Water-Induced Structural Transformations in Flexible Two-Dimensional Layered Conductive Metal–Organic Frameworks (original) (raw)
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2011
Density-functional based tight-binding is a powerful method to describe large molecules and materials. Metal-Organic Frameworks (MOFs), materials with interesting catalytic properties and with very large surface areas have been developed and have become commercially available. Unit cells of MOFs typically include hundreds of atoms, which make the application of standard Density-Functional methods computationally very expensive, sometimes even unfeasible. The aim of this paper is to prepare and to validate the Self-Consistent Charge Density-Functional based Tight Binding (SCC-DFTB) method for MOFs containing Cu, Zn and Al metal centers. The method has been validated against full hybrid density-functional calculations for model clusters, against gradient corrected density-functional calculations for supercells, and against experiment. Moreover, the modular concept of MOF chemistry has been discussed on the basis of their electronic properties. We concentrate on MOFs comprising three c...
Flexible linkers and dinuclear metallic nodes build up an original metal–organic framework
CrystEngComm, 2013
A Metal-Organic Framework (MOF) of formula [Cu 2 (m 3 -tmds) 2 (imH) 4 ]?H 2 tmds (imH = imidazole; H 2 tmds = 1,3-bis(3-carboxypropyl)tetramethyldisiloxane) 1 has been synthesized by successive additions of H 2 tmds and imidazole to a solution of copper(II) acetate. The crystal structure of compound 1 has been investigated by single-crystal X-ray diffraction. It crystallizes in the C2/c monoclinic space group. The crystals are composed of an extended coordination network welcoming H 2 tmds molecules. The network contains paddle-wheel dicopper(II) moieties where the two copper atoms are bridged by one of the carboxylate groups of two tmds 22 anion. The basal plane of their coordination sphere is complemented by two imidazole molecules whereas the apical position is occupied by one oxygen atom of the second carboxylate group of a neighboring tmds 22 anion leading to an overall square-pyramidal environment of the metal ions. These short and long bridging modes of the flexible tmds 22 dianion build up a complex bidimensional coordination network where the nodes are dinuclear clusters rather than simple metal centres. H-bonds are found within the network with imidazole as a H-bond donor and tmds 22 as a H-bond acceptor leading to a cis-oide conformation of the ligand. The coordination network is further H-bonded to H 2 tmds molecules leading to an overall three-dimensional supramolecular network mixing coordination and hydrogen bonds. Variable-temperature magnetic susceptibility measurements reveal antiferromagnetic interactions between the copper(II) ions within the paddle-wheel dinuclear units (J = 234.4(2) cm 21 ; H = 22JS 1 S 2 ).
Computational characterization and prediction of metal–organic framework properties
In this introductory review, we give an overview of the computational chemistry methods commonly used in the field of metal-organic frameworks (MOFs), to describe or predict the structures themselves and characterize their various properties, either at the quantum chemical level or through classical molecular simulation. We discuss the methods for the prediction of crystal structures, geometrical properties and large-scale screening of hypothetical MOFs, as well as their thermal and mechanical properties. A separate section deals with the simulation of adsorption of fluids and fluid mixtures in MOFs.
Improved Predictive Tools for Structural Properties of Metal–Organic Frameworks
Molecules
The accurate determination of structural parameters is necessary to understand the electronic and magnetic properties of metal–organic frameworks (MOFs) and is a first step toward accurate calculations of electronic structure and function for separations and catalysis. Theoretical structural determination of metal-organic frameworks is particularly challenging because they involve ionic, covalent, and noncovalent interactions, which must be treated in a balanced fashion. Here, we apply a diverse group of local exchange-correlation functionals (PBE, PBEsol, PBE-D2, PBE-D3, vdW-DF2, SOGGA, MN15-L, revM06-L, SCAN, and revTPSS) to a broad test set of MOFs to seek the most accurate functionals to study various structural aspects of porous solids, in particular to study lattice constants, unit cell volume, two types of pore size characteristics, bond lengths, bond angles, and torsional angles). The recently developed meta functionals revM06-L and SCAN, without adding any molecular mechani...
