Heterosynthons in molecular complexes of azopyridine and 1,2-bis(4-pyridyl)ethylene with dicarboxylic acids

A series of co-crystals of azaaromatic molecule with the present of dicarboxylic acid, [SA·BPE], [FA·AZP], [AA·BPE], [AA·AZP], [SEA·AZP] and [OA·AZP] (BPE=1,2-bis(4-pyridyl)ethylene, AZP=azopyridine, SA=succinic acid, FA=fumaric acid, AA=adipic acid, SEA=sebacic acid, OA=oxalic acid), have been synthesized for the regularity investigation of their supramolecular alignments driven by hydrogen bonding. It is significant for the design and synthesis of supramolecular co-crystals with multiple components. For linear molecules with recognition sites on both ends, the stacking regularity of the molecules in the co-crystals is proposed that the interlaced arrangement (motif III) is preferred when the size of the azaaromatic molecule is comparable with that of dicarboxylic acid and the inclined arrangement (motif II) is adopted when the length of azaaromatic molecule is much different from those of dicarboxylic acids.     

Hydrogen-bonded block mesogens derived from semiperfluorinated benzoic acids and the non-mesogenic 1,2-bis(4-pyridyl)ethylene

Thermal properties of benzoic acids carrying one or two semiperfluorinated alkoxy tails on the aromatic core have been investigated in binary mixtures with the non-liquid crystalline bidirectional trans-1,2-bis(4-pyridyl)ethylene. The hydrogen bonded complexes built from the complementary molecular species show a significantly enhanced mesophase stability compared with the fluorinated acids in their pure states. The mesophase morphologies of the complexes are governed mainly by the number of the partially fluorinated chains grafted to the acid component. Mixed systems comprising the one-chain acids exhibit a smectic C phase followed by a smectic A phase at more elevated temperatures. Incorporation of a second semiperfluorinated chain into the acid leads to the formation of columnar mesophases. These columnar phases of the H-bonded complexes should represent ribbon phases resulting from the collapse of the smectic layers.     

Spectroscopic, thermal and structural studies of cocrystal of 2,2′-diamino-4,4′-bis(1,3-thiazole) with 4,4′-bipyridine, 1,2-bis(4-pyridyl)ethylene and 1,3-bis(4-pyridyl)propane

Three new cocrystals based upon 2,2′-diamino-4,4′-bis(1,3-thiazole) (DABTZ) with 4,4′-bipyridine (4,4′-bipy), 1,2-bis(4-pyridyl)ethylene (bpe) and 1,3-bis(4-pyridyl)propane (bpp): [(DABTZ) (4,4′-bipy)], [(DABTZ) (bpe)] and [(DABTZ) (bpp)] have been synthesized and characterized by elemental analysis, IR-, ¹H NMR-, ¹³C NMR spectroscopy and studied by thermal and X-ray crystallography. Self-assembly of these compounds in the solid state is likely caused by both hydrogen bonding, and π-π stacking.     

Far-IR spectra of charge-transfer complexes between IX (X = Cl,Br or I) and trans-1,2-bis(4-pyridyl)ethylene, 1,2-bis(4-pyridyl)ethane and 4,4′-

Far-IR spectra of charge-transfer complexes of trans-1,2-bis(4-pyridyl)ethylene (Bpe), 1,2-bis(4-pyridyl)ethane (Bpa) and 4,4′-bipyridyl (4,4′-     

Network diversity and supramolecular isomerism in copper(II)/1,2-bis(4-pyridyl)ethane coordination polymers

Reactions of copper(II) sources with 1,2-bis(4-pyridyl)ethane (bpe) yielded metal-organic networks with diverse topologies and dimensionalities. Compounds [Cu(bpe)₂(dmf)₂]_n(ClO₄)_2n·2ndmf (1·2ndmf), [Cu(bpe)₂(dmf)₂]_n(ClO₄)_2n·3.5ndmf (2·3.5ndmf), [Cu(bpe)₂(NO₃)₂]_n·2nH₂O (4·2nH₂O) and [Cu₂(bpe)(O₂CMe)₄]_n·0.7nH₂O (5·0.7nH₂O) have been isolated by altering the copper(II) source, the reaction solvent and the crystallization process. Compounds 1·2ndmf and 2·3.5ndmf consist of cationic [Cu(bpe)₂(dmf)₂]²⁺ repeating units assembled to 1D and 2D (4,4) networks, respectively, and represent supramolecular isomers due to the conformational isomerism of the bridging bpe molecules. Compound 4·2nH₂O consists of neutral mononuclear [Cu(dpe)₂(NO₃)₂] repeating units assembled to inclined interpenetrating (4,4) sheets describing an overall entanglement that is 3D in nature, and compound 5·0.7nH₂O consists of neutral dinuclear repeating units assembled to cross-linked 1D chains.     

