The influence of the negative hyperconjugation is relevant for the analysis of the π-π<Superscript>*</Superscript> conjugation with the mono-substitution and di-substitution of H<Subscript>2</Subscript>C= by O= and/or HN= in <Emphasis Type="Italic">trans</Emphasis>-buta-1,3-diene?

We have studied prop-2-en-1-imine (1), prop-2-enal (2), ethane-1,2-diimine (3), ethanedial (4), and 2-iminoacetaldehyde (5) to investigate the influence of the negative hyperconjugation in π-π^* interaction with the substitution of =CH₂ by =NH and/or =O in trans-buta-1,3-diene (6). The analyzes of the π-π^* interaction performed from evaluation of the π molecular orbital diagrams and electron localization function method demonstrated, that compared to 6, the substituted compounds 1-5 presented lower electron conjugation, especially in the structures bearing =O. The geometric parameters, natural bond orders, and topological analysis realized by quantum theory of atoms in molecules method indicated a predominant C-C and C=C character for the simple and double C-C bonds in the substituted compounds, 1-5, as compared to 6. Compound 4 had the highest enthalpy of formation, which reflected the lowest π-π^* interaction, maintained by the two =O conjugated groups. The natural bond orbital (NBO) and natural resonance theory (NRT) methods revealed that the π-π^* electron delocalization in substituted compounds, 1-5, is lower than in 6 from, firstly, of the less favorable interactions: π(X=C) ? π^*(C=C) and π(X=C) ? π^*(C=X), despite of the larger π(C=C) ? π^*(C=X) conjugation, with X = N and/or O, of 1-5 than π(C=C) ? π^*(C=C) of 6. But, most importantly, the weight of the interaction: n_π(O) ? σ^*(C-C), was determined from NBO and NRT methods as proportional to the π-π^* conjugation and thus demonstrating be decisive to establish the level of π electronic delocalization.     

Gelation capability of cysteine-modified cyclo(L-Lys-L-Lys)s dominated by Fmoc and Trt protecting groups

A series of symmetrical peptidomimetics(3–8) based on cysteine-modified cyclo(L-Lys-L-Lys)s were synthesized, and their gelation capability in organic solvents was dominated by fluorenylmethyloxycarbonyl(Fmoc) and triphenylmethyl(Trt) protecting groups and the exchange of thiol-to-disulfide as well. The peptidomimetics holding Trt(3 and 4) showed no gel performance, while the Fmoc groups promoted 5 and 6 to give rise to thermo-reversible organogels in a number of organic solvents. The self-assembled fibrillar networks were distinctly evidenced in the organogels by transmission electron microscopy(TEM) and scanning electron microscopy(SEM) observations. Fourier transform infrared spectroscopy(FT-IR) and fluorescence analyses revealed that the hydrogen bonding and ?-? stacking play as major driving forces for the self-assembly of these organogelators. A ?-turn secondary structure was deduced for the organogel of 6 by virtue of X-ray diffraction, FT-IR and circular dichroism(CD) measurements, and an interdigitated bilayer structure was also presented.     

Two new mononuclear cobalt(II) complexes of pyrazole-based ligands: synthesis,structures and magnetic studies

We have synthesized two mononuclear cobalt(II) complexes (1 and 2) of pyrazole-based bidentate (NN) and tridentate (NNN) tripodal ligands. X-ray crystal structure determination reveals that complex 1 has a tetrahedral geometry, while complex 2 has a trigonal–bipyramidal geometry. Both the complexes have been characterized by variable-temperature magnetic measurements between 2 and 300 K. A weak ferromagnetic exchange interaction (J = +1.5 cm^?1) is observed for complex 2. Due to the presence of supramolecular CH···Cl and π···π interactions, a good magnetostructural correlation was found between the D parameter and angular distortion (δ) for complex 1 and related complexes reported in the literature.     

