Palladium and platinum complexes based on pyridine bases induced anticancer effectiveness via apoptosis protein signaling in cancer cells

Palladium and platinum complexes, especially those that include cisplatin, can be useful chemotherapeutic drugs. Alternatives that have less adverse effects and require lower dosages of treatment could be provided by complexes containing pyridine bases. The complexes [Pd(SCN)2(4-Acpy)2] (1), [Pd(N3)2(4-Acpy)2] (2) [Pd(paOH)2].2Cl (3) and [Pt(SCN)2(paO)2] (4) were prepared by self-assembly method at ambient temperature; (4-Acpy = 4-acetylpyridine and paOH = pyridine-2-carbaldehyde-oxime). The structure of complexes 1-4 was confirmed using spectroscopic and X-ray crystallography methods. Complexes 1-4 have similar features in isomerism that include the trans coordination geometry of pyridine ligands with Pd or Pt ion. The 3D network structure of complexes 1-4 was constructed by an infinite number of discrete mononuclear molecules extending via H-bonds. The Pd and Pt complexes 1-4 with pyridine ligands were assessed on MCF-7, T47D breast cancer cells and HCT116 colon cancer cells. The study evaluated cell death through apoptosis and cell cycle phases in MCF-7 cells treated with palladium or platinum conjugated with pyridine base. Upon treatment of MCF-7 with these complexes, the expression of apoptotic signals (Bcl2, p53, Bax and c-Myc) and cell cycle signals (p16, CDK1A, CDK1B) were evaluated. Compared to other complexes and cisplatin, IC50 of complex 1 was lowest in MCF-7 cells and complex 2 in T47D cells. Complex 4 has the highest effectiveness on HCT116. The selective index (SI) of complexes 1-4 has a value of more than two for all cancer cell lines, indicating that the complexes were less toxic to normal cells when given the same dose. MCF-7 cells treated with complex 2 and platinum complex 4 exhibited the highest level of early apoptosis. p16 may be signal arrest cells in Sub G, which was observed in cells treated with palladium complexes that suppress excessive cell proliferation. High c-Myc expression of treated cells with four complexes 1-4 and cisplatin could induce p53. All complexes 1-4 elevated the expression of Bax and triggered by the tumor suppressor gene p53. p53 was downregulating the expression of Bcl2.

Confronting Sulfur Electrode Passivation and Li Metal Electrode Degradation in Lithium-Sulfur Batteries Using Thiocyanate Anion

Salt anions with a high donor number (DN) enable high sulfur utilization in lithium-sulfur (Li-S) batteries by inducing three-dimensional (3D) Li₂ S growth. However, their insufficient compatibility with Li metal electrodes limits their cycling stability. Herein, a new class of salt anion, thiocyanate (SCN^- ), is presented, which features a Janus character of electron donor and acceptor. Due to a strong Li⁺ coordination by SCN^- and the direct interaction of SCN^- with polysulfide anions, the LiSCN electrolyte has a remarkably high lithium polysulfide solubility. This electrolyte induces 3D Li₂ S formation and ameliorates cathode passivation, even more than Br^- , a typical high DN anion. Moreover, SCN^- forms a Li₃ N-enriched stable SEI layer at the surface of the Li metal electrode, enhancing cycling stability. A Li-S battery with the LiSCN electrolyte shows high current density operation (2.54 mA cm⁻² ) with high discharge capacity (1133 mAh g⁻¹ ) and prolonged cycle life (100 cycles). This work demonstrates that the cathode and anode performance in a Li-S battery can be simply and concurrently enhanced by the single salt anion.

