Bond Critical Points Research Articles

The effect of second coordination sphere interactions on the magnetic anisotropy of transition metals.

In the study of mononuclear transition metal single molecule magnets (SMMs), extensive research has concentrated on identifying optimal coordination geometries around the central metal ion to enhance SMM properties. However, the role of non-covalent interactions in the second coordination sphere has been relatively underexplored. Here, we study the impact of non-covalent Cl⋯H interactions on the magnetic anisotropy of the central Co(II) ion in the distorted axially compressed octahedral complex CoCl2(tu)4 (1) (tu = SC(NH2)2). By performing cantilever torque magnetometry on 1, the orientation of the magnetic easy axis is found to deviate by almost 40° from the axial Co-Cl bond. Theoretical modelling on structural modifications of the structure of 1, quantifies how the distance between the Cl ligand and the nearest H-atom significantly influences the orientation of the magnetic easy axis and the D-value. Experimental chemical bonding analysis based on multipole modelling of synchrotron X-ray diffraction data on 1 reveal that the nearby H-atoms polarize the electron density of the Cl-ligands. This polarization results in reduced electron density at the axial positions on the Co octahedra, explaining the calculated increase in the magnitude of the D-value, when the H-atoms are moved away from Cl in silico. Topological analysis of theoretical electron densities on modified structures of 1 corroborates an increase in the electron density at the Co-Cl bond critical point, as the nearby H-atoms are moved further from Cl. These findings demonstrate the significant influence that non-covalent interactions have on the magnetic anisotropy of mononuclear transition metals and opens the possibility of utilizing these interactions in the design of transition metal based SMMs.

From 'halogen' to 'tetrel' bonds: matrix isolation IR spectroscopic and quantum mechanical studies of the effect of central atom substitution in donor tetrahalogens on binary complex formation with formic acid.

Binary complex formation between silicon tetrachloride (SiCl4) and formic acid (FA) has been observed in an argon matrix environment. Such complex formation manifests as spectral shifts in signature vibrations of the latter, namely the νCO, νC-O and νO-H vibrations. Quantum chemical calculations reveal that the most stable conformers of the complex involve predominantly the tetrel bond, which has been defined in existing literature as a variant of the "σ-hole" interactions. Here, regions of positive electrostatic potential on the tetrahedral face of SiCl4 act as electrophilic centers (σ-hole) to which the nucleophilic carbonyl group of FA is able to bind. Atoms-in-molecules analysis predicts a bond critical point along the non-covalent contact between the tetrel atom Si and the carbonyl oxygen on FA, corroborating the presence of the tetrel bond. The hyperconjugative interaction parameters at the binding interface obtained from Natural Bond Orbital (NBO) analysis are also consistent with such observations. Although apparently similar to SiCl4, there are noticeable differences in the binding preferences of the lower homologue carbon tetrachloride (CCl4). The binary complexes of the latter with the same FA acceptor molecule have been previously shown to involve halogen bonded, rather than tetrel bonded interactions (Banerjee and Bhattacharya, Spectrochim. Acta Mol. and Biomol. Spectrosc., 2021, 250, 119355). Such variations in the nature of non-covalent interactions of these tetrahalogens are attributed to differences in the distribution of electronic charge density surrounding the central tetrel atom, as obtained from mappings of their electrostatic potential surfaces. Our combined experimental and theoretical findings therefore provide direct evidence of the growing propensity of tetrel atoms to engage in tetrel bonding as we move lower down Group 14, and re-assert the reluctance of the smaller and more electronegative carbon atom to serve as a tetrel bond participant.

Influence of N-protonation on electronic properties of acridine derivatives by quantum crystallography.

