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Three N,N-substituted pyridine 2-carboxamide ligands, C5H4NCONRR′ (where, R, R′ = iC3H7 (L1); R, R′ = iC4H9 (L2); and R = H, R′ = tC4H9 (L3), as well as their coordination complexes (1–3) of uranyl nitrate have been synthesized. All the ligands and their corresponding complexes were characterized by CHN elemental analysis, infrared (FTIR) and NMR spectroscopy. The crystal structure of the complex 1 shows that the central uranium atom occupies a distorted hexagonal bipyramidal geometry, where the four oxygen atoms of the bidentate nitrate ligands with the oxygen and nitrogen atoms of the ligand L1 form the hexagonal plane and two axial oxygen atoms of uranyl occupy the trans axial position. Here, the ligand acts as a bidentate chelating ligand. The preliminary structural analysis of the complex 3 also indicates similar kind of structure as that of the complex 1. Quantum mechanical calculation at DFT level is supportive with the solid state structure obtained from X-ray crystallographic analysis.

“Third phase” formation is an aggregation phenomenon that arises due to the mutual attraction of the polar cores of reverse micelles in a non-polar medium. A major concern in the solvent extraction of actinides during processing of nuclear fuels is third phase formation at the aqueous-organic interface. When the metal loaded in the organic phase exceeds a threshold known as the limiting organic concentration (LOC) the organic phase splits into a metal-extractant rich third phase and a metal poor diluent rich phase; hampering the entire process. Pu(IV) behaviour towards third phase formation is crucial for its extraction and processing as a fissile material. In this light, in a preliminary study on the third phase behaviour of Ce(IV), which is chemically similar to Pu(IV) and normally considered as a surrogate of Pu(IV) has been carried out in the present work. Tri-sec-butyl phosphate (TsBP) and tri-n-butyl phosphate (TBP) have been evaluated for the extraction efficacy and their third phase thresholds. Superior extraction as well as resistance to third phase formation has been shown by TsBP as compared to the conventionally used TBP extractant. Apart from experimental studies, quantum chemical calculations using density functional theory (DFT) have also been carried out. The solvent corrected energetics of complex formation for these extraction systems with Ce(IV) have been computed and are in good agreement with experimental observations. It is known that Ce(III) is experimentally not extracted by organophosphates. In addition, Ce(III) complexation with TBP has been theoretically investigated and resulted in unfavourable binding. Furthermore, our electronic structure calculations have percolated into the experimentalist’s realm of third phase formation in metal-extractant systems, and shed new light on the reasons behind the lower tendency of Ce-TsBP complexes to form third phase.

Separation of f-block elements is a daunting task due to their similar chemical behaviour. Among these, the separation of uranium from a thorium matrix is one of the persisting challenges. This finds application both in the processing of thorium ores e.g. monazite, as well as in the separation of 233U from irradiated 232Th. U/Th separation has been conventionally achieved by solvent extraction using tri-n-butyl phosphate (TBP). This work is an extensive study on the use of tri-sec-butyl phosphate (TsBP), which shows significantly higher selectivity for U(VI) over Th(IV), leading to strikingly superior separation factors. This selectivity can be attributed to the combination of structural and electronic effects near the binding site. Systematic and comprehensive studies at both liquid-liquid as well as solid-liquid interfaces have been carried out under a wide range of experimental conditions. The effect of extractant concentration on selectivity towards U(VI) has been examined at the liquid interface. Further, the extractants TBP and TsBP were impregnated on to a XAD–7 polymer support and the separation of U(VI) from Th(IV) matrices of various U/Th ratios has been achieved using extraction chromatography. Strategically optimized conditions of loading and elution stages for varying U/Th feed ratios have been demonstrated using TsBP coated columns for efficient separation of U(VI) from a Th(IV) matrix. Additionally, electronic structure calculations using density functional theory (DFT) have been carried out to shed light on the energetics and specific complexation of U(VI) over Th(IV) with the extractant TsBP and compared with TBP. Theoretically calculated, solvent corrected complexation energies for the formation of U(VI) and Th(IV) complexes with TBP and TsBP are in good agreement with the experimental observations.

