Co-reporter:Rocio Semino, Johannes P. Dürholt, Rochus Schmid, and Guillaume Maurin
The Journal of Physical Chemistry C October 5, 2017 Volume 121(Issue 39) pp:21491-21491
Publication Date(Web):September 7, 2017
DOI:10.1021/acs.jpcc.7b07090
We present a computational multiscale study of a metal–organic framework (MOF)/polymer composite combining micro- and mesoscopic resolution, by coupling atomistic and coarse grained (CG) force field-based molecular dynamics simulations. As a proof of concept, we describe the copper paddlewheel-based HKUST-1 MOF/poly(vinyl alcohol) composite. Our newly developed CG model reproduces the salient features of the interface in excellent agreement with the atomistic model and allows the investigation of substantially larger systems. The polymer penetrates into the open pores of the MOF as a result of the interactions between its OH groups and the O and Cu atoms in the pores, suggesting an excellent MOF/polymer compatibility. Polymer structure is affected by the MOF surface up to a distance of ∼2.4 times its radius of gyration. This study paves the way toward understanding important interfacial phenomena such as aggregation and phase separation in these mixed matrix systems.
Co-reporter:Johannes P. Dürholt, Raimondas Galvelis and Rochus Schmid
Dalton Transactions 2016 vol. 45(Issue 10) pp:4370-4379
Publication Date(Web):21 Dec 2015
DOI:10.1039/C5DT03865K
We have adapted our genetic algorithm based optimization approach, originally developed to generate force field parameters from quantum mechanic reference data, to derive a first coarse grained force field for a MOF, taking the atomistic MOF-FF as a reference. On the example of the copper paddle-wheel based HKUST-1, a maximally coarse grained model, using a single bead for each three and four coordinated vertex, was developed as a proof of concept. By adding non-bonded interactions with a modified Buckingham potential, the resulting MOF-FF-CGNB is able to predict local deformation energies of the building blocks as well as bulk properties like the tbovs.pto energy difference or elastic constants in a semi-quantitative way. As expected, the negative thermal expansion of HKUST-1 is not reproduced by the maximally coarse grained model. At the expense of atomic resolution, substantially larger systems (up to tens of nanometers in size) can be simulated with respect to structural and mechanical properties, bridging the gap to the mesoscale. As an example the deformation of the [111] surface of HKUST-1 by a “tip” could be computed without artifacts from periodic images.
Co-reporter:Mohammad Alaghemandi
The Journal of Physical Chemistry C 2016 Volume 120(Issue 12) pp:6835-6841
Publication Date(Web):March 10, 2016
DOI:10.1021/acs.jpcc.5b12331
The temperature-responsive behavior of functionalized metal–organic frameworks (fu-MOF) with the general formula [Zn2(fu-L)2dabco]n has been investigated using molecular dynamics simulations (fu-L = alkoxy-functionalized 1,4-benzenedicarboxylate, dabco = 1,4-diazabicyclo[2.2.2]octane). The studied frameworks show a narrow pore (np) form at low temperatures, while at higher temperatures, large pore (lp) structures can be observed. The transition temperature is controlled by the chemical nature of the linker’s side chains as well as their length. In general, enhancing the side chain length decreases the transition temperature. On the other hand, more polar linkers shift the transition temperature to higher values. The so-called opening process of the narrow pores is caused by the thermally induced motion of the alkoxy side chains of the functionalized linkers. For qualitative comparison, the difference in internal energy as well as entropy between two forms (np and lp) was calculated for all studied linker types.
