PX4+, P2X5+, and P5X2+ (X=Br,I) salts of the superweak Al(OR)4- anion [R=C(CF3)3

PX(4) (+)[Al(OR)(4)](-) (X=I: 1 a, X=Br: 1 b) was prepared from X(2), PX(3), and Ag[Al(OR)(4)] [R=C(CF(3))(3)] in CH(2)Cl(2) at -30 degrees C in 69-86 % yield. P(2)X(5) (+) salts were prepared from 2 PX(3) and Ag[Al(OR)(4)] in CH(2)Cl(2) at -30 degrees C yielding almost quantitatively P(2)X(5) (+)[Al(OR)(4)](-) (X=I: 3 a, X=Br: 3 b). The phosphorus-rich P(5)X(2) (+) salts arose from the reaction of cold (-78 degrees C) mixtures of PX(3), P(4), and Ag[Al(OR)(4)] giving P(5)X(2) (+)[Al(OR)(4)](-) (X=I: 4 a, X=Br: 4 b) with a C(2v)-symmetric P(5) cage. Silver salt metathesis presumably generated unstable PX(2) (+) cations from PX(3) and Ag[Al(OR)(4)] (X=Br, I) that acted as electrophilic carbene analogues and inserted into the Xbond;X (Pbond;X/Pbond;P) bond of X(2) (PX(3)/P(4)) leading to the highly electrophilic and CH(2)Cl(2)-soluble PX(4) (+) (P(2)X(5) (+)/P(5)X(2) (+)) salts. Reactions that aimed to synthesize P(2)I(3) (+) from P(2)I(4) and Ag[Al(OR)(4)] instead led to anion decomposition and the formation of P(2)I(5)(CS(2))(+)[(RO)(3)Al-F-Al(OR)(3)](-) (5). All salts were characterized by variable-temperature solution NMR studies (3 b also by (31)P MAS NMR), Raman and/or IR spectroscopy as well as X-ray crystallography (with the exception of 4 a). The thermochemical volumes of the Pbond;X cations are 121 (PBr(4) (+)), 161 (PI(4) (+)), 194 (P(2)Br(5) (+)), 271 (P(2)I(5) (+)), and 180 A(3) (P(5)Br(2) (+)). The observed reactions were fully accounted for by thermochemical calculations based on (RI-)MP2/TZVPP ab initio results and COSMO solvation enthalpy calculations (CH(2)Cl(2) solution). The enthalpies of formation of the gaseous Pbond;X cations were derived as +764 (PI(4) (+)), +617 (PBr(4) (+)), +749 (P(2)I(5) (+)), +579 (P(2)Br(5) (+)), +762 (P(5)I(2) (+)), and +705 kJ mol(-1) (P(5)Br(2) (+)). The insertion of the intermediately prepared carbene analogue PX(2) (+) cations into the respective bonds were calculated, at the (RI-)MP2/TZVPP level, to be exergonic at 298 K in CH(2)Cl(2) by Delta(r)G(CH(2)Cl(2))=-133.5 (PI(4) (+)), -183.9 (PBr(4) (+)), -106.5 (P(2)I(5) (+)), -81.5 (P(2)Br(5) (+)), -113.2 (P(5)I(2) (+)), and -114.5 kJ mol(-1) (P(5)Br(2) (+)).     

Preparation of stable AsBr4+ and I2As-PI3+ salts. Why didn't we succeed to prepare AsI4+ and As2X5+? A combined experimental and theoretical study

In analogy to our successful "PX2+" insertion reactions, an "AsX2+" insertion route was explored to obtain new arsenic halogen cations. Two new salts were prepared: AsBr4+[Al(OR)4]-, starting from AsBr3, Br2 and Ag[Al(OR)4], and I2As-PI3+[Al(OR)]4 from AsI3, PI3 and Ag[Al(OR)4](R=C(CF3)3). The first cation is formally a product of an "AsBr2+" insertion into the Br2 molecule and the latter clearly a "PI2+" insertion into the As-I bond of the AsI3 molecule. Both compounds were characterized by IR and NMR spectroscopy, the first also by its X-ray structure. Reactions of Ag[Al(OR)4] with AsI3 do not lead to ionization and AgI formation but rather lead to a marginally stable Ag(AsI3)2+[Al(OR)]4 salt. Despite many attempts we failed to prepare other PX-cation analogues such as AsI4+, As2X5+ and P4AsX2+(X=Br, I). To explain these negative results the thermodynamics of the formation of EX2+, EX4+ and E2X5+(E = As, P; X = Br, I) was carefully analyzed with MP2/TZVPP calculations and inclusion of entropy and solvation effects. We show that As2Br5+ is in very rapid equilibrium with AsBr2+ and AsBr3(DeltaGo((CH2Cl2))=+30 kJ mol(-1)). The extremely reactive AsBr2+ cation available in the equilibrium accounts for the observed decomposition of the [Al(OR)4]- anion. By contrast, the stability of AsI3 against Ag[Al(OR)4] appears to be kinetic and, if prepared by a suitable route, As2I5+ would be expected to have a stability intermediate between the known P2I5+ and P2Br5+.     

