Azido-mediated intermolecular interactions of transition metal complexes.

The coordinated azido ligand has a variety of ways to establish intermolecular contacts whose nature is computationally analysed in this work on dimers of the [N3-Hg(CF3)] complex with different interactions involving only N⋯N contacts, or with an additional Hg⋯N contact. The applied tools include the molecular electrostatic map of the monomer, an energy decomposition analysis (EDA), a topological AIM analysis of the electron density and the study of NCI (non-covalent interactions) isosurfaces. The interactions between two azido ligands are found to be weakly stabilizing (by 0.2 to 2.7 kcal mol-1), topology-dependent and require dispersion forces to complement orbital and electrostatic stabilization. Those interactions are supplemented by the formation of simultaneous Hg⋯N secondary interactions by about -1 kcal mol-1, and by the ability of the monomer to simultaneously interact with several neighbours in the crystal structure.

Terminal Au-N and Au-O Units in Organometallic Frames.

Since gold is located well beyond the oxo wall, chemical species with terminal Au-N and Au-O units are extremely rare and limited to low coordination numbers. We report here that these unusual units can be trapped within a suitable organometallic frame. Thus, the terminal auronitrene and auroxyl derivatives [(CF3 )3 AuN]- and [(CF3 )3 AuO]- were identified as local minima by calculation. These open-shell, high-energy ions were experimentally detected by tandem mass spectrometry (MS2 ): They respectively arise by N2 or NO2 dissociation from the corresponding precursor species [(CF3 )3 Au(N3 )]- and [(CF3 )3 Au(ONO2 )]- in the gas phase. Together with the known fluoride derivative [(CF3 )3 AuF]- , they form an interesting series of isoleptic and alloelectronic complexes of the highly acidic organogold(iii) moiety (CF3 )3 Au with singly charged anions X- of the most electronegative elements (X=F, O, N). Ligand-field inversion in all these [(CF3 )3 AuX]- species results in the localization of unpaired electrons at the N and O atoms.

Alkali metal⋯methyl short contacts in aluminates: more than agostic interactions.

Knowing the nature and strength of noncovalent interactions is key to enhancing the synthetic methods and catalytic processes in which they are involved. We present herein the synthesis and characterization of a novel aluminium sodium oximate compound, followed by a comprehensive computational study of the sodium⋯methyl interaction that appears in its crystal structure. Our experimental results have been compared to a large set of structural data retrieved from the Cambridge Structural Database in order to assess the main geometrical preferences of these interactions. Moreover, representative model systems have been studied at the DFT level and the topology of their electron density analysed by means of QTAIM. Although alkali metal⋯methyl short contacts have been traditionally considered as agostic interactions, we have demonstrated here that the physical origin of the attraction relies on the electron-rich carbon atom bound to aluminium and its interaction with the cation.

Structure and Bonding of Halonium Compounds.

The geometrical parameters and the bonding in [D···X···D]+ halonium compounds, where D is a Lewis base with N as the donor atom and X is Cl, Br, or I, have been investigated through a combined structural and computational study. Cambridge Structural Database (CSD) searches have revealed linear and symmetrical [D···X···D]+ frameworks with neutral donors. By means of density functional theory (DFT), molecular electrostatic potential (MEP), and energy decomposition analyses (EDA) calculations, we have studied the effect of various halogen atoms (X) on the [D···X···D]+ framework, the effect of different nitrogen-donor groups (D) attached to an iodonium cation (X = I), and the influence of the electron density alteration on the [D···I···D]+ halonium bond by variation of the R substituents at the N-donor upon the symmetry, strength, and nature of the interaction. The physical origin of the interaction arises from a subtle interplay between electrostatic and orbital contributions (σ-hole bond). Interaction energies as high as 45 kcal/mol suggest that halonium bonds can be exploited for the development of novel halonium transfer agents, in asymmetric halofunctionalization or as building blocks in supramolecular chemistry.

Tetramethylammonium Cation: Directionality and Covalency in Its Interactions with Halide Ions.

The degree of interpenetration of the van der Waals crusts of two atoms, represented by a penetration index, is defined to better quantify the meaning of the nonbonding contact distances between two atoms, which should allow us to compare different atom pairs on the same footing. The structural trends of the intermolecular contacts between the tetramethylammonium cation (TMA) and halogen atoms are reviewed, and a computational study of model X···TMA ion pairs (X = F, Cl, Br, I, Au) is presented. The results disclose two energy minima, in each of which the anion simultaneously interacts with three hydrogen atoms. The bonding mechanisms in the two cases are discussed based on the results of the tools of the trade that provide a consistent picture in which a distribution of charges significantly varies not only around each different atom but is also strongly dependent on the distance to the central N atom. This behavior, together with some non-negligible covalent character of the interionic interaction, is not predicted from a single-molecular electrostatic potential map of the TMA cation.

