Search Results (19)

A pyridine-tricarboxylic acid, 5-(3′,5′-dicarboxylphenyl)nicotinic acid (H₃dpna), was employed as a adjustable block to assemble a series of coordination polymers under hydrothermal conditions. The seven new coordination polymers were formulated as [Co(μ₃-Hdpna)(μ-dpey)]_n·nH₂O (1), [Zn_4.5(μ₆-dpna)₃(phen)₃]_n (2), [Co_1.5(μ₆-dpna)(2,2′-bipy)]_n (3), [Zn_1.5(μ₆-dpna)(2,2′-bipy)]_n (4), [Co₃(μ₃-dpna)₂(4,4′-bipy)₂(H₂O)₈]_n·2nH₂O (5),[Co(bpb)₂(H₂O)₄]_n[Co₂(μ₃-dpna)₂(H₂O)₄]_n·3nH₂O (6), and [Mn_1.5(μ₆-dpna)(μ-dpea)]_n (7), wherein 1,2-di(4-pyridyl)ethylene (dpey), 1,10-phenanthroline (phen), 2,2′-bipyridine(2,2′-bipy),4,4′-bipyridine(4,4′-bipy),1,4-bis(pyrid-4-yl)benzene (bpb), and 1,2-di(4-pyridyl)ethane (dpea) were employed as auxiliary ligands. The structural variation of polymers 1–7 spans the range from a 2D sheet (1–4, 6, and 7) to a 3D metal–organic framework (MOF, 5). Polymers 1–7 were investigated as heterogeneous catalysts in the Knoevenagel condensation reaction, leading to high condensation product yields (up to 100%) under optimized conditions. Various reaction conditions, substrate scope, and catalyst recycling were also researched. This work broadens the application of H₃dpna as a versatile tricarboxylate block for the fabrication of functional coordination polymers. Full article

Metal-organic frameworks [M₂(2-I-bdc)₂bpe] (M = Zn(II) (1), Co(II) (2), 2-I-bdc = 2-iodoterephtalic acid, and bpe = 1,2-bis(4-pyridyl)ethane) were prepared and characterized by X-ray diffractometry. Both compounds retain their 3D structure after the removal of guest DMF molecules. Selectivity of sorption of different organic substrates from the gas phase was investigated for both complexes. Full article

A series of nitrogen-containing organic molecules (4,4’-bipyridyl; trans-1,2-bis(4-pyridyl)ethylene; 1,2-bis(4-pyridyl)ethane; 4-aminopyridine and trans-1,4-diaminocyclohexane) was envisaged for cocrystallization experiments together with fluorescein. These compounds, containing pyridyl or/and amino nitrogen atoms, can act either as hydrogen bond acceptors for the phenol groups of fluorescein-generating cocrystals or as proton acceptors forming organic salts. Five cocrystals were obtained with the partners containing only pyridyl groups: {(H₂Fl)₂(bipy)} (1); {(H₂Fl)₂(bipy)(MeOH)₂} (2); {(H₂Fl)₂(bpete)(EtOH)₂} (3); {(H₂Fl)(bpete)} (4); {(H₂Fl)(bpeta)} (5). The compounds bearing amino groups deprotonate fluorescein producing salts: [(HFl)(Hampy)]∙2H₂O (6); [(HFl)(Hampy)] (7); [(Fl)(H₂diach)]∙3H₂O (8); [(HFl)₂(H₂diach)]∙2H₂O∙EtOH (9); and [(HFl)₂(Fl)₂(H₂diach)₃]∙4H₂O (10). Optical properties of the cocrystals and salts were investigated. Full article