Co-reporter:Sareeya Bureekaew, Vishal Balwani, Saeed Amirjalayer and Rochus Schmid
CrystEngComm 2015 vol. 17(Issue 2) pp:344-352
Publication Date(Web):09 Sep 2014
DOI:10.1039/C4CE01574F
The theoretical structure prediction for a series of 4,4-connected copper paddle-wheel metal–organic frameworks has been performed by using the reverse topological approach, starting from the nbo-b topology. Since the rectangular-shaped tetracarboxylate linkers have a lower symmetry than the square vertices in nbo-b, two alternative insertion modes are possible for each linker. This leads, in principle, to the formation of multiple isoreticular isomers, which have been screened by a genetic global minimum search algorithm, using the first principles parameterized force field MOF-FF for structure optimization and ranking. It is found that isoreticular isomerism does, in this case, not lead to disorder but to a number of well-defined but structurally distinct phases, which all share the same network topology but have substantially different pore shapes and properties. In all cases, the experimentally observed structure is correctly predicted, but in addition a number of other slightly less stable phases are observed. Only one of these phases has been synthesized yet. The theoretical analysis of the molecular model systems of the pore cages revealed the reasons for the trends in conformational energy. This proof-of-concept study demonstrates that screening of isoreticular isomerism using an efficient but accurate force field allows prediction of the atomistic structure of even complex and flexible frameworks.
Co-reporter:Zhenlan Fang ; Johannes P. Dürholt ; Max Kauer ; Wenhua Zhang ; Charles Lochenie ; Bettina Jee ; Bauke Albada ; Nils Metzler-Nolte ; Andreas Pöppl ; Birgit Weber ; Martin Muhler ; Yuemin Wang ; Rochus Schmid ;Roland A. Fischer
Journal of the American Chemical Society 2014 Volume 136(Issue 27) pp:9627-9636
Publication Date(Web):June 10, 2014
DOI:10.1021/ja503218j
A series of defect-engineered metal–organic frameworks (DEMOFs) derived from parent microporous MOFs was obtained by systematic doping with defective linkers during synthesis, leading to the simultaneous and controllable modification of coordinatively unsaturated metal sites (CUS) and introduction of functionalized mesopores. These materials were investigated via temperature-dependent adsorption/desorption of CO monitored by FTIR spectroscopy under ultra-high-vacuum conditions. Accurate structural models for the generated point defects at CUS were deduced by matching experimental data with theoretical simulation. The results reveal multivariate diversity of electronic and steric properties at CUS, demonstrating the MOF defect structure modulation at two length scales in a single step to overcome restricted active site specificity and confined coordination space at CUS. Moreover, the DEMOFs exhibit promising modified physical properties, including band gap, magnetism, and porosity, with hierarchical micro/mesopore structures correlated with the nature and the degree of defective linker incorporation into the framework.
Co-reporter:Saeed Amirjalayer, Maxim Tafipolsky, and Rochus Schmid
The Journal of Physical Chemistry Letters 2014 Volume 5(Issue 18) pp:3206-3210
Publication Date(Web):September 1, 2014
DOI:10.1021/jz5012065
The surface morphology and termination of metal-organic frameworks (MOF) is of critical importance in many applications, but the surface properties of these soft materials are conceptually different from those of other materials like metal or oxide surfaces. Up to now, experimental investigations are scarce and theoretical simulations have focused on the bulk properties. The possible surface structure of the archetypal MOF HKUST-1 is investigated by a first-principles derived force field in combination with DFT calculations of model systems. The computed surface energies correctly predict the [111] surface to be most stable and allow us to obtain an unprecedented atomistic picture of the surface termination. Entropic factors are identified to determine the preferred surface termination and to be the driving force for the MOF growth. On the basis of this, reported strategies like employing “modulators” during the synthesis to tailor the crystal morphology are discussed.Keywords: crystal growth; force-field calculation; metal−organic framework; surface energy; surface termination;
Co-reporter:Sareeya Bureekaew and Rochus Schmid
CrystEngComm 2013 vol. 15(Issue 8) pp:1551-1562
Publication Date(Web):17 Dec 2012
DOI:10.1039/C2CE26473K
A scheme to predict as yet unknown, hypothetical covalent organic frameworks (COFs) from scratch by screening the possible space of supramolecular isomers is presented. This is achieved by extending our currently developed first principles derived force field MOF-FF with a parametrization for the boroxin unit. We considered four non-tetrahedral monomers with four boronic acid groups inspired by the corresponding carboxylate linkers known from metal–organic frameworks, and investigated the potential 3,4-connected topologies with edge-transitivity (ctn, bor, pto and tbo) or transitivity 32 (ofp, tfj, fjh, iab and nju). Due to the partly lower symmetry of the building blocks with respect to the vertex, beyond topological isomerism also isoreticular isomers are formed. We have used our reverse topological approach to construct the fictitious structures and employed an automated genetic algorithm based global minimum search approach to screen the vast configurational space of isoreticular isomerism and predicted a series of hypothetical 3D-COFs. All structures are completely relaxed by including the lattice parameters. From the atomistic structures, the accessible surface areas were determined, and, because of the isomer screening procedure, the question of crystallographic disorder could also be answered. Beyond the examples of hypothetical 3D-COFs serving as a lead for future synthetic investigations, this work is intended in particular to introduce the efficient predictive modeling method which can be applied to any kind of hypothetical COF system.
