Delocalised antimony(lone pair)- and bismuth-(lone pair)…π(arene) interactions: Supramolecular assembly and other considerations

Unlocking Arene Phosphorescence in Bismuth-Organic Materials

Three novel bismuth-organic compounds, with the general formula [Bi2(HPDC)2(PDC)2]·(arene)·2H2O (H2PDC = 2,6-pyridinedicarboxylic acid; arene = pyrene, naphthalene, and azulene), that consist of neutral dinuclear Bi-pyridinedicarboxylate complexes and outer coordination sphere arene molecules were synthesized and structurally characterized. The structures of all three phases exhibit strong π-π stacking interactions between the Bi-bound PDC/HPDC and outer sphere organic molecules; these interactions effectively sandwich the arene molecules between bismuth complexes and thereby prevent molecular vibrations. Upon UV irradiation, the compounds containing pyrene and naphthalene displayed red and green emission, respectively, with quantum yields of 1.3(2) and 30.8(4)%. The emission was found to originate from the T1 → S0 transition of the corresponding arene and result in phosphorescence characteristic of the arene employed. By comparison, the azulene-containing compound displayed very weak blue-purple phosphorescence of unknown origin and is a rare example of T2 → S0 emission from azulene. The pyrene- and naphthalene-containing compounds both display radioluminescence, with intensities of 11 and 38% relative to bismuth germanate, respectively. Collectively, these results provide further insights into the structure-property relationships that underpin luminescence from Bi-based materials and highlight the utility of Bi-organic molecules in the realization of organic emission.

Effect of Substituents on the Intramolecular n→π* Interaction in 3-[2-(Dimethylamino) phenyl] propanal: A Computational Study

n→π* non-covalent interaction (NCI) and hydrogen bond have similarity in terms of delocalization of the electron density between the two orbitals involved in the interaction. Hydrogen bond (X-H···Y) involves delocalization of the lone pair electrons (n) on the Y atom into the σ* orbital of the X-H bond. In contrast, the n→π* interaction deals with delocalizing the lone pair electrons (n) on the N, O, or S atom into the π* orbital of a C═O group or aromatic ring. Herein, we have shown a resemblance of this weak n→π* interaction with the relatively stronger hydrogen bond in terms of folding the side chains in flexible molecules. This work reports the study of folding of the flexible side-chain in 3-[2-(dimethylamino) phenyl] propanal (DMAPhP) through a N···C═O n→π* interaction using various computational approaches such as NBO, QTAIM, and NCI analyses. The folding of the molecule by the n→π* interaction observed in this study is found to be similar to that present in the secondary structures of peptides or proteins through hydrogen bonding interactions. Interestingly, the stabilization of the global minimum conformer of DMAPhP by the n→π* interaction demonstrates the importance of this NCI in providing conformational preferences in molecular systems. Another important finding of this study is that the theoretical redshift obtained in the C═O stretching frequency of the most stable conformer of the DMAPhP is contributed mostly by the n→π* interaction as the C═O group is not involved in hyperconjugation with any neighboring heteroatom, which is a common phenomenon in any ester or amide. We have also demonstrated here that the strength of the intramolecular n→π* interaction can be modulated by varying the electronic substituents at the para position of the donor group involved in the interaction.

Binuclear Triphenylantimony(V) Catecholates through N-Donor Linkers: Structural Features and Redox Properties