Design of Green-Emitting Salts from Substituted Pyridines: Understanding the Solid-State Photodimerization of trans-1,2-bis(4-pyridyl)ethylene

Polymorphic salts of trans-1,2-bis(4-pyridyl)ethylene (bpe), 2 [bpeH₂] ⋅ (SO₄)(2HSO₄) ( 1 ) and [bpeH₂] ⋅ 2HSO₄ ( 2 ) have been synthesized and their structures determined by X-ray crystallography. The Schmidt postulate predicts that neither of the salts will give rise to photodimerization so they can both potentially be applied as green light emitters. Despite the predictions, 1 undergoes a stereospecific solid-state photodimerization reaction with 100 % yield. This is due to UV induced combination of sliding and pedal-like movement of the pyridyl ring system that influences the alignment of C=C bonds. The sliding motion is restricted in 2 . Consequently, the green emission from 1 is completely quenched after photodimerization. It is evident that counter ions play a dominant role in dis- and enabling photodimerization; their degree of protonization and lattice placement are important solvent controlled design parameters towards crystal structures that can act as future light emitters.     

Polycrystalline and solution Raman spectra of t-1,2-bis(4-pyridyl)ethylene,its dihydrochloride and its dideuterochloride

The normal Raman spectra of trans-1,2-bis(4-pyridyl)ethylene and its dihydrochloride and dideuterochloride salts are reported. Frequency shifts observed upon salt formation and deuteration are utilized in the assignment of vibrational modes. Additional assignments are made by comparisons to other pyridine-containing molecules and trans-stilbene. Assignment of the normal Raman spectrum of trans-1,2-bis(4-pyridyl)ethylene is essential to interpretation of the surface Raman spectrum of this molecule reported elsewhere[1].     

Influence of organic carboxylic acids on self-assembly of silver(I) complexes containing 1,2-bis(4-pyridyl)ethane ligands

Four silver(I) complexes, namely [Ag₂(bpe)₂](bdc)·8H₂O (1), [Ag₂(bpe)₂(da)]·4H₂O (2), [Ag₄(bpe)₃(bptc)]·9H₂O (3), and Ag(bpe)₂(bpdc)₂ (4), have been successfully synthesized by the reactions between AgNO₃, 1,2-bis(4-pyridyl)ethane (bpe) and different carboxylic acids, including 1,3-benzenedicarboxylic acid (H₂bdc), diphenic acid (H₂da), 3,3′,4,4′-biphenyltetracarboxylic acid (H₄bptc), and 2,2′-bipyridine-3,3′-dicarboxylic acid (H₂bpdc). All four compounds were characterized by elemental analysis, IR spectra, and single-crystal X-ray diffraction. In (1), the Ag(I) atoms, in linear geometry, are joined into 1-D infinite cationic bpe-silver chains, and discrete bdc²⁻ anions compensate the charge of the crystal structure. In (2), the Ag(I) atoms, adopting tetrahedral and trigonal geometries, are linked by bpe and da²⁻ ligands into neutral double chains. In (3), the Ag(I) atoms, in T-shaped and linear environments, are coordinated by bpe and multidentate bptc⁴⁻ ligands to construct a 2-D network. And in (4), the Ag(I) atoms, with trigonal and T-shaped coordination geometries, are coordinated by bpe and bpdc²⁻ ligands to build up a 3-D framework. The different anions play different and important roles in directing the final crystal structures.     

Photochemical modification of the surface area and tortuosity of a trans-1,2-bis(4-pyridyl)ethylene periodic mesoporous MCM organosilica

A periodic mesoporous MCM-41 organosilica containing trans-1,2-bis(4-pyridyl)ethylene (t-BE) (350 m2 g-1; 0.28 cm3 g-1) incorporated in the silica walls undergoes photochemical isomerization to the cis configured bis(4-pyridyl)ethylene resulting in a dramatic area (473 m2 g-1) and pore volume (0.38 cm3 g-1) increase.     