New Thiocyanatocadmate and Halo-thiocyanatocadmates Modified by Imidazole or Triazole Derivatives: Synthesis,Structural Characterization,and Photoluminescence Property

At pH 2, the simple room-temperature self-assemblies between Cd²⁺ salts, SCN^? and organic bases created one new thiocyanatocadmate as [H₂(L1)][Cd₂(SCN)₆] (L1?=?1,4-bis(2-methyl-1H-imidazol-1-ylmethyl)benzene) 1, and two new halo-thiocyanatocadmates as [H₂(L2)][CdI₂(SCN)₂]·H₂O (L2?=?3,5-bis (4-pyridyl)-1,2,4-triazole) 2, and [CdCl(SCN)(L3)] (L3?=?3-pyrazinyl-1,2,4-triazole) 3. X-ray single-crystal diffraction analysis reveals that (a) in 1, with H₂(L1)²⁺ as the countercation, the SCN^? groups tri-bridge the Cd²⁺ centers into a 1-D chained thiocyanatocadmate; (b) 2 is only a mononuclear iodo-thiocyanatocadmate, and H₂(L2)²⁺ acts as the countercation. But via the π···π and N_pyridyl–H···N_SCN interactions, H₂(L2)²⁺ and CdI₂(SCN) ₂ ^2? aggregate together to form a 1-D supramolecular tube. Amongst the tubes, a chained water cluster with a zig-zag shape is observed; (c) 3 is an organically extended chloro-thiocyanatocadmate. Note that the report on this type of material is rather rare. It possesses a 3-D network structure with a dia topology, in which a castellated CdCl⁺ single chain is observed. L3 and Cl^? act as a mixed bridge, whereas SCN^? just serves as a terminal ligand in 3. The photoluminescence analysis indicates that the title compounds 1–3 all emit light (green light for 1, blue light for 2 and 3), which should be attributed to the ligand-centered electronic excitations.     

Two naphthoate-based lead(II) complexes with different limited-nuclear motifs: Syntheses,crystal structures,and fluorescent properties

Two new naphthoate-based lead(II) complexes, [Pb(NA)₂(2,2’-Bipy)] (I) and [Pb₂(NA)₄(4,4’- Bipy)] (II) (NA–= 1-naphthoate, 2,2’-Bipy = 2,2’-bipyridine, and 4,4’-Bipy = 4,4’-bipyridine) (CIF files CCDC nos. 664900 (I), 664899 (II)) have been hydrothermally synthesized by varying the N-heterocyclic coligands. Structural analyses reveal that the two complexes possess different limited-nuclear motifs, the former one owns mononuclear unit and the last complex exhibits centrosymmetric binuclear motif bridged by 4,4’-Bipy connector. The coordination numbers of Pb(II) metal centers in I and II are four and five, respectively. The NA^– anions in both complexes show the same binding modes, it is obvious that the bipyridyl coligands in the present mixed-ligands system are responsible for the dissociation or dimerization of mononuclear structural units and the binding numbers of the metal ion. In both complexes, the 6s lone pair of electrons of Pb²⁺ has a stereochemistry activity resulting the distribution of the Pb–O and Pb–N bonds in a hemisphere. Furthermore, both of the two compounds are linked to 2D network by intermolecular C–H···O hydrogen bonding and π···π stacking interactions, exhibiting strong fluorescent emissions resulting from the NA^?-based intraligand charge transfer at room temperature, which can be hopefully used as fluorescent materials.     

Synthesis,structure, and catalytic application of a new (3-methoxy-N-salicylidene)aniline—derived Schiff base complex of methyltrioxorhenium

A new (3-methoxy-N-salicylidene)aniline—derived Schiff base complex of methyltrioxorhenium (C₁₄H₁₃NO₂ · CH₃ReO₃) (I), displaying a cis-arrangement of the Schiff base ligand to the Re-bonded methyl group, has been synthesized and characterized by elemental analysis, IR, ¹H NMR, and single-crystal X-ray diffraction. The X-ray diffraction analysis reveals that I crystallizes in the triclinic system, space group P \(\bar 1\), which displays a distorted trigonal-bipyramidal structure in the solid with the O^? moiety binding to the Lewis acidic Re atom. The intermolecular hydrogen bands link the molecules of the complex into a two-dimensional layer structure. The presence of the π-π stacking interactions enhances the stability of the layers, which are further linked via π-π stacking interactions forming a three-dimensional supramolecular network. The unit cell parameters for I: a = 7.0032(14), b = 9.3762(19), c = 11.649(2) Å, α = 84.60(3)°, β = 89.08(3)°, γ = 84.45(3)°, V = 757.9(3) ų, Z = 2, F(000) = 456, R ₁ = 0.0591, ωR ₂ = 0.1346. In order to study the catalytic activity of complex I, cis-cyclooctene epoxidation in dichloromethane is examined. The result shows that the electron-donating OCH₃ group on the Schiff base influences the catalytic behavior significantly.     