A series of binuclear triphenylantimony(V) bis-catecholato complexes 1–11 of the type (Cat)Ph₃Sb-linker-SbPh₃(Cat) was prepared by a reaction of the corresponding mononuclear catecholates (Cat)SbPh₃ with a neutral bidentate donor linker ligands pyrazine (Pyr), 4,4′-dipyridyl (Bipy), bis-(pyridine-4-yl)-disulfide (PySSPy), and diazobicyclo[2,2,2]octane (DABCO) in a dry toluene: Cat = 3,6-di-tert-butyl-catecholate (3,6-DBCat), linker = Pyr (1); PySSPy (2); Bipy (3); DABCO (4); Cat = 3,5-di-tert-butyl-catecholate (3,5-DBCat), linker = Bipy (5); DABCO (9); Cat = 4,5-(piperazine-1,4-diyl)-3,6-di-tert-butylcatecholate (pip-3,6-DBCat), linker = Bipy (6); DABCO (10); Cat = 4,5-dichloro-3,6-di-tert-butylcatecholate (4,5-Cl₂-3,6-DBCat), linker = Bipy (7); DABCO (11); and Cat = 4,5-dimethoxy-3,6-di-tert-butylcatecholate (4,5-(MeO)₂-3,6-DBCat), linker = Bipy (8). The same reaction of (4,5-Cl₂-3,6-DBCat)SbPh₃ with DABCO in an open atmosphere results in a formation of 1D coordination polymer {[(4,5-Cl₂-3,6-DBCat)SbPh₃·H₂O]·DABCO}_n (12). Bis-catecholate complex Ph₃Sb(Cat-Spiro-Cat)SbPh₃ reacts with Bipy as 1:1 yielding a rare macrocyclic tetranuclear compound {Ph₃Sb(Cat-Spiro-Cat)SbPh₃∙(Bipy)}₂ (13). The molecular structures of 1, 3, 4, 5, 8, 10, 12, and 13 in crystal state were established by single-crystal X-ray analysis. Complexes demonstrate different types of relative spatial positions of mononuclear moieties. The nature of chemical bonds, charges distribution, and the energy of Sb...N interaction were investigated in the example of complex 5. The electrochemical behavior of the complexes depends on the coordinated N-donor ligand. The coordination of pyrazine, Bipy, and PySSPy at the antimony atom changes their mechanism of electrooxidation: instead of two successive redox stages Cat/SQ and SQ/Cat, one multielectron stage was observed. The coordination of the DABCO ligand is accompanied by a significant shift in the oxidation potentials of the catecholate ligand to the cathodic region (by 0.4 V), compared to the initial complex.

Understanding the n → π* non-covalent interaction using different experimental and theoretical approaches

Herein, a perspective on the recent understanding of weak n → π* interaction obtained using different experimental and theoretical approaches is presented. This interaction is purely an orbital interaction that involves the delocalization of the lone pair electrons (n) on nitrogen, oxygen, and sulfur to the π* orbitals of CO, CN, and aromatic rings. The n → π* interaction has been found to profoundly influence the stabilization of peptides, proteins, drugs, and various small molecules. Although the functional properties of this non-covalent interaction are still quite underestimated, there are recent demonstrations of applying this interaction to the regulation of synthetic chemistry, catalysis, and molecular recognition. However, the identification and quantification of the n → π* interaction remain a demanding task as this interaction is quite weak and based on the electron delocalization between the two orbitals, while hyperconjugation interactions between neighboring atoms and the group involved in the n → π* interaction are simultaneously present. This review provides a comprehensive picture of understanding the n → π* interaction using different experimental approaches such as the X-ray diffraction technique, and electronic, NMR, microwave, and IR spectroscopy, in addition to quantum chemistry calculations. A detailed understanding of the n → π* interaction can help in modulating the strength of this interaction, which will be further helpful in designing efficient drugs, synthetic peptides, peptidomimetics, etc.

Formation of sandwich and multidecker complexes between O2 and alkali/alkaline earth metals: A DFT study

Abstract: Feasibility of formation of sandwich and multidecker complexes between O2 molecules and alkali/alkaline earth metal has been analyzed in the light of density functional theory (DFT). High value of...

Are Heavy Pnictogen-π Interactions Really "π Interactions"?