Uranium silicides are considered to be prominent accident tolerant fuel for the light water reactors due to their high metal density and high thermal conductivity. Among the uranium silicon binary compounds, U3Si2 is found to be advantageous. Here, we present a systematic first principles study of electronic structure and thermophysical properties of U3Si2 within the framework of quasi-harmonic approximation. The relativistic effects have been treated through incorporating the spin-orbit interactions for all the calculations. The optimized cell volume from PBE method is found to be slightly underestimated, however, from the PBE+U method, it is found to be slightly overestimated as compared to the experimental volume, all the electronic structure results are comparable to the reported results. Volume dependant phonon frequencies have been calculated using the density functional perturbation theory to incorporate the effect of anharmonicity indirectly through quasi-harmonic approximation. Various thermophysical properties like free energy, thermal expansion, heat capacity, bulk modulus, etc. have been evaluated. The vibrational contribution alone to molar specific heat is found to be underestimated as compared to the experimentally reported results. Interestingly, incorporation of the electronic contribution is found to improve the results significantly. Electronic component of thermal conductivity has been calculated using the Boltzmann transport theory. The computed results are comparable to the available experimental results, which supports the reliability of the present study. All these predicted properties are very much important to gain knowledge about the U3Si2 based fuel.

Adsorption and activation of CO 2 onto small-sized transition metal clusters is of practical importance for the conversion of this molecule to value-added products. We study the efficacy of small anionic vanadium carbide clusters, V n C 4 − with n = 1–6 towards the aforementioned key step by employing density functional theory based method. One of such clusters has been shown to perform very well in activating N 2 molecule as revealed in a recent experiment. The results of our calculations suggest that the binding of CO 2 molecule with the anionic vanadium carbide clusters becomes stronger with increase in number of vanadium atoms in the cluster. This adsorption energy trend can be properly rationalized by using the d-band center model. The strong adsorption of CO 2 molecule is also accompanied with its high degree of activation. The high activation of CO 2 is characterized by a significant amount of charge transfer from the anionic clusters to the molecule. We further find that the activation barrier heights for the dissociation of CO 2 to CO and O fragments are considerably small for V 4 C 4 − and V 5 C 4 − clusters. In particular, V 5 C 4 − cluster with an activation barrier of 0.83 eV may serve as a good candidate for activation and dissociation of a CO 2 molecule.

Boradiazaindacene (BODIPY) class of laser dyes are highly efficient but degrade rapidly in alcohol solution during lasing action, progressively reducing output power. Photodegradation of these dyes is mainly due to reaction with the in situ generated singlet oxygen ( 1 O 2 ). With the aim to increase the lasing lifetimes of these dyes, we have designed and synthesized a new congener of the widely used BODIPY dye (PM567) by substitution at its B-centre. The new dye was highly fluorescent, and showed comparable lasing efficiency, but better photostability relative to PM567 in both polar (ethanol) and non-polar (1,4-dioxane) solvents, when excited by 2nd harmonic (532 nm) of a pulsed Nd-YAG laser. More interestingly, the lasing efficiency and photostability of both the dyes were much better in 1,4-dioxane than in ethanol. The relative photostabilities of the dyes were rationalized by absorption spectroscopic analyses of their triplet state properties in the respective solvents in the presence of a 1 O 2 generator or quencher as an additive, pulse radiolysis studies and quantum chemical calculations.

A new series of neutral noble gas inserted compounds involving halocarbenes, mainly, FNgCX (Ng = Kr, and Xe; X = F, Cl, Br, and I) has been predicted through various ab initio quantum chemical techniques such as MP2, DFT, CCSD(T) and MRCI. The structure, stabilities, charge distribution, harmonic vibrational frequencies and topological properties of these compounds have been investigated. It is found that the predicted species are energetically stable with respect to all the plausible 2-body and 3-body dissociation pathways, with the exception of the 2-body channel that leads to the global minimum products (FCX + Ng). Despite this, existence of finite barrier heights indicates that these compounds are kinetically stable with respect to global minimum products. The computational results indicate that it might be possible to prepare and characterize the most stable singlet state of FNgCX molecules under cryogenic conditions through suitable experimental technique(s).

