Structure of 1-(arylselanyl)naphthalenes. 2. G dependence in 8-G-1-(p-YC(6)H(4)Se)C(10)H(6).

The structures of 8-G-1-(p-YC(6)H(4)Se)C(10)H(6) (1 (G = Cl) and 2 (G = Br): Y = H (a), OMe (b), Me (c), Cl (d), Br (e), COOEt (f), and NO(2) (g)) were investigated by X-ray crystallographic analysis, NMR spectroscopy, and ab initio MO calculations. The structures of all members in 1 and 2 are concluded to be type B, which is in striking contrast to the type A structure for 4d-g (4 (g(n)), where G = H). The Se-C(i) bond of the p-YC(6)H(4)Se group in 8-G-1-(p-YC(6)H(4)Se)C(10)H(6) is almost perpendicular to the naphthyl plane in type A, and it is located on the plane in type B. The chlorine and bromine substitution at the 8-position in 1 and 2 dramatically changes the type A structure of 4 (g(n)) to type B. The nonbonded G- - -Se-C 3c-4e type interaction must contribute to stabilize the type B structure. The type B structure in 1 and 2 should also be more stabilized than the same structure in 4 by the 3c-4e type interaction: The structure of 4b is type B in the crystals and type B would be more stable for 4c and might be for 4a in solutions. Ab initio MO calculations are performed on 8-G-1-(p-YC(6)H(4)Se)C(10)H(6), 8-G-C(10)H(6)SeH-1, and models HG- - -SeH(2), where G = Cl, Br, and F, to clarify the reason for the dramatic change in the structures. The type B structure is optimized to be more stable than the type A for all species examined, which supports the observations. The energy differences between type B and type A are larger for the models than for the naphthalenes. While the superiority of the type B for the former is Br > Cl > F, that of the latter is Br approximately Cl >/= F. These results show that the main factor of the structural change from type A to type B is the nonbonded G- - -Se-C 3c-4e interaction. The electronic effect of halogens through the naphthalene pi-framework would also contribute to some extent, although the direct comparison of the evaluated values between the naphthalene systems and the models is not so easy. Factors to stabilize the two structures of 1, 2, 4, and 8-(MeSe)-1-(p-YC(6)H(4)Se)C(10)H(6) are reexamined from a viewpoint of the nonbonded G- - -Se-C 3c-4e interaction (G dependence), together with the electronic effect of Y (Y dependence).     

Orientational effect of aryl groups on 77Se NMR chemical shifts: experimental and theoretical investigations

The orientational effect of p-YC6H4 (Ar) on delta(Se) is elucidated for ArSeR, based on experimental and theoretical investigations. The effect is examined in the cases in which Se--CR in ArSeR is either in the Ar plane (pl) or is perpendicular to the plane (pd). 9-(Arylselanyl)anthracenes (1) and 1-(arylselanyl)anthraquionones (2) are employed to establish the effect in pl and pd, respectively. Large upfield shifts are observed for Y=NMe2, OMe, and Me, and large downfield shifts for Y=COOEt, CN, and NO2 in 1, relative to Y=H, as is expected. Large upfield shifts are brought by Y=NMe2, OMe, Me, F, Cl, and Br, and downfield shifts by Y=CN and NO2 in 2, relative to Y=H, with a negligible shift by Y=COOEt. Absolute magnetic shielding tensors of Se (sigma(Se)) are calculated for ArSeR (R=H, Me, and Ph), assuming pl and pd, based on the DFT-GIAO method. Observed characters are well explained by the total sigma(Se). Paramagnetic terms (sigmap(Se)) are governed by (sigmap(Se)xx+sigmap(Se)yy), in which the direction of np(Se) (constructed by 4pz(Se)) is set to the z axis. The main interaction in pl is the np(Se)-pi(C6H4)-pz(Y) type. The Y dependence in pl occurs through admixtures of 4pz(Se) in pi(SeC6H4Y) and pi*(SeC6H4Y), modified by the conjugation, with 4px(Se) and 4py(Se) in sigma(CSeX) and sigma*(CSeX) (X=H or C) under a magnetic field. The main interaction in pd is the sigma(CSeX)-pi(C6H4)-px(Y) type, in which Se-X is nearly on the x axis. The Y dependence in pd mainly arises from admixtures of 4pz(Se) in np(Se) with 4px(Se) and 4py(Se) in modified sigma*(CSeX), since np(Se) is filled with electrons. It is demonstrated that the effect of Y on sigmap(Se) in the pl conformation is the same regardless of whether Y is an electron-donor or electron-acceptor, whereas for pd conformations the effect is greater when Y is an electron donor, as observed in 1 and 2, respectively. Contributions of each molecular orbital and each transition on sigmap(Se) are evaluated, which enables us to recognize and visualize the effect clearly.     