Polysiloxanes (PSs) have been widely utilized in the industry as lubricants, varnishes, paints, release agents, adhesives, and insulators. In addition, their applications have been expanded to include the development of new biomedical materials. To modify PS for application in therapeutic purposes, a flexible antibacterial Cu-MOF (metal–organic framework) consisting of glutarate and 1,2-bis(4-pyridyl)ethane ligands was embedded in PS via a hydrosilylation reaction of vinyl-terminated and H-terminated PSs at 25 °C. The bactericidal activities of the resulting Cu-MOF-embedded PS (PS@Cu-MOF) and the control polymer (PS) were tested against Escherichia coli, Staphylococcus aureus, and methicillin-resistant Staphylococcus aureus. PS@Cu-MOF exhibited more than 80% bactericidal activity toward the tested bacteria at a concentration of 100 μg⋅mL⁻¹ and exhibited a negligible cytotoxicity toward mouse embryonic fibroblasts at the same concentration. Release tests of the Cu(II) ion showed PS@Cu-MOF to be particularly stable in a phosphate-buffered saline solution. Furthermore, its physical and thermal properties, including the phase transition, rheological measurements, swelling ratio, and thermogravimetric profile loss, were similar to those of the control polymer. Moreover, the low cytotoxicity and bactericidal activities of PS@Cu-MOF render it a promising candidate for use in medicinal applications, such as in implants, skin-disease treatment, wound healing, and drug delivery. Full article

The biomolecule chelidonic acid (H₂chel, 4-oxo-4H-pyran-2,6-dicarboxylic acid) has been used to build new coordination polymers with the bridging N,N′-ligands 4,4′-bipyridine (4,4-bipy) and 1,2-bis(4-pyridyl)ethane (bpe). Four compounds have been obtained as single crystals: 1D cationic coordination polymers [M(4,4-bipy)(OH₂)₄]²⁺ with chelidonate anions and water molecules in the second coordination sphere in ¹_∞[Zn(4,4-bipy)(H₂O)₄]chel·3H₂O (2) and in the two pseudopolymorphic ¹_∞[Cu(4,4-bipy)(H₂O)₄]chel·nH₂O (n = 3, 4a; n = 6, 4b), and the 2D neutral coordination polymers ²_∞[Zn(chel)(4,4-bipy)(H₂O)]·2H₂O (1) and ²_∞[Zn(chel)(bpe)(H₂O)]·H₂O (3) where the chelidonate anion acts as a bridging ligand. The effects of the hydrogen bonds on the crystal packing were analyzed. The role of the water molecules hosted within the crystals lattices was also studied. Full article

The synthesis of amide-based molecules, possessing pre-organized structures, has received significant attention due to their potential applications as molecular receptors and as components of nanomaterials. In this study, four extended tetraamide ligands incorporating ethylene and propylene spacers, namely 1,2-bis[N,N′-6-(3-pyridylmethylamido)pyridyl-2-carboxyamido]ethane (L1), 1,2-bis[N,N′-6-(4-pyridylmethylamido)pyridyl-2-carboxyamido]ethane (L2), 1,2-bis[N,N′-6-(3-pyridylmethylamido)pyridyl-2-carboxyamido]propane (L3) and 1,2-bis[N,N′-6-(4-pyridylmethylamido)pyridyl-2-carboxyamido]propane (L4), were successfully synthesized. Further, reaction of L2 and L4, incorporating pendant 4-pyridyl donors as the metal coordinating sites, with cadmium salts, produced two close-packed one-dimensional coordination polymers, {[Cd₃(L2)₄(H₂O)₁₀](NO₃)₆·12H₂O·CH₃OH}_n and {[Cd(SO₄)(L4)(H₂O)₂]·4H₂O·CH₃OH}_n. X-ray crystallography reveals that the flexible tetraamide ligands fold upon themselves in the coordination polymer structure. As a consequence, the anion pocket in {[Cd(SO₄)(L4)(H₂O)₂]·4H₂O·CH₃OH}_n incorporating the ligand with the propylene spacer was blocked from encapsulating charge-balancing anions, which were involved in bridging the di-cadmium units. Interestingly, a strong interaction between the 2,6-pyridine dicarboxamide moiety with the nitrate anions was found in {[Cd₃(L2)₄(H₂O)₁₀](NO₃)₆·12H₂O·CH₃OH}_n, showing potential for materials made from these ligands to serve as anion receptors. Full article