The noncovalent interactions of heavy pnictogens with π-arenes play a fundamental role in fields like crystal engineering or catalysis. The strength of such bonds is based on an interplay between dispersion and donor/acceptor interactions, and is generally attributed to the presence of π-arenes. Computational studies of the interaction between the heavy pnictogens As, Sb and Bi and cyclohexane, in comparison with previous studies on the interaction between heavy pnictogens and benzene, show that this concept probably has to be revised. A thorough analysis of all the different energetic components that play a role in these systems, carried out with state-of-the-art computational methods, sheds light on how they influence one another and the effect that their interplay has on the overall system. Furthermore, the analysis of such interactions leads us to the unexpected finding that the presence of the pnictogen compounds strongly affects the conformational equilibrium of cyclohexane, reversing the relative stability of the chair and boat-twist conformers, and thus suggesting a possible application of tuneable dispersion energy donors to stabilise the desired conformation.

Antimony diiminopyridine complexes

The stoichiometric reactions of antimony trichloride, trimethylsilyl trifluoromethanesulfonate, and diiminopyridine ligands lead to the formation of N,N',N''-chelated SbCl₂ cationic complexes. Methyl and phenyl substituents on the imine carbons of the ligand yielded structures with a lone pair on antimony and the hydrogen substituted variant was notably different as it forms a Menshutkin complex with meta-xylene in the solid-state.

A new C-anionic tripodal ligand 2-{bis(benzothiazolyl)(methoxy)methyl}phenyl and its bismuth complexes

A new tripodal C-anionic ligand, 2-{bis(benzothiazolyl)(methoxy)methyl}phenyl (L), was stably generated by the reaction of the ligand precursor (L'), the corresponding bromide (2-BrC6H4)(MeO)C(C7H4NS)2 (C7H4NS = 2-benzothiazolyl), with nBuLi at -104 °C in the presence of TMEDA (N,N,N',N'-tetramethylethylenediamine). The ligand lithium salt reacted with BiCl3 to give a 2 : 1 complex L2BiCl. A 1 : 1 complex LBiCl2 was obtained in good yield by the redistribution reaction between L2BiCl and BiCl3. X-ray diffraction analysis revealed that the ligand L coordinated in an expected κ3-C,N,N' coordination mode in LBiCl2, while it coordinated in κ3-C,N,O and κ2-C,O coordination modes in L2BiCl. The ligand precursor reacted with BiX3 (X = Cl, Br) to give 1 : 1 complexes L'BiX3 and was found to act as a neutral tripodal C(π),N,N-ligand.

Using a Porphyrin Diacid Cation to Stabilize a Square-Pyramidal BiX5 (X = Br, Cl/Br) Unit

Main-group halogenido metalates are a diverse class of compounds with an intricate structural chemistry and a wide range of applications. Here, we present an unprecedented anion motif in the structural chemistry of halogenido bismuthates, a square-pyramidal BiX₅ unit. We show how the porphyrin diacid used as our compounds' counterion is templating the formation of this new motif, suggesting that other strong anion receptors may be able to stabilize unique metalate anions in future work.

Zero-, one-, two- and three-dimensional supramolecular architectures sustained by Se…O chalcogen bonding: A crystallographic survey

The Cambridge Structural Database was evaluated for crystals containing Se…O chalcogen bonding interactions. These secondary bonding interactions are found to operate independently of complementary intermolecular interactions in about 13% of the structures they can potentially form. This number rises significantly when more specific interactions are considered, e.g. Se…O(carbonyl) interactions occur in 50% of cases where they can potentially form. In about 55% of cases, the supramolecular assemblies sustained by Se…O(oxygen) interactions are one-dimensional architectures, with the next most prominent being zero-dimensional assemblies, at 30%.

Supramolecular architectures sustained by delocalised C–I⋯π(arene) interactions in molecular crystals and the propensity of their formation

A survey of delocalised C–I⋯π(chelate ring) interactions is presented.