Syntheses,crystal structures and biological activities of two new drum-shaped organotin(IV) carboxylate complexes with 2-(4-alkylbenzoyl)benzoic acid (alkyl = methyl or ethyl)

Two new organotin(IV) carboxylate complexes, [PhSnO(L¹)]₆ ·4(toluene) (1) (HL¹ = 2-(4-methylbenzoyl)benzoic acid) and [PhSnO(L²)]₆ (2) (HL² = 2-(4-ethylbenzoyl)benzoic acid), were synthesized by the reaction of ligand acids with mono-organotin complex in 1:1 molar ratio. The synthesized complexes have been structurally characterized by elemental analysis, IR, ¹H, ¹³C, ¹¹⁹Sn NMR spectroscopy and X-ray crystallography diffraction analyses. Both 1 and 2 are hexanuclear organotin complex with drum-shaped structure. In the solid state of 1 and 2, 1D and 2D supramolecular networks are formed by hydrogen bonds, C–H···π or π···π interactions. Furthermore, the preliminary antitumor activities of 1 and 2 have been studied. The antitumor results show they exhibit good biological activities and may be explored for potential antitumor drugs.     

Relative substituent position on the strength of π-π stacking interactions

It was observed that the relative position of the arene substituents has a profound influence on the strength of π-π stacking in the 9-benzyl-substituted triptycene system. A new series of model compounds (3a-i) capable of revealing quantitatively π-π stacking interactions was studied. This series of compounds (3a-i) has an ortho-substituted methyl group in one of the two interacting arenes and the syn/anti ratios were determined and compared to a series previously studied compounds (4a-i) that have a para methyl group on the corresponding arene. A greater than 50% increase in the strength of π-π stacking interactions was observed with the methyl group in the ortho position comparing to that in the para position. No difference in π-π stacking interactions was observed when the other aromatic ring was a pentafluorobenzoate group.     

Glassy carbon electrode modified with hemin and new melamine compounds for H<Subscript>2</Subscript>O<Subscript>2</Subscript> amperometric detection

In an attempt to increase the stability and efficiency of hemin-modified electrodes, the present work reports the preparation of a new modified glassy carbon electrode obtained by immobilization of hemin (Hm) on the electrode surface together with a new N-substituted melamine (2,4,6-triamino-1,3,5-triazine) based G-2 dendrimer comprising p-aminophenol as peripheral unit (Den) or with one of its analogues, a melamine G-0 dimer (Dim). Basic structural features, able to determine intimate relationships between Hm and Dim (or Den) at room temperature in solid state, were evidenced with the use of vibrational analysis carried out by FT-IR. This method revealed contacts between Hm and Dim or Den respectively as H-bond interactions, proton-interchange, and π-π stacking interactions. The new modified electrodes were characterized by cyclic voltammetry and electrochemical impedance spectroscopy and tested for amperometric detection of H₂O₂. In this purpose, GC/Hm-Dim electrode exhibited better catalytic properties than GC/Hm-Den electrode, but lower stability.     

Synthesis and structural properties of thiapyridinophane and its complex with Ni(II) and Ag(I)

The 2,11-dithia[3.3](3,5)pyrdinophane (L¹) has been synthesized by a new method and characterized by ¹H NMR, which is used to form coordination complexes C₁₄H₁₄N₄O₆S₂Ni (I) by addition of Ni²⁺ cation and C₁₄H₁₄N₃O₃S₂Ag (II) by addition of Ag⁺ cation. 2,11,20-Trithia[3.3.3](3,5)pyridinophane (L²) and 2,11,20,29-tetrathia[3.3.3.3](3,5)pyridinophane (L³) have also been synthesized as by-products. Single-crystal X-ray analysis reveals that the conformation of the L¹ is syn(boat-chair), complexes I and II also adopt syn(boat-chair) (CIF files CCDC nos. 1400332 (I) and 700724 (II)). While in I, Ni(II) is coordinated with L¹ with two nitrogen and four oxygen atoms, in II, Ag(^I) is coordinated with L¹ by two nitrogen and two sulfur atoms came from four ligands. In complexes I and II, the formation of three-dimensional structure depends on π???π stacking and hydrogen bonds.     

