Synthetic and Structural Studies of 1,8‐Chalcogen Naphthalene Derivatives

Four novel 1,8‐disubstituted naphthalene derivatives 4 – 7 that contain chalcogen atoms occupying the peri positions have been prepared and fully characterised by using X‐ray crystallography, multinuclear NMR spectroscopy, IR spectroscopy and MS. Molecular distortion due to noncovalent substituent interactions was studied as a function of the bulk of the interacting chalcogen atoms and the size and nature of the alkyl group attached to them. X‐ray data for 4 – 7 was compared to the series of known 1,8‐bis(phenylchalcogeno)naphthalenes 1 – 3 , which were themselves prepared from novel synthetic routes. A general increase in the E???E′ distance was observed for molecules containing bulkier atoms at the peri positions. The decreased S???S distance from phenyl‐ 1 and ethyl‐ 4 analogues is ascribed to a weaker chalcogen lone pair–lone pair repulsion acting in the ethyl analogue due to the presence of two equatorial S(naphthyl) ring conformations. Two novel peri‐substituted naphthalene sulfoxides of 1 , Nap(O?SPh)(SPh) 8 and Nap(O?SPh)₂ 9 , which contain different valence states of sulfur, were prepared and fully characterised by using X‐ray crystallography and multinuclear NMR spectroscopy, IR spectroscopy and MS. Molecular structures were analysed by using naphthalene ring torsions, peri‐atom displacement, splay angle magnitude, S???S interactions, aromatic ring orientations and quasi‐linear O?S???S arrangements. The axial S(naphthyl) rings in 8 and 9 are unfavourable for S???S contacts due to stronger chalcogen lone pair–lone pair repulsion. Although quasi‐linear O?S???S alignments suggest attractive interaction is conceivable, analysis of the B3LYP wavefunctions affords no evidence for direct bonding interactions between the S atoms.     

Unusually Short Chalcogen Bonds Involving Organoselenium: Insights into the Se–N Bond Cleavage Mechanism of the Antioxidant Ebselen and Analogues

Structural studies on the polymorphs of the organoselenium antioxidant ebselen and its derivative show the potential of organic selenium to form unusually short Se???O chalcogen bonds that lead to conserved supramolecular recognition units. Se???O interactions observed in these polymorphs are the shortest such chalcogen bonds known for organoselenium compounds. The FTIR spectral evolution characteristics of this interaction from solution state to solid crystalline state further validates the robustness of this class of supramolecular recognition units. The strength and electronic nature of the Se???O chalcogen bonds were explored using high‐resolution X‐ray charge density analysis and atons‐in‐molecules (AIM) theoretical analysis. A charge density study unravels the strong electrostatic nature of Se???O chalcogen bonding and soft‐metal‐like behavior of organoselenium. An analysis of the charge density around Se?N and Se?C covalent bonds in conjunction with the Se???O chalcogen bonding modes in ebselen and its analogues provides insights into the mechanism of drug action in this class of organoselenium antioxidants. The potential role of the intermolecular Se???O chalcogen bonding in forming the intermediate supramolecular assembly that leads to the bond cleavage mechanism has been proposed in terms of electron density topological parameters in a series of molecular complexes of ebselen with reactive oxygen species (ROS).     

α‐Halogenoacetanilides as Hydrogen‐Bonding Organocatalysts that Activate Carbonyl Bonds: Fluorine versus Chlorine and Bromine

α‐Halogenoacetanilides (X=F, Cl, Br) were examined as H‐bonding organocatalysts designed for the double activation of C?O bonds through NH and CH donor groups. Depending on the halide substituents, the double H‐bond involved a nonconventional C?H???O interaction with either a H?CX_n (n=1–2, X=Cl, Br) or a H?C_Ar bond (X=F), as shown in the solid‐state crystal structures and by molecular modeling. In addition, the catalytic properties of α‐halogenoacetanilides were evaluated in the ring‐opening polymerization of lactide, in the presence of a tertiary amine as cocatalyst. The α‐dichloro‐ and α‐dibromoacetanilides containing electron‐deficient aromatic groups afforded the most attractive double H‐bonding properties towards C?O bonds, with a N?H???O???H?CX₂ interaction.     