Rare antimony(III) imidazole selone complexes: steric controlled structural and bonding aspects

Novel antimony(iii) imidazole selone complexes in a super crowded environment are reported for the first time. The super bulky selone antimony complexes, [{IPr*Se}(SbCl3)2] (1) and [{IPr*Se}(SbBr3)2] (2), were isolated from the reactions between IPr*Se (IPr*Se = [1,3-bis(2,6-diphenylmethylphenyl)imidazole selone]) and suitable antimony(iii) halides. 1 and 2 are dinuclear complexes with a Sb : Se ratio of 1 : 0.5 with an unusual coordination mode of selone. The molecules 1 and 2 consist of both Menshutkin-type Sbπaryl interactions and a Sb-Se coordination bond. However, the reaction between antimony(iii) halides and [(IPaul)Se] ([(IPaul)Se] = [1,3-bis(2,4-methyl-6-diphenyl phenyl)imidazole selone]) with a spatially defined steric impact gave the dinuclear complex [{(IPaul)Se}(SbCl3)]2 (3) and the mononuclear complex [{(IPaul)Se}(SbBr3)] (4) without Menshutkin-type interactions. The Sb : Se ratio in 3 and 4 is 1 : 1. Interestingly, the Menshutkin-type interaction was absent in 3 and 4 due to the efficient coordinating ability of the ligand [(IPaul)Se] with the Sb(iii) center compared to that of the super bulky ligand IPr*Se. The thermal property of these antimony selone complexes was also investigated. Density functional theory (DFT) calculations were carried out on the model systems [L(SbCl3)2] (1A), [L(SbCl3)] (1B), [L'(SbCl3)2] (1C), and [L'(SbCl3)] (1D), where L = [1,3-bis(2,6-diisopropyl-4-methyl phenyl)imidazole selone] and L' = [1,3-bis(phenyl)imidazole selone], to understand the nature of orbitals and bonding situations. The computed metrical parameters of 1A are in good agreement with the experimental values. Natural population analysis of the model system reveals that the natural charge and total population of antimony(iii) are comparable. The unequal interaction between selenium and antimony obtained using Wiberg bond indices (WBIs) is fully consistent with the findings of the single-crystal X-ray studies.

Molecular Bismuth Cations: Assessment of Soft Lewis Acidity

Three-coordinate cationic bismuth compounds [Bi(diaryl)(EPMe3 )][SbF6 ] have been isolated and fully characterized (diaryl=[(C6 H4 )2 C2 H2 ]2- , E=S, Se). They represent rare examples of molecular complexes with Bi⋅⋅⋅EPR3 interactions (R=monoanionic substituent). The 31 P NMR chemical shift of EPMe3 has been found to be sensitive to the formation of LA⋅⋅⋅EPMe3 Lewis acid/base interactions (LA=Lewis acid). This corresponds to a modification of the Gutmann-Beckett method and reveals information about the hardness/softness of the Lewis acid under investigation. A series of organobismuth compounds, bismuth halides, and cationic bismuth species have been investigated with this approach and compared to traditional group 13 and cationic group 14 Lewis acids. Especially cationic bismuth species have been shown to be potent soft Lewis acids that may prefer Lewis pair formation with a soft (S/Se-based) rather than a hard (O/N-based) donor. Analytical techniques applied in this work include (heteronuclear) NMR spectroscopy, single-crystal X-ray diffraction analysis, and DFT calculations.

PSb+P Ligand: Platform for a Stibenium to Transition-Metal Interaction

The coordination chemistry of cationic divalent pnictogen ligands, such as nitrenium and phosphenium, has been well-explored in recent years. However, corresponding studies of a heavier congener, stibenium ion, are rare. To better facilitate a Sb⁺-metal interaction, a tridentate P-Sb⁺-P ligand with two phosphine buttresses was designed and synthesized, and its coordination chemistry toward late transition metals was investigated. The stibenium ligand was delivered as an activated P(SbCl)P-AgOTf complex (2) that releases AgCl and the P-Sb⁺-P ligand upon the treatment with transition metals. Reacting 2 with Rh(I) and Ir(I) metals yielded the anticipated stibenium-transition-metal complexes [(Rh(COD)Cl)₂(μ-PSb⁺P)] OTf ([3][OTf]) and [(Ir(COD)Cl)₂(μ-PSb⁺P)] OTf ([4][OTf]). The M-Sb⁺-M bridging structure was confirmed by single-crystal X-ray crystallography, and the bonding situation was examined computationally. Theoretical studies revealed the presence of three-center delocalized M-Sb⁺-M bonding interactions in [3][OTf] and [4][OTf].