Role of p(Z)-π(Ar/Nap) conjugation in structures of 1-(arylchalcogena)naphthalenes for Z = Te versus Se, S and O: experimental and theoretical investigations

Magnitudes of the p(Z)-π(Ar/Nap) conjugation were evaluated for 1-(arylchalcogena)naphthalenes (1-(ArZ)Nap, 1-(p-YC(6)H(4)Z)C(10)H(7); 1 (Z = Te), 2 (Se), 3 (S) and 4 (O)). Structures of 1 were determined by X-ray analysis for Y = NMe(2) (b), OMe (c) and CN (i). For 1b and 1c that have electron donating Y, the Z-C(Ar) bond is located on the naphthyl plane with Z-C(Nap) being perpendicular to the aryl plane, which we define as (B: pd). On the other hand, the structure of 1i with electron donating Y is (A: pl), of which Z-C(Ar) is placed almost perpendicular to the naphthyl plane with Z-C(Nap) being located on the aryl plane. Each structure of 1a (Y = H), 1b, 1c, 1d (Me), 1e (F), 1f (Cl), 1g (Br), 1h (COOEt), 1i and 1j (NO(2)) was determined by NMR in chloroform-d. Structures of 1 in the solutions are (B: pd) for b, c and e that have electron donating Y, (A: pl) for f-j with electron accepting Y, and in equilibrium between (B: pd) and (A: pl) for a and d of which Y are rather neutral. The results for 2-4 are very similar to those of 1 in solutions. Quantum chemical calculations were performed on 1-4 with Y of a, b' (NH(2)), d, f and j. Magnitudes of the p(Z)-π(Ar/Nap) conjugation were well-evaluated by NBO (natural bond orbital) analysis. The values were 12.6 and 13.0 kcal mol(-1) for the typical forms of (A: pl) and (B: pd) of 1a, respectively, resulting in a much smaller energy difference between the two (0.4 kcal mol(-1)), which should correspond to the observed result. It is well-demonstrated that the p(Te)-π(Ar/Nap) conjugation operates effectively in 1, although the magnitudes increase in the order of Z = Te < Se < S < O. Thermal effect of the Gibbs free energies is shown to play an important role in the energy profiles of 1a-4a.     

77Se NMR chemical shifts of 9-(arylselanyl)triptycenes: new standard for planar structures of ArSeR and applications to determine the structures in solutions

A set of new delta(Se) parameters is proposed as a standard for the planar (pl) orientational effect of p-YC(6)H(4) (Ar) in ArSeR, employing 9-(arylselanyl)triptycenes (1: p-YC(6)H(4)SeTpc). The Se-C(R) bond in ArSeR is placed on the Ar plane in pl and it is perpendicular to the plane in pd. Large upfield shifts are observed for Y = NMe(2), OMe, and Me (-22 to -6 ppm) and large downfield shifts for Y = COOEt, CN, and NO(2) (19-37 ppm), relative to Y = H, with small upfield and moderate downfield shifts by Y of halogens (-1 ppm for Y = F and 4 ppm for Y = Cl and Br). This must be the result of the p(Se)-pi(C(6)H(4))-p(Y) conjugation in 1 (pl). While the character of delta(Se) in 1 (pl) is very similar to that in 9-(arylselanyl)anthracenes (2 (pl)), it is very different from that of 1-(arylselanyl)anthraquinones (3 (pd)). Sets of delta(Se) of 1 and 2 must serve as the standard for pl and that of 3 does for pd in solutions. Structures of various ArSeR in solutions are determined from the viewpoint of the orientational effect based on the standard delta(Se) of 1-3. While the structure of 2-methyl-1-(arylselanyl)naphthalenes is concluded to be all pl in solutions, those of 8-chloro- and 8-bromo-1-(arylselanyl)naphthalenes are all pd, except for Y = COOEt, CN, and NO(2): The equilibrium between pd and pl contributes to those with Y = COOEt, CN, and NO(2). The structure of 1-(arylselanyl)naphthalenes changes depending on Y. The structures of ArSeMe and ArSeCOPh are shown to be pl and pd, respectively, in solutions. Those of ArSePh and ArSeAr seem to change depending on Y. delta(Se) of 1-3 are demonstrated to serve as the standard to determine the structures in solutions. The rules of thumb derived from the characters in delta(Se) for 1-3 are very useful to determine the structures of ArSeR in solutions, in addition to the analysis based on the plots.     

Synthesis and characterization of Mo(6) chalcobromides and cyano-substituted compounds built from a novel [(Mo(6)Br(i)(6)Y(i)(2))L(a)(6)](n)()(-) discrete cluster unit (Y(i) = S or Se and L(a) = Br or CN)

The syntheses, crystal structures determined by single-crystal X-ray diffraction, and characterizations of new Mo(6) cluster chalcobromides and cyano-substituted compounds with 24 valence electrons per Mo(6) cluster (VEC = 24), are presented in this work. The structures of Cs(4)Mo(6)Br(12)S(2) and Cs(4)Mo(6)Br(12)Se(2) prepared by solid state routes are based on the novel [(Mo(6)Br(i)(6)Y(i)(2))Br(a)(6)](4)(-) (Y = S, Se) discrete units in which two chalcogen and six bromine ligands randomly occupy the inner positions, while the six apical ones are fully occupied by bromine atoms. The interaction of these two compounds with aqueous KCN solution results in apical ligand exchange giving the two first Mo(6) cyano-chalcohalides: Cs(0.4)K(0.6)(Et(4)N)(11)[(Mo(6)Br(6)S(2))(CN)(6)](3).16H(2)O and Cs(0.4)K(0.6)(Et(4)N)(11)[(Mo(6)Br(6)Se(2))(CN)(6)](3).16H(2)O. Their crystal structures, built from the original [(Mo(6)Br(i)(6)Y(i)(2))(CN)(a)(6)](4)(-) discrete units, will be compared to those of the two solid state precursors and other previously reported Mo(6) cluster compounds. Their redox properties and (77)Se NMR characterizations will be presented. Crystal data: Cs(4)Mo(6)Br(12)S(2), orthorhombic, Pbca (No. 61), a = 11.511(5) A, b = 18.772(5) A, c = 28.381 A (5), Z = 8; Cs(4)Mo(6)Br(12)Se(2), Pbca (No. 61), a = 11.6237(1) A, b = 18.9447(1) A, c = 28.4874(1) A, Z = 8; Cs(0.4)K(0.6)(Et(4)N)(11)[(Mo(6)Br(6)S(2))(CN)(6)](3).16H(2)O, Pm-3m (No. 221), a = 17.1969(4) A, Z = 1; Cs(0.4)K(0.6)(Et(4)N)(11)[(Mo(6)Br(6)Se(2))(CN)(6)](3).16H(2)O, Pm-3m (No. 221), a = 17.235(5) A, Z = 1.     

Orientational effect of aryl groups in aryl selenides: how can 1h and 13c NMR chemical shifts clarify the effect?

Two sets of delta(H) and delta(C) are proposed by employing 9-(arylselanyl)anthracenes [9-(p-YC6H4Se)Atc: 1] and 1-(arylselanyl)anthraquinones [1-(p-YC6H4Se)Atq: 2] with various Y's. Structures of 1 and 2 are (A: pl) and (B: pd), respectively, for all Y examined in chloroform-d. After elucidation of the behavior of delta(H, C: 1) and delta(H, C: 2), they are applied to determine the structures in chloroform-d solutions for 1-(arylselanyl)naphthalenes (3), 1-(arylselanyl)-2-methylnaphthalenes (4), and 1-(arylselanyl)-8-bromonaphthalenes (5). Although the structure of 4 remains in (A: pl) in the solutions for all Y examined, that of 5 is (B: pd), except for Y = CN and NO2. On the other hand, 3 is shown to equilibrate between (A: pl) and (B: pd). Although the contributions of (B: pd) and (A: pl) are predominant for Y = NMe2 and NO2, respectively, the equilibrium constants change from Y to Y in the solutions. The results are supported by the quantum chemical calculations, containing the solvent effect of chloroform. These results demonstrate that delta(H, C: 1) and delta(H, C: 2), as well as delta(Se), serve as the practical standards for pl and pd, respectively, to analyze the structures of p-YC6H4ZR (Z = Se) in solutions.     

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.     

Cluster oxalate complexes [M3(mu3-Q)(mu2-Q2)3(C2O4)3]2- and [Mo3(mu3-Q)(mu2-Q)3(C2O4)3(H2O)3]2- (M = Mo, W; Q = S, Se): mechanochemical synthesis and crystal structure

Mechanochemical reaction of cluster coordination polymers 1infinity[M3Q7Br4] (M = Mo, W; Q = S, Se) with solid K2C2O4 leads to cluster core excision with the formation of anionic complexes [M3Q7(C2O4)3]2-. Extraction of the reaction mixture with water followed by crystallization gives crystalline K2[M3Q7(C2O4)3].0.5KBr.nH2O (M = Mo, Q = S, n = 3 (1); M = Mo, Q = Se, n = 4 (2); M = W, Q = S, n = 5 (3)). Cs2[Mo3S7(C2O4)3].0.5CsCl.3.5H2O (4) and (Et4N)1.5H0.5K{[Mo3S7(C2O4)3]Br}.2H2O (5) were also prepared. Close Q...Br contacts result in the formation of ionic triples {[M3Q7(C2O4)3](2)Br}5- in 1-4 and the 1:1 adduct {[Mo3S7(C2O4)3]Br}3- in 5. Treatment of 1 or 2 with PPh(3) leads to chalcogen abstraction with the formation of [Mo3(mu3-Q)(mu2-Q)3(C2O4)3(H2O)3]2-, isolated as (Ph4P)2[Mo3(mu3-S)(mu2-S)3(C2O4)3(H2O)3].11H2O (6) and (Ph4P2[Mo3(mu3-Se)(mu2-Se)3(C2O4)3(H2O)3].8.5H2O.0.5C2H5OH (7). All compounds were characterized by X-ray structure analysis. IR, Raman, electronic, and 77Se NMR spectra are also reported. Thermal decomposition of 1-3 was studied by thermogravimetry.     

Manifestation of stereoelectronic effects on the calculated carbon-hydrogen bond lengths and one-bond 1J(C-H) NMR coupling constants. Relative acceptor ability of the carbonyl (C=O), thiocarbonyl (C=S), and methylidene (C=CH2) groups toward C-H donor bonds

Theoretical examination [B3LYP/6-31G(d,p), PP/IGLO-III//B3LYP/6-31G(d,p), and NBO methods] of six-membered cyclohexane 1 and carbonyl-, thiocarbonyl-, or methylidene-containing derivatives 2-27 afforded precise structural (in particular, C-H bond distances) and spectroscopic (specifically, one-bond (1)J(C)(-)(H) NMR coupling constants) data that show the consequences of stereoelectronic hyperconjugative effects in these systems. Major observations include the following. (1) sigma(C)(-)(H)(ax)() -->(C)(=)(Y) and pi(C)(=)(Y) --> sigma(C)(-)(H)(ax)() (Y = O, S, or CH(2)) hyperconjugation leads to a shortening (strengthening) of the equatorial C-H bonds adjacent to the pi group. This effect is reflected in smaller (1)J(C)(-)(H)(ax)() coupling constants relative to (1)J(C)(-)(H)(eq)(). (2) Comparison of the structural and spectroscopic consequences of sigma(C)(-)(H)(ax)() --> pi(C)(=)(Y) hyperconjugation in cyclohexanone 2, thiocyclohexanone 3, and methylenecyclohexane 4 suggests a relative order of acceptor orbital ability C=S > C=O > C=CH(2), which is in line with available pK(a) data. (3) Analysis of the structural and spectroscopic data gathered for heterocyclic derivatives 5-12 reveals some additivity of sigma(C)(-)(H)(ax)() --> pi(C)(=)(Y), pi(C)(=)(Y) --> sigma(C)(-)(H)(ax)(), n(X) --> sigma(C)(-)(H)(ax)(), n(beta)(O) --> sigma(C)(-)(H)(eq)(), and sigma(S)(-)(C) --> sigma(C)(-)(H)(eq)() stereoelectronic effects that is, nevertheless, attenuated by saturation effects. (4) Modulation of the C=Y acceptor character of the exocyclic pigroup by conjugation with alpha-heteroatoms O, N, and S in lactones, lactams, and methylidenic analogues 13-24 results in decreased sigma(C)(-)(H)(ax)() --> pi(C)(=)(Y) and pi(C)(=)(Y) --> sigma(C)(-)(H)(ax)() hyperconjugation. (5) Additivity of sigma(C)(-)(H)(ax)() --> pi(C)(=)(Y) and pi(C)(=)(Y) --> sigma(C)(-)(H)(ax)() hyperconjugative effects is also apparent in 1,3-dicarbonyl derivative 25 (C=Y equal to C=O), 1,3-dithiocarbonyl derivative 26 (C=Y equal to C=S), and 1,3-dimethylidenic analogue 27 (C=Y equal to C=CH(2)).     

