Counter-current chromatographic estimation of hydrophobicity of Z-(cis) and E-(trans) enalapril and kinetics of cis/trans isomerization

The kinetics of Z-(cis)/E-(trans) isomerization of enalapril was investigated by reversed phase high-performance liquid chromatography (RP-HPLC) using a monolith ODS column under a series of different temperature and pH conditions. At a neutral pH 7, the rate (k(obs)) of Z-(cis)/E-(trans) isomerization of enalapril at 4 degrees C (9.4 x 10(-3)min(-1)) is much lower than at 23 degrees C (1.8 x 10(-1)min(-1)), while the fractional concentration of Z-(cis) isomer is always higher than that of E-(trans) isomer in the pH range 2-7. The fractional concentration of the E-(trans) isomer becomes a maximum (about 40%) in the pH range 3-6, where enalapril exists as a zwitterion. The hydrophobicity (logP(O/W)) of both isomers was estimated by high-speed counter-current chromatography (HSCCC). Normal phase HSCCC separation using a tert-butyl methyl ether-acetonitrile-20mM potassium phosphate buffer (pH 5) two-phase solvent system (2:2:3, v/v/v) at 4 degrees C was effective in partially separating the isomers, and the partition coefficient (K) of each isomer was directly calculated from the retention volume (V(R)). The logP(O/W) values of Z-(cis) and E-(trans) isomers were -0.46 and -0.65, respectively.     

Structural Changes and Phase Transitions in Whitlockite-Like Phosphates

New compounds with a g -Ca 3 (PO 4 ) 2 structure type were found in three systems: Sr 9+ x M 1.5 m x (PO 4 ) 7 ( M = Mn, Fe, Co, Ni, Cu, and Cd; space group R 3 m ; Z = 3), Sr 9 R (PO 4 ) 7 ( R = Al, Sc, Cr, Fe, Ga, In, and Gd-Lu; space group P 2/ c , Z = 4), and Sr 9+2 x M 1+ x A 1 m 6 x (PO 4 ) 7 ( M = Mn, Ni, Cd; space group R 3 c and Z = 6 for A = Na, K; space group P 2/ m and Z = 4 for A = Li). Crystal structures of these compounds were determined by time-of-flight neutron, synchrotron X-ray, and laboratory X-ray powder diffraction. Reversible polar-to-centrosymmetric phase transitions ( R 3 c {\begin{array}{c}\\[-14pt]\hspace*{.5pt}\to\\[-7pt]\hspace*{-.5pt}\gets \end{array}} R 3 m ) were observed at high temperatures in Ca 3 m x Sr x (PO 4 ) 2 (0 h x h 12/7), Ca 10.5 m 1.5 x Fe x (PO 4 ) 7 (0 h x h 1), and Ca 9 R (PO 4 ) 7 . Solid solutions Ca 3 m x Sr x (PO 4 ) 2 (13/7 h x h 16/7) are centosymmetric with space group R 3 m at room temperature. These phase transitions were studied by high-temperature X-ray diffraction, second-harmonic generation, DSC, electric-conductivity and dielectric measurements.     

Stacking design of inverse perovskites: the systems (Sr3-xBaxN)E, E = Bi, Sb

The first representatives of 4H (BaMnO3-type structure, P63/mmc, Z = 4) and 9R (BaMnO3-type structure, Rm, Z = 9) inverse Perovskite phases are presented. The phases are obtained within the solid solutions (Sr3-xBaxN)E with E = Bi, Sb. The crystal structures and homogeneity ranges were studied by combined X-ray and neutron diffraction as well as chemical analyses. The cubic Perovskite phase with Bi (Sb) is stable in the range of 0.00 < or = x < or = 0.90(5) (0.00 < or = x < or = 1.30(5)), the 4H variant is stable for 1.55(5) < or = x < or = 2.10(5) (1.85(5) < or = x < or = 2.45(5)), the 9R structure is stable for 2.50(2) < or = x < or = 2.55(2) (2.56(2) < or = x < or = 2.60(2)), and the 2H phase is stable for 2.75(5) < or = x < or = 3.00 (2.80(5) < or = x < or = 3.00). Ba occupies preferable sites in the hexagonal stacking of close packed layers of alkaline earth metal ions and E3-; Sr is mainly located in cubic stacked layers. The phase order upon going from cubic (Sr3N)E to 2H-type (Ba3N)E concomitant to the pronounced Sr/Ba partial order can, in general, be rationalized considering the Coulomb repulsion of nitride ions, as well as the size and charge density of the alkaline earth metal ions.     

