Observation of entropic effect on conformation changes of complex systems under well-controlled temperature conditions

We report direct observation of an entropic effect in determining the folding of a linear dicarboxylate dianion with a flexible aliphatic chain [(-)O(2)C-(CH(2))(6)-CO(2)(-)] by photoelectron spectroscopy as a function of temperature (18-300 K) and degree of solvation from 1 to 18 water molecules. A folding transition is observed to occur at 16 solvent water molecules at room temperature and at 14 solvent molecules below 120 K due to the entropic effect. The (-)O(2)C-(CH(2))(6)-CO(2)(-)(H(2)O)(14) hydrated cluster exhibits interesting temperature-dependent behaviors, and its ratio of folded over linear conformations can be precisely controlled as a function of temperature, yielding the enthalpy and entropy differences between the two conformations. A folding barrier is observed at very low temperatures, resulting in kinetic trapping of the linear conformation. The current work provides a simple model system to study the dynamics and entropic effect in complex systems and may be important for understanding the hydration and conformation changes of biological molecules.     

Cluster phase chemistry: collisions of vibrationally excited cationic dicarboxylic acid clusters with water molecules initiate dissociation of cluster components

A homologous series of cationic gas-phase clusters of dicarboxylic acids (oxalic acid, malonic acid, succinic acid, glutaric acid, and adipic acid) generated via electrospray ionization (ESI) are investigated using collision-induced dissociation (CID). Singly charged cationic clusters with the composition (Na(+))(2n+1)(dicarboxylate(2-))(n), where n = 1-5, are observed as major gas-phase species. Significant abundances of singly charged sodiated hydrogen dicarboxylate clusters with the composition (Na(+))(2n)(dicarboxylate(2-))(n)(H+), where n = 1-6, are observed with oxalic acid, malonic acid, and succinic acid. Isolation of the clusters followed by CID results mainly in sequential loss of disodium dicarboxylate moieties for the clusters of succinic acid, glutaric acid, and adipic acid. However, the dimer of sodiated hydrogen succinate, all malonate clusters, and all oxalate clusters, with the exception of the dimer, exhibit complex chemical reactions initiated by the collision of vibrationally excited clusters with water molecules. Generally, water molecules serve as proton donors for reacting dicarboxylate anions in the cluster, initiating dissociation pathways such as the decomposition of the malonate ion to yield an acetate ion and CO(2). The reactivity of several mixed dicarboxylate clusters is also reported. For example, malonate anion is shown to be more reactive than oxalate anion for decarboxylation when both are present in a cluster. The energetics of several representative cluster phase reactions are evaluated using computational modeling. The present results for cationic clusters are compared and contrasted to earlier studies of anionic sodiated dicarboxylic acid clusters.     

Copper and Bismuth Complexes Containing Dipyridyl gem-Diolato Ligands: Bi(III)(2)[(2-Py)(2)CO(OH)](2)(O(2)CCF(3))(4)(THF)(2), Cu(II)[(2-Py)(2)CO(OH)](2)(HO(2)CCH(3))(2), and Cu(II)(4)[(2-Py)(2)CO(OH)](2)(O(2)CCH(3))(6)(H(2)O)(2), a Ferromagnetically Coupled Tetranuclear Copper(II) Chain

