From a cycloheptatrienylzirconium allyl complex to a cycloheptatrienylzirconium imidazolin-2-iminato "pogo stick" complex with imido-type reactivity

The reaction of the cycloheptatrienylzirconium half-sandwich complex [(η(7)-C(7)H(7))ZrCl(tmeda)] (1) (tmeda = N,N,N',N'-tetramethylethylenediamine) with Li(Im(Dipp)N), generated from bis(2,6-diisopropylphenyl)imidazolin-2-imine (Im(Dipp)NH) with methyllithium, yields the imidazolin-2-iminato complex [(η(7)-C(7)H(7))Zr(Im(Dipp)N)(tmeda)] (2). The corresponding tmeda-free complex [(η(7)-C(7)H(7))Zr(Im(Dipp)N)] (5) can be synthesized via the 1,3-bis(trimethylsilyl)allyl complex [(η(7)-C(7)H(7))Zr{η(3)-C(3)H(3)(TMS)(2)}(THF)] (3; TMS = SiMe(3)), which undergoes an acid-base reaction with Im(Dipp)NH to form 5 and 1,3-bis(trimethylsilyl)propene. 5 exhibits an unusual one-legged piano stool ("pogo stick") geometry with a particularly short Zr-N bond of 1.997(2) ?. Addition of 2,6-dimethylphenyl or tert-butyl isocyanide affords the complexes [(η(7)-C(7)H(7))Zr(Im(Dipp)N)(CNR)] (R = o-Xy, 6; R = t-Bu, 7), while the reaction with 2,6-dimethylphenyl isocyanate results in a [2 + 2] cycloaddition to form the ureato(1-) complex [(η(7)-C(7)H(7))Zr{Im(Dipp)N(C═O)N-o-Xy}] (8). 5 can also act as an initiator for the ring-opening polymerization of ε-caprolactone. These reactivity patterns together with density functional theory calculations reveal a marked similarity of the bonding in imidazolin-2-iminato and conventional imido transition-metal complexes.     

Mono(cycloheptatrienyl) tantalum chemistry: synthesis and characterization of new tantalum halide, hydride, and alkyl species

The new tantalum(II) complex (eta (6)-C 7H 8)TaCl 2(PMe 3) 2 ( 1) was synthesized by the reduction of TaCl 5 with n-butyllithium in the presence of PMe 3 and cycloheptatriene. Compound 1 adopts a four-legged piano stool structure in which the tantalum center is bound to a eta (6)-cycloheptatriene ring in addition to two chlorides and two phosphine ligands in a transoid arrangement. Treatment of 1 with methyllithium results in a loss of the equivalents of HCl and formation of the eta (7)-cycloheptatrienyl complex (eta (7)-C 7H 7)TaCl(PMe 3) 2 ( 2), whereas treatment of 1 with sodium or sodium borohydride affords small amounts of the eta (5)-cycloheptadienyl complex (eta (5)-C 7H 9)TaCl 2(PMe 3) 2 ( 3). Compound 2 adopts a three-legged piano stool structure; the eta (7)-C 7H 7 ring is fully aromatic and planar. The molecular structure of 3 is similar to that of 1, except for the eta (5) binding mode of the seven-membered ring. Treatment of the previously described sandwich compound (C 5Me 5)Ta(C 7H 7) with allyl bromide affords the tantalum(V) product (C 5Me 5)Ta(C 7H 7)Br ( 4), which reacts with LiAlH 4 to give the tantalum(V) hydride (C 5Me 5)Ta(C 7H 7)H ( 5). Compound 4 also reacts with alkylating agents to generate the methyl, allyl, and cyclopropyl complexes (C 5Me 5)Ta(C 7H 7)Me ( 6), (C 5Me 5)Ta(C 7H 7)(eta (1)-CH 2CHCH 2) ( 7), and (C 5Me 5)Ta(C 7H 7)(c-C 3H 5) ( 8). Compounds 4- 8 all adopt bent sandwich structures in which the dihedral angle between the two carbocyclic rings is 34.9 degrees for the bromo compound 4, 26.6 degrees for the hydride 5, 33.1 degrees for the methyl compound 6, 34.2 degrees for the allyl compound 7, and 37.5 degrees for the cyclopropyl compound 8. (1)H and (13)C NMR data are reported for the diamagnetic compounds.     

