Solid-state supramolecular array through cooperative π-π interactions of 1-(2-methoxyphenyl)-o-carborane

Dicarba-closo-dodecaborane (carborane) has received much attention as a building block for supramolecular assemblies and bioactive compounds. Among the carborane isomers, 1,2-dicarba-closo-dodecaborane (o-carborane) has unique chemical properties, including the ability of the o-carborane C-H hydrogens to form H-bonds. We have designed and synthesized 1-(2-methoxyphenyl)-o-carborane 1a to study its ability to form an intramolecular H-bond between the o-carborane C-H hydrogen and various H-bond acceptors both in solution and in the solid state. Intramolecular H-bonding ability in solution was evaluated by means of ¹H NMR spectroscopic measurements of the C-H hydrogen signal. The signal of the C-H hydrogen of 1a showed a remarkable downfield shift in CDCl₃ and various other solvents, i.e., the shift was almost solvent-independent. We suggest that 1a forms an intramolecular H-bond in these solvents. Crystal structure analysis of 1a showed a C-H?O distance of 2.05 Å and a nearly planar torsion angle C(2)-C(1)-C(7)-C(8) of 6.5°, indicating intramolecular C-H?O H-bond formation in the solid state. The crystal packing of 1a indicates that a supramolecular array is stabilized by cooperative π-π stacking interactions among the methoxyphenyl groups and by hydrophobic interactions of the o-carborane cages. DFT calculations indicate that the strength of the intramolecular H-bond of 1a is about 3.53 kcal/mol. These observations indicate the potential value of o-carborane in supramolecular chemistry and materials chemistry; it should be possible to design novel materials by utilizing both the H-bonding ability of the o-carborane C-H hydrogen and the high hydrophobicity of the o-carborane cage.     

2D and 3D supramolecular assemblies of double cyclopalladated azobenzenes realized by C-H?Cl-Pd, π?π and C-H?π interactions

The double cyclopalladated complex with azobenzene, μ-[(E)-1,2-diphenyldiazene-C^2,8, N^1,2]-di-[chloro(dimethylsulfoxide)palladium(II)]; (DMSO)PdCl(μ-C₆H₄NNC₆H₄)(DMSO)PdCl (1) and its analogous complex with DMF as ancillary ligand, (DMF)PdCl(μ-C₆H₄NNC₆H₄)(DMF)PdCl; μ-[(E)-1,2-diphenyldiazene-C^2,8,N^1,2]-di-[chloro(dimethylformamide)palladium(II)] (2a) were synthesized and the function of cyclopalladated moiety in molecular assembling in the solid state is illustrated by their crystal packings. The polymorphism of 2a and 2b is discussed. The crystal structures reveal assemblies with molecular components self-organized by C-H?Cl-Pd hydrogen bonds, π?π, and C-H?π interactions. The double cyclopalladated complexes of azobenzene, with two Pd-Cl moieties participating in the hydrogen bond formation and π-conjugated system involved in the π?π or C-H?π interactions, represent a new class of building blocks for construction of solid state supramolecular assemblies.     

Stabilization of β-hairpin structures via inter-strand π-π and hydrogen bond interactions in α-, β-, γ-hybrid peptides

Synthesis and conformational studies of α-, β-, γ-hybrid peptides containing a pyrrole amino acid (Paa, 1) and a furan amino acid (Faa, 2), namely Boc-β-Phe-Faa-d-Pro-Gly-Paa-β-HGly-Faa-OMe (3) and Boc-Paa-β-Phe-Faa-d-Pro-Gly-Paa-β-HGly-Faa-OMe (4), were carried out and they adopt β-hairpin structures stabilized via inter-strand π-π and hydrogen bonding interactions.     