The Halogen Bonding Proclivity of the sp3 Sulfur Atom as a Halogen Bond Acceptor in Cocrystals of Tetrahydro-4H-thiopyran-4-one and Its Derivatives

In this work, we present a systematic study of the capability of the sp³ hybridized sulfur atom for halogen bonding both in a small building block, tetrahydro-4H-thiopyran-4-one, and two larger ones derived from it, Schiff bases with a morpholine fragment on the other end of the molecule. These three building blocks were cocrystallized with six perhalogenated aromates: 1,4-diiodotetrafluorobenzene, 1,3,5-triiodotrifluorobenzene, 1,3-diiodotetrafluorobenzene, 1,2-diiodotetrafluorobenzene, iodopentafluorobenzene, and 1,4-dibromotetrafluorobenzene. Out of the 18 combinations, only 7 (39%) yielded cocrystals, although with a high occurrence of the targeted I···S halogen bonding motif in all cocrystals (71%), and in imine cocrystals the I···O_morpholine motif (100%) as well as, surprisingly, the I···N_imine motif (100%). The I···S halogen bonds presented in this work feature lower relative shortening values than those for other types of sulfur atoms; however, the sp³ sulfur atom could potentially be more specific an acceptor for halogen bonding.

Experimental and Computational Tuning of Metalla-N-Heterocyclic Carbenes at Palladium(II) and Platinum(II) Centers

Palladium(II) and platinum(II) complexes featuring metalla-N-heterocyclic carbenes (7–12) were synthesised via metal-mediated coupling between equimolar cis-[MCl2(CNR)2] (R = 2,6-Me2C6H3 (Xyl), 2,4,6-Me3C6H3 (Mes)] and 2-aminopyridine or 2-aminopyrazine. Thiocyanate complexes 13–18 with...

Studies of Nature of Uncommon Bifurcated I-I···(I-M) Metal-Involving Noncovalent Interaction in Palladium(II) and Platinum(II) Isocyanide Cocrystals

Two isostructural trans-[MI2(CNXyl)2]·I2 (M = Pd or Pt; CNXyl = 2,6-dimethylphenyl isocyanide) metallopolymeric cocrystals containing uncommon bifurcated iodine···(metal-iodide) contact were obtained. In addition to classical halogen bonding, single-crystal X-ray diffraction analysis revealed a rare type of metal-involved stabilizing contact in both cocrystals. The nature of the noncovalent contact was studied computationally (via DFT, electrostatic surface potential, electron localization function, quantum theory of atoms in molecules, and noncovalent interactions plot methods). Studies confirmed that the I···I halogen bond is the strongest noncovalent interaction in the systems, followed by weaker I···M interaction. The electrophilic and nucleophilic nature of atoms participating in I···M interaction was studied with ED/ESP minima analysis. In trans-[PtI2(CNXyl)2]·I2 cocrystal, Pt atoms act as weak nucleophiles in I···Pt interaction. In the case of trans-[PdI2(CNXyl)2]·I2 cocrystal, electrophilic/nucleophilic roles of Pd and I are not clear, and thus the quasimetallophilic nature of the I···Pd interaction was suggested.

In silico characterization and prediction of thiourea-like neutral bidentate halogen bond catalysts

Preorganization is a common strategy to align halogen bond (XB) donors to form two or more halogen bonds simultaneously. Previous approaches have utilized various non-covalent interactions such as steric interactions, ππ stacking, and hydrogen bond interactions. However, some of the introduced aligning interactions may compete with halogen bond interactions if the donors are employed in catalysis. To achieve thiourea-like properties, we have designed in silico several neutral bidentate halogen bond donors in whose structures the donor moieties are connected via covalent bonds. Compared to previous XB catalyst designs, the new design does not involve other potentially competitive non-covalent interactions such as hydrogen bonds. One of the designed XB donors can deliver strong halogen bonds, with a O-I distance as short as 2.64 Å. Density functional theory (DFT) calculations predicted that our designed catalysts may catalyze important organic reactions on their own, particularly for those reactions that involve (developing) soft anions such as thiolates.