Low-dimensional ferromagnetic properties of SrCuV2O7 and BaCuV2O7

The crystal structure of isostructural SrCuV(2)O(7) and BaCuV(2)O(7) consists of one-dimensional (1D) zigzag chains of Cu atoms with next-nearest-neighbor interaction. The main intrachain interaction was found to be ferromagnetic and estimated at 4.6 K (Hamiltonian H approximately -2J). SrCuV(2)O(7) and BaCuV(2)O(7) are new examples in the scanty family of 1D ferromagnets. Isothermal magnetization measurements at 0.08 K and specific heat data showed that MCuV(2)O(7) exhibits antiferromagnetic long-range ordering at T(N) = 1.36 K for SrCuV(2)O(7) and T(N) = 1.47 K for BaCuV(2)O(7). Spin-flop transitions were observed in the antiferromagnetic state at 0.08 K near 0.5 kOe in SrCuV(2)O(7) and 2 kOe in BaCuV(2)O(7). In air, SrCuV(2)O(7) and BaCuV(2)O(7) melted incongruently above 983 and 1018 K, respectively.     

Activation energies for dissociation of double strand oligonucleotide anions: evidence for watson-crick base pairing in vacuo

The dissociation kinetics of a series of complementary and noncomplementary DNA duplexes, (TGCA)(2) (3-), (CCGG)(2) (3-), (AATTAAT)(2) (3-), (CCGGCCG)(2) (3-), A(7).T(7) (3-), A(7).A(7) (3-), T(7).T(7) (3-), and A(7).C(7) (3-) were investigated using blackbody infrared radiative dissociation in a Fourier transform mass spectrometer. From the temperature dependence of the unimolecular dissociation rate constants, Arrhenius activation parameters in the zero-pressure limit are obtained. Activation energies range from 1.2 to 1.7 eV, and preexponential factors range from 10(13) to 10(19) s(-1). Dissociation of the duplexes results in cleavage of the noncovalent bonds and/or cleavage of covalent bonds leading to loss of a neutral nucleobase followed by backbone cleavage producing sequence-specific (a - base) and w ions. Four pieces of evidence are presented which indicate that Watson-Crick (WC) base pairing is preserved in complementary DNA duplexes in the gas phase: i. the activation energy for dissociation of the complementary dimer, A(7).T(7) (3-), to the single strands is significantly higher than that for the related noncomplementary A(7).A(7) (3-) and T(7).T(7) (3-) dimers, indicating a stronger interaction between strands with a specific base sequence, ii. extensive loss of neutral adenine occurs for A(7).A(7) (3-) and A(7).C(7) (3-) but not for A(7).T(7) (3-) consistent with this process being shut down by WC hydrogen bonding, iii. a correlation is observed between the measured activation energy for dissociation to single strands and the dimerization enthalpy (-DeltaH(d)) in solution, and iv. molecular dynamics carried out at 300 and 400 K indicate that WC base pairing is preserved for A(7).T(7) (3-) duplex, although the helical structure is essentially lost. In combination, these results provide strong evidence that WC base pairing can exist in the complete absence of solvent.     

Synthesis,Structure, and Haptotropic Interconversions of Tungsten Cycloheptatrienyl–Acetonitrile–Carbonyl Complexes

Russian Journal of Coordination Chemistry - Tungsten cycloheptatrienyl complexes (η7-C7H7)W(CO)2I (I), [(η3-C7H7)W(CO)2(CH3CN)3]PF6 (II), and [(η7-C7H7)W(CO)2(CH3CN)]PF6 (III) (CIF...     

