. The results obtained by the method are in agreement with those by the CV methods.     

Structure of 2-[(Phenyl)-(3,5-Dimethyl-Pyrazol-1-yl)-Methyl]-Malonic Acid Diethyl Ester

Abstract  

The titled new functionalized ligand of type 2-[(phenyl)-(3,5-dimethyl-pyrazol-1-yl)-methyl]-malonic acid diethyl ester (4) is prepared in good yield through condensation of 3,5-dimethyl-pyrazole, with 2-arylidene-malonic acid diethyl esters 3. The structure of 4 was determined by spectral (IR, ¹H and ¹³C NMR), elemental analyses and X-ray diffraction data. The title compound (4) crystallizes in the monoclinic space group P2₁/a, with a = 7.9253 (2), b = 17.1299 (5), c = 13.4522 (4) ?, β = 90.220 (2)°, V = 1,826.25 (9) ?³, Z = 4 and with R _int = 0.021. The molecular conformation shows two possible pockets ready to coordinate two metal atoms. The crystal structure of (4) is stabilized by inter-molecular C–H⋯O and C–H⋯N hydrogen bonding.     

NH?O and NH?N Hydrogen Bonded Networks in Imidazole-Based Phosphane Oxides: Structures of Tris(2-Isopropylimidazol-4(5)-yl)Phosphane Oxide, Bis(2-Isopropylimidazol-4(5)-yl)Phosphane Oxide and Diphenyl-2-Isopropylimidazol-4(5)-yl Phosphane Oxide

Abstract  

The three title compounds show extensive hydrogen bonding networks in the solid state. The structure of diphenyl-2-isopropylimidazol-4(5)yl phosphane oxide (3) is dominated by N–H⋯OP hydrogen bonds, whereas in bis(2-isopropylimidazol-4(5)-yl)phenyl- (2) and tris(2-isopropylimidazol-4(5)yl)phosphane oxide (1) both, N–H⋯N and N–H⋯OP hydrogen bonds determine the solid-state structures. Compound 1 crystallises in the monoclinic space group Cc with cell parameters a = 19.5447(6) ?, b = 10.45764(16) ?, c = 10.8549(3) ? and β = 121.418(4)°; 2 in the orthorhombic space group Pna2₁, with a = 11.5997(3) ?, b = 9.5836(2) ?, c = 16.1860(4) ? and 3 in the orthorhombic space group Pca2₁, with a = 10.8430(2) ?, b = 10.9277(2) ? and c = 27.7088(6) ?.     

Synthesis and Crystal Structure of (E)-1-(2,3-Dihydroxybenzlidene)-4,4-Dimethythiosemicarbazide

Abstract  

The Schiff base C₁₀H₁₃N₃O₂S is monoclinic, having unit cell parameters a = 9.788(1) ?, b = 9.615(1) ?, c = 12.605(1) ?, β = 108.41(1)° and V = 1125.56(2) ?³ and belongs to P2_1/n space group. The molecule is almost planar. The two hydroxyl groups present on the phenyl ring are involved in intermolecular H-bonding, which results in the stacking of molecules in the anti-parallel fashion leading an interesting network of channels. Besides this C–H⋯π and π–π (edge to edge) interactions appear to provide stability to the crystal lattice.     

Crystal Structure of Tetrakis Imidazole Copper(II) Diadipate Complex

Abstract  The title compound, [Cu(C₃H₄N₂)₄(COO–(CH₂)₄–COOH)₂] is a neutral complex and exist as a monomeric unit. The Cu atom occupies at the center of symmetry (0, 0.5, 0) with a distorted octahedral geometry. Imidazole nitrogens N1 and N6 (Cu1–N1 = 1.993(3) ?; Cu1–N6 = 2.008(3) ?) from two different imidazole group which are symmetrically disposed provides the square base and the long carboxylate oxygens (Cu1–O2 = 2.582(3) ?) from the protonated end of symmetrically oriented dibasic acid at the trans axial position. The adipate monoanion is in weak coordination with the metal center via monodentate fashion. The strong carboxylate-carboxylic acid intermolecular O–H…O interaction between the adjacent molecules is present in this structure as observed in the crystal structure of hexanedioic acid is noteworthy. In addition to the O–H…O H-bonding other molecular interactions such as N–H…O and C–H…O in packing generates a 3-D hydrogen bond network. Graphical Abstract  The title compound tetrakis imidazole Cu(II) diadipate is a neutral complex and exist as a monomeric unit with the metal atom occupies at the center of symmetry. Strong inter and intramolecular H-bonding interactions such as O–H…O, N–H…O and C–H…O in packing generates a 3-D hydrogen bond network.     

