[N⋅⋅⋅I+⋅⋅⋅N] Halogen‐Bonded Dimeric Capsules from Tetrakis(3‐pyridyl)ethylene Cavitands

Two [N???I⁺???N] halogen‐bonded dimeric capsules using tetrakis(3‐pyridyl)ethylene cavitands with different lower rim alkyl chains are synthesized and analyzed in solution and the gas phase. These first examples of symmetrical dimeric capsules making use of the iodonium ion (I⁺) as the main connecting module are characterized by ¹H NMR spectroscopy, diffusion ordered NMR spectroscopy (DOSY), electrospray ionization mass spectrometry (ESI‐MS), and ion mobility‐mass spectrometry (TW‐IMS) experiments. The synthesis and effective halogen‐bonded dimerization proceeds through analogous dimeric capsules with [N???Ag⁺???N] binding motifs as the intermediates as evidenced by the X‐ray structures of (CH₂Cl₂)₂@[ 3 a ₂?Ag₄?(H₂O)₂?OTs₄] and (CH₂Cl₂)₂@[ 3 a ₂?Ag₄?(H₂O)₄?OTs₄], two structurally different capsules.     

Multinuclear Solid‐State Magnetic Resonance as a Sensitive Probe of Structural Changes upon the Occurrence of Halogen Bonding in Co‐crystals

Although the understanding of intermolecular interactions, such as hydrogen bonding, is relatively well‐developed, many additional weak interactions work both in tandem and competitively to stabilize a given crystal structure. Due to a wide array of potential applications, a substantial effort has been invested in understanding the halogen bond. Here, we explore the utility of multinuclear (¹³C, ^14/15N, ¹⁹F, and ¹²⁷I) solid‐state magnetic resonance experiments in characterizing the electronic and structural changes which take place upon the formation of five halogen‐bonded co‐crystalline product materials. Single‐crystal X‐ray diffraction (XRD) structures of three novel co‐crystals which exhibit a 1:1 stoichiometry between decamethonium diiodide (i.e., [(CH₃)₃N⁺(CH₂)₁₀N⁺(CH₃)₃][2 I^?]) and different para‐dihalogen‐substituted benzene moieties (i.e., p‐C₆X₂Y₄, X=Br, I; Y=H, F) are presented. ¹³C and ¹⁵N NMR experiments carried out on these and related systems validate sample purity, but also serve as indirect probes of the formation of a halogen bond in the co‐crystal complexes in the solid state. Long‐range changes in the electronic environment, which manifest through changes in the electric field gradient (EFG) tensor, are quantitatively measured using ¹⁴N NMR spectroscopy, with a systematic decrease in the ¹⁴N quadrupolar coupling constant (C_Q) observed upon halogen bond formation. Attempts at ¹²⁷I solid‐state NMR spectroscopy experiments are presented and variable‐temperature ¹⁹F NMR experiments are used to distinguish between dynamic and static disorder in selected product materials, which could not be conclusively established using solely XRD. Quantum chemical calculations using the gauge‐including projector augmented‐wave (GIPAW) or relativistic zeroth‐order regular approximation (ZORA) density functional theory (DFT) approaches complement the experimental NMR measurements and provide theoretical corroboration for the changes in NMR parameters observed upon the formation of a halogen bond.     

Halogen bonds on demand: I...S contacts in cocrystals of trans‐bis(thiocyanato‐κN)tetrakis(4‐vinylpyridine‐κN)nickel(II) and 2,3,5,6‐tetrafluoro‐1,4‐diiodobenzene