Bimetallic uranyl/cobalt(II) isothiocyanates: structure, property and spectroscopic analysis of homo- and heterometallic phases

We report the synthesis and characterization of a family of UO22+/Co2+ isothiocyanate materials containing [UO2(NCS)5]3- and/or [Co(NCS)4]2- building units charged balanced by tetramethylammonium cations and assembled via SS or SOyl non-covalent interactions (NCIs), namely (C4H12N)3[UO2(NCS)5], (C4H12N)2[Co(NCS)4], and (C4H12N)5[Co(NCS)4][UO2(NCS)5]. The homometallic uranyl phase preferentially assembles via SS interactions, whereas in the heterometallic phase SOyl interactions are predominant. The variation in assembly mode is explored using electrostatic surfaces potentials, revealing that the pendant -NCS ligands of the [Co(NCS)4]2- anion is capable of outcompeting those of the [UO2(NCS)5]3- anion. Notably, the heterometallic phase displays atypical blue shifting of the uranyl symmetric stretch in the Raman spectra, which is in contrast to many other compounds featuring non-covalent interactions at uranyl oxygen atoms. A combined experimental and computational (density functional theory and natural bond orbital analyses) approach revealed that coupling of the uranyl symmetric stretch with isothiocyanate modes of equatorial -NCS ligands was responsible for the atypical blue shift in the heterometallic phase.

Controlling multiple orderings in metal thiocyanate molecular perovskites A x {Ni[Bi(SCN)6]}

We report four new A-site vacancy ordered thiocyanate double double perovskites, , A = K+, NH4 +, CH3(NH3)+ (MeNH3 +) and C(NH2)3 + (Gua+), including the first examples of thiocyanate perovskites containing organic A-site cations. We show, using a combination of X-ray and neutron diffraction, that the structure of these frameworks depends on the A-site cation, and that these frameworks possess complex vacancy-ordering patterns and cooperative octahedral tilts distinctly different from atomic perovskites. Density functional theory calculations uncover the energetic origin of these complex orders and allow us to propose a simple rule to predict favoured A-site cation orderings for a given tilt sequence. We use these insights, in combination with symmetry mode analyses, to show that these complex orders suggest a new route to non-centrosymmetric perovskites, and mean this family of materials could contain excellent candidates for piezo- and ferroelectric applications.

Electron belt-to-σ-hole switch of noncovalently bound iodine(i) atoms in dithiocarbamate metal complexes

The nature of metals in the isostructural series of dithiocarbamate complexes affects the electron belt-to-σ-hole switch of noncovalently bound iodine(i) leading to either semicoordination, or halogen bonding.

Halogen bonding in the co-crystallization of potentially ditopic diiodotetrafluorobenzene: a powerful tool for constructing multicomponent supramolecular assemblies

Halogen bonding is emerging as a significant driving force for supramolecular self-assembly and has aroused great interest during the last two decades. Among the various halogen-bonding donors, we take notice of the ability of 1,4-diiodotetrafluorobenzene (1,4-DITFB) to co-crystallize with diverse halogen-bonding acceptors in the range from neutral Lewis bases (nitrogen-containing compounds, N-oxides, chalcogenides, aromatic hydrocarbons and organometallic complexes) to anions (halide ions, thio/selenocyanate ions and tetrahedral oxyanions), leading to a great variety of supramolecular architectures such as discrete assemblies, 1D infinite chains and 2D/3D networks. Some of them act as promising functional materials (e.g. fluorescence, phosphorescence, optical waveguide, laser, non-linear optics, dielectric and magnetism) and soft materials (e.g. liquid crystal and supramolecular gel). Here we focus on the supramolecular structures of multicomponent complexes and their related physicochemical properties, highlight representative examples and show clearly the main directions that remain to be developed and improved in this area. From the point of view of crystal engineering and supramolecular chemistry, the complexes summarized here should give helpful information for further design and investigation of the elusive category of halogen-bonding supramolecular functional materials.