Structural diversity and magnetic properties in 1D and 2D azido-bridged cobalt(II) complexes with 1,2-bis(2-pyridyl)ethylene

By utilizing a flexible co-ligand 1,2-bis(2-pyridyl)ethylene (2,2'-bpe), two new azido-bridged cobalt(II) complexes with the formulae [Co?(N?)?(OH?)?(2,2'-bpe)?](n)(2,2'-bpe)(n) (1) and [Co(N?)?(2,2'-bpe)?](n) (2) have been synthesized and structurally characterized. Compound 1 shows an uncommon 1D chain comprised of double EO azido bridged five- and six-coordinated Co(II) geometries in a unique (-5-5-6-)(n) sequence of the coordination number. The 2,2'-bpe acts as a terminal co-ligand and an uncoordinated molecule in the crystal lattice. Moreover the adjacent 1D chain is assembled by C-Hπ interactions and the intermolecular hydrogen bonding between uncoordinated 2,2'-bpe and coordinated water molecules building a 2D layer. Whereas, compound 2 is a 2D coordination network containing the alternating double EO and double EE bridging modes of azides and ditopic 2,2'-bpe bridges. The magnetic investigation of 1 reveals dominant intra-chain ferromagnetic interactions, with the double EO azide-bridge and weak inter-chain antiferromagnetic interactions, with overall metamagnetic behaviour, having magnetic ordering at 6 K. The magnetic behaviour of 2 shows spin-canted antiferromagnetism below a T(N) of 12 K.     

Supramolecular structures of metal complexes containing barbiturate and 1,2-bis(4-pyridyl)-ethane

This work describes the synthesis, thermal, spectroscopic properties (Raman and infrared), and crystal structures of five new supramolecular compounds [Mn(bpa)(H₂O)₄]B₂?·?4H₂O (1), [Fe(bpa)(H₂O)₄]B₂?·?4H₂O (2), [Co(bpa)(H₂O)₄]B₂?·?4H₂O (3), [Zn(bpa)(H₂O)₄]B₂?·?4H₂O (4), and Co₂mal₂bpa?·?2H₂O (5), where B is the anion of barbituric acid, bpa is 1,2-bis(4-pyridyl)-ethane, and mal is malonate ion. Compounds 1–4 are isostructural, showing covalent linear 1-D [M(bpa)(H₂O)₄]²⁺ chains, which interact by hydrogen-bonding and π-stacking interactions with barbiturate and crystallization water molecules resulting in a 3-D arrangement, belonging to Pbcn space group. Compound 5 has been obtained from the opening of the barbituric acid ring, with the formation of malonate, coordinated simultaneously to three cobalts in a 1-D chain along the c-axis, whereas bpa ligand gives rise to another 1-D chain along the a- and b-axes, resulting in a 3-D coordination polymer containing cavities. The vibrational spectra of 1–4 are also very similar; Raman spectra display two intense bands related to bpa at 1616 and 1020?cm^?1, assigned to the (ν _CC/ν _CN) and ring stretching modes, respectively. The barbiturate is also confirmed by a band at 684?cm^?1; the interesting point to be emphasized is this vibrational mode is not observed for 5, corroborating the absence of this building block in the structure.     

The experimental electron density distribution in the complex of (E)-1,2-bis(4-pyridyl)ethylene with 1,4-diiodotetrafluorobenzene at 90 K

The experimental electron density of the donor-acceptor complex of (E)-1,2-bis(4-pyridyl)ethylene (bpe) with 1,4-diiodotetrafluorobenzene (F(4)DIB) at 90 K has been determined with the aspherical atom formalism and analyzed by means of the topological theory of molecular structure. The bpe and F(4)DIB molecules are connected by intermolecular I.N bonds into infinite 1D chains. F.H bonds link these chains together to form the crystal assembly. The topological analysis reveals that the Cbond;I bond is of the "closed shell" type. Its bond-critical properties run parallel to those found in metal-metal and metal-ligand bonds of organometallic compounds. The integrated net charges show that the I.N halogen bond has an essentially electrostatic nature. F.F, F.C, and C.C intermolecular interactions, for which a bond path was found, contribute to reinforce the crystal structure.     

Surface-enhanced Raman scattering of trans-1,2-bis (4-pyridyl)-ethylene on silver by theory calculations

Surface-enhanced Raman spectra of trans-1,2-bis (4-pyridyl)-ethylene (t-BPE) on silver foil were detected at laser line of 514.5, 633, 785 and 1064 nm, respectively. The structure of Ag-t-BPE, Ag4-t-BPE, Ag6-t-BPE, Ag10-t-BPE and Ag20-t-BPE complexes has been calculated using a local version of the Amsterdam density functional program package. The Raman spectra and electronic polarizability of t-BPE-Ag at 514.5, 633, 785 and 1064 nm excitation lines were calculated. The Raman bands of t-BPE were assigned according to the calculation of potential energy distribution. The experimental and calculated Raman spectra of t-BPE-Ag at 514.5, 633, 785 and 1064 nm were compared. The relative Raman intensities change at different excitation lines were discussed based on the Raman enhanced mechanism and surface selection rules.     

