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The central moiety of porphyrins is shown to control the charge state of the inner complex and links it by covalent interaction to the peripheral substituents. This link, which enables the versatile functions of porphyrins, is not picked up in the established, reduced four orbital picture [Gouterman, J. Mol. Spectrosc., 1961, 6, 138]. X-ray absorption spectroscopy at the N K-edge with density functional theory approaches gives access to the full electronic structure, in particular the π* manifold beyond the Gouterman orbitals. Systematic variation of the central moiety highlights two linked, governing trends: The ionicity of the porphyrin center increases from the aminic N–H to N–Cu to N–Zn to N–Mg to the iminic N:. At the same time covalency with peripheral substituents increases and compensates the buildup of high charge density at the coordinated nitrogen sites., The porphyrin center is shown to control both the covalency of the central complex and π hybridization with peripheral substituents.

Exploring high-efficiency catalysts for the electrochemical hydrogen evolution reaction (HER) in alkaline environments is attractive but remains challenging. Here we report a coordination regulation strategy to tune the atomic structure of Ru cluster catalysts supported on Ti3C2Tx MXene (Ru-Ti3C2Tx) for the HER. We identify that the coordination number (CN) of Ru-Ru could be slightly regulated from 2.1 to 2.8 by adjusting the synthesized temperature so as to achieve an optimal catalytic configuration. The Ru-Ti3C2Tx with a CNRu-Ru of 2.8 exhibits the best catalytic activity with a low overpotential of 96 mV at 10 mA cm-2 and a mass activity about 11.5 times greater than the commercial Pt/C catalyst. Density functional theory calculations demonstrated that the small Ru clusters have a stronger covalent interaction with Ti3C2Tx support leading to an optimal ΔGH* value. This work opens up a general avenue to modulate the coordination environment of catalysts for the HER.

Among the various carbon capture and storage (CCS) technologies, the direct air capture (DAC) of CO2 by engineered chemical reactions on suitable adsorbents has attained more attention in recent times. Guanidine (G) is one of such promising adsorbent molecules for CO2 capture. Recently Lee et al. (Phys. Chem. Chem. Phys., 2015, 17, 10925–10933) reported an interaction energy (ΔE) of −5.5 kcal mol−1 for the G⋯CO2 complex at the CCSD(T)/CBS level, which was one of the best non-covalent interactions observed for CO2 among several functional molecules. Here we show that the non-covalent G⋯CO2 complex can transform to a strongly interacting G–CO2 covalent complex under the influence of multiple molecules of G and CO2. The study, conducted at M06-2X/6-311++G** level density functional theory, shows ΔE = −5.7 kcal mol−1 for G⋯CO2 with an N⋯C distance of 2.688 A while almost a five-fold increase in ΔE (−27.5 kcal mol−1) is observed for the (G–CO2)8 cluster wherein the N–C distance is 1.444 A. All the (G–CO2)n clusters (n = 2–10) show a strong N–CO2 covalent interaction with the N–C distance gradually decreasing from 1.479 A for n = 2 to 1.444 A for n = 8 ≅ 9, 10. The N–CO2 bonding gives (G+)–(CO2−) zwitterion character for G–CO2 and the charge-separated units preferred a cyclic arrangement in (G–CO2)n clusters due to the support of three strong intermolecular O⋯HN hydrogen bonds from every CO2. The O⋯HN interaction is also enhanced with an increase in the size of the cluster up to n = 8. The high ΔE is attributed to the large cooperativity associated with the N–CO2 and O⋯HN interactions. The quantum theory of atoms in molecules (QTAIM) analysis confirms the nature and strength of such interactions, and finds that the total interaction energy is directly related to the sum of the electron density at the bond critical points of N–CO2 and O⋯HN interactions. Further, molecular electrostatic potential analysis shows that the cyclic cluster is stabilized due to the delocalization of charges accumulated on the (G+)–(CO2−) zwitterion via multiple O⋯HN interactions. The cyclic (G–CO2)n cluster formation is a highly exergonic process, which reveals the high CO2 adsorption capability of guanidine.

The typical electron-deficiency of the boron element renders fascinating architectures and chemical bonding to boron-based nanoclusters. We theoretically predict two di-Ca-doped boron clusters, B6Ca2 (D2h, 1Ag) and B8Ca2 (D8h, 1A1g), and both adopt interesting inverse sandwich geometries, showing an elongated D2h B6 or perfectly planar D8h B8 ring being sandwiched by two Ca atoms only, respectively. Natural atomic charge analyses indicate that the Ca atoms donate nearly all the 4s electrons to the B6 (or B8) ring, forming [Ca]2+[B6]4−[Ca]2+ and [Ca]2+[B8]4−[Ca]2+ charge transfer complexes. The interaction between the two Ca atoms and the boron rings is governed by robust electrostatics albeit by weaker B–Ca covalent interaction. Chemical bonding analyses show that B6Ca2 has 4σ and 6π delocalized electrons on the elongated B6 ring, leading to a conflicting aromatic system. B8Ca2, possessing 6σ and 6π delocalized electrons on the B8 ring, is doubly aromatic. Additionally, the B6Ca2 and B8Ca2 clusters show noticeable structural and electronic transmutation relative to their equivalent electronic B6Be2 and B8Mg2 clusters, respectively. The intrinsic reasons behind the transmutations are elucidated via in-depth bonding analyses.

Bent metallocene dichlorides (Cp2MCl2, M = Ti, Mo, Nb, …) have found interest as anti-cancer drugs in order to overcome the drawbacks associated with platinum-based therapeutics. However, they suffer from poor hydrolytic stability at physiological pH. A promising approach to improve their hydrolytic stability is the formation of host-guest complexes with macrocyclic structures, such as cyclodextrins. In this work, we utilized nanoelectrospray ionization tandem mass spectrometry to probe the interaction of titanocene dichloride with β-cyclodextrin. Unlike the non-covalent binding of phenylalanine and oxaliplatin to β-cyclodextrin, the mixture of titanocene and β-cyclodextrin led to signals assigned as [βCD + Cp2Ti–H]+, indicating a covalent character of the interaction. This finding is supported by titanated cyclodextrin fragment ions occurring from collisional activation. Employing di- and trimethylated β-cyclodextrins as hosts enabled the elucidation of the influence of the cyclodextrin hydroxy groups on the interaction with guest structures. Masking of the hydroxy groups was found to impair the covalent interaction and enabling the encapsulation of the guest structure within the hydrophobic cavity of the cyclodextrin. Findings are further supported by breakdown curves obtained by gas-phase dissociation of the various complexes.