Lewis acid stabilized OPI3: implications for the nature of free OPI3

While reinvestigating the published synthesis of OPI(3), it became evident from the experiments that phosphoryl triodide may only be formed as an intermediate and that the end products of the reaction of OPCl(3) with LiI are P(V) oxides, PI(3), I(2), and LiCl. This is also in agreement with MP2/TZVPP calculations, which assign Delta(r)H degrees (Delta(r)G degrees ) [Delta(r)G degrees in CHCl(3)] for the disproportionation of OPI(3) as -7 (-18) [-17 kJ mol(-1)] (assuming P(4)O(10) as the P(V) oxide). The first products of this reaction visible in a low-temperature in situ (31)P NMR experiment are P(2)I(4) and PI(3), as well as traces of a compound that may be OPCl(2)I. By contrast, it was possible to prepare and structurally characterize Lewis acid [A] stabilized [A]<--OPX(3) adducts, where [A] is Al(OR(F))(3) for X=Br and Al(OR(F))(2)(mu-F)Al(OR(F))(3) for X=I (R(F)=C(CF(3))(3)). These adducts are formed on decomposition of PX(4) (+)[Al(OR(F))(4)](-); high yields of Br(3)PO-->Al(OR(F))(3) (delta((31)P)=-65) were obtained, while I(3)PO-->Al(OR(F))(3) (delta((31)P)=-337) and I(3)PO-->Al(OR(F))(2)(mu-F)Al(OR(F))(3) (delta((31)P)=-332) are only formed as by-products. The main product of the room-temperature decomposition of PI(4) (+)[Al(OR(F))(4)](-) is PI(4) (+)[(R(F)O)(3)Al(mu-F)Al(OR(F))(3)](-), which was also characterized by X-ray crystallography and was independently prepared from Ag(+)[(R(F)O)(3)Al(mu-F)Al(OR(F))(3)](-), PI(3), and I(2).     

A theoretical study on the formation of EX4+ and E2X5+(E = P, As; X = Br, I) from Ag+ and EX3/X2

The mechanism and the thermodynamics of the formation of EX2+, EX4+ and E2X5+ (E = As, P; X = Br, I) was carefully analyzed with MP2/TZVPP calculations and inclusion of entropy and solvation effects (COSMO model approximating CH2Cl2). Thus, as likely intermediates the complexes of Ag+ and one or two EX3 as well as EX3/X2 were optimized. The global minimum isomers of the Ag(EX3)2+ intermediates were found to be P-coordinated Ag(PI3)2+ and (BrPBr2)Ag(PBr3)+ but exclusively halogen coordinated Ag(X2AsX)2+ complexes. Similarly complicated is the situation for the Ag(EX3)(X2)+ intermediates: (I3E)Ag(I2)+, (BrAsBr2)Ag(Br2)+ and (Br3P)(Br-Br)Ag+ complexes were found to be the global minima. Based on all available results likely mechanisms for the formation of the known PX4+, AsBr4+, P2X5+ salts (X = Br, I) from these intermediates were proposed. An explanation for the failure to prepare an AsI4+ salt is also given.     

Experimental determination of energy disposal in the dissociative electron recombinations of CS2(+) and HCS2(+)

Vibronic optical emissions from CS(A1pi --> X1sigma+) and CS(a3pi --> X1sigma+) transitions have been identified from dissociative recombination (DR) of CS2(+) and HCS2(+) plasmas. All of the spectra were taken in flowing afterglow plasmas using an optical monochromator in the UV-visible wavelength region of 180-800 nm. For the CS(A --> X) and CS(a --> X) emissions, the relative vibrational distributions have been calculated for v' < 5 and v' < 3 in both types of plasmas for the CS(A) and CS(a) states, respectively. Both recombining plasmas show a population inversion from the v' = 0 to v' = 1 level of the CS(A) state, similar to other observations of the CS(A) state populations, which were generated using two other energetic processes. The possibility of spectroscopic cascading is addressed, such that transitions from upper level electronic states into the CS(A) and CS(a) states would affect the relative vibrational distribution, and there is no spectroscopic evidence supporting the cascading effect. Additionally, excited-state transitions from neutral sulfur (S(5S(2)0 --> 3P(2)) and S(5S(2)0 --> 3P(1))) and the products of ion-molecule reactions (CS(B1sigma+ --> A1pi), CS(+)(B2sigma+ --> A2pi(i)), and CS2(+) (A2pi(u) --> X2pi(g))) have been observed and are discussed.     

Univalent gallium and indium phosphane complexes: from pyramidal M(PPh3)3(+) to carbene-analogous bent M(PtBu3)2(+) (M=Ga, In) complexes

In a new oxidative route, Ag(+)[Al(OR(F))(4)](-) (R(F)=C(CF(3))(3)) and metallic indium were sonicated in aromatic solvents, such as fluorobenzene (PhF), to give a precipitate of silver metal and highly soluble [In(PhF)(n)](+) salts (n=2, 3) with the weakly coordinating [Al(OR(F))(4)](-) anion in quantitative yield. The In(+) salt and the known analogous Ga(+)[Al(OR(F))(4)](-) were used to synthesize a series of homoleptic PR(3) phosphane complexes [M(PR(3))(n)](+), that is, the weakly PPh(3)-bridged [(Ph(3)P)(3)In-(PPh(3))-In(PPh(3))(3)](2+) that essentially contains two independent [In(PPh(3))(3)](+) cations or, with increasing bulk of the phosphane, the carbene-analogous [M(PtBu(3))(2)](+) (M=Ga, In) cations. The M(I)-P distances are 27 to 29 pm longer for indium, and thus considerably longer than the difference between their tabulated radii (18 pm). The structure, formation, and frontier orbitals of these complexes were investigated by calculations at the BP86/SV(P), B3LYP/def2-TZVPP, MP2/def2-TZVPP, and SCS-MP2/def2-TZVPP levels.     

Study on the photodissociation spectra of CS2+ via B2Sigma u+ and C2Sigma g+ electronic states

The photodissociation spectra of CS(2)(+) ions via B(2)Sigma(u)(+) and C(2)Sigma(g)(+) electronic states have been studied by using two-photon excitation, where the parent CS(2)(+) ions were prepared by [3 + 1] REMPI (resonance-enhanced multiphoton ionization) at 483.2 nm from the jet-cooled CS(2) molecules. The [1 + 1] photodissociation spectrum of CS(2)(+) via the B(2)Sigma(u)(+)(upsilon(1)upsilon(2)0) <-- X(2)Pi(g,3/2)(000) transition was obtained by scanning the dissociation laser in the wavelength range of 270-285 nm and detecting the signal of both S(+) and CS(+). The [1 + 1'] photodissociation spectra of CS(2)(+) were obtained by fixing the first dissociation laser at 281.94 or 277.15 nm to excite the B(2)Sigma(u)(+) (000 or 100) <-- X(2)Pi(g,3/2)(000) transitions and scanning the second dissociation laser in the range of 606-763 nm to excite C(2)Sigma(g)(+)(upsilon(1)upsilon(2)0) <-- B(2)Sigma(u)(+)(000,100) transitions. New spectroscopic constants of nu(1) = 666.2 +/- 2.5 cm(-1), nu(2) = 363.2 +/- 1.9 cm(-1), chi(11) = -5.5 +/- 0.1 cm(-1), chi(22) = 1.6 +/- 0.1 cm(-1), chi(12) = -8.6 +/- 0.2 cm(-1), and k(122) = 44.9 +/- 2.5 cm(-1) (Fermi resonance constant) for the C(2)Sigma(g)(+) state are deduced from the [1 + 1'] photodissociation spectra. On the basis of the [1 + 1] and [1 + 1'] photodissociation spectra, the wavelength and level dependence of the product branching ratios CS(+)/S(+) has been found and the dissociation dynamics of CS(2)(+) ions via B(2)Sigma(u)(+) and C(2)Sigma(g)(+) electronic states are discussed.     

气相离子-分子反应B2H3-+CS2——B2H3S-+CS的理论研究

用密度泛函方法B3LYP/6-311++G(d,p)和高级电子相关的偶合簇法CCSD(T)/6-311++G(d,p)研究了气相离子-分子反应B₂H₃^-+CS₂B₂H₃S^-+CS的机理.结果表明,B₂H₃最可能进攻CS₂中碳原子形成三元环中间体,随后通过氢迁移和最终消除CS的反应步骤形成硫原子转移产物H₃BBS^-+CS,反应大量放热且不需要活化能.B₂H₃直接对CS₂中硫原子进攻夺取硫原子的反应方式存在一定能垒阻碍.计算结果有助于深入了解B₂H₃,B₃H-6和B₄H₇^-等缺电子硼氢负离子的反应行为.     

Tetrachloro- and tetrabromoarsonium(V) cations: raman and 75As, 19F NMR spectroscopic characterization and X-ray crystal structures of [AsCl4][As(OTeF5)6] and [AsBr4][AsF(OTeF5)5]

The salts [AsX4][As(OTeF5)6] and [AsBr4][AsF(OTeF5)5] (X = Cl, Br) have been prepared by oxidation of AsX3 with XOTeF5 in the presence of the OTeF5 acceptors As(OTeF5)5 and AsF(OTeF5)4. The mixed salts [AsCl4][Sb(OTeF5)6-nCl(n-2)] and [AsCl4][Sb(OTeF5)6-nCl(n)] (n > or = 2) have also been prepared. The AsBr4+ cation has been fully structurally characterized for the first time in SO2ClF solution by 75As NMR spectroscopy and in the solid state by a single-crystal X-ray diffraction study of [AsBr4][AsF(OTeFs)5]: P1, a = 9.778(4) A, b = 17.731(7) A, c = 18.870(8) A, alpha = 103.53(4)degrees, beta = 103.53(4) degrees, gamma = 105.10(4) degrees, V = 2915(2) A3, Z = 4, and R1 = 0.0368 at -183 degrees C. The crystal structure determination and solution 75As NMR study of the related [AsCl4][As(OTeF5)6] salt have also been carried out: [AsCl4][As(OTeF5)6], R3, a = 9.8741(14) A, c = 55.301(11) A, V= 4669(1) A3, Z = 6, and R1 = 0.0438 at -123 degrees C; and R3, a = 19.688(3) A, c = 55.264(11) A, V= 18552(5) A3, Z = 24, and R1 = 0.1341 at -183 degrees C. The crystal structure of the As(OTeF5)6- salt reveals weaker interactions between the anion and cation than in the previously known AsF6- salt. The AsF(OTeF5)5- anion is reported for the first time and is also weakly coordinating with respect to the AsBr4+ cation. Both cations are undistorted tetrahedra with bond lengths of 2.041(5)-2.056(3) A for AsCl4+ and 2.225(2)-2.236(2) A for AsBr4+. The Raman spectra are consistent with undistorted AsX4+ tetrahedra and have been assigned under Td point symmetry. The 35Cl/37Cl isotope shifts have been observed and assigned for AsCl4+, and the geometrical parameters and vibrational frequencies of all known and presently unknown PnX4+ (Pn = P, As, Sb, Bi; X = F, Cl, Br, I) cations have been calculated using density functional theory methods.     

Cs3AgAs4Se8 and CsAgAs2Se4: selenoarsenates with infinite 1 infinity[AsSe2]- chains in different Ag+ coordination environments

Two quaternary silver selenoarsenates Cs3AgAs4Se8 (I) and CsAgAs2Se4 (II) have been discovered by methanothermal reaction of Li3AsSe3 with AgBF4 in the presence of the respective alkali metal sources Cs2CO3 and CsCl. Orange crystals of Cs3AgAs4Se8 (I) were formed after reaction at 120 degrees C for 72 h, whereas red CsAgAs2Se4 (II) was obtained under slightly different conditions at 140 degrees C for 70 h. Both compounds possess novel two-dimensional (2D) polyanions consisting of infinite 1 infinity[AsSe2]- chains that are interconnected by Ag+ ions in different coordination patterns. In I, a double layer of 1 infinity[AsSe2]- chains is bridged by distorted trigonal planar coordinated Ag+ atoms to form a 2 infinity[AgAs4Se8]3- layer with a thickness of about 11.3 A. The nonbonding Ag...Ag distances are about 4.220 A, and large cavities within the layers accommodate for three of the four crystallographic Cs+ cations. The double amount of Ag+ atoms per AsSe2 chain unit in II leads to simple layers 2 infinity[AgAs2Se4]- [=[Ag2As4Se8]2-] in which the Ag+ atoms are arranged in rows between the 1 infinity[AsSe2]- chains, with alternating Ag...Ag distances of 3.053(3) and 3.488(3) A. Hereby the 1 infinity[AsSe2]- polyanions show a disorder within the central (-As-Seb)- chain (b = bridging), while the positions of the terminal Se atoms (Set) remain unaffected. The thermal, optical, and spectroscopic properties of the compounds are reported. Both I and II melt with decomposition and are wide band gap semiconductors with values of 2.07 and 1.79 eV, respectively. Raman spectroscopic data show typical band patterns expected for infinite [AsSe2]- chains. Crystal Data: Cs3AgAs4Se8 (I), monoclinic, C2/c, a = 25.212(2) A, b = 8.0748(7) A, c = 22.803(2) A, beta = 116.272(2) degrees, Z = 8; CsAgAs2Se4 (II), monoclinic, P2(1)/n, a = 10.9211(1) A, b = 6.5188(2) A, c = 13.7553(3) A, beta = 108.956(1) degrees, Z = 4.     

Silver complexes of cyclic hexachlorotriphosphazene

The first solid-state structures of complexed P3N3X6 (X = halogen) are reported for X = Cl. The compounds were obtained from P3N3Cl6 and Ag[Al(OR)4] salts in CH2Cl2/CS2 solution. The very weakly coordinating anion with R = C(CF3)3 led to the salt Ag(P3N3Cl6)2+[Al(OR)4]- (1), but the more strongly coordinating anion with R' = C(CH3)(CF3)2 gave the molecular adduct (P3N3Cl6)AgAl(OR')4 (3). Crystals of [Ag(CH2Cl2)(P3N3Cl6)2]+[Al(OR)4]- (2), in which Ag+ is coordinated by two phosphazene and one CH2Cl2 ligands, were isolated from CH2Cl2 solution. The three compounds were characterized by their X-ray structures, and 1 and 3 also by NMR and vibrational spectroscopy. Solution and solid-state 31P NMR investigations in combination with quantum chemically calculated chemical shifts show that the 31P NMR shifts of free and silver-coordinated P3N3Cl6 differ by less than 3 ppm and indicate a very weakly bound P3N3Cl6 ligand in 1. The experimental silver ion affinity (SIA) of the phosphazene ligand was derived from the solid-state structure of 3. The SIA shows that (PNCl2)3 is only a slightly stronger Lewis base than P4 and CH2Cl2, while other ligands such as S8, P4S3, toluene, and 1,2-Cl2C2H4 are far stronger ligands towards the silver cation. The energetics of the complexes were assessed with inclusion of entropic, thermal, and solvation contributions (MP2/TZVPP, COSMO). The formation of the cations in 1, 2, and 3 was calculated to be exergonic by delta(r)G(degrees)(CH2Cl2) = -97, -107, and -27 kJ mol(-1), respectively. All prepared complexes are thermally stable; formation of P3N3Cl5+ and AgCl was not observed, even at 60 degrees C in an ultrasonic bath. Therefore, the formation of P3N3Cl5+ was investigated by quantum chemical calculations. Other possible reaction pathways that could lead to the successful preparation of P3N3X5+ salts were defined.     

Approaching the gas-phase structures of [AgS8]+ and [AgS16]+ in the solid state

Upon treating elemental sulfur with [AgSbF(6)], [AgAl(hfip)(4)], [AgAl(pftb)(4)] (hfip=OCH(CF(3))(2), pftb =OC(CF(3))(3)) the compounds [Ag(S(8))(2)][SbF(6)] (1), [AgS(8)][Al(hfip)(4)] (2), and [Ag(S(8))(2)](+)[[Al(pftb)(4)](-) (3) formed in SO(2) (1), CS(2) (2), or CH(2)Cl(2) (3). Compounds 1-3 were characterized by single-crystal X-ray structure determinations: 1 by Raman spectroscopy, 2 and 3 by solution NMR spectroscopy and elemental analyses. Single crystals of [Ag(S(8))(2)](+)[Sb(OTeF(5))(6)](-) 4 were obtained from a disproportionation reaction and only characterized by X-ray crystal structure analysis. The Ag(+) ion in 1 coordinates two monodentate SbF(6) (-) anions and two bidentate S(8) rings in the 1,3-position. Compound 2 contains an almost C(4v)-symmetric [AgS(8)](+) moiety; this is the first example of an eta(4)-coordinated S(8) ring (d(Agbond;S)=2.84-3.00 A). Compounds 3 and 4, with the least basic anions, contain undistorted, approximately centrosymmetric Ag(eta(4)-S(8))(2) (+) cations with less symmetric eta(4)-coordinated S(8) rings (d(Agbond;S)=2.68-3.35 A). The thermochemical radius and volume of the undistorted Ag(S(8))(2) (+) cation was deduced as r(therm)(Ag(S(8))(2) (+))=3.378+ 0.076/-0.120 A and V(therm)(Ag(S(8))(2) (+))=417+4/-6 A(3). AgS(8) (+) and several isomers of the Ag(S(8))(2) (+) cation were optimized at the BP86, B3LYP, and MP2 levels by using the SVP and TZVPP basis sets. An analysis of the calculated geometries showed the MP2/TZVPP level to give geometries closest to the experimental data. Neither BP86 nor B3LYP reproduced the longer weak dispersive Agbond;S interactions in Ag(eta(4)-S(8))(2) (+) but led to Ag(eta(3)-S(8))(2) (+) geometries. With the most accurate MP2/TZVPP level, the enthalpies of formation of the gaseous [AgS(8)](+) and [Ag(S(8))(2)](+) cations were established as Delta(f)H(298)([Ag(S(8))(2)](+), g)=856 kJ mol(-1) and Delta(f)H(298)([AgS(8)](+), g)=902 kJ mol(-1). It is shown that the [AgS(8)](+) moiety in 2 and the [AgS(8)](2) (+) cations in 3 and 4 are the best approximation of these ions, which were earlier observed by MS methods. Both cations reside in shallow potential-energy wells where larger structural changes only lead to small increases in the overall energy. It is shown that the covalent Agbond;S bonding contributions in both cations may be described by two components: i) the interaction of the spherical empty Ag 5s(0) acceptor orbital with the filled S 3p(2) lone-pair donor orbitals and ii) the interaction of the empty Ag 5p(0) acceptor orbitals with the filled S 3p(2) lone-pair donor orbitals. This latter contribution is responsible for the observed low symmetry of the centrosymmetric Ag(eta(4)-S(8))(2) (+) cation. The positive charge transferred from the Ag(+) ion in 1-4 to the coordinated sulfur atoms is delocalized over all the atoms in the S(8) ring by multiple 3p(2)-->3sigma* interactions that result in a small long-short-long-short Sbond;S bond-length alternation starting from S1 with the shortest Agbond;S length. The driving force for all these weak bonding interactions is positive charge delocalization from the formally fully localized charge of the Ag(+) ion.     

Accounting for the differences in the structures and relative energies of the highly homoatomic np pi-np pi (n > or = 3)-bonded S2I4 2+, the Se-I pi-bonded Se2I4 2+, and their higher-energy isomers by AIM, MO, NBO, and VB methodologies

The bonding in the highly homoatomic np pi-np pi (n > or = 3)-bonded S2I42+ (three sigma + two pi bonds), the Se-I pi-bonded Se2I42+ (four sigma + one pi bonds), and their higher-energy isomers have been studied using modern DFT and ab initio calculations and theoretical analysis methods: atoms in molecules (AIM), molecular orbital (MO), natural bond orbital (NBO), and valence bond (VB) analyses, giving their relative energies, theoretical bond orders, and atomic charges. The aim of this work was to seek theory-based answers to four main questions: (1) Are the previously proposed simple pi*-pi* bonding models valid for S2I42+ and Se2I42+? (2) What accounts for the difference in the structures of S2I42+ and Se2I42+? (3) Why are the classically bonded isolobal P2I4 and As2I4 structures not adopted? (4) Is the high experimentally observed S-S bond order supported by theoretical bond orders, and how does it relate to high bond orders between other heavier main group elements? The AIM analysis confirmed the high bond orders and established that the weak bonds observed in S2I42+ and Se2I42+ are real and the bonding in these cations is covalent in nature. The full MO analysis confirmed that S2I42+ contains three sigma and two pi bonds, that the positive charge is essentially equally distributed over all atoms, that the bonding between S2 and two I2+ units in S2I42+ is best described by two mutually perpendicular 4c2e pi*-pi* bonds, and that in Se2I42+, two SeI2+ moieties are joined by a 6c2e pi*-pi* bond, both in agreement with previously suggested models. The VB treatment provided a complementary approach to MO analysis and provided insight how the formation of the weak bonds affects the other bonds. The NBO analysis and the calculated AIM charges showed that the minimization of the electrostatic repulsion between EI2+ units (E = S, Se) and the delocalization of the positive charge are the main factors that explain why the nonclassical structures are favored for S2I42+ and Se2I42+. The difference in the structures of S2I42+ and Se2I42+ is related to the high strength of the S-S pi bond compared to the weak S-I sigma bond and the additional stabilization from increased delocalization of positive charge in the structure of S2I42+ compared to the structure of Se2I42+. The investigation of the E2X42+ series (E = S, Se, Te; X = Cl, Br, I) revealed that only S2I42+ adopts the highly np pi-np pi (n > or = 3)-bonded structure, while all other dications favor the pi-bonded Se2I42+ structure. Theoretical bond order calculations for S2I42+ confirm the previously presented experimentally based bond orders for S-S (2.1-2.3) and I-I (1.3-1.5) bonds. The S-S bond is determined to have the highest reported S-S bond order in an isolated compound and has a bond order that is either similar to or slightly less than the Si-Si bond order in the proposed triply bonded [(Me3Si)2CH]2(iPr)SiSi triple bond SiSi(iPr)[CH(SiMe3)2]2 depending on the definition of bond orders used.     

CS2 +多光子光解产生CS+的动力学研究

The dynamics on the multi-photon dissociation of CS2+ molecular ions to produce CS + ions has been investigated by measuring the CS + photofragment excitation（PHOFEX）spectrum in the wavelength range of 385～435 nm,where the CS2+ molecular ions were prepared purely by［3+1］multiphoton ionization of the neutral CS2molecules at 483.2 nm. With the ～60 ns delay,which is much more than the laser pulse width（～5 ns）,between ionization laser and dissociation laser,the threshold wavelength of dissociation laser to produce CS+ fragment ion from CS2+ molecular ions was obviously observed in the PHOFEX spectrum. The adiabatic appearance potential of the CS+ was determined to be（5.852 ± 0.005）eV above the X 2Σg,3/2（0,0,0）level of CS2+. The product branching ratios,（CS+/S+）,as measured from the PHOFEX spectra,increase from 0 to slightly larger than 1 in the wavenumber range of 47200～50400 cm-1 . The［1+1］dissociation mechanism to get to CS++S from CS2+ was discussed and preliminarily attributed to（i）CS2+（X 2Πg）→ CS2+（A2Πu）through one-photon excitation,（ii）CS2+（A2Πu）→ CS2+（X*）via internal conversion process due to the vibronic coupling between the A and X states,（iii）CS2+（X*）→ CS2+（B 2Σ+u）through the second photon excitation,and（iv）CS2+（B 2Σ+u）→CS +（X 2Σ+）+S（3P）,because of the potential curve crossing with the repulsive 4Σ- state and/or the 2Σ- state correlated with the second dissociation limit. However,when the dissociation laser overlaps the ionization laser in time scale in the laser-molecule interaction zone,the appearance threshold is not available in the PHOFEX spectrum. This fact shows that there are other mixed three-photon paths of［1+1+1'］,［1+1'+1'］,and［1+1'+1］to produce CS+ fragment ion from CS2+ molecular ions besides the above［1+1］dissociation mechanism,that is,CS2+（X 2Πg）→ CS2+（A 2Πu）through one-photon excitation［1］of dissociation laser,CS2+（A 2Πu）→CS2+（X*）via internal conversion process due to the vibronic coupling between the A and X states,CS2+（X*）→ CS2+（B 2Σ +u）through the second photon excitation by dissociation laser［1］or ionization laser［1'］,and third photon excitation by ionization laser［1'］or dissociation laser［1］to reach the adiabatic appearance potential to produce CS+ with the dissociation laser wavelengths longer than 423. 89 nm,at which the［1+1］dissociation mechanism to get to CS+ is unavailable.     

Photoinduced [4 + 4] cycloadditions of o-quinones with oxazoles

[reaction: see text] Photocycloadditions of 9,10-phenanthraquinone (PQ) with oxazoles (1a and 1b) gave [4 + 4] products 2 with the O=C-C=O functionality in PQ and the 2-azadiene moiety in oxazole as 4pi addends. Photoreactions of 1-acetylisatin (IS) with 1a, 1c, and 1d gave [4 + 4] product A, which underwent further [2 + 2] reactions with another (3)IS to furnish 5. These regioselective and diastereoselective [4 + 4] photocycloadditions are rationalized by the intervening of the key conformers for ISC and bond formation of the most stable 1,6-diradical intermediates.     

Multiphoton dissociation dynamics of BrCl and the BrCl+ cation

Ion imaging methods have enabled identification of three mechanisms by which (79)Br(+) and (35)Cl(+) fragment ions are formed following one-color multiphoton excitation of BrCl molecules in the wavelength range 324.6 > lambda > 311.7 nm. Two-photon excitation within this range populates selected vibrational levels (v'= 0-5) of the [X (2)Pi(1/2)]5ssigma Rydberg state. Absorption of a third photon results in branching between (i) photoionization (i.e. removal of the Rydberg electron-a traditional 2 + 1 REMPI process) and (ii)pi*<--pi excitation within the core, resulting in formation of one or more super-excited states with Omega= 1 and configuration [A (2)Pi(1/2)]5ssigma. The fate of the latter states involves a further branching. They can autoionize (yielding BrCl(+)(X (2)Pi) ions in a wider range of v(+) states than formed by direct 2 + 1 REMPI). Further, one-photon absorption by the parent ions resulting from direct ionization or autoionization leads to formation of Br(+) and (energy permitting) Cl(+) fragment ions. Alternatively, the super-excited molecules can fragment to neutral atoms, one of which is in a Rydberg state. Complementary ab initio calculations lead to the conclusion that the observed [Cl**[(3)P(J)]4s + Br/Br*] products result from direct dissociation of the photo-prepared super-excited states, whereas [Br**[(3)P(J)]5p + Cl/Cl*] product formation involves interaction between the [A (2)Pi(1/2)]5ssigma and [X (2)Pi(1/2)]5psigma Rydberg potentials at extended Br-Cl bond lengths. Absorption of one further photon by the resulting Br** and Cl** Rydberg atoms leads to their ionization, and thus their appearance in the Br(+) and Cl(+) fragment ion images.     

Metastable Se6 as a ligand for Ag+: from isolated molecular to polymeric 1D and 2D structures

Attempts to prepare the hitherto unknown Se(6)(2+) cation by the reaction of elemental selenium and Ag[A] ([A](-) = [Sb(OTeF(5))(6)](-), [Al(OC(CF(3))(3))(4)](-)) in SO(2) led to the formation of [(OSO)Ag(Se(6))Ag(OSO)][Sb(OTeF(5))(6)](2)1 and [(OSO)(2)Ag(Se(6))Ag(OSO)(2)][Al(OC(CF(3))(3))(4)](2)2a. 1 could only be prepared by using bromine as co-oxidant, however, bulk 2b (2a with loss of SO(2)) was accessible from Ag[Al(OC(CF(3))(3))(4)] and grey Se in SO(2) (chem. analysis). The reactions of Ag[MF(6)] (M = As, Sb) and elemental selenium led to crystals of 1/∞{[Ag(Se(6))](∞)[Ag(2)(SbF(6))(3)](∞)} 3 and {1/∞[Ag(Se(6))Ag](∞)}[AsF(6)](2)4. Pure bulk 4 was best prepared by the reaction of Se(4)[AsF(6)](2), silver metal and elemental selenium. Attempts to prepare bulk 1 and 3 were unsuccessful. 1-4 were characterized by single-crystal X-ray structure determinations, 2b and 4 additionally by chemical analysis and 4 also by X-ray powder diffraction, FT-Raman and FT-IR spectroscopy. Application of the PRESTO III sequence allowed for the first time (109)Ag MAS NMR investigations of 4 as well as AgF, AgF(2), AgMF(6) and {1/∞[Ag(I(2))](∞)}[MF(6)] (M = As, Sb). Compounds 1 and 2a/b, with the very large counter ions, contain isolated [Ag(Se(6))Ag](2+) heterocubane units consisting of a Se(6) molecule bicapped by two silver cations (local D(3d) sym). 3 and 4, with the smaller anions, contain close packed stacked arrays of Se(6) rings with Ag(+) residing in octahedral holes. Each Ag(+) ion coordinates to three selenium atoms of each adjacent Se(6) ring. 4 contains [Ag(Se(6))(+)](∞) stacks additionally linked by Ag(2)(+) into a two dimensional network. 3 features a remarkable 3-dimensional [Ag(2)(SbF(6))(3)](-) anion held together by strong Sb-FAg contacts between the component Ag(+) and [SbF(6)](-) ions. The hexagonal channels formed by the [Ag(2)(SbF(6))(3)](-) anions are filled by stacks of [Ag(Se(6))(+)](∞) cations. Overall 1-4 are new members of the rare class of metal complexes of neutral main group elemental clusters, in which the main group element is positively polarized due to coordination to a metal ion. Notably, 1 to 4 include the commonly metastable Se(6) molecule as a ligand. The structure, bonding and thermodynamics of 1 to 4 were investigated with the help of quantum chemical calculations (PBE0/TZVPP and (RI-)MP2/TZVPP, in part including COSMO solvation) and Born-Fajans-Haber-cycle calculations. From an analysis of all the available data it appears that the formation of the usually metastable Se(6) molecule from grey selenium is thermodynamically driven by the coordination to the Ag(+) ions.     