The reactions of the singly deprotonated di-2-pyridylmethanediol ligand (dpmdH(-)) with copper(II) and bismuth(III) have been investigated. A new dinuclear bismuth(III) complex Bi(2)(dpmdH)(2)(O(2)CCF(3))(4)(THF)(2), 1, has been obtained by the reaction of BiPh(3) with di-2-pyridyl ketone in the presence of HO(2)CCF(3) in tetrahydrofuran (THF). The reaction of Cu(OCH(3))(2) with di-2-pyridyl ketone, H(2)O, and acetic acid in a 1:2:2:2 ratio yielded a mononuclear complex Cu[(2-Py)(2)CO(OH)](2)(HO(2)CCH(3))(2), 2, while the reaction of Cu(OAC)(2)(H(2)O) with di-2-pyridyl ketone and acetic acid in a 2:1:1 ratio yielded a tetranuclear complex Cu(4)[(2-Py)(2)CO(OH)](2)(O(2)CCH(3))(6)(H(2)O)(2), 3. The structures of these complexes were determined by single-crystal X-ray diffraction analyses. Three different bonding modes of the dpmdH(-) ligand were observed in compounds 1-3. In 2, the dpmdH(-) ligand functions as a tridentate chelate to the copper center and forms a hydrogen bond between the OH group and the noncoordinating HO(2)CCH(3) molecule. In 1 and 3, the dpmdH(-) ligand functions as a bridging ligand to two metal centers through the oxygen atom. The two pyridyl groups of the dpmdH(-) ligand are bound to one bismuth(III) center in 1, while in 3 they are bound two copper(II) centers, respectively. Compound 3 has an unusual one dimensional hydrogen bonded extended structure. The intramolecular magnetic interaction in 3 has been found to be dominated by ferromagnetism. Crystal data: 1, C(38)H(34)N(4)O(14)F(12)Bi(2), triclinic P&onemacr;, a = 11.764(3) ?, b = 11.949(3) ?, c = 9.737(1) ?, alpha =101.36(2) degrees, beta = 105.64(2) degrees, gamma = 63.79(2) degrees, Z = 1; 2, C(26)H(26)N(4)O(8)Cu/CH(2)Cl(2), monoclinic C2/c, a = 25.51(3) ?, b = 7.861(7) ?, c = 16.24(2) ?, beta = 113.08(9) degrees, Z = 4; 3, C(34)H(40)N(4)O(18)Cu(4)/CH(2)Cl(2), triclinic P&onemacr;, a = 10.494(2) ?, b = 13.885(2) ?, c = 7.900(4) ?, alpha =106.52(2) degrees, beta = 90.85(3) degrees, gamma = 94.12(1) degrees, Z = 1.     

Structure and Properties of [Fe(4)S(4){2,6-bis(acylamino)benzenethiolato-S}(4)](2)(-) and [Fe(2)S(2){2,6-bis(acylamino)benzenethiolato-S}(4)](2)(-): Protection of the Fe-S Bond by Double NH.S Hydrogen Bonds

Iron-sulfur clusters containing a singly or doubly NH.S hydrogen-bonded arenethiolate ligand, [Fe(4)S(4)(S-2-RCONHC(6)H(4))(4)](2)(-) (R = CH(3), t-Bu, CF(3)), [Fe(4)S(4){S-2,6-(RCONH)(2)C(6)H(3)}(4)](2)(-), [Fe(2)S(2)(S-2-RCONHC(6)H(4))(4)](2)(-) (R = CH(3), t-Bu, CF(3)), and [Fe(2)S(2){S-2,6-(RCONH)(2)C(6)H(3)}(4)](2)(-), were synthesized as models of bacterial [4Fe-4S] and plant-type [2Fe-2S] ferredoxins. The X-ray structures and IR spectra of (PPh(4))(2)[Fe(4)S(4){S-2,6-(CH(3)CONH)(2)C(6)H(3)}(4)].2CH(3)CN and (NEt(4))(2)[Fe(2)S(2){S-2,6-(t-BuCONH)(2)C(6)H(3)}(4)] indicate that the two amide NH groups at the o,o'-positions are directed to the thiolate sulfur atom and form double NH.S hydrogen bonds. The NH.S hydrogen bond contributes to the positive shift of the redox potential of not only (Fe(4)S(4))(+)/(Fe(4)S(4))(2+) but also (Fe(4)S(4))(2+)/(Fe(4)S(4))(3+) in the [4Fe-4S] clusters as well as (Fe(2)S(2))(2+)/(Fe(2)S(2))(3+) in the [2Fe-2S] clusters. The doubly NH.S hydrogen-bonded thiolate ligand effectively prevents the ligand exchange reaction by benzenethiol because the two amide NH groups stabilize the thiolate by protection from dissociation.     

Structural diversity of lithium sulfenamides: 7Li NMR studies in solution and crystal structures of [Li2(eta2-(CH3)3C-NS-C6H4CH(3)-4)2(THF)2] and [Li2(eta1-4-CH3C6H4-NS-C6H4CH(3)-4)2(THF)4

Two lithium sulfenamides were prepared by reaction of (CH(3))(3)C-N(H)-S-C(6)H(4)CH(3)-4 (1) and 4-CH(3)C(6)H(4)-N(H)-S-C(6)H(4)CH(3)-4 (2) with an alkyllithium. The unsolvated sulfenamide Li[(CH(3))(3)C-NS-C(6)H(4)CH(3)-4] (3) was soluble enough for variable-temperature (VT) (7)Li NMR to provide evidence of a dynamic exchange of oligomers in solution. The crystal structures of the solvated sulfenamides of [Li(2)(eta(2)-(CH(3))(3)C-NS-C(6)H(4)CH(3)-4)(2)(THF)(2)] (4) and of [Li(2)(eta(1)-4-CH(3)C(6)H(4)-NS-C(6)H(4)CH(3)-4)(2)(THF)(4)] (6) consisted of dimers in which the anions display different hapticities. The VT (7)Li NMR spectra of 4 suggest that the two different structures exist in equilibrium in toluene-THF mixtures. These compounds are easily oxidized to the neutral thioaminyl radicals as identified by EPR spectroscopy.     