In the process of spent fuel reprocessing, it is highly difficult to extract transplutonium elements from adjacent actinides. A deep understanding of the electronic structure of transplutonium complexes is essential for development of steady ligands for in-group separation of transplutonium actinides. In this work, we have systematically explored the potential in-group separation ability of transplutonium elements of typical quadridentate N-donor ligands (phenanthroline-derived bis-triazine, BTPhen derivatives) through quasi-relativistic density functional theory (DFT). Our calculations demonstrate that ligands with electron-donating groups have stronger coordination abilities, and the substitutions of Br and phenol at the 4-position of the 1,10-phenanthroline have a higher effect on the ligand than those at the 5-position. Bonding analysis indicates that the covalent interaction of An3+ complexes becomes stronger from Am to Cf apart from Cm, which is because the energy of the 5f orbital gradually decreases and becomes energy-degenerate with the 2p orbitals of ligands. The most negative values of binding energies indicate the higher stability of Cf3+ complexes, in line with the larger covalency in the Cf-L bonds compared with An-L (An = Am, Cm, Bk). In addition, electron-donating group phenol can enhance the covalent interaction between ligands and heavy actinides. Consequently, the extraction ability of ligands with electron-donating substituents for heavy actinides is generally stronger than other ligands. Nevertheless, these ligands exhibit diverse separation abilities to in-group actinide recovery. Therefore, the enhancement of covalency does not necessarily lead to the improvement of separation ability, which may be caused by different extraction abilities. Compared with the tetradentate N, O-donor ligands (2,9-diamide-1,10-phenanthrolinel, DAPhen derivatives), species with BTPhen ligands display stronger covalent interaction and higher extraction capacity. In terms of in-group separation ability, the BTPhen ligands seem to have advantages in separation of californium from curium, while the DAPhen ligands possess stronger abilities to separate americium from curium. These results may afford some afflatus for the development of effective agents for in-group separation of transplutonium elements.

In this paper, first-principles molecular dynamics simulations are applied to study the ionic structure and electronic properties of KF-NaF-AlF3 system. The results show that the main forms of complex ion groups are [AlF4]−, [AlF5]2− and [AlF6]3−. With KF concentration increasing, the covalent interaction between Al F ions first increases and then decreases, resulting in the increase of Al F coordination number and then decreases. The calculation results of Raman spectra on [AlF4]−, [AlF5]2− and [AlF6]3− are close to the experimental values, which indicates FPMD is applicable to similar molten salt systems.

Density functional theory (DFT) computation was carried out to investigate the crystal, molecular and electronic structures of high energy crystal [2,2′-bi(1,3,4-oxadiazole)]-5,5′-dinitramide (BODN) with the pressure 0–120 GPa. The relaxed crystal structure by the GGA/PBE-TS functional matches well with the experimental data at ambient pressure condition. With the intensifying of pressure, the lattice parameters, volumes, bond lengths, H-bond energies, atomic charges, bond populations, band gaps and density of states of crystal BODN change gently. Under the pressure of 48, 104, and 107 GPa, three pressure-induced transformations occurred. The intramolecular six membered rings pose strong affect in stabilizing systems in the pressure range 0–120 GPa. Between O1 and H2 atoms, the H-bond interaction transforms into covalent interaction under the circumstance of 48 GPa. At 104 GPa, structural transformation occurs with the distortion of the intramolecular six membered ring. In addition, O1⋅⋅⋅H2 and O2⋅⋅⋅H1 have the largest H-bond energies in comparison with the others. When the pressure reaches 107 GPa, the H-bond O1⋅⋅⋅H2 is formed again with the deformation and non-coplanarity of two oxadiazoles in crystal BODN. The electrons can be moved easily based on the density of states and energy bands under high pressure. Helpful information will be conveyed by this work in the field of further analysis connected the pressure effect on molecular transformations.

Previously, a universal relation for the energy and length of homopolar covalent bond has been derived with the use of the theory of generalized charges, which represents an asymptotic approximation for interatomic forces of the quantum-statistical model of a multicomponent electron gas. The article discusses the new implications of the theory, obtained to describe the donor-acceptor bond. The bond energy includes the contribution of the donor atom characteristic of a homopolar bond and the Coulomb interaction of the atoms, with allowance for the probability of fixation of the bond electrons on the acceptor. Regularities for the donor-acceptor bond length and energy have been discovered. In particular, for the particular case realized in hydrides, expressions are obtained for the length and bond energy versus the atomic number of the acceptor.

The self-recognition and self-assembly of biomolecules are spontaneous processes that occur in Nature and allow the formation of ordered structures, at the nanoscale or even at the macroscale, under thermodynamic and kinetic equilibrium as a consequence of specific and local interactions. In particular, peptides and peptidomimetics play an elected role, as they may allow a rational approach to elucidate biological mechanisms to develop new drugs, biomaterials, catalysts, or semiconductors. The forces that rule self-recognition and self-assembly processes are weak interactions, such as hydrogen bonding, electrostatic attractions, and van der Waals forces, and they underlie the formation of the secondary structure (e.g., α-helix, β-sheet, polyproline II helix), which plays a key role in all biological processes. Here, we present recent and significant examples whereby design was successfully applied to attain the desired structural motifs toward function. These studies are important to understand the main interactions ruling the biological processes and the onset of many pathologies. The types of secondary structure adopted by peptides during self-assembly have a fundamental importance not only on the type of nano- or macro-structure formed but also on the properties of biomaterials, such as the types of interaction, encapsulation, non-covalent interaction, or covalent interaction, which are ultimately useful for applications in drug delivery.

This review describes the mechanism of non-covalent/covalent interaction of whey protein-pectin (WPP) complexes, including electrostatic interaction, steric hindrance, cross-linking and Maillard reaction. The interaction between whey protein and pectin determines the form of the complex in the system, i.e. co-dissolution, precipitation, separation, complex coacervation and compounding. The interaction of WPP is affected by environmental conditions and its own properties, including several factors such as pH, polymer concentration and ratio, temperature, and ionic strength. In addition, the functional properties of WPP complexes are discussed through illustrative examples. The complexes with good emulsification, heat stability, gelling properties and biological activity have promising application prospects. WPP complexes have been widely studied for application in food colloidal systems, including protein beverages, delivery systems for bioactive substances, fat substitutes and food preservation films/coatings. The understanding of the interaction and functional properties of WPP complexes provides theoretical support for the improvement and design of new food colloidal systems.