Hydrogen bonds are considered a powerful organizing force in designing supramolecular architectures because they are directional, selective and reversible at room temperature. trans‐Dithiocyanatotetrakis(4‐vinylpyridine)nickel(II) is a popular host for the inclusion of small molecules and 2,3,5,6‐tetrafluoro‐1,4‐diiodobenzene (TFDIB) represents a strong halogen‐bond donor. These constituents cocrystallize in a 1:1 stoichiometry, [Ni(NCS)₂(C₇H₇N)₄]·C₆F₄I₂, in the tetragonal space group I4₁/a. Both residues occupy special positions, i.e. the pseudo‐octahedral Ni^II complex is located on a twofold axis and the TFDIB molecule sits about a crystallographic centre of inversion. The components interact via a short S...I contact of 3.2891 (12) Å between the thiocyanate S atom of the host and the iodine substituent at the perhalogenated aromatic ring of the smaller guest molecule. This interaction meets the commonly accepted criteria for a halogen bond. Such halogen bonds to sulfur are significantly less common than to smaller electronegative atoms.     

Ditopic halogen bonding with bipyrimidines and activated pyrimidines

The potential of pyrimidines to serve as ditopic halogen‐bond acceptors is explored. The halogen‐bonded cocrystals formed from solutions of either 5,5′‐bipyrimidine (C₈H₆N₄) or 1,2‐bis(pyrimidin‐5‐yl)ethyne (C₁₀H₆N₄) and 2 molar equivalents of 1,3‐diiodotetrafluorobenzene (C₆F₄I₂) have a 1:1 composition. Each pyrimidine moiety acts as a single halogen‐bond acceptor and the bipyrimidines act as ditopic halogen‐bond acceptors. In contrast, the activated pyrimidines 2‐ and 5‐{[4‐(dimethylamino)phenyl]ethynyl}pyrimidine (C₁₄H₁₃N₃) are ditopic halogen‐bond acceptors, and 1:1 halogen‐bonded cocrystals are formed from 1:1 mixtures of each of the activated pyrimidines and either 1,2‐ or 1,3‐diiodotetrafluorobenzene. A 1:1 cocrystal was also formed between 2‐{[4‐(dimethylamino)phenyl]ethynyl}pyrimidine and 1,4‐diiodotetrafluorobenzene, while a 2:1 cocrystal was formed between 5‐{[4‐(dimethylamino)phenyl]ethynyl}pyrimidine and 1,4‐diiodotetrafluorobenzene.     

Synthesis,Characterization, and Symmetry Relations of the Crystal Structures of Some Bis(dioxane) Adducts of Group 1 / Group 13 Heterometallic Trifluoroacetates

Four bis(dioxane) adducts of mixed‐metal trifluoroacetates, M[M′(O₂CCF₃)₄(C₄H₈O₂)₂] (M = Na, K, Cs, M′ = In and M = Cs, M′ = Ga) were synthesized by reaction of alkali metal trifluoroacetate and group 13 element trifluoroacetate in 1,4‐dioxane and completely characterized including X‐ray structure determination. Geometric parameters, empirical bond valences and frequencies of the symmetric C=O stretching vibrations show that the moisture sensitive solids are composed of dimeric structural moieties with site symmetry 1 , containing alkali metal ions and bis(dioxane)tetrakis(trifluoroacetato)indate or ‐gallate ions. The dimeric units are further connected by weaker “intermolecular” dioxane interactions to neighboring alkali metal ions. Closer inspection of space group symmetry, unit cell parameters and atom sites allows to rationalize the compounds as members of two isotypic pairs that are further closely related due to the group‐subgroup relation of their monoclinc space groups to a common orthorhombic supergroup.     

Comparative Study of Halogen‐ and Hydrogen‐Bond Interactions between Benzene Derivatives and Dimethyl Sulfoxide