Vibrational spectra of mono, di and trimethyl ammonium double sulphates of rare earths Pr, Nd, Ho and Eu

Infrared and Raman spectra of four rare earth (Ho, Eu, Nd and Pr) double sulphates have been recorded and analysed based on the vibrations of methyl ammonium cations, sulphate anions and water molecules. Formation of hydrogen bonds of the type N-H...O and O-H...O are identified in all the compounds. Bifurcated hydrogen bonds are present in the compounds with dimethyl ammonium cations. The sulphate anions are distorted and occupy a lower site symmetry in the compounds. The bands obtained for (CH(3))(2)NH(2) and SO(4)(2-) ions indicate that the structural bonding of (CH(3))(2)NH(2)Eu(SO(4))(2).H(2)O and (CH(3))(2)NH(2)Ho(SO(4))(2).4H(2)O is identical. Electronic transition bands of Eu(3+) and Nd(3+) observed in the Raman spectra of these two compounds have been identified and discussed.     

pi-Bonding versus oligomerisation in the aromatic anions [C(6)H(4)N(2)E](-): formation of the cyclic tetrameric tetraanion [C(6)H(4)N(2)Sb](4)(4-)

The reaction of 1,2-(NH(2))(2)C(6)H(4) with Sb(NMe(2))(3)/(n)BuLi gives the formally-aromatic heterocyclic anion [C(6)H(4)N(2)Sb](-) which oligomerises into a cyclic tetrameric arrangement in the complex [C(6)H(4)N(2)SbLi.PMDETA](4) () (PMDETA = {Me(2)NCH(2)CH(2)}(2)NMe) using a donor-acceptor bonding mode that is unique in related main group heterocyclic anions.     

Structures of [(CO2)n(H2O)m]- (n=1-4, m=1,2) cluster anions. I. Infrared photodissociation spectroscopy

The infrared photodissociation spectra of [(CO(2))(n)(H(2)O)(m)](-) (n=1-4, m=1, 2) are measured in the 3000-3800 cm(-1) range. The [(CO(2))(n)(H(2)O)(1)](-) spectra are characterized by a sharp band around 3570 cm(-1) except for n=1; [(CO(2))(1)(H(2)O)(1)](-) does not photodissociate in the spectral range studied. The [(CO(2))(n)(H(2)O)(2)](-) (n=1, 2) species have similar spectral features with a broadband at approximately 3340 cm(-1). A drastic change in the spectral features is observed for [(CO(2))(3)(H(2)O)(2)](-), where sharp bands appear at 3224, 3321, 3364, 3438, and 3572 cm(-1). Ab initio calculations are performed at the MP2/6-311++G(**) level to provide structural information such as optimized structures, stabilization energies, and vibrational frequencies of the [(CO(2))(n)(H(2)O)(m)](-) species. Comparison between the experimental and theoretical results reveals rather size- and composition-specific hydration manner in [(CO(2))(n)(H(2)O)(m)](-): (1) the incorporated H(2)O is bonded to either CO(2) (-) or C(2)O(4) (-) through two equivalent OH...O hydrogen bonds to form a ring structure in [(CO(2))(n)(H(2)O)(1)](-); (2) two H(2)O molecules are independently bound to the O atoms of CO(2) (-) in [(CO(2))(n)(H(2)O)(2)](-) (n=1, 2); (3) a cyclic structure composed of CO(2) (-) and two H(2)O molecules is formed in [(CO(2))(3)(H(2)O)(2)](-).     