Applications of 9-aminoacridine (9aa) and its derivatives span fields such as chemistry, biology, and medicine, including anticancer and antimicrobial activities. Protonation of such molecules can alter their bioavailability as weakly basic drugs like aminoacridines exhibit reduced solubility at high pH levels potentially limiting their effectiveness in patients with elevated gastric pH. In this study, we analyse the influence of protonation on the electronic characteristics of the molecular organic crystals of 9-aminoacridine. The application of quantum crystallography, including aspherical atom refinement, has enriched the depiction of electron density in the studied systems and non-covalent interactions, providing more details than previous studies. Our experimental results, combined with a topological analysis of the electron density and its Laplacian, provided detailed descriptions of how protonation changes the electron density distribution around the amine group and water molecule, concurrently decreasing the electron density at bond critical points of N/O-H bonds. Protonation also alters the molecular architecture of the systems under investigation. This is reflected in different proportions of the N⋯H and O⋯H intermolecular contacts for the neutral and protonated forms. Periodic DFT calculations of the cohesive energies of the crystal lattice, as well as computed interaction energies between molecules in the crystal, confirm that protonation stabilises the crystal structure due to a positive synergy between strong halogen and hydrogen bonds. Our findings highlight the potential of quantum crystallography in predicting crystal structure properties and point to its possible applications in developing new formulations for poorly soluble drugs.

Unravelling ionic liquid solvent effects for a non-polar Cope rearrangement reaction.

The impact of ionic liquids (ILs) on polar reactions is well recognised, however the impact of ILs on non-polar reactions is less well understood or explored. Pericyclic Cope rearrangements are highly concerted, exhibit minimal charge localisation and pass through an uncharged but well-defined transition state, and thus provide a good mechanism for exploring the impact of IL polarizability on chemical reactivity. Recently, a 10× rate enhancement has been observed for the Cope rearrangement of 3-phenyl-1,5-hexadiene in the IL 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C4C1im][NTf2] compared to benzene. In this work we undertake a DFT based computational study (B3LYP-D3BJ/6-311+G(d,p) and M06-2X-D3/6-311+G(d,p)) of the Cope rearrangement of 3-phenyl-1,5-hexadiene and 3-propyl-hexa-1,5-diene in molecular solvents (acetonitrile, benzene and ethanol) and the IL [C4C1im][NTf2] using the SMD solvation model. The impact of benzene and [C4C1im][NTf2] on the Cope rearrangement of 3-phenyl-1,5-hexadiene is studied in more detail and we provide insight into the reason for the rate enhancement in an IL. The volume of activation is evaluated and the potential impact of 'solvent pressure' is discussed. We identify two potential mechanisms for volume effects to contribute to the rate enhancement. Solvent association energies are evaluated at the DLNPO-CCSD(T) level. Specific solvent interactions are explored through atomic partial charge, molecular orbital and bond critical point analysis, as well as via non-colvalent interaction (NCI) plots, electrostatic potential (ESP) differences and density difference Δρ(r) plots. We find that the cation and anion together form an extensive van der Waals pocket in-which the transition state (TS) sits. Electron density within the TS is anisotropically polarised via a 'push-pull' effect due to the dual cation-anion nature of the IL, stabilising the TS relative to benzene. We also provide experimental evidence that these effects are generalisable to other ILs. Overall, our aim is to provide a deeper moleuclar level understanding of the impact of ILs on non-polar reactions.

Quantification of hydrogen bond energy based on equations using spectroscopic, structural, QTAIM-based, and NBO-based descriptors which calibrated by the molecular tailoring approach