Hydrocarbon-Soluble Mercuracarborands: Syntheses, Halide Complexes, and Supramolecular Chemistry

The syntheses of macrocyclic species composed of carborane derivatives joined via their carbon vertices by electrophilic mercury atoms are described. The reaction of closo-1,2-Li(2)[C(2)B(10)H(10)(-)(x)()R(x)()] with HgI(2) gives Li(2)[(1,2-C(2)B(10)H(10)(-)(x)()R(x)()Hg)(4)I(2)] [R = Et, x = 2 (5.I(2)Li(2)); R = Me, x = 2 (6.I(2)Li(2)); R = Me, x = 4 (7.I(2)Li(2))]. 6.I(2)(K.[18]dibenzocrown-6)(2) crystallizes in the monoclinic space group C2/m [a = 28.99(2) ?, b = 18.19(1) ?, c = 13.61(1) ?, beta = 113.74(2) degrees, V = 6568 ?(3), Z = 4, R = 0.060, R(w) = 0.070]; 7.I(2)(NBu(4))(2) crystallizes in the monoclinic space group P2(1)/c [a = 12.77(1) ?, b = 21.12(2) ?, c = 20.96(2) ?, beta = 97.87(2) degrees, V = 5600 ?(3), Z = 2, R = 0.072, R(w) = 0.082]. The precursor to 7, closo-8,9,10,12-Me(4)-1,2-C(2)B(10)H(8) (4), is made in a single step by reaction of closo-1,2-C(2)B(10)H(12) with MeI in trifluoromethanesulfonic acid. The free hosts 5, 6, and 7 are obtained by reaction of the iodide complexes with stoichiometric quantities of AgOAc. A (199)Hg NMR study indicates that sequential removal of iodide from 5.I(2)Li(2) and 6.I(2)Li(2) with aliquots of AgOAc solution leads to formation of two intermediate host-guest complexes in solution, presumed to be 5(6)ILi and 5(2)(6)(2).ILi. Crystals grown from a solution of 6.I(2)Li(2) to which 1 equiv of AgOAc solution had been added proved to be an unusual stack structure with the formula 6(3).I(4)Li(4) [tetragonal, I4/m, a = 21.589(2) ?, c = 21.666(2) ?, V = 10098 ?(3), Z = 2, R = 0.058, R(w) = 0.084]. Addition of 2 equiv of NBu(4)Br ion to 5 or 6 gives 5.Br(2)(NBu(4))(2) and 6.Br(2)(NBu(4))(2), respectively, while addition of 1 equiv of KBr to 6 forms 6.BrK. 5.Br(2)(NBu(4))(2) crystallizes in the triclinic space group P&onemacr;, [a = 10.433(1) ?, b = 13.013(1) ?, c = 15.867(2) ?, alpha = 91.638(2) degrees, beta = 97.186(3) degrees, gamma = 114.202(2) degrees, V = 1492 ?(3), Z = 1, R = 0.078, R(w) = 0.104]. The hosts 5 and 6 form 1:1 supramolecular adducts with the polyhedral anions B(10)I(10)(2)(-) and B(12)I(12)(2)(-) in solution.     

Syntheses, structures, and reactivities of heteroleptic magnesium amide thiolates

The syntheses and characterizations of a family of novel heteroleptic magnesium amide thiolates are presented. The compounds are synthesized by ligand redistribution chemistry involving reactions of equimolar amounts of magnesium amides and magnesium thiolates. Utilization of the smaller thiolates [Mg(SPh)2]n and [Mg(S-2,4,6-iPr3C6H2)2]n results in the isolation of dimeric species, [Mg(THF)(N(SiMe3)2)(mu-SR)]2 (R = Ph (1), 2,4,6-iPr3C6H2 (2)), with four-coordinate metal centers and bridging thiolate functions. The sterically more encumbered thiolate S-2,4,6-tBu3C6H2 induces the formation of the four-coordinate, monomeric species Mg(THF)2(N(SiMe3)2)(S-2,4,6-tBu3C6H2) (3)). Careful choice of reaction conditions allows the successful syntheses of pure heteroleptic compounds; however, it remains difficult to obtain the compounds in high yields, since a tendency toward product symmetrization and ligand redistribution under re-formation of the starting materials is prevalent. One of these symmetrized products is also included in this report: the dimeric, four-coordinate magnesium thiolate [Mg-(THF)(S-2,4,6-tBu3C6H2)(mu-S-2,4,6-tBu3C6H2)]2 (4), isolated as the product of the reaction between [Mg-(N(SiMe3)2)2]2 and Mg(THF)2(S-2,4,6-tBu3C6H2)2. All compounds were characterized by NMR and IR spectroscopy, elemental analyses, and X-ray crystallography. Crystal data obtained with Mo K alpha (lambda = 0.710 73 A) radiation are as follows. 1: C16H31MgNOSSi2, a = 11.2100(1) A, b = 17.4512(3) A, c = 11.2999(2) A, beta = 97.952(1) degrees, V = 2189.32(6) A3, Z = 4, monoclinic, space group P2(1)/n, R1 (all data) = 0.0934. 2: C25H49MgNOSSi2, a = 11.1691(1) A, b = 11.0578(1) A, c = 26.0671(4) A, beta = 99.906(1) degrees, V = 3171.44(6) A3, Z = 4, monoclinic, space group P2(1)/c, R1 (all data) = 0.0557. 3: C36H71MgNO3SSi2, a = 42.8293(16) A, b = 10.9737(5) A, c = 16.8305(7) A, beta = 98.755(3) degrees, V = 7818.1(6) A3, Z = 8, monoclinic, space group C2/c, R1 (all data) = 0.1331. 4: C80H132Mg2O2S4, a = 18.8806(2) A, b = 19.3850(2) A, c = 27.3012(4) A, beta = 97.250(1) degrees, V = 9912.4(2) A3, Z = 4, monoclinic, space group P2(1)/n, R1 (all data) = 0.1023.     