The remarkable propensity for the formation of C–H⋯π(chelate ring) interactions in the crystals of the first-row transition metal dithiocarbamates and the supramolecular architectures they sustain

C–H⋯π(chelate ring) interactions play an important role in assembling first-row transition metal dithiocarbamates in their crystals.

Evaluation of bismuth-based dispersion energy donors – synthesis, structure and theoretical study of 2-biphenylbismuth(iii) derivatives

Intramolecular Bi⋯π arene London dispersion interactions in (biphenyl)_3−xBiX_x amount to ca. 20 kJ mol⁻¹ with distances of 3.8–4.0 Å.

A theoretical insight into non-covalent supramolecular interactions in the solid state structures of two octahedral iron(iii) complexes

The nature and characteristics of the C–H⋯π interactions that play an important role in crystal packing of two iron(iii) complexes have been discussed. The DFT calculations have been conducted to determine the interaction energies in these complexes.

Distibanes and Distibenes from Reduction of Sb(NONR )Cl by using MgI Reagents

The bis(amidodimethyl)disiloxane antimony chlorides Sb(NON^R )Cl (NON^R =[O(SiMe₂ NR)₂ ]^2- ; R=tBu, Ph, 2,6-Me₂ C₆ H₃ =Dmp, 2,6-iPr₂ C₆ H₃ =Dipp, 2,6-(CHPh₂ )₂ -4-tBuC₆ H₂ =tBu-Bhp) are reduced to Sb^II and Sb^I species by using Mg^I reagents, [Mg(BDI^R' )]₂ (BDI=[HC{C(Me)NR'}₂ ]^- ; R'=2,4,6-Me₃ C₆ H₂ =Mes, Dipp). Stoichiometric reactions with Sb(NON^R )Cl (R=tBu, Ph) form dimeric Sb^II stibanes [Sb(NON^R )]₂ , shown crystallographically to contain Sb-Sb single bonds. The analogous distibane with R=Dmp substituents has an exceptionally long Sb-Sb interaction and exhibits spectroscopic and reactivity properties consistent with radical character in solution. When R=Dipp, reductions with Mg^I reagents directly give distibenes [Sb(μ-NON^Dipp )Mg(BDI^R' )(THF)_n ]₂ (R'=Mes, n=1; R'=Dipp, n=0). Crystallographic analysis shows a trans-substitution of the Sb=Sb double bond, with bridging NON^Dipp -ligands between the Sb^I and Mg^II centres. An attempt to access the NON^Ph -analogue using the same protocol afforded the polystibide cluster Sb₈ [μ₄ ,η^2:2:2:2 -Mg(BDI^Mes )]₄ , which co-crystallized with the ligand transfer product, [Mg(BDI^Mes )]₂ (μ-NON^Ph ).

Balancing Donor-Acceptor and Dispersion Effects in Heavy Main Group Element π Interactions: Effect of Substituents on the Pnictogen⋅⋅⋅π Arene Interaction

High-level ab initio calculations using the DLPNO-CCSD(T) method in conjunction with the local energy decomposition (LED) were performed to investigate the nature of the intermolecular interaction in bismuth trichloride adducts with π arene systems. Special emphasis was put on the effect of substituents in the aromatic ring. For this purpose, benzene derivatives with one or three substituents (R=NO2 , CF3 , OCHO, OH, and NH2 ) were chosen and their influence on donor-acceptor interaction as well as on the overall interaction strength was examined. Local energy decomposition was performed to gain deeper insight into the composition of the interaction. Additionally, the study was extended to the intermolecular adducts of arsenic and antimony trichloride with benzene derivatives having one substituent (R=NO2 and NH2 ) in order to rationalize trends in the periodic table. The analysis of natural charges and frontier molecular orbitals shows that donor-acceptor interactions are of π→σ* type and that their strength correlates with charge transfer and orbital energy differences. An analysis of different bonding motifs (Bi⋅⋅⋅π arene, Bi⋅⋅⋅R, and Cl⋅⋅⋅π arene) shows that if dispersion and donor-acceptor interaction coincide as the donor highest occupied molecular orbital (HOMO) of the arene is delocalized over the π system, the M⋅⋅⋅π arene motif is preferred. If the donor HOMO is localized on the substituent, R⋅⋅⋅π arene bonding motifs are preferred. The Cl⋅⋅⋅π arene bonding motif is the least favorable with the lowest overall interaction energy.