ContextHydrogen bonds critically influence the structure and properties of both organic molecules and biomolecules, as well as supramolecular assemblies. For this reason, the development and elaboration of methods for quantitative assessment of hydrogen bond energy is an urgent challenge. In this study, using a large series of hydroxycarbonyl aliphatic compounds with the O‒H···O = C intramolecular hydrogen bond, a bank of hydrogen bond descriptors was created, including spectroscopic, structural, QTAIM-based, and NBO-based parameters. It was shown that the O‒H vibration frequency, OH chemical shift as the spectroscopic descriptors, the O···H hydrogen bond length, O···O distance, and O‒H covalent bond length as the structural descriptors, the electron density and its Laplacian, electron potential energy density in the hydrogen bond critical point, the electron density at the ring critical point as the QTAIM-based descriptors change in a correlated manner. The same correlation is found in change of the charge transfer energy through a hydrogen bond, the occupancy of the O‒H bond antibonding orbital, the Wiberg indices of the O···H hydrogen bond, and the O‒H covalent bond, as well as the polarization of the O‒H bond, which are the NBO-based descriptors. It was also recognized that the specified descriptors from the spectroscopic, structural, QTAIM-based, and NBO-based categories are functionally related to the values of intramolecular hydrogen bond energy, quantified via the molecular tailoring approach. This allowed one to obtain a system of equations for quantitative estimation of intramolecular hydrogen bond energy based on the spectroscopic, structural, QTAIM, and NBO descriptors, which makes such quantification more dependable and reliable.MethodsTo obtain the spectroscopic descriptors, the vibrational spectra and shielding constants were calculated using the GIAO method. Structural descriptors were obtained for the equilibrium geometry of molecules, calculated at the MP2(FC)/6–311 + + (2d,2p) level using the Gaussian 09 program. The QTAIM-based descriptors were calculated using the AIMAll program within the framework of the quantum theory “Atoms in Molecules.” The NBO-based descriptors were calculated using the NBO 3.1 program implemented into Gaussian 09. To quantify the energy of intramolecular hydrogen bonds, molecular fragmentation was used within the molecular tailoring approach.

Computational study of conductance through Cu, Ag, Au and Pt atomic chain contacts

Atomic size wires are basic devices of molecular electronics and a common model for simulation of transport properties of other molecular devices, where hypothetical semi-infinite equidistant atomic chains are considered as electrodes. In this work, structure of infinite linear Cu, Ag, Au and Pt atomic chains was studied at nonrelativistic, scalar and spin–orbit zeroth order relativistic approximation levels. Bonds in chains were characterized within Quantum Theory of “Atoms In Molecules” approach. Conductance through finite chains of six atom length between bulk leads for bias voltage range of 0.0–1.0 V was calculated within non-equilibrium Green’s function approach combined with density functional theory. Chain conductance at high bias voltages correlates with product of Jenkins’ metallicity and positively defined kinetic energy density at bond critical points of corresponding infinite atomic chains. Variation of number of atoms in finite Au and Pt chains showed weak “odd-even” oscillations of chain conductance at some bias voltages.

Silatranes: Relationship between the experimental Si ← N dative bond length and its calculated energy according to AIM analysis data

X-ray structures of a number of silatranes with Si ← N dative bonds of various lengths were analyzed using the AIM analysis method. The features of the effect of substituents at the silicon atom and in the silatranyl core on the length of the Si ← N dative bond have been established. The relationship between optimazed in the crystal length of the Si ← N dative bond and its calculated energy with a high correlation coefficient is obtained. A similar dependence was obtained for the electron density at the bond critical point of the Si ← N dative contact. The calculated value of the positive charge on silicon atoms is determined by the electronegative properties of the axial substituent.

N⋯H[sbnd]N versus O⋯H[sbnd]N intramolecular hydrogen bonding in E- and Z-isomers of para-substituted phenylhydrazones: Differential nature of the H-bonds and the exception of para-CN substituent

The present work demonstrates a computational investigation into the N⋯HN (E-isomer) and O⋯HN (Z-isomer) intramolecular H-bonding (IMHB) in a miscellany of para-substituted phenylhydrazone compounds. The application of resonance-assisted H-bonding theory to N⋯HN H-bonding systems, especially those involving an aromatic nucleus, has remained scarcely addressed. The results of NBO and QTAIM methods indicate that resonance-assistance from aromatic pyridyl nucleus leads to a stronger N⋯HN IMHB in the E-isomer in comparison to the O⋯HN IMHB in Z-isomer with the exception of para-CN substitution (Z-isomer) probably due to an extended conjugation. The results of QTAIM analyses reveal that the N⋯HN IMHB is described by a considerable degree of covalence (total electron density at bond critical point, Hc<0) as contrary to the predominantly electrostatic (Hc>0) interaction describing the O⋯HN H-bond in Z-isomer, with the exception of para-CN substitution showing a shared interaction. The existence of non-hydrogen bonding noncovalent interactions is also established.