Stabilizing Heterobimetallic Complexes Containing Unsupported Ti-M Bonds (M = Fe, Ru, Co): The Nature of Ti-M Donor-Acceptor Bonds

The stabilization of unsupported Ti-M (M = Fe, Ru, Co) heterodinuclear complexes has been achieved by use of amidotitanium building blocks containing tripodal amido ligands. Salt metathesis of H(3)CC(CH(2)NSiMe(3))(3)TiX (1) and C(6)H(5)C(CH(2)NSiMe(3))(3)TiX (2) as well as HC{SiMe(2)N(4-CH(3)C(6)H(4))}(3)TiX (3) (X = Cl, a; Br, b) with K[M(CO)(2)Cp] (M = Fe, Ru) and Na[Co(CO)(3)(PR(3))] (R = Ph, Tol) gave the corresponding stable heterobimetallic complexes of which H(3)CC(CH(2)NSiMe(3))(3)Ti-M(CO)(2)Cp (M = Fe, 6; Ru, 7) and HC{SiMe(2)N(4-CH(3)C(6)H(4))}(3)Ti-M(CO)(2)Cp (M = Fe, 12; Ru, 13) have been characterized by X-ray crystallography. 6: monoclinic, P2(1)/n, a = 15.496(3) ?, b = 12.983(3) ?, c = 29.219(3) ?, beta = 104.52(2) degrees, Z = 8, V = 5690.71 ?(3), R = 0.070. 7: monoclinic, P2(1)/c, a = 12.977(3) ?, b = 12.084(3) ?, c = 18.217(3) ?, beta = 91.33(2) degrees, Z = 4, V = 2855.91 ?(3), R = 0.048. 12: monoclinic, I2/c, a = 24.660(4) ?, b = 15.452(3) ?, c = 20.631(4) ?, beta = 103.64(3) degrees, Z = 8, V = 7639.65 ?(3), R = 0.079. 13: monoclinic, I2/c, a = 24.473(3) ?, b = 15.417(3) ?, c = 20.783(4) ?, beta = 104.20(2) degrees, Z = 8, V = 7601.84 ?(3), R = 0.066. (1)H- and (13)C-NMR studies in solution indicate free internal rotation of the molecular fragments around the Ti-M bonds. Fenske-Hall calculations performed on the idealized system HC(CH(2)NH)(3)Ti-Fe(CO)(2)Cp (6x) have revealed a significant degree of pi-donor-acceptor interaction between the two metal fragments reinforcing the Ti-Fe sigma-bond. Due to the availability of energetically low-lying pi-acceptor orbitals at the Ti center this partial multiple bonding is more pronounced that in the tin analogue HC(CH(2)NH)(3)Sn-Fe(CO)(2)Cp (15x) in which an N-Sn sigma-orbital may act as pi-acceptor orbital.     

Structure-transport correlation for the diffusive tortuosity of bulk, monodisperse, random sphere packings

The mass transport properties of bulk random sphere packings depend primarily on the bed (external) porosity ε, but also on the packing microstructure. We investigate the influence of the packing microstructure on the diffusive tortuosity τ=D(m)/D(eff), which relates the bulk diffusion coefficient (D(m)) to the effective (asymptotic) diffusion coefficient in a porous medium (D(eff)), by numerical simulations of diffusion in a set of computer-generated, monodisperse, hard-sphere packings. Variation of packing generation algorithm and protocol yielded four Jodrey-Tory and two Monte Carlo packing types with systematically varied degrees of microstructural heterogeneity in the range between the random-close and the random-loose packing limit (ε=0.366-0.46). The distinctive tortuosity-porosity scaling of the packing types is influenced by the extent to which the structural environment of individual pores varies in a packing, and to quantify this influence we propose a measure based on Delaunay tessellation. We demonstrate that the ratio of the minimum to the maximum void face area of a Delaunay tetrahedron around a pore between four adjacent spheres, (A(min)/A(max))(D), is a measure for the structural heterogeneity in the direct environment of this pore, and that the standard deviation σ of the (A(min)/A(max))(D)-distribution considering all pores in a packing mimics the tortuosity-porosity scaling of the generated packing types. Thus, σ(A(min)/A(max))(D) provides a structure-transport correlation for diffusion in bulk, monodisperse, random sphere packings.     

Crystal structures of N,N'-(m-tolyl)thiourea and N,N'-(p-tolyl)thiourea.