The Chair–Envelope Conformation of Two Derivatives of Triethylammonium 3-Oxo-8,9-Dinitro-Bicyclo [3.3.1] Non-7-En-6-Nitronate [I] and [II]

Abstract  

The title compounds C₁₉H₁₈N₃O₉ ⁻·C₆H₁₆N⁺ (I) [triethylammonium 2-benzyl-2-ethoxycarbonyl-3-oxo-8,9-dinitro-bicyclo [3.3.1] non-7-en-6-nitronate] and C₁₉H₁₇N₄O₁₁ ⁻·C₆H₁₆N⁺ (II) [triethylammonium 2(4-nitrophenylmethyl)-2-ethoxycarbonyl-3-oxo-8,9-dinitro-bicyclo [3.3.1] non-7-en-6-nitronate] crystallize in monoclinic crystal system with P2 ₁ /c space group. In compounds I and II, the bicyclo [3.3.1] nonane has chair–envelope conformation. The crystal structure of compound (I) is stabilized by N–H⋯O, N–H⋯N hydrogen bonds. In both the crystal structures weak C–H⋯O hydrogen bond is observed. Both compounds adopt chair–envelope conformation. An examination of puckering parameters, torsion angles and model (Dreiding) of the title compounds clearly indicates that the ring A has slightly distorted chair conformation and ring B has slightly distorted envelope conformation.     

Synthesis and Molecular Structure Investigation by DFT and X-Ray Diffraction of ARNO

Abstract  

We report here the synthesis of (Z)-5-(4-nitrobenzyliden)-3-N(2-ethoxyphenyl)-2-thioxo-thiazolidin-4-one (ARNO) compound. The crystal structure has been determined by X-ray diffraction. The compound crystallizes in the triclinic system with space group P[`1] P\bar{1} and cell parameters: a = 9.1289(19), b = 9.3717(7), c = 12.136(3) ?, α = 102.133(11)°, β = 90.99(2)°, γ = 117.165(9)°, V = 895.4(3) ?³ and Z = 2. The structure has been refined to a final R = 0.05 for 2591 observed reflections. The refined structure was found to be significantly non planar. The molecule exhibits intermolecular hydrogen bond of type C–H⋯O and C–H⋯S. ab initio calculations were also were performed at Hartree–Fock and density functional theory levels. The full HF and DFT geometry optimization was carried out using LANL2DZ, 6-31G* and B3LYP/6-31+G** basis sets. The optimized geometry of the title compound was found to be consistent structure determined by X-ray diffraction. The minimum energy of geometrical structure is obtained by using level HF/LANL2DZ basis sets.     

Unclassical Hydrogen Bonds of C–H⋯N and C–H⋯Cl in the Crystal Structures of 2-((<Emphasis Type="Italic">E</Emphasis>)-1,3-diarylallylidene)malononitriles

Abstract  

The 2-((E)-3-(2-nitrophenyl)-1-(4-methoxyphenyl)allylidene)malononitrile and 2-((E)-3-(2-chlorophenyl)-1-(4-bromophenyl)allylidene)malononitrile were synthesized and characterized by IR, ¹H NMR, and elemental analysis. The molecular structures were further confirmed by X-ray diffraction analysis. The former 1, C₁₉H₁₃N₃O₃, is triclinic, space group P−1, a = 7.3834(13), b = 10.901(3), c = 11.227(2) ?, α = 88.64(2), β = 71.596(14), γ = 78.186(18), Z = 2, V = 838.5(3) ?³. The unclassical hydrogen bond of C–H⋯N links the molecules forming polymers. The latter 2, C₃₆H₂₀Br₂Cl₂N₄, is orthorhombic, space group Pnma, a = 20.900 (4), b = 7.0710 (11), c = 10.9170 (18) ?, Z = 2, V = 1613.4(5) ?³. The same hydrogen bond of C–H⋯N and another type of C–H⋯Cl hydrogen bond link the adjacent molecules forming polymers along a axis.     

Crystal and Molecular Structure of Rhaponticin from Rheum hotaoense

Abstract  

Rhaponticin was isolated from the rhizome and root of Rheum hotaoense C.Y. Cheng et C.T. Kao and its crystal structure was determined by single crystal X-ray diffraction. The compound compactly packs in a triclinic unit cell in the P1 space group with unit cell dimensions a = 5.1240(12) ?, b = 7.0453(17) ?, c = 14.535(4) ?, α = 83.182(3)°, β = 89.212(3)°, γ = 68.956(3)°, V = 1486.0(2) ?³, Z = 1, D _calcd = 1.436 Mg m⁻³ and F(000) = 222. The atoms of the stilbene moiety are nearly coplanar, and the dihedral angle between ring (C2–C7) and ring (C10–C15) is 9.0°. The O–H⋯O hydrogen bonding interactions link the molecules into a complicated 3D framework.     