Synthesis,crystal structure,and photoluminescence of zinc complex [Zn(Qina)<Subscript>2</Subscript>(DMSO)<Subscript>2</Subscript>] · 2DMSO

A novel complex [Zn(Qina)₂(DMSO)₂] · 2DMSO (I) (Qina = quinaldic acid, DMSO = dimethyl sulfoxide) has been synthesized and characterized by X-ray diffraction, elementary analysis, and IR spectrum. The unit cell parameters for complex I: a = 8.2884(11), b = 22.015(3), c = 9.0685(12) Å, β = 100.61(0)°, V = 1626.41(40) ų, Z = 2, space group, P2₁/n. In the complex I, the Zn(II) atom was six-coordinated to form a distorted octahedral geometry by two Qina ligands and two dimethyl sulfoxide molecules. The crystal structure is stabilized by hydrogen bonds, C - H... π, π-π stacking interaction between adjacent complexes. The binding of the complex I with calf thymus DNA has been investigated by fluorescence spectroscopic studies. The result suggested that the complex intercalates into DNA base pairs.     

Two novel coordination polymers: Synthesis,structure, luminescent properties,and selective sensing of Cu<Superscript>2+</Superscript> and Mn<Superscript>2+</Superscript> ions

Two novel coordination polymers, namely {[Co(Ttac)_0.5(1,4-Bib)(H₂O)] · H₂O}_n (I) and {[La(HTtac)₂(2H₂O)] · H₂O}n (II) (H4Ttac = 4,5-di(3'-carboxylphenyl)-phthalic acid, 1,4-Bib = 1,4-bis(1-imidazoly) benzene), have been designed and successfully prepared via hydrothermal process, and characterized by elemental analyses, IR spectroscopy, and single crystal X-ray diffraction (CIF files CCDC nos. 1039298 (I), 1039300 (II)). Structural analysis reveals that the H₄Ttac ligands adopt different coordination modes in the as-synthesized I and II, and thus give rise to the targeted coordination polymers with different configurations. It is worth mentioning that, coordination polymer I is assembled from low-dimensional structures into three-dimensional (3D) via π···π stacking interactions, while three-dimensional coordination polymer II is formed by covalent bonds. Luminescent properties of coordination polymer II have been studied at ambient temperature. Significantly, luminescent measurement indicates that coordination polymer II may be acted as potential luminescent recognition sensors towards Cu²⁺ and Mn²⁺ ions.     

Synthesis,crystal and molecular structures of 1D and 2D supramers of copper(II) with <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′-{bis(pyridin-2-yl) benzylidene}butane-1,4-diamine

Reaction of copper(II) perchlorate with N,N′-{bis(pyridin-2-yl)benzylidene}butane-1,4-diamine (bpbd) yielded monoclinic crystals of bluish green [Cu(bpbd)(ClO₄)]ClO₄ (1), and a similar reaction in presence of azide anion, N₃ ^? formed monoclinic crystals of dark green [Cu(bpbd)(N₃)]₂ClO₄ (2). Crystal data for 1: space group P21/c, Z=4, a=17.3968(4) Å, b=9.3182(2) Å, c=17.6794(4) Å, β=102.149(1)°. The geometry around Cu(II) centre is distorted square pyramidal with axial site occupied by O atom of perchlorate and in plane Cu is bonded to four N atoms of the organic ligand. The intermolecular C–H...π stacking in 1 forms a zigzag chain (1D) supramer. Crystal data for 2: space group C2/c, Z=4, a=22.3109(4) Å, b=17.7832(3) Å, c=14.3389(2) Å, β=92.553(1)°. In dinuclear 2, Cu(II) has tetragonally distorted octahedral geometry coordinated by four N atoms of bpbd, with the fifth and sixth positions occupied by N atoms of two end-on bridging azides. The π...π interaction leads to a two dimensional (2D) sheet within which the counter anions are embedded. Both the compounds 1 and 2 show simple paramagnetism. Cyclic voltammetry and fluorescence spectra are also reported.     