Supramolecular gold(I) thiobarbiturate chemistry: combining aurophilicity and hydrogen bonding to make polymers,sheets, and networks

The cooperative forces of aurophilic and hydrogen bonding have been used in the self-assembly of phosphine or diphosphine complexes of gold(I) with the thiolate ligands derived from 2-thiobarbituric acid, SC(4)H(4)N(2)O(2), by single or double deprotonation. The reaction of the corresponding gold(I) trifluoroacetate complex with SC(4)H(4)N(2)O(2) gave the complexes [Au(SC(4)H(3)N(2)O(2))(PPh(3))], 1, [(AuSC(4)H(3)N(2)O(2))(2)(micro-LL)], with LL = Ph(2)PCH(2)PPh(2), 2a, Ph(2)P(CH(2))(3)PPh(2), 2b, or Ph(2)PCH=CHPPh(2), 2c, or the cyclic complex [Au(2)(micro-SC(4)H(2)N(2)O(2))(micro-Ph(2)PCH(2)CH(2)PPh(2))], 3. In the case with LL = Ph(2)P(CH(2))(6)PPh(2), the reaction led to loss of the diphosphine ligand to give [Au(6)(SC(4)H(3)N(2)O(2))(6)], 4, a hexagold(I) cluster complex in which each gold(I) center has trigonal AuS(2)N coordination. Structure determinations show that 1 has no aurophilic bonding, 2b, 3, and 4 have intramolecular aurophilic bonding, and 2c has intermolecular aurophilic bonding that contributes to the supramolecular structure. All the complexes undergo supramolecular association through strong NH...O and/or OH...N hydrogen bonding, and complex 3 also takes part in CH...O hydrogen bonding. The supramolecular association leads to formation of interesting polymer, sheet, or network structures, and 4 has a highly porous and stable lattice structure.     

Weakly coordinating anions HA2-generated from oxoanions A- and their conjugate acids. Coordination equilibria,ionic conductivities,and the structures of [Cu2(H(CH3SO3)2)4]n and [Cu(CO)(H(CF3CO2)2)]2

The coordination or ion pairing of the hydrogen-bonded anions H(CF3CO2)2- and H(CH3SO3)2- to NEt4+, Li+, Cu+, and/or Cu2+ was investigated. The structure of [Cu2(H(CH3SO3)2)4]n consists of centrosymmetric dimeric moieties that contain two homoconjugated (CH3SO2O-H...OSO2CH3)- anions per Cu2+ ion, forming typical Jahn-Teller tetragonally elongated CuO6 coordination spheres. The oxygen atoms involved in the nearly linear O-H...O hydrogen bonds (O...O approximately 2.62 A) are not coordinated to the Cu2+ ions. The structure of Cu2(CO)2(H(CF3-CO2)2)2 consists of pseudo-C2-symmetric dimers that contain one homoconjugated (CF3COO-H...OCOCF3)- anion per Cu+ ion, forming highly distorted tetrahedral Cu(CO)O3 coordination spheres. Three of the four oxygen atoms in each hydrogen-bonded H(CF3CO2)2- anion are coordinated to the Cu+ ions, including one of the oxygen atoms in each O-H...O hydrogen bond (O...O approximately 2.62 A). Infrared spectra (v(CO) values) of Cu(CO)(CF3CO2) or Cu(CO)(CH3SO3) dissolved in acetonitrile or benzene, with and without added CF3COOH or CH3SO3H, respectively, demonstrate that HA2- anions involving carboxylates or sulfonates are more weakly coordinating than the parent anions RCO2- and RSO3-. Direct current conductivities of THF solutions of Li(CF3CO2) containing varying concentrations of added CF3COOH further demonstrate that Li+ and NEt4+ ion pair much more weakly with H(CF3CO2)2- than with CF3CO2-.     

Infrared predissociation spectroscopy of M+ (C6H6)(1-4)(H2O)(1-2)Ar(0-1) cluster ions, M = Li, Na

Infrared predissociation (IRPD) spectra of Li(+)(C(6)H(6))(1-4)(H(2)O)(1-2)Ar(0-1) and Na(+)(C(6)H(6))(2-4)(H(2)O)(1-2)Ar(1) are presented along with ab initio calculations. The results indicate that the global minimum energy structure for Li(+)(C(6)H(6))(2)(H(2)O)(2) has each water forming a π-hydrogen bond with the same benzene molecule. This bonding motif is preserved in Li(+)(C(6)H(6))(3-4)(H(2)O)(2)Ar(0-1) with the additional benzene ligands binding to the available free OH groups. Argon tagging allows high-energy Li(+)(C(6)H(6))(2-4)(H(2)O)(2)Ar isomers containing water-water hydrogen bonds to be trapped and detected. The monohydrated, Li(+) containing clusters contain benzene-water interactions with varying strength as indicated by shifts in OH stretching frequencies. The IRPD spectra of M(+)(C(6)H(6))(1-4)(H(2)O)(1-2)Ar are very different for lithium-bearing versus sodium-bearing cluster ions emphasizing the important role of ion size in determining the most favorable balance of competing noncovalent interactions.     

