Polyhalide Anions in Crystals. 3. The Br82? anion in diquinuclidinium octabromide, the crystal structures of Me4PBr3 and quinuclidinium tribromide, and Ab initio calculations on polybromide anions

Crystal structure of bis-(3-carb-oxy-1-methyl-pyrid-inium) octa-bromide

The crystal structure of the title salt, bis-(3-carb-oxy-1-methyl-pyridinium) octa-bromide, 2C7H8NO2 +·Br8 2-, consists of 3-carb-oxy-1-methyl-pyridinium (N-methyl-nicotinic acid) cations, which are stacked between relatively rare [Br8]2- anions. The polybromide [Br8]2- anion has point group symmetry and can be described as being composed of two [Br3]- anions connected with a Br2 mol-ecule in a Z-shaped manner. Contacts between neighboring octa-bromide anions ensure the creation of pseudo-polymeric chains propagating along [111]. The organic cations are located between anionic chains and are connected to each other through O-H⋯O hydrogen bonds and to the [Br8]2- anions through π⋯Br inter-actions that induce the creation of a supra-molecular tri-periodic network. In addition, the presence of weak C-H⋯Br contacts leads to the creation of layers, which align parallel to (11).

Self-Assembly of Supramolecular Architectures Driven by σ-Hole Interactions: A Halogen-Bonded 2D Network Based on a Diiminedibromido Gold(III) Complex and Tribromide Building Blocks

The reaction of the complex [Au(phen)Br₂](PF₆) (phen = 1,10-phenanthroline) with molecular dibromine afforded {[Au(phen)Br₂](Br₃)}_∞ (1). Single crystal diffraction analysis showed that the [Au(phen)Br₂]⁺ complex cations were bridged by asymmetric tribromide anions to form infinite zig-zag chains featuring the motif ···Au–Br···Br–Br–Br···Au–Br···Br–Br–Br···. The complex cation played an unprecedented halogen bonding (XB) donor role engaging type-I and type-II XB noncovalent interactions of comparable strength with symmetry related [Br₃]⁻ anions. A network of hydrogen bonds connects parallel chains in an infinite 2D network, contributing to the layered supramolecular architecture. DFT calculations allowed clarification of the nature of the XB interactions, showing the interplay between orbital mixing, analyzed at the NBO level, and electrostatic contribution, explored based on the molecular potential energy (MEP) maps of the interacting synthons.

Molecular self-assembly of 1D infinite polyiodide helices in a phenanthrolinium salt

A new linear polymeric polyiodide, catena-poly[tris(1,10-phenanthrolin-1-ium)tris(1,10-phenanthroline)heptaiodide], was prepared by one-step synthesis. Its formation is driven by hydrogen-bond assisted supramolecular assembly in the presence of chromium(iii) acetate. Its structure has been characterized by the means of single-crystal X-ray diffraction. To date, this is only one of the few examples of organized linear infinite polyiodides with a known structure. The interplay between the interactions within the hypervalent iodine chain and its supramolecular environment is elucidated. The electrical, thermal, and spectroscopic properties of the studied compound were investigated and associated with the structural features. The infinite character of the polyiodide chain and its similarity to the blue starch-iodine complex has been additionally confirmed by Raman spectroscopy. Despite the apparent structural and spectroscopic similarities with the previously reported 1D polymeric polyiodide, its physical properties, i.e. electrical conductivity and thermal stability, differ significantly. This can be rationalized by the differences in the orbital overlap within the iodine chain, as well as the distinct interactions with the cation.

Rational Synthesis, Structures and Properties of the Ionic Liquid Binary Iodine-Bromine Octahalide Series [In Br8-n ]2- (n=0, 2, 3, 4)

A series of octanuclear iodine-bromine interhalides [I_n Br_8-n ]^2- (n=0, 2, 3, 4) were prepared systematically in two steps. Firstly, addition of a dihalogen (Br₂ or IBr) to the triaminocyclopropenium bromide salt [C₃ (NEt₂ )₃ ]Br forms the corresponding trihalide salt with Br₃ ^- or IBr₂ ^- anions, respectively. Secondly, addition to Br₃ ^- of half an equivalent of Br₂ gives the octabromine polyhalide [Br₈ ]^2- , whereas addition to IBr₂ ^- of half an equivalent of Br₂ , IBr or I₂ gives the corresponding interhalides: [I₂ Br₆ ]^2- , [I₃ Br₅ ]^2- , and [I₄ Br₄ ]^2- , respectively. The four octahalides were characterized by X-ray crystallography, computational studies, Raman and Far-IR spectroscopies, as well as by TGA and melting point. All of the salts were found to be ionic liquids.