Diversity and uniformity in anion-π complexes of thiocyanate with aromatic, olefinic and quinoidal π-acceptors

Despite the progress in the study of anion-π interactions, there are still inconsistencies in the use of this term and the experimental data about factors affecting the strength of such bonding are limited. To shed light on these issues, we explored supramolecular associations between NCS^- anions and a series of aromatic, olefinic or quinoidal π-acceptors. Combined experimental and computational studies revealed that all these complexes were formed by an attraction of the anion to the face of the π-system, and the arrangements of thiocyanate followed the areas of the most positive potentials on the surfaces of the π-acceptors. The stabilities of the complexes increased with the π-acceptor strength (reflected by their reduction potentials), and were essentially independent of the magnitudes of the maximum electrostatic potentials on their surfaces. The complexes showed intense absorption bands in the UV-Vis range, and the energies of these bands were correlated with the difference of the redox potentials of the anions and π-acceptors. Such features, as well as results of atoms-in-molecules and non-covalent index analyses suggested that besides electrostatics, molecular orbital interactions play a substantial role in the formation of these complexes. The unified trends in variations of the characteristics of the complexes between thiocyanate and a variety of π-acceptors point to their common nature. To embrace diversity and uniformity of the anion-π associates, we suggest (following the halogen bond's definition) that anion-π bonding occurs when there is evidence of a net attraction between the anions and the face of the electrophilic π-system.

Choline-Based Ionic Liquids-Incorporated IRMOF-1 for H2S/CH4 Capture: Insight from Molecular Dynamics Simulation

The removal of H2S and CH4 from natural gas is crucial as H2S causes environmental contamination, corrodes the gas stream pipelines, and decreases the feedstock for industrial productions. Many scientific researches have shown that the metal-organic framework (MOF)/ionic liquids (ILs) have great potential as alternative adsorbents to capture H2S. In this work, molecular dynamics (MD) simulation was carried out to determine the stability of ILs/IRMOF-1 as well as to study the solubility of H2S and CH4 gases in this ILs/IRMOF-1 hybrid material. Three choline-based ILs were incorporated into IRMOF-1 with different ratios of 0.4, 0.8, and 1.2% w/w, respectively, in which the most stable choline-based ILs/IRMOF-1 composite was analysed for H2S/CH4 solubility selectivity. Among the three choline-based ILs/IRMOF-1, [Chl] [SCN]/IRMOF-1 shows the most stable incorporation. However, the increment of ILs loaded in the IRMOF-1 significantly reduced the stability of the hybrid due to the crowding effect. Solvation free energy was then computed to determine the solubility of H2S and CH4 in the [Chl] [SCN]/IRMOF-1. H2S showed higher solubility compared to CH4, where its solubility declined with the increase of choline-based IL loading.

Halogen Bonding Provides Heterooctameric Supramolecular Aggregation of Diaryliodonium Thiocyanate

The crystal structure of the newly synthesized 4-methoxyphenyl(phenyl)iodonium thiocyanate, [PhI(4-C6H4OMe)](SCN), represents the first example of 16-membered cyclic heterooctamer formed by halogen bonding between the iodonium cation and SCN−. Results of density functional theory (DFT) calculations followed by the topological analysis of the electron density distribution within the framework of the quantum theory of atoms in molecules (QTAIM) method at the ωB97XD/DZP-DKH level of theory reveal that energies of attractive intermolecular noncovalent interactions I···S and I···N (responsible for the formation of heterooctameric supramolecular clusters {PhI(4-C6H4OMe)}4·{SCN}4 in the solid state structure of [PhI(4-C6H4OMe)](SCN)) vary from 0.9 to 8.5 kcal/mol.

A Novel Halogen Bond Acceptor: 1-(4-Pyridyl)-4-Thiopyridine (PTP) Zwitterion

Sulfur is a widely used halogen bond (XB) acceptor, but only a limited number of neutral XB acceptors with bifurcated sp3-S sites have been reported. In this work a new bidentate XB acceptor, 1-(4-pyridyl)-4-thiopyridine (PTP), which combines sp3-S and sp2-N acceptor sites, is introduced. Three halogen bonded cocrystals were obtained by using 1,4-diiodobenzene (DIB), 1,4-diiodotetrafluorobenzene (DIFB), and iodopentafluorobenzene (IPFB) as XB donors and PTP as acceptor. The structures of the cocrystals showed some XB selectivity between the S and N donors in PTP. However, the limited contribution of XB to the overall molecular packing in these three cocrystals and the results from DSC measurements clearly point out the synergetic influence and interplay of all noncovalent interactions in crystal packing of these compounds.