Co-reporter:Heshmat Noei, Olesia Kozachuk, Saeed Amirjalayer, Sareeya Bureekaew, Max Kauer, Rochus Schmid, Bernd Marler, Martin Muhler, Roland A. Fischer, and Yuemin Wang
The Journal of Physical Chemistry C 2013 Volume 117(Issue 11) pp:5658-5666
Publication Date(Web):February 26, 2013
DOI:10.1021/jp3056366
The mixed-valence metal–organic framework [Ru3II,III(btc)2Cl1.5] (Ru-MOF) was synthesized by the controlled SBU approach and characterized by combined powder XRD, XPS, and FTIR methods. The interaction of CO molecules with Ru-MOF was studied by a novel instrumentation for ultra-high-vacuum (UHV) FTIR spectroscopy. The high-quality IR data demonstrate the presence of two different CO species within the framework: a strongly bonded CO showing a low-lying band at 2137 cm–1 and a second CO species at 2171 cm–1 with a lower binding energy. It was found that these IR bands cannot be assigned in a straightforward manner to CO molecules adsorbed on the coordinatively unsaturated RuII site (CUS) and RuIII site connected to an additional Cl– ion for charge compensation. The accurate DFT calculations reveal that the structural and electronic properties of the mixed-valence Ru-MOF are much more complex than expected. One of the Cl– counterions could be transferred to a neighboring paddle-wheel, forming an anionic SBU blocked by two Cl– counterions, whereas the other positively charged paddle-wheel with a Ru2II,III dimer exposes two “free” CUS, which can bind two CO molecules with different frequencies and binding energies.
Co-reporter:Sareeya Bureekaew, Saeed Amirjalayer and Rochus Schmid
Journal of Materials Chemistry A 2012 vol. 22(Issue 20) pp:10249-10254
Publication Date(Web):17 Feb 2012
DOI:10.1039/C2JM15778K
We have used density functional theory calculations to study non-periodic model systems for the ubiquitous layer-pillar metal organic frameworks built from paddle-wheel building blocks. Experimentally, these porous materials show nearly identical structures for both copper and zinc forming the paddle-wheel, but differ depending on the type of the metal center in their properties. Our theoretical results clearly reveal orbital directing effects for the d9 Cu(II) center, enforcing a square planar conformation, to be the main reason for the difference in contrast to the flexible d10 Zn(II) system. Surprisingly, this difference is directly visible in the structure of the bare vertex model without axial ligands, whereas in the case of pyridine coordination both copper and zinc complexes are structurally nearly indistinguishable. However, in the vibrational normal modes the higher degree of flexibility for the zinc-based systems is still noticeable, explaining the higher flexibility of the corresponding periodic MOFs.