New triorganotin(IV) complexes of polyfunctional S,N,O-ligands: Supramolecular structures based on π?π and/or C-H?π interactions

A series of new triorganotin(IV) complexes with 4-hydroxy-2-mercapto-6-methylpyrimidine (L¹H₂), 4-hydroxy-2-mercapto-pyrimidine (L²H₂), 2,4(1H,3H)-pyrimidinedithione (L³H₂) (Scheme 1) of the type R₃SnLSnR₃ (R = Me 1, 4, 7; R = Ph 2, 5, 8; R = PhCH₂3, 6, 9) have been synthesized by reactions of triorganotin(IV) chloride and corresponding ligands. All complexes are characterized by elemental analyses, IR spectra and NMR spectra analyses. Among them, complexes 2, 5 and 8 are also characterized by X-ray crystallography diffraction analyses. Significant π?π stacking, C-H?π interactions and intramolecular hydrogen bonds stabilize these structures.     

Thiacalix[4]arene-alkali metal assemblies: crystal structures and guest-binding capabilities of supramolecular architectures supported by metal coordination and cation-π interactions

To investigate alkali metal complexation with sulfur-linked calixarene analogues and their guest-binding properties for gaseous organic guest molecules, we elucidated a crystal structure of a cesium complex with p-H-thiacalix[4]arene (1·4H) ligands and guest-binding properties of the cesium complex (2) and the previously reported rubidium complex (3). In crystals of the complex 2, a ‘sandwich-like’ binuclear complex was formed by inter-molecular coordination of cesium cations to the thiacalixarene molecules and methanol molecules, mutually interacting by aromatic-H?S hydrogen bonding and alkali metal cation-π interactions between the alkali metal cation and thiacalixarene aromatic rings outside of the cavities. On the guest-binding behaviors both complexes 2 and 3 toward organic guest molecules, methanol, ethanol, and 1-propanol as polar molecules, the complex 2 has no methanol adsorption ability, but the complex 3 showed vapor adsorption properties for all guest molecules. In particular, both complexes exhibited a high adsorption capability toward ethanol molecule. As results of gaseous guest adsorption measurements for alcohol molecules, the guest-binding of these complexes are significantly different because the properties depend heavily on structural natures between complexes 2 and 3.     

C-H?Br, C-Br?Br, and C-Br?π interactions in the crystal structures of mesitylene- and dimesitylmethane-derived compounds bearing bromomethyl units

X-ray structure determinations of mesitylene- and dimesitylmethane-derived compounds bearing bromomethyl units (compounds 1-3) show that the crystal packing of the molecules is characterized by the presence of C-H?Br interactions, such as BrCH₂?Br, CH₃?Br, and C_PhH?Br. In addition, C-Br?Br and C-Br?π interactions determine the crystal packing. The bromomethyl groups play a major role in the packing of 1-3.     

Strong phenyl-perfluorophenyl π-π stacking and C-H?F-C hydrogen bonding interactions in the crystals of the corresponding aromatic aldimines

The X-ray diffraction analysis of two co-crystals, 1·2 (aldimines 1 and 2) and 3·4 (aldimines 3 and 4), reveals that there are strong phenyl-perfluorophenyl π-π stacking and intermolecular hydrogen bonding interactions. The new perfluoroaryl-aryl face-to-face interaction of the crystalline aldimines provides a design motif for a new class of self-assembling system.     

Exchange interactions through π-π stacking in the lamellar compound [{Cu(bipy)(en)}{Cu(bipy)(H2O)}{VO3}4]n