Metal–organic supramolecular architecture of oxo-bridged molybdenum(VI) complexes: Synthesis, structural elucidation and Hirshfeld surface analysis

New Binuclear monooxo, Mo2O4L21(H2O)CHCl3 (1), tetranuclear tetraoxo, Mo4O8L41 (2) and binuclear dioxo, Mo2O4L22 (3) bridged molybdenum(VI) complexes have been synthesized using two diprotic tridentate ONS donor Schiff base ligands H2L1 and H2L2 (H2L1 = S-benzyl-β-N-(2-hydroxyphenyl) methylene dithiocarbazate and H2L2 = S-benzyl-β-N-(5‑bromo-2-hydroxyphenyl) methylene dithiocarbazate. All the three complexes have been characterized by elemental analyses and IR, UV–vis and 1H NMR spectroscopies and their crystal structures were solved by single crystal X-ray diffraction technique. Complexes (1) and (3) crystallized in triclinic space group P-1 and complex (2) in monoclinic space group P21/n. Complexes 1, 2 and 3 exhibit distorted octahedral geometry around Mo(VI) center. X-ray crystallography reveals that in the crystal packing of the complexes C–H···O, O–H···O, O–H···N, C–X···π (X = Br) and π···π stacking interactions cooperatively take part. A detailed analysis of Hirshfeld surfaces and fingerprint plots facilitates a comparison of intermolecular interactions which are crucial in building different supramolecular architectures of three molybdenum complexes. Crystal structure analysis supported with the Hirshfeld surface and fingerprint plots enabled the identification of the significant intermolecular interactions. The intermolecular interactions are further characterized by analyzing the topological parameters through Bader's theory of ‘atoms in molecule’ (QTAIM) along with the ‘non-covalent interaction’ (NCI) plot index. The investigation of topological parameters of electron density at the (3, −1) bond critical point classified the interactions as ‘closed-shell’ interactions.

Insights into the structural investigation of metal-complexes with 1,3-diamino-2-hydroxypropanetetraacetic acid: Inputs from X-ray and computational studies

A new 1,3-diamino-2-hydroxypropanetetraacetate copper complex (1) [{Cu(Hpdta)}{Cu(H2O)6}] has been synthesized and structurally characterized by single crystal X-ray diffraction and compared with a similar cobalt complex (2) of H4Hpdta (H4Hpdta = 1,3-diamino-2-hydroxypropanetetraacetic acid) retrieved from CSD (CSD ref code: TELBAN) with a detailed analysis of intermolecular interactions. X-ray crystallography reveals that both complexes are stabilized through C−H⋯O and O−H⋯O interactions generating different supramolecular networks. Detailed analysis of Hirshfeld surfaces and 2D fingerprint plot has been carried out for the title complexes to quantify the intermolecular interactions. Further, the noncovalent interactions are characterized through the Bader’s theory of ‘Atoms in Molecules’ (AIM) and noncovalent interaction (NCI) plot index. At the bond critical point (BCP), the electron density (ρBCP) and the Laplacian of electron density (∇2(ρBCP)) differ significantly for strong and weak noncovalent interactions. The dissociation energies are evaluated for validating the intermolecular interactions required to stabilize the complexes. The analysis of topological parameters extracted from AIM calculation characterized the interactions as closed-shell interactions.

Hydrogen storage on the lithium and sodium-decorated inorganic graphenylene

Efficient H2 storage is one of the keys to the energy transition toward global sustainability. Hydrogen energy sources on functionalized 2D materials by metals have been shown as promising alternatives for clean energy systems. In a particular way, we have demonstrated here that the inorganic graphenylene-like silicon carbide (IGP-SiC) weakly adsorbs H2. At the same time, the Li/Na decoration significantly enhances the H2 interaction, accommodating up to 48H2 molecules by a stronger physisorption. Also, scanning bond critical points (BCPs) confirms a great interaction between the Li(Na)@IGP-SiC systems and the hydrogen, a distinct scenario for the pristine IGP-SiC. Gravimetrically, hydrogen densities reach 8.27 wt% (Li) and 6.78 wt% (Na), exceeding the U.S. Department of Energy (5.6 wt%) benchmark. Regarding thermodynamic stability, the desorption temperatures at ambient conditions are suitable for hydrogen storage devices. Therefore, Li(Na)@IGP-SiC systems emerge as high-capacity hydrogen storage materials.