Derivatives of 1,5-diamino-1H-tetrazole: a new family of energetic heterocyclic-based salts

1,5-Diamino-1H-tetrazole (2, DAT) can easily be protonated by reaction with strong mineral acids, yielding the poorly investigated 1,5-diaminotetrazolium nitrate (2a) and perchlorate (2b). A new synthesis for 2 is introduced that avoids lead azide as a hazardous byproduct. The reaction of 1,5-diamino-1H-tetrazole with iodomethane (7a) followed by the metathesis of the iodide (7a) with silver nitrate (7b), silver dinitramide (7c), or silver azide (7d) leads to a new family of heterocyclic-based salts. In all cases, stable salts were obtained and fully characterized by vibrational (IR, Raman) spectroscopy, multinuclear NMR spectroscopy, mass spectrometry, elemental analysis, X-ray structure determination, and initial safety testing (impact and friction sensitivity). Most of the salts exhibit good thermal stabilities, and both the perchlorate (2b) and the dinitramide (7c) have melting points well below 100 degrees C, yet high decomposition onsets, defining them as new (7c), highly energetic ionic liquids. Preliminary sensitivity testing of the crystalline compounds indicates rather low impact sensitivities for all compounds, the highest being that of the perchlorate (2b) and the dinitramide (7c) with a value of 7 J. In contrast, the friction sensitivities of the perchlorate (2b, 60 N) and the dinitramide (7c, 24 N) are relatively high. The enthalpies of combustion (Delta(c)H degrees ) of 7b-d were determined experimentally using oxygen bomb calorimetry: Delta(c)H degrees (7b) = -2456 cal g(-)(1), Delta(c)H degrees (7c) = -2135 cal g(-)(1), and Delta(c)H degrees (7d) = -3594 cal g(-)(1). The standard enthalpies of formation (Delta(f)H degrees ) of 7b-d were obtained on the basis of quantum chemical computations using the G2 (G3) method: Delta(f)H degrees (7b) = 41.7 (41.2) kcal mol(-)(1), Delta(f)H degrees (7c) = 92.1 (91.1) kcal mol(-)(1), and Delta(f)H degrees (7d) = 161.6 (161.5) kcal mol(-)(1). The detonation velocities (D) and detonation pressures (P) of 2b and 7b-d were calculated using the empirical equations of Kamlet and Jacobs: D(2b) = 8383 m s(-)(1), P(2b) = 32.2 GPa; D(7b) = 7682 m s(-)(1), P(7b) = 23.4 GPa; D(7c) = 8827 m s(-)(1), P(7c) = 33.6 GPa; and D(7d) = 7405 m s(-)(1), P(7d) = 20.8 GPa. For all compounds, a structure determination by single-crystal X-ray diffraction was performed. 2a and 2b crystallize in the monoclinic space groups C2/c and P2(1)/n, respectively. The salts of 7 crystallize in the orthorhombic space groups Pna2(1) (7a, 7d) and Fdd2 (7b). The hydrogen-bonded ring motifs are discussed in the formalism of graph-set analysis of hydrogen-bond patterns and compared in the case of 2a, 2b, and 7b.     

Synthesis of Novel Ethyl (substituted)phenyl‐4‐oxothiazolidin‐3‐yl)‐1‐ethyl‐4‐oxo‐1,4‐dihydroquinoline‐3‐Carboxylates as Potential Anticancer Agents

