Synthesis, structure, and bonding in polyiodide and metal iodide-iodine systems

From monomer to bulk: appearance of the structural motif of solid iodine in small clusters

Formation of iodine clusters in a solid krypton matrix was studied using resonance Raman spectroscopy with a 1 cm(-1) resolution. The clusters were produced by annealing of the solid and recognized by appearance of additional spectral transitions. Two distinct regions, red-shifted from the fundamental vibrational wavenumber of the isolated I(2) at 211 cm(-1), were observed in the signal. The intermediate region spans the range 196-208 cm(-1), and the ultimate region consists of two peaks at 181 and 190 cm(-1) nearly identical to crystalline I(2). The experimental results were compared to DFT-D level electronic structure calculations of planar (I(2))(n) clusters (n = 1-7). The dimer, trimer, and tetramer structures, where the I(2) molecule is complexed from one end, were found to exhibit vibrational shifts corresponding to the intermediate size clusters. The larger, bulklike shift appears when the iodine molecule is coordinated from two opposite directions as in the case of a pentamer and higher clusters. Starting from the pentamer, the structural motif of crystalline iodine is clearly recognized in the clusters.

8-Iodo-quinolinium triiodide tetra-hydro-furan solvate

The title compound, C(9)H(7)IN(+)·I(3) (-)·C(4)H(8)O, was synthesized from 8-amino-quinoline using the Sandmeyer reaction. The 8-iodo-quinolinium cation is essentially planar and the triiodide ion is almost linear. N-H⋯O hydrogen bonds, and inter-molecular I⋯I [3.7100 (5) Å] and I⋯H inter-actions, between the cation, anion and solvent mol-ecules result in the formation of sheets oriented parallel to the (03) plane. Between the sheets, 8-iodo-quinolinium and triiodide ions are stacked alternately, with I⋯C distances in the range ∼3.8-4.0 Å.

Metal-heptaiodide interactions in cyclomaltoheptaose (beta-cyclodextrin) polyiodide complexes as detected via Raman spectroscopy

The Raman spectra of the cyclomaltoheptaose (beta-cyclodextrin, beta-CD) polyiodide complexes (beta-CD)(2).NaI(7).12H(2)O, (beta-CD)(2).RbI(7).18H(2)O, (beta-CD)(2).SrI(7).17H(2)O, (beta-CD)(2).BiI(7).17H(2)O and (beta-CD)(2).VI(7).14H(2)O (named beta-M, M stands for the corresponding metal) are investigated in the temperature range of 30-140 degrees C. At room temperature all systems show an initial strong band at 178 cm(-1) that reveals similar intramolecular distances of the disordered I(2) units (approximately 2.72 A). During the heating process beta-Na and beta-Rb display a gradual shift of this band to the final single frequency of 166 cm(-1). In the case of beta-Sr and beta-Bi, the band at 178 cm(-1) is shifted to the final single frequencies of 170 and 172 cm(-1), respectively. These band shifts imply a disorder-order transition of the I(2) units whose I-I distance becomes elongated via a symmetric charge-transfer interaction I(2)<--I3(-)-->I(2). The different final frequencies correspond to different bond lengthening of the disordered I(2) units during their transformation into well-ordered ones. In the Raman spectra of beta-V, the initial band at 178 cm(-1) is not shifted to a single band but to a double one of frequencies 173 and 165 cm(-1), indicating a disorder-order transition of the I(2) molecules via a non-symmetric charge-transfer interaction I(2)<--I3(-)-->I(2). The above spectral data show that the ability of I3(-) to donate electron density to the attached I(2) units is determined by the relative position of the different metal ions and their ionic potential q/r. The combination of the present results with those obtained from our previous investigations reveals that cations with an ionic potential that is lower than approximately 1.50 (Cs(+), Rb(+), Na(+), K(+) and Ba(2+)) do not affect the Lewis base character of I3(-). However, when the ionic potential of the cation is greater than approximately 1.50 (Li(+), Sr(2+), Cd(2+), Bi(3+) and V(3+)), the M(n+)...I3(-) interactions become significant. In the case of a face-on position of the metal (Sr(2+), Bi(3+)) relative to I3(-), the charge-transfer interaction is symmetric. On the contrary, when the metal (Li(+), Cd(2+), V(3+)) presents a side-on position relative to I3(-), the charge-transfer interaction is non-symmetric.