A family of octahedral rhenium cluster complexes [Re6Q8(H2O)n(OH)6-n]n-4 (Q=S, Se; n=0-6): structural and pH-dependent spectroscopic studies

The conversions of hexahydroxo rhenium cluster complexes [Re6Q8(OH)6]4- (Q=S, Se) in aqueous solutions in a wide pH range were investigated by chemical methods and spectroscopic measurements. Dependences of the spectroscopic and excited-state properties of the solutions on pH have been studied in detail. It has been found that a pH decrease of aqueous solutions of the potassium salts K4[Re6Q8(OH)6].8H2O (Q=S, Se) results in the formation of aquahydroxo and hexaaqua cluster complexes with the general formula [Re6Q8(H2O)n(OH)6-n]n-4 that could be considered as a result of the protonation of the terminal OH- ligands in the hexahydroxo complexes. The compounds K2[Re6S8(H2O)2(OH)4].2H2O (1), [Re6S8(H2O)4(OH)2].12H2O (2), [Re6S8(H2O)6][Re6S6Br8].10H2O (3), and [Re6Se8(H2O)4(OH)2] (4) have been isolated and characterized by X-ray single-crystal diffraction and elemental analyses and infrared (IR) spectroscopy. In crystal structures of the aquahydroxo complexes, the cluster units are connected to each other by an extensive system of very strong hydrogen bonds between terminal ligands.     

Solid state structure and solution behaviour of organoselenium(II) compounds containing 2-{E(CH2CH2)2NCH2}C6H4 groups (E = O, NMe)

Cleavage of the Se-Se bond in [2-{O(CH(2)CH(2))(2)NCH(2)}C(6)H(4)](2)Se(2) (1) and [2-{MeN(CH(2)CH(2))(2)NCH(2)}C(6)H(4)](2)Se(2) (2) by treatment with SO(2)Cl(2), bromine or iodine (1 : 1 molar ratio) yielded [2-{O(CH(2)CH(2))(2)NCH(2)}C(6)H(4)]SeX [X = Cl (3), Br (4), I (5)] and [2-{MeN(CH(2)CH(2))(2)NCH(2)}C(6)H(4)]SeI (6). The compounds were characterized in solution by NMR spectroscopy (1H, 13C, 15N, 77Se, 2D experiments). The solid-state molecular structures of 1-3, 4.HBr, 5 and 6 were established by single crystal X-ray diffraction. In all cases T-shaped coordination geometries, i.e. (C,N)SeSe (1, 2), (C,N)SeX (3, 5, 6; X = halogen) or CSeBr(2) (4.HBr), were found. Supramolecular associations in crystals based on hydrogen contacts are discussed.     

Unexpected ligand substitutions in the cluster core {Re6Se8}: synthesis and structure of the novel cluster compound Cs11(H3O)[Re6Se4(O)4Cl6]3.4H2O

The compound Cs11(H3O)[Re6Se4(O)4Cl6]3.4H2O containing a novel cluster core {Re6Se4(O)4} with ordered ligands, where the 4 positions of one face of a Se4(O)4 cube are occupied exclusively by Se atoms and 4 O atoms lie in the opposite face was synthesized via the interaction of solid Re6Se8Br2 with molten KOH.     

(PPh3)Ag(CB11H6Y6)] (Y = H,Br): highly active,selective and recyclable Lewis acids for a hetero-Diels-Alder reaction

The complex [(PPh3)Ag(CB11H6Br6)] 1 is an effective and selective catalyst (0.1 mol% loading) for a hetero-Diels-Alder reaction, which shows a marked dependence on the presence of trace amounts of water, while addition of Ag[Y] [Y = CB11H12, CB11H6Br6, O3SCF3] to a phosphine functionalized support gives an efficient and recyclable Lewis acid catalyst for this transformation.     

Synthesis and Crystal Structure of 4-（2-Bromophenyl）-3,4,7,8-tetrahydro- 7,7-dimethyl-1-p-tolylquinoline-2,5（1H,6H）-dione

The title compound 4-（2-bromophenyl）-3,4,7,8-tetrahydro-7,7-dimethyl-1-p-tolylquinoline-2,5（1H,6H）-dione 1 （C24H24BrNO2, Mr = 438.35） was synthesized and characterized by IR, 1H NMR and elemental analysis. The crystal belongs to monoclinic, space group C2/c with a = 27.565（14）, b = 10.079（5）, c = 15.917（8） A,β = 111.059（9）°, Z = 8, V = 4127（4）A3, Dc = 1.411 g·cm^-3,μ（MoKa） = 2.011 mm^-1, F（000） = 1808, the final R = 0.0417 and wR = 0.1032 for 2393 observed reflections （I 〉 2σ（I））. X-ray analysis reveals that the pyridine ring adopts a distorted boat conformation, while another six-membered ring takes a half-chair conformation. In addition, there are non-classical hydrogen bonds of C-H…O and C-H…Br in the structure. The short distance （3.481A） between the adjacent 2-bromophenyl rings indicates the existence of π-π interaction.     

