Pradeep R. Varadwaj

In addition to the underlying basic concepts and early recognition of halogen bonding, this paper reviews the conflicting views that consistently appear in the area of noncovalent interactions and the ability of covalently bonded halogen atoms in molecules to participate in noncovalent interactions that contribute to packing in the solid-state. It may be relatively straightforward to identify Type-II halogen bonding between atoms using the conceptual framework of σ-hole theory, especially when t

The CH₃NH₃PbI₃ (methylammonium lead triiodide) perovskite semiconductor system has been viewed as a blockbuster research material during the last five years. Because of its complicated architecture, several of its technological, physical and geometrical issues have been examined many times. Yet this has not assisted in overcoming a number of problems in the field nor in enabling the material to be marketed. For instance, these studies have not clarified the natur

Spin-unrestricted DFT-X3LYP/6-311++G(d,p) calculations have been performed on a series of complexes of the form [Co(H(2)O)(6-n)(NH(3))(n)](2+) (n = 0-6) to examine their equilibrium gas-phase structures, energetics, and electronic properties in their quartet electronic ground states. In all cases Co(2+) in the energy-minimised structures is in a pseudo-octahedral environment. The calculations overestimate the Co-O and Co-N bond lengths by 0.04 and 0.08 A, respectively, compared to the crystallog

DFT calculations with the UX3LYP hybrid functional and a medium-sized 6-311++G(d,p) basis set were performed to examine the gas-phase structure of paramagnetic (S = 1) six-coordinate complexes [Ni(NH3)n(H2O)(6-n)](2+), 0 < or = n < or = 6. Significant interligand hydrogen bonding was found in [Ni(H2O)6](2+), but this becomes much less significant as NH3 replaces H2O in the coordination sphere of the metal. Bond angles and bond lengths obtained from these calculations compare reasonably well with

With an interest to quest for transition metal-based halogenated double perovskites <i>A</i>BBX₆ as high performance semiconducting materials for optoelectronics, this study theoretically examined the electronic structures, stability, electronic (density of states and band structures), transport (effective masses of charge carriers), and optical properties (dielectric function and absorption coefficients, etc<i>.</i>) of the series <i>A</i>₂AgCrBr₆ (<i>A</i> = K,

Noncovalent interactions in 18 weakly bound binary complexes formed between either of the two end-on orientations of the CO molecule and the methylated carbon positive σ-hole associated with the hydrophobic part of the CH3-X molecules are exploited using the density functional theory to examine the physical chemistry of the recently introduced 'carbon bonds' (Phys. Chem. Chem. Phys., 2013, 15, 14377), where X = -NO2, -CN, -F, -Cl, -Br, -OH, -CF3, -CCl3, and -NH2. The two important types of inter

<i>A</i>-Site doping with alkali ions, and/or metal substitution at the B and B'-sites, are among the key strategies in the innovative development of <i>A</i> ₂BB'X₆ halide double perovskite semiconducting materials for application in energy and device technologies. To this end, we have investigated an intriguing series of five halide-based non-toxic systems, <i>A</i> ₂AgRhCl₆ (<i>A</i> = Li, Na, K, Rb, and Cs), using density functional theory at the S

We have theoretically examined the geometries, electronic density of states and band structures of cubic and hexagonal A₂AgCrCl₆ (A = Cs, Rb, K, Na, Li) using meta-GGA SCAN-rVV10. The optimized lattice density was found to vary between 2.68 and 4.08 g cm^-3 for cubic-A₂AgCrCl₆, with the fundamental electronic bandgap (direct) in the range of 0.66-0.69 eV. The cell density of hexagonal A₂AgCrCl₆ was between 2.97 and 3.93

Several recent studies have shown that chalcogen bonds originate from the σ-holes localized on the electron-deficient surface of the Group 16 atoms (sulfur, selenium and tellurium) in molecules; however, the oxygen atom in molecules does not appear to form such a bond. In this study, we have considered oxygen difluoride (OF2) as a prototypical Lewis acid, and 11 Lewis bases as partner interacting species (CH3F, CH3Cl, CH3Br, H2CO, HFCO, HF, SO, CH3CN, PN, HSCN and HCN). Their complexes are exami

A density functional theory study of the structure of the title compounds with the divalent metal ions in their high-spin ground state, obtained using B3LYP/6-311++G(d,p) in vacuo and in aqueous solution simulated using a polarized continuum medium, is reported for the first time. The modeling reproduces the pseudo pentagonal bipyramidal crystallographic structures very well, including some asymmetry in the equatorial bonds lengths to the crown ether O donors. The very marked asymmetry in the Ni

With the goal of understanding the reason for the specific binding affinity of the chlorine in Cl-CH3 in the H2C=O···Cl-CH3 complex, we performed molecular electrostatic surface potential (MESP) analysis for isolated H3C-Cl with B3PW91, M06-2X, and MP2(full), all in conjunction with twenty-three Dunning- and Pople-type basis sets of double- and triple-ς valence qualities. The results obtained were benchmarked against the best level of theory employed, CCSD/6-311++G(3d,2p). It was found that the

The divergence of fluorine-based systems and significance of their nascent non-covalent chemistry in molecular assemblies are presented in a brief review of the field. Emphasis has been placed to show that type-I and -II halogen-centered F···F long-ranged intermolecular distances viable between the entirely negative fluorine atoms in some fluoro-substituted dimers of C6H6 can be regarded as the consequence of significant non-covalent attractive interactions. Such attractive interactions observed

This Article revisits the “Definition of the Halogen Bond (IUPAC Recommendations 2013)” [Desiraju, G. R. Pure Appl. Chem. 2013, 85 (8), 1711–1713], recommendations that fail to include the fundamental, underlying concept of (electrophilic) σ- and p-/π-hole theory and orbital-based charge transfer interactions that accompany halogen bond formation. An electrophilic σ-hole, or p-/π-hole, is an electron-density-deficient region of positive polarity (and positive potential) on the electrostatic surf

Using the second-order Møller-Plesset perturbation theory (MP2), together with Dunning's all-electron correlation consistent basis set aug-cc-pVTZ, we show that the covalently bound oxygen atom present in a series of 21 prototypical monomer molecules examined does conceive a positive (or a negative) σ-hole. A σ-hole, in general, is an electron density-deficient region on a bound atom M along the outer extension of the R-M covalent bond, where R is the reminder part of the molecule, and M is the