Supramolecular insulating networks sheathing conducting nanowires based on organic radical cations

Six materials, (EDT-TTF)(4)BrI(2)(TIE)(5) (1, where EDT-TTF = ethylenedithiotetrathiafulvalene and TIE = tetraiodoethylene), (EDST)(4)I(3)(TIE)(5) (2, where EDST = ethylenedithiodiselenadithiafulvalene), (MDT-TTF)(4)BrI(2)(TIE)(5) (3, where MDT-TTF = methylenedithiotetrathiafulvalene), (HMTSF)(2)Cl(2)(TIE)(3) (4, where HMTSF = hexamethylenetetraselenafulvalene), (PT)(2)Cl(DFBIB)(2) (5, where PT = bis(propylenedithio)tetrathiafulvalene and DFBIB = 1,4-difluoro-2,5-bis(iodoethynyl)benzene), and (TSF)Cl(HFTIEB) (6, where TSF = tetraselenafulvalene and HFTIEB = 1,1',3,3',5,5'-hexafluoro-2,2',4,4'-tris(iodoethynyl)-biphenyl), consisting of conducting nanowires were obtained by galvanostatic oxidation of the donor molecules in the presence of the corresponding halide anions and iodine-containing neutral molecules. We report their characterizations using single-crystal crystallography, electrical resistance measurements, and electron spin resonance. The structures are built on stacks of planar cations of the donors that are isolated electrically by an insulating network consisting of supramolecular assemblies of the halide anions and neutral molecules held together by a halogen bond. The size and shape as well as the orientation (tilt) of the donors are matched by the self-organization of the insulating sheaths in all cases, providing a pea-in-a-pod example in the field of supramolecular chemistry. The observed resistivities, resistivity anisotropies, and electron spin resonance behaviors of these salts are analyzed by tight-binding band calculations and resistance-array modeling. Crystal 6 with insulating layer of 1 nm thickness exhibits 8 orders of magnitude anisotropy in its resistivity, indicating high potential of the supramolecular network as sheathing material. The observation of such networks leads us to propose a roadmap for future development toward multidimensional memory devices.

Two interconverting pentaiodide forms in the cyclomaltohexaose (α-cyclodextrin) polyiodide inclusion complex with sodium ion: dielectric and Raman spectroscopy studies

The polycrystalline inclusion complex of cyclomaltohexaose, (alpha-CD)(2) x NaI(5) x 8H(2)O, has been investigated via dielectric spectroscopy over a frequency range of 0-100 kHz and the temperature range of 125-450 K. Additionally, a Raman spectroscopy study was accomplished in the temperature ranges of (i) 153-298 K and (ii) 303-413 K. The ln sigma versus 1/T variation revealed the order-disorder transition of some normal hydrogen bonds to those of a flip-flop type at 200.9 K. From 278.3 up to 357.1K, the progressive transformation (H(2)O)(tightly bound)-->(H(2)O)(easily movable) takes place resulting in an Arrhenius linear increment of the ac-conductivity with activation energy E(a)=0.32 eV. In the range of 357.1-386.1K a second linear part with E(a)=0.55 eV is observed, indicating the contribution of sodium ions via the water-net. The rapid decrease of the ac-conductivity at T>386.1K is due to the removal of the water molecules from the crystal lattice, whereas the abrupt increase at T>414.9 K is caused by the sublimation of iodine. The Raman bands at 160 and 169 cm(-1) indicate the coexistence of (I(2) x I(-) x I(2)) and (I3(-) x I(2)<-->I(2) x I3(-)) units, respectively. The (I3(-) x I(2)<-->I(2) x I3(-)) units are presented as form (I), and their central I(-) ion is disordered in occupancy ratio different from 50/50 (e.g., ...60/40...70/30...). The(I(2) x I(-) x I(2)) units are displayed by the 2 equiv forms (IIa) and (IIb). In (IIa) the central I(-) ion is twofold disordered in an occupancy ratio of 50:50, whereas in (IIb) the central I(-) ion is well-ordered and equidistant from the two I(2) molecules. At low temperatures the transformation (I)-->(IIa) takes place, whereas at high temperatures the inverse one (IIa)-->(I) happens. X-ray powder diffraction and Rietveld analysis revealed a triclinic crystal form with space group P1 and lattice parameters that are in good agreement with the theoretical values.