In this study the coordination chemistry of three ligands, C5H4NOCONRR′ (where, R, R′ = iC3H7 (L1); R, R′ = iC4H9 (L2); and R = H, R′ = tC4H9 (L3) composed of N-oxide and carboxamide groups have been explored with uranyl nitrate and some selected lanthanide (La, Sm, and Eu) nitrates. All the synthesized ligands as well as their complexes (1–12) of type UO2(NO3)2L (where, L = L1, L2, and L3 for 1, 2, and 3 respectively) and Ln(NO3)3(H2O)L2 (where, Ln = La, L = L1 for 4, L = L2 for 5, and L = L3 for 6; Ln = Sm, L = L1 for 7, L = L2 for 8, and L = L3 for 9; Ln = Eu, L = L1 for 10, L = L2 for 11, and L = L3 for 12) have been characterized by elemental analysis, spectroscopic analyses such as FTIR, 1H NMR, and electrospray ionization mass spectrometry (ESI-MS). Solid-state structural analysis of L1, 3, and 10 is carried out by X-ray crystallographic technique. The CO and NO groups of L1 are placed almost mutually perpendicular to each other in the crystal structure of L1. The X-ray data show that in [UO2(NO3)2{C5H4NOCONH(tC4H9)}] (3), the ligand acts as a bidentate chelating ligand and is bonded through both the N-oxo and amide oxygen atoms, whereas, in [Eu(NO3)3(H2O){C5H4NOCON(iC3H7)2}2] (10), the ligands show monodentate behavior and are bonded only through N-oxo oxygen atoms. Quantum mechanical calculation at DFT level corroborates the possibility of various bonding modes of these ligands towards uranium and europium nitrate with the preference of bonding as observed in the synthesized complexes. Solvent extraction studies using N,N-dioctyl N-oxo pyridine 2-carboxamide ligand (L4) in n-dodecane with UO22+, Pu4+, Am3+ and Eu3+ indicate the trend Pu4+ ˃ UO22+ > Am3+ > Eu3+ at acidity range from 0.01 M to 6 M HNO3. The ligands show good radiation stability at gamma dose up to 500 kGy and chemical stability at 3 M HNO3 for up to 200 h without much affecting the metal ion extraction. Theoretical calculations show the possibility of presence of different metal species in the organic phase, other than the products obtained from dichloromethane during the solvent extraction of UO22+ and Eu3+ in water/dodecane biphasic media. Energy decomposition analysis supports the higher extraction coefficient of UO22+ than Eu3+ with an evidence of higher orbital interaction of the ligands with UO22+.

Radioactive Xe and Kr released from nuclear reactors and spent nuclear fuel reprocessing plants can be converted in to useful ones after the radioactive decay. The adsorption techniques employing porous materials are a cost effective solution for the capture of these volatile radionuclides compared to expensive cryogenic distillation process. Among various porous materials, metal-organic frameworks (MOFs) show excellent storage and separation properties. In this paper, we investigate the Xe and Kr adsorption properties of recently reported SBMOF-2 using van der Waals corrected density functional theory. In particular, SBMOF-2 has two types of pores with distinct linker groups along pore channels. Our studies show that Xe is preferred over Kr in both the pore channels, which are in complete agreement with experimental observations. The adsorption energies obtained for SBMOF-2 is comparable to other efficient MOFs reported in the literature for Xe/Kr separation. The two pore channels show slightly different binding energies depending on their linker groups and pore characteristics. The impact of central metal atom on adsorption properties is evaluated. A new SBMOF-2(Mg) with magnesium as central metal atom shows Xe/Kr adsorption behavior similar to the experimentally studied SBMOF-2(Ca). Next, we have investigated the effect of polarizable groups in the pore channels where linker hydrogen atoms are substituted with halogen atoms. There is a significant increase in the adsorption energy of noble gases in the halogenated pore channels. Due to the presence of halogen atoms, electron charge density redistribution takes place in the MOF network leading to permanent dipoles. Accordingly, the adsorption energies increase with the polarizability of halogen atoms. The ab initio calculations performed in this study suggest that Xe/Kr separation properties of MOFs depend upon many competing interactions, which originate from their structural and chemical properties.