C15H16N2S is monoclinic [orthorhombic], P2(1)/c [Pbcn]. Unit-cell dimensions at 293 K are a = 9.506(1), b = 7.629(1), c = 20.077(1)A, beta = 99.93(1) degrees, V= 1434.2(2)A(3), D(x) = 1.187 g/cm3, and Z = 4 [a = 11.806(2), b = 13.954(2), c = 8.466(1)A, V = 1394.7(3)A(3), D(x) = 1.221 g/cm3, and Z = 8]. The R value is 0.049 [0.045] for 1620 [1229] observed reflections. The dihedral angle between the tolyl rings is 53.6(1) degrees [47.9(1)degrees]. The crystal structures are stabilized by N-H...S hydrogen bonds and van der Waals forces.     

Isolation of the new cubic phases RE4FeGa(12-x)Ge(x) (RE = Sm,Tb; x = 2.5) from molten gallium: single-crystal neutron diffraction study of the Ga/Ge distribution

The compounds RE4FeGa(12-x)Ge(x) (RE = Sm, Tb) were discovered in reactions employing molten Ga as a solvent at 850 degrees C. However, the isostructural Y4FeGa(12-x)Ge(x) was prepared from a direct combination reaction. The crystal structure is cubic with space group Imm, Z = 2, and a = 8.657(4) A and 8.5620(9) A for the Sm and Tb analogues, respectively. Structure refinement based on full-matrix least squares on F(o)2 resulted in R1 = 1.47% and wR2 = 4.13% [I > 2(I)] for RE = Sm and R1 = 2.29% and wR2 = 7.12% [I > 2(I)] for RE = Tb. The compounds crystallize in the U4Re7Si6 structure type, where the RE atoms are located on 8c (1/4, 1/4, 1/4) sites and the Fe atoms on 2a (0, 0, 0) sites. The distribution of Ga and Ge in the structure, investigated with single-crystal neutron diffraction on the Tb analogue, revealed that these atoms are disordered over the 12d (1/4, 0, 1/2) and 12e (x, 0, 0) sites. The amount of Ga/Ge occupying the 12d and 12e sites refined to 89(4)/11 and 70(4)/30%, respectively. Transport property measurements indicate that these compounds are metallic conductors. Magnetic susceptibility measurements and M?ssbauer spectroscopy performed on the Tb analogue show a nonmagnetic state for Fe, while the Tb atoms carry a magnetic moment corresponding to a mu(eff) of 9.25 mu(B).     

Alkoxo Bound Monooxo- and Dioxovanadium(V) Complexes: Synthesis, Characterization, X-ray Crystal Structures, and Solution Reactivity Studies

A large variety of oxovanadium(V) complexes, mononuclear VO(2)(+) and VO(3+) in addition to the dinuclear VO(3+), of the structural type (VOL)(2), (VOHL)(2), VOLHQ, K(VO(2)HL), K(VO(2)H(2)L), or (salampr) (VO(2)L) {where L = Schiff base ligand possessing alkoxo group(s); HQ = 8-hydroxyquinoline; salampr = cation of reduced Schiff base derived from salicylaldehyde and 2-amino-2-methylpropan-1-ol}, bound to alkoxo, phenolate and imine groups have been synthesized in high yields and characterized by several spectral and analytical methods, including single crystal X-ray studies. While the mononuclear VO(2)(+) complexes have been synthesized at alkaline pH, the dinuclear VO(3+) complexes have been synthesized under neutral conditions using alkoxo rich Schiff base ligands. The X-ray structures indicate that the cis-dioxo complexes showed longer V-O(alkoxo) bond lengths compared to the monooxo counterparts. The plot of V-O(phen) bond distances of several VO(3+) complexes vs the lmct showed a near linear correlation with a negative slope. The cyclic voltammograms revealed a reversible V(V)/V(IV) couple with the reduction potentials increasing to more negative ones as the number of alkoxo groups bound to V increases from 1 to 2. Moreover, the cis-dioxo VO(2)(+) complexes are easier to reduce than their monooxo counterparts. The solution stability of these complexes was studied in the presence of added water (1:4, water:solvent), where no decomposition was observed, unlike other Schiff base complexes of V. The conversion of the dioxo complexes to their monooxo counterparts in the presence of catalytic amounts of acid is also demonstrated. The reactivity of alkoxo bound V(V) complexes is also reported. X-ray parameters are as follows. H(4)L(3): monoclinic space group, P2(1)/c; a = 10.480(3), b = 8.719(6), c = 12.954(8) ?; beta = 101.67(4) degrees; V = 1126(1) ?(3); Z = 4; R = 0.060, R(w) = 0.058. Complex 1: monoclinic space group, P2(1)/n; a = 12.988(1), b = 9.306(2), c = 19.730(3) ?; beta = 99.94(1) degrees; V = 2348.9(7) ?(3); Z = 4; R = 0.031, R(w) = 0.027. Complex 2: monoclinic space group, P2(1)/n; a = 12.282(3), b = 11.664(2), c = 12.971(4) ?; beta = 97.89(2) degrees; V = 1840.5(8) ?; Z = 4; R = 0.035, R(w) = 0.038. Complex 5: monoclinic space group, P2(1)/c; a = 17.274(2), b = 6.384(2), c = 16.122(2) ?; beta = 116.67(1) degrees; V = 1588.7(7) ?(3); Z = 4; R = 0.039, R(w) = 0.043. Complex 8: monoclinic space group, P2(1)/c; a = 11.991(1), b = 11.696(4), c = 12.564(3) ?; beta = 110.47(1) degrees; V = 1650.8(8) ?(3); Z = 2; R = 0.045, R(w) = 0.049.     

