ABSTRACT
A family of coordination polymers (CPs) based on dynamic structural elements are of great fundamental and commercial interest addressing modern problems in controlled molecular separation, catalysis, and even data processing. Herein, the endurance and fast structural dynamics of such materials at ambient conditions are still a fundamental challenge. Here, we report on the design of a series of Cu-based CPs [Cu(bImB)Cl2] and [Cu(bImB)2Cl2] with flexible ligand bImB (1,4-bis(imidazol-1-yl)butane) packed into one- and two-dimensional (1D, 2D) structures demonstrating dimensionality mediated flexibility and reversible structural transformations. Using the laser pulses as a fast source of activation energy, we initiate CP heating followed by anisotropic thermal expansion and 0.2-0.8% volume changes with the record transformation rates from 2220 to 1640 s-1 for 1D and 2D CPs, respectively. The endurance over 103 cycles of structural transformations, achieved for the CPs at ambient conditions, allows demonstrating optical fiber integrated all-optical data processing.
ABSTRACT
Separation of hydrocarbon molecules, such as benzene/cyclohexane and o-xylene/m-xylene/p-xylene, is relevant due to their widespread application as chemical feedstock but challenging because of their similar boiling points and close molecular sizes. Physisorption separation could offer an energy-efficient solution to this problem, but the design and synthesis of sorbents that exhibit high selectivity for one of the hydrocarbons remain a largely unmet challenge. Herein, we report a new heterometallic MOF with a unique tortuous shape of channels decorated with aromatic sorption sites [Li2Zn2(bpy)(ndc)3] (NIIC-30(Ph), bpy = 4,4'-bipyridine, ndc2- = naphthalene-1,4-dicarboxylate) and study of its benzene/cyclohexane and xylene vapor and liquid separation. For an equimolar benzene/cyclohexane mixture, it is possible to achieve a 10-fold excess of benzene in the adsorbed phase. In the case of xylenes, microporous framework NIIC-30(Ph) demonstrates outstanding selective sorption properties and becomes a new benchmark for m-/o-xylene separation. In addition, NIIC-30(Ph) is stable enough to carry out at least three separation cycles of benzene/cyclohexane mixtures or ternary o-xylene/m-xylene/p-xylene mixtures both in the liquid and in the vapor phase. Insights into the performance of NIIC-30(Ph) are gained from X-ray structural studies of each aromatic guest inclusion compound.
ABSTRACT
Rational design of a series of new heterometallic MOFs was carried out by the judicious choice of the corresponding synthesis conditions and ligand geometry. Three heterometallic MOFs (H2NMe2)[LiZn(dmf)(tdc)2]·DMF·H2O (1), [{LiZn}2Li2Zn2(dmf)6(tdc)6]·6DMF·H2O (2) and [Li2Zn2(dmf)2(fdc)3]·2DMF·2H2O (3) were obtained on the basis of the pre-synthesized pivalate complex [Li2Zn2(py)2(piv)6]. The angle between carboxylic groups greatly affects the possibility of retaining the initial tetranuclear node in the structure of the obtained MOFs. Compound 3 demonstrates permanent porosity with a calculated BET surface area value of 287 m2 g-1. Compounds 2 and 3 are capable of heavy metal sorption from their nitrate solution, and a significant flare-up of the luminescence of the obtained inclusion compounds is observed, where the quantum yield of luminescence increases by an order of magnitude in the case of cadmium inclusion.
