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Noble gas donor–acceptor type complexes in triplet electronic state! First ever report of very strong, noble gas–beryllium complexes (3NgBeY+; Ng = He–Rn; Y = N, P) in the triplet state with a large singlet–triplet energy gap and Ng–Be covalent bonding.

Prediction of noble gas-inserted phosphorus fluorides, FNgPF2 and FNgPF4 (Ng = Ar–Rn), with Ng–P covalent bonding through ab initio quantum chemical calculations.

Adsorption and activation of CO2 is a key step in any chemical reaction, which aims to convert it to other useful chemicals. Therefore, it is important to understand the factors that drive the activation process and also search for materials that promote the process. We employ the density functional theory to explore the possibility of using small-sized bimetallic Cu-Zr clusters, Cu4-nZrn, with n = 1-3 for the above-mentioned key step. Our results suggest that after adsorption, a CO2 molecule preferably resides on Zr atoms or at the bridge and triangular faces formed by Zr atoms in bimetallic Cu-Zr clusters accompanied with its high degree of activation. Importantly, maximum activation occurs when CO2 is adsorbed on the CuZr3 cluster. Interestingly, we find that the adsorption energy of CO2 can be tuned by varying the extent of the Zr atom in Cu-Zr clusters. We rationalize the high adsorption of CO2 with the increase in the number of Zr atoms using the d-band center model and the concept of chemical hardness. The strong chemisorption and high activation of CO2 are ascribed to charge migration between Cu-Zr clusters and the CO2 molecule. We find an additional band in the infrared vibrational spectra of CO2 chemisorbed on all of the clusters, which is absent in the case of free CO2. We also observe that the energy barriers for the direct dissociation of the CO2 molecule to CO and O decrease significantly on bimetallic Cu-Zr clusters as compared to that on pure Cu4. In particular, the barrier heights are considerably small for Cu3Zr and CuZr3 clusters. This study demonstrates that Cu3Zr and CuZr3 clusters may serve as good candidates for activation and dissociation of the CO2 molecule.

The analogy between gold and hydrogen is a subject of long-standing debate. In the present work, we examine the validity of the gold-hydrogen analogy in a series of small-sized H-doped gold clusters, Au

It is well known that a nuclear reactor generates various fission products including radioactive fission gases made of isotopes of Xe and Kr. The separation of Xe and Kr isotopes and their entrapme...

Metallocarbohedrenes or metcars belong to one of the classes of stable nanoclusters having a specific stoichiometry. In spite of the available theoretical and experimental studies, the structure of pristine Ti8C12 metcar is still uncertain. We study the geometric structure of a titanium metcar, Ti8C12, together with its electronic properties and chemical activity towards adsorption and activation of CO2 molecule by means of density functional theory. Our results suggest that the CO2 molecule is strongly adsorbed and undergoes a significantly high degree of activation onto the Ti8C12 metcar. The migration of charge from titanium metcar to CO2 molecule attributes the high degree of activation of this molecule. In the infrared vibrational spectra for CO2 molecule adsorbed onto Ti8C12, we find a new signal which is absent in the corresponding spectra for gaseous CO2. In addition to adsorption energy, we also estimate the energy barrier for the dissociation of CO2 molecule to CO and O fragments on a Ti8C12 cluster. As a whole, this work reveals the ground state geometry of Ti8C12 metcar and highlights the role of this metcar in CO2 adsorption and activation, which are the key steps in designing potential catalysts for CO2 capture and its conversion to industrially valuable chemicals.