Modification of Wiener Index and its application

A novel topological index based on the Wiener Index is proposed as W* = 1/2 sigma (n)(i,j=1) S(*)(ij), the element S(*)(ij) of the distance matrix is defined either as S(*)(ij) = alpha x square root of I(i)I(j)/R(ij) (atoms i and j are adjacent) or as S(*)(ij) = = alpha x (j-i+1)square root of I(i) x x x x x I(j)/R(ij) (atoms i and j are not adjacent), where I(i) and I(j) represent the electronegativity of vertices i or j, respectively, R(ij)() is the sum of the bond length between the vertices i and j in a molecular graph, and alpha = (Z(i)/Z(j))(0.5), where Z(i) and Z(j) are the atomic numbers of the positive valence atom i and the negative valence atom j, respectively. The properties and the interaction of the vertices in a molecule are taken into account in this definition. That is why the application of the index W to heteroatom-containing and multiple bond organic systems and inorganic systems is possible. Correlation coefficients above 0.97 are achieved in the prediction of the retention index of gas chromatography of the hydrocarbons, the standard formation enthalpy of methyl halides, halogen-silicon, and inorganic compounds containing transition metals.     

Reaction of mercury(II) and xylenol orange-I Effect of the buffering media

The influence of the buffering medium on the reaction of Hg(II) with Xylenol Orange has been studied. Amine-type compounds are complexed by Hg(II)/Xylenol Orange with a sharp hyperchromic effect on the reagent itself, at 590 nm, but complex formation of Hg(II)/Xylenol Orange in non-amine-type buffer, such as citric acid-phosphate, gives a hypochromic effect on Xylenol Orange at 580 nm. Hg(II) is determined at pH 7.5 in two ranges of concentration, 2-9 ppm in citrate buffer, measured at 580 nm ( = 2.50 x 10(4)), and 6-11 ppm in hexamine buffer, at 590 nm ( = 4.18 x 10(4)).     

Acid-base equilibria and dynamics in sodium dodecyl sulfate micelles: geminate recombination and effect of charge stabilization

The synthetic flavylium salt 4-carboxy-7-hydroxy-4'-methoxyflavylium chloride (CHMF) exhibits two acid-base equilibria in the range of pH 1-8 in both aqueous and micellar sodium dodecyl sulfate (SDS) solutions. The values of pK(a1) and pK(a2) for the cation-zwitterion (AH(2)(+) <--> Z + H(+)) and the zwitterion-base (Z <--> A(-) + H(+)) equilibria increase from 0.73 and 4.84 in water to 2.77 and 5.64 in SDS micelles, respectively. The kinetic study of the Z <--> A(-) + H(+) ground-state reactions in SDS points to the diffusion-controlled protonation of A(-) in the aqueous phase (k(p2w) = 4.2 x 10(10) M(-)(1) s(-)(1)) and in the micelle (k(p2m) = 2.3 x 10(11) M(-)(1) s(-)(1)). The deprotonation rate of Z did not significantly change upon going from water (k(d2) = 6.3 x 10(5) s(-)(1)) to SDS (k(d2) = 5.2 x 10(5) s(-)(1)), in contrast with the behavior of ordinary cationic flavylium salts, for which k(d2) strongly decreases in SDS micelles. These results suggest that deprotonation of the zwitterionic acid is not substantially perturbed by the micellar charge. Electronic excitation of the Z form of CHMF induces fast adiabatic deprotonation of the hydroxyl group of Z() (2.9 x 10(10) s(-)(1) in water and 8.4 x 10(9) s(-)(1) in 0.1 M SDS), followed by geminate recombination on the picosecond time scale. Interestingly, while recombination in water (k(rec) = 1.7 x 10(9) s(-)(1)) occurs preferentially at the carboxylate group, at the SDS micelle surface, recombination (k(rec) = 9.2 x 10(9) s(-)(1)) occurs at the hydroxyl group. The important conclusion is that proton mobility at the SDS micelle surface is substantially reduced with respect to the mobility in water, which implies that geminate recombination should be a general phenomenon in SDS micelles.     