Structures of Trichloromethyl Thiocyanate,CCl3SCN,in Gaseous and Crystalline State

Trichloromethyl thiocyanate, CCl₃SCN, was structurally studied in both the gas and crystal phases by means of gas electron diffraction (GED) and single‐crystal X‐ray diffraction (XRD), respectively. Both experimental studies and quantum chemical calculations indicate a staggered orientation of the CCl₃ group relative to the SCN group. This conclusion is supported by the similarity of the C?SCN bond length to that of the anti‐structure of CH₂ClSCN (Berrueta Martínez et al. Phys. Chem. Chem. Phys. 2015, 17, 15805–15812). 1 Bond lengths and angles are similar for gas and crystal CCl₃SCN structures; however, the crystal structure presents different intermolecular interactions. These include halogen and chalcogen type interactions, the geometry of which was studied. Characteristic C‐Y???N angles (Y=Cl or S) close to 180° provide evidence for typical σ‐hole interactions along the halogen/chalcogen?carbon bond in N???Cl and N???S, intermolecular units.     

Persistent Room Temperature Phosphorescence from Triarylboranes: A Combined Experimental and Theoretical Study

Achieving highly efficient phosphorescence in purely organic luminophors at room temperature remains a major challenge due to slow intersystem crossing (ISC) rates in combination with effective non‐radiative processes in those systems. Most room temperature phosphorescent (RTP) organic materials have O‐ or N‐lone pairs leading to low lying (n, π*) and (π, π*) excited states which accelerate k_isc through El‐Sayed's rule. Herein, we report the first persistent RTP with lifetimes up to 0.5 s from simple triarylboranes which have no lone pairs. RTP is only observed in the crystalline state and in highly doped PMMA films which are indicative of aggregation induced emission (AIE). Detailed crystal structure analysis suggested that intermolecular interactions are important for efficient RTP. Furthermore, photophysical studies of the isolated molecules in a frozen glass, in combination with DFT/MRCI calculations, show that (σ, B p)→(π, B p) transitions accelerate the ISC process. This work provides a new approach for the design of RTP materials without (n, π*) transitions.     

Tuning the Optical Properties of 2‐Thienylpyridyl Iridium Complexes through Carboranes and Anions

2‐Thienylpyridyl iridium(III) complexes containing an o‐, m‐, or p‐carboranylvinyl‐2,2′‐bipyridine ligand and various counteranions (denoted o ‐ PF₆ , m ‐ BF₄ , m ‐ PF₆ , m ‐ SbF₆ , m ‐ ClO₄ , m ‐ OTf , m ‐ NO₃ , m ‐ BPh₄ , m ‐ F , m ‐ Cl , and p ‐ PF₆ ) were synthesized by using C‐formyl carboranes as starting materials. The solid‐state structures of o ‐ PF₆ , m ‐ PF₆ , m ‐ ClO₄ , and m ‐ BF₄ showed that the cations form twisted cavities in which the anions are fixed by multiple hydrogen bonds. Anion–hydrogen interactions were investigated for nine m‐carborane‐based complexes with different counteranions. All carborane‐based iridium(III) complexes show similar phosphorescence yields in solution but significantly different emission in the solid state. Anion‐exchange titration and theoretical calculations revealed the relationships between structures and optical properties. The size of the anion and C?H ??? X anion–hydrogen bonds strongly influence the phosphorescence quantum yield in the solid state. In particular, the C_car?H ??? X hydrogen bonds between the carboranyl unit and the anion play an important role in solid‐state phosphorescence. Complex p ‐ PF₆ was successfully applied in phosphorescence‐lifetime bioimaging owing to its low toxicity and near‐infrared emission.     

