Seminal insights provided by the iconic R. S. Mulliken and his "charge-transfer" theory, H. Taube "outer/inner-sphere" mechanisms, A. Marcus "two-state non-adiabatic" N. Hush "intervalence" theory are each separately woven into rich panoramic tapestry constituting chemical research electron-transfer dynamics, its mechanistic dominance for past half century more. In this Account, we illustrate how simultaneous melding of all four key concepts allows sharp focus on charge-transfer character...

Intense colorations and new charge-transfer absorption bands are observed upon addition of a halide (Cl−, Br−, I−) to neutral organic π acceptors with electron-deficient olefinic aromatic centers. These phenomena results from noncovalent anion–π interactions (shown schematically), which were confirmed by X-ray crystallography. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2004/z460337_s.pdf or author. Please note: The publisher...

The high symmetry and stability of phenalenyl systems, both as the planar pi-radical (P*) pi-cation (P+), are desirable characteristics prototypical aromatic donor/acceptor pairs that encourage their use (binary) models for study intermolecular interactions extant in stacked molecular arrays. Thus, quantitative ESR spectroscopy paramagnetic P* identifies its spontaneous self-association to diamagnetic P2, previously characterized pi-dimer by X-ray crystallography. Likewise, rapid...

Unusual dimers with wide interplanar separations, that is, very long bonds d(D) approximately 3.05 A, are common to the spontaneous self-association of various organic pi-radicals in solution and crystalline solid state, independent whether they derived from negatively charged anion radicals planar electron acceptors (TCNE-*, TCNQ-*, DDQ-*, CA-*), positively biphenylene cation-radical (OMB+*), or neutral phenalene radical (PHEN*). All dimeric species characterized by intense absorption bands...

Intermolecular electron transfer (ET) between the free phenothiazine donor (PH) and its cation radical (PH*+) proceeds via [1:1] precursor complex (PH)(2)*+ which is transiently observed for first time by diagnostic (charge-resonance) absorption band in near-IR region. Similar intervalence (optical) transitions are also mixed-valence radicals with generic representation: P(br)P*+, two redox centers interlinked p-phenylene, o-xylylene, o-phenylene (br) bridges. Mulliken-Hush analysis of bands...

Tetrathiafulvalene (TTF) as the prototypical electron donor for solid-state (electronics) applications is converted to unusual cation-radical salt, TTF+* CB- (where non-coordinating closo-dodecamethylcarboranate), crystallographic and spectral analyses. Near-IR studies establish spontaneous self-association of form diamagnetic [TTF+,TTF+] dication also undergo equally rapid cross-association with its parent mixed-valence [TTF+*,TTF] cation-radical. The latter, most importantly, represents...

Abstract The nature of halogen bonding is examined via experimental and computational characterizations a series associates between electrophilic bromocarbons RBr (RBr=CBr 3 F, CBr NO 2 , COCBr CONH CN, etc.) bromide anions. [RBr, Br − ] complexes show intense absorption bands in the 200–350 nm range which follow same Mulliken correlation as those observed for charge‐transfer anions with common organic π‐acceptors. For wide associates, intermolecular RBr⋅⋅⋅Br separations decrease...

Carbon tetrabromide and bromoform are employed as prototypical electron acceptors to demonstrate the charge-transfer nature of various intermolecular complexes with three different structural types donors represented by (1) halide pseudohalide anions, (2) aromatic (π-bonding) hydrocarbons, (3) aromatics (n-bonding) oxygen or nitrogen centers. UV–Vis spectroscopy identifies electronic transition inherent such [1:1] complexes; their Mulliken correlation donor/acceptor strength verifies...

Transient 1:1 precursor complexes for intermolecular self-exchange between various organic electron donors (D) and their paramagnetic cation radicals (D+•), as well different acceptors (A) paired with anion (A-•), are spectrally (UV−NIR) observed structurally (X-ray) identified the cofacial (π-stacked) associates [D, D+•] [A-•, A], respectively. Mulliken−Hush (two-state) analysis of diagnostic intervalence bands affords electronic coupling elements (HDA), which together Marcus reorganization...

Interchange of complex formation and electron-transfer reactions between halide anions p-benzoquinones were established via UV-vis spectral X-ray structural measurements computational analysis. Solution-phase interaction the p-benzoquinone acceptors with Cl-, Br-, or I- donors led to anion-π complexes showing strong absorption bands in range. Formation constants calculated energies these increased, donor/acceptor separations decreased increasing reduction potentials p-benzoquinones. Mulliken...

Transient [1:1] complexes formed in the bimolecular interactions of electron acceptors (A) with their reduced anion radicals (A-•) are detected and characterized solution for first time. The recognition such metastable intermediates as heretofore elusive precursor complex (A2-•) electron-transfer processes self-exchange allows principal parameters λ (Marcus reorganization energy) HDA (electronic coupling element) to be experimentally determined from optical (charge-transfer) transitions...

X-ray crystallography identifies the aromatic donor group D = 2,5-dimethoxy-4-methylphenyl to be a suitable redox center for construction of organic mixed-valence crystals owing its large structural change attendant upon 1e oxidation cation-radical (D*(+)). The combination cyclic voltammetry, dynamic ESR line broadening, and electronic (NIR) spectroscopy allows intervalence electron transfer between centers in system D-br-D*(+) [where br can an aliphatic trimethylene or (poly)phenylene...