Transition between the Noncovalency and Covalency of σ-Hole Bonds.

The properties of the bond between a N-ligand and a Lewis acid containing a σ-hole are studied by quantum chemical methods. Interactions considered include pnicogen bonds involving SbX5, PX5, and PX3, where X represents any of the halogen atoms F, Cl, Br, or I. Also studied are the tetrel bonds of PbX4 and SiX4, as well as the chalcogen bond involving TeOX4. Both NH3 and NCH are applied as two possible bases of differing potency. Some of the bonds are very strong with interaction energies easily exceeding 25 kcal/mol and with AIM bond critical point densities much higher than 0.04 au, suggesting their classification as coordinate covalent bonds. The pentavalent SbX5 and PX5 fall into this category when combined with NH3, as does TeOX4. Although the tetrel bonds involving PbX4 are only slightly weaker, they are probably better viewed as a strong noncovalent bond on the cusp of covalency. Changing the internal bonding of hypervalent SbX5 to the more conventional SbX3 weakens the interaction to a classical noncovalent pnicogen bond. Reducing the base nucleophilicity from NH3 to NCH weakens the bonds so that they are clearly noncovalent.

Nanostructures of boron nitride: A promising nanocarrier for anti-cancer drug delivery

Within this study, we investigate the interaction of the hydroxyurea molecule with a boron nitride nanocone (BNC), a boron nitride nanosheet (BNS), and a boron nitride nanotube (BNT) as nano-structures for the purpose of drug delivery by performing DFT computations. DFT computations on the models under study are performed by considering gas and water phases. Based on the adhesion energy values, we obtain a stabilized complex of hydroxyurea and BNC, BNS and BNT in the gas and water phases. The negative values of adhesion energy demonstrate that the reaction is exothermic. Based on the results of the QTAIM, the electron density values in the bond critical points are positive and low in all hydroxyurea-bonding complexes. Based on the calculational results, there are weak interaction forces for the significant and efficient release of hydroxyurea from the carriers at target sites. The impact of molecular adhesion upon the electronic attributes of BNC, BNS and BNT is examined by investigating the density of states, and based on the results, BNC is nearer to the Fermi energy compared to BNS and BNT. The adhesion energy values are higher in the gaseous phase compared to the water phase, which indicates that the interaction of the molecule with BNC, BNS and BNT is stronger in the gaseous phase. The interaction of hydroxyurea with BN stronger than its interaction with BNS and BNT based on the adhesion energy values. Following the adhesion of hydroxyurea, ΔEg was – 1.56 eV, −0.16 eV, and −0.12 eV for BNC, BNS, and BNT, respectively, which showed the higher sensitivity of BNC compared to BNS and BNT. Based on the computations, BNC, BNS, and BNT can be used as a promising carrier for hydroxyurea.

The Theoretical Investigation by QTAIM Approach to Chemical Bonding of a Di-Rhenium Bis(Triphenylphosphine) Carbonyl Cluster Containing Sulfuric and Hydrido Bridge: [Re2(CO)6(μ-S)(μ-H)(PPh3)2

Scientists used the quantum theory of atoms in molecules (QTAIM) to calculate and interpret various electron density parameters for a di-rhenium bis(triphenylphosphine) carbonyl cluster containing sulfuric and hydrido bridge: [Re2(CO)6(μ-S)(μ-H)(PPh3)2]. They analyzed the bond critical points and compared them with data from previous organometallic system studies. The researchers were able to compare the topological processes of different atom-atom interactions based on these results.&#x0D; The calculations showed that there were no bond critical points or identical bond paths between Re-Re in the core of the cluster. The electron density distribution was affected by the position of bridging hydride and sulfur atoms coordinated to Re-Re, which significantly affected the bonds between these transition metal atoms. However, the calculations did confirm the presence of a 6c–8e bonding interaction delocalized over HRe2SP2 in the cluster.&#x0D; The scientists found that the Re-H and Re-S bonds in this cluster exhibited typical closed-shell interactions, with small values for ρ(b) and Laplacian ∇2ρ(b) above zero and small positive values for total energy density H(b). Similarly, the bond interactions between phosphine metal atoms and the C atoms of the phenyl ring ligands showed properties similar to open-shell interactions in the QTAIM classification.