Exploring the different mechanisms involved in the application of actinide is necessary to obtain a more comprehensive understanding of actinide science. In this study, the mechanisms of gas-phase Np and Pu atoms dissociating NH3 molecules forming Neptunimine and Plutonimine complexes were systematically investigated using different approaches of density functional theory. A new dehydrogenation channel was discovered. The results reveal that the intermediates HAn-NH2 are the lowest energy in the overall reaction, and the direct planar evolution dehydrogenations are the lowest energy reaction path. Besides, the mechanism of the initial complexation process is discussed on the electron localization function, atoms-in-molecules, atomic dipole moment corrected Hirshfeld atomic charges, and electron density difference analysis. The results indicate that An-N in complex I exhibits a very weak covalent interaction, and it comes down to pulling the original dipole moment of the NH3 molecule and stretched between An atom and three H atoms. Graphical abstract.

Covalent binding of G protein-coupled receptors by small molecules is a useful approach for better understanding of the structure and function of these proteins. We designed, synthesized and characterized a series of 6 potential covalent ligands for the histamine H3 receptor (H3R). Starting from a 2-amino-pyrimidine scaffold, optimization of anchor moiety and warhead followed by fine-tuning of the required reactivity via scaffold hopping resulted in the isothiocyanate H3R ligand 44. It shows high reactivity toward glutathione combined with appropriate stability in water and reacts selectively with the cysteine sidechain in a model nonapeptide equipped with nucleophilic residues. The covalent interaction of 44 with H3R was validated with washout experiments and leads to inverse agonism on H3R. Irreversible binder 44 (VUF15662) may serve as a useful tool compound to stabilize the inactive H3R conformation and to study the consequences of prolonged inhibition of the H3R.

A series of functionalized N-alkylimidazolium based ionic liquids (ImILs) were designed, through anion (carboxylates and halogenated) and cation (N-alkyl side chains) structural modifications, and studied as potential sorbents for CO2 . The sorption capacities of as prepared bare ImILs could be enhanced from 0.20 to 0.60 molar fraction by variation of cation-anion-CO2 and IL-CO2 -water interaction. By combining NMR spectroscopy with molecular dynamics simulations, a good description of interactions between ImIL and CO2 can be obtained. Three types of CO2 sorption modes have been evidenced depending on the structure of the ImIL ion pair: Physisorption, formation of bicarbonate, and covalent interaction through the nucleophilic addition of CO2 to the cation or anion. The highest CO2 sorption capacity was observed with the ImIL containing the 1-n-butyl-3-methylimidazolium cation associated with the carboxylate anions (succinate and malonate). This study provides helpful clues for better understanding the structure-activity relationship of this class of materials and the ion pair influence on CO2 capture.

In this work, halogen bonding interactions in the complexes of two new nitroxide radicals, which contain both a halogen-bond-donor group and an electron-spin-resonance-active radical unit, were investigated using density functional theory calculations. For comparison, the corresponding hydrogen-bonded complexes were also examined. Halogen bonds in these systems are predicted to be linear and much stronger than hydrogen bonds. To further understand the nature of these interactions, many theoretical methods, such as atoms in molecules, noncovalent interaction index, localized orbital locator, energy decomposition analysis, electron density difference, and electron spin densities, were employed. Compared with hydrogen bonds, halogen bonds have more open shell and covalent interaction components. Particularly, the formation of halogen bonds changes the ratio of different conformations, leading to spin density shift on certain atoms. The results reported herein will assist in the design of new functional probes for the detection of halogen bonding.

The present article discusses a theoretical possibility of a novel class of sandwiched organometallic compounds based on the group 13 analogues of N-Heterocyclic carbene. The structure, stability and bonding pattern of the Fe(NHE)2 complexes (where E = B, Al and Ga) have been studied using density functional theory. The bond dissociation energy and binding energy are comparable with ferrocene. In addition, the topological study of the electron density describes the partial covalent interaction of the ligands with the metal atom. The synthetic possibility of such complexes with bulky substituent at the nitrogen center are addressed as well.

The B12 responding btuB riboswitch is a short, non-coding RNA sequence involved in the gene-regulation of an outer membrane B12-transport protein in E. coli. This RNA is characterized by its selective high-affinity binding to coenzyme B12 and by the structural rearrangement it undergoes upon this interaction. Due to their involvement in (mostly) bacterial gene regulation, the btuB riboswitch as well as the further about twenty known classes of riboswitches received much attention in recent years. In case of the btuB riboswitch, the light sensitivity of its ligand, coenzyme B12, poses one of the greater challenges for its investigation. Vitamin B12 derivatives carrying a cyanide-bridged platinum(II) moiety offer an ideal strategy for the design of light stable coenzyme B12 analogs. Developed by Alberto and coworkers in 2005 these conjugates provide the possibility to coordinate an additional nucleobase making them potential coenzyme B12 mimics. However, although these derivatives show a high structural similarity to coenzyme B12, their functionality might differ and offers the opportunity to develop new classes of antibiotic agents. Especially the platinum(II)-complex could interact with RNA in an unexpected way, which is the main question addressed in the work presented here. We characterized the binding of three vitamin B12-platinum(II) complexes to two different RNAs: the B12-specific btuB riboswitch and the short RNA D1-45, which is a non-B12-binder. cisPt(II)VitB12+ (1) and enPt(II)VitB12+ (2) carry both a labile chloride ligand at the platinum(II) moiety whereas dienPt(II)VitB122+ (3), that carries no labile chloride ligand anymore, can be considered chemically inert under the applied conditions. Complexes 1 and 2 covalently bind to both RNAs as monitored by band-shift assays. In the case of the short D1-45 the shifted bands are well separated and were further analyzed by MALDI-MS proving the covalent interaction. Complex 3 is unable to covalently bind any of the two RNAs, which proves the general stability of the Pt(II) complex. However, the presence of this moiety has a dramatic influence on the binding property towards the B12-sensing riboswitch, as was observed in in-line probing assays by comparison to the natural ligand coenzyme B12.

Th@C76 has been studied by density functional theory combined with statistical mechanics calculations. The results reveal that Th@Td(19151)-C76 satisfying the isolated pentagon rule possesses the lowest energy. Nevertheless, considering the enthalpy–entropy interplay, Th@C1(17418)-C76 with one pair of adjacent pentagons is thermodynamically favorable at elevated temperatures, which is reported for the first time. The bonding critical points in both isomers were analyzed to disclose covalent interactions between the inner Th and cages. In addition, the Wiberg bond orders of M–C bonding in different endohedral metallofullerenes (EMFs) were investigated to prove stronger covalent interactions of Th–C in Th-based EMFs.