Co-reporter:Saeed Amirjalayer ; Randall Q. Snurr
The Journal of Physical Chemistry C 2012 Volume 116(Issue 7) pp:4921-4929
Publication Date(Web):January 23, 2012
DOI:10.1021/jp211280m
We present a method to theoretically predict structures in arbitrary network topologies for all currently known boron based covalent organic frameworks (COFs). This is particularly useful because these materials are accessible experimentally only as polycrystalline powders. The method is based on a new fully flexible molecular mechanics force field. The consistent parameter set is derived by a genetic algorithm optimization approach from first-principles reference computed data. To achieve high accuracy, the convergence with respect to the level of theory is carefully controlled for this reference. The force field is used to investigate the relative stability of the two high symmetry topologies ctn and bor. Interestingly, for all systems, the ctn topology is found to be energetically more stable. This preference is observed experimentally, too, with the single exception of COF-108, which forms the bor topology. This exception can thus be attributed to the different synthesis conditions, demonstrating that other topologies might be accessible in principle for all COFs. The force field is further used to compute first benchmark surface areas for ideal systems, thermal expansion coefficients, elastic constants, and CO2 adsorption isotherms for all systems in both topologies, which are experimentally unavailable. Our force field opens the way for theoretical structure prediction and prescreening of properties for these fascinating materials.
Co-reporter:Saeed Amirjalayer and Rochus Schmid
The Journal of Physical Chemistry C 2012 Volume 116(Issue 29) pp:15369-15377
Publication Date(Web):June 20, 2012
DOI:10.1021/jp302713m
For the application of metal–organic frameworks (MOFs), the understanding of host–guest interactions on a molecular level is crucial, and often only theoretical methods allow such an insight. However, to obtain quantitative information from such calculations, a validation of the applied methods is indispensable. In this work we investigate for the first time the physisorption of benzene, as a probe molecule for larger guest molecules, within the matrix of MOF-5 using high-level quantum mechanical methods. The calculations reveal a large contribution of dispersion effects on the host–guest interaction. The importance of both reliable and efficient quantum mechanical techniques, which are able to properly cover these effects, is discussed. We find that in particular a double-hybrid functional together with an empirical long-range dispersion correction is an accurate and robust method for the rather large model systems. In addition, our quantum mechanical results enabled us to benchmark for the first time the performance of force fields to describe the interaction of hydrocarbons with the periodic framework. This kind of bottom-up validation of host–guest interactions strengthens the predictive power of theoretical methods in the area of MOF research.
Co-reporter:Saeed Amirjalayer ; Maxim Tafipolsky
The Journal of Physical Chemistry C 2011 Volume 115(Issue 31) pp:15133-15139
Publication Date(Web):June 24, 2011
DOI:10.1021/jp200123g
We have applied an accurate molecular mechanics force field, parametrized with respect to first-principles calculated reference data, for copper paddle wheel (Cu2(O2C)4) based metal organic frameworks to investigate possible systems with a 3,4-connected network topology. The results explain why the well-known HKUST-1 forms a tbo net, whereas for an extended linker, as in MOF-14, the pto topology is preferred. In particular, the complex structure of the latter system, consisting of two deformed and “interwoven” nets, is accurately predicted, and the necessary deformation energy can be quantified. In this context also all possible forms of interpenetration were considered. Finally, by designing a bromine-substituted extended linker the system can be forced back into the more open tbo topology. This first molecular mechanics investigation of the relative strain energies of MOF network topologies demonstrates that the structure is to a large extent defined by the intrinsic conformational preferences of the building blocks. Our approach allows to analyze and understand the reasons for this preference and can be used as a computational tool for the design of specific topologies.