The Journal of Physical Chemistry C
The copper paddle-wheel is the building unit of many metal organic frameworks. Because of the ability of the copper cations to attract polar molecules, copper paddle-wheels are promising for carbon dioxide adsorption and separation. They have therefore been studied extensively, both experimentally and computationally. In this work we investigate the copper− CO 2 interaction in HKUST-1 and in two different cluster models of HKUST-1: monocopper Cu(formate) 2 and dicopper Cu 2 (formate) 4. We show that density functional theory methods severely underestimate the interaction energy between copper paddle-wheels and CO 2 , even including corrections for the dispersion forces. In contrast, a multireference wave function followed by perturbation theory to second order using the CASPT2 method correctly describes this interaction. The restricted open-shell Møller−Plesset 2 method (ROS-MP2, equivalent to (2,2) CASPT2) was also found to be adequate in describing the system and used to develop a novel force field. Our parametrization is able to predict the experimental CO 2 adsorption isotherms in HKUST-1, and it is shown to be transferable to other copper paddle-wheel systems.
2011
The increasingly rapid development of metal organic frameworks (MOFs) or porous coordination polymers (PCPs) over the past two decades has attracted considerable attention from both academic and industrial researchers because they offer unprecedented levels of permanent porosity and exceptional opportunities for design of materials from the molecule up. 1aÀn,2aÀ2k Furthermore, their chemical and structural diversity offers the possibility of combining porosity with other important properties, such as magnetism, luminescence, semiconductivity, and catalytic activity. 1fÀh,m,pÀu The fact that MOFs are amenabled prior to design distinguishes them from most other classes of materials and is a consequence of the geometry of their chemical building blocks which manifests itself in the topology of the resulting crystal structures. 3aÀg "Design" implies a blueprint or some other formal description developed prior to and in fact directing synthesis of the crystal in mind. 2c,d In this communication, we outline an algorithm for generating such designs, and we present output from two demonstration programs based on this algorithm. To discuss these designs, we employ a formalism variously called (in various communities) an "embedded net" or an "embedded graph" or a "geometric graph" or a "Euclidean graph", among other things; to eliminate ambiguity, we will refer to an embedded net as a geometric structure in 3D-space consisting of the following: 33 • a set of points, which we call nodes (although they are often 34 called vertices); 35 • a set of line segments, which we call edges (although they are 36 often called linkers), each with two nodes as end points. 37 If an embedded net is employed as a blueprint for a MOF, the 38 nodes would represent positions of atoms or molecular building 39 blocks (MBBs), positioned at specific points in 3D-space, while 40 the edges would represent bonds or molecular linkers between 41 atoms or MBBs, each linking the two end point nodes. 42 Such a geometric (as opposed to topological or combinatorial) 43 representation serves as a de facto blueprint for the design of 44 related MOFs because it tells us the shape of MBBs and the range 45 of their possible spatial arrangements; that is, just as a represen-46 tation is constructed from nodes linked by edges, a MOF can be 47 48 We should distinguish the geometric notion of an embedded 49 net from two other extant notions: 50 • The combinatorial notion of a net (or a graph), consisting of 51 nodes and vertices and incidence relations between the two, 52 but with no spatial relations. Thus, two nets are combinato-53
Inorganic Chemistry, 2007