The halogen bond, similar to the hydrogen bond, is an important noncovalent interaction and plays important roles in diverse chemistry‐related fields. Herein, bromine‐ and iodine‐based halogen‐bonding interactions between two benzene derivatives (C₆F₅Br and C₆F₅I) and dimethyl sulfoxide (DMSO) are investigated by using IR and NMR spectroscopy and ab initio calculations. The results are compared with those of interactions between C₆F₅Cl/C₆F₅H and DMSO. First, the interaction energy of the hydrogen bond is stronger than those of bromine‐ and chlorine‐based halogen bonds, but weaker than iodine‐based halogen bond. Second, attractive energies depend on 1/rⁿ, in which n is between three and four for both hydrogen and halogen bonds, whereas all repulsive energies are found to depend on 1/r^8.5. Third, the directionality of halogen bonds is greater than that of the hydrogen bond. The bromine‐ and iodine‐based halogen bonds are strict in this regard and the chlorine‐based halogen bond only slightly deviates from 180°. The directional order is iodine‐based halogen bond>bromine‐based halogen bond>chlorine‐based halogen bond>hydrogen bond. Fourth, upon the formation of hydrogen and halogen bonds, charge transfers from DMSO to the hydrogen‐ and halogen‐bond donors. The CH₃ group contributes positively to stabilization of the complexes.     

Conformational behavior of nylon 6 in mixed solvents

The intrinsic viscosity [η], Huggins constant (K_H), laser light scattering, UV and IR measurements of Nylon 6 are made in m‐cresol and its mixture with 1,4‐dioxane at 20–60 °C. The intrinsic viscosity, R_g, A₂, (<S>²)^1/2 (calculated from viscosity data), R_H, and UV absorbance initially increase and then decrease with the rise in 1,4‐dioxane contents. The K_H and the transmittance of ? OH group in IR spectra show an opposite trend to that of [η]. The dielectric constant calculated from the refractive index of the solvent (m‐cresol with 1,4‐dioxane) and polymer solution shows a continuous decrease with the amount of 1,4‐dioxane. Activation energy shows a minimum while linear expansion coefficient (α³) maximum with the addition of 1,4‐dioxane. Change in [η], K_H, and other characteristics of the polymer solutions with alterations in solvent composition and temperature are the result of variation in the thermodynamic quality of the solvent, its selective adsorption, hydrogen bonding, and conformational transitions. It has been concluded that the addition of 1,4‐dioxane first enhances the quality of the solvent, encourages hydrogen bonding, and specific adsorption, and then deteriorates, bringing conformational transitions in the polymer molecules. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 534–541, 2005     

Benchmarking of Halogen Bond Strength in Solution with Nickel Fluorides: Bromine versus Iodine and Perfluoroaryl versus Perfluoroalkyl Donors

The energetics of halogen bond formation in solution have been investigated for a series of nickel fluoride halogen bond acceptors; trans-[NiF(2-C₅NF₄)(PEt₃)₂] ( A1 ), trans-[NiF{2-C₅NF₃(4-H)}(PEt₃)₂] ( A2 ), trans-[NiF{2-C₅NF₃(4-NMe₂)}(PEt₃)₂] ( A3 ) and trans-[NiF{2-C₅NF₂H(4-CF₃)}(PCy₃)₂] ( A4 ) with neutral organic halogen bond donors, iodopentafluorobenzene ( D1 ), 1-iodononafluorobutane ( D2 ) and bromopentafluorobenzene ( D3 ), in order to establish the significance of changes from perfluoroaryl to perfluoroalkyl donors and from iodine to bromine donors. ¹⁹F NMR titration experiments have been employed to obtain the association constants, enthalpy, and entropy for the halogen bond formed between these donor-acceptor partners in protiotoluene. For A2 – A4 , association constants of the halogen bonds formed with iodoperfluoroalkane ( D2 ) are consistently larger than those obtained for analogous complexes with the iodoperfluoroarene ( D1 ). For complexes formed with A2 – A4 , the strength of the halogen bond is significantly lowered upon modification of the halogen donor atom from I (in D1 ) to Br (in D3 ) (for D1 : 5≤K₂₈₅≤12 m ⁻¹, for D3 : 1.0≤K₁₉₃≤1.6 m ⁻¹). The presence of the electron donating NMe₂ substituent on the pyridyl ring of acceptor A3 led to an increase in −ΔH, and the association constants of the halogen bond complexes formed with D1 – D3 , compared to those formed by A1 , A2 and A4 with the same donors.     