Synthesis and Crystal Structure of [Te{S(C<Subscript>6</Subscript>H<Subscript>3</Subscript>S)<Subscript>2</Subscript>O}]: A Tetracyclic Tellurium(II) Compound Displaying a Boat–Chair Conformation

Abstract  

The synthesis and molecular structure of (phenoxathiin-4,6-dithiolate)tellurium(II) is described. [Te{S(C₆H₃S)₂O}] was synthesized from the reaction of 4,6-dimercaptophenoxatiin and TeCl₄ in 36% yield. The crystal structure was determined by single crystal X-ray diffraction analysis. Crystal data: [Te{S(C₆H₃S)₂O}], formula weight = 389.95, crystallized in monoclinic system, space group P2(1)/n with a = 7.7898(10) ?, b = 18.513(2) ?, c = 8.9898(11) ?, β = 105.974(2)°, V = 1246.4(3) ?³ and Z = 4. The tetracyclic compound is non-planar with a di-coordinate Te^II atom. The eight-membered central ring is in a boat–chair conformation. The title compound displays weak intermolecular contacts Te–S, S–S and C–H⋯S.     

Crystallographic and Conformational Analysis of [(<Emphasis Type="Italic">E</Emphasis>)-2-[(3-Chlorophenylimino)methy])-4-methoxyphenol]

Abstract  The crystal structure of C₁₄H₁₂ClNO₂ was determined by X-ray analysis. It crystallizes in the triclinic space group Pc with a = 12.5346(10) ?, b = 4.5101(3) ?, c = 12.0534(11) ?, α = 90.00o, β = 113.669(6)o, γ = 90.00o, Z = 2, Dx = 1.393 mg/m³, μ (MoK_α) = 0.298 mm⁻¹. The title compound is photochromic and molecule is non-planar. It adopts a phenol–imine tautomeric form with a strong intramolecular O–H···N hydrogen bond and a strong intermolecular C–H···O hydrogen bond. Minimum energy conformations AM1 were calculated as a function of the three torsion angles θ1(C10–C9–N1–C8), θ2(C9–N1–C8–C1) and θ3(N1–C8–C1–C6), varied every 10°. As in the X-ray experiment results, molecule has an angle that makes it non-planar between two aromatic rings in AM1 optimized geometry. Graphical Abstract  Molecular and crystal structure of [(E)-2-[(3-chlorophenylimino)methy])-4-methoxyphenol], C₁₄H₁₂ClNO₂, have been determined by single crystal X-ray diffraction study, and conformational analysis of the title molecule with respect to the selected torsion angle has been achieved by AM1 semi-empirical calculations.      

Experimental and Semi-Empirical and DFT Calculational Studies on (<Emphasis Type="Italic">E</Emphasis>)-2-[(2,4-Dichlorophenylimino) methyl]-<Emphasis Type="Italic">p</Emphasis>-cresol

Abstract  

The molecular and crystal structure of the title compound, C₁₄H₁₁Cl₂NO, has been determined by X-ray single crystal diffraction technique. The compound crystallizes in the orthorhombic, space group Pbca with unit cell dimensions a = 7.5537(10) ?, b = 11.5518(13) ?, c = 29.760(4) ?, M _r  = 280.14, V = 2596.8(6) ?³, Z = 8, R ₁ = 0.065 and wR ₂ = 0.191. The title compound exists in the enol–imine tautomeric form with a strong intramolecular O–H···N hydrogen bond. The dihedral angle between the two benzene rings is 37.66(15)°. The asymmetric unit in the crystal structure contains only one neutral molecule. Calculational studies were performed by using AM1, PM3, PM6 semi-empirical and DFT methods. Geometry optimizations of compound have been carried out by using three semi-empirical methods and DFT method and bond lengths, bond and torsion angles of title compound have been determined. Dipole moments (Debye) and the energy parameters of compound (kcal/mol) were calculated by using above mentioned calculation methods. Atomic charge distribution has been obtained from AM1, PM3, PM6 and DFT. In order to determine conformational flexibility on the molecule, molecular energy profile of the title compound was obtained with respect to the selected torsion angle T(N1–C7–C1–C2), which is varied from −180° to +180° in every 10 via PM3 semi-empirical method.     

Synthesis and Crystal Structure of 1,3-Bis[2-(pyrrol-2-carbonyloxy)ethoxy]Benzene

Abstract  

A new compound, 1,3-bis[2-(pyrrol-2-carbonyloxy)ethoxy]benzene (1), was synthesized and characterized by X-ray diffraction. The crystal is monoclinic, space group P2₁/c with a = 6.3571(7), b = 11.0416(11), c = 28.156(3) ?, b = 92.821(2), V = 1974.0(4) ?³, Z = 4, Dc = 1.293 g/cm³, F(000) = 808, μ = 0.097 mm⁻¹. The final R = 0.0395 and wR = 0.0927 for 3478 observed reflections with I > 2 σ(I), and R = 0.0660 and wR = 0.1058 for all reflections. The title compound assembles into 2-D structure through a catemer type N–H⋯O hydrogen bonding motif and further forms 3-D structure through C–H···O hydrogen bonds.     