A series of ethyl (substituted)phenyl‐4‐oxothiazolidin‐3‐yl)‐1‐ethyl‐4‐oxo‐1,4‐dihydroquinoline‐3‐carboxylates ( 7a , 7b , 7c , 7d , 7e , 7f , 7g ) has been prepared from reactions between aminoquinolones 6 with arenealdehydes and mercaptoacetic acid. The critical intermediates, 6 a and 6b , were obtained from appropriate amines by a sequence of steps involving (i) reaction with diethylethoxymethylenemalonate, (ii) thermal cyclization in diphenyl ether, (iii) ethylation and (iv) Pd/C catalyzed reduction. New compounds 7a , 7b , 7c , 7d , 7e , 7f , 7g were fully identified and characterized by NMR (¹H and ¹³C) and specifically for 7d by X‐ray crystallography. Compounds 7b , 7c , 7d , 7e , 7f were found not to exhibit activity at 10 uM concentrations against gastric ascitis (AGP‐01), gastric adenocarcinoma kind intestinal (ACP‐02), colon (HCT‐116) and murine melanome (B16F10) cancer cells. However, none exhibited cytotoxicity against normal cells human fibroblast (MRC‐5), murine fibroblast (NIH3T3) and normal human melanocyte (Melan‐A).     

Electron correlation effects at semiconductor surfaces and interfaces: Si(111)-5x5, Si(111)-7x7 and Sn/Ge(111)

Electron correlation effects associated with the dangling bond surface states of Si(111)-5×5, Si(111)-7×7 and Sn/Ge(111)-3×3 are analyzed. In all the cases, extensive LDA-calculations are performed and effective two-dimensional Hamiltonians are deduced. Our analysis of these Hamiltonians shows that: (a) the Si(111)-5×5 surface states exhibits a metal-insulator transition; (b) the Si(111)-7×7 surface shows important similarities with the Si(111)-5×5 case, but it has a dangling bond surface band having a metallic character; (c) finally, the Sn/Ge(111)-3×3 dangling bond surface bands also shows important correlation effects that are found, however, not to affect the metallic character of the surface bands.     

pH transients during salt removal in isoelectric trapping separations: a curse revisited

The pH transients that occur during isoelectric trapping separations as a result of the removal of nonampholytic ionic components have been re-examined. Salts containing strong electrolyte anions and cations, both with equal and dissimilar mobilities, have been studied using anodic and cathodic buffering membranes whose pH values were both equidistant and nonequidistant from pH 7. The direction and magnitude of the pH transient (acidic or basic) was found to depend on both the mobilities of the anion and cation (mu(anion)/mu(cation)) and the pH difference between pH 7 and the pH of the buffering membranes (|pH(memb) (anodic) - 7|/|7 - pH(memb) (cathodic)|). When |pH(memb) (anodic) - 7|/|7 - pH(memb) (cathodic)| = 1, mu(anion)/mu(cation)<1 leads to an acidic pH transient, mu(anion)/mu(cation) = 1 eliminates the pH transient and mu(anion)/mu(cation)>1 leads to a basic pH transient. When mu(anion)/mu(cation) = 1, |pH(memb) (anodic) - 7|/|7 - pH(memb) (cathodic)|<1 leads to a basic pH transient, |pH(memb) (anodic) - 7|/|7 - pH(memb) (cathodic)| = 1 eliminates the pH transient and |pH(memb) (anodic) - 7|/|7 - pH(memb) (cathodic)|>1 leads to an acidic pH transient. By selecting appropriate anodic and cathodic buffering membranes to adjust the |pH(memb) (anodic) - 7|/|7 - pH(memb) (cathodic)| value, pH transients caused by dissimilar anion and cation mobilities can be avoided.     

Cycloheptatrienyl zirconium sandwich complexes with lewis basic phospholyl ligands (phosphatrozircenes): synthesis, structure, bonding and coordination chemistry