Hydrogen-Bond Interaction in Organic Conductors: Redox Activation, Molecular Recognition, Structural Regulation, and Proton Transfer in Donor−Acceptor Charge-Transfer Complexes of TTF-Imidazole

Hydrogen-bond interaction in donor-acceptor charge-transfer complexes of TTF-imidazole demonstrated the electronic effects in terms of control of component ratio and redox activation. These unprecedented effects of hydrogen bonds renewed the criteria giving "a high probability of being organic metals" and produced a number of highly conductive complexes with various acceptors having a wide range of electron-accepting ability. In p-chloranil complex, both molecules were linked by hydrogen bonds and formed a D-A-D triad, regulating the donor-acceptor composition to be 2:1. Theoretical calculations have revealed that the polarizability of hydrogen bonds controls the redox ability of the donor and p-benzoquinone-type acceptors and afforded different ionicity in complexes from those expected by the difference of redox potentials between donor and acceptors. In the p-chloranil complex, this electronic and structural regulation by hydrogen bond realized the first metallic donor-acceptor charge-transfer complex based on hydrogen bond functionalized TTF. Hydrogen bonds controlled also molecular arrangements in charge-transfer complexes, giving diverse and highly ordered assembled structures, D-A-D triad in the p-chloranil complex, one-dimensional zigzag chain in I(5) salt, alternating donor-acceptor chain in chloranilic acid complex, and D-A-D-A cyclic tetramer in nitranilic acid complex. Furthermore, TTF-imidazole acted as electron donor as well as proton acceptor in anilic acid complexes and realized the simultaneous charge- and proton-transfer complexes. These investigations demonstrated the new and intriguing potentials of the hydrogen bond in the development of organic conductors and multifunctional molecular materials.

Selective oxidation and reduction of trinuclear titanium(II) hexaazatrinaphthylene complexes-synthesis, structure, and electrochemical investigations

Titanocene complexes with chelating N-heterocyclic ligand bridges react with ferrocenium salts as selective oxidants to afford air-stable cationic complexes and allow the preparation of exceptional mixed valence hexaazatrinaphthylene complexes [(Cp2Ti)3(mu3-HATNMe6)]n+ (1n+) (n=1, 2, 3, 4). Cyclic voltammograms (CV) and differential pulse voltammograms (DPV) show that nine oxidation states of 1 are generated without decomposition. Comproportionation constants Kc have been calculated in order to determine the extent of electronic communication between the titanium centers. The Kc values of the mixed valence states are indicative of uncoupled (14+), moderately coupled (15+), and strongly coupled (1-, 1+, and 12+) systems. Small but significant structural changes occurring upon oxidation of neutral 1 are observed by X-ray structural analysis on 1+-14+. Anion-pi interactions between the electron-deficient central ring of the HATNMe6 moiety and PF6- and BF4- counterions, respectively, are found for 12+, 13+, and 14+. The short cation-anion contacts cause interesting molecular allignments in terms of molecular architecture. For 12+ the assembly of an one-dimensional (1D) polymer is observed. Electrochemical investigations on the mononuclear cationic titanocene complexes [(Cp2Ti)(L)]+ (L=2,2'-biquinoline (2+), 4,4'-dimethyl-2,2'-biquinoline (3+), and 5,8'-dimethyl-2,3'-biquinoxaline (4+)) showed similar oxidation and reduction characteristics among each other. Conversion to monoanionic, neutral, and dicationic states is enabled. As found for the trinuclear compounds 1n+, the molecular structures of 2+-4+ reveal significant differences compared to their neutral parents.

Insulin amyloid fibrils form an inclusion complex with molecular iodine: a misfolded protein as a nanoscale scaffold

The study describes formation of an intensely violet inclusion complex of insulin amyloid fibrils and molecular iodine. Resonance Raman spectra of complexes formed by staining mature insulin fibrils with iodine and by seeding fibrils in the presence of iodine imply similar topologies of entrapped iodine and oligoiodide species. Iodine captured by growing fibrils remains accessible to a bulk chemical reagent. In light of its small size and the fact that iodine can partition into polar as well as nonpolar media, the data suggest that intrafibrillar structure of insulin amyloid is densely packed with no appreciable void volumes capable of accommodating iodine atoms. The complex is stable: only drastic perturbation of the beta-pleated fibrous scaffold by dimethyl sulfoxide (rather than of the beta-sheet conformation) leads to the release of iodine atoms from surface moieties. While the reaction between iodine and in vivo amyloid deposits was first described by Virchow in the 19th Century [Virchow, R. (1854) Virchows Arch. 6, 268-271], the underlying molecular mechanism has not been thoroughly explored since then. This work shows how the long-forgotten concept can be utilized as a probe of void volumes in protein fibrils, providing a new tool for structural studies on amyloids, and a model for design of protein-based drug delivery media.