An Acyclic Arsenium Cation Stabilised by a Single P-As π-Interaction and a Cyclic Diphosphinophosphonium Salt

Stable acyclic arsenium cations R₂ As⁺ , isoelectronic analogues of germylenes, are rare in comparison to the corresponding phosphenium cations. The first example of a diphosphaarsenium salt, [{(Dipp)₂ P}₂ As][Al{OC(CF₃ )₃ }₄ ]⋅1 1 / 2  PhMe, is described. This salt exhibits remarkable stability due to the delocalisation of a lone pair from a planar phosphorus centre into the vacant p-orbital at arsenic; the bonding in 2 has been probed by DFT calculations. An attempt to synthesise an analogous diphosphaphosphenium salt unexpectedly generated the cyclic phosphonium salt [cyclo-{(Mes)P}₂ P(Mes)₂ ][BAr^F ₄ ]⋅CyMe through the cyclisation of a putative phosphine-substituted diphosphene cation intermediate.

A Million Crystal Structures: The Whole Is Greater than the Sum of Its Parts

The founding in 1965 of what is now called the Cambridge Structural Database (CSD) has reaped dividends in numerous and diverse areas of chemical research. Each of the million or so crystal structures in the database was solved for its own particular reason, but collected together, the structures can be reused to address a multitude of new problems. In this Review, which is focused mainly on the last 10 years, we chronicle the contribution of the CSD to research into molecular geometries, molecular interactions, and molecular assemblies and demonstrate its value in the design of biologically active molecules and the solid forms in which they are delivered. Its potential in other commercially relevant areas is described, including gas storage and delivery, thin films, and (opto)electronics. The CSD also aids the solution of new crystal structures. Because no scientific instrument is without shortcomings, the limitations of CSD research are assessed. We emphasize the importance of maintaining database quality: notwithstanding the arrival of big data and machine learning, it remains perilous to ignore the principle of garbage in, garbage out. Finally, we explain why the CSD must evolve with the world around it to ensure it remains fit for purpose in the years ahead.

Intramolecular Metal⋅⋅⋅π-Arene Interactions in Neutral and Cationic Main Group Compounds

The role of intramolecular metal⋅⋅⋅π-arene interactions has been investigated in the solid-state structures of a series of main group compounds supported by the bulky amide ligands, [N(^tBu Ar^≠ )(SiR₃ )]^- (^tBu Ar^≠ =2,6-(CHPh₂ )₂ -4-tBuC₆ H₂ , R=Me, Ph). The lithium and potassium amide salts showed different patterns of solvation and demonstrated that the SiPh₃ substituent is able to be involved in stabilizing the electrophilic metal. These group 1 metal compounds served as ligand transfer reagents to access a series of bismuth(III) halides. Chloride extraction from Bi(N{^tBu Ar^≠ }{SiPh₃ })Cl₂ using AlCl₃ afforded the 1:1 salt [Bi(N{^tBu Ar^≠ }{SiPh₃ })Cl][AlCl₄ ]. This was accompanied by a significant rearrangement of the stabilizing π-arene contacts in the solid-state. Attempted preparation of the corresponding tetraphenylborate salt resulted in phenyl-transfer and generation of the neutral Bi(N{^tBu Ar^≠ }{SiPh₃ })(Ph)Cl.