In this paper, a joint strategy was proposed to investigate the microscopic origin of the second-harmonic-generation (SHG) response in nonpolar ABCO3F compounds. The SHG coefficients of ABCO3F were evaluated using finite-field and sum-over-states methods. The tendency of the obtained SHG tensors is in good agreement with the powder SHG response. The atomic contribution was investigated using variation of the atomic charges and bandwidth of occupied atomic states. The results show that oxygen states play a key role in determining the SHG response, and the neighboring divalent cations exert a indirect influence via covalent interaction. The bidentate bonding pattern is beneficial to obtaining a largely enhanced SHG response.

The structural and chemical states of the second-row impurities in liquid lead-bismuth eutectic (LBE) are studied by first-principles molecular dynamics. First, several structural quantities such as the number of first-neighboring atoms and the LBE-impurity-LBE characteristic angle are obtained to determine the impurity-LBE local structure. Next, the impurity charge states and the electronic density of states are analyzed to reveal the chemical states of the impurities in the liquid LBE. It is observed that for the majority of impurities the 2p-6p interaction specifies the local structure around the impurity as well as the chemical state of the impurity. The anisotropy in the 2p-6p covalent interaction causes the tetrahedron-wise structures for B, C, N, and O, and the ionic interaction is relatively strong for Li and F. The change in the interaction scheme over the second-row impurities can be explained from the downward shift of the 2s and 2p orbital energy levels as the atomic number increases. Further, some impurities indicate interaction preferences for either Pb or Bi. These findings can assist the understanding and prediction of the behavior of impurity atoms in liquid LBE.

The efficacy of B40 borospherene to act as a host for noble gas atoms is explored via density functional theory based computations. Although the Ng@B40 complexes are thermochemically unstable with respect to dissociation into free Ng and B40, it does not rule out their viability as all the systems possess a high activation free energy barrier (84.7-206.3 kcal mol-1). Therefore, once they are formed, it is hard to take out the Ng atom. Two Ng atoms can also be incorporated within B40 for the lighter Ng atoms (He and Ne). In fact, the destabilization offered by the encapsulation of one and two He atoms and one Ne atom inside B40 is significantly less than that in experimentally synthesized He@C20H20, highlighting their greater possibility for synthesis. Although Ar2 and Kr2 encapsulated B40 systems are very much destabilized by the repulsive interaction between Ng2 and B40, an inspection of the bonding situation reveals that the confinement can even induce some degree of covalent interaction between two otherwise non-bonded Ng atoms. Ng atoms transfer electrons towards B40 which is smaller for lighter Ng atoms and gradually increases along He to Rn. Even if the electrostatic interaction between Ng and B40 is the most predominant term in these systems, the extent of the orbital interaction is also considerable. However, the very large Pauli repulsion counterbalances the attractive interaction, eventually turning the interaction repulsive in nature. Ng@B40 also shows dynamical behaviour involving continuous exchange between hexagonal and heptagonal holes, similar to the host cage, as understood from the very little variation in the activation barrier because of the Ng encapsulation. Furthermore, sandwich complexes like [(η5-C5Me5)Fe(η6-B40)]+ and [(η5-C5Me5)Fe(η7-B40)]+ are noted to be viable with the latter being slightly more stable than the former. The encapsulation of Xe slightly improves the dissociation energy associated with the decomposition into Xe@B40 and [Fe(η5-C5Me5)]+ compared to that in the bare one.

The synthesis and characterization of Pt(II) (1 and 2) and Ru(II) arene (3 and 4) or polypyridine (5 and 6) complexes is described. With the aim of having a functional group to form bioconjugates, one uncoordinated carboxyl group has been introduced in all complexes. Some of the complexes were selected for their potential in photodynamic therapy (PDT). The molecular structures of complexes 2 and 5, as well as that of the sodium salt of the 4'-(4-carboxyphenyl)-2,2':6',2″-terpyridine ligand (cptpy), were determined by X-ray diffraction. Different techniques were used to evaluate the binding capacity to model DNA molecules, and MTT cytotoxicity assays were performed against four cell lines. Compounds 3, 4, and 5 showed little tendency to bind to DNA and exhibited poor biological activity. Compound 2 behaves as bonded to DNA probably through a covalent interaction, although its cytotoxicity was very low. Compound 1 and possibly 6, both of which contain a cptpy ligand, were able to intercalate with DNA, but toxicity was not observed for 6. However, compound 1 was active in all cell lines tested. Clonogenic assays and apoptosis induction studies were also performed on the PC-3 line for 1. The photodynamic behavior for complexes 1, 5, and 6 indicated that their nuclease activity was enhanced after irradiation at λ = 447 nm. The cell viability was significantly reduced only in the case of 5. The different behavior in the absence or presence of light makes complex 5 a potential prodrug of interest in PDT. Molecular docking studies followed by molecular dynamics simulations for 1 and the counterpart without the carboxyl group confirmed the experimental data that pointed to an intercalation mechanism. The cytotoxicity of 1 and the potential of 5 in PDT make them good candidates for subsequent conjugation, through the carboxyl group, to "selected peptides" which could facilitate the selective vectorization of the complex toward receptors that are overexpressed in neoplastic cell lines.

Graphene oxide was an effective supporting material for immobilizing a dioxomolybdenum Schiff base complex via covalent interaction. The large surface of graphene oxide plays important roles to obt...