Direct experimental observation of CS2OH.

The first experimental detection of CS(2)OH is reported. CS(2)OH was observed for about one microsecond after its formation, as an intact isolated species in the gas phase. It was generated by electron transfer to the CS(2)OH(+) ion, prepared in the source of a multisector mass spectrometer by suitable ion-molecule reactions. The vertical formation process allowed characterization of CS(2)OH by structural analysis of CS(2)OH(+). Theoretical calculations were performed at the B3LYP/6-311+G(2d,p) and CCSD(T)/aug-cc-pVTZ//B3LYP/6-311+G(2d,p) levels of theory. The computed structure and stability of CS(2)OH and CS(2)OH(+) as well as the energetics of the involved processes satisfactorily fit with the experimental results.     

Mechanistic twist of the [8+2] cycloadditions of dienylisobenzofurans and dimethyl acetylenedicarboxylate: stepwise [8+2] versus [4+2]/[1,5]-vinyl shift mechanisms revealed through a theoretical and experimental study

Recently, it was reported that both dienylfurans and dienylisobenzofurans could react with dimethyl acetylenedicarboxylate (DMAD) to give [8+2] cycloadducts. Understanding these [8+2] reactions will aid the design of additional [8+2] reactions, which have the potential for the synthesis of 10-membered and larger carbocycles. The present Article is aimed to understand the detailed mechanisms of the originally reported [8+2] cycloaddition reaction between dienylisobenzofurans and alkynes at the molecular level through the joint forces of computation and experiment. Density functional theory calculations at the (U)B3LYP/6-31+G(d) level suggest that the concerted [8+2] pathway between dienylisobenzofurans and alkynes is not favored. A stepwise reaction pathway involving formation of a zwitterionic intermediate for the [8+2] reactions between dienylisobenzofurans that contain electron-donating methoxy groups present in their diene moieties and DMAD has been predicted computationally. This pathway is in competition with a Diels-Alder [4+2] reaction between the furan moieties of dienylisobenzofurans and DMAD. When there is no electron-donating group present in the diene moieties of dienylisobenzofurans, the [8+2] reaction occurs through an alternative mechanism involving a [4+2] reaction between the furan moiety of the tetraene and DMAD, followed by a [1,5]-vinyl shift. This computationally predicted novel mechanism was supported experimentally.     

Schlenk's early "free" carbanions

Nearly a century ago, Schlenk published the syntheses and isolation of two most remarkable and unstable complexes: crystalline [Ph(3)C(-)][Me(4)N(+)] and [PhCH(2) (-)][Me(4)N(+)]. The crystal structure of the first complex contains a "free" Ph(3)C(-) ion, which displays the expected planar trigonal geometry at its central carbon atom. The phenyl groups are not orientated in the typical propeller arrangement, but instead display various orientations with respect to the molecular plane. These orientations can be directly related to the extent of charge delocalization and correlate well with other structural characteristics related to charge delocalization. The crystal structure also shows a network of C-H(delta+)...C(delta-) and C-H...pi interactions. Only C-H...pi interactions to the most negative charged phenyl rings are observed. The absolute Br?nsted acidity of Me(4)N(+) is calculated by the G2(MP2) method (287.7 kcal mol(-1)) and is compared to the calculated acidity of Me(4)P(+) (268.4 kcal mol(-1)). On this basis, the pK(a) value for Me(4)N(+) is estimated at 29.6. This makes the existence, and especially Schlenk's early isolation, of the "free" carbanions [Ph(3)C(-)][Me(4)N(+)] and [PhCH(2) (-)][Me(4)N(+)] quite noteworthy.