Factors influencing the formation of polybromide monoanions in solutions of ionic liquid bromide salts

Six different bromide salts - tetraethylammonium bromide ([N2,2,2,2]Br, Br), 1-ethyl-1-methylpiperidinium bromide ([C2MPip]Br, Br), 1-ethyl-1-methylpyrrolidinium bromide ([C2MPyrr]Br, Br), 1-ethyl-3-methylimidazolium bromide ([C2MIm]Br, Br), 1-ethylpyridinium bromide ([C2Py]Br, Br), and 1-(2-hydroxyethyl)pyridinium bromide ([C2OHPy]Br, Br) - were studied in regards to their capacity to form polybromide monoanion products on addition of molecular bromine in acetonitrile solutions. Using complementary spectroscopic and computational methods for the examination of tribromide and pentabromide anion formation, key factors influencing polybromide sequestration were identified. Here, we present criteria for the targeted synthesis of highly efficient bromine sequestration agents.

Structural Proof for the First Dianion of a Polychloride: Investigation of [Cl8 ](2.)

The polychloride salt [CCl(NMe2 )2 ](+) 2 [Cl8 ](2-) was synthesized and crystallized in the ionic liquid [BMP]OTf. The compound was fully characterized by Raman spectroscopy as well as X-ray single-crystal structure determination, and represents the first example of a polychloride dianion to be described. Detailed gas-phase and solid-state calculations concerning the nature of the bonding situation were also performed.

Bi(iii) polybromides: a new chapter in coordination chemistry of bismuth

A new family of bismuth coordination compounds – Bi(iii) polybromides – is introduced.

The formation of high-order polybromides in a room-temperature ionic liquid: from monoanions ([Br5 ](-) to [Br11 ](-) ) to the isolation of [PC16 H36 ]2 [Br24 ] as determined by van der Waals Bonding Radii

An unprecedented diversity of high-order bromine catenates (anionic polybromides) was generated in a tetraalkylphosphonium-based room temperature ionic liquid system. Raman spectroscopy was used to identify polybromide monoanions ranging from [Br5 ](-) to [Br11 ](-) in the bulk solution, while single-crystal X-ray diffraction identified extended networks of linked [Br11 ](-) units, forming a previously unknown polymeric [Br24 ](2-) dianion. This represents the largest polybromide species identified to date. In combination with recent work, this suggests that other, higher order molecular polybromide ions might be isolated.

Structures, vibrational frequencies, and stabilities of halogen cluster anions and cations, X(n)(+/-), n = 3, 4, and 5

The structures, vibrational frequencies, and thermodynamic stabilities of the homonuclear polyhalogen ions, X3(+), X3(-), X4(+), X4(-), X5(+), and X5(-) (X = Cl, Br, I), have been calculated at the CCSD(T) level. The energetics were calculated using the Feller-Peterson-Dixon approach for the prediction of reliable enthalpies of formation. The calculations allow the following predictions where stabilities are defined in terms of thermodynamic quantities. (1) The X3(+) cations are stable toward loss of X2; (2) the X3(-) anions are marginally stable toward loss of X2 with Cl3(-) being the least stable; (3) the X4(+) cations and X4(-) anions are only weakly bound dimers of X2(+1/2) and X2(-1/2) units, respectively, but the cations are marginally stable toward decomposition to X3(+) and X, with I4(+) having the lowest dissociation energy, whereas the X4(-) anions decompose spontaneously to X3(-) and X; (4) the X5(+) cations are only marginally stable at low temperatures toward loss of X2, with Cl5(+) being the least stable; and (5) the X5(-) anions are also only stable at low temperatures toward loss of X2, with Cl5(-) being the least stable.