Sequestration of radioactive noble gases xenon (Xe) and krypton (Kr) from off-gas streams of nuclear reactors and spent nuclear fuel reprocessing plants are essential. The Generally employed cryogenic distillation process for Xe/Kr separation is expensive and adsorption based techniques using porous materials are viable alternative. Recently, carbon allotropes such as graphynes (Gyn) and graphdiynes (Gdyn) attained importance due to their significance in many applications similar to graphene. In both graphyne and graphdiyne, the carbon atoms are sp-sp2 hybridized where benzene rings are linked through acetylenic and diacetylenic linkages respectively. They are good candidates for gas adsorption/separation due to their chemical stability and large surface area. In this regard, we have investigated the noble gas adsorption properties of doped/undoped graphyne and graphdiyne materials using density functional theory calculations. The graphyne and graphdiyne display enhanced adsorption affinity for Xe and Kr when doped with selective heteroatoms.

Structural diversity in dimethylgallium hydroxide noted on recrystallization from different solvents has been investigated by single crystal structural analysis. The conformation of the cyclic structures (tri- and tetra-nuclear) remains unchanged irrespective of the solvents used (benzene, hexane, hexane–dioxane mixtures) for crystallization. Higher nuclearity structures show intra-molecular hydrogen bonding in addition to inter-molecular hydrogen bonding. DFT calculations reveal that stability increases with the degree of oligomerization.

The reactions of triorgano-gallium etherate with azo linked salicylaldimine Schiff bases in benzene gave complexes of the type [R2GaOC6H3(N NPh) (CH NAr)], [R2GaOC6H3(N NPh) (CH NCH2–)]2, [{R2GaOC6H3(N NPh) (CH NCH2CH2}3N] and [C6H5–N N–C6H3(4′-OGaRO)-3′-CH N–C6H4] (R = Me or Et; Ar = Ph or tol-4). These complexes have been characterized by elemental analysis, IR, UV–Vis, NMR (1H and 13C{1H}) spectroscopy. The molecular structures of [Me2GaOC6H3(N NPh)CH NPh]·½C6H6 (5a·½C6H6) and [Me2GaOC6H3(N NPh) (CH Ntol-4)] (5c) were established by X-ray crystallography. Density functional calculations have also been performed to obtain structure and energetic information for the bare ligands and the metal-ligand complexes. Photoluminescence studies of these complexes showed that the quantum yield is always higher than that of the corresponding ligands and the emission peaks of complexes are blue shifted with respect to ligand.

Among the intermetallic compounds of uranium, U-Al alloy is found to be promising nuclear fuel for high-power research reactors due to its high thermal conductivity and structural stability. U-Al system can form three different intermetallic compounds namely, UAl2, UAl3 and UAl4. Here, we systematically explored the electronic structure and various thermal properties of the cubic UAl3 system. Pseudo-potential plane wave based DFT calculations are used along with the spin-orbit coupling. The structural parameter calculated using the generalised gradient approximation is comparable to the experimental results. The phonon dispersion plot indicates the dynamic stability of the structure. Thermophysical properties including free energy, molar specific heat, coefficient of thermal expansion, bulk modulus, etc. have been evaluated within the framework of quasi-harmonic approximation. Both the electronic and lattice contribution to thermal conductivity has been evaluated through the Boltzmann transport theory.

Adsorption of a CO molecule on various isomers of Au19Li cluster has been investigated within the framework of density functional theory. For a particular isomer, initial geometries of CO adsorbed Au19Li clusters are obtained by placing a CO molecule at each of the non-equivalent positions. It is observed that Li doping can enhance the adsorption energy of CO on Au19Li cluster over that of pure Au20 cluster. Moreover, our study reveals that the endohedrally doped cage-like Au19Li clusters show better propensity to adsorb CO than the corresponding exohedrally doped tetrahedral isomers. Elongation of C–O bond length and the red-shift in C–O stretching frequency have been observed for some of the isomers with high value of adsorption energy including the one with highest value of adsorption energy. Our results indicate that the endohedrally doped cage-like Au19Li clusters may be better catalytic agent than pure Au20 cluster for CO oxidation.