Recent theoretical prediction and experimental identification of fluorinated noble gas cyanides and isocyanides motivate us to explore a unique novel series of neutral noble gas-inserted heavier cyanofluoride isomers, FNgYSi and FNgSiY (Ng = Kr, Xe, and Rn; Y = N and P), theoretically using quantum chemical calculations. The concerned minima and saddle point geometries have been optimized using DFT, MP2, and CCSD(T) methods. The precursor molecule FSiY is more stable than its isomer FYSi, and the stability order is found to be reversed after the insertion of a noble gas (Ng) atom into them which is in contrast to the previously reported FCN/FNC systems where the stability order in the precursors remains intact after the insertion of a Ng atom into them. The predicted FNgYSi molecules are metastable in nature as they are kinetically stable but thermodynamically unstable with respect to the global minima products (FYSi and Ng). All the calculations for the corresponding FNgSiY molecules clearly indicate that the less stable FNgSiY behaves similarly to the FNgYSi in all respects. The energetics, force constant, and spectroscopic data strongly reinforce the possibility of occurrence of these predicted FNgYSi and FNgSiY molecules which might be experimentally realized under suitable cryogenic condition(s).

The recent experimental synthesis of 2D graphitic C3N5 has attracted lot of interests in its electronic and optical properties and its comparison with other graphitic C3N4 and C3N3. To this end, we performed DFT calculations using more accurate HSE06 functional and estimated the corresponding electronic properties. From a comparative study of the band structures of C3N3, C3N4, and C3N5, we found that, the electronic band-gap decreases as 3.24 eV (C3N3) > 2.81 eV (C3N4) > 2.19 eV (C3N5) with increase in the number of nitrogen atoms in the unit cell of these graphitic carbon nitrides. Further, the strain dependency of the band structure of 2D g-C3N5 under uniaxial and biaxial strain is performed using the same HSE- 06 functional. We found a systematic decrease of band-gap as strain increases. Out of the two types of strain, the biaxial strain has been found to be more efficient in modulating the band-gap. The effect of strain on the structure is also explored by analyzing the bond lengths and bond-angles as well as the charge density plots. Furthermore, we found that at a biaxial strain of 20% strain an interesting structural rearrangement occurs in 2D g-C3N5, which reults in a finite magnetic moment arising from the loss of spin-degeneracy of electronic levels. Finally, by studying the evolution of band-gap, band-alignments and optical absorption as a function of strain we are able to predict that biaxially compressed C3N5 with strain in the range 12-14% can be a promising photocatalyst in overall water-splitting with an excellent optical absorption in the visible light spectrum., 27 pages, 25 figures

Invited for the cover of this issue are Sourav Pal, Gopalan Rajaraman and co-workers at the Indian Institute of Technology Bombay, the Bhabha Atomic Research Centre and the Indian Institute of Science Education and Research. The image depicts how a mixture of atmospheric gases such as CO

Entrapment of radioactive inert gases, Xe and Kr, generated from the spent nuclear fuel reprocessing or nuclear accidents is one of the challenging issues in successful implementation of nuclear en...

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.

By computing and analyzing the magnetic exchange coupling, binding energies, the partial density of states (pDOS), and adsorption isotherms for the pristine and gas bound MOFs [(Cr4(X)4Cl)3(BTT)8]3- (X=O2, N2, and H2), we unequivocally establish the role of spin-states and spin-coupling in controlling the gas selectivity. The computed geometries and gas adsorption isotherms are consistent with the earlier experiments. The O2 binding to the MOF follows an electron-transfer mechanism resulting in a Cr(III) superoxo species (O2-•) with a very strong antiferromagnetic coupling between the two centers, while N2/H2 found to only weakly perturb the metal center. Although the gas bound and unbound MOFs have S =0 ground state (GS), the nature of spin configurations and the associated magnetic exchanges are dramatically different. This study offers a hitherto unknown strategy of utilizing spin-state/spin-couplings to control gas adsorption selectivity in MOFs.

The first step in the conversion of CO2 to useful chemicals involves the adsorption of this molecule on a catalyst accompanied with its high degree of activation. In this paper, we explore the efficacy of small sized zirconium clusters, Zrn (n = 2-7), in the adsorption and activation of the CO2 molecule by using the density functional theory based ab initio method. The results of our calculations provide compelling evidence for the chemisorption and very high degree of activation of CO2 with the elongation of the C-O bond in the range of 1.27-1.42 Å compared to 1.16 Å for free CO2 and the deformation of the O-C-O bond angle from linear to 115-136°. This activation takes place through a charge migration from the Zrn cluster to the CO2 molecule resulting in the formation of CO2δ- species. To assess the catalytic potential of Zr-clusters for CO2 conversion, we also analyse the reaction pathways and the transition barrier heights for the dissociation of CO2 (CO2 → CO + O) on all the Zrn clusters. Our results for the dissociation of CO2 to CO and O fragments reveal that the transition barrier is small for all the Zrn clusters except for Zr2 and Zr4 and it attains a minimum value of 0.11 eV for an isomer of the Zr6 cluster. The present work clearly demonstrates that small-sized monometallic Zr-clusters are highly efficient in activating and dissociating a CO2 molecule adsorbed on these clusters.