Synthesis and Crystal Structure of (PzCH<Subscript>2</Subscript>CHOHCH<Subscript>2</Subscript>PzH)·(Ph<Subscript>2</Subscript>SnCl<Subscript>3</Subscript>) (Pz = 3,5-dimethylpyrazol-1-yl)

Abstract  

Reaction of Ph₂SnCl₂ with 1,3-bis(3,5-dimethylpyrazol-1-yl)-2-propanol (L) in a 1:1 ratio yields L(SnPh₂Cl₂)₂ adduct, which partly hydrolyzes to the title complex (C₂₅H₃₁Cl₃N₄OSn, Mr = 628.58) during crystal growing in the air. The title complex is of monoclinic, space group P2₁/n with a = 9.0338(9), b = 17.890(1), c = 17.340(1) ?, β = 95.533(1)^o, V = 2798.9(5) ?³, Z = 4, Dc = 1.492 Mg/m³, λ(MoKα) = 0.71073 ?, μ = 1.224 mm⁻¹, F(000) = 1272, R = 0.023, wR = 0.054 for 4212 observed reflections with I ≥ 2σ(I). The crystal structure indicates that there is no direct interaction between the pyrazolyl ligand and the tin atom, but this complex forms a supramolecular structure through weak intermolecular C–H⋯Cl and O–H⋯Cl hydrogen bonds.     

Synthesis and Single Crystal X-Ray Structure of [Na(H2O)2(C18H15O6SO3)]2

Abstract  [Na(H₂O)₂(C₁₈H₁₅O₆SO₃)]₂ was synthesized by sulfated 5-hydroxy-6,7,4′-trimethoxyisoflavone with concentrated sulfuric acid. Single-crystal X-ray diffraction study indicates that it is a dimeric centrosymmetric species. The coordination polyhedron of each Na(I) atom exhibits a distorted trigonal bipyramidal geometry. The dimeric units are linked by intermolecular hydrogen bonds C–H⋯π, C–H⋯O and O–H⋯O to result in a three-dimensional framework. Graphical Abstract  [Na(H₂O)₂(C₁₈H₁₅O₆SO₃)]₂ was synthesized by sulfated 5-hydroxy-6,7,4′-trimethoxyisoflavone with concentrated sulfuric acid. The coordination polyhedron of each Na(I) atom exhibits a distorted trigonal bipyramidal geometry. The dimeric centrosymmetric units are linked by intermolecular hydrogen bonds C–H⋯π, C–H⋯O and O–H⋯O to result in a three-dimensional framework. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

X-ray diffraction, DFT, and spectroscopic study of N , N ′-difluoroboryl-5-(2-thienyl)dipyrrin and fluorescence studies of related dipyrromethanes, dipyrrins and BF2-dipyrrins and DFT conformational study of 5-(2-thienyl)dipyrrin

To explore the characteristics of potential fluorescent probes that could be used to screen prospective HDS catalysts, new 5-thienyl dipyrromethene derivatives have been prepared. 5-(2-thienyl)- (1a), 5-(3-thienyl)- (1b), and 5-(3-(2,5-dibromothienyl))-dipyrromethane (1c), were oxidized with DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone) separately to give the corresponding dipyrrins 2a–2c. These were subsequently treated with F₃B·OEt₂ to afford the respective N,N′-difluoroboryl-5-(thienyl)dipyrrin compounds, 3a–3c; the latter two may serve as polymer precursors. Significant fluorescence signal enhancement is achieved with 3a–3c over 2a–2c. Orange fluorescence is observed for 3a whereas its isomer 3b gives green fluorescence (365 nm). An X-ray diffraction study of 3a was performed (orthorhombic, P2₁2₁2₁, a=10.684(10) ?, b=15.208(13) ?, c=7.256(6) ?, V=1179.0(17) ?³, Z=4, R ₁=0.0428, wR ₂=0.0686) and its geometry was studied by way of DFT (Gaussian 03; B3LYP/6-31G^*) to give a HOMO/LUMO energy level difference of 414 nm, and a 2-thienyl group rotational barrier of ∼6 kcal/mol, compared to that of ∼12 kcal/mol for the phenyl derivative. Theoretical modeling of 2a demonstrated that the [N–H⋯N] interaction is favored by ca. 10 kcal/mol, whereas [N–H⋯S] bonding is sterically unattainable.