A systematic study on the H-bonding interaction of hydroperoxyl radical with formic, acetic, chloroformic and fluoroformic acids has been carried out using B3LYP/6-311++G(2df,2p) and MP2/aug-cc-pVTZ methods. Several possible geometries have been considered, and the calculated global minima of RCOOH–HO 2 have been found to be planar cyclic structure with two hydrogen bonds. A definite trend has been found between the electron donating character of the R group with calculated bond lengths, binding energies and vibrational frequencies. The most stable complex of RCOOH–HO 2 with H 2 O has been found to be associated with a planar cyclic structure involving three hydrogen bonds.

Complexation of thorium with pyridine monocarboxylates namely picolinic acid (pyridine-2-carboxylic acid), nicotinic acid (pyridine-3-carboxylic acid) and isonicotinic acid (pyridine-4-carboxylic acid) has been studied by potentiometry and calorimetry to determine the thermodynamic parameters (log K , Δ G , Δ H and Δ S ) of complexation. All the studies were carried out at 1.0 M ionic strength adjusted by NaClO 4 and at a temperature of 298 K. The detailed analysis of potentiometric data by Hyperquad confirmed the formation of four complexes, ML i ( i = 1–4) in case of picolinate but only one complex (ML) in case of nicotinate and isonicotinate. The stepwise formation constant for ML complex (log K ML ) of thorium-picolinate is higher than those of thorium-nicotinate and thorium-isonicotinate complexes. Further the changes in enthalpy during formation of thorium-picolinate complexes are negative whereas the same for the complexes of thorium with the other two isomers was positive. This difference in the complexation process is attributed to chelate formation in case of thorium-picolinate complexes in which the thorium ion is bound to the picolinate through both the nitrogen in the pyridyl ring and one of the carboxylate oxygen atoms. The complexation process of thorium-nicotinate and thorium-isonicotinate are found to be endothermic in nature and are entropy driven confirming the similar binding nature as in simple carboxylate complexes of thorium. The complexation energies, bond lengths and charges on each atom in the complexes of various possible geometries were calculated theoretically using TURBOMOLE and the most stable configurations were optimized. The detail analysis of calculated complexation energy values in solvent phase and higher value of stability constant indicates that isonicotinate forms stronger complex with thorium than nicotinate. The results are corroborating the experimental observations.

The thermodynamic parameters (log K , Δ G , Δ H and Δ S ) of complexation of Eu(III), a chemical analogue of trivalent actinides, with pyridine monocarboxylates, namely, picolinic acid (pyridine-2-carboxylic acid), nicotinic acid (pyridine-3-carboxylic acid), isonicotinic acid (pyridine-4-carboxylic acid) have been studied at 1.0 M ionic strength adjusted by NaClO 4 and 298 K by potentiometry, fluorescence spectroscopy and calorimetry. The potentiometric results revealed formation of four complexes, ML i ( i = 1–4) in case of picolinate whereas only ML complexes in case of nicotinate and isonicotinate. The log K ML for Eu(III) picolinate complex is higher than that for complexes of Eu(III) with the other two acids. The complexation reaction between Eu(III) and picolinate was found to be exothermic due to chelate formation via pyridyl nitrogen. In case of complexation of Eu(III) with nicotinate and isonicotinate, the enthalpy changes are similar as in the case of simple mono carboxylates and are positive. Life time measurements by time resolved fluorescence spectroscopy, for the decay of 5 D 0 state of Eu(III) also indicated the formation of ML 4 with picolinate and formation of ML only with the other two acids. The experimental observations on the stability and binding mode of the complexes are corroborated by theoretical calculations using the TURBOMOLE software. The detail analysis of calculated charge values of the free ligands and the complexes indicates that charge polarization is more in the isonicotinate than in nicotinate upon complexation.