Octahedral Rhenium Cluster Complexes with 1,2-Bis(4-pyridyl)ethylene and 1,3-Bis(4-pyridyl)propane as Apical Ligands

A series of eight new octahedral rhenium cluster complexes with the general formula trans-[{Re₆Q₈}L₄X₂] (Q = S or Se; L = 1,2-Bis(4-pyridyl)ethylene (bpe) or 1,3-Bis(4-pyridyl)propane (bpp); X = Cl or Br) was synthesized and investigated. While bpe is a ligand with a conjugated aromatic system, bpp represents a molecule of opposite type and has independent aromatic systems of the two pyridine rings. It was shown that this difference in the electronic structure of the ligands has a fundamental effect on the electronic structure, electrochemical and luminescent properties of the corresponding cluster complexes. Specifically, the [{Re₆Q₈}(bpe)₄X₂] complexes in solutions show multiple quasi-reversible electrochemical transitions associated with reduction of the organic ligands. At the same time, the trans-[{Re₆Q₈}(bpp)₄X₂] complexes show multielectron quasi-irreversible reduction processes, which correlate with the mixed character of the lowest unoccupied molecular orbitals of these complexes. All the obtained new compounds exhibit red photoluminescence. The photophysical parameters (emission lifetimes and quantum yields) measured for the bpp complexes exceed those revealed for bpe complexes by more than an order of magnitude.     

Density functional theory calculation of vibrational spectroscopy of trans-1,2-bis(4-pyridyl)-ethylene

The molecular geometry and vibrational frequencies of trans-1,2-bis(4-pyridyl)-ethylene (t-BPE) in the ground state were calculated using density functional theory (DFT) methods with 6–31++G(2d,p) basis set. The optimized geometric bond lengths and bond angles are obtained by DFT employing the hybrid of Beckes nonlocal three-parameter exchange and correlation functional and Lee–Yang–Parr correlation functional (B3LYP). Fourier transform Infrared (FTIR), Fourier transform Raman (FT-Raman) and near-infrared surface-enhanced Raman scattering (NIR-SERS) spectra of t-BPE on the silver foil substrate were recorded. All FTIR, FT-Raman and NIR-SERS band were assigned on the basis of the B3LYP/6-31++G(2d,p) method. The vibrational frequencies obtained by DFT(B3LYP) are in good agreement with observed results. Surface selection rules derived from the electromagnetic enhancement model were employed to infer the orientations of t-BPE on the silver foil substrate surface.     

Synthesis of 1,4-bis(4-pyridyl)butadiyne

2-Methyl-4-(4-pyridyl)-3-butyn-2-ol ( 2 ) was prepared in 70% yield by the reaction of 4-bromopyridine with 2-methyl-3-butyn-2-ol in diethylamine in the presence of bis(triphenylphosphine)palladium(II) chloride and copper(I) iodide. Removal of the protective group in 2 by refluxing with sodium hydroxide in toluene yields (90%) 4-ethynylpyridine ( 3 ). Oxidative coupling of 3 in pyridine by dioxygen in the presence of copper(I) chloride produces a 92% yield of 1,4-bis(4-pyridyl)butadiyne.     

Low-dimensional porous coordination polymers based on 1,2-bis(4-pyridyl)hydrazine: from structure diversity to ultrahigh CO2/CH4 selectivity

Solvothermal reactions of metal salts, benzenedicarboxylic acids, and 4,4'-azopyridine (azpy) in different conditions produced four coordination polymers, namely, [Zn(3)(bdc)(3)(bphy)(3)]·2DMF·10H(2)O (3; H(2)bdc = 1,4-benzenedicarboxylic acid, bphy = 1,2-bis(4-pyridyl)hydrazine, and DMF = N,N-dimethylformamide), [Ni(bdc)(bphy)]·DMF·3.5H(2)O (4), [Zn(nipa)(bphy)]·EtOH (5; H(2)nipa = 5-nitroisophthalic acid), and [CoBr(bdc)(0.5)(bphy)]·2DMA·H(2)O (6; DMA = N,N-dimethylacetamide), in which the azpy ligand was in situ reduced. Structural determination reveals that 3-5 consist of the same metal/ligand ratio and similar coordination modes, as well as similar two-dimensional square-grid networks, but differ from their packing/interpenetration modes. 3 consists of alternately arranged single layers and interweaved double layers. Single layers in 4 directly stack in an offset fashion, while 5 is constructed of interdigitated double layers. 6 is a one-dimensional ladderlike structure, which could be regarded as that half of the bridging benzenedicarboxylate ligands in 3-5 are replaced by monodentate bromide ions. Interestingly, the crystal structures of these low-dimensional coordination polymers contain considerable solvent-accessible voids. Thermogravimetric curves, powder X-ray diffraction, and gas sorption experiments were used to study the potential porosity of these structures, which indicated that they can all reversibly desorb and adsorb solvent molecules. In particular, 4 showed gated sorption behavior and high CO(2)/CH(4) selectivity because of its flexible structure.