Existence of untypical halogen-involving interactions in crystal packings: a statistical and first-principles study

There is a common perception by the scientific community that a halogen-involving interaction forms when the distance between the donor atom and the acceptor atom is less than the sum of their van der Waals (vdW) radii.

Diaryliodonium as a double σ-hole donor: the dichotomy of thiocyanate halogen bonding provides divergent solid state arylation by diaryliodonium cations

The reactivity of [Ar¹Ar²I](SCN) toward the solid-state arylation depends on the preorganization of halogen bond (XB)-bound SCN⁻: N-XB-bound thiocyanates, which, in contrast to N,S-XB-bound, undergoes the extremely rare N-arylation of SCN⁻.

Straightening out halogen bonds

A new parameter is proposed to quantify the linearity of halogen bonds.

Noncovalent Interactions between 1,3,5-Trifluoro-2,4,6-triiodobenzene and a Series of 1,10-Phenanthroline Derivatives: A Combined Theoretical and Experimental Study

How many strong C−I⋯N halogen bonds can one 1,3,5-trifluoro-2,4,6-triiodobenzene molecule form in a crystal structure? To answer this question, we investigated in detail the noncovalent interactions between 1,3,5-trifluoro-2,4,6-triiodobenzene and a series of 1,10-phenanthroline derivatives by employing a combined theoretical and experimental method. The results of the quantum chemical calculations and crystallographic experiments clearly show that there is a structural competition between a C−I⋯N halogen bond and π⋯π stacking interaction. For example, when there are much stronger π⋯π stacking interactions between two 1,10-phenanthroline derivative molecules or between two 1,3,5-trifluoro-2,4,6-triiodobenzene molecules in the crystal structures, then one 1,3,5-trifluoro-2,4,6-triiodobenzene molecule forms only one C−I⋯N halogen bond with one 1,10-phenanthroline derivative molecule. Another example is when π⋯π stacking interactions in the crystal structures are not much stronger, one 1,3,5-trifluoro-2,4,6-triiodobenzene molecule can form two C−I⋯N halogen bonds with two 1,10-phenanthroline derivative molecules.

Halogen bonding, chalcogen bonding, pnictogen bonding, tetrel bonding: origins, current status and discussion

The role of the closing lecture in a Faraday Discussion is to summarise the contributions made to the Discussion over the course of the meeting and in so doing capture the main themes that have arisen. This article is based upon my Closing Remarks Lecture at the 203^rd Faraday Discussion meeting on Halogen Bonding in Supramolecular and Solid State Chemistry, held in Ottawa, Canada, on 10-12^th July, 2017. The Discussion included papers on fundamentals and applications of halogen bonding in the solid state and solution phase. Analogous interactions involving main group elements outside group 17 were also examined. In the closing lecture and in this article these contributions have been grouped into the four themes: (a) fundamentals, (b) beyond the halogen bond, (c) characterisation, and (d) applications. The lecture and paper also include a short reflection on past work that has a bearing on the Discussion.

Comparison of the DFT-SAPT and Canonical EDA Schemes for the Energy Decomposition of Various Types of Noncovalent Interactions

Interaction energies computed with density functional theory can be divided into physically meaningful components by symmetry-adapted perturbation theory (DFT-SAPT) or the canonical energy decomposition analysis (EDA). In this work, the decomposition results obtained by these schemes were compared for more than 200 hydrogen-, halogen-, and pnicogen-bonded, dispersion-bound, and mixed complexes to investigate their similarity in the evaluation of the nature of noncovalent interactions. BLYP functional with D3(BJ) correction was used for the EDA scheme, whereas asymptotically corrected PBE0 functional for DFT-SAPT provided some of the best combinations for description of noncovalent interactions. Both schemes provide similar results concerning total interaction energies and insight into the individual energy components. For most complexes, the dominant energetic term was identified equally by both decomposition schemes. Because the canonical EDA is computationally less demanding than the DFT-SAPT, the former can be especially used in cases where the systems investigated are very large.