PbnI4n+2(2n+2)- ribbons (n = 3, 5) as dimensional reductions of 2D perovskite layers in cystamine cation based hybrids, also incorporating iodine molecules or reversible guest water molecules

Pb(n)I(4n+2)((2n+2)-) (n = 3, 5) ribbons, which can be regarded as dimensional reductions of 2D perovskite layers, are stabilized by diprotonated cystamine cations in (NH(3)(CH(2))(2)SS(CH(2))(2)NH(3))(4)Pb(3)I(14),I(2) (1) and (NH(3)(CH(2))(2)SS(CH(2))(2)NH(3))(6)Pb(5)I(22).4H(2)O (2). Both 1 and 2 have interesting structural characteristics; it is unprecedented that the ribbons are linked via I(2) molecules incorporated in the lattice of 1, while tetrameric water clusters are trapped in the structure of 2. 2 undergoes a (reversible) water desorption process at 310 K leading to (NH(3)(CH(2))(2)SS(CH(2))(2)NH(3))(6)Pb(5)I(22).2H(2)O (3). The electrical behavior of 2 and 3 has been investigated in the ranges 293-310 K and 310-358 K respectively. Above 310 K, the electronic contribution remains constant while the ionic transference number tends towards unity showing almost pure ionic transport at 360 K (6 x 10(-7) S cm(-1) at 330 K) originating probably from the migration of protons through the hydrogen bonds connecting the water molecules to the cystamine counter cations.

The nature of the chemical bond in linear three-body systems: from i3- to mixed chalcogen/halogen and trichalcogen moieties

The 3 centre-4 electrons (3c-4e) and the donor/acceptor or charge-transfer models for the description of the chemical bond in linear three-body systems, such as I(3) (-) and related electron-rich (22 shell electrons) systems, are comparatively discussed on the grounds of structural data from a search of the Cambridge Structural Database (CSD). Both models account for a total bond order of 1 in these systems, and while the former fits better symmetric systems, the latter describes better strongly asymmetric situations. The 3c-4e MO scheme shows that any linear system formed by three aligned closed-shell species (24 shell electrons overall) has reason to exist provided that two electrons are removed from it to afford a 22 shell electrons three-body system: all combinations of three closed-shell halides and/or chalcogenides are considered here. A survey of the literature shows that most of these three-body systems exist. With some exceptions, their structural features vary continuously from the symmetric situation showing two equal bonds to very asymmetric situations in which one bond approaches to the value corresponding to a single bond and the second one to the sum of the van der Waals radii of the involved atoms. This indicates that the potential energy surface of these three-body systems is fairly flat, and that the chemical surrounding of the chalcogen/halogen atoms can play an important role in freezing different structural situations; this is well documented for the I(3) (-) anion. The existence of correlations between the two bond distances and more importantly the linearity observed for all these systems, independently on the degree of their asymmetry, support the state of hypervalency of the central atom.

Investigation into the reactivity of the coordinatively unsaturated phosphonodithioato [Ni(MeOpdt)2] towards 2,4,6-tris(2-pyridyl)-1,3,5-triazine: goals and achievements