Motivated by the discovery of neutral noble gas hydrides, herein, we have explored the possibility of the existence of a novel class of neutral noble gas compounds, HNgBO, HNgOB, HNgAlO and HNgOAl (Ng = Xe and Rn), through the insertion of a Ng atom into the hydroxides of icosagens and their isomers, namely, HBO, HOB, HAlO and HOAl. Second-order Moller–Plesset perturbation theory (MP2), density functional theory (DFT), and coupled-cluster theory (CCSD(T))-based methods have been employed to investigate the structures, stabilities, energetics, harmonic vibrational frequencies, and charge distribution of the predicted molecules. The HXeBO, HXeOAl, HRnBO, HRnAlO and HRnOAl molecules are found to be thermodynamically stable with respect to all plausible 2-body and 3-body dissociation channels except the 2-body dissociation pathway, leading to the formation of global minimum products (Ng + HBO), (Ng + HOAl) and (Ng + HAlO). However, the very large activation energy barrier heights provide enough kinetic stability to the predicted metastable molecules, which in turn can prevent them from dissociating into the global minimum products. Between the HNgBO-HNgOB isomers, HNgBO is found to be more stable, where both HNgBO and the precursor molecule HBO are linear. On the other hand, HNgOAl is more stable between the HNgAlO–HNgOAl isomers, where the precursor molecule HOAl is bent and HNgOAl is linear in contradiction and in agreement with Walsh's rule, respectively. Moreover, in contrast to the more stable HNgBO case, where the Ng atom is bonded with the icosagen atom, in the more stable HNgOAl, the Ng atom is connected to the chalcogen atom. All the detailed aforementioned analyses concerning the predicted molecules clearly indicate that a strong covalent bond exists between the H and Ng atoms, while an ionic interaction is found between the Ng and B atoms in HNgBO and Ng and O atoms in the HNgOAl molecules. In addition, the charge distribution and atoms-in-molecules (AIM) analyses are in agreement with the above-mentioned conclusion and also suggest that the predicted metastable HNgBO and HNgOAl molecules should essentially exist in the form of [HNg]+[BO]− and [HNg]+[OAl]−, respectively. All the calculated results reported in this work indicate that it might be possible to prepare and characterize the predicted molecules via suitable experimental technique(s) under cryogenic conditions.

The present communication reports unprecedented stabilization of multiply charged anion, B12F122−, through insertion of noble gas (Ng) atoms possessing negative electron affinity into B–F bonds, resulting in the formation of stable icosahedral B12Ng12F122−, where the HOMO is stabilized significantly and the binding energy of the second excess electron is increased remarkably. Unprecedented stability enhancement with Ng is attributed to a strong covalent B–Ng bond, increased charge delocalization and increased electrostatic interaction between the oppositely charged centers.

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.