The σ-hole tetrel bond in pyrazine/1,4-dicyanobenzene⋅⋅⋅TH3 F (T=C and Si) and the π-hole tetrel bond in pyrazine/1,4-dicyanobenzene⋅⋅⋅F2 TO have been compared. The π-hole tetrel bond is stronger than the corresponding σ-hole tetrel bond, with a larger interaction energy, shorter binding contact, greater electron density, and bigger charge transfer. Pyrazine forms a more stable tetrel-bonded complex than 1,4-dicyanobenzene even though the nitrogen atom in the former has a smaller negative electrostatic potential than the latter. An interesting cooperative effect was found when anion-π and tetrel-bond interactions coexisted in the same multicomponent complex of X- ⋅⋅⋅pyrazine/1,4-dicyanobenzene⋅⋅⋅TH3 F/F2 TO (X=F, Cl, and Br). Both interactions displayed a positive cooperative effect, as shown by the larger interaction energies, shorter binding separations, and greater electron densities. The enhancement in the tetrel bond is dependent on the strength of the anion-π interaction and it becomes larger in the order Br

Nitrogen binding in open structure body-centered-cubic (bcc) metals was studied to understand atomic nitrogen absorption in these systems in order to assess their feasibility as membrane materials for nitrogen separation and subsequent reactivity for ammonia production. For a metallic membrane to be feasible for this application, it must exhibit adequate solubility that allows for sufficient permeability. Using first-principle calculations it was demonstrated that nitrogen is too soluble in pure vanadium due to its strong binding in this metal (i.e., binding energy of −2.80 eV/atom), but through alloying, the binding energy may be tuned to mimic the weaker hydrogen binding exhibited in Group V metals, leading to high permeability. In particular, alloys of Ru and Mo were investigated. The Bader charge and density of states analyses showed that nitrogen binding in pure V is enhanced by the electrostatic and covalent interaction between nitrogen and surrounding V atoms, whereas repulsive interaction with an ...

The central objective of this work is to revisit the development of the widely used Lewis acidity/basicity scales and seek possibilities for their eventual unification. The primary focus is on hydrogen bonding interactions which are dealt with the estimation of hydrogen-bond-donor (HBD) and hydrogen-bond-acceptor (HBA) capacity of the compounds. The developments are made by having in mind their implementation in a thermodynamic equation-of-state framework for the reliable estimation of all basic thermodynamic quantities of compounds over a broad range of external conditions. Gutmann’s donor and acceptor numbers, the Hard–Soft Acid and Base principle, Drago’s electrostatic and covalent interaction parameters E and C , the LFER/LSER acidity and basicity, α and β ( A and B ), parameters, the Hansen partial hydrogen – bonding solubility parameters and Klamt’s quantum-chemically derived hydrogen – bonding cosmoments are all combined with the recent partial solvation parameter (PSP) approach in an effort to develop a unified hydrogen bonding scale. The challenges and the perspectives of this unification are critically discussed.

The encapsulation of nucleobases inside CB7 has gained prominence due to its use as anticancer and antiviral drugs. With this respect, the nonconvalent interactions existing in the nucleobases encapsulated inside the CB7 cavity have been analyzed employing the dispersion corrected density functional theory. The CBn cavity has the ability to encapsulate two guest nucleobases molecules when they are aligned in parallel configuration. The computed association energy using the two- and three-body correction method computed at B3LYP-D3 level is close to the experimental estimate. The use of dispersion corrected DFs is essential to identify the correct binding energies. The solvation energy plays a vital role in the estimation of association energy. QTAIM analysis shows that the Laplacian of the charge density (∇2ρ) is negative and the presence of covalent interaction between the guest and host molecule. The NCI-RDG isosurface shows the presence of noncovalent intermolecular interactions such as van der Waals a...

In this paper, we report two main-group p-block metal complexes [Pb(LH)(NIC)L]·H2O 1 and [Pb(LH)(NIC)(Ac)]·H2O 2 (HNIC = Nicotinic acid, LH = 2-(4-methoxyphenyl)-1H-imidazo[4,5-f][1,10] phenanthroline) by hydrothermal processing and structural characterization by elemental analysis and single-crystal X-ray diffraction. The results reveal that the coordination preferences of pH play a critical role in the framework construction of the two complexes. Meanwhile, natural bond orbital (NBO) analysis was performed by the PBE0/LANL2DZ method in gaussian 09 Program. The calculation results show the obvious covalent interaction between the coordinated atoms and metal ions.

Transition metal hydrides play important roles in organometallic catalysis and synthetic reactions. Metallocenes niobium or tantalum hydride derivatives show high reactivities with variety of main group 13 Lewis acids. In this work, the nature of MH···B/Al interaction between Cp2M(L)H(M = V, Nb, and Ta) and BF3/AlF3 in 1:1 Lewis acid–base adducts as well as the influences of different types of ligands on the interactions is investigated. The results show that in Cp2M(L)H···BF3/AlF3, the MH···B interaction belongs to covalent interaction, and MH···Al shows partly covalent character. The covalent character of MH···B/Al bonds decreases with the increasing period of metal atom. The strength of MH···B/Al interaction is related to the type of metal atom (M) and ligand (L) in Cp2M(L)H, and the influences of L are larger than those of M. For the same M, the strength of MH···B/Al bonds is mainly influenced by the type of ligand, and they increase in the sequence of L = CO, C2H4, and P(CH3)3. The formation of Cp2M(L)H···BF3/AlF3 increases the polarity of M–H bond of Cp2M(L)H.

Noble gases (Ngs) are the least reactive elements in the periodic table towards chemical bond formation when compared with other elements because of their completely filled valence electronic configuration. Very often, extreme conditions like low temperatures, high pressures and very reactive reagents are required for them to form meaningful chemical bonds with other elements. In this personal account, we summarize our works to date on Ng complexes where we attempted to theoretically predict viable Ng complexes having strong bonding to synthesize them under close to ambient conditions. Our works cover three different types of Ng complexes, viz., non-insertion of NgXY type, insertion of XNgY type and Ng encapsulated cage complexes where X and Y can represent any atom or group of atoms. While the first category of Ng complexes can be thermochemically stable at a certain temperature depending on the strength of the Ng-X bond, the latter two categories are kinetically stable, and therefore, their viability and the corresponding conditions depend on the size of the activation barrier associated with the release of Ng atom(s). Our major focus was devoted to understand the bonding situation in these complexes by employing the available state-of-the-art theoretic tools like natural bond orbital, electron density, and energy decomposition analyses in combination with the natural orbital for chemical valence theory. Intriguingly, these three types of complexes represent three different types of bonding scenarios. In NgXY, the strength of the donor-acceptor Ng→XY interaction depends on the polarizing power of binding the X center to draw the rather rigid electron density of Ng towards itself, and sometimes involvement of such orbitals becomes large enough, particularly for heavier Ng elements, to consider them as covalent bonds. On the other hand, in most of the XNgY cases, Ng forms an electron-shared covalent bond with X while interacting electrostatically with Y representing itself as [XNg]+Y−. Nevertheless, in some of the rare cases like NCNgNSi, both the C-Ng and Ng-N bonds can be represented as electron-shared covalent bonds. On the other hand, a cage host is an excellent moiety to examine the limits that can be pushed to attain bonding between two Ng atoms (even for He) at high pressure. The confinement effect by a small cage-like B12N12 can even induce some covalent interaction within two He atoms in the He2@B12N12 complex.