Eight mixed-ligand coordination networks, [Cd(2-aba)(NO₃)(4-bphz)_3/2]_n·n(dmf) (1), [Cd(2-aba)₂(4-bphz)]_n·0.75n(dmf) (2), [Cd(seb)(4-bphz)]_n·n(H₂O) (3), [Cd(seb)(4-bpmhz)]_n·n(H₂O) (4), [Cd(hpa)(3-bphz)]_n (5), [Zn(1,3-bdc)(3-bpmhz)]_n·n(MeOH) (6), [Cd(1,3-bdc)(3-bpmhz)]_n ·0.5n(H₂O)·0.5n(EtOH) (7), and [Cd(NO₃)₂(3-bphz)(bpe)]_n·n(3-bphz) (8) were obtained by interplay of cadmium nitrate tetrahydrate or zinc nitrate hexahydrate with 2-aminobenzenecarboxylic acid (H(2-aba)), three dicarboxylic acids, sebacic (decanedioic acid, H₂seb), homophthalic (2-(carboxymethyl)benzoic acid, H₂hpa), isophthalic (1,3-benzenedicarboxylic acid, H₂(1,3-bdc)) acids, bis(4-pyridyl)ethane (bpe) and with four azine ligands, 1,2-bis(pyridin-4-ylmethylene)hydrazine (4-bphz), 1,2-bis(1-(pyridin-4-yl)ethylidene) hydrazine (4-bpmhz), 1,2-bis(pyridin-3-ylmethylene)hydrazine (3-bphz), and 1,2-bis(1-(pyridin-3-yl) ethylidene)hydrazine (3-bpmhz). Compounds 1 and 2 are 1D coordination polymers, while compounds 3–8 are 2D coordination polymers. All compounds were characterized by spectroscopic and X-ray diffraction methods of analysis. The solvent uptakes and stabilities to the guest evacuation were studied and compared for 1D and 2D coordination networks. The de-solvated forms revealed a significant increase of emission in comparison with the as-synthesized crystals. Full article

A series of five neutral mononuclear lanthanide complexes [Ln(HL)(L)] (Ln = Dy³⁺, Ho³⁺ Er³⁺ and Tb³⁺) with rigid pentadentate N₃O₂-type Schiff base ligands, H₂L^H (1-Dy, 3-Ho, 4-Er and 6-Tb complexes) or H₂L^OCH3, (2-Dy complex) has been synthesized by reaction of two equivalents of 1,1′-(pyridine-2,6-diyl)bis(ethan-1-yl-1-ylidene))dibenzohydrazine (H₂L^H, [H₂DAPBH]) or 1,1′-(pyridine-2,6-diyl)bis(ethan-1-yl-1-ylidene))di-4-methoxybenzohydrazine (H₂L^OCH3, [H₂DAPMBH]) with common lanthanide salts. The terbium complex [Tb(L^H)(NO₃)(H₂O)₂](DME)₂ (5-Tb) with one ligand H₂L^H was also obtained and characterized. Single crystal X-ray analysis shows that complexes 1–4 have the composition {[Ln³⁺(HL)⁻(L)²⁻] solv} and similar molecular structures. In all the compounds, the central Ln³⁺ ion is chelated by two interlocked pentadentate ligands resulting in the coordination number of ten. Each lanthanide ion is coordinated by six nitrogen atoms and four oxygen atoms of the two N₃O₂ chelating groups forming together a distorted bicapped square antiprismatic polyhedron N₆O₄ with two capping pyridyl N atoms in the apical positions. The ac magnetic measurements reveal field-induced single-molecule magnet (SMM) behavior of the two dysprosium complexes (with barriers of U_eff = 29 K at 800 Oe in 1-Dy and U_eff = 70 K at 300 Oe in 2-Dy) and erbium complex (U_eff = 87 K at 1500 Oe in 4-Er); complex 3-Ho with a non-Kramers Ho³⁺ ion is SMM-silent. Although 2-Dy differs from 1-Dy only by a distant methoxy-group in the phenyl ring of the ligand, their dynamic magnetic properties are markedly different. This feature can be due to the difference in long-range contributions (beyond the first coordination sphere) to the crystal-field (CF) potential of 4f electrons of Dy³⁺ ion that affects magnetic characteristics of the ground and excited CF states. Magnetic behavior and the electronic structure of Ln³⁺ ions of 1–4 complexes are analyzed in terms of CF calculations. Full article