In recent years, actinide containing clusters have attracted immense attention because of the distinctive bonding properties of their 5f and 6d electrons. In this context, in the present work, we have studied the isoelectronic series of actinide (An = Np+, Pu2+, Am3+) doped B12H122− and Al12H122− clusters using density functional theory (DFT). Similarly, corresponding isoelectronic lanthanide (Ln = Pm+, Sm2+, Eu3+) doped clusters are also investigated using DFT for comparison. Both exohedral and endohedral metal doped Al12H122− clusters are investigated in various possible spin states, whereas for B12H122− only exohedral metal doped clusters are studied due to its smaller cage diameter. Among all the metal doped clusters, the exohedral metal doped B12H122− and Al12H122− clusters in a septet spin state with retained high spin population on the doped actinide ion, are the most stable, indicating that all these doped clusters are magnetic in nature. The high stability of exohedral clusters is due to small steric repulsion as compared to that in the corresponding endohedral clusters. A prominent charge transfer from cage to metal ion is responsible for the strong interaction of the doped metal ion with the cage atoms. The studied Ln@B12H122− (Ln@Al12H122−) and An@B12H122− (An@Al12H122−) clusters are not only thermodynamically stable, but also kinetically stable. Metal ion encapsulated endohedral Al12H122− clusters are found to satisfy the 32-electron principle corresponding to the completely filled s, p, d and f shells of the central f-block atom. Theoretical predictions of these lanthanide and actinide doped stable B12H122− and Al12H122− clusters could encourage experimentalists for the preparation of these metal-doped clusters. Thus, the present work offers borane and alane clusters as new hosts for encapsulating radioactive actinides. Furthermore, various functional derivatives of these actinide doped B12H122− clusters may find applications in the field of radiation medicine.

Among the varied classes of weak hydrogen bond, the CHO type is one of immense interest as it governs the finer structures of biological and chemical molecules, hence determining their functionalities. In the present work, this weak hydrogen bond has been shown to strongly influence the complexation behaviour of uranyl nitrate [UO2(NO3)2] with diamyl-H-phosphonate (DAHP) and its branched isomer disecamyl-H-phosphonate (DsAHP). The structures of the bare ligands and complexes have been optimized by density functional theory (DFT) calculations. Surprisingly, despite having the same chemical composition the branched UO2(NO3)2·2DsAHP complex shows a remarkably higher stability (by ∼14 kcal mol-1) compared to the UO2(NO3)2·2DAHP complex. Careful inspection of the optimized structures reveals the existence of multiple CHO hydrogen-bonding interactions between the nitrate oxygens or U[double bond, length as m-dash]O oxygens and the α-hydrogens in the alkyl chains of the ligands. Comparatively stronger such bonds are found in the UO2(NO3)2·2DsAHP complex. The binding free energies associated with the complexes are computed and favoured superior binding energetics for the more stable UO2(NO3)2·2DsAHP complex. Calculations involving diisoamyl-H-phosphonate (DiAHP) and its complexes have also been performed. Theoretical predictions are experimentally tested by carrying out the extraction of U(vi) from nitric acid media using these ligands. DAHP, DsAHP and DiAHP are synthesised, characterised by NMR and evaluated for their physicochemical properties viz. viscosity, density and aqueous solubility. It was experimentally discovered that indeed DsAHP complexation with uranyl nitrate is more favoured. H-phosphonates are generically classified as acidic extractants owing to the formation of an enol tautomer at lower acidities, hence complexing the metal ion by proton exchange. Our experiments interestingly reveal a neutral ligand characteristic for DsAHP alone which is generically an acidic extractant. Furthermore, the enol tautomer of H-phosphonates that governs their extraction profiles at low acidities is also explored by DFT and the anomalous pH dependent complexation trend of DsAHP could be successfully explained. The extractions of Pu(iv) and Th(iv) have also been carried out in addition to U(vi). Solvent extraction behaviour of Am(iii) was also studied with all three ligands; the positive binding energies computed for the Am(iii) complexation corroborate with our experimental results on the poor extraction of Am(iii).

The present communication shows an unprecedented superelectrophilic behaviour of dianion [BeB11(CN)11]2-, containing a positively charged electrophilic center embedded in a negatively charged framework. This dianion is shown to form stable [NgBeB11(CN)11]2- (Ng = He, Ne, Ar, Kr and Xe) compounds associated with either a Ng-Be or Ng-B bond. The dianion [BeB11(CN)11]2- binds covalently with Ar, Kr and Xe via its uncoordinated B atom.