Competing intermolecular interactions in some `bridge‐flipped' isomeric phenylhydrazones

To examine the roles of competing intermolecular interactions in differentiating the molecular packing arrangements of some isomeric phenylhydrazones from each other, the crystal structures of five nitrile–halogen substituted phenylhydrazones and two nitro–halogen substituted phenylhydrazones have been determined and are described here: (E)‐4‐cyanobenzaldehyde 4‐chlorophenylhydrazone, C₁₄H₁₀ClN₃, (Ia); (E)‐4‐cyanobenzaldehyde 4‐bromophenylhydrazone, C₁₄H₁₀BrN₃, (Ib); (E)‐4‐cyanobenzaldehyde 4‐iodophenylhydrazone, C₁₄H₁₀IN₃, (Ic); (E)‐4‐bromobenzaldehyde 4‐cyanophenylhydrazone, C₁₄H₁₀BrN₃, (IIb); (E)‐4‐iodobenzaldehyde 4‐cyanophenylhydrazone, C₁₄H₁₀IN₃, (IIc); (E)‐4‐chlorobenzaldehyde 4‐nitrophenylhydrazone, C₁₃H₁₀ClN₃O₂, (III); and (E)‐4‐nitrobenzaldehyde 4‐chlorophenylhydrazone, C₁₃H₁₀ClN₃O₂, (IV). Both (Ia) and (Ib) are disordered (less than 7% of the molecules have the minor orientation in each structure). Pairs (Ia)/(Ib) and (IIb)/(IIc), related by a halogen exchange, are isomorphous, but none of the `bridge‐flipped' isomeric pairs, viz. (Ib)/(IIb), (Ic)/(IIc) or (III)/(IV), is isomorphous. In the nitrile–halogen structures (Ia)–(Ic) and (IIb)–(IIc), only the bridge N—H group and not the bridge C—H group acts as a hydrogen‐bond donor to the nitrile group, but in the nitro–halogen structures (III) (with Z′ = 2) and (IV), both the bridge N—H group and the bridge C—H group interact with the nitro group as hydrogen‐bond donors, albeit via different motifs. The occurrence here of the bridge C—H contact with a hydrogen‐bond acceptor suggests the possibility that other pairs of `bridge‐flipped' isomeric phenylhydrazones may prove to be isomorphous, regardless of the change from isomer to isomer in the position of the N—H group within the bridge.     

The diiodine basicity scale: toward a general halogen-bond basicity scale

The new diiodine basicity scale pK_BI2 is quasi‐orthogonal to most known Lewis basicity scales (hydrogen‐bond, dative‐bond and cation basicity scales). The diiodine basicity falls in the sequence N>P≈Se>S>I≈O>Br>Cl>F for the iodine‐bond acceptor atomic site and SbO≈NO≈AsO>SeO>PO>SO>C?O>? O? >SO₂ or PS?? S? >C?S?N?C?S for the functionality of oxygen or sulfur bases. Substituent effects are quantified through linear free energy relationships, which allow the calculation of individual complexation constants for each site of polybases and thus the classification of aromatic ethers as carbon π bases and of aromatic amines, thioethers and selenoethers as N, S and Se bases, respectively. The pK_BI2 values of nBu₃N⁺‐N^?C≡N, 2‐aminopyridine and 1,10‐phenanthroline reveal a superbasic nitrile, a hydrogen‐bond‐assisted iodine bond and a two‐centre iodine bond, respectively. The diiodine basicity scale is a general inorganic but family‐dependent organic halogen‐bond basicity scale because organic halogen‐bond donors such as IC≡N and ICF₃ have a stronger electrostatic character than I₂. The family independence can be restored by the addition of an electrostatic parameter, either the experimental pK_BHX hydrogen‐bond basicity scale or the computed minimum electrostatic potential.     