Structural preferences in strong anion–π and halogen-bonded complexes: π- and σ-holes vs. frontier orbitals interaction

Intermolecular contacts in strong anion–π and halogen-bonded complexes follow frontier orbitals (instead of most positive or negative surface potentials) of reactants.

Connectivity and Topology Invariance in Self-Assembled and Halogen-Bonded Anionic (6,3)-Networks

We report here that the halogen bond driven self-assembly of 1,3,5-trifluorotriiodobenzene with tetraethylammonium and -phosphonium bromides affords 1:1 co-crystals, wherein the mutual induced fit of the triiodobenzene derivative and the bromide anions (halogen bond donor and acceptors, respectively) elicits the potential of these two tectons to function as tritopic modules (6,3). Supramolecular anionic networks are present in the two co-crystals wherein the donor and the acceptor alternate at the vertexes of the hexagonal frames and cations are accommodated in the potential empty space encircled by the frames. The change of one component in a self-assembled multi-component co-crystal often results in a change in its supramolecular connectivity and topology. Our systems have the same supramolecular features of corresponding iodide analogues as the metric aspects seem to prevail over other aspects in controlling the self-assembly process.

Experimental investigation of halogen-bond hard-soft acid-base complementarity

The halogen bond (XB) is a topical noncovalent interaction of rapidly increasing importance. The XB employs a `soft' donor atom in comparison to the `hard' proton of the hydrogen bond (HB). This difference has led to the hypothesis that XBs can form more favorable interactions with `soft' bases than HBs. While computational studies have supported this suggestion, solution and solid-state data are lacking. Here, XB soft-soft complementarity is investigated with a bidentate receptor that shows similar associations with neutral carbonyls and heavy chalcogen analogs. The solution speciation and XB soft-soft complementarity is supported by four crystal structures containing neutral and anionic soft Lewis bases.

Co-crystallization of 1,3,5-trifluoro-2,4,6-triiodobenzene (1,3,5-TFTIB) with a variety of Lewis bases through halogen-bonding interactions

Co-crystallization of 1,3,5-trifluoro-2,4,6-triiodobenzene (1,3,5-TFTIB) with a variety of halogen-bonding acceptors.

The Halogen Bond

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

From single-point to three-point halogen bonding between zinc(ii) tetrathiocyanate and tetrabromomethane

The strengths of three- and two-point halogen bonding in CBr₄·[Zn(NCS)₄]²⁻dyads are close to that of single-point CBr₄·NCS⁻interaction.

From charge transfer to electron transfer in halogen-bonded complexes of electrophilic bromocarbons with halide anions

Experimental and computational studies of the halogen-bonded complexes, [R-Br, X(-)], of bromosubstituted electrophiles, R-Br, and halide anions, X(-), revealed that decrease of a gap between the frontier orbitals of interacting species led to reduction of the energy of the optical charge-transfer transition and to increase in the ground-state charge transfer (X(-) → R-Br) in their associates. These variations were accompanied by weakening of the intramolecular, C-Br, and strengthening of the intermolecular, BrX(-), bonds. In the limit of the strongest electron donor-acceptor pairs, formation of the halogen-bonded complexes was followed by the oxidation of iodide to triiodide, which took place despite the fact that the I(-) → R-Br electron-transfer step was highly endergonic and the calculated outer-sphere rate constant was negligibly small. However, the calculated barrier for the inner-sphere electron transfer accompanied by the halogen transfer, R-BrI(-) → R˙Br-I(-)˙, was nearly 24 kcal mol(-1) lower as compared to that calculated for the outer-sphere process and the rate constant of such reaction was consistent with the experimental kinetics. A dramatic decrease of the electron-transfer barriers (leading to 18-orders of magnitude increase of the rate constant) was related to the strong electronic coupling of the donor and acceptor within the halogen-bonded precursor complex, as well as to the lower solvent reorganization energy and the successor-complex stabilization.