The structure, hydrogen bonding and binding energy of hydroxymethoxy radical–water complexes, HO C(X)(Y) O·nH2O (n = 0, 1, 2 and X, Y = H/F/Cl), have been investigated using MP2 method with the 6-311++G(d, p) basis set. Hessian calculations have been done to check the nature of the equilibrium geometry. The energy values of selective HO C(X)(Y) O·nH2O complexes (n = 0,1) have also been calculated by CCSD/aug-cc-pVDZ and CCSD/aug-cc-pVTZ methods. The HO C(X)(Y) O·nH2O complexes (n = 1, 2 and X, Y = H/F/Cl) have been found to possess cyclic structures with binding energies between 8.0 and 22.2 kcal/mol. Cooperative effect on the hydrogen bond energy is found to be quite significant for the HO C(X)(Y) O·2H2O complexes. The effect of type and number of halogen atoms bonded to the central carbon atom of HO C(X)(Y) O radical on structure, hydrogen bonding, Mulliken spin, Mulliken charge and vibrational frequency is discussed.

A first-principles study has been performed to understand the effect of oxygen vacancy on the electronic properties of cadmium doped rutile TiO 2 . We observe that Cd incorporation on rutile TiO 2 induces Cd p-states on the top of the valence band which is consistent with an earlier result of Zhang et al. (2008) [5] . Furthermore, by creating an oxygen vacancy, some new states are induced, which originate from the Ti 3d electrons at the middle of the band gap and spread up to the conduction band. Therefore, the band gap of the material reduces significantly, making it suitable to act as a better photocatalyst.

The thermodynamic parameters (Δ G , Δ H and Δ S ) of complexation of U(VI) and Eu(III) by unsaturated dicarboxylic acids, namely, maleic and fumaric acid, has been determined by potentiometric and microcalorimetric titrations at fixed ionic strength ( I = 1.0 M) and temperature (298 K). The results show formation of 1:1 complexes by both the ligands with Eu(III). In the case of U(VI), maleate forms both 1:1 and 1:2 complexes, while only 1:1 complex was formed with fumarate. The fluorescence emission spectra of Eu(III)–dicarboxylate solutions at varying ligand to metal ratio were also used to obtain their stability constants. In addition, the fluorescence lifetimes reveal higher dehydration of Eu(III)–maleate compared to Eu(III)–fumarate which corroborates the Δ S values. The thermodynamic quantities suggest charge polarization effects in the case of U(VI) and Eu(III) complexes of fumarate, which is further corroborated by theoretical calculations. For the same ligand, U(VI) complexes were found to be more stable which was mainly due to higher entropy term.

The ionization potential (IP), O–H bond dissociation energy (BDE) and intra-molecular hydrogen bonding in selected para-substituted salicylic acids, 5-R-SA, with R as –NO 2 , –CHO, –COOH, -halogen, –OH, –OCH 3 , -alkyl, –NH 2 , –NH(CH 3 ), –N(CH 3 ) 2 and their radicals have been investigated by density functional theory with B3LYP functional in conjunction with 6-31G(d) and 6-311++G(d,p) basis sets. All the calculations have also been performed using BHLYP functional in conjunction with 6-311++G(d,p) basis set. A common order of IPs and BDEs for the studied 5-R-SAs is found as –NO 2 > –COOH (–CHO) > –H > –OCH 3 > –NH 2 > –NH(CH 3 ) > –N(CH 3 ) 2 . The effect of substituents on the structure, charge distribution and intra-molecular hydrogen bond has also been discussed.

Embelin, 2,5-dihydroxy-3-undecyl-1,4-benzoquinone, has two intra-molecular hydrogen bonds between the quinone and hydroquinone groups present on the same ring. Therefore, it is expected to produce semiquinone radical in the oxidation as well reduction reactions. To investigate this aspect, kinetics and mechanism of reduction reactions of embelin have been studied using nanosecond electron pulse radiolysis technique and compared with the oxidation process. Two distinct transients observed in the reduction (λmax = 450 nm) and the oxidation (λmax = 410 nm) processes with various free radicals have been characterized and assigned to two different embelin semiquinone radicals on the basis of pulse radiolysis studies. The structures of these transients have been further ascertained using density functional theory with B3LYP functional and 6-31+G(d,p) basis set. Reduction reaction of embelin has been found to produce delocalized semiquinone anion radical. On the other hand, oxidation of embelin is expected to produce several transient species. However, the calculations suggest that oxidation of hydroquinone group is the first step, which is followed by transformation into carbon-centered radical.