Synthesis and resolution of (R,R)-(+/-)-1,1,4,7,10,10-hexaphenyl-1,10-diarsa-4,7-diphosphadecane: new ligand for the stereoselective self-assembly of dicopper(I), disilver(I), and digold(I) helicates

Diphenylvinylarsine oxide reacts with 1,2-bis(phenylphosphino)ethane in the presence of potassium tert-butoxide to give the anti-Markovnikov product (R,R)-(+/-)/(R,S)-1,1,4,7,10,10-hexaphenyl-1,10-diarsa-4,7-diphosphadecane dioxide-1AsO,10AsO, which, upon reduction with HSiCl(3)/NEt(3) in boiling acetonitrile, affords in 84% overall yield the di(tertiary arsine)-di(tertiary phosphine) (R,R)-(+/-)/(R,S)-diphars. After separation of the diastereomers by fractional crystallization, the (R,R)-(+/-) form of the ligand was resolved by metal complexation with (+)-di(mu-chloro)bis[(R)-1-[1-(dimethylamino)ethyl]-2-phenyl-C(2),N]dipalladium(II): (R,R)-diphars, mp 87-88 degrees C, has [alpha](D)(21) = -18.6 (c 1.0, CH(2)Cl(2)); (S,S)-diphars has [alpha](D)(21) = +18.4 (c 1.0, CH(2)Cl(2)). The crystal and molecular structures of the complexes (M)-[M(2)[(R,R)-diphars](2)](PF(6))(2) (M = Cu, Ag, Au) have been determined: [M-(S(Cu),S(Cu))]-(-)-[Cu(2)[(R,R)-diphars](2)](PF(6))(2), orthorhombic, P2(1)2(1)2(1) (No. 19), a = 16.084(3) A, b = 18.376(3) A, c = 29.149(6) A, Z = 4; [M-(S(Ag),S(Ag))]-(+)-[Ag(2)[(R,R)-diphars](2)](PF(6))(2), triclinic, P1, a = 12.487(2) A, b = 12.695(4) A, c = 27.243(4) A, alpha = 92.06 degrees, beta = 95.19 degrees, gamma = 98.23 degrees, Z = 2; [M-(S(Au),S(Au))]-(-)-[Au(2)[(R,R)-diphars](2)](PF(6))(2), orthorhombic, P2(1)2(1)2(1) (No. 19), a = 16.199(4) A, b = 18.373(4) A, c = 29.347(2) A, Z = 4. In the copper(I) and gold(I) helicates, each ligand strand completes 1.5 turns of an M helix in a parallel arrangement about the two chiral MAs(2)P(2) stereocenters of S configuration. The unit cell of the silver(I) complex contains one molecule each of the parallel helicate of M configuration and the conformationally related double alpha-helix of M configuration in which each ligand strand completes 0.5 turns of an M helix about two metal stereocenters of S configuration. Energy minimization calculations of the three structures with use of the program SPARTAN 5.0 gave results that were in close agreement with the core structures observed.     

Modeling of the adsorption breakthrough behaviors of Pb2+ in a fixed bed of ETS-10 adsorbent

On the basis of experimental breakthrough curves of lead ion adsorption on ETS-10 particles in a fixed-bed column, we simulated the breakthrough curves using the two-phase homogeneous diffusion model (TPHDM). Three important model parameters, namely the external mass-transfer coefficient (k(f)), effective intercrystal diffusivity (D(e)), and axial dispersion coefficient (D(L)), were optimally found to be 8.33x10(-5) m/s, 2.57x10(-10) m(2)/s, and 1.93x10(-10) m(2)/s, respectively. A good agreement was observed between the numerical simulation and the experimental results. Sensitivity analysis revealed that the value of D(e) dictates the model performance while the magnitude of k(f) primarily affects the initial breakthrough point of the breakthrough curves.     

Tetracyanoborate salts M[b(CN)4] with M = singly charged cations: properties and structures

A series of tetracyanoborate salts M[B(CN)4] with the singly charged cations of Li+, Na+, Rb+, Cs+, [NH4]+, Tl+, and Cu+ as well as the THF solvate tetracyanoborates Na[B(CN)4] x THF and [NH4][B(CN)4] x THF were synthesized and their X-ray structures, vibrational spectra, solubilities in water, and thermal stabilities determined and compared with already known M[B(CN)4] salts. Crystallographic data for these compounds are as follows: Na[B(CN)4], cubic, Fd3m, a = 11.680(1) A, Z= 8; Li[B(CN)4], cubic, P43m, a = 5.4815(1) A, Z= 1; Cu[B(CN)4], cubic, P43m, a = 5.4314(7) A, Z= 1; Rb[B(CN)4], tetragonal, /4(1)/a, a = 7.1354(2) A, c= 14.8197(6) A, Z= 4; Cs[B(CN)4], tetragonal, /4(1)/a, a = 7.300(2) A, c = 15.340(5) A, Z= 4; [NH4][B(CN)4], tetragonal, /4(1)/a, a = 7.132(1) A, c = 14.745(4) A, Z= 4; Tl[B(CN)4], tetragonal, /4(1)/a, a = 7.0655(2) A, c = 14.6791(4) A, Z= 4; Na[B(CN)4] x THF, orthorhombic, Pnma, a = 13.908(3) A, b = 9.288(1) A, c = 8.738(1) A, Z= 4; [NH4][B(CN)4] x THF, orthorhombic, Pnma, a = 8.831(1) A, b = 9.366(2) A, c = 15.061(3) A, Z= 4. The cubic Li+, Na+, and Cu+ salts crystallize in a structure consisting of two interpenetrating independent tetrahedral networks of M cations and [B(CN)4]- ions. The compounds with the larger countercations (Rb+, Cs+, Tl+, and [NH4]+) crystallize as tetragonal, also with a network arrangement. The sodium and ammonium salts with the cocrystallized THF molecules are both orthorhombic but are not isostructural. In the vibrational spectra the two CN stretching modes A1 and T2 coincide in general and the band positions are a measure for the strength of the interionic interaction. An interesting feature in the Raman spectrum of the copper salt is the first appearance of two CN stretching modes.     

