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A set of 35 representative neutral and charged tetrel complexes was investigated with the objective of finding the factors that influence the strength of tetrel bonding involving single bonded C, Si, and Ge donors and double bonded C or Si donors. For the first time, we introduced an intrinsic bond strength measure for tetrel bonding, derived from calculated vibrational spectroscopy data obtained at the CCSD(T)/aug-cc-pVTZ level of theory and used this measure to rationalize and order the tetrel bonds. Our study revealed that the strength of tetrel bonds is affected by several factors, such as the magnitude of the σ-hole in the tetrel atom, the negative electrostatic potential at the lone pair of the tetrel-acceptor, the positive charge at the peripheral hydrogen of the tetrel-donor, the exchange-repulsion between the lone pair orbitals of the peripheral atoms of the tetrel-donor and the heteroatom of the tetrel-acceptor, and the stabilization brought about by electron delocalization. Thus, focusing on just one or two of these factors, in particular, the σ-hole description can only lead to an incomplete picture. Tetrel bonding covers a range of −1.4 to −26 kcal/mol, which can be strengthened by substituting the peripheral ligands with electron-withdrawing substituents and by positively charged tetrel-donors or negatively charged tetrel-acceptors.

Information resulting from a comprehensive investigation into the intrinsic strengths of hydrated divalent magnesium clusters is useful for elucidating the role of aqueous solvents on the Mg2+ ion, which can be related to those in bulk aqueous solution. However, the intrinsic Mg–O and intermolecular hydrogen bond interactions of hydrated magnesium ion clusters have yet to be quantitatively measured. In this work, we investigated a set of 17 hydrated divalent magnesium clusters by means of local vibrational mode force constants calculated at the ωB97X-D/6-311++G(d,p) level of theory, where the nature of the ion–solvent and solvent–solvent interactions were interpreted from topological electron density analysis and natural population analysis. We found the intrinsic strength of inner shell Mg–O interactions for [Mg(H2O)n]2+ (n = 1–6) clusters to relate to the electron density at the bond critical point in Mg–O bonds. From the application of a secondary hydration shell to [Mg(H2O)n]2+ (n = 5–6) clusters, stronger Mg–O interactions were observed to correspond to larger instances of charge transfer between the lp(O) orbitals of the inner hydration shell and the unfilled valence shell of Mg. As the charge transfer between water molecules of the first and second solvent shell increased, so did the strength of their intermolecular hydrogen bonds (HBs). Cumulative local vibrational mode force constants of explicitly solvated Mg2+, having an outer hydration shell, reveal a CN of 5, rather than a CN of 6, to yield slightly more stable configurations in some instances. However, the cumulative local mode stretching force constants of implicitly solvated Mg2+ show the six-coordinated cluster to be the most stable. These results show that such intrinsic bond strength measures for Mg–O and HBs offer an effective way for determining the coordination number of hydrated magnesium ion clusters.

In this work, we investigated the strength of the H- and H2 interaction with the Fe atom of a [NiFe] hydrogenase mimic, and how this interaction can be modulated by changing the Fe ligand in trans-position relative to H- and H2 . We used as a quantitative measure of bond strength local vibrational force constants derived from the Konkoli–Cremer local mode analysis, complemented by the topological analysis of the electronic density and the natural bond orbital analysis. Seventeen different ligands were investigated utilizing density functional theory calculations, including σ -donor ligands such as CH3- , C2H5- , NH3 , and H2O , π -donor ligands such as Cl- , F- , and OH- , and σ -donor/ π -acceptor ligands such as CN- and CO. According to the local mode analysis, Fe–H interactions are strengthened by σ -donor or π -donor ligands and weakened by σ -donor/ π -acceptor ligands. In contrast, the H–H bond of H2 is weakened by σ -donor or π -donor ligands and strengthened by σ -donor/ π -acceptor ligands. We also present a new metal–ligand electronic parameter (MLEP) for Fe–H ligands which can be generally applied to evaluate the Fe–H bond strength in iron complexes and iron hydrides. These results form a valuable basis for future [NiFe] hydrogenase-based catalyst design and fine tuning, as well as for the development of efficient biomimetic catalysts for H2 generation.