Dehydration reaction of hydroxyl substituted alkenes and alkynes on the Ru(2)S(2) complex

A variety of inter- and intramolecular dehydration was found in the reactions of [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)(mu-S(2))](CF(3)SO(3))(4) (1) with hydroxyl substituted alkenes and alkynes. Treatment of 1 with allyl alcohol gave a C(3)S(2) five-membered ring complex, [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-SCH(2)CH(2)CH(OCH(2)CH=CH(2))S]](CF(3)SO(3))(4) (2), via C-S bond formation after C-H bond activation and intermolecular dehydration. On the other hand, intramolecular dehydration was observed in the reaction of 1 with 3-buten-1-ol giving a C(4)S(2) six-membered ring complex, [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2) [mu-SCH(2)CH=CHCH(2)S]](CF(3)SO(3))(4) (3). Complex 1 reacts with 2-propyn-1-ol or 2-butyn-1-ol to give homocoupling products, [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-SCR=CHCH(OCH(2)C triple bond CR)S]](CF(3)SO(3))(4) (4: R = H, 5: R = CH(3)), via intermolecular dehydration. In the reaction with 2-propyn-1-ol, the intermediate complex having a hydroxyl group, [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-SCH=CHCH(OH)S]](CF(3)SO(3))(4) (6), was isolated, which further reacted with 2-propyn-1-ol and 2-butyn-1-ol to give 4 and a cross-coupling product, [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-SCH=CHCH(OCH(2)C triple bond CCH(3))S]](CF(3)SO(3))(4) (7), respectively. The reaction of 1 with diols, (HO)CHRC triple bond CCHR(OH), gave furyl complexes, [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-SSC=CROCR=CH]](CF(3)SO(3))(3) (8: R = H, 9: R = CH(3)) via intramolecular elimination of a H(2)O molecule and a H(+). Even though (HO)(H(3)C)(2)CC triple bond CC(CH(3))(2)(OH) does not have any propargylic C-H bond, it also reacts with 1 to give [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-SCH(2)C(=CH(2))C(=C=C(CH(3))(2))]S](CF(3)SO(3))(4) (10). In addition, the reaction of 1 with (CH(3)O)(H(3)C)(2)CC triple bond CC(CH(3))(2)(OCH(3)) gives [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(2)][mu-S=C(C(CH(3))(2)OCH(3))C=CC(CH(3))CH(2)S][Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)]](CF(3)SO(3))(4) (11), in which one molecule of CH(3)OH is eliminated, and the S-S bond is cleaved.     

Isolation of (CO)1- and (CO2)1- radical complexes of rare earths via Ln(NR2)3/K reduction and [K2(18-crown-6)2]2+ oligomerization

Deep-blue solutions of Y(2+) formed from Y(NR(2))(3) (R = SiMe(3)) and excess potassium in the presence of 18-crown-6 at -45 °C under vacuum in diethyl ether react with CO at -78 °C to form colorless crystals of the (CO)(1-) radical complex, {[(R(2)N)(3)Y(μ-CO)(2)][K(2)(18-crown-6)(2)]}(n), 1. The polymeric structure contains trigonal bipyramidal [(R(2)N)(3)Y(μ-CO)(2)](2-) units with axial (CO)(1-) ligands linked by [K(2)(18-crown-6)(2)](2+) dications. Byproducts such as the ynediolate, [(R(2)N)(3)Y](2)(μ-OC≡CO){[K(18-crown-6)](2)(18-crown-6)}, 2, in which two (CO)(1-) anions are coupled to form (OC≡CO)(2-), and the insertion/rearrangement product, {(R(2)N)(2)Y[OC(═CH(2))Si(Me(2))NSiMe(3)]}[K(18-crown-6)], 3, are common in these reactions that give variable results depending on the specific reaction conditions. The CO reduction in the presence of THF forms a solvated variant of 2, the ynediolate [(R(2)N)(3)Y](2)(μ-OC≡CO)[K(18-crown-6)(THF)(2)](2), 2a. CO(2) reacts analogously with Y(2+) to form the (CO(2))(1-) radical complex, {[(R(2)N)(3)Y(μ-CO(2))(2)][K(2)(18-crown-6)(2)]}(n), 4, that has a structure similar to that of 1. Analogous (CO)(1-) and (OC≡CO)(2-) complexes of lutetium were isolated using Lu(NR(2))(3)/K/18-crown-6: {[(R(2)N)(3)Lu(μ-CO)(2)][K(2)(18-crown-6)(2)]}(n), 5, [(R(2)N)(3)Lu](2)(μ-OC≡CO){[K(18-crown-6)](2)(18-crown-6)}, 6, and [(R(2)N)(3)Lu](2)(μ-OC≡CO)[K(18-crown-6)(Et(2)O)(2)](2), 6a.     