Sterically Crowded peri‐Substituted Naphthalene Phosphines and their PV Derivatives

Three sterically crowded peri‐substituted naphthalene phosphines, Nap[PPh₂][ER] (Nap=naphthalene‐1,8‐diyl; ER=SEt, SPh, SePh) 1–3 , which contain phosphorus and chalcogen functional groups at the peri positions have been prepared. Each phosphine reacts to form a complete series of P^V chalcogenides Nap[P(E′)(Ph₂)(ER)] (E′=O, S, Se). The novel compounds were fully characterised by using X‐ray crystallography and multinuclear NMR spectroscopy, IR spectroscopy and MS. X‐ray data for 1 , 2 , n O , n S , n Se (n=1–3) are compared. Eleven molecular structures have been analysed by naphthalene ring torsions, peri‐atom displacement, splay angle magnitude, X???E interactions, aromatic ring orientations and quasi‐linear arrangements. An increase in the congestion of the peri region following the introduction of heavy chalcogen atoms is accompanied by a general increase in naphthalene distortion. P???E distances increase for molecules that contain bulkier atoms at the peri positions and also when larger chalcogen atoms are bound to phosphorus. The chalcogenides adopt similar conformations that contain a quasi‐linear E???P? C fragment, except for 3 O , which displays a twist‐axial‐twist conformation resulting in the formation of a linear O???Se? C alignment. Ab initio MO calculations performed on 2 O , 3 O , 3 S and 3 Se reveal Wiberg bond index values of 0.02 to 0.04, which indicates only minor non‐bonded interactions; however, calculations on radical cations of 3 O , 3 S and 3 Se reveal increased values (0.14–0.19).     

The Carbonyl⋅⋅⋅Tellurazole Chalcogen Bond as a Molecular Recognition Unit: From Model Studies to Supramolecular Organic Frameworks

In the last years, chalcogen bonding, the noncovalent interaction involving chalcogen centers, has emerged as interesting alternative to the ubiquitous hydrogen bonding in many research areas. Here, we could show by means of high‐level quantum chemical calculations that the carbonyl???tellurazole chalcogen bond is at least as strong as conventional hydrogen bonds. Using the carbonyl???tellurazole binding motif, we were able to design complex supramolecular networks in solid phase starting from tellurazole‐substituted cyclic peptides. X‐ray analyses reveal that the rigid structure of the cyclic peptides is caused by hydrogen bonds, whereas the supramolecular network is held together by chalcogen bonding. The type of the supramolecular network depends on peptide used; both linear wires and a honeycomb‐like supramolecular organic framework (SOF) were observed. The unique structure of the SOF shows two channels filled with different types of solvent mixtures that are either locked or freely movable.     

Resonance Character of Copper/Silver/Gold Bonding in Small Molecule⋅⋅⋅MX (X=F,Cl, Br,CH3, CF3) Complexes

The resonance character of Cu/Ag/Au bonding is investigated in B???M?X (M=Cu, Ag, Au; X=F, Cl, Br, CH₃, CF₃; B=CO, H₂O, H₂S, C₂H₂, C₂H₄) complexes. The natural bond orbital/natural resonance theory results strongly support the general resonance‐type three‐center/four‐electron (3c/4e) picture of Cu/Ag/Au bonding, B:M?X?B⁺?M:X^?, which mainly arises from hyperconjugation interactions. On the basis of such resonance‐type bonding mechanisms, the ligand effects in the more strongly bound OC???M?X series are analyzed, and distinct competition between CO and the axial ligand X is observed. This competitive bonding picture directly explains why CO in OC???Au?CF₃ can be readily replaced by a number of other ligands. Additionally, conservation of the bond order indicates that the idealized relationship b_B???M+b_MX=1 should be suitably generalized for intermolecular bonding, especially if there is additional partial multiple bonding at one end of the 3c/4e hyperbonded triad.     