Synthesis and characterization of 8-(dimethylamino)-1-naphthyl derivatives of aluminum, gallium, and indium

The group 13 dichlorides of formula Ar'MCl2 [Ar' = 8-(dimethylamino)-1-naphthyl (8-(Me2N)C10H6)], M = Al (1), Ga (2), and In (3), have been prepared via the salt elimination reaction of 1 equiv of Ar'Li with MCl3 in toluene solution at -78 degrees C. The reaction of 1 with LiAlH4 in diethyl ether solution at -78 degrees C produced the dihydride [Ar'AlH2]2 (4). The X-ray crystal structures of 1-4 have been determined and show that 1 and 2 are monomeric while 3 and 4 are dimeric in the solid state. The reaction of 1 with RLi in toluene solution at -78 degrees C results in ligand redistribution and formation of Ar'2AlR (R = Me (5), t-Bu (6)). The chloride analogue of 5 and 6, Ar'2AlCl (7), can be prepared directly from the reaction of 2 equiv of Ar'Li with AlCl3 in toluene solution at -78 degrees C. The homoleptic derivative Ar'3Al (8) was obtained when 3 equiv of Ar'Li was employed. Crystal data for 1: monoclinic, space group P2(1), a = 6.534(1) A, b = 10.801(1) A, c = 9.631(2) A, beta = 105.57(2) degrees, V = 654.8(2) A3, Z = 2, R = 0.0453. Crystal data for 2: monoclinic, space group P2(1), a = 6.552(2) A, b = 10.833(2) A, c = 9.601(2) A, beta = 106.05(2) degrees, V = 654.9(3) A3, Z = 2, R = 0.0609. Crystal data for 3: monoclinic, space group P2(1)/c, a = 7.401(2) A, b = 15.746 A, c = 10.801(4) A, beta = 92.37(3) degrees, V = 1257.6(7) A3, Z = 2, R = 0.0712. Crystal data for 4: monoclinic, space group P2(1)/c, a = 13.343(2) A, b = 11.228(2) A, c = 7.505(1) A, beta = 100.64(1) degrees, V = 1105.0(4) A3, Z = 4, R = 0.0560.     

Novel ground- and excited-state prototropic reactivity of a hydroxycarboxyflavylium salt

Synthetic and natural hydroxyflavylium salts are super-photoacids, exhibiting values of the rate constant for proton transfer to water in the excited state as high as 1.5 x 10(11) s(-1). The synthetic flavylium salt 4-carboxy-7-hydroxy-4'-methoxyflavylium chloride (CHMF) has an additional carboxyl group at the 4-position of the flavylium cation that deprotonates in the ground state at a lower pH (pK(a1) = 0.73; AH2+ --> Z) than the 7-hydroxy group (pK(a2) = 4.84; Z --> A-). Ground-state deprotonation of the carboxyl group of the acid (AH2+) to form the zwitterion (Z) is too fast to be detected by nanosecond laser flash perturbation of the ground-state equilibrium, while deprotonation of the hydroxyl group of Z to form the anionic base (A-) occurs in the microsecond time range (k(d2) = 0.6 x 10(6) s(-1) and k(p2) = 4.2 x 10(10) M(-1) x s(-1)). In the excited state, the cationic form (AH2+) deprotonates in approximately 9 ps, resulting in the excited neutral base form (AH), which is unstable in the ground state. Deprotonation of Z occurs in 30 ps (k(d2) = 2.9 x 10(10) s(-1)), to form excited A-, which either reprotonates (k(p3)* = 3.7 x 10(10) M(-1) x s(-1)) or decays in 149 ps, and shows an important contribution from geminate recombination to give the excited neutral base (AH). Predominant reprotonation of A- at the carboxylate group reflects both the presence of the negative charge on the carboxylate and the increase in the excited-state pK(a) of the carboxyl group. Thus, while the hydroxyl pK(a) decreases by approximately 5 units upon going from the ground state (pK(a) = 4.84) to the excited state (pK(a) = -0.2), that of the carboxyl group increases by at least this much. Consequently, the excited state of the Z form of CHMF acts as a molecular proton transporter in the picosecond time range.     