Co-reporter:Maxim Tafipolsky, Saeed Amirjalayer, Rochus Schmid
Microporous and Mesoporous Materials 2010 Volume 129(Issue 3) pp:304-318
Publication Date(Web):15 April 2010
DOI:10.1016/j.micromeso.2009.07.006
In this contribution, available atomistic theoretical models for the new class of functional porous hybrid materials are critically overviewed. These hybrid materials (including covalent- and metal–organic frameworks, COFs and MOFs) are characterized by organic linkers, allowing for conformational flexibility and connecting nodes formed by a wide variety of elements and coordination modes. The flexibility and variability of these porous materials represent one of their potentials for application, but also afford that theoretical methods, tailored for more traditional materials like zeolites, need to be extended or modified. The current status of both periodic and non-periodic quantum mechanic, as well as molecular mechanic models are considered, focusing on the peculiarities of an application on hybrid frameworks. Atomistic models are used for structural prediction, computation of materials properties and in particular for the modeling of host–guest interactions.
Co-reporter:Maxim Tafipolsky ; Saeed Amirjalayer
The Journal of Physical Chemistry C 2010 Volume 114(Issue 34) pp:14402-14409
Publication Date(Web):August 12, 2010
DOI:10.1021/jp104441d
We present a fully flexible and ab initio-derived molecular mechanics force field for the ubiquitous copper paddle-wheel building block Cu2(O2C)4 in metal−organic frameworks. The force field expression is based on the established MM3 force field, extended by additional cross terms and specific bond-stretching and angle-bending terms for the square-planar CuO4 coordination environment. Using reference data computed at the DFT level for nonperiodic reference systems, the parametrization is performed using an automated genetic algorithm optimization strategy in order to reproduce structure and low normal modes of the model systems. It is validated on the much investigated Cu-btc (HKUST-1) metal−organic framework. Beyond the structure, lattice-dynamic-dependent properties such as the bulk modulus and the observed negative thermal expansion effect of Cu-btc are quantitatively predicted by the force field without recourse with respect to experimental data. In connection with available parametrizations of various organic linkers, it can be useful for aiding the structure determination of known MOFs, but it also paves the way for the computational prescreening of yet unknown copper paddle-wheel-based frameworks.
Co-reporter:Maxim Tafipolsky and Rochus Schmid
Journal of Chemical Theory and Computation 2009 Volume 5(Issue 10) pp:2822-2834
Publication Date(Web):September 16, 2009
DOI:10.1021/ct900304q
In the light of the important role played by the carboxylate group in bio- and coordination chemistry, its consistent and reliable parametrization for molecular simulations is crucial. The experimental vibrational spectra of three carboxylate anions (formate, acetate, and benzoate) both in the gas phase and in the condensed phase (as sodium salts) are interpreted on the basis of high-quality ab initio calculations. The interaction with the counterion (metal cation) is shown to be of major importance in the interpretation of the spectral features of the carboxylate group both in the solid state and in aqueous solution. Previous attempts to parametrize the carboxylate group within the molecular mechanics approach is critically reviewed, and a new set of the consistent valence force field parameters based on first principles calculations is proposed, which is able to reproduce accurately both the structure and the dynamics of the carboxylate moiety both free and coordinated with metal cations.
Co-reporter:Saeed Amirjalayer, Rochus Schmid
Microporous and Mesoporous Materials 2009 Volume 125(1–2) pp:90-96
Publication Date(Web):1 October 2009
DOI:10.1016/j.micromeso.2009.02.006
In this contribution, the diffusion of benzene in the porous metal organic framework MOF-5 is investigated by molecular dynamics simulations. Previously, we have shown that by using a first principles derived fully flexible force field the experimentally determined self-diffusion coefficients DselfDself could be well reproduced [S. Amirjalayer, M. Tafipolsky, R. Schmid, Angew. Chem. Int. Ed. 46 (2007) 463]. Here, we use the same methodology to determine the loading dependence on the diffusion. It is found that diffusivity, which is in the range of liquid benzene, slightly increases up to a load of 32 molecules per unit cell and then falls off at higher load. Free energy maps reveal that additional sites appear at higher load due to attractive guest–guest interactions. The topology of these sites is very close to the experimentally determined locations of ferrocene molecules in MOF-5, which corroborates that attractive π–ππ–π interactions govern these systems. The site–site and site-phenylene distances are very similar to the first solvation radius of liquid benzene. For the very open MOF-5, the main barrier for diffusive transport is to overcome the attractive interaction in the binding pockets, which is in contrast to zeolitic microporous systems, where the barrier for diffusion is the hindrance of the pore window. Spatial free energy maps are used to investigate the diffusion pathway on a molecular level and the load dependence of the free energy barriers for these transport processes.