The transmetalation reaction between [(η(7) -C(7) H(7) )ZrCl(tmeda)] (1; tmeda=N,N,N',N'-tetramethylethylenediamine) and various phospholide anions leads to a new class of mixed sandwich complexes: [(η(7)-C(7)H(7))Zr(η(5)-C(4)PMe(4))] (2), [(η(7)-C(7)H(7))Zr(η(5)-C(4)PH(2)Me(2))] (3) and [(η(7)-C(7)H(7))Zr(η(5)-C(4)PPhHMe(2))] (4). The presence of Lewis basic phosphorus atoms and Lewis acidic zirconium atoms allows ambiphilic behaviour to be observed, and X-ray diffraction analysis reveals dimeric arrangements for 2 and 3 with long intermolecular Zr-P bonds, whereas 4 remains monomeric in the solid state. DFT calculations indicate that the metal-phosphorus interaction is weak, and accordingly, complexes 2-4 act as monodentate ligands upon reaction with [W(CO)(5)(thf)]. The resulting complexes [W(CO)(5)(L)] 5-7 (L=2-4) were studied by IR spectroscopy and compared with the [W(CO)(5) ] complex 9, containing the phosphane-functionalised trozircene [(η(7)-C(7)H(7))Zr(η(5)-C(5)H(4)PPh(2))] (8). They all show a close resemblance to simple phosphanes, such as PMe(3) , although molecular orbital analysis of 2 reveals that the free electron pair in the phosphatrozircenes is not the HOMO. Four equivalents of 2 can replace 1,4-cyclooctadiene (COD) in [Ni(cod)(2)] to form the homoleptic, distorted tetrahedral complex [Ni{2}(4)] (10).     

Synthesis of derivatives of 7-iodo-4-aminoquinolines

7-Iodo- and 7,8-diiodo-4-(3-dimethylaminopropylamino)quinolines and 7-iodo-4-(3) dipropyl-aminopropylamlno)- and 7-iodo-4-(3-diallylaminopropylamino)quinoline were obtained by the reaction of 7-iodo- and 7,8-diodo-4-chloroquinolines with the corresponding diamines. The catalytic hydrogenation of 7-iodo-4-(3-diallylaminopropylamino)quinoline at normal pressure leads to 7-iodo-4-(3-dipropylaminopropylamino)quinoline.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 972–975, July, 1980.     

Fluorogenic and fluorescent labeling reagents with a benzofurazan skeleton

Fluorogenic and fluorescent labeling reagents having a benzofurazan (2,1,3-benzoxadiazole) skeleton such as 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F), 4-N,N-dimethylaminosulfonyl-7-fluoro-2,1,3-benzoxadiazole (DBD-F), 4-aminosulfonyl-7-fluoro-2,1,3-benzoxadiazole (ABD-F), ammonium 7-fluoro-2,1,3-benzoxadiazole-4-sulfonate (SBD-F), 4-hydrazino-7-nitro-2,1,3-benzoxadiazole (NBD-H), 4-N,N-dimethylaminosulfonyl-7-hydrazino-2,1,3-benzoxadiazole (DBD-H), 4-nitro-7-N-piperazino-2,1,3-benzoxadiazole (NBD-PZ), 4-N,N-dimethylaminosulfonyl-7-N-piperazino-2,1,3-benzoxadiazole (DBD-PZ), 4-(N-chloroformylmethyl-N-methyl)amino-7-N,N-dimethylaminosulfonyl-2,1,3-benzoxadiazole (DBD-COCl) and 7-N,N-dimethylaminosulfonyl-4-(2,1,3-benzoxadiazolyl) isothiocyanate (DBD-NCS) are reviewed in terms of synthetic method, reactivity, fluorescence characteristics, sensitivity and application to analytes.     

2 + 2] cross coupling of benzene and tropylium ligands in reductively activated piano stool complexes of Mn,Cr, and W

We have established cation/anion coupling reactions between the tropylium ligand in [M(eta7-C7H7)(CO)3]+ (M = Cr, W) and the reductively activated eta4-benzene ligand in [Mn(eta4-C6H6)(CO)3]- (3-) to form [M(CO)3(mu2-eta6:eta5-C7H7-C6H6)Mn(CO)3]; [Cr(CO)3(mu2-eta6:eta5-C7H7-C6H6)Mn(CO)3] can be further reduced to [Cr(CO)3(mu2-eta5:eta4-C7H7-C6H6)Mn(CO)3]2-, in which the tropylium and benzene ligands have undergone a [2 + 2] cross coupling reaction.     

