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In this review article we present all the recent research on stacking interactions of aromatic ligands that coordinate to transition metals through their pi-electrons (eta-coordination). These studies were mostly based on searchin...
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In this review article we present all the recent research on stacking interactions of aromatic ligands that coordinate to transition metals through their pi-electrons (eta-coordination). These studies were mostly based on searching the crystal structures from the Cambridge Structural Database (CSD) and on quantum chemical calculations. Stacking interactions between coordinated and uncoordinated benzene reach the energy of -4.40 kcal/mol, while the strongest calculated staking between two coordinated benzenes has the energy of -4.01 kcal/mol; this is significantly stronger than stacking between two uncoordinated benzenes (-2.73 kcal/mol). It was determined that in crystal structures both coordinated benzene and coordinated cyclopentadienyl anion form stacking interactions that dominantly have large horizontal displacements (more than 4.5 angstrom). This dominance is caused by the relatively strong stacking interactions at large displacements between benzene or Cp ligands in sandwich compounds, while for half-sandwich compounds they are supported by additional interactions of the other (usually branched) ligands. Larger aromatic ligands, tropylium and cyclooctatetraenide, almost exclusively form stacking interactions with large horizontal displacements. Methyl substituted benzene and Cp ligands dominantly form stacking interactions in combination with C-H/pi interactions. Moreover, there is an interplay of stacking and aromatic C-H/pi interactions in the CSD crystal structures, both interactions being important energy contributors to the stability of supramolecular systems. Stacking interactions of eta-coordinated aromatic ligands are important in materials science, crystal engineering and medicinal chemistry, primarily in the application of ruthenium-arene complexes, where they determine the strength of bonding of these complexes to the DNA. (C) 2020 Published by Elsevier B.V.
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Analysis of crystal structure data deposited in the Cambridge Structural Database (CSD) has shown that aromatic rings tend to stack with square planar transition metal complexes when they contain chelate rings. In these interactio...
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Analysis of crystal structure data deposited in the Cambridge Structural Database (CSD) has shown that aromatic rings tend to stack with square planar transition metal complexes when they contain chelate rings. In these interactions, the orientation between chelate and aryl ring is a parallel-displaced orientation, like stacking interactions between aromatic molecules. In fused systems containing chelate and aryl rings, the aryl rings prefer to stack with the chelate rather than with other aryl rings. Quantum chemical calculations show that chelate-aryl stacking is stronger than aryl-aryl stacking. Interaction energies of six-membered chelates of the acetylacetonato type with benzene exceed -6 kcal/mol (CCSD(T)/CBS), more that twice as strong as that for two benzene molecules. Further analysis of the CSD has shown that chelate rings, both isolated and fused stack with other chelate rings. These chelate-chelate stacking interactions can have both face-to-face and parallel-displaced geometries, unlike the stacking interactions between aromatic molecules, for which face-to-face geometry is not typical. Chelate-chelate stacking is stronger than aryl-aryl stacking and stronger even than chelate-aryl stacking. Stacking energies between six-membered chelates of acetylacetonato type exceed -9 kcal/mol, while those between five-membered dithiolene chelates are even stronger. Calculated interaction energies and analysis of supramolecular structures have shown that chelate-chelate and chelate-aryl stacking must be considered in understanding the packing and organization of supramolecular systems and crystal engineering. (C) 2017 Elsevier B.V. All rights reserved.
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The analysis of crystal structures deposited in the Cambridge Structural Database showed that indenyl ligands of transition metal complexes prefer to form stacking interactions with one of the three geometries: two of them (types ...
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The analysis of crystal structures deposited in the Cambridge Structural Database showed that indenyl ligands of transition metal complexes prefer to form stacking interactions with one of the three geometries: two of them (types 1 and 2) at small horizontal displacements and one (type 3) at large horizontal displacements. Density functional theory calculations on several model molecules showed that types 1 and 2 are minima at potential energy surfaces, with substantial interaction energies that surpass -8.0 kcal/mol. Type 3 has a small energy contribution (around -2.0 kcal/mol) to the stability of supramolecular structures; however, it is combined with simultaneous stronger stacking or aromatic C-H/pi interactions. Stacking of indenyl ligands is significantly stronger than the stacking of corresponding cyclopentadienyl ligands (-3.0 kcal/mol), due to the larger size of the indenyl ligand. The strength of stacking interactions depends on the electrostatic potential surface of indenyl ligands, depending on the nature and number of the other ligands of the transition metal.
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Potential energy surfaces of borazine-benzene and borazine-borazine stacking interactions were studied by performing DFT, CCSD(T)/CBS and SAPT calculations. The strongest borazine-benzene stacking was found in a parallel-displaced...
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Potential energy surfaces of borazine-benzene and borazine-borazine stacking interactions were studied by performing DFT, CCSD(T)/CBS and SAPT calculations. The strongest borazine-benzene stacking was found in a parallel-displaced geometry, with a CCSD(T)/CBS interaction energy of -3.46 kcal mol(-1). The strongest borazine-borazine stacking has a sandwich geometry, with a CCSD(T)/CBS interaction energy of -3.57 kcal mol(-1). The study showed that borazine forms significant stacking interactions at large horizontal displacements (over 4.5 angstrom), with energies of -2.20 kcal mol(-1) for the borazine-benzene and -1.96 kcal mol(-1) for the borazine-borazine system. The strength of interactions and their geometrical preferences can be rationalized by observing the electrostatic potentials of borazine and benzene, which is in agreement with SAPT analysis showing that electrostatics is the most important energy component for borazine stacking. All the interactions found in crystal structures of borazine and related compounds were identified either as potential curve minima or the geometries obtained from their optimizations. We also report a new dihydrogen bonding dimer with a CCSD(T)/CBS interaction energy of -2.37 kcal mol(-1), which is encountered in the borazine crystal structures and enables the formation of additional simultaneous interactions that contribute to the overall stability of the crystals.
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Orange single crystals of new polymeric cobalt(II) complex {[Co(bipy)(H2O)(4)](2)[Co(mu-mell)(H2O)(2)].10H(2)O}(n), 1, were synthesized by slow evaporation method at room temperature (bipy = 2,2 '-bipyridine, mell = hexaanion of m...
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Orange single crystals of new polymeric cobalt(II) complex {[Co(bipy)(H2O)(4)](2)[Co(mu-mell)(H2O)(2)].10H(2)O}(n), 1, were synthesized by slow evaporation method at room temperature (bipy = 2,2 '-bipyridine, mell = hexaanion of mellitic acid) and its crystal structure was determined by single-crystal X-ray diffraction. The complex 1 was characterized based on elemental analysis, FTIR spectroscopy and thermal (TG/DTA) analysis followed by computational analysis of noncovalent interactions and quantum chemical calculations of interaction energies. In 1, two crystallographically different Co(II) atoms adopt a deformed octahedral geometry, while bridging mell acts as a tetrakis monodentate ligand allowing the development of wavy-like anionic chains running along [100] direction. The 3D supramolecular network of 1 is composed of alternating supramolecular and water layers connected by hydrogen bonds. The supramolecular layer is formed of ionic interactions between complex cations and polymeric complex anions, established mainly through O-H...O hydrogen bonds, as well as stacking interactions between bipy ligands, while the water layers are comprised of hydrogen bonded lattice water molecules. Upon heating up to 1200 degrees C in nitrogen and air atmosphere, complex 1 showed multiple-step degradation that resulted in the formation of Co and Co3O4, respectively. Computed Hirshfeld surfaces and 2D fingerprint plots indicated that O-H...O hydrogen bonds are the most dominant in the crystal structure, while the shape index and curvedness mapped on the Hirshfeld surfaces of 1 revealed that stacking interactions have an important role in the stabilization of the crystal packing. Quantum chemical calculations showed that, aside from ionic hydrogen-bonded interaction between cation and anionic polymer, the important role in the stability of supramolecular structure of 1 is played by hydrogen bonds of cation and anionic polymer with lattice water, as well as by stacking interactions between bipy ligands. (C) 2021 Elsevier B.V. All rights reserved.
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A Cambridge Structural Database (CSD) search was performed in order to study the stacking interactions of the 7-membered tropylium ring and 8-membered cyclooctatetraenide (COT) ring, coordinated to transition metals via their pi-e...
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A Cambridge Structural Database (CSD) search was performed in order to study the stacking interactions of the 7-membered tropylium ring and 8-membered cyclooctatetraenide (COT) ring, coordinated to transition metals via their pi-electrons. The search showed that both ligands have very high preference for stacking interactions with large horizontal displacements. These interactions leave tropylium and COT faces available for additional simultaneous (mostly C-H/pi and in some cases stacking) interactions, which lead to very stable supramolecular structures. DFT calculations on model molecules derived from CSD crystal structures showed that large offset stacking of both tropylium and COT ligands surpasses -3.0 kcal mol(-1), which makes them important contributors to the overall stability of the systems they are found in. Small offset stacking of tropylium and COT ligands, which is the strongest type of stacking, is almost not found in the CSD crystal structures, which can be explained based on the fact that they do not enable additional simultaneous interactions with molecules from the environment. Stacking of tropylium and COT ligands occurs at larger offsets than stacking of benzene and cyclopentadienyl ligands, which can be rationalized with their larger size, as well as with their electrostatic potential surfaces.
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Chelate-aryl and chelate-chelate stacking interactions of nickel bis(dithiolene) were studied at the CCSD(T)/CBS and DFT levels. The strongest chelate-aryl stacking interaction between nickel bis(dithiolene) and benzene has a CCSD...
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Chelate-aryl and chelate-chelate stacking interactions of nickel bis(dithiolene) were studied at the CCSD(T)/CBS and DFT levels. The strongest chelate-aryl stacking interaction between nickel bis(dithiolene) and benzene has a CCSD(T)/CBS stacking energy of -5.60 kcal mol(-1). The strongest chelate-chelate stacking interactions between two nickel bis(dithiolenes) has a CCSD(T)/CBS stacking energy of -10.34 kcal mol(-1). The most stable chelate-aryl stacking has the benzene center above the nickel atom, while the most stable chelate-chelate dithiolene stacking has the chelate center above the nickel atom. Comparison of chelate-aryl stacking interactions of dithiolene and acac-type nickel chelate shows similar strength. However, chelate-chelate stacking is stronger for dithiolene nickel chelate than for acac-type nickel chelate, which has a CCSD(T)/CBS interaction energy of -9.50 kcal mol(-1).
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Stacking interactions of organometallic sandwich and half-sandwich compounds with cyclopentadienyl (Cp) were studied by searching and observing the crystal structures in the Cambridge Structural Database and performing density fun...
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Stacking interactions of organometallic sandwich and half-sandwich compounds with cyclopentadienyl (Cp) were studied by searching and observing the crystal structures in the Cambridge Structural Database and performing density functional calculations. The strongest calculated interactions are at an offset of 1.5 angstrom with energies for sandwich and half-sandwich dimers of -3.37 and -2.87 kcal mol(-1), respectively, somewhat stronger than the stacking interaction between two benzene molecules, -2.73 kcal mol(-1). At large offsets of 5.0 angstrom, 74% of the strongest energy is preserved for the sandwich dimer and only 29% for the half-sandwich dimer. In crystal structures, for sandwich compounds, the stacking at large offsets is dominant (73%), since the interaction at large offsets is relatively strong, and the geometries enable additional simultaneous interactions with Cp faces. The stacking at large offsets between half-sandwich compounds is less dominant, since the interaction is weaker. However, Cp half-sandwich compounds stack at large offsets unexpectedly often (almost 60%), since the branching of their other ligands in the compound favors more simultaneous interactions with Cp faces. Strong interaction at large offsets for sandwich compounds is the consequence of favorable electrostatic interaction, which is not the feature of stacking between half-sandwich compounds.
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Quantum chemical calculations were performed on model systems of stacking interactions between the acac type chelate rings of nickel, palladium, and platinum. CCSD(T)/CBS calculations showed that chelate-chelate stacking interacti...
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Quantum chemical calculations were performed on model systems of stacking interactions between the acac type chelate rings of nickel, palladium, and platinum. CCSD(T)/CBS calculations showed that chelate-chelate stacking interactions are significantly stronger than chelate-aryl and aryl-aryl stacking interactions. Interaction energy surfaces were calculated at the LC-PBE-D3BJ/aug-cc-pVDZ level, which gives energies in good agreement with CCSD(T)/CBS. The stacking of chelates in an antiparallel orientation is stronger than the stacking in a parallel orientation, which is in agreement with the larger number of antiparallel stacked chelates in crystal structures from the Cambridge Structural Database. The strongest antiparallel chelate-chelate stacking interaction is formed between two platinum chelates, with a CCSD(T)/CBS interaction energy of -9.70 kcal mol(-1), while the strongest stacking between two palladium chelates and two nickel chelates has CCSD(T)/CBS energies of -9.21 kcal mol(-1) and -9.50 kcal mol(-1), respectively. The strongest parallel chelate-chelate stacking was found for palladium chelates, with a LC-PBE-D3BJ/aug-cc-pVDZ energy of -6.51 kcal mol(-1). The geometries of the potential surface minima are not the same for the three metals. The geometries of the minima are governed by electrostatic interactions, which are the ones determining the positions of the energy minima. Electrostatic interactions are governed by different electrostatic potentials above the metals, which are very positive for nickel, slightly positive for palladium, and slightly negative for platinum.
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CCSD(T)/CBS energies for stacking of nickel and copper chelates are calculated and used as benchmark data for evaluating the performance of dispersion-corrected density functionals for calculating the interaction energies. The bes...
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CCSD(T)/CBS energies for stacking of nickel and copper chelates are calculated and used as benchmark data for evaluating the performance of dispersion-corrected density functionals for calculating the interaction energies. The best functionals for modeling the stacking of benzene with the nickel chelate are M06HF-D3 with the def2-TZVP basis set, and B3LYP-D3 with either def2-TZVP or aug-cc-pVDZ basis set, whereas for copper chelate the PBE0-D3 with def2-TZVP basis set yielded the best results. M06L-D3 with aug-cc-pVDZ gives satisfying results for both chelates. Most of the tested dispersion-corrected density functionals do not reproduce the benchmark data for stacking of benzene with both nickel (no unpaired electrons) and copper chelate (one unpaired electron), whereas a number of these functionals perform well for interactions of organic molecules.
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