Synthetic and Structural Studies of 1‐Halo‐8‐(alkylchalcogeno)naphthalene Derivatives

A series of eight 1‐halo‐8‐(alkylchalcogeno)naphthalene derivatives ( 1 – 8 ; halogen=Br, I; alkylchalcogen=SEt, SPh, SePh, TePh) containing a halogen and a chalcogen atom occupying the peri positions have been prepared and fully characterised by using X‐ray crystallography, multinuclear NMR spectroscopy, IR spectroscopy and MS. Naphthalene distortion due to non‐covalent substituent interactions was studied as a function of the bulk of the interacting chalcogen atoms and the size and nature of the alkyl group attached to them. X‐ray data for 1 , 2 , 4 and 5 – 8 were compared. Molecular structures were analysed in terms of naphthalene ring torsions, peri‐atom displacement, splay angle magnitude, X???E interactions, aromatic ring orientations and quasi‐linear X???E? C arrangements. A general increase in the X???E distance was observed for molecules that contain bulkier atoms at the peri positions. The I???S distance of 4 is comparable with the I???Te distance of 8 , and is ascribed to a stronger lone pair–lone pair repulsion due to the presence of an axial S(naphthyl) ring conformation. Density functional theory (B3LYP) calculations performed on 5 – 8 revealed Wiberg bond index values of 0.05–0.08, which indicate minor interactions taking place between the non‐bonded atoms in these compounds.     

The Role of Molecular Electrostatic Potentials in the Formation of a Halogen Bond in Furan⋅⋅⋅XY and Thiophene⋅⋅⋅XY Complexes

The halogen bonding of furan???XY and thiophene???XY (X=Cl, Br; Y=F, Cl, Br), involving σ‐ and π‐type interactions, was studied by using MP2 calculations and quantum theory of “atoms in molecules” (QTAIM) studies. The negative electrostatic potentials of furan and thiophene, as well as the most positive electrostatic potential (V_S,max) on the surface of the interacting X atom determined the geometries of the complexes. Linear relationships were found between interaction energy and V_S,max of the X atom, indicating that electrostatic interactions play an important role in these halogen‐bonding interactions. The halogen‐bonding interactions in furan???XY and thiophene???XY are weak, “closed‐shell” noncovalent interactions. The linear relationship of topological properties, energy properties, and the integration of interatomic surfaces versus V_S,max of atom X demonstrate the importance of the positive σ hole, as reflected by the computed V_S,max of atom X, in determining the topological properties of the halogen bonds.     

Rational Topological Design for Fluorescence Enhancement upon Aggregation of Distyrylfuran Derivatives

A series of 2,5‐distyrylfuran derivatives bearing pentafluorophenyl‐ and cyanovinyl units have been synthesized for aggregation‐induced emission (AIE). The effect of the type and extent of the supramolecular connections on the AIE of the furan derivatives were examined and correlated with their X‐ray crystal structures. It was found that the simultaneous presence of cyano and perfluorophenyl units strongly enhances the fluorescence upon aggregation. Single‐crystal X‐ray diffraction analysis confirmed that C?H???F, F???F, C?H???nitrile, Ar???Ar_F (Ar=aryl, Ar_F=fluoroaryl), and nitrile???Ar_F intra‐ and intermolecular interactions drive the topology of the molecule and that solid‐state supramolecular contacts favor AIE of the furan derivatives.     

Chalcogenide Derivatives of the seco‐Cubane [Sn3(μ2‐NHtBu)2(μ2‐NtBu)(μ3‐NtBu)]

A series of monochalcogenide derivatives of the seco‐cubane [Sn₃(μ₂‐NHtBu)₂(μ₂‐NtBu)(μ₃‐NtBu)] has been prepared and characterized by NMR and X‐ray crystallographic studies. These complexes exhibit different tin‐chalcogen bonding modes. In the case of the monotelluride, a terminal Sn=Te bond was observed in solution and in the solid state, whereas for the monosulfide, a μ₂ bridging mode was adopted by the sulfur atoms. The monoselenide was found to employ both bonding modes in solution, although only the terminal Sn=Se bonding mode was structurally characterized. The complexes undergo chalcogen exchange between tin atoms in solution, and this process was studied by variable temperature NMR.     