Evaluation of dispersion type metal···π arene interaction in arylbismuth compounds - an experimental and theoretical study

The dispersion type Bi···π arene interaction is one of the important structural features in the assembly process of arylbismuth compounds. Several triarylbismuth compounds and polymorphs are discussed and compared based on the analysis of single crystal X-ray diffraction data and computational studies. First, the crystal structures of polymorphs of Ph₃Bi (1) are described emphasizing on the description of London dispersion type bismuth···π arene interactions and other van der Waals interactions in the solid state and the effect of it on polymorphism. For comparison we have chosen the substituted arylbismuth compounds (C₆H₄-CH═CH₂-4)₃Bi (2), (C₆H₄-OMe-4)₃Bi (3), (C₆H₃-t-Bu₂-3,5)₃Bi (4) and (C₆H₃-t-Bu₂-3,5)₂BiCl (5). The structural analyses revealed that only two of them show London dispersion type bismuth···π arene interactions. One of them is the styryl derivative 2, for which two polymorphs were isolated. Polymorph 2a crystallizes in the orthorhombic space group P2₁2₁2₁, while polymorph 2b exhibits the monoclinic space group P2₁/c. The general structure of 2a is similar to the monoclinic C2/c modification of Ph₃Bi (1a), which leads to the formation of zig-zag Bi–arene_centroid ribbons formed as a result of bismuth···π arene interactions and π···π intermolecular contacts. In the crystal structures of the polymorph 2b as well as for 4 bismuth···π arene interactions are not observed, but both compounds revealed C–H_Ph···π intermolecular contacts, as likewise observed in all of the three described polymorphs of Ph₃Bi. For compound 3 intermolecular contacts as a result of coordination of the methoxy group to neighboring bismuth atoms are observed overruling Bi···π arene contacts. Compound 5 shows a combination of donor acceptor Bi···Cl and Bi···π arene interactions, resulting in an intermolecular pincer-type coordination at the bismuth atom. A detailed analysis of three polymorphs of Ph₃Bi (1), which were chosen as model systems, at the DFT-D level of theory supported by DLPNO-CCSD(T) calculations reveals how van der Waals interactions between different structural features balance in order to stabilize molecular arrangements present in the crystal structure. Furthermore, the computational results allow to group this class of compounds into the range of heavy main group element compounds which have been characterized as dispersion energy donors in previous work.

Sulfur(lone-pair)…π interactions with FAD in flavoenzymes

The interactions of π-systems with lone-pairs of electrons are known and have been described in biological systems, involving lone-pairs derived from metals, metalloids, sulfur, oxygen and nitrogen. This study describes a bibliographic survey of the disulfide-bound sulfur(lone-pair) interactions with π-systems residing in the flavin adenine dinucleotide (FAD) cofactor of oxidoreductase enzymes (flavoenzymes). Thus, of the 172 oxidoreductase enzymes evaluated for gamma-S(lone-pair)…π(FAD) interactions, 96 proteins (56%) exhibited these interactions corresponding; 61% of 350 the constituent monomers featured at least one gamma-S(lone-pair)…π(FAD) interaction. Two main points of association between the S(lone-pair) and the isoalloxazine moiety of FAD were identified, namely at the centroid of the bond linking the uracil and pyrazine rings (60%), and the centroid of the uracil ring (37%). Reflecting the nature of the secondary structure in three prominent classes of oxidoreductase enzymes: glutathione disulfide reductases (GR; 21 proteins), trypanothione disulfide reductases (TR, 14) and sulfhydryl oxidases (SOX, 22), the approach of the gamma-S(lone-pair) to the FAD residue was to the si-face of the isoalloxazine ring system, i.e. to the opposite side as the carbonyl residue, for all GR and TR examples, and to the re-face for all SOX examples. Finally, the attractive nature of the gamma-S(lone-pair)…π(FAD) interactions was confirmed qualitatively by an examination of the non-covalent interaction plots.

