Laboratory-based separation techniques for insoluble compound mixtures: methods for the purification of metal-organic framework materials

In this article, techniques for separating mixtures of insoluble compounds are discussed with respect to the small quantities found in laboratory preparations, as opposed to industrial quantities. The techniques include separations based on density, surface area and differences in particle size. Also discussed are simple apparatus, readily available in the laboratory or from commercial suppliers, for achieving these techniques

Adsorption dynamics of gases and vapors on the nanoporous metal organic framework material Ni-2(4,4 '-bipyridine)(3)(NO3)(4): guest modification of host sorption behavior

This study combines measurements of the thermodynamics and kinetics of guest sorption with powder X-ray diffraction measurements of the nanoporous metal organic framework adsorbent (host) at different adsorptive (guest) loadings. The adsorption characteristics of nitrogen, argon, carbon dioxide, nitrous oxide and ethanol and methanol vapors on Ni2(4,4'-bipyridine)3(NO3)4 were studied over a range of temperatures as a function of pressure. Isotherm steps were observed for both carbon dioxide and nitrous oxide adsorption at approximately 10-20% of the total pore volume and at approximately 70% of total pore volume for methanol adsorption. The adsorption kinetics obey a linear driving force (LDF) mass transfer model for adsorption at low surface coverage. At high surface coverage, both methanol and ethanol adsorption follow a combined barrier resistance/diffusion model. The rates of adsorption in the region of both the carbon dioxide and methanol isotherm steps were significantly slower than those observed either before or after the step. X-ray diffraction studies at various methanol loadings showed that the host structure disordered initially but underwent a structural change in the region of the isotherm step. These isotherm steps are ascribed to discrete structural changes in the host adsorbent that are induced by adsorption on different sites. Isotherm steps were not observed for ethanol adsorption, which followed a Langmuir isotherm. Previous X-ray crystallography studies have shown that all the sites are equivalent for ethanol adsorption on Ni2(4,4'-bipyridine)3(NO3)4, with the host structure undergoing a scissoring motion and the space group remaining unchanged during adsorption. The activation energies and preexponential factors for methanol and ethanol adsorption were calculated for each pressure increment at which the linear driving force model was obeyed. There was a good correlation between activation energy and ln(preexponential factor), indicating a compensation effect. The results are discussed in terms of reversible adsorbate/adsorbent (guest/host) structural changes and interactions and the adsorption mechanism. The paper contains the first evidence of specific interactions between guests and functional groups leading to structural change in flexible porous coordination polymer frameworks

New metal organic frameworks incorporating the ditopic macrocyclic ligand dipyridyldibenzotetraaza[14]annulene

The synthesis and crystal structures of three new metal organic frameworks of type [Zn(L-2H)](n) (1), {[ZnLCl2](CH3CN)(0.5)(DMF)(0.5)(H2O)(0.5)}(n) (2) and {[CdL (DMF)(NO3)(2)]center dot DMF}(n) (3), all based on the dipyridyl-derivatised macrocycle, dipyridyldibenzotetraaza[14]annulene (L), are reported along with the X-ray structure of the protonated metal-free ligand as its perchlorate salt, [(HL) (ClO4)](n) (4). In [Zn(L-2H)](n), the zinc ion occupies the macrocyclic cavity, being bound to the N-4-donor set of the macrocyclic ring in its doubly deprotonated form. Each zinc atom is also axially bound by a pyridyl moiety from an adjacent complex, resulting in formation of an infinite one-dimensional chain of the 'herringbone' type in which pairs of macrocyclic complexes interact via face-to-face pi-pi stacking interactions. In contrast, the zinc ion in {[ZnLCl2] (CH3CN)(0.5)(DMF)(0.5)(H2O)(0.5)}(n) does not occupy the macrocyclic cavity but is bound to a pyridyl nitrogen from two ligands such that it acts as a bridge between macrocyclic units and results in the generation of a one-dimensional chain. Two chloro ligands also bind to each zinc centre to yield a distorted tetrahedral coordination geometry. Offset pi-pi stacking occurs between adjacent chains involving alternate macrocycles in each chain, giving rise to a zig-zag arrangement. Pairs of interacting chains pass through the above-mentioned chains to generate further pi-pi stacking to yield an overall three-dimensional structure that contains large ellipsoidal-shaped channels. In {[CdL(DMF)(NO3)(2)]center dot DMF}(n) the cadmium ion again does not occupy the macrocyclic cavity but acts as a bridge between macrocycles to once again afford a linear chain structure. Each cadmium is bound to two pyridyl groups (arising from different molecules of L), two nitrato ligands and one oxygen-bound dimethylformamide molecule to yield a distorted pentagonal bipyramidal coordination geometry. The protonated ligand, [(HL)(ClO4)](n), adopts a linear chain structure in which one pyridyl group is protonated and interacts intermolecularly via a hydrogen bond with the non-protonated pyridyl group of an adjacent macrocyclic unit to yield a hydrogen-bonded linear chain structure

Photoactive and physical properties of an azobenzene-containing coordination framework

Published online: 8 August 2017A new three-dimensional coordination framework, [Zn₄(tbazip)₃(bpe)₂(OH)₂]·bpe·{solvent} (where bpe = 1,2-di(4-pyridyl)ethene) containing the novel photoactive ligand tbazip (tbazip = 5-((4-tert-butyl)phenylazo)isophthalic acid) has been synthesised and crystallographically characterised. The photoactivity of discrete tbazip was investigated and compared with its photoactivity while incorporated within the framework. The effect of isomerisation of the incorporated azobenzene on the chemical and physical properties of the framework were investigated using UV-vis and Raman spectroscopies. The framework is porous only to hydrogen gas at 77 K, but displayed an appreciable uptake for CO₂ at 195 K.James S. Caddy, Thomas B. Faust, Ian M. Walton, Jordan M. Cox, Jason B. Benedict, Marcello B. Solomon, Peter D. Southon, Cameron J. Kepert, and Deanna M. D'Alessandr

