Preparation and characterization of some Cr(III) chloro-complexes with nicotinic acid esters

The preparation and characterisation of the trichlorotris(alkylnicotinate)chromium(III) complexes of general formula CrCl₃(py·3COOR)₃·nH₂O, where R = Me, Et, Pr and Bu are reported, n being 3.5, 1.0, 0 and 0 respectively. It is concluded that the ligation of the three chloride ions and that of the three nitrogen atoms is consistent with a C_2u arrangement in each case.     

Structural differences among phosphatidylcholine, phosphatidylethanolamine, and mixed phosphatidylcholine/phosphatidylethanolamine multilayers: an infrared absorption study

We have examined the infrared absorption spectra from 4000 to 250 cm^?1 of multilayers of phosphatidylcholine, phosphatidylethanolamine, and phosphatidylcholine/phosphatidylethanolamine (1:1 m/m) as a function of hydration, pH, and fatty acid composition. Characteristic splittings of the CH₂ bending and rocking modes and the position of the phosphoryl absorption at ca. 1240 cm^?1 reveal differences in acyl chain packing and head group conformation in the various films. Spectra demonstrate the importance of NH → O hydrogen bonding of the ethanolamine head group and the prerequisite head group conformation (tangent to the multilayer plane) in establishing these structural differences. The general appearance of the P-O-C stretching region (~1050 cm^?1) in the pure and mixed films further supports these conclusions and shows that the spectra clearly distinguish among the different head group orientations. Self-association of phosphatidylethanolamine is sometimes sufficient to prevent formation of mixed phases with phosphatidylcholine at neutral pH. The amount of fine structure, particularly in the low-frequency (800?200 cm^?1) region, in spectra of films of anhydrous, saturated-chain phospholipids decreases considerably when the films are monohydrated, when mixed phases exist, or when there are unsaturations in the acyl chains. These changes likely result from decreased crystal field effects in the spectra as the phosphatide packing density is decreased by any of the above procedures. Furthermore, the absence of other changes upon complete hydration of phosphatidylcholine films suggests that only the initial water is tightly bound to the lipid.     

Interaction of hexacyanoferrate(III) with some copper(II) complexes

The interaction between hexacyanoferrate(III) and some copper complexes of different geometry was studied. In solution, and in the presence of coordination unsaturation of copper, 1:1 and 2:1 Cu:Fe adducts formed and were characterized by the absence of any copper electron paramagnetic resonance (EPR) signal. The magnetic susceptibility of the 1:1 adducts is essentially equal to the sum of those due to the parent compounds. Solid state studies confirm the solution data. In the light of the present results the absence of the EPR signal of [Fe(CN)₆]^3?-treated galactose oxidase is discussed.     

Structural features of group V A xanthates. The crystal and molecular structures of tris(O-isopropylxanthatoarsenic(III), antimony(III) and -bismuth(II)

The crystal structures of the title compounds, M(S₂COⁱC₃H₇)₃, M = As(III), (1); Sb(III), (2); and Bi(III), (3) have been determined by three dimensional X-ray diffraction techniques and refined by a least square method. Crystals of (1) and (2) are isomorphous and both crystallize in the rhombohedral space group R$\text{3}$, with unit cell parameters for (1) a_hex = 11.559(2), c_hex = 28.131(3) Å and for (2) a_hex = 11.696(2) and c_hex = 28.135(2) Å, Z = 6. The central metal atom in both (1) and (2) is coordinated by three asymmetrically chelating xanthate ligands [AsS 2.305(2) and 2.978(2) Å and SbS 2.508(1) and 3.006(1) Å] which form a distorted octahedral environment consistent with the presence of a stereochemically active lone pair of electrons. Crystals of (3) are orthorhombic, space group Pnma, Z = 4 with dimensions a = 11.003(3), b = 20.833(4) and c = 9.428(2) Å. The environment of the bismuth atom in (3) is seven coordinate and is comprised of six sulphur atoms, derived from three asymmetrically coordinating xanthate ligands, and a bridging sulphur atom from a neighbouring molecule which results in the formation a polymeric array. For (1) final R and R_W 0.050 and 0.047 respectively for 936 reflections [I ? 3σ(I); (2) R 0.040, R_w 0.040 for 1455 reflections I ? 2σ(I)]; and (3) R 0.052, R_w 0.039 for 1796 reflections [I ? 2σ(I).     

119Sn Mössbauer spectroscopic studies of the products of the reaction of triorganotin(IV) derivatives with 6-thiopurine

A structural study of the products of the reaction of R₃Sn^IV derivatives (R = Me, Buⁿ, Ph) with 6-thiopurine, 6-TPH₂, and its sodium salt, 6-TPHNa, has been undertaken using Mössbauer spectroscopy and the point-charge model rationalization of the Mössbauer parameter nuclear quadrupole splitting. The synthetic reactions have been carried out at ca. 0 °C, 20 °C and 50 °C. The Mössbauer spectra of the complexes AlK₃Sn(6-TPH) are consistent with the occurrence of two distinct tin(IV) sites in samples prepared at the lower temperature, while one only site appears by increasing the temperature of the reaction. Two tin sites constantly occur in the products of the reactions involving the Ph₃Sn^IV moiety; the stoichiometry is assumed to be (Ph₃Sn)₃(6-TPH)(6-TP) for the uniquely-formed complex. Solid state polymeric structures with trigonal bipyramidal environments of the tin atoms and planar SnC₃ skeletons have been proposed. The apical ligand atoms have been assumed to be N, S and N, N in the samples showing two individual tin(IV) sites, and N, N when a single site was present.     

Studies on the reaction of fluorescamine with primary amines

Fluorescamine is a useful reagent for the fluorometric assay of primary amines. The extent of the reaction between fluorescamine and primary amines, as well as the fluorescence intensities of the resulting fluorophors depend on pH, solvent composition and reagent concentration. Optimum values for these variables further depend on the amine under study. The influence of these parameters on the fluorogenic reaction of representative amines, and on their fluorophoric derivatives has been investigated, and the results are reported here.     

In-plane ligand effects on oxygenation of cobalt(II) schiff base complexes

A series of cobalt(II) complexes of Schiff base with some peripheral substituents was employed for the measurements of redox potentials of the cobalt(II) complexes and stability constants for those pyridine and oxygen adducts. The electron-withdrawing substituents favor the reduction of a cobalt(II) ion, but make its oxidation difficult. While a Hammett reaction constants for log Kpy is positive, that for log KO₂ is negative, indicating that pyridine nucleophilically attacks the cobalt(II) ion, but molecular oxygen attacks the ion electrophilically.     

Proton nuclear magnetic resonance study of N,N-diethylformamide exchange on (N,N-diethylformamide)2,2′2″-tris(dimethylamino)triethylamine)cobalt(II) and its copper(II) analogue

Proton NMR studies of N,N-diethylformamide (def) exchange on [M(Me₆tren)def]²⁺ where M = Co and Cu yield: k_ex (298.2K) = 26.3 ± 2.2, 980 ± 70 s⁻¹; ΔH^≠ = 58.3 ± 1.7, 36.3 ± 0.9 kJ mol⁻¹; ΔS^≠= −22.2 ± 4.6, −65.9 ± 2.5 J K⁻¹ mol⁻¹; and ΔV^≠ = −1.3 ± 0.2, 5.3 ± 0.3 cm³ mol⁻¹ respectively. These data which are consistent with a and d activation modes operating when M = Co and Cu respectively are compared with data for related systems.     

Preparation and crystal structure of manganese(II) isothiocyanate tetrahydrate

Crystals of Mn(NCS)₂·4H₂O were isolated from an aqueous solution obtained by mixing solutions of barium thiocyanate and manganese(II) sulphate tetrahydrate. The crystals are monoclinic with a = 7.827(7), b = 9.208(1), c = 7.456(5) Å, β = 112.57(5)°, space group P2₁/c. The structure consists of discrete centrosymmetric trans-[Mn(NCS)₂(H₂O)₄] octahedra linked by hydrogen bonds.     

Dioxouranium(VI) thiocyanate complexes of schiff bases of p-nitro,chloro, bromo,hydroxy and methoxy aniline and salicylaldehyde

A series of dioxouranium(VI) complexes was synthesised with some Schiff base ligands containing substituent groups at para positions to CHN groups. These molecules were obtained by the condensation of para-nitro, chloro, bromo, hydroxy, methyl and methoxy aniline with salicylaldehyde. The bidentate ligands formed complexes of the type UO₂(NCS)₂ (X-N-Sal)_n·mH₂O, where n = 2, m = 3, x = NO₂, Cl, Br and OH; n = 3, m = 2, x = CH₃ and OCH₃.Conductivity measurements indicate that all the complexes are non-electrolytes in nitromethane solution, whereas in DMF they correspond to 1:1 electrolytes.IR spectral data suggest that the molecules and not the anions of the Schiff base are coordinated to the central uranium atom. IR and Raman spectra suggest that the complexes UO₂(NCS)₂(X-N-Sal)₂· 3H₂O (X = NO₂, Cl, Br) have C_2h molecular symmetry, whereas UO₂(NCS)₂(X-N-Sal)₃·2H₂O (X = OCH₃, CH₃) have C_2v symmetry.The frequencies of UO_2(asym) (IR) and UO_2(sym) (R) in the complexes seem to vary with the various substituents of the Schiff base ligand, in the order:NO₂ > Cl > Br > OH > CH₃ > OCH₃     

Synthesis of α,ω-bis(diphenylphosphino)alkane and α,ω-bis(diphenylphosphino)(poly)ether ligands and complexes of rhodium(I)

α,ω-Bis(diphenylphosphino)alkane and α,ω-bis(diphenylphosphino)(poly)ether ligands can be prepared in very high yields via reaction of the appropriate dihalide with two equivalents of LiPPh₂. For the [Rh(COD)($\text{P P}$)][ClO₄] complexes of these ligands, the $\text{P P}$ ligands with five or less atoms in the alkane or ether bridge form monomeric complexes via η²-coordination. In general the ligands with eight or more atoms in the bridge give di- or polynuclear species. In addition the long chain diphosphino-polyethers form – to a small extent – monomeric species by η²-coordination.     

New methods for the preparation of biospecific adsorbents and immobilized enzymes utilizing trichloro-s-triazine

Methods for preparing biospecific adsorbents and immobilized enzymes utilizing Sepharose CL as a support and trichloro-s-triazine as the linking agent are described. The difficulties encountered during conventional aqueous and mixed aqueous-phase reactions of trichloro-s-triazine with insoluble polyols, particularly reagent hydrolysis, are avoided by performing the activation reactions in anhydrous organic phase and replacing the second chlorine on the triazine ring by an aromatic amine. Ligands can be coupled to the activated support in either aqueous or organic phase. The methods have been applied to the attachment of a number of different enzymes, proteins, and small-molecule ligands to Sepharose. The superiority of the triazine linkage to the cyanogen bromide linkage is demonstrated.     

Preparation and characterization of (9-methyladenine)triammineplatinum(II) and trans-dihydroxo(9-methyladenine)triammineplatinum(IV) complexes

The preparation is reported of [(NH₃)₃Pt(9- MeA)] X₂ (9-MeA = 9-methyladenine) with XCl (1a) and XClO₄ (1b) and of trans-[(OH)₂Pt(NH₃)₃- (9-MeA)]X₂ with XCl (2a) and XClO₄ (2b), and the crystal structure of 1b. [(NH₃)₃Pt(C₆H₇N₅)](ClO₄)₂ crystallizes in space group P2₁/n with a = 20.810(7) Å, b = 7.697(3) Å, c = 10.567(4) Å, β = 91.57(6)°, Z = 4. The structure was refined to R = 0.054, R_w = 0.063. In all four compounds Pt coordination is through N7 of 9-MeA, as is evident from ³J coupling between H8 of the adenine ring and ¹⁹⁵Pt. Pt(II) and Pt(IV) complexes can be differentiated on the basis of different ³J values, larger for Pt(II) than for Pt(IV) by a factor of 1.57 (av). In Me₂SO-d₆, hydrogen bonding occurs between Cl^? and C(8)H of 9-MeA as weil as between Cl^? and the NH₃ groups in the case of the Pt(II) complex 1a. Protonation of the 9-MeA ligands was followed using ¹H NMR spectroscopy and pK_a values for the N1 protonated 9-MeA ligands were determined in D₂O. They are 1.9 for 1a and 1.8 for 2a, which compares with 4.5 for the non-platinated 9-MeA. