Venkatesha R. Hathwar

Nature of Cl···Cl Intermolecular Interactions via Experimental and Theoretical Charge Density Analysis: Correlation of Polar Flattening Effects with Geometry

The experimental charge density distribution in three compounds, 2-chloro-3-quinolinyl methanol, 2-chloro-3-hydroxypyridine, and 2-chloro-3-chloromethyl-8-methylquinoline, has been obtained using high-resolution X-ray diffraction data collected at 100 K based on the aspherical multipole modeling of electron density. These compounds represent type I (cis), type I (trans), and type II geometries, respectively, as defined for short Cl···Cl interactions. The experimental results are compared with the theoretical charge densities using theoretical structure factors obtained from a periodic quantum calculation at the B3LYP/6-31G** level. The topological features derived from the Baders theory of atoms in molecules (AIM) approach unequivocally suggest that both cis and trans type I geometries show decreased repulsion, whereas type II geometry is attractive based on the nature of polar flattening of the electron density around the Cl atom.

Extending the Supramolecular Synthon Based Fragment Approach (SBFA) for Transferability of Multipole Charge Density Parameters to Monofluorobenzoic Acids and their Cocrystals with Isonicotinamide: Importance of C–H···O, C–H···F, and F···F Intermolecular Regions

An extension of the supramolecular synthon-based fragment approach (SBFA) method for transferability of multipole charge density parameters to include weak supramolecular synthons is proposed. In particular, the SBFA method is applied to C-H···O, C-H···F, and F···F containing synthons. A high resolution charge density study has been performed on 4-fluorobenzoic acid to build a synthon library for C-H···F infinite chain interactions. Libraries for C-H···O and F···F synthons were taken from earlier work. The SBFA methodology was applied successfully to 2- and 3-fluorobenzoic acids, data sets for which were collected in a routine manner at 100 K, and the modularity of the synthons was demonstrated. Cocrystals of isonicotinamide with all three fluorobenzoic acids were also studied with the SBFA method. The topological analysis of inter- and intramolecular interaction regions was performed using Baders AIM approach. This study shows that the SBFA method is generally applicable to generate charge density maps using information from multiple intermolecular regions.

Quantitative analysis of intermolecular interactions in orthorhombic rubrene

A combination of single-crystal X-ray and neutron diffraction experiments are used to determine the electron density distribution in orthorhombic rubrene. The topology of electron density, NCI analysis and energetics of intermolecular interactions clearly demonstrate the presence of π⋯π stacking interactions in the crystalline state.

Contemporary X-ray electron-density studies using synchrotron radiation.

The use of synchrotron radiation for experimental electron-density determination during the last decade is reviewed. Possible future directions of this field are examined.

X-ray electron density investigation of chemical bonding in van der Waals materials

Van der Waals (vdW) solids have attracted great attention ever since the discovery of graphene, with the essential feature being the weak chemical bonding across the vdW gap. The nature of these weak interactions is decisive for many extraordinary properties, but it is a strong challenge for current theory to accurately model long-range electron correlations. Here we use synchrotron X-ray diffraction data to precisely determine the electron density in the archetypal vdW solid, TiS2, and compare the results with density functional theory calculations. Quantitative agreement is observed for the chemical bonding description in the covalent TiS2 slabs, but significant differences are identified for the interactions across the gap, with experiment revealing more electron deformation than theory. The present data provide an experimental benchmark for testing theoretical models of weak chemical bonding.Electron density in TiS2 is determined by synchrotron X-ray diffraction, which reveals significant differences between experimental data and theory for interlayer van der Waals interactions.

Characterization of fluorine‐centred `F…O' σ‐hole interactions in the solid state

In the current study, the crystal structure of 1-(3-nitrophenyl)-2,2,2-trifluoroethanone (A1) and (E)-4-((4-fluorophenyl) diazenyl)phenol (A2) has been analyzed for the characterization of the presence of a `unique and `rare intermolecular C(sp3/sp2)-F...O contact, which has been observed to play a significant role in the crystal packing. Theoretical charge-density calculations have been performed to study the nature and strength associated with the existence of this intermolecular F...O contact, wherein the F atom is attached to an sp3-hybridized C atom in the case of A1 and to an sp2 hybridized carbon in the case of A2. The crystal packing of the former contains two `electronically different Csp3-F...O contacts which are present across and in between the layers of molecules. In the latter case, it is characterized by the presence of a very `short (2.708u2005Å) and `highly directional (168° at ∠C4-F1...O1 and 174° at ∠C10-O1...F1) Csp2-F...O contact. According to the Cambridge Structural Database (CSD) study, it is a rare example in molecular crystals. Topological features of F...O contacts in the solid state were compared with the gas-phase models. The two-dimensional and three-dimensional static deformation density obtained from theoretical multipole modeling confirm the presence of a charge depleted region on the F atoms. Minimization of the electrostatic repulsion between like charges are observed through subtle arrangements in the electronic environment in two of the short intermolecular F...O contacts. These contacts were investigated using inputs from pair energy decomposition analysis, Baders quantum theory of atoms in molecules (QTAIM), Hirshfeld surface analysis, delocalization index, reduced density gradient (RDG) plot, electrostatic potential surface and distributed atomic polarizability. The intermolecular energy decomposition (PIXEL) and RDG-NCI (non-covalent interaction) analysis of the F...O contacts establish the interaction to be dispersive in nature. The mutual polarization of an O atom by fluorine and vice versa provides real physical insights into the role of atomic polarizability in interacting atoms in molecules in crystals.

Accurate atomic displacement parameters from time-of-flight neutron-diffraction data at TOPAZ

Accurate atomic displacement parameters (ADPs) are a good indication of high-quality diffraction data. Results from the newly commissioned time-of-flight Laue diffractometer TOPAZ at the SNS are presented. Excellent agreement is found between ADPs derived independently from the neutron and X-ray data emphasizing the high quality of the data from the time-of-flight Laue diffractometer.

Investigation of Chemical Bonding in In Situ Cryocrystallized Organometallic Liquids

This Communication presents the crystal structure of the organometallic complexes (η4 -1,3-cyclohexadiene) iron tricarbonyl (I) and (methyl cyclopentadienyl) manganese tricarbonyl (II) which are both liquid at room temperature. The crystal structures were determined using a state-of-the-art inu2005situ cryocrystallization technique. The bonding features were elucidated using topological analysis of charge density in the framework of quantum theory of atoms in molecules (QTAIM) and theoretical charge density analysis (multipolar refinement), to decipher the metal-carbonyl, metal-olefin and metal-carbocyclic ligand interactions in these complexes. Complex I displayed a simultaneous interplay of a synergic effect (σ-donation and π-back-bonding in the metal and an end-on coordinated carbonyl interaction) as well as consistency with the Dewar-Chatt-Duncanson (DCD) model (metal and side-on coordinated π-ligand interactions).

Electron Density Analysis of the "O-O" Charge-Shift Bonding in Rubrene Endoperoxide.

Rubrene endoperoxide p-xylene (1) has been obtained in crystalline form from recrystallization and purification of the organic semiconductor, rubrene, and for the first time characterized by single-crystal X-ray diffraction methods. 1 is produced by reaction of rubrene with molecular oxygen to create rubrene endoperoxide, C42H28O2, in which an O2-bridge is joining the two phenyl-substituted C atoms opposite each other in the second of the four aromatic rings in tetracene thereby breaking the resonance along the tetracene moiety. The electron density distribution of 1 reveals that the intramolecular O-O bond is best characterized as charge-shift bonding with loss of electronic concentration in the interatomic region evidenced by the Laplacian. Likewise the ELI-D indicates little electron localization in this region. Furthermore, source function and ELI-D analysis of 1 clearly quantifies the lack of electronic delocalization across the six-membered ring that carries the peroxide-bridge.

Relationships between electron density and magnetic properties in water-bridged dimetal complexes

The electron densities in two analogous dimetallic transition metal compounds, namely, [M2(μ-OH2)((t)BuCOO)4((t)BuCOOH)2(C5H5N)2] (M = Co(1), Ni(2)), were determined from combined X-ray and neutron single-crystal diffraction at 100 K. Excellent correspondence between the thermal parameters from X- and N-derived atomic displacement parameters is found, indicating high-quality X-ray data and a successful separation of thermal and electronic effects. Topological analysis of electron densities derived from high-resolution X-ray diffraction, as well as density functional theory calculations, shows no direct metal-metal bonding in either compound, while the total energy density at the bond critical points suggests stronger metal-oxygen interactions for the Ni system, in correspondence with its shorter bond distances. The analysis also allows for estimation of the relative strength of binding of terminal and bridging ligands to the metals, showing that the bridging water molecule is more strongly bound than terminal carboxylic acid, but less so than bridging carboxylates. Recently, modeling of magnetic and spectroscopic data in both of these systems has shown weak ferromagnetic interactions between the metal atoms. Factors related to large zero-field splitting effects complicate the magnetic analysis in both compounds, albeit to a much greater degree in 1. The current results support the conclusion drawn from previous magnetic and spectroscopic measurements that there is no appreciable direct communication between metal centers.