Structural, magnetic, and powder and single-crystal electron paramagnetic resonance (EPR) studies were performed on [{Cu(bipy)(en)}{Cu(bipy)(H(2)O)}{VO(3)}(4)](n) (bipy = 2,2'-bipyridine, en = ethylenediamine), which is a new copper-vanadium hybrid organic-inorganic compound containing Cu(II) and V(V) centers. The oxovanadium units provide an anionic scaffolding to the structure, where two types of Cu(II) coordination modes, octahedral (Cu1) and square pyramidal (Cu2), contribute to the magnetic properties. The crystal structure contains layers including Cu1 and Cu2 ions, separated by stacked arrangements of 2,2'-bipyridine molecules. Each type of Cu(II) ion in these layers forms parallel spin chains described by exchange coupling parameters J(1) and J(2) for Cu1 and Cu2, respectively (exchange couplings defined as H(ex)(i,j) = -J(ij)S(i)S(j)), which, for necessity, are assumed to be equal to J. These chains are coupled by much weaker Cu1-Cu2 exchange interactions J(3) connecting neighbor Cu1 and Cu2 ions within a layer, through paths acting as rungs of a ladder chain structure. The average coupling J, which is antiferromagnetic (J < 0), according to the susceptibility data, is estimated with similar results with a mean field approximation (J = -1.4 cm(-1)), and with a uniform chain model (J = -1.7 cm(-1)). The EPR spectra of powdered samples and oriented single crystals are shown to be independent of J(1) and J(2), but are dependent on the weak coupling J(3), and the data allow a lower limit to be established: |J(3)| > 0.04 cm(-1). The spectra are also strongly sensitive to extremely weak coupling interactions with average magnitude J(4) between copper atoms in neighboring layers, separated by ～10 ?, using the stacked 2,2'-bipyridine molecules, which produce a 2D-to-3D quantum phase transition. This is observed in single-crystal samples when the energy levels are changed with the orientation of the magnetic field. From the characteristics of these transitions, we estimate a value of |J(4)| = 0.0034 ± 0.0004 cm(-1) between Cu(II) ions in neighboring layers. This work emphasizes the important possibilities of EPR to evaluate extremely small exchange couplings between metal ions in a solid material, even in the presence of other much larger couplings.     

Associative combination of lone pair-π, π-π and anion-π interactions observed in a ternary system comprising Mg(II)-malonate-2-aminopyridine-hexafluoridophosphate

One Mg(II) malonate complex with protonated 2-aminopyridine and hexafluoridophosphate as counterions, (C₅H₇N₂)₄[Mg(C₃H₂O₄)₂(H₂O)₂](PF₆)₂ (1) [C₅H₇N₂ = protonated 2-aminopyridine, C₃H₄O₄ = malonic acid] has been synthesized from purely aqueous media just by mixing the reactants in their stoichiometric proportion and its crystal structure has been determined by single-crystal X-ray diffraction. The role of weak forces like lone pair?π and anion?π interactions in influencing the self-assembly process appears to be of importance. A rare combination of lone pair?π and anion?π interactions in 1, of the type lone pair?π/π?π/π?anion, is observed, and this unusual supramolecular network is fully described here.     

The interplay of coordinative,hydrogen bonding and π–π stacking interactions in sustaining supramolecular solid-state architectures.: A study case of bis(4-pyridyl)- and bis(4-pyridyl-N-oxide) tectons

Bis-monodentate ligands, such as bis(4-pyridyl) derivatives and bis(4-pyridyl-N-oxide), are able to generate polymetallic coordination networks with interesting supramolecular solid-state architectures. This review is devoted to high-dimensionality systems, which are extended by combining two or three organizing forces: metal-coordination, hydrogen bonds and π–π stacking interactions. A special emphasis is given to the following molecules, which play the role of linkers and spacers in the construction of extended frameworks: 4,4′-bipyridine, 1,2-bis(4-pyridyl)ethane, trans-1,2-bis(4-pyridyl)ethene, trans-4,4′-azo-pyridine, 4,4′-bipyridyl-N,N′-dioxide.     