Tetrel bonds, the purportedly non-covalent interaction between a molecule that contains an atom of group 14 and an anion or (more generally) an atom or molecule with lone electron pairs, are under intense scrutiny. In this work, we perform an interacting quantum atoms (IQA) analysis of several simple complexes formed between an electrophilic fragment (A) (CH3F, CH4, CO2, CS2, SiO2, SiH3F, SiH4, GeH3F, GeO2, and GeH4) and an electron-pair-rich system (B) (NCH, NCO-, OCN-, F-, Br-, CN-, CO, CS, Kr, NC-, NH3, OC, OH2, SH-, and N3-) at the aug-cc-pvtz coupled cluster singles and doubles (CCSD) level of calculation. The binding energy ( E bind AB ) is separated into intrafragment and inter-fragment components, and the latter in turn split into classical and covalent contributions. It is shown that the three terms are important in determining E bind AB , with absolute values that increase in passing from electrophilic fragments containing C, Ge, and Si. The degree of covalency between A and B is measured through the real space bond order known as the delocalization index ( &delta, AB ). Finally, a good linear correlation is found between &delta, AB and E xc AB , the exchange correlation (xc) or covalent contribution to E bind AB .

High Resolution Transmission Electron Microscopy (HR TEM) is used to identify the size, shape, and interface structure of platinum nanoparticles and carbon support of a fuel cell catalyst. Using these insights, models accessible to quantum chemical methods are designed in order to rationalize the observed features. Thus, basal plane and prism face models of the carbon black material are considered, interacting with Pt clusters of sizes up to 1 nm. Particular attention is paid to the electronic structure of the carbon support, namely, the radical character of graphene zig-zag edges. The results show that a stronger interaction is found when the nanoparticle is at the zig-zag edge of a basal plane due to the combination of dispersion interaction with the support structure and covalent interaction with carbon atoms at the edge. In this case, a distortion of both the Pt nanoparticle and the carbon support is observed, which corresponds to the observations from the HR TEM investigation. Furthermore, the analysis of the charge transfer upon interaction and the influence of the potential on the charge states and structure is carried out on our model systems. In all cases, a clear charge transfer is observed from the carbon support to the Pt nanoparticle. Finally, we show that changing the potential not only can change the charge state of the system but can also affect the nature of the interaction between Pt nanoparticles and carbon supports.

Halogen bonds have received increasing interest in non-covalent interactions. Recently, a new kind of non-covalent interaction, spodium bond, was proposed to refer to a net attractive interaction between any element of group 12 and electron rich atoms. Due to strong relativistic effect, Hg is much different from the other group 12 elements, which prefers more linear coordination. Thus, we theoretically studied the model of HgCl2⋯L (where L = ClR, SR2, PR3 families) to explore the nature of the linear coordinated spodium bonds. Analyses of electrostatic potential surfaces, together with ELF, LOL, and chemical bonding analyses, suggest the presence of covalent interaction. Complexes with nitrogen, oxygen, and fluorine donors result in more coulombic component, whereas others are dominated by covalent interaction, indicating coexistence of coulombic and covalent interaction. Besides, covalent interaction is significantly stronger with phosphorus donor. This model can provide intriguing perspectives for future weak intermolecular interactions studies.

A theoretical calculation has been performed for the ternary complexes XCl∙∙∙FH∙∙∙F− (X = CCH, CN, OH, NC, and F) and the corresponding binary complexes. The halogen bond in the dyad is very weak with the interaction energy less than 2.5 kcal/mol. Interestingly, the halogen bond gets a big enhancement when it combines with a very strong hydrogen bond in FH∙∙∙F−, and the largest interaction energy is up to ∼25.6 kcal/mol in FCl∙∙∙FH∙∙∙F−. The enhancement of halogen bond not only results in a larger elongation of X–Cl bond and a bigger redshift of the bond stretch vibration but also makes the blue-shifting halogen bond in NCCl∙∙∙FH be a red-shifting one in NCCl∙∙∙FH∙∙∙F−. The halogen bond belongs to a purely close-shell interaction in the dyad, while it becomes a partially covalent interaction in XCl∙∙∙FH∙∙∙F− (X = OH, NC, and F) with negative energy density. In FH∙∙∙F−, the proton is shared between the two F atoms, however, this proton transfers towards the F− end in XCl∙∙∙FH∙∙∙F−.

We report a rare example of the preparation of HKUST-1 metal-organic framework nanoplatelets through a step-by-step seeding procedure. Sodium ion exchanged zirconium phosphate, NaZrP, nanoplatelets were judiciously selected as support for layer-by-layer (LBL) assembly of Cu(II) and benzene-1,3,5-tricarboxylic acid (H3BTC) linkers. The first layer of Cu(II) is attached to the surface of zirconium phosphate through covalent interaction. The successive LBL growth of HKUST-1 film is then realized by soaking the NaZrP nanoplatelets in ethanolic solutions of cupric acetate and H3BTC, respectively. The amount of assembled HKUST-1 can be readily controlled by varying the number of growth cycles, which was characterized by powder X-ray diffraction and gas adsorption analyses. The successful construction of HKUST-1 on NaZrP was also supported by its catalytic performance for the oxidation of cyclohexene.

The molecular structures of a series of uranyl (UO2(2+)) complexes in which the uranium center is equatorially coordinated by a first-row species are calculated at the density functional theory level and binding energies deduced. The resulting electronic structures are investigated using a variety of density-based analysis techniques in order to quantify the degree of covalency in the equatorial bonds. It is shown that a consideration of the properties of both the one-electron and electron-pair densities is required to understand and rationalize the variation in axial bonding effected by equatorial complexation. Strong correlations are found between density-based measures of the covalency and equatorial binding energies, implying a stabilizing effect due to covalent interaction, and it is proposed that uranyl U-Oyl stretching vibrational frequencies can serve as an experimental probe of equatorial covalency.