Molybdän‐ und Wolfram‐Komplexe mit MNS‐Sequenzen. Die Kristallstrukturen von [MoCl3(N3S2)(1,4‐Dioxan)2] und [Mo2Cl2(μ‐NSN)2(μ‐O)(NCMe3)(OCMe3)2]2

Molybdenum and Tungsten Complexes with MNS Sequences. Crystal Structures of [MoCl₃(N₃S₂)(1,4‐dioxane)₂] and [Mo₂Cl₂(μ‐NSN)₂(μ‐O)(NCMe₃)(OCMe₃)₂]₂ The cyclo‐thiazeno complexes [Cl₃MNSNSN]₂ of molybdenum and tungsten react with 1,4‐dioxane in dichloromethane suspension to give the binuclear donor‐acceptor complexes [μ‐(1,4‐dioxane){MCl₃(N₃S₂)}₂] which are characterized by IR spectroscopy. With excess 1,4‐dioxane the molybdenum compound forms the complex [MoCl₃(N₃S₂)(1,4‐dioxane)₂] in which, according to the crystal structure determination, one of the dioxane molecules coordinates at the molybdenum atom, the other one at one of the sulfur atoms of the cyclo‐thiazeno ring. The μ‐(NSN^2–) complex [Mo₂Cl₂(μ‐NSN)₂(μ‐O)(NCMe₃)(OCMe₃)₂]₂ has been obtained by the reaction of [MoN(OCMe₃)₃] with trithiazyle chloride in carbontetrachloride solution. According to the crystal structure determination this compound forms centrosymmetric dimeric molecules via two of the nitrogen atoms of two of the μ‐(NSN) groups to give a Mo₂N₂ fourmembered ring. [MoCl₃(N₃S₂)(1,4‐dioxane)₂]: Space group P2₁/c, Z = 4, lattice dimensions at –70 °C: a = 1522.9(2); b = 990.3(1); c = 1161.7(1) pm; β = 106.31(1)°, R₁ = 0.0317. [Mo₂Cl₂(μ‐NSN)₂(μ‐O)(NCMe₃)(OCMe₃)₂]₂ · 4 CCl₄: Space group P2₁/c, Z = 2, lattice dimensions at –83 °C: a = 1216.7(1); b = 2193.1(2); c = 1321.8(1) pm; β = 98.23(1)°; R₁ = 0.0507.     

Boron as an Electron‐Pair Donor for B⋅⋅⋅Cl Halogen Bonds

MP2/aug′‐cc‐pVTZ calculations were performed to investigate boron as an electron‐pair donor in halogen‐bonded complexes (CO)₂(HB):ClX and (N₂)₂(HB):ClX, for X=F, Cl, OH, NC, CN, CCH, CH₃, and H. Equilibrium halogen‐bonded complexes with boron as the electron‐pair donor are found on all of the potential surfaces, except for (CO)₂(HB):ClCH₃ and (N₂)₂(HB):ClF. The majority of these complexes are stabilized by traditional halogen bonds, except for (CO)₂(HB):ClF, (CO)₂(HB):ClCl, (N₂)₂(HB):ClCl, and (N₂)₂(HB):ClOH, which are stabilized by chlorine‐shared halogen bonds. These complexes have increased binding energies and shorter B?Cl distances. Charge transfer stabilizes all complexes and occurs from the B lone pair to the σ* Cl?A orbital of ClX, in which A is the atom of X directly bonded to Cl. A second reduced charge‐transfer interaction occurs in (CO)₂(HB):ClX complexes from the Cl lone pair to the π* C≡O orbitals. Equation‐of‐motion coupled cluster singles and doubles (EOM‐CCSD) spin–spin coupling constants, ^1xJ(B‐Cl), across the halogen bonds are also indicative of the changing nature of this bond. ^1xJ(B‐Cl) values for both series of complexes are positive at long distances, increase as the distance decreases, and then decrease as the halogen bonds change from traditional to chlorine‐shared bonds, and begin to approach the values for the covalent bonds in the corresponding ions [(CO)₂(HB)?Cl]⁺ and [(N₂)₂(HB)?Cl]⁺. Changes in ¹¹B chemical shieldings upon complexation correlate with changes in the charges on B.     