ABSTRACT
Two solvent-controlled topological isomers of scandium-organic frameworks [Sc(Hpzc)(pzc)]·DMF·2H2O (1·DMF·2H2O) and [Sc(Hpzc)(pzc)]·DMA·4H2O (2·DMA·4H2O) were synthesized using 2,5-pyrazinedicarboxylate (pzc2-) (DMF = dimethylformamide; DMA = dimethylacetamide). Despite the isomeric nature of the obtained metal-organic frameworks (MOFs), they possess different structural features and unique adsorption properties toward gases and iodine. The compound 1 has widely spread among MOF structures a dia topology with ultranarrow channels, which together with inner surface functionalization leads to enhanced CO2 adsorption and high selectivity factors in CO2/CH4 and CO2/N2 gas mixtures (25.9 and 35.6, respectively, 1/1 v/v). Moreover, a rare preferable adsorption of CO2 over C2H2 was demonstrated. The biporous isomeric framework 2 has a crb topology inherent in zeolites. A remarkable adsorption affinity to C2H2 with the ideal adsorbed solution theory selectivity factor of 127.1 for a C2H2/C2H4 mixture (1/99 v/v) was achieved for 2. Both compounds have exceptional chemical stability in a wide range of pH from acidic to basic media.
ABSTRACT
Using a series of isoreticular MOFs with void connections of varying diameters, the selective separation of benzene and cyclohexane in both liquid and vapor phases is shown. The driving force of the highly efficient adsorption process is the formation of weak interactions between the adsorbed benzene molecules and the host framework.
ABSTRACT
A series of lanthanide and yttrium MOFs of two structural types [M2(H2O)2(nmp)2(pzc)3] (1M) and [M2(H2O)4(pzc)3]·NMP·5H2O (2M) (where M - lanthanide or yttrium cation, nmp - N-methyl-2-pyrrolidone, pzc2- - 2,5-pyrazinedicarboxylate) was synthesized and characterized by single crystal and powder X-ray diffraction crystallography, TG, elemental analyses and IR-spectroscopy. The effect of lanthanide contraction has led to the fact that lanthanides at the beginning of the series (from lanthanum to gadolinium) have a structure different from the structure of lanthanides at the end of the series and yttrium (from terbium and beyond). According to PXRD patterns of the obtained samples mixed metal materials could be obtained not only as crystalline mixtures of two structure types but also as crystalline products of single structure type. Varying the ratio of lanthanides in the initial reaction mixture allowed us to obtain a wide color range of luminescence, including several near-white-light emitting samples.
ABSTRACT
Two new isostructural microporous coordination frameworks [Mn3(Hpdc)2(pdc)2] (1) and [Mg3(Hpdc)2(pdc)2] (2) (pdc2- = pyridine-2,4-dicarboxylate) showing primitive cubic (pcu) topology have been prepared and characterized. The pore aperture of the channels is too narrow for the efficient adsorption of N2; however, both compounds demonstrate substantially higher uptake of CO2 (119.9 mL·g-1 for 1 and 102.5 mL·g-1 for 2 at 195 K, 1 bar). Despite of their structural similarities, 2 shows a typical reversible type I isotherm for adsorption/desorption of CO2, while 1 features a two-step adsorption process with a very broad hysteresis between the adsorption and desorption curves. This behavior can be explained by a combination of density functional theory calculations, sorption, and X-ray diffraction analysis and gives insights into the further development of new sorbents showing adsorption/desorption hysteresis.
ABSTRACT
The paper presents a novel multi-purpose enzymatic system and procedures for fluorescent determination of several flavonoids in herbal pharmaceuticals and plant materials after their enzyme-catalyzed oxidation by hydrogen peroxide and further derivatization with meso-1,2-diphenylethylenediamine. This system may be used for rapid (15-30min/20 samples) simultaneous screening of samples containing a certain flavonoid in a standard microplate, or as a HPLC detection system for analyzing plant extracts with uncertain composition. In the first case, this indicator system provides sensitive and reproducible microplate determination of quercetin, epicatechin, caffeic acid, and taxifolin in the ranges 0.1-5, 1-10, 0.1-10, 0.5-5µM, respectively. In the second case, quercetin, epicatechin, and caffeic acid can be determined in the ranges 0.05-0.75, 0.05-0.75, and 0.01-0.75µg/ml (0.16-2.5, 0.17-2.6, 0.06-4.2µM), respectively. We have demonstrated the application of the system for the analysis of 3 pharmaceuticals and 3 types of plants.