The geometric and electronic structures of bis(cyclopentadienyl)cerium compounds of the type Cp2CeZ (Z = CH2, CH−, NH, O, F+) are analyzed paying special attention to the terminal metal–ligand multiple bonding in the Ce Z units. Complete active space self-consistent field calculations were performed, followed by unitary transformations in the active orbital space in order to monitor the weights of the leading configurations, as well as the Ce and Z character of the orbitals. It is shown that all compounds, except the closed-shell Ce(IV) complex Cp2CeF+, have an open-shell singlet ground state and the 4f orbitals are important for their electronic structure. In case of Z = CH2, CH− the singlet ground state consists to more than 90% of the Ce f π 1 Z p π 1 configuration when using nearly pure cerium 4f and carbon 2p orbitals of the Z group, implying Ce(III) systems. In contrast, the systems containing Z = NH, O revealed a more mixed Ce(III)/Ce(IV) ground state wavefunction. The interactions of the active orbitals were characterized by calculating the expectation values of the charge fluctuation operator and the local spin operator. The results are evaluated by comparison with the values achieved by stretching the covalent bond of a H2 molecule. The CH2 and the CH− complexes show, besides a Ce Z σ bond, a quite weak covalent Ce f Z p orbital interaction in π symmetry, while the other two complexes (Z = NH, O) exhibit a stronger covalent interaction with a noticeable ionic character because of the higher electronegativities of nitrogen and oxygen.

Using the density functional theory calculations, we explored the electronic, and magnetic properties of Au and Pt adsorbed MoS2 systems. We examined the binding of some gas molecules (CO, CO2, NH3, NO, NO2, and O3) on these noble metal adsorbed structures. Stability analysis based on binding energy calculations indicate that both Au-adsorbed and Pt-adsorbed MoS2 monolayers are energetically stable and can be considered as a promising nanostructure media for gas sensing and capturing. The binding strength of gas molecules over the Au-adsorbed structures was found to be higher than that over the non-adsorbed systems, being attributed to their higher adsorption energies. Band structure calculations reveal a metallic characteristics for Au-adsorbed MoS2 systems, while Pt-adsorbed ones show semiconductor nature. The substantial overlaps of the local density of states of the Au atom and substrate’s interacting atoms are an indication of a covalent interaction and consequently chemisorption process at the interface.

The development of a new method for covalent immobilization of biomolecules on the surface of bare gold nanoparticles (AuNPs) by using crosslinking agents in one step is presented. A very compatible biopolymer such as chitosan has been used as a target molecule to probe the viability of the proposed methodology. Click chemistry, based on biocompatible reactions and coupling with 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide allow to analyze the covalent interactions between the metal nanoparticles and the biopolymer. Spectra deconvolution technique and Zeta potential measurements confirm the covalent interaction. The present study allows to quantify the proportion of AuNPs covalently adhered to the chitosan, which depends on the solution pH. The obtained results indicates that covalent interactions can be increased up to 25% in relation to total system interactions, which are mostly electrostatic. The proposed strategy opens up a new pathway for biomedical applications because the control of the chemical linkage can be directly performed on the nanoparticle surface without using any molecular intermediate, which may improve the encapsulation efficiency on drug delivery therapies.

Oxidation mechanism of Pyrene (Py) by OH radicals is studied in two possible reactions by density functional theory (DFT) at the M06-2X/6-311++G(2df,2p) theoretical level. OH-addition reaction in compare with the H-abstraction reaction is a more favored pathway in the gas-phase. Hence, the studies continued for investigating the kinetic aspects of the OH-addition reaction. Furthermore, Rice-Ramsperger-Kassel-Marcus (RRKM) theory as well to calculate the kinetic rate constant for the initial steps and investigate the effects of diversity in pressure and temperature. Pathway 2 (attack onto C2 carbon atom) and following that forming of the related complex which has a lower energy barrier is the most efficient process. The good agreement with the available experimental data reveals that a two-step reaction scheme prevails. These ratios also show a decrease in the regioselectivity by increasing the temperatures and decreasing the pressures. The Pyrene lifetime in the atmospheric condition with OH is estimated ∼5.5 days. An atom in Molecules theory (AIM) in critical point and natural bond orbital (NBO) analysis use to describe the nature of covalent interaction, and is as a confirmation of DFT. The NBO analysis shows a decrease in the HOMO-LUMO gaps to form the stable complex, which is parallel with the decreasing of activation energy.

The potential energy surface of [Cu(H2O)n]2+ clusters with n = 12, 16, and 18 was explored by using a modified version of the simulated annealing method. Such exploration was carried out by using the PM7 semiempirical method to obtain around 100,000 isomers, which provide candidates to be optimized with PBE0-D3, M06-2X, and BHLYP exchange-correlation functionals coupled with the 6–311++G** basis set. These methods based on the Kohn-Sham approach delivered isomers with coordination numbers of 4, 5, and 6. The analysis used to obtain coordination numbers was based on geometrical parameters and the quantum theory of atoms in molecules (QTAIM) approach. Our methodology found only one isomer with fourfold coordination and its probabilities to appear in these clusters are quite small for high temperatures. The procedure used in this article predicts important populations of fivefold and sixfold coordination clusters, in fact, the fivefold coordination dominates for PBE0-D3 and BHLYP methods, although the sixfold coordination starts to be important when the number of water molecules is increased. The nature of axial and equatorial contacts is discussed in the context of the QTAIM and the noncovalent interaction index (NCI), which gives a clear classification of such orientations. Also, these methods suggest a partial covalent interaction between the Cu2+ and water molecules in both positions; equatorial and axial.

As one of the most widely used chemical concepts whose origin can be traced back to Lewis theory of bonding a century ago, a covalent bond involves sharing one or more pairs of electrons between atoms. A strong covalent interaction (SCI) is such a covalent bond that two or more electron pairs are shared, yielding a double, triple, quadruple, or even higher bond order. Despite its ubiquity and usefulness, a robust and generally applicable approach to accurately identify strong covalent interactions and determine their bond orders is still lacking. In this work, an SCI index is proposed from density functional theory using the Pauli energy, which is the contribution of the Pauli exclusion principle to the kinetic energy. Illustrative examples from organic, inorganic, and organometallic systems were provided. Its close relationship with the electron localization function (ELF) was elucidated. Both ELF and SCI generate similar results. Two complexes with a quintuple metal-metal bond have been confirmed. A stronger than quintuple bond has been showcased. This work should provide a robust approach to determine bond orders for strong covalent interactions in complex systems, pinpoint the physiochemical origin of strong covalent interactions, and rationalize the usefulness of both SCI and ELF. These tools should be able to be applied to other systems in different fields to effectively appreciate strong covalent interactions.