QTAIM analysis for Metal - Metal and Metal- Non-metal Bonds in Tri-Osmium cluster

Electron density of the interaction of the compound's chemical bonding has been computed using topological analysis. The findings suggest that Os-Os, Os-N, and Os-H bonds have experienced bond critical points (BCP) with corresponding bonds paths (BP). The presence of N-C bridging atoms is significantly impacted by electron density of Os2-Os3 bond distribution therefore no critical point found and bond path. So, due to their positive electron density (b), negative laplacian 2(b), and positive the total energy density H(b) values, the Os-NC, Os-H, and Os-CO bonds all have transit closed-shell topological properties.

Enhancement of nonlinear optical properties of nanocarbon cluster C60 by aluminum doping

AbstractThe search for good nonlinear optical (NLO) materials is of utmost importance in laser technology and optical information science, making it a popular research topic in materials science. It is reported that the introduction of alkali metal Li can enhance the NLO properties of nanocarbon materials. Here, metal Al, which exhibits similar electron transfer characteristics to Li, was used for the first time to enhance the NLO properties of nanocarbon cluster C60, which possesses a large delocalized π structure and the highest yield in the fullerene family. Density functional theory calculations in combination with Boltzmann distribution showed that the most thermodynamically stable Al@Ih(1812)‐C60 exhibited good second‐order NLO properties, which originated from the noncentrosymmetry geometry and one extra delocalized electron on Ih(1812)‐C60 from the 3p shell of inner Al. Density of state analysis indicated that the molecular orbitals of Al@Ih(1812)‐C60 were primarily formed by Ih(1812)‐C60 with minimal Al participation, and the presence of Al always resulted in an antibonding orbital effect. Bond critical point and electron localization function analyses indicated almost no covalent interaction between Al and Ih(1812)‐C60. Exohedral functionalization was employed to further stabilize Al@Ih(1812)‐C60 with radical character, and the infrared spectrum was also analyzed in detail. This study has promising implications for expanding the potential applications of fullerenes in optical devices.

Halogen Bonding and/or Covalent Bond: Analogy of 3c-4e N···I···X (X = Cl, Br, I, and N) Interactions in Neutral, Cationic, and Anionic Complexes.

X-ray structural measurements and computational analysis demonstrated the similarity of the geometries and electronic structures of the X-I···N (X = Cl, Br, I, and N) bonding in strong halogen-bonded (HaB) complexes and in the anionic or cationic halonium ions. In particular, I···N bond lengths in the solid-state associations formed by strong HaB donors (e.g., I2, IBr, ICl, and N-iodosuccinimide) and acceptors (e.g., quinuclidine or pyridines) were in the same range of 2.3 ± 0.1 Å as those in the halonium ions [e.g., the bis(quinuclidine)iodonium cation or the 1,1'-iodanylbis(pyrrolidine-2,5-dione) anion]. In all cases, bond lengths were much closer to those of the N-I covalent bond than to the van der Waals separations of these atoms. The strong N···I bonding in the HaB complexes led to a substantial charge transfer, lengthening and weakening of the I···X bonds, and polarization of the HaB donors. As a result, the central iodine atoms in the strong HaB complexes bear partial positive charges akin to those in the halonium ions. The energies and Mayer bond orders for both N···I and I···X bonds in such associations are also comparable to those in the halonium ions. The similarity of the bonding in such complexes and in halonium ions was further supported by the analysis of electron densities and energies at bond critical (3, -1) points in the framework of the quantum theory of atoms in molecules and by the density overlap region indicator. Overall, all these data point out the analogy of the symmetric N···I···N bonding in the halonium ions and the asymmetric X···I···N bonding in the strong HaB complexes, as well as the weakly covalent character of these 3c-4e interactions.