Herein, we have shown that La(III), Ac(III), Th(III), Th(IV), Pa(IV) and U(IV) can directly bind with a maximum of 24 hydrogen atoms in M(H2)12 in the first sphere of coordination, which would be a new record in any metal–hydrogen complex investigated at the molecular level, where all the hydrogen atoms are directly connected to the central metal ion through M–η2(H2) bonds. Moreover, Ac(H2)n3+ (n = 9–12) systems satisfy the 18-electron rule.

Currently, development of rechargeable Mg ion batteries is an important and hot topic of research. For its development, the major challenge is to find suitable stable electrolyte anions, which possess solubility in low-polarity solvents. In this context, new organic and hybrid organic–inorganic functional derivatives of closo dodecaborane dianion, namely B12X122– (X = −C≡CH, −C≡C–CN, and −C≡C–BO), are proposed here using density functional theory. The second excess electron in B12(C≡C–CN)122– and B12(C≡C–BO)122– is very strongly bound with the ΔE2 value of 4.90 and 5.14 eV, respectively, in the gas phase, which is almost six-times higher than that of B12H122– (0.81 eV). The various other factors responsible for the high stability of these predicted dianions have been explained in detail. We have explored the implications of these stable dianions as electrolytes in the Li and Mg ion batteries, and the results are found to be highly promising. Among all the dianions considered here, B12(C≡C–BO)122– and B12(...

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.

Aromaticity has been traditionally used for decades to explain the exceptional stability of certain conjugated organic compounds. Only in the recent past, this concept has crossed the bounds of org...

The positions of lawrencium (Lr), lutetium (Lu), actinium (Ac) and lanthanum (La) in the periodic table have been a controversial topic for quite some time. According to studies carried out by different groups with their justifications, these elements may potentially be placed in the d-block, p-block or all four in a 15 element f-block. The present work looks into this issue from a new perspective, which involves encapsulation of these four elements into Zintl ion clusters, Pb122− and Sn122−, followed by the determination of the structural, thermodynamic and electronic properties of these endohedral M@Pb122− and M@Sn122− clusters (M = Lrn+, Lun+ with n = 0, 1, 2, 3) using first principles based density functional theory (DFT). These parameters are compared with similar clusters encapsulated La3+ and Ac3+ ions in order to seek out similarities and differences to draw conclusions about their placement in the periodic table. For the first time the structural, energetic, and electronic properties of these metal atom/ion encapsulated Pb122− and Sn122− clusters have been investigated thoroughly. Structural parameters such as bond distances, geometry and symmetry, electronic properties viz. the density of states, the molecular orbital ordering, the electron localization function, bond critical point properties and charge distributions have been analyzed. Additionally, the thermodynamic property of the binding energy during the encapsulation process has also been calculated. All M@Pb12+ and M@Sn12+ (M = Lr and Lu) clusters form stable 18 bonding electron magic number systems with shell closing. They show negative values of binding energy and relatively large HOMO–LUMO energy gaps indicating the stability of such clusters. All the calculated parameters for Lr encapsulated clusters closely match with the corresponding calculated parameters of Lu encapsulated clusters, confirming the similarity between Lr and Lu metal atoms in various oxidation states, though their atomic ground state valence electronic configurations are different. The effect of spin orbit coupling has also been investigated using the ZORA approach. It is interesting to discover that La and Ac showed striking similarities to Lr and Lu with respect to all the properties investigated and have formed a stable 18-electron system.

Motivated by the very recent investigations of neutral noble gas compounds in the open-shell configuration, we explored a new series of noble gas hydrides in the triplet state. The possible existence of noble gas-inserted ketenyl cations, HNgCCO+ (Ng = He, Ne, Ar, Kr, and Xe), in their triplet electronic state has been predicted by various ab initio quantum chemical techniques. Density functional theory (DFT), second-order Moller–Plesset perturbation theory (MP2), and coupled-cluster theory (CCSD(T)) based methods have been employed to investigate the structures, energetics, harmonic vibrational frequencies, and charge distribution analysis of these ions. The aforementioned ions have been found to be thermodynamically stable with respect to all plausible 2-body and 3-body dissociation channels, except the 2-body dissociation pathway leading to the formation of global minima products (Ng + HCCO+). Nevertheless, each of the predicted HNgCCO+ ions is connected to the global minima products through a transition state with a finite barrier height on the potential energy surface, which confirms the kinetic stability of the metastable species. Detailed analysis of the optimized structural parameters, energetics, and harmonic vibrational frequencies of the predicted species clearly indicated that a strong covalent bond exists between H and Ng atoms, while a comparatively weak interaction is found between Ng and C atoms. Moreover, charge distribution and atoms-in-molecules (AIM) analysis strongly concurred with the above inferences and also suggested that the predicted metastable ions should exist essentially in the form of [HNg]+[CCO] complex. These results ultimately indicate that these predicted species may be prepared and characterized by suitable experimental technique(s) under a cryogenic environment.