The three-component cocrystal 1,3,5-trifluoro-2,4,6-triiodobenzene–pyridineN-oxide–water (1/2/1) built up by halogen bonds, hydrogen bonds and π–π interactions

The title three-component cocrystal, C6F3I3·2C5H5NO·H2O, has been prepared as a strong candidate for multiple I...O interactions. Its crystal structure is compared with its 1:1 close relative, C6F3I3·C5H5NO [Aakeröyet al.(2014a).CrystEngComm,16, 28–31]. The 1,3,5-trifluoro-2,4,6-triiodobenzene and water species both have crystallographic twofold axial symmetry. The main synthon in both structures is the π–π stacking of benzene rings, complemented by a number of O—H...O, C—F...π and, fundamentally, C—I...O interactions. As expected, the latter are among the strongest and more directional interactions of the sort reported in the literature, confirming that pyridineN-oxide is an eager acceptor. On the other hand, the structure presents only two of these contacts per 1,3,5-trifluoro-2,4,6-triiodobenzene molecule instead of the expected three. Possible reasons for this limitation are analyzed.

Halogen-bonded halide networks from chiral neutral spacers

Chiral, ditopic, bis-iodinated molecules can form helical networks due to halogen bonding interactions when co-crystallised with halide tetraalkylammonium salts.

Theoretical description of efficiency enhancement in DSSCs sensitized by newly synthesized heteroleptic Ru complexes

Recently, some new series of heteroleptic ruthenium-based dyes, the so-called RD dyes, were designed and synthesized showing better performances compared to the well-known homoleptic N719.

Halogen bonding of electrophilic bromocarbons with pseudohalide anions

Spectral, thermodynamic and structural features of the complexes of bromocarbons with polydentate azide, cyanate or thiocyanate anions are presented. They suggest a significant role of the molecular-orbital interactions in formation of these halogen-bonded associates.

Magnitude and origin of the attraction and directionality of the halogen bonds of the complexes of C6F5X and C6H5X (X = I, Br, Cl and F) with pyridine

The geometries and interaction energies of complexes of pyridine with C(6)F(5)X, C(6)H(5)X (X = I, Br, Cl, F and H) and R(F)I (R(F) = CF(3), C(2)F(5) and C(3)F(7)) have been studied by ab initio molecular orbital calculations. The CCSD(T) interaction energies (E(int)) for the C(6)F(5)X-pyridine (X = I, Br, Cl, F and H) complexes at the basis set limit were estimated to be -5.59, -4.06, -2.78, -0.19 and -4.37 kcal  mol(-1) , respectively, whereas the E(int) values for the C(6)H(5)X-pyridine (X = I, Br, Cl and H) complexes were estimated to be -3.27, -2.17, -1.23 and -1.78 kcal  mol(-1), respectively. Electrostatic interactions are the cause of the halogen dependence of the interaction energies and the enhancement of the attraction by the fluorine atoms in C(6)F(5)X. The values of E(int) estimated for the R(F)I-pyridine (R(F) = CF(3), C(2)F(5) and C(3)F(7)) complexes (-5.14, -5.38 and -5.44 kcal  mol(-1), respectively) are close to that for the C(6)F(5)I-pyridine complex. Electrostatic interactions are the major source of the attraction in the strong halogen bond although induction and dispersion interactions also contribute to the attraction. Short-range (charge-transfer) interactions do not contribute significantly to the attraction. The magnitude of the directionality of the halogen bond correlates with the magnitude of the attraction. Electrostatic interactions are mainly responsible for the directionality of the halogen bond. The directionality of halogen bonds involving iodine and bromine is high, whereas that of chlorine is low and that of fluorine is negligible. The directionality of the halogen bonds in the C(6)F(5)I- and C(2)F(5)I-pyridine complexes is higher than that in the hydrogen bonds in the water dimer and water-formaldehyde complex. The calculations suggest that the C-I and C-Br halogen bonds play an important role in controlling the structures of molecular assemblies, that the C-Cl bonds play a less important role and that C-F bonds have a negligible impact.