Co-reporter:Maxim Tafipolsky and Rochus Schmid
The Journal of Physical Chemistry B 2009 Volume 113(Issue 5) pp:1341-1352
Publication Date(Web):January 9, 2009
DOI:10.1021/jp807487f
A systematic strategy is proposed to derive the necessary force field parameters directly from first principles calculations of nonperiodic model systems to reproduce both the structure and curvature of the reference potential energy surface. The parameters are determined using a genetic algorithm combined with a novel fitness criterion based on a representation of structure and curvature in a set of redundant internal coordinates. Due to the efficiency of this approach it is possible to abandon the need for transferability of the parameters. The method is targeted for the application on metal−organic frameworks (MOFs), where parameters for molecular mechanics force fields are often not available, because of the wide range of possible inorganic fragments involved. The scheme is illustrated for Zn4O−based IRMOF materials on the example of MOF-5. In a “building block” approach parameters are derived for the two model systems basic zinc formate (Zn4O(O2CH)6), and dilithium terephthalate with reference data obtained from density functional theory. The resulting potential gives excellent agreement with the structure, vibrational frequencies, thermal behavior and elastic constants of the periodic MOF-5.
Co-reporter:Saeed Amirjalayer
The Journal of Physical Chemistry C 2008 Volume 112(Issue 38) pp:14980-14987
Publication Date(Web):August 30, 2008
DOI:10.1021/jp8061948
For the family of isoreticular metal organic frameworks (IRMOFs), a supramolecular conformational isomer, where the carboxylic planes in one linker are orthogonal to each other, is in principle possible. This polymorphic form has been investigated by means of molecular mechanics calculations using an accurate MM3 type force field. In the case of the parent structure IRMOF-1, the regular form is more stable by 17.8 kcal/mol (per formula unit) than this isomer. However, due to steric repulsions, in the case of the naphthalene and anthracene based IRMOF-7 and 993, this is reduced to only 2.0 and 5.6 kcal/mol, respectively. Due to a complex network of interlinker interactions, a broad variety of different rotational isomers is predicted, and only by using a genetic algorithm search algorithm the global minimum structure could be located. The low energy difference between the isomeric forms explains the disorder observed for IRMOF-7 experimentally. For IRMOF-10 and 16 with a flexible biphenyl bond in the linker, an even lower energy separation of 2.7 and 0.4 kcal/mol, respectively, is observed. The study demonstrates that theoretical calculations can be a viable tool in order to determine the actual atomistic structure of more complex porous functional materials.
Co-reporter:M. Tafipolsky;R. Schmid
Chemical Vapor Deposition 2007 Volume 13(Issue 2-3) pp:
Publication Date(Web):14 MAR 2007
DOI:10.1002/cvde.200606516
Small stoichiometric, as well as some nonstoichiometric, gallium nitride clusters of the type GanNm (n + m ≤ 8) are investigated by density functional theory (DFT), MP2, and coupled cluster, CCSD(T), calculations. The lowest energy structures of the stoichiometric clusters and the corresponding products after the loss of a nitrogen molecule have been determined. It is shown that, above room temperature, they are unstable against the loss of nitrogen molecules and therefore are even less stable than the bulk material. Thus, these clusters can be ruled out as direct intermediates for the formation of bulk GaN. This has been ignored up to now and is of crucial importance for the decomposition mechanism of single-molecule precursor systems. It is argued that the azide group can stabilize a tetrahedral arrangement of four gallium atoms around the N atom, and a nonstoichiometric gallium nitrogen cluster like gallium azide, GaN3, can play an important role as an intermediate during the formation of bulk GaN in CVD.