First homo- and hetero-nuclear complexes of a chemical messenger-histamine: Cu(II) complex being a supramolecular assembly based on hydrogen bond, Ni(II)?π and C-H?π non-covalent interactions

In this study, the first homo- and hetero-nuclear cyanocomplexes of histamine (His), namely, [Cu(His)₂][Ni(CN)₄], [Ni(His)₂Ni(CN)₄]_n and [Cd(His)Ni(CN)₄]_n are investigated by X-ray diffraction (XRD) technique, electron paramagnetic resonance (EPR) and infrared (IR) spectroscopy. Besides being the first hetero-nuclear complex of histamine, [Cu(His)₂][Ni(CN)₄] complex has an interesting property as being a supramolecular structure constructed by three different non-covalent interactions as hydrogen bond, Ni(II)?π and C-H?π interactions. In [Cu(His)₂][Ni(CN)₄] complex histamine exists in gauche conformation and N^τ-H tautomeric form, and plays an important role in supramolecular structure formation by participating in non-covalent interactions through its aminoethyl side chain and imidazole group. The shifts and splittings in the stretching vibrations of cyano groups show that [Ni(His)₂Ni(CN)₄]_n and [Cd(His)Ni(CN)₄]_n complexes are one-dimensional and three-dimensional coordination polymers, respectively. In [Ni(His)₂Ni(CN)₄]_n complex, histamine acts as a chelating ligand by adopting gauche conformation. In [Cd(His)Ni(CN)₄]_n complex, Cd(II) ions and [Ni(CN)₄]²⁻ anions form two-dimensional layered structure and histamine has a novel bonding mode as a bridging ligand between these layered structures. It is concluded that histamine may have trans conformation and Nπ-H tautomer as a bridging ligand in [Cd(His)Ni(CN)₄]_n complex, which has not been reported so far for the solid structures of bidentate histamine. EPR studies on [Cu(His)₂][Ni(CN)₄] and Cu²⁺-doped [Cd(His)Ni(CN)₄]_n complexes show that the ground state of the unpaired electron in both complexes is dominantly d_x²-y².     

Synthesis and Characterization of Complexes of Te(IV) with Sulfur and Selenium Containing Ligands: Crystal and Molecular Structure of Trichloro(4-methoxyphenyl)tellurium(IV)· N -methylbenzothiazole-2-( 3H )-thione

We report the synthesis and characterization of two new complexes of trichloro(4-methoxyphenyl)tellurium(IV) with N -methylbenzothiazole-2-( 3H )-thione ( 1 ) and N -methylbenzothiazole-2-( 3H )-selone ( 2 ). Both are obtained as air-stable complexes by the addition of a 1:1 molar ratio of the substituted tellurium(IV) trichloride with the appropriate ligand in tetrahydrofuran under an atmosphere of dry nitrogen. Both ( 1 ) and ( 2 ) have been characterized by 1 H and 13 C NMR spectroscopy, elemental analysis, and, in the case of ( 1 ), by a single crystal x-ray diffraction study. The molecular structure of ( 1 ) shows an approximately square-based pyramidal structure with one short Te--Cl bond [2.388(2)Å] trans to a very long Te--S linkage [2.883(2)Å]. A comparison with the related structures of some heavy main group elements is included.     

Synthesis, structure and photophysical properties of binuclear methylplatinum complexes containing cyclometalating 2-phenylpyridine or benzo{h}quinoline ligands: a comparison of intramolecular Pt-Pt and π-π interactions

The binuclear cyclometalated complexes [Pt(2)Me(2)(ppy)(2)(μ-dppm)], 1a, and [Pt(2)Me(2)(bhq)(2)(μ-dppm)], 1b, in which ppy = 2-phenylpyridyl, bhq = benzo{h}quinoline and dppm = bis(diphenylphosphino)methane, were synthesized by the reaction of [PtMe(SMe(2))(ppy)] or [PtMe(SMe(2))(bhq)] with 1/2 equiv of dppm at room temperature, respectively. Complexes 1a and 1b were fully characterized by multinuclear ((1)H, (31)P, (13)C, and (195)Pt) NMR spectroscopy and were further identified by single crystal X-ray structure determination. A comparison of the intramolecular Pt-Pt and π-π interactions in complexes 1a and 1b has been made on the basis of data on crystal structures and wave functions analysis. The binuclear complexes 1a and 1b are luminescent in the solid state, and showing relatively intense orange-red emissions stemming from (3)MMLCT excited states. The reaction of complex 1b with excess MeI gave the binuclear cyclometalated Pt(IV)-Pt(IV) complex [Pt(2)Me(4)(bhq)(2)(μ-I)(2)], 2. Crystal structure of complex 2 shows intermolecular C-H···I and C-H···π interactions in solid state.     