Observation of cysteine thiolate and -S...H-O intermolecular hydrogen bond

The cysteine anion was produced in the gas phase by electrospray ionization and investigated by photoelectron spectroscopy at low temperature (70 K). The cysteine anion was found to exhibit the thiolate form [-SCH2CH(NH2)CO2H], rather than the expected carboxylate form [HSCH2CH(NH2)CO2-]. This observation was confirmed by two control experiments, that is, methyl cysteine [CH3SCH2CH(NH2)CO2-] and cysteine methyl ester [-SCH2CH(NH2)CO2CH3]. The electron binding energy of [-SCH2CH(NH2)CO2H] was measured to be about 0.7 eV blue-shifted relative to [-SCH2CH(NH2)CO2CH3] due to the formation of an intramolecular -S-...HO2C- hydrogen bond in the cysteine thiolate. Theoretical calculations at the CCSD(T)/6-311++G(2df,p) and B3LYP/6-311++G(2df,p) levels were carried out to estimate the strength of this intramolecular -S-...HO2C- hydrogen bond. Combining experimental measurements and theoretical calculations yielded an estimated value of 16.4 +/- 2.0 kcal/mol for the -S-...HO2C- intramolecular hydrogen-bond strength.     

Insignificance of P-H...P hydrogen bonding: structural chemistry of neutral and protonated 1,8-di(phosphinyl)naphthalene

While there is extensive information on 1,8-di(amino)naphthalene (i.e., the parent compound of the "proton sponge" series), the corresponding phosphorus compound has not been described. A high-yield synthesis of 1,8-di(phosphinyl)naphthalene (9) and the 1-naphthylphosphine reference compound (4) is now reported. Thermal decomposition of 9 leads to intramolecular dehydrogenative P-P coupling to afford 1,2-dihydro-1,2-diphosphaacenaphthene (10). Protonation of 9 and 4 with CF(3)SO(3)H gives quantitative yields of the monophosphonium salts 11 and 5, respectively. With excess acid and traces of moisture, the hydronium salt [C(10)H(6)(PH(2))(PH(3))](+)[H(3)O](+)2[CF(3)SO(3)](-) (13) is obtained. The structures of 9, 11, and 13 have been determined. Molecules of 9 have a planar naphthalene skeleton, C(10)H(6)P(2), with the two -PH(2) groups in a transoid conformation. The molecules form loose dimers in the crystal, the individual chiral enantiomers of which are related by a center of inversion. In contrast to the situation for the amino analogue, and despite the proximity of the two -PH(2) functions, there is no intra- or intermolecular hydrogen bonding. Solutions of 9 (in CD(2)Cl(2)) show equivalent P-bound hydrogen atoms due to conformational fluctionality. By analysis of the ABCD(2)XX'D'(2)C'B'A' spin system, it was shown that, in 9, there are strong through-space pericouplings [(n)J(P(X)P(X)(')) = 221.6 Hz, (n)J(P(X)H(D)(')) = 31.7 Hz, (n)J(H(D)H(D)(')) = 3.9 Hz]. In the cations of 11, the C(10)H(6)P(2) skeleton is also planar (by C(s) symmetry), with the -PH(2) and -PH(3)(+) groups in a conformation which rules out any P-H...P hydrogen bonding. The hydronium cation and the two triflate anions in 13 are associated into an anionic network through extensive hydrogen bonding surrounding stacks of the phosphonium cations. In solution, the cations of 11 and 13 show separate (31)P resonances for the two phosphorus atoms with fully resolved (1)J(PH) couplings, which indicate that there is no intra- or intercationic proton exchange. By contrast, the NMR spectra of solutions of [C(10)H(6)(NH(2))(NH(3))](+)X(-) salts show proton scrambling equilibrating all five N-bound hydrogen atoms, and in the crystal, the conformations of the cations feature intramolecular N-H...N hydrogen bonding.     