Electronic-structure calculations for the self-association of phenalenyl radical (P•) predict formation dimeric species (σ-P2) in which both moieties are connected by a σ-bond with rP-P ∼ 1.59 Å and bond dissociation enthalpy ΔHD 16 kcal mol-1. Such an unusually weak is related to loss aromatic stabilization energy ∼34 mol-1 per moiety, largely owing rehybridization. Ab initio also reveal that corresponding (one-electron) between its closed-shell cation σ-P2+• unstable relative dissociation....

The interaction of diiodine with quinuclidine (QN) and 4‐dimethylaminopyridine (DMAP) in solutions 1:1 molar ratio reactants at room temperature produced (in essentially quantitative yields) pure charge‐transfer QN·I2 adducts iodine(I) salt [DMAP‐I‐DMAP]I3, respectively. In comparison, the formation iodine (I) [QN‐I‐QN]I5 was observed for room‐temperature reactions QN a 50% excess I2, I2 DMAP (and other pyridines) were formed when carried out low temperatures. Computational analysis related...

[reaction: see text] Spontaneous self-associations of various tricyclic phenalenyl radicals lead reversibly to either pi- or sigma-dimers, depending on alkyl-substitution patterns at the alpha- and beta-positions. Thus, sterically encumbered all-beta-substituted tri-tert-butylphenalenyl radical (2*) affords only long-bonded pi-dimer in dichloromethane solutions, under conditions which parent (1*) leads sigma-dimer. Further encumbrances 1* with a pair alpha, beta- beta, tert-butyl...

Intensive Farben und neue Charge-Transfer-Banden treten bei der Zugabe von Halogeniden (Cl−, Br−, I−) zu neutralen organischen π-Acceptoren mit elektronenarmen olefinischen aromatischen Zentren auf. Ursache sind nichtkovalente Anion-π-Wechselwirkungen (siehe Schema), wie röntgenkristallographisch bestätigt wurde.

The highly disparate rates of aromatic nitrosation and nitration, despite the very similar (electrophilic) properties active species: NO(+) NO(2)(+) in Chart 1, are quantitatively reconciled. First, thorough mappings potential-energy surfaces by high level (ab initio) molecular-orbital methodologies involving extensive coupled-cluster CCSD(T)/6-31G optimizations establish intervention two reactive intermediates nitration (Figure 8) but only one 7). Second, same distinctive topologies double...

Metastable (pre-reactive) intermediates, as commonplace transients in simple bimolecular reactions, are usually unobserved (and ignored)-though they provide vital mechanistic insight. Thus, the preequilibrium (charge-transfer) complexes of various aromatic donors with rather typical electron acceptors such Br(2), NO(+), and NO(2)(+) examined quantitatively (via their molecular electronic structures) to reveal surprisingly unorthodox aspects what is conventionally referred organic chemistry...

The charge-resonance phenomenon originally identified by Badger and Brocklehurst lies at the core of basic understanding electron movement delocalization that is possible within p-doped aromatic (face-to-face) arrays. To this end, we now utilize a series different aryl-donor groups (Ar) around central platform to precisely evaluate intramolecular among these tethered redox centers. As such, unique (intervalence) absorption bands observed upon one-electron oxidation or p-doping various...

Successful isolation of a series pure (crystalline) salts labile quinone anion radicals suitable for X-ray crystallographic analysis allows the first time their rigorous structural distinction as "separated" ion pairs (SIPs) vs "contact" (CIPs). The quantitative evaluation precise changes in geometries these quinones (Q) upon one-electron reduction to afford radical (Q-•) is viewed relative corresponding (two-electron) hydroquinone (H2Q) via Pauling bond-length/bond-order paradigm....

Pi and doughnuts: Highly effective through-space conjugation among cofacial (aromatic) redox centers is established in stable hexaanilinylbenzene radical cations (1.+; π shown by toroid). The show unusual intervalence absorption bands are quantitatively analyzed Mulliken–Hush formulation. Supporting information for this article (synthesis, characterization, X-ray data the hexaarylbenzene donors 1–3, spectral (Vis-NIR) characterization of their cations, (six-state) analysis cation 1)...

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

Abstract Halogen bonding occurs between molecules featuring Lewis acidic halogen substituents and bases. It is often rationalized as a predominantly electrostatic interaction thus interactions ions of like charge (e. g., anionic bond donors with halides) seem counter‐intuitive. Herein, we provide an overview on such complexes. First, theoretical studies are described their findings compared. Next, experimental evidences presented in the form crystal structure database analyses, recent...

The relationship between covalent and supramolecular bonding, the criteria of assignments different interactions were explored via review selenium tellurium containing structures in Cambridge Structural Database their computational analysis using Quantum Theory Atoms Molecules (QTAIM). This combined study revealed continuums interatomic Se⋯Br Te⋯I distances, dCh⋯X, series associations from sums van der Waals radii these atoms (rCh + rX) to bond lengths. electron densities, ρ(r), at Bond...

The role of halogen bonding (HaB) in the reactions N-chlorosuccinimide (SimCl), a versatile reagent organic synthesis, was investigated through experimental and computational analyses its interactions with halides. SimCl Br− or I− resulted crystallization HaB complexes chloride N-iodosuccinimide (SimI) N-bromosuccinimide (SimBr). Computational analysis revealed that rearrangements, which occurred even at −73 °C, were facilitated by bonding. dissociation SimCl∙Y− (Y = I Br) into Sim− + ClY...