Synthesis,characterization, spectroscopy,X-ray structure and gaussian hybrid computational investigation of (−)-(S)-1-[2-(benzenesulfonamido)-3-phenylpropanoyl]-4-[(4-methyl)phenyl]thiosemicarbazide

Abstract

The molecule (?)-(S)-1-[2-(benzenesulfonamido)-3-phenylpropanoyl]-4-[(4-methyl)phenyl] thiosemicarbazide was synthesized and its structure analyzed by X-ray diffraction to understand its geometry, and inter/intra-molecular interactions. Theoretical calculations were carried out using DFT and TD-DFT methods with B3LYP/6-31G(d, p) and B3LYP/6-31G?+?(d, p) basis sets. Theoretical bond parameters, harmonic vibration frequencies, and chemical shifts are in good agreement with the experimental results. Electronic properties of the molecule derived from frontier orbitals, molecular electrostatic potential, and theoretical UV-Visible spectrum are validated experimentally.     

β-diketone interactions: Part 4. The structures and properties of 1,3-diphenyl-2-methylpropane-1,3-dione,C16H14O2, and 1,3-diphenyl-2-(4-methoxyphenyl)propane-1,3-dione,C22H18O3

The X-ray crystal structures of 1,3-diphenyl-2-methylpropane-1,3-dione and 1,3-diphenyl-2-(4-methoxyphenyl)propane-1,3-dione show them both to adopt cis-diketo (Z,Z) conformations with carbonyl—carbonyl dihedral angles of 89.0(3)° (2-methyl derivative), and 85.5(4)° and 77.7(4)° for the two molecules in the asymmetric unit of the 2-(4-methoxyphenyl) derivative. These are the first acyclic β-diketones with an α-hydrogen to be reported which do not have an enol configuration in the solid state.     

Tandem ESI mass spectrometry of 11α- and 11β-{4-[N,N-bis(2-chloroethyl)amino]phenyl}acetates of the estrane steroids

ESI MS studies showed that the major collision-activated fragmentation pathway of the [M + Na]⁺ ions of the title estranes involves elimination of NaCl and HCl molecules. Fragmentation of the [M + H]⁺ ions involves the functional groups, which provides information on their structures. The fragmentation of the [M + Na]⁺ and [M + H]⁺ ions was estimated by quantum-chemical calculations. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 92–95, January, 2008.     

Reactivity of the metalloligand [Pt2(µ-S)2(PPh3)4] toward tellurium(II) thiourea complexes: synthesis and structural characterization of the ditellurium(I) derivative [{Pt2(µ-S)2(PPh3)4}2Te2]2+

Abstract

Reaction of the platinum(II) sulfide metalloligand [Pt₂(µ-S)₂(PPh₃)₄] with the tellurium(II) source TeCl₂(tu)₂ (tu?=?thiourea) is dependent on reaction conditions employed. In the presence of added acid, the dominant species observed in the electrospray ionization (ESI) mass spectrum is the tetraplatinum species [{Pt₂(µ-S)₂(PPh₃)₄}₂Te₂]²⁺. This contains the Te₂²⁺ moiety and is related to the previously reported tellurium(I) dithiophosphinate analog [(Ph₂PS₂)₂Te₂]. However, in the absence of acid, considerable degradation of the {Pt₂S₂} metalloligand occurs as evidenced by the formation of the mononuclear complex [Pt{SC(NH₂)NH}(PPh₃)₂]⁺ containing a deprotonated thiourea ligand, together with other thiourea-containing ions, identified by ESI MS. Likewise, attempted use of a fully substituted thiourea, viz. Me₂NC(S)NMe₂ (tmtu) in TeCl₂(tmtu)₂, also resulted in degradation of the {Pt₂S₂} core and detection of the known complex [(Ph₃P)₂PtCl{SC(NMe₂)₂}]⁺. The [{Pt₂(µ-S)₂(PPh₃)₄}₂Te₂]²⁺ cation was isolated with several anions, and unequivocal confirmation of the structure of the complex was obtained by an X-ray structure determination on the BF₄^- salt, which shows the presence of the Te₂²⁺ unit, with the Te–Te bond bridged by two {Pt₂S₂} metalloligands. Density functional theory was used to further probe the Te₂²⁺ bonding interactions in [{Pt₂(μ-S)₂(PPh₃)₄}₂Te₂]²⁺ and the previously reported [(Ph₂PS₂)₂Te₂].     