Cooperativity between the Halogen Bond and the Hydrogen Bond in H3N⋅⋅⋅XY⋅⋅⋅HF Complexes (X,Y=F,Cl, Br)

Ab initio calculations are used to provide information on H₃N???XY???HF triads (X, Y=F, Cl, Br) each having a halogen bond and a hydrogen bond. The investigated triads include H₃N???Br₂‐HF, H₃N???Cl₂???HF, H₃N???BrCI???HF, H₃N???BrF???HF, and H₃N???ClF???HF. To understand the properties of the systems better, the corresponding dyads are also investigated. Molecular geometries, binding energies, and infrared spectra of monomers, dyads, and triads are studied at the MP2 level of theory with the 6‐311++G(d,p) basis set. Because the primary aim of this study is to examine cooperative effects, particular attention is given to parameters such as cooperative energies, many‐body interaction energies, and cooperativity factors. The cooperative energy ranges from ?1.45 to ?4.64 kcal mol^?1, the three‐body interaction energy from ?2.17 to ?6.71 kcal mol^?1, and the cooperativity factor from 1.27 to 4.35. These results indicate significant cooperativity between the halogen and hydrogen bonds in these complexes. This cooperativity is much greater than that between hydrogen bonds. The effect of a halogen bond on a hydrogen bond is more pronounced than that of a hydrogen bond on a halogen bond.     

Methyl 2‐acetamido‐2‐deoxy‐β‐d‐glucopyranoside dihydrate and methyl 2‐formamido‐2‐deoxy‐β‐d‐glucopyranoside

Methyl 2‐acetamido‐2‐deoxy‐β‐d ‐glucopyranoside (β‐GlcNAcOCH₃), (I), crystallizes from water as a dihydrate, C₉H₁₇NO₆·H₂O, containing two independent molecules [denoted (IA) and (IB)] in the asymmetric unit, whereas the crystal structure of methyl 2‐formamido‐2‐deoxy‐β‐d ‐glucopyranoside (β‐GlcNFmOCH₃), (II), C₈H₁₅NO₆, also obtained from water, is devoid of solvent water molecules. The two molecules of (I) assume distorted ⁴C₁ chair conformations. Values of ϕ for (IA) and (IB) indicate ring distortions towards B_C2,C5 and ^C3,O5B, respectively. By comparison, (II) shows considerably more ring distortion than molecules (IA) and (IB), despite the less bulky N‐acyl side chain. Distortion towards B_C2,C5 was observed for (II), similar to the findings for (IA). The amide bond conformation in each of (IA), (IB) and (II) is trans, and the conformation about the C—N bond is anti (C—H is approximately anti to N—H), although the conformation about the latter bond within this group varies by ∼16°. The conformation of the exocyclic hydroxymethyl group was found to be gt in each of (IA), (IB) and (II). Comparison of the X‐ray structures of (I) and (II) with those of other GlcNAc mono‐ and disaccharides shows that GlcNAc aldohexopyranosyl rings can be distorted over a wide range of geometries in the solid state.     