Rational Modification of the Hierarchy of Intermolecular Interactions in Molecular Crystal Structures by Using Tunable Halogen Bonds

A family of 16 isomolecular salts (3‐XpyH)₂[MX′₄] (3‐XpyH=3‐halopyridinium; M=Co, Zn; X=(F), Cl, Br, (I); X′=Cl, Br, I) each containing rigid organic cations and tetrahedral halometallate anions has been prepared and characterized by X‐ray single crystal and/or powder diffraction. Their crystal structures reflect the competition and cooperation between non‐covalent interactions: N? H???X′? M hydrogen bonds, C? X???X′? M halogen bonds and π–π stacking. The latter are essentially unchanged in strength across the series, but both halogen bonds and hydrogen bonds are modified in strength upon changing the halogens involved. Changing the organic halogen (X) from F to I strengthens the C? X???X′? M halogen bonds, whereas an analogous change of the inorganic halogen (X′) weakens both halogen bonds and N? H???X′? M hydrogen bonds. By so tuning the strength of the putative halogen bonds from repulsive to weak to moderately strong attractive interactions, the hierarchy of the interactions has been modified rationally leading to systematic changes in crystal packing. Three classes of crystal structure are obtained. In type A (C? F???X′? M) halogen bonds are absent. The structure is directed by N? H???X′? M hydrogen bonds and π‐stacking interactions. In type B structures, involving small organic halogens (X) and large inorganic halogens (X′), long (weak) C? X???X′? M interactions are observed with type I halogen–halogen interaction geometries (C? X???X′ ≈ X???X′? M ≈155°), but hydrogen bonds still dominate. Thus, minor but quite significant perturbations from the type A structure arise. In type C, involving larger organic halogens (X) and smaller inorganic halogens (X′), stronger halogen bonds are formed with a type II halogen–halogen interaction geometry (C? X???X′ ≈180°; X???X′? M ≈110°) that is electrostatically attractive. The halogen bonds play a major role alongside hydrogen bonds in directing the type C structures, which as a result are quite different from type A and B.     

Influence of Sulfur Atoms on TADF Properties from Through-Space Charge Transfer Excited States

The harnessing of heavy atom effect of chalcogen elements offers a way for boosting the thermally activated delayed fluorescence (TADF) of purely organic luminescent materials that can harvest triplet excitons. However, the conformational and electronic variations induced by the heavy and large atoms may also have adverse effects on the TADF properties. Herein, the design, synthesis, and structures of a new type of through-space charge transfer (TSCT) emitters containing benzothiazino[2,3,4-kl]phenothiazine (DPTZ) as the donor unit are reported. The influences of S atoms on the emission properties have been systematically investigated by means of theoretical simulations, electrochemical and spectroscopic studies. Although the presence of π-stacking interactions and calculated spin-orbit coupling (SOC) values are beneficial for TSCT-TADF properties, the triplet TSCT states are uplifted to above the locally excited (LE) state of the acceptor moieties. As a result, the new emitters display longer delayed fluorescence lifetimes (τ_DF) of 255.0–114.3 μs and lower PLQYs of 45–61 % in comparison with the O-containing congeners (τ_DF=26.9–6.8 μs; PLQYs=74–71 %). This work highlights that a full consideration of various effects is essential when making use of heavy chalcogen atoms for the design of TADF emitters.     

Die Bildung von Gallium-Chalkogen-Heterokubanstrukturen durch Umsetzung der Alkylgallium(I)-Verbindung Ga4[C(SiMe3)3]4 mit Schwefel,Selen und Tellur

The Formation of Gallium Chalcogen Heterocubanes by the Reaction of the Alkylgallium(I) Compound Ga₄[C(SiMe₃)₃]₄ with Sulfur, Selenium, and Tellurium The alkylgallium(I) compound Ga₄[C(SiMe₃)₃]₄ 1 , which monomerizes in dilute solutions, reacts with elemental sulfur, selenium, and tellurium in boiling n-hexane to yield the corresponding Ga₄X₄R₄ cage compounds in a high yield. As shown by crystal structure determinations, the products have distorted Ga₄X₄ heterocubanes in their molecular centers with a slightly increasing distortion for the heavier chalcogen atoms. While the selenium and tellurium derivatives show a very low solubility in benzene, the sulfur compound dissolves readily accompanied by the dissociation into the (RGaS)₂ dimer.     