Single crystals of three coordination networks containing the Cu 2 (COO) 4 core bridged by cyclohexane have been hydrothermally prepared by the reaction of 1,4-cyclohexanedicarboxylic (1,4-H 2 chdc) or 1,3,5-cyclohexanetricarboxylic (1,3,5-H 3 chtc) acid and Cu(NO 3) 2 •6H 2 O. We report their characterizations by single-crystal X-ray structure determinations, IR spectroscopy, thermal analyses, and their magnetic properties. [Cu 2 (trans-1,4-chdc) 2 ] (1) consists of 4 × 4 grids with the dimeric nodes connected by the trans-1,4-chdc, and these grids are then connected to each other by Cu−O bonds, resulting in a porous network (void volume of 130 Å 3 per cell or 25%) with no solvent in its cavities. [Cu 2 (cis-1,4-chdc) 2 (H 2 O) 2 ] (2) consists of two-legged ladders where the dimer nodes are bridged by pairs of cis-1,4-chdc and the water molecules cap the ends of the Cu dimers. [Cu 2 (1,3,5-Hchtc) 2 ] (3) displays 4 × 4 grids, but each dimeric node is connected to its neighbors within the same grid by Cu−O bonds to form a layered network which further makes hydrogen-bond interactions with its neighbors. 2 and 3 have compact structures without any space for solvents. IR and DT-TGA confirm the absence of water in the empty channels of 1, while IR shows the presence of both protonated and deprotonated carboxyl groups for 3. The magnetic properties of all three compounds are dominated by the strong Cu−Cu antiferromagnetic interaction resulting in singlet−triplet gaps of 450−500 K.
Chem.Comm., 2020
Herein, we present, for the first time, a 2D-MOF based on copper and 4-hydroxypyrimidine-5-carbonitrile as the linker. Each MOF layer is perfectly flat and neutral, as is the case for graphene. High pressure X-ray diffraction measurements reveal that this layered structure can be modulated between 3.01 to 2.78 Å interlayer separation, with an evident piezochromism and varying conductive properties. An analysis of the band structure indicates that this material is conductive along different directions depending on the application of pressure or H doping. These results pave the way for the development of novel layered materials with tunable and efficient properties for pressure-based sensors. The design and synthesis of new materials that have high electrical conductivity and switchable properties are of great interest due to the current demand in the field of sensors. 1,2 Some of the most interesting materials applicable in this respect, metal-organic frameworks (MOFs), which are materials constituted by organic ligands coordinated to metal ions or clusters defining a porous and crystalline network, 3 have received great interest due to their structural tunability and the properties that arise from their topological features. 4 In particular, the study of transition metal ion-based MOFs has evolved enormously in many areas. 5 The great advantage of coordination chemistry is that, thanks to its simple synthetic routes, it allows us to design materials with applications in virtually all fields. To this end, in recent years, several groups have worked on the design of novel MOFs to explore their properties in luminescence, 6 gas adsorption, 7 optical storage, 8 magnetism 9 and biology as drug-delivery systems, 10 cytotoxic agents 11 and sensors. 12 However, the use of MOFs to construct materials for pressure-based sensors is almost completely unexplored. 13 Taking into account the above, we set our minds to designing a novel 2D-MOF with a potentially large number of applications. For this, and inspired by multilayer graphene, we generated graphene-like layers as a template, promoting coordination links at 120 degree angles. To generate some asymmetry in the network, we could have used pyrimidine-5-carbonitrile as the ligand; however , we decided to use 4-hydroxypyrimidine-5-carbonitrile as this linker possesses an oxygen atom in the para position, which can be an excellent alternative to increase the extended aromaticity and introduce electronic density in the channels of the possible MOF (Scheme 1). Finally, we had to choose the ideal metal ion. In this case, we decided to use copper(II) because of its easy plasticity of its coordination sphere, which would allow it to display a trigonal bipyramid geometry. Moreover, another possibility could be that within the solvothermal reaction, Cu(II) could be reduced to Cu(I) with a flat trigonal geometry, as it would have to maintain the desired graphene type network. The choice of copper as the metal ion is the perfect choice that would favour the formation of the desired two-dimensional network, thereby achieving graphene-like networks. The copper-ligand linkage, moreover, enables p-d conjugation in a 2D plane.