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).

The recently observed “new form of condensed hydrogen” has motivated us to investigate the structures of H@H24–, H@H64–, and H@H88– clusters and to explore their stability by using dispersion-corrected density functional theory. Stability of these clusters has been explained with the help of high values of the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gap and geometrically closed shell of 12, 32, and 44 hydrogen molecules around the central hydride ion, which in turn form electronically closed shell systems. The H@H24– cluster has been observed as the most stable cluster followed by H@H64– and H@H88–. Apart from the hydride-centered clusters, we have also predicted various other metal and nonmetal atom- and ion-centered new clusters with large HOMO–LUMO gap and high binding energy. The structures and stability of some of the smaller clusters have been investigated by using MP2 and CCSD(T) methods as well, and the MP2-calculated binding energies are found to be very...

The periodic table of elements, organised as blocks of elements that contain similar properties, occupies a central role in chemistry. However, the position of some of the elements in the periodic table is a debate that has been ensuing over the past one and a half long centuries. Particularly, the positions of lanthanum (La), lutetium (Lu), actinium (Ac) and lawrencium (Lr) in the periodic table have been quite controversial. Different kinds of studies carried out by various research groups have yet left the fate of these elements undecided as the results of these investigations suggested that these elements could potentially be placed in the d-block, p-block or all four in the f-block. Our recent work looked into this question from a new perspective, involving encapsulation of La, Lu, Ac and Lr into Zintl ion clusters, Pb122− and Sn122−. These clusters were chosen as they provide a fitting environment for the determination of structural, thermodynamic and electronic properties of the encapsulated species. Various results that have been evaluated and subsequently analysed (Joshi et al. in Phys. Chem. Chem. Phys. 20:15253–15272, 2018) in order to seek out similarities and differences for making justified conclusions about the placement of all these four elements in the periodic table are the subject matter of this review article. This review highlights a unique methodology wherein Ln and An encapsulated Pb122− and Sn122− clusters provided in-depth insights on the long-drawn controversy: positions of lutetium, lawrencium, lanthanum and actinium in the modern periodic table. Electronic, thermodynamic and structural parameters have been comprehensively investigated by DFT to yield a justified conclusion.

In recent years, actinide containing clusters have attracted immense attention because of the distinctive bonding properties of their 5f and 6d electrons. In this context, in the present work, we have studied the isoelectronic series of actinide (An = Np

Herein, we have shown that La(iii), Ac(iii), Th(iii), Th(iv), Pa(iv) and U(iv) can directly bind with a maximum of 24 hydrogen atoms in M(H2)12 in the first sphere of coordination, which would be a new record in any metal-hydrogen complex investigated at the molecular level, where all the hydrogen atoms are directly connected to the central metal ion through M-η2(H2) bonds. Moreover, Ac(H2)n3+ (n = 9-12) systems satisfy the 18-electron rule.