Anion Binding Based on Hg3 Anticrowns as Multidentate Lewis Acidic Hosts.

We present herein a combined structural and computational analysis of the anion binding capabilities of perfluorinated polymercuramacrocycles. The Cambridge Structural Database (CSD) has been explored to find the coordination preference of these cyclic systems toward specific Lewis bases, both anionic and neutral. Interaction energies with different electron-rich species have been computed and further decomposed into chemically meaningful terms by means of energy decomposition analysis. Furthermore, we have investigated, by means of the natural resonance theory and natural bond orbital analyses how the orbitals involved in the interaction are key in determining the final geometry of the adduct. Finally, a generalization of the findings in terms of the molecular orbital theory has allowed us to understand the formation of the pseudo-octahedral second coordination sphere in linear Hg(II) complexes.

Delocalized Bonding in Li2X2 Rings: Probing the Limits of the Covalent and Ionic Bonding Models.

In spite of the highly ionic character of most lithium-element bonds, the bonding within Li2X2 rings presents similarities with that found in analogous transition metal systems. They obey simple framework electron counting rules that allow us to predict whether they will form a regular ring or a squeezed one with short Li-Li or X-X distances. A combined computational and structural database analysis discloses the orbital conditions that determine the framework electron counting rules. These systems probe the borderline between the covalent and ionic bonding models since, paradoxically, a non-negligible covalent contribution of the two Li atoms (formally Li+ ions in the ionic model) to the Li-X framework bonding favors them approaching each other within bonding distance.

A Multifunctional Dysprosium-Carboxylato 2D Metall-Organic Framework.

We report the microwave assisted synthesis of a bidimensional (2D) MOF of formula [Dy(MeCOO)(PhCOO)2 ]n (1) and its magnetically diluted analogue [La0.9 Dy0.1 (MeCOO)(PhCOO)2 ] (1 d). 1 is a 2D material with single-ion-magnet (SIM) behaviour and 1 d is a multifunctional, magnetic and luminescent 2D material. 1 can be exfoliated into stable nanosheets by sonication.

Intermolecular Carbonyl···Carbonyl Interactions in Transition-Metal Complexes.

We performed a comprehensive analysis of intermolecular carbonyl-carbonyl interactions in transition-metal complexes. Those interactions can be classified in two main types depending on the organometallic or organic nature of the donor carbonyl: M-CO···CO and R-CO···CO, respectively. By means of a combined structural and computational study we unraveled their geometrical features and strength. Moreover, electronic structure, natural bond orbitals, energy decomposition analysis, and quantum theory of atoms in molecules calculations were performed to try to understand their nature. Remarkably, we discovered that these carbonyl-carbonyl contacts have several features of the n → π* interaction. The charge transfer from an oxygen lone pair to an empty antibonding π orbital of the acceptor carbonyl is also accompanied by an electrostatic Oδ-···Cδ+ interaction. To the best of our knowledge this is the first report of an intermolecular n → π* interaction in metal complexes. These results might be significant, for instance, for the catalytic activation of carbonyl-containing small molecules with metal compounds or in the design of hybrid organic-inorganic materials, metal-organic frameworks, and other extended structures.

Understanding the Molecule-Electrode Interface for Molecular Spintronic Devices: A Computational and Experimental Study.

A triple-decker SYML-Dy2 single-molecule magnet (SMM) was synthetized and grafted onto the surface of iron oxide nanoparticles (IO-NPs) coated by an oleic acid monolayer. The magnetism of the SYML-Dy2 complex, and the hybrid system, NP-Dy2, were studied by a superconducting quantum interference device (SQUID). Density functional theory (DFT) calculations were carried out to study both the energetics of the interaction between SYML-Dy2 complex to the organic capping, and the assembly presented by the oleic acid chains.

Frustrated Lewis Trios and Long-Range Hole Interactions: A Combined Structural and Theoretical Study of LB-AX3 ⋠⋠⋠LB and LB⋠⋠⋠AX3 ⋠⋠⋠LB (A=B, Al, Ga, In) Systems.

Herein, we present a theoretical study of systems with long-range Lewis acid-base interactions that involve a triel center and two electron donor species. These intermediate situations, between LB-AX3 and LB-AX3 -LB (LB=Lewis base, A=group 13 element), exist experimentally and their interaction topologies obey precise geometrical rules, such that they show a marked directionality and a clear dependence between the two A-LB distances. Despite the relatively long acid⋅⋅⋅base distances of up to 4 Å, the interaction energies calculated at the M06-2X/aug-cc-pVTZ level are considerably large (5-25 kcal mol-1 ). A significant contribution to the interaction is related to the lone-pair-containing species that interacts with the π hole of the acid center, as revealed by the natural bond order, atoms in molecules, and molecular electrostatic potential analyses. Remarkably, this n(N)→σAl-N * interaction persists even at distances greater than the sum of the van der Waals radii.

The silane-methane dimer revisited: more than a dispersion-bound system?

We present here a comprehensive computational and theoretical analysis of the silane-methane dimer with the goal of understanding the origin of the interactions that hold it together and the factors that affect its strength. Several interaction topologies have been analysed and the associated interaction energies have been evaluated at the CCSD(T)/aug-cc-pVTZ level of theory. Next, substitution effects have been studied on several silane and methane derivatives. The molecular electrostatic potential (MEP) maps of the molecules involved in the interactions have been built to try to correlate the interaction energies with the maximum/minimum EP values (Vs). Furthermore, we have performed an energy decomposition analysis to gain deeper insight into the physical nature of the interactions and to unravel whether dispersion is the primary component of the attraction. Finally, we complete the theoretical analysis with the study of several experimental crystal structures in which there are silylmethyl short contacts.

Mercurophilic interactions: a theoretical study on the importance of ligands.

In this work, a theoretical analysis of intermolecular HgHg contacts in the presence of different ligands is presented. A survey of structural databases to explore the geometrical preferences among experimental structures presenting short Hg(ii)Hg(ii) contacts reveals the main interaction topologies depending on the nature of the ligand. A benchmark study of several dispersion corrected-density functional methods is carried out to determine the optimal computational methodology for the theoretical study of such interaction. This methodology is later used in the study of several dimers of dicoordinated mercury compounds [HgX2]2 (X = Cl, Br, I, CN, CH3, CF3, SiH3, SiMe3) as well as to evaluate the stability of different interacting topologies in such dimers. It is found that, whenever possible, two mercury-containing molecules will preferentially join through intermolecular HgX donor-acceptor interactions and only ligands devoid of atoms with lone pairs available for such interactions can form dimers attached predominantly via mercurophilic interactions.

Attractive PHHP interactions revealed by state-of-the-art ab initio calculations.

We report in this work a combined structural and state-of-the-art computational study of homopolar P-HH-P intermolecular contacts. Database surveys have shown the abundance of such surprisingly unexplored contacts, which are usually accompanied by other weak interactions in the solid state. By means of a detailed theoretical study utilizing SAPT(DFT), MP2, SCS-MP2, MP2C and CCSD(T) methods and both aug-cc-pVXZ and aug-cc-pCVXZ (X = D, T, Q, 5) basis sets as well as extrapolation to the CBS limit, we have shown that P-HH-P contacts are indeed attractive and considerably strong. SAPT(DFT) calculations have revealed the dispersive nature of the P-HH-P interaction with only minor contribution of the inductive term, whereas the first-order electrostatic term is clearly overbalanced by the first-order exchange energy. In general the computed interaction energies follow the trend: E ≈ E < E < E. Our results have also shown that the aug-cc-pVDZ (or aug-cc-pCVDZ) basis set is not yet well balanced and that the second-order dispersion energy term is the slowest converging among all SAPT(DFT) energy components. Compared to aug-cc-pVXZ basis sets, their core-correlation counterparts have a modest influence on all supermolecular interaction energies and a negligible influence on both the SAPT(DFT) interaction energy and its components.

Zinc-Zinc Double Bonds: A Theoretical Study.

While double bonds are known for transition metals of Groups 9 and 10 as well as for boron and p-block elements of Groups 14-16, Zn sits in a small region of the periodic table with no well-characterized double bonds. A qualitative reasoning indicates that zero-valent zinc has the potential to form Zn=Zn double bonds. A computational study in search for complexes that might showcase this new bond type is presented here.

Current-Driven Supramolecular Motor with In Situ Surface Chiral Directionality Switching.

Surface-supported molecular motors are nanomechanical devices of particular interest in terms of future nanoscale applications. However, the molecular motors realized so far consist of covalently bonded groups that cannot be reconfigured without undergoing a chemical reaction. Here we demonstrate that a platinum-porphyrin-based supramolecularly assembled dimer supported on a Au(111) surface can be rotated with high directionality using the tunneling current of a scanning tunneling microscope (STM). Rotational direction of this molecular motor is determined solely by the surface chirality of the dimer, and most importantly, the chirality can be inverted in situ through a process involving an intradimer rearrangement. Our result opens the way for the construction of complex molecular machines on a surface to mimic at a smaller scale versatile biological supramolecular motors.

Seeding molecular rotators on a passivated silicon surface.

Thermally activated rotation of single molecules adsorbed on a silicon-based surface between 77 and 150 K has been successfully achieved. This remarkable phenomenon relies on a nanoporous supramolecular network, which acts as a template to seed periodic molecule rotors on the surface. Thermal activation of rotation has been demonstrated by STM experiments and confirmed by theoretical calculations.