Two polymorphs and the diethylammonium salt of the barbiturate eldoral

Polymorph (Ia) of eldoral [5‐ethyl‐5‐(piperidin‐1‐yl)barbituric acid or 5‐ethyl‐5‐(piperidin‐1‐yl)‐1,3‐diazinane‐2,4,6‐trione], C₁₁H₁₇N₃O₃, displays a hydrogen‐bonded layer structure parallel to (100). The piperidine N atom and the barbiturate carbonyl group in the 2‐position are utilized in N—H...N and N—H...O=C hydrogen bonds, respectively. The structure of polymorph (Ib) contains pseudosymmetry elements. The two independent molecules of (Ib) are connected via N—H...O=C(4/6‐position) and N—H...N(piperidine) hydrogen bonds to give a chain structure in the [100] direction. The hydrogen‐bonded layers, parallel to (010), formed in the salt diethylammonium 5‐ethyl‐5‐(piperidin‐1‐yl)barbiturate [or diethylammonium 5‐ethyl‐2,4,6‐trioxo‐5‐(piperidin‐1‐yl)‐1,3‐diazinan‐1‐ide], C₄H₁₂N⁺·C₁₁H₁₆N₃O₃⁻, (II), closely resemble the corresponding hydrogen‐bonded structure in polymorph (Ia). Like many other 5,5‐disubstituted derivatives of barbituric acid, polymorphs (Ia) and (Ib) contain the R₂²(8) N—H...O=C hydrogen‐bond motif. However, the overall hydrogen‐bonded chain and layer structures of (Ia) and (Ib) are unique because of the involvement of the hydrogen‐bond acceptor function in the piperidine group.     

Controlled Formation of Thiol‐Thiolate Hydrogen versus Disulfide Bonds between Two Iridium(III) Centers

Here, we report an iridium(III) coordination system with 2‐aminoethanethiolate (aet), which shows the formation of S?H???S hydrogen and S?S disulfide bonds in a controlled manner. Treatment of fac‐[Ir(aet)₃] with aqueous HBF₄ under aerobic conditions gave dinuclear [Ir₂(aet)₄(cysta)]²⁺ ([ 1 ]²⁺; cysta=cystamine) with a single S?S disulfide bond, while dimeric [Ir₂(aet)₃(Haet)₃](BF₄)₃ ([ 2 ](BF₄)₃) with a triple S?H???S hydrogen bond was formed by similar treatment under anaerobic conditions. Upon exposure to air, [ 2 ]³⁺ was converted to dinuclear [Ir₂(aet)₂(Haet)₂(cysta)]⁴⁺ ([ 3 ]⁴⁺), in which two Ir^III centers are spanned by a double S?H???S hydrogen bond and a single S?S disulfide bond. Complex [ 3 ]⁴⁺ was interconvertible with [ 1 ]²⁺ via the removal/addition of protons on S donors, accompanied by the intermolecular exchange of the fac‐[Ir(aet)₃] units. Complexes [ 1 ]²⁺, [ 2 ]³⁺, and [ 3 ]⁴⁺, isolated as BF₄^? salts, were fully characterized by single‐crystal X‐ray crystallography.     

Frozen Dissymmetric Cavities in Resorcinarene‐Based Coordination Capsules

By introducing slight structural modifications to a D₄‐symmetric coordination capsule, we succeeded in isolating the nearly enantiopure capsules (P)‐ and (M)‐ 2 a (BF₄)₄. Chiral guest, dibenzyl 4,4′‐diacetoxy‐6,6′‐dimethyl‐[1,1′‐biphenyl]‐2,2′‐dicarboxylate ( 3 ) was encapsulated within the dissymmetric cavity of 2 a (BF₄)₄, resulting in a high diastereoselectivity of >99 % de. The encapsulated guest was successfully removed from the complex without racemization through precipitation of the empty capsule. CD spectra confirmed that the chirality of the capsule was maintained in THF and 1,4‐dioxane for long periods, whereas a small amount of acetonitrile accelerated racemization of the empty capsule. The activation parameters of the racemization reaction were determined in dichloromethane and 1,2‐dichloroethane, resulting in positive enthalpic contributions and large negative entropic contributions, respectively. Accordingly, the racemization fits a first‐order kinetic model. Mechanically coupled Cu⁺‐2,2′‐bipyridine coordination centers were responsible for the high‐energy barrier of racemization and led to the unique chiral memory of the dissymmetric cavity, which was turned off by the addition of acetonitrile.     