Structural isomerism in tris-tolyl halo-phosphonium and halo-arsonium tri-halides, [(CH3C6H4)3EX][X3], (E = P, As; X = Br, I)

The group 15 ligands (o-CH(3)C(6)H(4))(3)P, (m-CH(3)C(6)H(4))(3)P, (p-CH(3)C(6)H(4))(3)P, Ph(3)As, (o-CH(3)C(6)H(4))(3)As and (p-CH(3)C(6)H(4))(3)As have been reacted with two equivalents of di-iodine or di-bromine to yield complexes of formula R(3)EX(4) (E = P, As; X = I, Br). These halogenated group 15 compounds are ionic, [R(3)EX][X(3)] consisting of halo-phosphonium or halo-arsonium cations and trihalide anions. These adducts exhibit structural isomerism and may exist either as simple 1:1 ion pairs, [R(3)EX][X(3)], isomer (A), which display a weak XX interaction between cation and anion, or as a 2:1 complex, which consists of a [{R(3)EX}(2)X(3)](+) cationic species made up of two [R(3)EX](+) cations interacting with one [X(3)](-) anion. The overall charge is balanced by a second [X(3)](-) anion. These 2:1 species also exhibit structural isomerism due to subtle differences in the connectivity of the [{R(3)EX}(2)X(3)](+) fragment, as the {R(3)EX}(+) units may either interact at the same end of the [X(3)](-) ion, to give a Y-shaped motif, isomer (B), or at opposite ends, giving a Z-shaped motif, isomer (C). The type of structural isomer formed is related to the way in which [Ar(3)EX](+) cations pack together via aryl embraces. Isomer (A) and (C) structures form chains of side-to-side, anti-parallel embracing cations. In (A) and (C) structures a square-like stacking motif of cations is observed. In contrast, isomer (B) structures feature side-to-side, parallel embracing cations, and do not exhibit the square motif.

What Makes the Trifluoride Anion F3-So Special? A Breathing-Orbital Valence Bond ab Initio Study

The ground states of the F(3)(-) and H(3)(-) hypercoordinated anions are investigated and analyzed in terms of valence bond structures by means of the breathing-orbital valence bond method. While H(3)(-) is described reasonably well as the interplay of two major Lewis structures, H(2) + H(-) and its mirror image, the description of F(3)(-) requires a further structure, of the type F(*)F(-)F(*), which strongly stabilizes the trimer relative to the dissociation products, and endows the F(3)(-) ground state with a predominant three-electron bond character. It follows that the simple picture that is closest to the true nature of F(3)(-) is a resonating combination of F(2)(-) + F(*) and its mirror image. This peculiarity of the F(3)(-) electronic structure is at the origin of its preferred dissociation channel leading to F(2)(-) + F(*) rather than to the most stable product F(2) + F(-), at high collision energies. The three-electron bond character of F(3)(-) is also the root cause for the failure of the Hartree-Fock and density functional methods for this species, and for its strong tendency to artifactual symmetry-breaking. As an alternative to the Rundle-Pimentel model, the origins of the stability of F(3)(-), as opposed to the instability of H(3)(-), CH(5)(-), and other S(N)2 transition states, are analyzed in the framework of valence bond state correlation diagrams [Shaik, S.; Shurki, A. Angew. Chem., Int. Ed. 1999, 38, 586]. It is found that a fundamental factor of stability for X(3)(-) is the presence of lone pairs on the X fragment. The explanation carries over to other trihalide anions, and to isoelectronic 22-valence electron hypercoordinated anions.