Characteristics of antiaromatic ring pi multi-hydrogen bonds in (H2O)n-C4H4 (n = 1, 2) complexes

By counterpoise-corrected optimization method, the six antiaromatic ring pi multi-hydrogen bond structures with diversiform shapes for (H2O)n-C4H4 (n = 1,2) have been obtained at the MP2/aug-cc-pVDZ level. At the CCSD(T)/aug-cc-pVDZ level, the interaction energy obtained mainly depends on the numbers of H2O and fold numbers of the pi multi-hydrogen bond. The interaction energy order is -2.342 (1a with pi mono-hydrogen) < -2.777 (1b with pi bi-hydrogen) < -4.683 (2a with pi bi-hydrogen) < -4.734 (2b with pi tri-hydrogen) < -4.782 (2c with pi tri-hydrogen) < -5.009 kcal/mol (2d with pi tetra-hydrogen bond). Strangely, why is the interaction energy of the pi bi-hydrogen bond in 1b close to that of the pi mono-hydrogen bond in 1a (their difference is only 15.7%)? The reason is that a pi-type H-bond (as an accompanying interaction) between two lone pairs of the O-atom and a near pair of H-atoms of C4H4 exists shoulder by shoulder in structures 1a, 2a, 2b, and 2c and contributes to the interaction energy. Another accompanying interaction, a repulsive interaction between the pi H-bond (using the H-atom(s) of H2O) and the near pair of H-atoms of C4H4, is also found. For the structures and interaction energies, the pi-type H-bond produces four effects: bending the strong pi H-bond, attracting the pair of H-atoms of C4H4 so that they deviate from the C4 ring plane, showing the interaction energy contribution, and bringing the larger electron correlation contribution. The repulsive interaction also produces four effects: pushing the pair of H-atoms of C4H4 so that they deviate from its ring plane, elongating the distance of the pi H-bond, promoting the formation of pi-type H-bond, and slightly influencing the interaction energy. In the present paper, one C=C bond with two H2O (over and below the ring plane) forms a pi H-bond link in two ways: a strong-weak pi H-bond link and a strong-strong pi H-bond link. The stability contribution of the former is more favorable than the latter. One H2O forms a pi H-bond with C4H4 in two ways. One strong pi H-bond part (over or below the ring plane) always is accompanied by another H-bond part. The accompanying part is either a weak pi H-bond or pi-type H-bond.     

Energetics of the O-H bond and of intramolecular hydrogen bonding in HOC6H4C(O)Y (Y = H, CH3, CH2CH=CH2, C[triple bond]CH, CH2F, NH2, NHCH3, NO2, OH, OCH3, OCN, CN, F, Cl, SH, and SCH3) compounds

The energetics of the phenolic O-H bond in a series of 2- and 4-HOC 6H 4C(O)Y (Y = H, CH3, CH 2CH=CH2, C[triple bond]CH, CH2F, NH2, NHCH 3, NO2, OH, OCH3, OCN, CN, F, Cl, SH, and SCH3) compounds and of the intramolecular O...H hydrogen bond in 2-HOC 6H 4C(O)Y, was investigated by using a combination of experimental and theoretical methods. The standard molar enthalpies of formation of 2-hydroxybenzaldehyde (2HBA), 4-hydroxybenzaldehyde (4HBA), 2'-hydroxyacetophenone (2HAP), 2-hydroxybenzamide (2HBM), and 4-hydroxybenzamide (4HBM), at 298.15 K, were determined by micro- or macrocombustion calorimetry. The corresponding enthalpies of vaporization or sublimation were also measured by Calvet drop-calorimetry and Knudsen effusion measurements. The combination of the obtained experimental data led to Delta f H m (o)(2HBA, g) = -238.3 +/- 2.5 kJ.mol (-1), DeltafHm(o)(4HBA, g) = -220.3 +/- 2.0 kJ.mol(-1), Delta f H m (o)(2HAP, g) = -291.8 +/- 2.1 kJ.mol(-1), DeltafHm(o)(2HBM, g) = -304.8 +/- 1.5 kJ.mol (-1), and DeltafHm(o) (4HBM, g) = -278.4 +/- 2.4 kJ.mol (-1). These values, were used to assess the predictions of the B3LYP/6-31G(d,p), B3LYP/6-311+G(d,p), B3LYP/aug-cc-pVDZ, B3P86/6-31G(d,p), B3P86/6-311+G(d,p), B3P86/aug-cc-pVDZ, and CBS-QB3 methods, for the enthalpies of a series of isodesmic gas phase reactions. In general, the CBS-QB3 method was able to reproduce the experimental enthalpies of reaction within their uncertainties. The B3LYP/6-311+G(d,p) method, with a slightly poorer accuracy than the CBS-QB3 approach, achieved the best performance of the tested DFT models. It was further used to analyze the trends of the intramolecular O...H hydrogen bond in 2-HOC 6H 4C(O)Y evaluated by the ortho-para method and to compare the energetics of the phenolic O-H bond in 2- and 4-HOC 6H 4C(O)Y compounds. It was concluded that the O-H bond "strength" is systematically larger for 2-hydroxybenzoyl than for the corresponding 4-hydroxybenzoyl isomers mainly due to the presence of the intramolecular O...H hydrogen bond in the 2-isomers. The observed differences are, however, significantly dependent on the nature of the substituent Y, in particular, when an intramolecular H-bond can be present in the radical obtained upon cleavage of the O-H bond.     

Ligand Substitution Reactions at the Nickel of [Mo(3)NiS(4)(H(2)O)(10)](4+) with Two Water Soluble Phosphines, CO, Br(-), I(-), and NCS(-) and the Inertness of the 1,4,7-Triazacyclononane (L) Complex [Mo(3)(NiL)S(4)(H(2)O)(9)](4+)

Comparisons (25 degrees C) are made of substitution reactions, X replacing H(2)O, at the tetrahedral Ni of the heterometallic sulfido cuboidal cluster [Mo(3)NiS(4)(H(2)O)(10)](4+), I = 2.00 M (LiClO(4)). Stopped-flow formation rate constants (k(f)/M(-)(1) s(-)(1)) for six X reagents, including two water soluble air-stable phosphines, 1,3,5-triaza-7-phosphaadamantane PTA (119) and tris(3-sulfonatophenyl)phosphine TPPTS(3)(-) (58), and CO (0.66), Br(-) (14.6), I(-) (32.3), and NCS(-) (44) are reported alongside the previous value for Cl(-) (9.4). A dependence on [H(+)] is observed with PTA, which gives an unreactive form confirmed by NMR as N-protonated PTA (acid dissociation constant K(a) = 0.61 M), but in no other cases with [H(+)] in the range 0.30-2.00 M. The narrow spread of rate constants for all but the CO reaction is consistent with an I(d) dissociative interchange mechanism. In addition NMR studies with H(2)(17)O enriched solvent are too slow for direct determination of the water-exchange rate constant indicating a value <10(3) s(-)(1). Equilibrium constants/M(-)(1) for 1:1 complexing with the different X groups at the Ni are obtained for PTA (2040) and TPPTS(3)(-) (8900) by direct spectrophotometry and from kinetic studies (k(f)/k(b)) for Cl(-) (97), Br(-) (150), NCS(-) (690), and CO (5150). No NCS(-) substitution at the Ni is observed in the case of the heterometallic cube [Mo(3)Ni(L)S(4)(H(2)O)(9)](4+), with tridentate 1,4,7-triazacyclononane(L) coordinated to the Ni. Substitution of NCS(-) for H(2)O, at the Mo's of [Mo(3)NiS(4)(H(2)O)(10)](4+) and [Mo(3)(NiL)S(4)(H(2)O)(9)](4+) are much slower secondary processes, with k(f) = 2.7 x 10(-)(4) M(-)(1) s(-)(1) and 0.94 x 10(-)(4) M(-)(1) s(-)(1) respectively. No substitution of H(2)O by TPPTS(3)(-) or CO is observed over approximately 1h at either metal on [Mo(3)FeS(4)(H(2)O)(10)](4+), on [Mo(4)S(4)(H(2)O)(12)](5+) or [Mo(3)S(4)(H(2)O)(9)](4+).     