Tuning and controlling the solid-state photophysical properties of organic luminophore are very important to develop next-generation organic luminescent materials. With the aim of discovering new functional luminescent materials, new cocrystals of 9-anthracene carboxylic acid (ACA) were prepared with two different dipyridine coformers: 1,2-bis(4-pyridyl)ethylene and 1,2-bis(4-pyridyl)ethane. The cocrystals were successfully obtained by both mechanochemical approaches and conventional solvent crystallization. The newly obtained crystalline solids were characterized thoroughly using a combination of single crystal X-ray diffraction, powder X-ray diffraction, Fourier-transform infrared spectroscopy, differential thermal analysis, and thermogravimetric analysis. Structural analysis revealed that the cocrystals are isostructural, exhibiting two-fold interpenetrated hydrogen bonded networks. While the O–H···N hydrogen bonds adopts a primary role in the stabilization of the cocrystal phases, the C–H···O hydrogen bonding interactions appear to play a significant role in guiding the three-dimensional assembly. Both π···π and C–H···π interactions assist in stabilizing the interpenetrated structure. The photoluminescence properties of both the starting materials and cocrystals were examined in their solid states. All the cocrystals display tunable photophysical properties as compared to pure ACA. Density functional theory simulations suggest that the modified optical properties result from charge transfers between the ACA and coformer molecules in each case. This study demonstrates the potential of crystal engineering to design solid-state luminescence switching materials through cocrystallization. Full article

Herein we report the synthesis and detailed structural characterization of two new centrosymmetric dinuclear coordination compounds of Pb(II) [Pb₂L₂(NCS)₄] (1) and [Pb₂L₂(NO₃)₄]∙2MeOH (2), using the organic ligand 1,2-diphenyl-1,2-bis((methyl(pyridin-2-yl)methylene)hydrazono)ethane (L). In both complexes, each subunit [PbLX₂ (X = NO₃ or NCS)] adopts a quasi-aromatic Möbius metal chelate structure. Each ligand L is coordinated in a tetradentate coordination mode to Pb(II), yielding the 12π electron chelate ring via two pyridyl-imine units. In compound (1), the coordination sphere is completed by one disordered N,S-coordinated thiocyanate anion and two μ_1,1-bridging N-coordinated thiocyanate anions. In compound (2), the coordination sphere of Pb(II) is completed by two monodentate and two bidentate nitrato ligands (two of them acting as bridging ligands). Crystal packing of both compounds is stabilized by intermolecular hydrogen bonds, intra- and intermolecular C–H∙∙∙π interactions. The Hirshfeld molecular surfaces of (1) and (2) demonstrate that their packing is dominated by C–H∙∙∙O/N/S interactions as well as by far less favored H∙∙∙H contacts. Full article

A typical approach of a multicomponent crystal design starts with a retrosynthetic analysis of the target molecule followed by a one-pot reaction of all components. To develop protocols for multicomponent crystal syntheses, controlled stepwise syntheses of a selected crystalline ternary multicomponent system 1 involving 2-methylresorcinol (MRS), tetramethyl-pyrazine (TMP), and 1,2-bis(4-pyridyl)ethane (BPE) are presented. The obtained binary cocrystals 2 (involving MRS and TMP) and 3 (involving MRS and BPE) as well as the final resulting ternary multicomponent system 1 were characterized by X-ray analysis. Full article

A family of fifteen quaternary ammonium salts (QAs), bearing the 1,2-bis(4-pyridyl)ethane core, were obtained using for the first time two different green methods, such as microwave (MW) and ultrasounds (US) irradiation, with very good yields and in much shorter times compared to the classical method, and an assay on their antimicrobial action against Escherichia coli (E. coli) was carried out. While 12 to 24 h were required for complete alkylation of 1,2-bis(4-pyridyl)ethane by reactive halogenated derivatives in anhydrous solvent under reflux conditions, MW and US irradiation reduced the reaction time and the desired products were achieved in a few min. One of the aims of this study was to evaluate the antibacterial potential of the synthesized QAs against pathogenic bacteria, along with their impact on germination activity of wheat seeds (Triticum aestivum L.). The antibacterial activity of the QAs against Escherichia coli was explored by determining the minimum inhibitory concentration (MIC). The MIC values varied from 0.312 to 2.5 mg/mL, highlighting the lowest values attained for the derivatives containing methoxy, chlorine and benzofurane functional groups. The viability of aerobic bacteria was determined with the Tetrazolium/Formazan Test, a method that was found to be the best alternative approach with respect to the difuzimetric method. Seeds of Triticum aestivum L. were used for the evaluation of the germination indicators, such as seed germination (SG), the relative seed germination (RSG), the relative radicle growth (RRG), and the seed germination index (GI). The toxicity studies of QAs 1, 4 and 7, at two different concentrations, showed no inhibitory effect on seed germination. Full article