Occurrence and stability of lone pair-π stacking interactions between ribose and nucleobases in functional RNAs

The specific folding pattern and function of RNA molecules lies in various weak interactions, in addition to the strong base-base pairing and stacking. One of these relatively weak interactions, characterized by the stacking of the O4' atom of a ribose on top of the heterocycle ring of a nucleobase, has been known to occur but has largely been ignored in the description of RNA structures. We identified 2015 ribose-base stacking interactions in a high-resolution set of non-redundant RNA crystal structures. They are widespread in structured RNA molecules and are located in structural motifs other than regular stems. Over 50% of them involve an adenine, as we found ribose-adenine contacts to be recurring elements in A-minor motifs. Fewer than 50% of the interactions involve a ribose and a base of neighboring residues, while approximately 30% of them involve a ribose and a nucleobase at least four residues apart. Some of them establish inter-domain or inter-molecular contacts and often implicate functionally relevant nucleotides. In vacuo ribose-nucleobase stacking interaction energies were calculated by quantum mechanics methods. Finally, we found that lone pair-π stacking interactions also occur between ribose and aromatic amino acids in RNA-protein complexes.

Towards the liquid phase exfoliation of bismuth iodide

Liquid phase exfoliation (LPE) of layered compounds towards few- or monolayers has been established as one of the prime methods in the growing field of 2D material research. Here, we present first steps towards an effective LPE of bismuth(iii) iodide, a semiconductor with potential as a photovoltaic absorber material. We highlight guidelines in the choice of exfoliating solvent, which differ significantly from those used with transition metal dichalcogenides or graphene. We also present first evidence of successful few-layer formation from spectroscopic, electron microscopy and electron diffraction investigations.

Neutral and cationic bismuth compounds supported by bis(amidodimethyl)disiloxane ligands

Bis(amidodimethyl)disiloxane ligands derived from O{SiMe₂N(H)R}₂ (abbreviated as (NON^R)H₂) are a stable support for neutral and cationic bismuth compounds. Attempts to extend the series Bi(NON^R)Cl (R = Ar = 2,6-iPr₂C₆H₃; R = tBu) to include compounds where R = Ar' = 2,6-Me₂C₆H₃ were complicated by concomitant formation of the bimetallic compound {Bi(NON^Ar')}₂(μ-NON^Ar'). Compounds containing [Bi(NON^R)]⁺ cations were obtained from reactions with group 13 chlorides MCl₃ (M = Al, Ga). X-ray crystallographic analysis showed intermolecular interactions with the [M_nCl_(3n+1)] anion.

The n → π* interaction: a rapidly emerging non-covalent interaction

This perspective describes the current status of a recently discovered non-covalent interaction named as the n → π* interaction, which is very weak and counterintuitive in nature. In this review, we have provided a brief overview of the widespread presence of this interaction in biomacromolecules, small biomolecules and materials, as well as the physical nature of this interaction explored using various experimental and theoretical techniques. It has been found that this interaction is equally important to other non-covalent interactions for the stability and specific structures of biomolecules and materials. An in-depth understanding of this interaction can help in designing more efficient functional materials as well as drugs. The review also provides a future outlook in terms of exploring the detailed functional role of this interaction in biological processes and its direct spectroscopic evidence, which other commonly known non-covalent interactions (conventional hydrogen bonding, π-hydrogen bonding, π-stacking, etc.) have.

Persistence of C–H⋯π(chelate ring) interactions in the crystal structures of Pd(S2COR)2. The utility of Pd(S2COR)2as precursors for palladium sulphide materials

The influence of C–H⋯π(PdS₂C) interactions in the molecular packing of Pd(S₂COR)₂increases as the steric bulk ofRincreases.

Supramolecular architectures sustained by arene-C–H…π(quasi-chelate ring) interactions in the crystal structures of copper(I) complexes

A review of the crystallographic literature is presented whereby structures featuring a quasi-six-membered chelate ring of the type {CuCl…HNCS} were evaluated for the presence of intermolecular C–H…π(quasi-chelate) interactions. These are shown to stabilise crystal structures leading to zero-, one-, two- and even three-dimensional architectures. Details of these interactions are described and a comparison to analogous interactions formed intramolecularly has been made. The C–H…π(quasi-chelate) interactions in these structures occur in one-third of structures where such contacts can potentially form.