The reaction between the coordinatively unsaturated phosphonodithioato complex [Ni(MeOpdt)2] (1) [MeOpdt = (MeO)(4-MeOC(6)H(4))PS2-] and tptz [2,4,6-tris(2-pyridyl)-1,3,5-triazine] has been investigated. Spectrophotometric and conductometric titrations showed the formation of a neutral and an ionic species, i.e. [Ni(MeOdtp)2(tptz)] (2) and [Ni(tptz)2](MeOdtp)2 (3), in correspondence to 1 : 1 and 2 : 1 tptz : ratios, respectively. XRD studies confirmed the formation of both complexes isolated in the compounds 2.MeOH and 3.4H(2)O. In the neutral complex 2 the central Ni(II) ion features a distorted octahedral coordination, achieved through three N-atoms of tptz and three S-atoms belonging to two MeOpdt anions, one of which unexpectedly acts as a monodentate S-donor. In 3.4H(2)O, the two phosphonodithioato anions are non-coordinating and counterbalance the charge of the [Ni(tptz)2](2+) distorted octahedral complex. From the reaction 2 of with I2 and Br2, crystals of [Ni(tptz)2](I3)2 (5) and [Ni(tptz)Br(micro-Br)]2 (6) have been obtained. The dinuclear complex 6 features a structure showing tubular canals with openings of about 6 x 6 A.

A Dinuclear Ni(II) Complex with Two Types of Intramolecular Magnetic Couplings: Ni(II)−Ni(II) and Ni(II)−TTF•+

A dinuclear Ni(II) complex involving tetrathiafulvalene (TTF) radicals as ligands has been prepared and characterized, [Ni2(mu-Cl)2(L*+)2(I3)4(I2)3.(H2O)2.(C4H8O)3 (1), L = 4,5-bis(2-pyridylmethylsulfanyl)-4',5'-ethylenedithiotetrathiafulvalene. There are two types of intramolecular magnetic exchange interactions, namely one ferromagnetic Ni(II)-Ni(II) and one antiferromagnetic Ni(II)-TTF*+. This study is new in the respect of revealing a magnetic exchange interaction between a TTF*+ radical and a paramagnetic transition metal ion. This is due to the fact of a direct binding of the transition metal ion to the skeleton of the TTF*+ radical.

Measurement of nitric oxide levels in the red cell: validation of tri-iodide-based chemiluminescence with acid-sulfanilamide pretreatment

The tri-iodide-based chemiluminescence assay is the most widely used methodology for the detection of S-nitrosothiols (RSNOs) in biological samples. Because of the low RSNO levels detected in a number of biological compartments using this assay, criticism has been raised that this method underestimates the true values in biological samples. This claim is based on the beliefs that (i) acidified sulfanilamide pretreatment, required to remove nitrite, leads to RSNO degradation and (ii) that there is auto-capture of released NO by heme in the reaction vessel. Because our laboratories have used this assay extensively without ever encountering evidence that corroborated these claims, we sought to experimentally address these issues using several independent techniques. We find that RSNOs of glutathione, cysteine, albumin, and hemoglobin are stable in acidified sulfanilamide as determined by the tri-iodide method, copper/cysteine assay, Griess-Saville assay and spectrophotometric analysis. Quantitatively there was no difference in S-nitroso-hemoglobin (SNOHb) or S-nitroso-albumin (SNOAlb) using the tri-iodide method and a recently described modified assay using a ferricyanide-enhanced reaction mix at biologically relevant NO:heme ratios. Levels of SNOHb detected in human blood ranged from 20-100 nM with no arterial-venous gradient. We further find that 90% of the total NO-related signal in blood is caused by erythrocytic nitrite, which may partly be bound to hemoglobin. We conclude that all claims made thus far that the tri-iodide assay underestimates RSNO levels are unsubstantiated and that this assay remains the "gold standard" for sensitive and specific measurement of RSNOs in biological matrices.

Dinuclear Cu(I) Complexes of 1,2,4,5-Tetra(7-azaindolyl)benzene: Persistent 3-Coordinate Geometry, Luminescence, and Reactivity