Substituent effects to the electrochromic behaviors of electropolymerized metallophthalocyanine thin films

Metallophthalocyanines (MPcs) (M = 2H⁺, Zn²⁺, Co²⁺, and Cu²⁺) bearing diethylaminophenoxy and chloro substituents at the peripheral positions (MPc-tdea-tCl) were coated on the working electrodes with the electropolymerization and tested as electrochromic materials. Altering the metal center of MPcs affected the redox activities of MPc-tdea-tCl films. All electropolymerized MPc-tdea-tCl films behaved as conductive and redox active films in different electrolyte systems. Electrochromic properties of MPc-tdea-tCl films were investigated via the voltammetric, in situ spectroelectrochemical, and in situ spectroelectrocolorimetric measurements. H ₂ Pc-tdea-tCl film did not give any electrochromic response, while ZnPc-tdea-tCl and CuPc-tdea-tCl films behave as a reasonable electrochromic material. Distinctive color changes with short response times, high optical contrast, and better optical and coulombic stabilities were only observed with CoPc-tdea-tCl film.     

Syntheses,structures and properties of complexes of indole-3-propionic acid

Three complexes [Zn₂(IPA)₂(phen)₄](HIPA)₂(NO₃)₂·H₂O (1), {[Zn(IPA)₂(bipy)]·3H₂O}_n (2), and {[Mn(IPA)₂(bipy)(H₂O)]·2H₂O}_n (3) (HIPA = indole-3-propionic acid, phen = 1,10-phenanthroline, bipy = 4,4′-bipyridine) were synthesized and characterized by physico-chemical and spectroscopic methods. Complex 1 displays a zero-dimensional structure, whilst 2 and 3 show one-dimensional chains, which are linked into supramolecular networks through hydrogen bonding interactions and/or π···π stacking interactions. The luminescence properties of complexes 1 and 2 were investigated.     

Four supramolecular transition metal(II) complexes based on triazole-benzoic acid derivatives: crystal structure,Hirshfeld surface analysis,and spectroscopic and thermal properties

Four new complexes [M(3-tba)₂(H₂O)₄] (1–3) and [Co(4-tba)₂(H₂O)₄] (4) {M = Zn (1), Ni (2), Co (3), 3-Htba = 3-(1H-1,2,4-triazol-1-yl)benzoic acid, 4-Htba = 4-(1H-1,2,4-triazol-1-yl)benzoic acid} have been synthesized under solvothermal conditions and structurally characterized by single crystal X-ray diffraction. Complexes 1–4 are also determined by elemental analysis, X-ray powder diffraction, IR and electronic spectroscopy. Single crystal X-ray diffraction reveals that complexes 1–3 are isostructural and they crystallize in the orthorhombic space group of Pbca, while complex 4 belongs to triclinic system with Pī space group. Based on different intermolecular hydrogen bonding and π···π stacking interactions, complexes 1–4 further assembled into 3D supramolecular frameworks. Hirshfeld surface analysis was used to further study the intermolecular interactions of the complexes. The thermogravimetric analyses (TGA) reveal that these complexes possess good thermal stability, and the differential scanning calorimetry (DSC) analyses show intense exothermic phenomena in the decomposition processes of triazole groups. Besides, the photoluminescence property of complex 1 in the solid state is also determined.     

Synthesis,crystal structures and magnetic properties of three complexes containing bis(maleonitriledithiolate) copper(II) anion and <Emphasis Type="Italic">meta</Emphasis>-substituted benzyl isoquinolinium cations

Three complexes, [3RBzIQl]₂[Cu(mnt)₂] (mnt^2? = maleonitriledithiolate; [3RBzIQl]⁺ = 1-(3′-R-benzyl)isoquinolinium, R = Cl (1), I (2) or NO₂ (3)), have been prepared and characterized by spectroscopic and physicochemical methods as well as by X-ray crystallography. The [Cu(mnt)₂]^2? anions formed a 1D chain in complex 1, a dimer in 2 and a sheet structure in 3 through C···N and/or N···N interactions. The neighboring dimers of the cations arranged in a boat-type pattern stack into columns through weak π···π, Cl···π or O···π, C–H···π interactions. The anions and cations stack together into a columnar structure with a ···A–CC–A–CC–A··· sequence. The magnetic susceptibilities measured in the temperature range 2.0–300 K reveal that complex 1 undergoes a change from weak ferromagnetic to antiferromagnetic exchange around 132 K, while 2 shows antiferromagnetic behavior and 3 shows a weak ferromagnetic interaction when the temperature is lowered.     