First structurally characterized silver(I) derivatives with nonfluorinated beta-diketones

Synthetic, spectroscopic, and single-crystal X-ray structural studies of diverse complexes of silver(I) acylpyrazolonate salts AgQ(R') (QH = 1-phenyl-3-methyl-4-R'(C=O)-pyrazol-5-one; Q(1), R = Ph; Q(2), R' = CF(3); Q(3), R' = Me) with neutral ligands L = unidentate PR(3) (R = Ph, o-tolyl, cyclohexyl) and Hmimt (1-methyl-2-mercaptoimidazole) and bidentate dppe (Ph(2)P(CH(2))(2)PPh(2)) and trimen (N,N,N'-trimethylethylenediamine) define the donor capability of the anionic Q(R') ligand in a variety of roles. In the free ligand Q(3)H (which crystallizes in the monoclinic space group C2/c (no. 15), Z = 8, unit cell parameters a = 17.981(6) A, b = 5.0641(4) A, c = 24.271(6) A, and beta = 99.67(2)), the acidic OH group hydrogen-bonds intramolecularly to the adjacent pyrazolone oxygen, i.e., the two oxygen atoms are cis, true of the other Q(R') species structurally characterized here in their anionic complexed forms, in which they chelate the silver in the usual beta-diketonate manner, but not of the free anion, found in the array [Ag(Ph(3)P)(Hmimt)(2)](Q(1)) (triclinic space group P(-)1(no. 2), Z = 2, unit cell parameters a = 11.553(1) A, b = 11.943(1) A, c = 15.479(2) A, alpha = 74.829(2), beta = 76.094(2), and gamma = 78.185(2)), or [Ag(trimen)Q(1)] (monoclinic space group P2(1)/c (no. 14), Z = 4, unit cell parameters a = 7.982(1) A, b = 12.299(2) A, c = 21.507(3) A, and beta = 95.119(3)), which forms an infinite one-dimensional polymer string, Q(1) linking successive silver(I) atoms by coordination by way of the unsubstituted nitrogen and the pyrazolonate oxygen. In all [Ag(R(3)P)(2)(chelate-Q(1))] (R = Ph, Cy) complexes, P(2)Ag(O,O') arrays are found (R = Ph, monoclinic space group C2/c (no. 15), Z = 8, unit cell parameters a = 16.193(8) A, b = 13.859(7) A, c = 39.306(7) A, and beta = 100.02(3); R = Cy, triclinic space group P(-)1(no. 2), Z = 2, unit cell parameters a = 10.4655(9) A, b = 12.079(1) A, c = 22.804(2) A, alpha = 104.872(2), beta = 95.180(2), and gamma = 104.144(2)), also true of [Ag(Ph(3)P)(2)(O,O'-Q(2))] (triclinic space group P(-)1(no. 2), Z = 2, unit cell parameters a = 10.672(2) A, b = 10.710(2) A, c = 18.713(3) A, alpha = 87.573(2), beta = 80.972(2), and gamma = 81.734(2)), whereas [Ag(o-tol(3)P)Q(1)] (monoclinic space group P2(1)/c (no. 14), Z = 2 dimers, unit cell parameters a = 11.8221(6) A, b = 13.2601(6) A, c = 20.5141(10) A, and beta = 91.758(1)) exists as a dinuclear species containing two AgO(2)NP units where the acylpyrazolonate is coordinated in a bridging O,O'-Q-Nfashion. Silver atoms are four-coordinate in all except the Hmimt complex.     

Thermodynamic, kinetic and pH studies on the reactions of NCS-, N3-, and CH3CO2- with Fusarium galactose oxidase

Thermodynamic and kinetic studies on the X- = NCS-, N3-, and CH3CO2- replacement of H2O/OH- at the CuII exogenous site of the tyrosyl-radical-containing enzyme galactose oxidase (GOaseox) from Fusarium (NRR 2903), have been studied by methods involving UV-vis spectrophotometry (25 degrees C), pH range 5.5-8.7, I = 0.100 M (NaCl). In the case of N3- and CH3CO2- previous X-ray structures have confirmed coordination at the exogenous H2O/OH- site. From the effect of pH on the UV-vis spectrum of GOaseox under buffer-free conditions, acid dissociation constants of 5.7 (pK1a; coordinated H2O) and 7.0 (pK2a; H+Tyr-495) have been determined. At pH 7.0 formation constants K(25 degrees C)/M-1 are NCS- (480), N3- (1.98 x 10(4)), and CH3CO2- (104), and from the variations in K with pH the same two pKa values are seen to apply. No pK1a is observed when X- is coordinated. From equilibration stopped-flow studies rate constants at pH 7.0 for the formation reaction kf(25 degrees C)/M-1 s-1 are NCS- (1.13 x 10(4)) and N3- (5.2 x 10(5)). Both K and kf decrease with increasing pH, consistent with the electrostatic effect of replacing H2O by OH-. In the case of the GOaseox Tyr495Phe variant pK1a is again 5.7, but no pK2a is observed, confirming the latter as acid dissociation of protonated Tyr-495. At pH 7.0, K for the reaction of four-coordinate GOaseox Tyr495Phe with NCS- (1.02 x 10(5) M-1) is more favorable than the value for GOaseox. Effects of H+Tyr-495 deprotonation on K are smaller than those for the H2O/OH- change. The pK1a for GOasesemi is very similar (5.6) to that for GOaseox (both at CuII), but pK2a is 8.0. At pH 7.0 values of K for GOasesemi are NCS- (270 M-1), N3- (4.9 x 10(3)), and CH3CO2- (107).