Five Cu(I) complexes [Cu2(ttab)(CH3CN)2][BF4]2 (1), [Cu(2)(ttab)(PPh3)2][BF4]2 (2), [Cu2(ttab)I2] (3), [Cu2(ttab)(I3)2] (4), and [Cu2(ttab)(I)BF4]n (5) with 1,2,4,5-tetra(7-azaindolyl)benzene (ttab) have been synthesized and characterized. The structures of compound 1, 2, 4, and 5 have been determined by single-crystal X-ray diffraction analyses, which established that 1, 2, and 4 are discrete dinuclear Cu2 compounds while compound 5 is a 1D coordination polymer with the I- ligand bridging two dinuclear Cu2 units. The ttab ligand in all four complexes adopts a 1,3-chelation mode. The Cu(I) center in all complexes is three-coordinate. Close contact between the Cu(I) center and the benzene ring in the ttab ligand was observed in all four structures, which is believed to play a role in stabilizing the three-coordinate geometry of the Cu(I) center. The crystals of 1, 2, and 5 contain channels in the lattice that host solvent molecules such as CH2Cl2 and toluene. Fluorescent measurements established that, in solution, compounds 1-3 display weak blue luminescence which originates from the ttab but is significantly red-shifted and has a much lower emission intensity, compared to the free ttab ligand. The application of compound 1 in C-N cross-coupling reactions was examined by using the reaction of phenyl halides with imidazole as a model system. For the reaction with phenyl iodide, 1 was found to be as effective a catalyst as the CuI/1,10-phenanthroline system. For the reaction with phenyl bromide, 1 is less effective than the CuI/1,10-phenanthroline system. Compound 1 reacts with O2 gas, as established by UV-vis spectra, but the oxidized products have not been characterized.

Structural, electronic, and chemical properties of multiply iodized aluminum clusters

The electronic structure, stability, and reactivity of iodized aluminum clusters, which have been investigated via reactivity studies, are examined by first-principles gradient corrected density functional calculations. The observed behavior of Al13I(x)- and Al14I(x)- clusters is shown to indicate that for x < or = 8, they consist of compact Al13- and Al14++ cores, respectively, demonstrating that they behave as halogen- or alkaline earth-like superatoms. For x > 8, the Al cores assume a cagelike structure associated with the charging of the cores. The observed mass spectra of the reacted clusters reveal that Al13I(x)- species are more stable for even x while Al14I(x)- exhibit enhanced stability for odd x(x > or = 3). It is shown that these observations are linked to the formation and filling of "active sites," demonstrating a novel chemistry of superatoms.

A Fluent Transition from Triiodide, I3−, to Tris(trifluoromethyltellurate)(1−), [(TeCF3)3]−—A Structural Study

A complete series of compounds with the anions [(TeCF3)(3-x)I(x)]- (x = 0-2) had been prepared and characterised in the solid state and by NMR spectroscopic methods. Dynamic behaviour in solution can be assumed for [(TeCF3)3]- and [(TeCF3)2I]-, while in the solid state all three bis(triphenylphosphoranyliden)ammonium (PNP) salts resemble structures found in triiodides. The molecular structures of [PNP][(TeCF3)(3-x)I(x)]- (x = 0-2) are discussed in comparison with [PNP]I3, I2, and Te2(CF3)2. On this basis, the structures of the [(TeCF3)3]- and [(TeCF3)I2]- ions are comparable to symmetric I3- ions, while the [(TeCF3)2I]- ion resembles an asymmetric I3- unit.

Pressure-tuning Raman spectra of diiodine thioamide compounds: models for antithyroid drug activity

The pressure-tuning Raman spectra of five solid, diiodine heterocyclic thioamide compounds (mbztS)I(2) (mbztS = N-methyl-2-mercaptobenzothiazole) (1); [(mbztS)(2)I](+)[I(7)](-) (2); (pySH)I(2) (pySH = 2-mercaptopyridine) (3); [(pySH)(pyS](+)[I(3)](-) (4); (thpm)(I(2))(2) or possibly [(thpm)I(2)](+)[I(3)](-) (thpm = 2-mercapto-3,4,5,6-tertahydropyrimidine (5) have been measured for pressures up to approximately 50 kbar using a diamond-anvil cell. Compounds 1, 4, and 5 undergo pressure-induced phase transitions at approximately 35, approximately 25, and approximately 32 kbar, respectively. Following the phase transition in 1, the pressure dependences of the vibrational modes, which were originally located at 84, 111, and 161 cm(-1) and are associated with the S(cdots, three dots, centered)I-I linkage, are 2.08, 1.78, and 0.57 cm(-1)/kbar, respectively. These pressure dependences are typical of low-energy vibrations. The pressure-tuning FT-Raman results for the pairs of compounds 1 , 2, 3, and 4 are remarkably similar to each other suggesting that the compounds are most probably perturbed diiodide compounds rather than ionic ones. The Raman data for 5 show that it is best formulated as (thpm)(I(2))(2) rather than [(thpm)(2)I](+)[I(3)](-).