In accordance with the well established gold-hydrogen analogy, a hydrogen atom mimics the properties of a gold atom in gold clusters. In a recent study it has been demonstrated that the properties of a hydrogen atom doped small gold cluster (Au7H) are not in conformity with the aforementioned analogy. In this paper we study the properties of the Au7H cluster exhaustively to re-examine the validity of the gold-hydrogen analogy in the context of adsorption of CO and O2 molecules on pristine gold and hydrogen atom doped gold clusters. For this purpose we first determine the most stable structure of the Au7H cluster by using an ab initio density functional theory based method with generalized gradient approximation (GGA) and Meta-GGA exchange-correlation functionals. We carry out geometry optimization by considering various planar and three-dimensional isomers of the Au7H cluster as initial geometries. We find that the lowest energy structure of Au7H is a planar one with C2 v symmetry, and it is very close to the structure of the Au8 cluster with D4 h symmetry. Furthermore, to examine the validity of the gold-hydrogen analogy we carry out a detailed investigation of the adsorption of CO and O2 molecules on the most stable as well as various other low energy isomers of the Au7H cluster. We find that the adsorption energies and the extent of activation of CO and O2 molecules on the most stable planar isomer of Au7H are almost the same as those on the parent Au8 cluster with D4 h symmetry proving the validity of the gold-hydrogen analogy. On the other hand, for the high energy three-dimensional isomers of the Au7H cluster obtained from the pristine Au8 cluster with T d symmetry, we find a significant enhancement in adsorption energy as well as the extent of activation of CO and O2 molecules as compared to those for the corresponding pristine cluster. Therefore, the high reactivity of the 3D isomer of the Au7H cluster may be attributed to its existence in a state which is higher in energy than its most stable planar isomer.

Across the actinide period, the stability of the trivalent oxidation state predominates in the heavy actinides, making their chemical nature close to that of rare earth elements. The resemblance in their chemistry poses difficulties in separating heavy actinides from lanthanides, which is a vital separation in the minor actinide partitioning process. Actinide contraction has conventionally implied electrostatic actinide-ligand interactions among the heavy actinides. The present study challenges this conventional understanding and reveals increasing covalency in the actinide-ligand bond across Am to Cf. Complexes of Am, Cm, Bk, and Cf have been examined for their electronic structure with a focus on the nature of their interactions with different ligands within the framework of density functional theory, where the relativistic effects have been incorporated by using zero-order regular approximation and spin-orbit coupling. The choice of ligands selected for this study facilitates the effect of the donor atom as well as denticity to be accounted for. Hence, heavy actinide complexes of the N- and O-donor ligand dipicolinic acid, S and O mixed donor ligands of the Cyanex type, and an octadentate ligand N, N, N' N'-tetrakis[(6-carboxypyridin-2-yl)methyl]ethylenediamine have been optimized and evaluated. In each case energy decomposition analysis has been used to explicitly decompose the metal-ligand interaction energy into components which have then been analyzed. Irrespective of the hard-soft characteristics of donor atoms or the denticity of the ligands, steadily increased covalency has been observed across Am to Cf. Inspection of the ligand highest energy occupied molecular orbitals and metal orbitals sheds light on the origin of the unexpected covalency. An overall increase in bonding and also the orbital contribution along the Am-Cf series is clearly due to the enhancement in covalency, which is complementary to the orbital degeneracy induced covalency proposed very recently by Batista and co-workers.

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.

Complexation of Am3+ and Ln3+ (La3+, Eu3+, and Er3+) with two bis(1,2,4-triazinyl)bipyridine (C2BTBP, C5BTBP) derivatives has been studied in acetonitrile medium with use of various experimental techniques such as electrospray ionization mass spectrometry (ESI-MS), time-resolved fluorescence spectroscopy (TRFS), UV/Vis spectrophotometry, and solution calorimetry. Metal–ligand stoichiometries and conditional stability constants of these complexes were determined. To the best of our knowledge, this is the first report on the complexation of Am3+ with any of the BTBP derivatives with use of UV/Vis spectrophotometric titration to determine the conditional stability constants. Density functional theory (DFT) calculations are carried out on the An3+ (U3+ and Am3+) and Ln3+ (La3+, Nd3+, Eu3+, Er3+, and Lu3+) complexes of BTBP in order to understand the difference between the bonding in actinide and lanthanide complexes. The results indicate a stronger covalent interaction in the An–N bonds as compared to the Ln–N bonds, which leads to an actinide selectivity of this class of ligands.