Crystal growth, observation, and characterization of the low-temperature structure of the fluorite-related ruthenates: Sm(3)RuO(7) and Eu(3)RuO(7)

The compounds Sm(3)RuO(7) and Eu(3)RuO(7) were grown as single crystals from molten hydroxide fluxes. They crystallize in the orthorhombic space group Cmcm and are part of a well-known family of fluorite-related oxides of stoichiometry Ln(3)MO(7). This structure contains rare earth cations in two different coordination environments, 8-fold pseudocubic and 7-fold pentagonal bipyramidal, and contains Ru(V) cations that are octahedrally coordinated. The RuO(6) octahedra are trans vertex-sharing to yield chains oriented along the c-axis. Upon cooling, single crystals of Sm(3)RuO(7) and Eu(3)RuO(7) undergo a structural transition at 190 and 280 K, respectively, from space group Cmcm to P2(1)nb. The structure transition results in a loss of lattice centering, a doubling of the b-axis, a distortion of the vertex-shared Ru-O chains, and a reduction in the coordination of one of the rare earth cations from 8-fold to 7-fold. Accompanying this structural transition are anomalies in the magnetic susceptibility at about 190 and 280 K for Sm(3)RuO(7) and Eu(3)RuO(7), respectively. The structures of these low-temperature phases of Ln(3)RuO(7) have been determined for the first time and are described.     

Total synthesis of optically active lycopladine A by utilizing diastereoselective protection of carbonyl group in a 1,3-cyclohexanedione derivative

We successfully synthesized two enantiomers of bicyclic enones, (7R,7aR)- and (7S,7aS)-9, from the hemiacetal 2a, which we first synthesized from the symmetrical diketone 1a via diastereoselective carbon-oxygen bond formation between one of the carbonyl groups and the chiral alcohol on the C2 side chain in a 2,2-disubstituted 1,3-cycloalkanedione derivative. We also report the total synthesis of natural (+)-lycopladine A [(+)-6] from (7R,7aR)-9 and the formal synthesis of unnatural (-)-lycopladine A [(-)-6] from (7S,7aS)-9.     

Chemical modification of an antitumor alkaloid camptothecin: synthesis and antitumor activity of 7-C-substituted camptothecins.

A radical substitution reaction of 20(S)-camptothecin (1) with methanol furnished 7-hydroxymethylcamptothecin (2). Reaction of 1 with primary alcohols higher than methanol gave 7-alkylcamptothecins (4), of which alkyl groups were one carbon less than the alcohols used and also 7-hydroxyalkylcamptothecins (5). For the preparation of 7-alkylcamptothecin (4), aldehydes were used as a radical source and several alkylated derivatives were synthesized. 7-Acyloxymethyl derivatives (6), 7-carbaldehyde (7), iminomethyl derivatives (10), acid (11), esters (12) and amides (13) were synthesized starting from 2. 7-Ethyl- (4b) and 7-propylcamptothecin (4c), acyloxymethyl compounds 6a, 6c and ethyl ester (12b) exhibited higher antitumor activity than 1 against L1210 in mice.     

A slipped multi-decker zirconium complex with an η7:η2-bridging cycloheptatrienyl ligand

The complex [(η(7)-C(7)H(7))Zr{N(SiMe(3))(2)}(thf)] (2) loses THF upon sublimation to afford a chain polymer consisting of [(η(7)-C(7)H(7))Zr{N(SiMe(3))(2)}] (3) units; they are connected by cycloheptatrienyl ligands in an unprecedented antifacial η(7):η(2)-bridging mode. The basicity of the bis(trimethylsilyl)amido ligand can also be used to introduce other ligands by acid-base reactions.     