Dinuclear nickel complexes with a Ni(2)O(2) core: a structural and magnetic study

The acetylacetonate complexes [Ni(2)L(1)(acac)(MeOH)] x H(2)O, 1 x H(2)O and [Ni(2)L(3)(acac)(MeOH)] x 1.5H(2)O, 2 x 1.5H(2)O (H(3)L(1) = (2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine and H(3)L(3) = (2-(5-bromo-2-hydroxyphenyl)-1,3-bis[4-(5-bromo-2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) were prepared and fully characterised. Their crystal structures show that they are dinuclear complexes, extended into chains by hydrogen bond interactions. These compounds were used as starting materials for the isolation of the corresponding [Ni(2)HL(x)(o-O(2)CC(6)H(4)CO(2))(H(2)O)] x n MeOH and [Ni(2)HL(x)(O(2)CCH(2)CO(2))(H(2)O)]x nH(2)O dicarboxylate complexes (x = 1, 3; n = 1-3). The crystal structures of [Ni(2)HL(1)(o-O(2)CC(6)H(4)CO(2))(H(2)O)] x MeOH, 3 x MeOH, [Ni(2)HL(3)(o-O(2)CC(6)H(4)CO(2))(H(2)O)] x 3 MeOH, 4 x 3 MeOH and [Ni(2)HL(1)(O(2)CCH(2)CO(2))(H(2)O)] x 2.5H(2)O x 0.25 MeOH x MeCN, 5 x 2.5H(2)O x 0.25 MeOH x MeCN, were solved. Complexes 3-5 show dinuclear [Ni(2)HL(x)(dicarboxylate)(H(2)O)] units, expanded through hydrogen bonds that involve carboxylate and water ligands, as well as solvate molecules. The variable temperature magnetic susceptibilities of all the complexes show an intramolecular ferromagnetic coupling between the Ni(II) ions, which is attempted to be rationalized by comparison with previous results and in the light of molecular orbital treatment. Magnetisation measurements are in accord with a S = 2 ground state in all cases.     

Yttrium complexes incorporating the chelating diamides [ArN(CH2)xNAr]2- (Ar = C6H3-2,6-iPr2, x= 2, 3) and their unusual reaction with phenylsilane

Novel yttrium chelating diamide complexes [(Y[ArN(CH(2))(x)NAr](Z)(THF)(n))(y)] (Z = I, CH(SiMe(3))(2), CH(2)Ph, H, N(SiMe(3))(2), OC(6)H(3)-2,6-(t)Bu(2)-4-Me; x = 2, 3; n = 1 or 2; y = 1 or 2) were made via salt metathesis of the potassium diamides (x = 3 (3), x = 2 (4)) and yttrium triiodide in THF (5,10), followed by salt metathesis with the appropriate potassium salt (6-9, 11-13, 15) and further reaction with molecular hydrogen (14). 6 and 11(Z = CH(SiMe(3))(2), x = 2, 3) underwent unprecedented exchange of yttrium for silicon on reaction with phenylsilane to yield (Si[ArN(CH(2))(x)NAr]PhH) (x = 2 (16), 3) and (Si[CH(SiMe(3))(2)]PhH(2)).     

A series of octanuclear-nickel(II) complexes supported by thiacalix[4]arenes

A series of discrete complexes, [Ni(8)(BTC4A)(2)(μ(6)-CO(3))(2)(μ-CH(3)COO)(4)(dma)(4)]·H(2)O (1), [Ni(8)(BTC4A)(2)(μ(6)-CO(3))(2)(μ-Cl)(2)(μ-HCOO)(2)(dma)(4)]·2DMF·2CH(3)CN (2), [Ni(8)(PTC4A)(2) (μ(6)-CO(3))(2)(μ-CH(3)COO)(4)(dma)(4)]·DMF (3), and [Ni(8)(PTC4A)(2)(μ(6)-CO(3))(2)(μ-OH)(μ-HCOO)(3) (dma)(4)] (4) (p-tert-butylthiacalix[4]arene = H(4)BTC4A, p-phenylthiacalix[4]arene = H(4)PTC4A, dma = dimethylamine, and DMF = N,N'-dimethylformamide), have been prepared under solvothermal conditions and structurally characterized by single-crystal X-ray diffraction analyses, powder XRD, and IR spectroscopy. These four complexes are stacked by dumbbell-like building blocks with one chairlike octanuclear-nickel(II) core, which is capped by two thiacalix[4]arene molecules and connected by two in situ generated carbonato anions and different auxiliary anions. This work implied that not only the solvent molecules but also the upper-rim groups of thiacalix[4]arenes have significant effects on the self-assembly of the dumbbell-like building blocks. The magnetic properties of complexes 1-4 were examined, indicating strong antiferromagnetic interactions between the nickel(II) ions in the temperature range of 50-300 K.     