Remote substituent effects on allylic and benzylic bond dissociation energies. Effects on stabilization of parent molecules and radicals

The effect of remote substituents on bond dissociation energies (BDE) is examined by investigating allylic C-F and C-H BDE, as influenced by Y substituents in trans-YCH=CHCH2-F and trans-YCH=CHCH2-H. Theoretical calculations at the full G3 level model chemistry are reported. The interplay of stabilization energies of the parent molecules (MSE) and of the radicals formed by homolytic bond cleavage (RSE) and their effect on BDE are established. MSE values of allyl fluorides yield an excellent linear free energy relationship with the electron-donating or -withdrawing ability of Y and decrease by 4.2 kcal mol-1 from Y = (CH3)2N to O2N. RSE values do not follow a consistent pattern and are of the order of 1-2 kcal mol-1. A decrease of 4.1 kcal mol-1 is found in BDE[C-F] from Y = CH3O to NC. BDE[YCH=CHCH2-H] generally increases with decreasing electron-donating ability of Y for electron-donating groups and does not follow a consistent pattern with electron-withdrawing groups, the largest change being an increase of 3.6 kcal mol-1 from Y = (CH3)2N to CF3. The G3 results are an indicator of benzylic BDE in p-YC6H4CH2-F and p-YC6H4CH2-H, via the principle of vinylogy, demonstrated by correlating MSE of the allylic compounds with physical properties of their benzylic analogues.     

Selection of the cis and trans phosph(III)azane macrocycles [{P(mu-NtBu)}2(1-Y-2-NH-C6H4)]2(Y=O, S)

The 1 : 1 reactions of [ClP(mu-NtBu)]2 with the difunctional aromatic amines 1,2-1-YH-2-NH2-C6H4 in the presence of Et3N give the dimeric phosph(III)azane macrocycles [{P(mu-NtBu)2(1-Y-2-HN-C6H4)]2, predominantly as the cis isomer in the case of Y=O (1.cis) and as the trans isomer for Y=S (2.trans). Model M.O. calculations suggest that the selection of the cis and trans isomers is not thermodynamically controlled. The alternative isomers 1.trans and 2.cis are generated exclusively by the deprotonation of the model intermediates [(1-Y-2-NH2-C6H4)P(mu-NtBu)]2[Y=O (3), S (4)] with nBuLi followed by cyclisation with [ClP(mu-NtBu)]2. The solid-state structures of 1.cis/trans(50 : 50), 2.cis, 3 and 4 are reported.     

Unprecedented association of [Mo6Br(i) 7Y(i)Br(a) 6]3- cluster units and [Mo(III)Br6]3- complexes: synthesis, crystal structures, and properties of the double salts Rb3[Mo6Br(i) 7Y(i)Br(a) 6](Rb3[MoBr6])3 (Y=Se, Te)

The double salts Rb(3)[Mo(6)Br(i) (7)Y(i)Br(a) (6)](Rb(3)[MoBr(6)])(3) (Y=Se, Te) result from the partial disproportionation of the Mo(6)Br(12) octahedral-cluster-based bromide, in the presence of corresponding chalcogenides and RbBr salt (crystal data: Rb(12)[MoBr(6)](3)[Mo(6)Br(i) (7)Te(i)Br(a) (6)] (1), Pm$\bar 3$m (No. 221), a=12.1558(2) A, Z=1, R(1)=0.028; wR(2)=0.050; Rb(12)[MoBr(6)](3)[Mo(6)Br(i) (7)Se(i)Br(a) (6)] (2), Pm$\bar 3$m, a=12.144(3) A, Z=1, R(1)=0.028; wR(2)=0.050). The structures of 1 and 2 are built up from [Mo(III)Br(6)](3-) complexes and [Mo(6)Br(i) (7)Y(i)Br(a) (6)](3-) cluster units characterised by a random distribution of seven bromine and one chalcogen ligands on all the eight inner positions that face cap the Mo(6) clusters. Such a distribution implies a static orientational disorder of the [Mo(6)Br(i) (7)Y(i)Br(a) (6)](3-) units around the origin of the unit cell. Close-packed anionic layers based on [Mo(III)Br(6)](3-) complexes and [Mo(6)Br(i) (7)Y(i)Br(a) (6)](3-) cluster units are stacked in the sequence ABC. This arrangement leads to very short Br(a)--Br(a) intercluster unit distances of 3.252 A, much lower than the sum of the van der Waals radii (3.70 A). The trivalent oxidation state of molybdenum in the Mo complexes and 24 valence electrons per Mo(6) cluster have been confirmed by magnetic susceptibility measurements. Salts 1 and 2 constitute the first examples of structurally characterised bromides containing discrete [Mo(III)Br(6)](3-) complexes obtained by means of solid-state synthesis.