Base-Induced Dismutation of POCl3 and POBr3: Synthesis and Structure of Ligand-Stabilized Dioxophosphonium Cations

The interaction between POCl(3) or POBr(3) and pyridine or DMAP has been reinvestigated to clarify the discrepancies between previously published results concerning the Lewis acidity of phosphoryl halides and their behavior toward pyridine bases. The obtained results show that POCl(3) virtually does not react with pyridine, while it does with 4-(dimethylamino)pyridine (DMAP), even in SO(2) solution, to yield an ionic compound [(DMAP)(2)PO(2)]Cl.3SO(2) (1.3SO(2)). Its recrystallization from acetonitrile gives [(DMAP)(2)PO(2)]Cl.CH(3)CN (1.CH(3)CN). The POBr(3) reacts readily with both DMAP and pyridine forming the analogous tribromides, [(DMAP)(2)PO(2)]Br(3) (2) and [(py)(2)PO(2)]Br(3) (3), respectively. Treatment of 3 with Me(3)SiOSO(2)CF(3) in acetonitrile solution led to [(py)(2)PO(2)][CF(3)SO(3)].CH(3)CN (4), while the reaction between 1.CH(3)CN and Me(3)SiOPOF(2) gave [(DMAP)(2)PO(2)][PO(2)F(2)] (5). The crystal structures of 1.CH(3)CN, 1.3SO(2), 2, and 4 revealed that all four compounds are ionic containing the distorted tetrahedral cations [(DMAP)(2)PO(2)](+) and [(py)(2)PO(2)](+). Both ions represent a donor-stabilized form of the so far unknown cation [PO(2)](+). The geometry of [(DMAP)(2)PO(2)](+), optimized by density functional calculations at the B3LYP/6-31G(d,p) level, is in good agreement with X-ray structural data. The NBO analysis of natural atomic charges shows an extensive delocalization of the [PO(2)](+) intrinsic positive charge and indicates a contribution of the electrostatic attraction to the formation of N-P donor-acceptor bonds. According to a (31)P NMR study, the reactions of both phosphoryl halides with DMAP proceed via successive formation of the intermediates [(DMAP)POX(2)](+) and (DMAP)PO(2)X to give an equimolar mixture of [(DMAP)(2)PO(2)](+) and PX(5) (X = Cl, Br) as the end products. The NMR spectroscopic identification of the cations [(DMAP)POX(2)](+) and [(DMAP)(2)PO(2)](+) was supported by ab initio calculations of their chemical shifts.

First example of an infinite polybromide 2D-network

The reaction of the neutral dithiolene [Pd(Et2timdt)2] (Et2timdt = formally monoreduced diethylimidazolidine-2,4,5-trithione) with an excess of Br2 yielded few crystals of [1(Et) x 2Br](2+)(Br-)2(Br2)3 as a by-product (1(Et) = 4,5,9,10-tetrathiocino-[1,2-b:5,6-b']-1,3,6,8-tetraethyl-diimidazolyl-2,7-dithione); X-ray diffraction analysis showed that this compound represents the first example of a polybromide 2D-network templated by [1(Et) x 2Br](+2) dications, and featuring all the Br-Br distances shorter than those found in solid state bromine.

Electron-rich three-center bonding: role of s,p interactions across the p-block

This paper analyzes the importance of s,p mixing-a necessary addition to the simplest Rundle-Pimentel picture-and periodic and group trends in electron-rich three-center bonding. Our analysis proceeds through a detailed quantum chemical study of the stability of electron-rich three-center bonding in triatomic 22-valence electron anions. To provide interpretations, a perturbational molecular orbital (MO) analysis of s,p mixing is carried out. This analysis of the orbitals and the overlap populations is then tested by density functional calculations for a number of linear trihalides, trichalcogenides, and tripnictides. The most important effect of s,p mixing on the in-line bonding is in destabilization of the 3sigma(g) orbital and is determined by the overlap between the s orbital of the central atom and the p orbital of the terminal atom. Further destabilization arises from the repulsion of p(pi) lone pairs. Both of these antibonding effects increase with increasing negative charge of the system. The stability of isoelectronic X(3) systems thus decreases when moving from right to left in the periodic table. Interesting group trends are discerned; for instance, for the electron-rich tripnictides, the ability to accommodate a hypervalent electron count is the largest in the middle rather at the end of the group. Particularly strong s,p mixing can reverse the bonding/antibonding character of MOs: thus MO 2sigma(u) that is responsible for bonding for trihalides and trichalcogenides is actually antibonding in N(3)(7)(-).