The structure and hydrogen bonding in dimer cation systems of H 3 O + with some chemical species have been studied using DFT/B3LYP and MP2 with 6-311++G(d,p) basis set, and CCSD/aug-cc-pVTZ methods. The order of binding energies of the studied system, (H 3 O⋯ A B) + , as calculated with UCCSD(T)/aug-cc-pVTZ method follow an order: HC N > H 2 O > HO O > O H > S H > H F > H Br > H Cl > O N > N O . The structure of (H 3 O⋯AB) + can be described as a hydrogen-bonded complex of H 3 O + with AB in which the hydrogen atom from H 3 O + makes a hydrogen bond with A-atom of AB species.

In the present work, a systematic study has been carried out on the hydration of uranyl ions with different oxidation states, namely, U(IV) and U(VI), ([U(OH) 2 (H 2 O) n ] 2+ and [UO 2 (H 2 O) n ] 2+ with n = 1-5) to examine the performance of the effective fragment potential (EFP) model for solvent. These systems are ideal to study any solvation models and the solute-solvent interactions are very essential to account for the solubility of these ions in aqueous media. In order to assess the reliability and reproducibility of the EFP method, the geometry as well as the energetics of hydrated uranyl ions obtained by the EFP method have been compared with the conventional Hartree-Fock as well as density functional theory based B3LYP level of theoretical results. Some issues regarding the utility of this method for the study of solute-solvent interactions with significant charge transfer contributions have been addressed.

The various possible structures of thiocyanate dimer radical anion, ( SCN ) 2 · − , have been optimized using Hartree–Fock (HF), density functional theory with B3LYP functional (DFT) and second order Moller–Plesset perturbation (MP2) methods. The most stable structure has been found to be the one where the two SCN subsystems are mutually out-of-plane with respect to each other involving a weak bonding between sulfur–sulfur atoms. The sulfur–sulfur bond length and dihedral angle have been calculated to be larger as compared to that of thiocyanogen, (SCN)2. Binding energy for the global minimum of ( SCN ) 2 · − has been obtained as 53.7, 129.3 and 139.0 kJ/mol with the aid of HF, DFT and MP2 methods, respectively, suggesting a strong electron correlation effect. Similar to other dimer radical ion systems, the agreement in binding energy between DFT and MP2 results is quite satisfactory for ( SCN ) 2 · − . However, the DFT calculated S⋯S bond distance is highly overestimated as compared to the corresponding MP2 value. Energy and geometry of these optimized structures have been discussed and compared with similar systems.

The synchrotron photoelectron spectra of allene (C3H4) and perdeuterated allene (C3D4) have been obtained at 40–127 eV photon energies. The study confirms the existence of a peak at 12.7 eV binding energy which was observed by Baltzer et al. [Chem. Phys. 196 (1995) 551]. High-level Complete Active Space Multiconfiguration SCF (CASSCF) and MRSDCI theoretical calculations indicate that the peak at 12.7 eV is most likely a peculiar correlation peak of 2 E symmetry which gains intensity as a result of strong vibronic coupling (Jahn–Teller-like) between at least two electronic states. The photon energy dependence of the 12.7 eV peak intensity is reported.

A new electronegativity-based approach to the potential energy curve for diatomic molecules is proposed where the covalent binding is formulated in terms of the accumulation of electron density at the bond centre using the concepts of bond electronegativity and bond hardness while the ionic binding is described in terms of interatomic charge transfer. The resulting expressions consisting of both these contributions yield the total bond energy at an arbitrary internuclear distance. Predicted numerical results on bond energies for the bond extension region and anharmonicity constants of selected diatomic molecules are shown to agree quite well with available data.

We propose a new approach to the calculation of partial atomic charges in polyatomic molecules. The method involves a locally groupwise electronegativity equalisation procedure and is able to incorporate the effect of connectivity of atoms in the molecule. The calculated charges for a number of isolated molecules and interacting molecular systems involving intermolecular charge transfer show good agreement with ab initio results. The “pile-up” and “spill-over” effects in donor-acceptor interaction is correctly predicted. The same approach has been used for the calculation of other reactivity indices such as the Fukui function and self or mutual softness, for which the numerical results are reported.