Cisplatin is an efficient anticancer drug, but its effects are often lost after several chemotherapy cycles, showing important secondary effects. For these reasons, new anticancer agents, with different coordination properties and mechanisms of action, are needed. Here we describe the reaction of 2-phenylaniline with cis-[PtCl2(dmso)(2)] and sodium acetate to afford a cycloplatinated compound 2 and the synthesis and some biological studies of 3-6 (two neutral and two ionic compounds): [PtCl(C-N)(L)], C-N cycloplatinated 2-phenylaniline with L = PPh3(3) or P(4-FC6H4)(3) (4) and [Pt(C-N)(L-L)]Cl with L-L = Ph2PCH2CH2Ph2(5) or (C6F5)(2)PCH2-CH2(C6F5)(2) (6). Ionic platinacycles 5 and 6 show a greater antiproliferative activity than that of cisplatin in human lung, breast, and colon cancer cell lines (A-549, MDA-MB-231 and MCF-7, and HCT-116), a remarkable result given the fact that they do not show covalent interaction with DNA. 5 and 6 have also been found able to oxidize NADH by a catalytic process prod- oducing H2O2 as ROS. The activity of these complexes to generate ROS seems to be the key factor to explain their potent anticancer activity; it should be noted that platinum(II) complexes showing biocatalytic activity for hydride transfer from NADH have not been described so far. Ionic complex 6 shows low affinity to some target proteins; the presence of perfluoroaromatic rings seems to hinder its interaction with some biomolecules.

Theoretical investigation is performed on LnSi 6 − /LnSi 6 clusters to find their stable structures and explain experimental photoelectron (PE) spectra. The calculation is done by quasi-relativistic density functional (DF) theory at scalar level. The ground state geometry of LnSi 6 − is found to be either C 5v or C 2v , according to 4f configuration, while the neutral clusters all prefer C 2v symmetry. Covalent interaction between Ln(5d) and Si(3p) helps stabilize the molecules. The experimental PE spectra are simulated and explained. LnSi 6 − /LnSi 6 (Ln = Eu, Yb) clusters have 4f-character peaks in their spectra.

The interaction of BN- and BP-doped graphene nanoflakes with some representative neutral molecules and anions (H2O, HF, SH−, CH3O−, BO2−, F−) has been studied through density functional theory (DFT) calculations. The neutral molecules remain physisorbed whereas all the anions but one remains chemisorbed. Thermodynamically, most of the studied systems are found to be stable. Conceptual DFT-based reactivity descriptors were employed in order to provide rationale behind such observation. The nature of interactions in cases of the anions is predominantly of covalent type whereas the same for neutral molecules is of non-covalent type. The electrostatic and orbital interactions play important roles in stabilising the absorbed moieties. The kinetic stability of the absorbed moieties is confirmed through an atom-centred density matrix propagation simulation at 298 K temperature up to 500 fs. All the studied systems show excellent kinetic stability and remain absorbed up to 500 fs exhibiting rich vibrational and r...

The knowledge of chemical bonding for actinide fluoride compounds is essential to understand and predict the physical and chemical behaviour of actinide elements in fluoride molten salt. In this work, the bonding nature of actinide tetrafluorides AnF(4) (An = Th-Cm) is investigated by using scalar relativistic density functional theory. Bond order analyses show relatively stronger An-F bonds for An = U-Np and weaker ones for An = Th, Am, and Cm. Despite the dominant ionic character of An-F bonds, a considerable covalent interaction is indicated by the overlap integral value of F 2p and actinide 5f, 6d orbitals. Both natural population analyses and electron density analyses show that An-F covalency rises initially before reducing in the latter systems with the maximum at Np and Pu and the obviously strong ionic bonding character in An = Th, Am, and Cm. Compared to AnCp(4) (Cp = (5)-C5H5) reported in the literature, our study on AnF(4) suggests a much more prominent actinide-ligand covalent interaction. And the roles of orbital overlap and near-degeneracy in driving covalency are discussed.

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The urotensin-II receptor (UTR) is a class A GPCR that predominantly binds to the pleiotropic cyclic peptide urotensin-II (U-II). U-II is constrained by a disulfide bridge that induces a β-turn structure and binds pseudo-irreversibly to UTR and is believed to result in a structural rearrangement of the receptor. However, it is not well understood how U-II binds pseudo-irreversibly and the nature of the reorganization of the receptor that results in G-protein activation. Here we describe a series of U-II peptidomimetics incorporating a non-reducible disulfide bond structural surrogate to investigate the feasibility that native U-II binds to the G protein-coupled receptor through disulfide bond shuffling as a mechanism of covalent interaction. Disubstituted 1,2,3-triazoles were designed with the aid of computational modeling as a non-reducible mimic of the disulfide bridge (Cys5–Cys10) in U-II. Solid phase synthesis using CuAAC or RuAAC as the key macrocyclisation step provided four analogues of U-II(4–11) incorporating either a 1,5-triazole bridge (5, 6) or 1,4-triazole bridge (9, 10). Biological evaluation of compounds 5, 6, 9 and 10 was achieved using in vitro [125I]UII binding and [Ca2+]i assays at recombinant human UTR. Compounds 5 and 6 demonstrated high affinity (KD ∼ 10 nM) for the UTR and were also shown to bind reversibly as predicted and activate the UTR to increase [Ca2+]i. Importantly, our results provide new insight into the mechanism of covalent binding of U-II with the UTR.

Infrared spectra of matrix isolated dibridged Si(μ-H)2MH2 and tribridged Si(μ-H)3MH molecules (M = Zr and Hf) were observed following the laser-ablated metal atom reactions with SiH4 during condensation in excess argon and neon, but only the latter species was observed with titanium. Assignments of the major vibrational modes, which included terminal MH, MH2 and hydrogen bridge Si–H–M stretching modes, were confirmed by the appropriate SiD4 isotopic shifts and density functional vibrational frequency calculations (B3LYP and BPW91). The Si–H–M hydrogen bridge bond is calculated as weak covalent interaction and compared with the C–H···M agostic interaction in terms of electron localization function (ELF) analysis and noncovalent interaction index (NCI) calculations. Furthermore, the different products of Ti, Zr, and Hf reactions with SiH4 are discussed in detail.

We analyze the effects of covalent interactions in Ni 2p3d resonant inelastic X ray scattering RIXS spectra from aqueous Ni2 ions and find that the relative RIXS intensities of ligand to metal charge transfer final states with respect to the ligand field final states reflect the covalent mixing between Ni 3d and water orbitals. Specifically, the experimental intensity ratio at the Ni L3 edge allows to determine that the Ni 3d orbitals have on average 5.5 of water character. We propose that 2p3d RIXS at the Ni L3 edge can be utilized to quantify covalency in Ni complexes without the use of external references or simulations