Microbial metabolism. Part 6. Metabolites of 3- and 7-hydroxyflavones

Fermentation of 3-hydroxyflavone (1) with Beauveria bassiana (ATCC 13144) yielded 3,4'-dihdroxyflavone (3), flavone 3-O-beta-D-4-O-methylglucopyranoside (4) and two minor metabolites. 7-Hydroxyflavone (2) was transformed by Nocardia species (NRRL 5646) to 7-methoxyflavone (5) whilst Aspergillus alliaceus (ATCC 10060) converted it to 4',7-dihydroxyflavone (6). Flavone 7-O-beta-D-4-O-metylglucopyranoside (7) and 4'-hydroxyflavone 7-O-beta-D-4-O-methylglucopyranoside (8) were the metabolic products of 7-hydroxyflavone (2) when fermented with Beauveria bassiana (ATCC 7159). One of the minor metabolites of 3-hydroxyflavone (1) was tentatively assigned a beta'-chalcanol structure (9). Compounds 4, 7 and 8 are reported as new compounds. Structure elucidation of the metabolites was based on spectroscopic data.     

Spectroscopic identification of oxonium and carbenium ions of protonated phenol in the gas phase: IR spectra of weakly bound C6H7O+ -L dimers (L = Ne, Ar, N2)

Structural isomers of isolated protonated phenol (C(6)H(7)O(+)) are characterized by infrared (IR) photodissociation spectroscopy of their weakly bound complexes with neutral ligands L (L = Ne, Ar, N(2)). IR spectra of C(6)H(7)O(+)-L recorded in the vicinity of the O-H and C-H stretch fundamentals carry unambiguous signatures of at least two C(6)H(7)O(+) isomers: the identified protonation sites of phenol include the O atom (oxonium ion, O-C(6)H(7)O(+)) and the C atoms of the aromatic ring in the ortho and/or para position (carbenium ions, o/p-C(6)H(7)O(+)). In contrast, protonation at the meta and ipso positions is not observed. The most stable C(6)H(7)O(+)-L dimer structures feature intermolecular H-bonds between L and the OH groups of O-C(6)H(7)O(+) and o/p-C(6)H(7)O(+). Extrapolation to zero solvation interaction yields reliable experimental vibrational frequencies of bare O-C(6)H(7)O(+) and o/p-C(6)H(7)O(+). The interpretation of the C(6)H(7)O(+)-L spectra, as well as the extrapolated monomer frequencies, is supported by B3LYP and MP2 calculations using the 6-311G(2df,2pd) basis. The spectroscopic and theoretical results elucidate the effect of protonation on the structural properties of phenol and provide a sensitive probe of the activating and ortho/para directing nature of the OH group observed in electrophilic aromatic substitution reactions.     

Comparative Structural Study of Three Tetrahalophthalic Anhydrides: Recognition of X···O(anhydride) Halogen Bond and πh···O(anhydride) Interaction

Structures of three tetrahalophthalic anhydrides (TXPA: halogen = Cl (TCPA), Br (TBPA), I (TIPA)) were studied by X-ray diffraction, and several types of halogen bonds (HaB) and lone pair···π-hole (lp···πh) contacts were revealed in their structures. HaBs involving the central oxygen atom of anhydride group (further X···O(anhydride) were recognized in the structures of TCPA and TBPA. In contrast, for the O(anhydride) atom of TIPA, only interactions with the π system (π-hole) of the anhydride ring (further lp(O)···πh) were observed. Computational studies by a number of theoretical methods (molecular electrostatic potentials, the quantum theory of atoms in molecules, the independent gradient model, natural bond orbital analyses, the electron density difference, and symmetry-adapted perturbation theory) demonstrated that the X···O(anhydride) contacts in TCPA and TBPA and lp(O)···πh in TIPA are caused by the packing effect. The supramolecular architecture of isostructural TCPA and TBPA was mainly affected by X···O(acyl) and X···X HaBs, and, for TIPA, the main contribution provided I···I HaBs.