Co-reporter:Saeed Amirjalayer;Maxim Tafipolsky
Angewandte Chemie International Edition 2007 Volume 46(Issue 3) pp:
Publication Date(Web):28 NOV 2006
DOI:10.1002/anie.200601746
Doing the locomotion: When benzene molecules diffuse through the metal organic framework MOF-5, they accumulate in pockets (see picture). Molecular dynamics simulations reveal that the correlated lattice motion increases this binding. Only when the the lattice dynamics are considered in the simulation, can the experimental diffusion constants be reproduced.
Co-reporter:Saeed Amirjalayer;Maxim Tafipolsky Dr. Dr.
Angewandte Chemie 2007 Volume 119(Issue 3) pp:
Publication Date(Web):28 NOV 2006
DOI:10.1002/ange.200601746
Bewegung zählt: Wenn Benzolmoleküle durch das metall-organische Gerüst MOF-5 diffundieren, sammeln sie sich in dessen Taschen (siehe Bild). Moleküldynamiksimulationen belegen, dass eine korrelierte Gitterbewegung diese Wirt-Gast-Wechselwirkung verstärkt, und experimentelle Selbstdiffusionskoeffizienten lassen sich nur mit Berücksichtigung dieser Netzwerkdynamik reproduzieren.
Co-reporter:Johannes P. Dürholt, Raimondas Galvelis and Rochus Schmid
Dalton Transactions 2016 - vol. 45(Issue 10) pp:NaN4379-4379
Publication Date(Web):2015/12/21
DOI:10.1039/C5DT03865K
We have adapted our genetic algorithm based optimization approach, originally developed to generate force field parameters from quantum mechanic reference data, to derive a first coarse grained force field for a MOF, taking the atomistic MOF-FF as a reference. On the example of the copper paddle-wheel based HKUST-1, a maximally coarse grained model, using a single bead for each three and four coordinated vertex, was developed as a proof of concept. By adding non-bonded interactions with a modified Buckingham potential, the resulting MOF-FF-CGNB is able to predict local deformation energies of the building blocks as well as bulk properties like the tbovs.pto energy difference or elastic constants in a semi-quantitative way. As expected, the negative thermal expansion of HKUST-1 is not reproduced by the maximally coarse grained model. At the expense of atomic resolution, substantially larger systems (up to tens of nanometers in size) can be simulated with respect to structural and mechanical properties, bridging the gap to the mesoscale. As an example the deformation of the [111] surface of HKUST-1 by a “tip” could be computed without artifacts from periodic images.
Co-reporter:Sareeya Bureekaew, Saeed Amirjalayer and Rochus Schmid
Journal of Materials Chemistry A 2012 - vol. 22(Issue 20) pp:NaN10254-10254
Publication Date(Web):2012/02/17
DOI:10.1039/C2JM15778K
We have used density functional theory calculations to study non-periodic model systems for the ubiquitous layer-pillar metal organic frameworks built from paddle-wheel building blocks. Experimentally, these porous materials show nearly identical structures for both copper and zinc forming the paddle-wheel, but differ depending on the type of the metal center in their properties. Our theoretical results clearly reveal orbital directing effects for the d9 Cu(II) center, enforcing a square planar conformation, to be the main reason for the difference in contrast to the flexible d10 Zn(II) system. Surprisingly, this difference is directly visible in the structure of the bare vertex model without axial ligands, whereas in the case of pyridine coordination both copper and zinc complexes are structurally nearly indistinguishable. However, in the vibrational normal modes the higher degree of flexibility for the zinc-based systems is still noticeable, explaining the higher flexibility of the corresponding periodic MOFs.
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![Ruthenium, [(1,2,5,6-h)-1,5-cyclooctadiene]bis[(1,2,3-h)-2-methyl-2-propenyl]- (9CI)](http://img.cochemist.com/ccimg/12300/12289-94-0_b.png)
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