两个含双(3,5－二甲吡唑基)甲烷配体的铅(II)配合物的合成与结构表征

Reactions of lead（Ⅱ） nitrate or perchlorate with bis（3,5-dimethylpyrazolyl）methane （dmpzm）, produced two new Pb（Ⅱ） chelated complexes [Pb（dmpzm）2X2] （X=NO3^- 1, ClO4^- 2）. Both compounds were structurally characterized by elemental analysis, IR spectroscopy, thermal analysis, and single crystal X-ray diffraction. Both compounds are mononuclear with a distorted square antiprismatic PbN4O4 coordination geometry incorporating a pair of O,O＇-bidentate anions and N,N＇-bidentate dmpzm ligands. In the crystals of 1 or 2, the methyl or methylene groups of dmpzm ligand interact with the oxygen atoms of nitrates or perchlorates to afford intra- and intermolecular hydrogen bonding, thereby forming a two-dimensional network 1 or a three-dimensional structure 2.     

Cation–Cation Pairing by NCH⋅⋅⋅O Hydrogen Bonds

The pairing of ions of opposite charge is a fundamental principle in chemistry, and is widely applied in synthesis and catalysis. In contrast, cation–cation association remains an elusive concept, lacking in supporting experimental evidence. While studying the structure and properties of 4‐oxopiperidinium salts [OC₅H₈NH₂]X for a series of anions X^? of decreasing basicity, we observed a gradual self‐association of the cations, concluding in the formation of an isolated dicationic pair. In 4‐oxopiperidinium bis(trifluoromethylsulfonyl)amide, the cations are linked by N? H???O?C hydrogen bonds to form chains, flanked by hydrogen bonds to the anions. In the tetra(perfluoro‐tert‐butoxy)aluminate salt, the anions are fully separated from the cations, and the cations associate pairwise by N? C? H???O?C hydrogen bonds. The compounds represent the first genuine examples of self‐association of simple organic cations based merely on hydrogen bonding as evidenced by X‐ray structure analysis, and provide a paradigm for an extension of this class of compounds.     

Chalcogen Bonding Catalysis of a Nitro‐Michael Reaction

Chalcogen bonding is the non‐covalent interaction between Lewis acidic chalcogen substituents and Lewis bases. Herein, we present the first application of dicationic tellurium‐based chalcogen bond donors in the nitro‐Michael reaction between trans‐β‐nitrostyrene and indoles. This also constitutes the first activation of nitro derivatives by chalcogen bonding (and halogen bonding). The catalysts showed rate accelerations of more than a factor of 300 compared to strongly Lewis acidic hydrogen bond donors. Several comparison experiments, titrations, and DFT calculations support a chalcogen‐bonding‐based mode of activation of β‐nitrostyrene.     

Supramolecular Assembling through Anionic Iodine Secondary Bonds: Synthesis and X‐ray Characterization of (Et4N)[PhTeI4] and (Et4N)[(β‐Naphthyl)TeI4]

[PhTe]₂ and [(β‐naphthyl)Te]₂ react with iodine and tetraethylammonium iodide in toluene/methanol to give (Et₄N)[PhTeI₄] and (Et₄N)[(β‐Naphthyl)TeI₄]. The complexes were analysed by single crystal X‐ray diffraction affording the centrosymmetric monoclinic space group P2₁/c. In the novel compounds only anionic interactions of the types Te···I and I···I take place, cation‐anion effective contacts do not occur. Both anions [PhTeI₄] and [(β‐naphthyl)TeI₄] exhibit square pyramidal coordination at tellurium, with the iodine atoms in the basal positions and the organic groups apical. The tellurium centers achieve an octahedral coordination in the whole lattices through Te···I secondary bonds with the adjacent ionic species. Only the Te–I‐ and I–I‐secondary bonds behave as structure‐forming interactions in the self‐organization of the supramolecular anionic gatherings. New evidences show that for organyltellurates (Q)[PhTeX₄] (Q = protonated amines, amides or amino acids; X = Cl, Br, I), NH···X hydrogen bondings are able to hinder the anionic halogen‐halogen secondary interactions. In case of the more frequent I···I interactions, they have been observed only in the absence of NH···I hydrogen bonds.