Structural and computational insights into two trimethylenedipyridine co-crystals: Inputs from X-ray diffraction, Hirshfeld surface, PIXEL, QTAIM and NCI plots

Two trimethylenedipyridine co-crystals, [(TMDP)·(H2OBA)] (1) and [(TMDP)·(SUC)] (2) [TMDP = 4, 4′-trimethylenedipyridine, H2OBA = 4,4′-oxybis(benzoic acid), and SUC = succinic acid) were designed, synthesized and their single crystals were grown by slow evaporation technique. The grown crystals were characterized by elemental analysis and UV–Vis spectroscopic technique, and the structures of the grown crystals were elucidated using single-crystal X-ray diffraction analysis. Supramolecular assemblies of co-crystal (1) are stabilized through several intermolecular hydrogen bonds such as O‒H···N, C‒H···O, C‒H···π, as well as π···π interactions whereas for co-crystal (2) only intramolecular hydrogen bonding interaction, O‒H···N is responsible for stabilization of supramolecular network. Hirshfeld surfaces were used to gain additional insight into non-covalent interactions in molecular crystals, and 2D fingerprint plots provided a quantitative analysis of different non-covalent interactions in the crystal structures. The interaction energies of the molecular pairs, as well as the lattice energies of the crystal structures, have been studied using the PIXEL method. The nature and strength of the non-covalent interactions at their (3, –1) bond critical points (BCPs) have been explored using Bader's quantum theory of “Atoms in Molecules” (QTAIM). The non-covalent interactions were further characterized through the NCI plots.

Luminescent heterobimetallic Au(I)/Ag(I) complex stabilized by a unique acetylide fragment: A spectroscopic and computational study of aurophilic ‒ argentophilic interactions

This paper investigates the luminescence and metallophilic interaction in the heterobimetallic Au(I)-Ag(I) acetylide cluster [Au2Ag2(CCPh)4(PPh3)2]. Analysis using single-crystal X-rays shows short Au∙∙∙Ag separations (2.8806(3)-3.0212(3) Å), showing favorable closed shell (d10⋯d10) aurophilic-argentophilic interactions. DFT calculations and ELF analysis reveal electron localization between Au⋯Ag contacts and electron density dispersion around gold and silver ions. Quantum Theory of Atoms in Molecules (QTAIM) research reveals electron density at bond critical points (bcp) and assesses Au(I)⋯Ag(I) interaction strengths. Natural Bond Orbital (NBO) analysis identifies donor–acceptor characteristics of orbitals involved in aurophilic ‒ argentophilic interactions.

Actinide‐Pnictide Chemistry: A Uranium Primary Alkyl Stibinide and a Diuranium Hexaantimonide‐Tetralithium Zintl Cluster

AbstractStructurally characterised U−Sb bonds are rare. Here, the synthesis and characterisation of [U(TrenDMBS){Sb(H)C(H)(SiMe3)2}] (5, TrenDMBS=N(CH2CH2NSiMe2But)3) and [{U(TrenTIPS)}2{Sb3(μ6‐Li)(μ‐Li[THF]2)3Sb3}] (6, TrenTIPS=N(CH2CH2NSiPri3)3) are reported. Complex 5 is an unprecedented primary stibinide actinide complex and 6 can be formulated as containing a unique triple decker 20 skeletal‐electron distorted closo tricapped Zintl cluster (Sb3Li4Sb3)2− that is analogous to the D3h closo tricapped trigonal prism form of [Ge9]2−. Quantum chemical calculations emphasise polar U−Sb bonding in 5 and 6, and that viewing (Sb3Li4Sb3)2− as a single unit rather than two distinct but contiguous (Sb3)3− units, themselves unprecedented in molecular actinide chemistry, is valid due to the presence of three weak (Sb3)⋯(Sb3) (3, −1)‐bond critical points. Complexes 5 and 6 highlight the challenges of preparing polar U−Sb bonds and the underlying tendency for unpredictable cluster formation with Sb.