Guest-Induced Multistep to Single-Step Spin-Crossover Switching in a 2-D Hofmann-Like Framework with an Amide-Appended Ligand

A detailed study of the two-dimensional (2-D) Hofmann like framework [Fe(furpy)2Pd(CN)4]·nG (furpy: N-(pyridin-4-yl)furan-2- carboxamide, G = H2O,EtOH (A·H2O,Et), and H2O (A·H2O)) is presented, including the structural and spin-crossover (SCO) implications of subtle guest modification. This 2-D framework is characterized by undulating Hofmann layers and an array of interlayer spacing environments --this is a strategic approach that we achieve by the inclusion of a ligand with multiple host−host and host−guest interaction sites. Variable temperature magnetic susceptibility studies reveal an asymmetric multistep SCO for A·H2O,Et and an abrupt single-step SCO for A·H2O with an upshift in transition temperature of ∼75 K. Single-crystal analyses show a primitive orthorhombic symmetry for A·H2O,Et characterized by a unique FeII centers the multistep SCO character is attributed to local ligand orientation. Counterintuitively, A·H2O shows a triclinic symmetry with two inequivalent FeII centers that undergo a cooperative single-step high-spin (HS)-to-low-spin (LS) transition. We conduct detailed structure−function analyses to understand how the guest ethanol influences the delicate balance between framework communication and, therefore, the local structure and spin-state transition mechanism.Manan Ahmed, Kasun S. A. Arachchige, Zixi Xie, Jason R. Price, Jace Cruddas, Jack K. Clegg, Benjamin J. Powell, Cameron J. Kepert, and Suzanne M. Nevill

Spectroscopic, electronic and computational properties of a mixed tetrachalcogenafulvalene and its charge transfer complex

This paper reports additional properties of the electron donor molecule triselenathiafulvalene (TSTF) and its synthesis via a new route involving the precursor tetracarbomethoxytriselenathiafulvalene (TCMTSTF). The structural, electronic and computational properties of TSTF are fully profiled, and discussed in the context of the closely related archetypal electron donor molecule tetrathiafulvalene (TTF). TSTF was also incorporated into a charge transfer (CT) complex with the well-known electron acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ), to generate TSTF–TCNQ. In order to establish its position in the greater TXF–TCNQ series (where TXF = a tetrachalcogenafulvalene), spectral, electrochemical, magnetic, conductivity and computational studies were performed on TSTF and TSTF–TCNQ to extend what is known about the highly interesting and useful new donor molecule.Robert J. Walwyn, Bun Chan, Pavel M. Usov, Marcello B. Solomon, Samuel G. Duyker, Jin Young Koo, Masaki Kawano, Peter Turner, Cameron J. Kepert and Deanna M. D'Alessandr

Spectroscopic, electronic and computational properties of a mixed tetrachalcogenafulvalene and its charge transfer complex

This paper reports additional properties of the electron donor molecule triselenathiafulvalene (TSTF) and its synthesis via a new route involving the precursor tetracarbomethoxytriselenathiafulvalene (TCMTSTF). The structural, electronic and computational properties of TSTF are fully profiled, and discussed in the context of the closely related archetypal electron donor molecule tetrathiafulvalene (TTF). TSTF was also incorporated into a charge transfer (CT) complex with the well-known electron acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ), to generate TSTF-TCNQ. In order to establish its position in the greater TXF-TCNQ series (where TXF = a tetrachalcogenafulvalene), spectral, electrochemical, magnetic, conductivity and computational studies were performed on TSTF and TSTF-TCNQ to extend what is known about the highly interesting and useful new donor molecule. © 2018 The Royal Society of Chemistry

Regulation of Multistep Spin Crossover Across Multiple Stimuli in a 2-D Framework Material

We investigate the effects of a broad array of external stimuli on the structural, spin-crossover (SCO) properties and nature of the elastic interaction within the two dimensional Hofmann framework material [Fe(cintrz)2Pd(CN)4]·guest (cintrz = N cinnamalidene 4-amino-1,2,4-triazole; A·guest; guest = 3H2O, 2H2O, and Ø). This framework exhibits a delicate balance between ferro- and antiferro-elastic interaction characters; we show that manipulation of the pore contents across guests = 3H2O, 2H2O, and Ø can be exploited to regulate this balance. In A·3H2O, the dominant antiferroelastic interaction character between neighboring FeII sites sees the low-temperature persistence of the mixed spin-state species {HS−LS} for {Fe1−Fe2} (HS = high spin, LS = low spin). Elastic interaction strain is responsible for stabilizing the {HS−LS} state and can be overcome by three mechanisms: (1) partial (2H2O) or complete (Ø) guest removal, (2) irradiation via the reverse light-induced excited spin-state trapping (LIESST) effect (λ = 830 nm), and (3) the application of external hydrostatic pressure. Combining experimental data with elastic models presents a clear interpretation that while guest molecules cause a negative chemical pressure, they also have consequences for the elastic interactions between metals beyond the simple chemical pressure picture typically proposed.Manan Ahmed, Katrina A. Zenere, Natasha F. Sciortino, Kasun S. A. Arachchige, Gemma F. Turner, Jace Cruddas, Carol Hua, Jason R. Price, Jack K. Clegg, Francisco Javier Valverde-Mun, oz, Jose A. Real, Guillaume Chastanet, Stephen A. Moggach, Cameron J. Kepert, Benjamin J. Powell, and Suzanne M. Nevill