Synthesis, structure, and magnetochemical analysis of selected first-row transition-metal anilino- and anisolesquarate compounds

The isomorphous polymeric complexes [M(mu-C(6)H(5)NHC(4)O(3))(2)(CH(3)OH)(2)](n) [M = Mn (1), Co (2), Cu (4), Zn (5)] are produced by reacting the anilinosquarate anion with the appropriate metal nitrates in a methanolic solution. Each of these complexes contains the central metal atom in a slightly distorted octahedral environment, with the coordination polyhedron consisting of four mu-1,2-bridging anilinosquarate ligands and two trans-oriented methanols. The polymer chains propagate to form a two-dimensional net of metal centers, with the conformation of the component sheets in the net being controlled by intramolecular N-H...O and O-H...O hydrogen bonds. Under reaction conditions similar to those used in the synthesis of the polymers 1, 2, 4, and 5, the nickel(II) monomer [Ni(C(6)H(5)NHC(4)O(3))(2)(H(2)O)(4)].2H(2)O (3) is produced in which each nickel center is attached to two cis-coordinated anilinosquarate and four aqua ligands in a distorted octahedral arrangement. The ligand conformation in 3 is stabilized by both intra- and intermolecular hydrogen bonding, which results in the formation of a sheet polymer having distinct hydrophobic and hydrophilic surfaces. Magnetochemical analysis of 1 and 4 reveals normal paramagnetic behavior for 1 and a very weak ferromagnetic interaction in 4; the absence of significant magnetic interactions is attributed to the distortion of the C(4) cycle of the anilinosquarate ligand (lower than C(2)(v) symmetry) in these complexes. Reaction of anisolesquarate with M(NO(3))(2).xH(2)O in acetonitrile produced the set of isomorphous salts [M(H(2)O)(6)][CH(3)OC(6)H(5)C(4)O(3)](2) [M = Mn (6), Co (7), Ni (8), Zn (9)]. The anisolesquarate anions in 6-9 are hydrogen bonded to the [M(H(2)O)(6)](2+) ions to form polymer chains, which are further linked by hydrogen bonds to form complex sheets. Complexation of the anisolesquarate ligand was not observed even when other solvents and reaction conditions were employed.     

Strongly blue-shifted C-H stretches: interaction of formaldehyde with hydrogen fluoride clusters

The equilibrium structures, binding energies, and vibrational spectra of the cyclic, hydrogen-bonded complexes formed between formaldehyde, H(2)CO, and hydrogen fluoride clusters, (HF)(1< or =n < or =4), are investigated by means of large-scale second-order M?ller-Plesset calculations with extended basis sets. All studied complexes exhibit marked blue shifts of the C-H stretching frequencies, exceeding 100 cm(-1) for n = 2-4. It is shown that these blue shifts are, however, only to a minor part caused by blue-shifting hydrogen bonding via C-H...F contacts. The major part arises due to the structural relaxation of the H(2)CO molecule under the formation of a strong C=O...H-F hydrogen bond which strengthens as n increases. The close correlation between the different structural parameters in the studied series of complexes is demonstrated, and the consequences for the frequency shifts in the complexes are pointed out, corroborating thus the suggestion of the primary role of the C=O...H-F hydrogen bonding for the C-H stretching frequency shifts. This particular behavior, that the appearance of an increasingly stronger blue shift of the C-H stretching frequencies is mainly induced by the formation of a progressively stronger C=O...H-F hydrogen bond in the series of H(2)CO...(HF)(1< or =n < or =4), complexes and only to a lesser degree by the formation of the so-called blue-shifting C-H...F hydrogen bond, is rationalized with the aid of selected sections of the intramolecular H(2)CO potential energy surface and by performing a variety of structural optimizations of the H(2)CO molecule embedded in external, differently oriented dipole electric fields, and also by invoking a simple analytical force-field model.