The comparative effect of two quaternary ammonium salts from 1,2-bis(4-pyridyl)ethane (PyQAs), namely N,N′-diphenacyl-1,2-bis(4-pyridinium)ethane dibromide (PyQAs1) and N,N′-di(p-methoxyphenacyl)-1,2-bis(4-pyridinium)ethane dibromide (PyQAs2), upon the size and photoluminescence of zinc oxide nanoparticles (ZnO NPs) was investigated. The formation of ZnO NPs took place in the presence of variable amounts of the two PyQAs species (1, 2.5, and 5%), according to the chemical precipitation of zinc(II) acetate with potassium hydroxide in ethanol under reflux. The obtained ZnO NPs were structurally characterized by means of X-ray powder diffraction, infrared, and Raman spectroscopy. The fluorescence of all supernatant solutions, observed under ultraviolet light, determined us to make an investigation of the solutions by means of liquid chromatography coupled with electrospray ionization mass spectrometry (LC-MS-ESI) in order to elucidate the identity of the newly formed fluorescent species. Such an occurrence thus allowed the invocation of the catalytic effect of zinc(II) ions towards the organic transformation of both nonfluorescent PyQAs surfactants into new fluorescent organic species. Full article

Reactions between pyridinic ligands such as 1,2-bis(4-pyridyl)ethane (bpa) and transition metal cations are a very widespread technique to produce extended coordination polymers such as Metal-Organic Frameworks. In combination with a second ligand these systems could present different topologies and behaviors. In this context, the use of 1,2,4,5-benzenetetracarboxylic acid (H₄btec) gave us a novel 2D compound, [Cu₂(bpa)(btec)(H₂O)₄]_n (1), which was prepared by microwave-assisted synthesis and structurally characterized by means of single crystal X-ray diffraction. Its thermal behavior was analyzed through thermogravimetric analysis and variable temperature powder X-ray diffraction, concluding that thermal stability is influenced by the coordination water molecules, allowing two sequential thermochromic phase transformations to take place. These transformations were monitored by electronic paramagnetic resonance spectroscopy and magnetic susceptibility measurements. In addition, the crystal structure of the anhydrous compound [Cu₂(bpa)(btec)]_n (1.ah) was determined. Finally, a topological study was carried out for the bpa ligand considering all the structures deposited in the Cambridge Structural Databased. More than 1000 structures were analyzed and classified into 17 different topologies, according to the role of the ligand. Full article

Assembled complexes [[M(NCS)₂(bpa)₂]·biphenyl]_n (M = Fe, Co; bpa = 1,2-bis(4-pyridyl)ethane) have been synthesized because [Fe(NCBH₃)₂(bpa)₂·biphenyl]_n has a novel threefold spiral structure and shows stepwise spin-crossover phenomenon. We attempted to obtain spiral structures for [[Fe(NCS)₂(bpa)₂]·biphenyl]_n and [[Co(NCS)₂(bpa)₂]·biphenyl]_n using a one-step diffusion method, while the reported spiral structure of [[Fe(NCBH₃)₂(bpa)₂]·biphenyl]_n was obtained by diffusion method after synthesizing Fe(II)-pyridine complex. X-ray structural analysis revealed that [[Fe(NCS)₂(bpa)₂]·biphenyl]_n and [[Co(NCS)₂(bpa)₂]·biphenyl]_n had a chiral propeller structure of pyridines around the central metal, and they had a novel spiral structure and chiral space group P3₁2₁ without the presence of chiral auxiliaries. It was shown that the host 1D chain, having a chiral propeller structure of pyridines around the central metal along with its concerted interaction with an atropisomer of biphenyl, made a threefold spiral structure. Full article