Copper(I) coordination polymers of N,N'-bis[3-(methylthio)propyl]pyromellitic diimide: crystal transformation and solvatochromism by halogen-π interactions

Four copper(I) coordination polymers with ligand N,N'-bis[3-(methylthio)propyl]pyromellitic diimide (L), [Cu(2)I(2)L(2)](n) (1), [Cu(2)I(2)L(2)](n) (2), [Cu(2)I(2)L](n) (3), and {[Cu(2)I(2)L(2)]·CH(2)Cl(2)}(n) (4), have been successfully synthesized and structurally characterized by single-crystal X-ray diffraction. Structural transformations between the polymers were controlled by the appropriate solvent composition, mole ratio, or temperature. When a 1:1 CuI/L ratio was employed, dimorphic products, 1 and 2, based on a rhomboid Cu(2)I(2) cluster were obtained from an acetonitrile solution and from a dichloromethane/acetonitrile solution with ultrasonication, respectively. When a 1:2 CuI/L ratio was employed, polymer 3 based on infinite stair-step polymer (CuI)(∞) was crystallized. Crystalline product 4 was obtained by the transformation of 1 in a mixed-solvent system with a 1:5 acetonitrile/dichloromethane ratio. Polymers 1-4 were transformed into polymer 3 at 197 °C. X-ray structures of 2-4 show short distances (3.406-3.667 ?) between halogens (I(-) and Cl) and aromatic rings. 1 and 4 show solvatochromism; upon inclusion of the colorless electron donor CH(2)Cl(2), the red color changes as a result of the formation of a chloride-π charge-transfer complex 4 of a pale-colored electron acceptor, 1. Therefore, the origin of the red color from 2 and 3 is also assigned as iodide-to-electron-deficient aromatic π charge transfer.     

Interaction of 1-methyl-1-({2-[4-(trifluoromethyl)phenyl]-1,3-thiazol-4-yl}methyl) piperidinium chloride with β-CD: spectroscopic,calorimetric and molecular modeling approaches

Spectroscopic investigation supported by molecular modeling methods has been used to describe the inclusion complex of β-cyclodextrin (β-CD) with 1-Methyl-1-({2-[4-(trifluoromethyl)phenyl]-1,3-thiazol-4-yl}methyl) piperidinium chloride (1MPTMPC) in solution and in solid state. The formation of inclusion complex between the β-CD and the 1MPTMPC has been investigated both in solution and in the solid state. Solution-state complexation between the 1MPTMPC and β-CD was established using ¹H NMR spectroscopy and isothermal titration calorimetry (ITC). From the ¹H NMR spectroscopic studies, 1:1 complex stoichiometry was deduced with an association constant (K) of 925 M^?1. Using an independent binding model, the ITC technique provides a K value of the same order with the one determined by NMR and the thermodynamic parameters ΔH, ΔS and ΔG which reveals driving forces involved during complex formation. The formation of the solid inclusion compound was confirmed by X-ray powder diffraction and differential scanning calorimetry. The most probable conformation of the inclusion complex obtained through a molecular docking investigation corroborates well to ROESY experiment.