Coordination‐directed and Hydrogen‐bonded Assembly of Supramolecular Architectures Constructed from Diverse Coordination of Linear,Triangular, Tetragonal Pyramid,Trigonal Bipyramid,and Octahedral Mononuclear Units

Reaction of a imidazole phenol ligand 4‐(imidazlo‐1‐yl)phenol (L) with 3d metal salts afforded four complexes, namely, [Ni(L)₆] · (NO₃)₂ ( 1 ), [Cu(L)₄(H₂O)] · (NO₃)₂ · (H₂O)₅ ( 2 ), [Zn(L)₄(H₂O)] · (NO₃)₂ · (H₂O) ( 3 ), and [Ag₂(L)₄] · SO₄ ( 4 ). All complexes are composed of monomeric units with diverse coordination arrangements and corresponding anions. All the hydroxyl groups of monomeric cations are used as hydrogen‐bond donors to form O–H ··· O hydrogen bonds. However, the coordination habit of different metal ions produces various supramolecular structures. The Ni^II atom shows octahedral arrangement in 1 , featuring a 3D twofold inclined interpenetrated network through O–H ··· O hydrogen bond and π–π stacking interaction. The Cu^II atom of 2 displays square pyramidal environment. The O–H ··· O hydrogen bond from the [Cu(L)₄(H₂O)]²⁺ cation and lattice water molecule as well as π–π stacking produce one‐dimensional open channels. NO₃^– ions and lattice water molecules are located in the channels. 3 is a 3D supramolecular network, in which Zn^II has a trigonal bipyramid arrangement. Two different rings intertwined with each other are observed. The Ag^I in 4 has linear and triangular coordination arrangements. The mononuclear units are assembled into a 1D chain by hydrogen bonding interaction from coordination units and SO₄^2– anions.     

Towards a Stronger Halogen Bond Involving Astatine: Unexpected Adduct with Bu3PO Stabilized by Hydrogen Bonding

The halogen bond is a powerful tool for the molecular design and pushing the limits of its strength is of major interest. Bearing the most potent halogen-bond donor atom, astatine monoiodide (AtI) was recently successfully probed [Nat. Chem. 2018 , 10, 428–434]. In this work, we continue the exploration of adducts between AtI and Lewis bases with the tributylphosphine oxide (Bu₃PO) ligand, revealing the unexpected experimental occurrence of two distinct chemical species with 1:1 and 2:1 stoichiometries. The 1:1 Bu₃PO⋅⋅⋅AtI complex is found to exhibit the strongest astatine-mediated halogen bond so far (with a formation constant of 10^(4.24±0.35)). Quantum chemical calculations unveil the intriguing nature of the 2:1 2Bu₃PO⋅⋅⋅AtI adduct, involving a halogen bond between AtI and one Bu₃PO molecular unit plus CH⋅⋅⋅O hydrogen bonds chelating the second Bu₃PO unit.     

Three styryl‐substituted tetrahydro‐1,4‐epoxy‐1‐benzazepines: configurations,conformations and hydrogen‐bonded chains

(2SR,4RS)‐7‐Chloro‐2‐exo‐[(E)‐styryl]‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C₁₈H₁₆ClNO, (I), crystallizes as a racemic twin in the space group P2₁ and the molecules are linked into a chain of edge‐fused R₃³(9) rings by a combination of C—H...O and C—H...N hydrogen bonds. The diastereoisomer (2RS,4RS)‐7‐chloro‐2‐endo‐[(E)‐styryl]‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, (II), also crystallizes as a racemic twin, but in the space group P2₁2₁2₁, and a two‐centre C—H...N hydrogen bond and a three‐centre C—H...(O,N) hydrogen bond combine to link the molecules into a complex chain of rings. In (2R,4R)‐7‐fluoro‐2‐endo‐[(E)‐styryl]‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C₁₈H₁₆FNO, (III), which is not isomorphous with (II), the molecules are linked by a single C—H...O hydrogen bond into simple chains, but the molecular arrangements in (II) and (III) are nonetheless very similar. The significance of this study lies in its observation of the variations in molecular configuration and conformation, and in the variation in the supramolecular aggregation, consequent upon modest changes in the peripheral substituents.