Tetra-β-nitro-substituted phthalocyanines: a new organic electrode material for lithium batteries

Tetra-β-nitro-substituted nickel phthalocyanine (TN-NiPc) and hollow phthalocyanine (TN-H₂Pc) were synthesized and investigated as novel organic electrode materials for rechargeable lithium batteries. After the two H atoms in the center of TN-H₂Pc were replaced with Ni atoms, the interactive force between the phthalocyanine rings was reduced, which resulted in a fluffy morphology for the TN-NiPc that was beneficial to the transition of Li⁺. As a result, better electrochemical properties and reversibility were observed in the TN-NiPc electrodes compared to the TN-H₂Pc electrode. The capacity of TN-NiPc electrode was stable at about 280 mAh g^?1 at 0.2 C after 250 cycles at several different current rates of 0.1, 0.2, 0.5, and 1 C. The TN-NiPc based cathode materials may provide new opportunities for organic, flexible, and stable secondary lithium batteries.

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Graphical Abstract The TN-NiPc electrode shows better electrochemical properties than that of TN-H ₂ Pc electrode, which is due to the strong hydrogen bond interaction and π-π interaction of TN-H ₂ Pc molecules, resulting in more dense stacking degree of the phthalocyanine ring and restricting the transport of Li⁺ .

     

Directed assembly of cobalt(II) 1-H-indazole-3-carboxylic acid coordination networks by bipyridine and its derivatives: structural versatility,electrochemical properties,and antifungal activity

This paper describes the hydrothermal synthesis, full characterization, and architectural diversity of three intriguingly bioactive cobalt–organic frameworks, namely, 3D [Co(HL ^? )₂(BPY)] _n ·4nH₂O (1), 2D [Co(HL ^? )₂(BPE)] _n (2), and 2D [Co(HL ^? )₂(DPP)] _n (3) coordination polymers, synthesized through a mixed ligand strategy using H ₂ L (1-H-indazole-3-carboxylic acid) as a main structural block and the flexible bipyridine and its derivatives (BPY = 4,4′-bipydine, BPE = 1,2-bis(4-pyridyl)ethane, DPP = 1,3-bis(4-pyridyl)propane) as auxiliary ligand sources. Complexes 1–3 were isolated as air stable and slightly soluble crystalline solids and characterized using elemental analysis, FT-IR, electrochemical technique, thermogravimetric analysis, powder X-ray diffractometer, and single-crystal X-ray crystallography. The bipyridine derivatives played key roles in defining the structural space group and dimensionality feature of the obtained networks. The abundant H-bonding and π–π stacking interactions in complexes 1–3 gave rise to their intricate metal–organic structures of 3D (1), 2D (2), and 2D (3). In addition, the solutions of complexes 1–3 showed profound antifungal activities against the selected strain of Colletotrichum musae compared with the controlled group using benomyl as a traditional agrochemical fungicide.     

Binding of carboxylate and trimethylammonium salts to octa-acid and TEMOA deep-cavity cavitands

In participation of the fifth statistical assessment of modeling of proteins and ligands (SAMPL5), the strength of association of six guests (3–8) to two hosts (1 and 2) were measured by ¹H NMR and ITC. Each host possessed a unique and well-defined binding pocket, whilst the wide array of amphiphilic guests possessed binding moieties that included: a terminal alkyne, nitro-arene, alkyl halide and cyano-arene groups. Solubilizing head groups for the guests included both positively charged trimethylammonium and negatively charged carboxylate functionality. Measured association constants (K _a ) covered five orders of magnitude, ranging from 56 M^?1 for guest 6 binding with host 2 up to 7.43 × 10⁶ M^?1 for guest 6 binding to host 1.