Experimentalists recently characterized the difficulty in isolating gaseous histidine in its neutral form. To understand the factors which stabilize neutral histidine, the intrinsic nature of the intramolecular hydrogen bonding networks in the four most stable histidine conformers was investigated via density functional theory combined with the local vibrational mode analysis originally introduced by Konkoli and Cremer, quantum theory of atoms in molecules, non-covalent interaction analysis, and natural bond orbital population analysis. Our results show a positive correlation between intramolecular hydrogen bond strength and structural stability, where the presence of the O-H⋯Nα bond type is a major factor.

Laboratory X-ray powder diffraction was used to solve and refine the crystal structures of appended guest molecules within the pores of metal–organic frameworks (MOFs). Herein, we report the crystal structure of 1-propanethiol adsorbed in the pores of Co 2 (dobdc) (dobdc 4– = 2,5-dioxido-1,4-benzenedicarboxylate, MOF-74). Soaking the activated MOF in neat 1-propanethiol resulted in the formation of 1-propanethiol–Co 2 (dobdc). The thiol appendant MOF maintained the crystal symmetry, with a rhombohedral space group R- 3 and unit-cell parameters a = 25.9597(9) Å, c = 6.8623(5) Å, and V = 4005.0(4) Å 3 . As expected, the thiol sulfur formed a bond with the open cobalt metal site. The alkane chain was directed toward the center of the pore, participating in numerous van der Waals weak interactions with neighboring molecules. For the final Rietveld refinement, soft restrains were applied using bond distances obtained by periodic density functional theory (DFT) geometry optimization.

Copyright © International Centre for Diffraction Data 20202020International Centre for Diffraction DataLaboratory X-ray powder diffraction was used to solve and refine the crystal structures of appended guest molecules within the pores of metal–organic frameworks (MOFs). Herein, we report the crystal structure of 1-propanethiol adsorbed in the pores of Co2(dobdc) (dobdc4– = 2,5-dioxido-1,4-benzenedicarboxylate, MOF-74). Soaking the activated MOF in neat 1-propanethiol resulted in the formation of 1-propanethiol–Co2(dobdc). The thiol appendant MOF maintained the crystal symmetry, with a rhombohedral space group R-3 and unit-cell parameters a = 25.9597(9) Å, c = 6.8623(5) Å, and V = 4005.0(4) Å3. As expected, the thiol sulfur formed a bond with the open cobalt metal site. The alkane chain was directed toward the center of the pore, participating in numerous van der Waals weak interactions with neighboring molecules. For the final Rietveld refinement, soft restrains were applied using bond distances obtained by periodic density functional theory (DFT) geometry optimization.

In this report, three versions of SCF/KS-DFT orbital optimization are described and benchmarked. The methods are a modified version of the geometry version of the direct inversion in the iterative subspace approach (which we call r-GDIIS), the modified restricted step rational function optimization method (RS-RFO), and the novel subspace gradient enhanced Kriging method, combined with restricted variance optimization (S-GEK/RVO). The modifications introduced are aimed to improve the robustness and computational scaling of the procedures. In particular, the subspace approach in S-GEK/RVO allows the application to SCF/KS-DFT optimization of a machine technique that has proved successful in geometry optimizations. The performance of the three methods is benchmarked for a large number of small to medium-sized organic molecules, at equilibrium structures and close to a transition state, and a second set of molecules containing closed- and open-shell transition metals. The results indicate the importance of the resetting technique in boosting the performance of the r-GDIIS procedure. Moreover, it is demonstrated that already at the inception of the subspace version of GEK to optimize SCF wave functions, it displays superior and robust convergence properties as compared to standard state-of-the-art SCF/KS-DFT optimization methods.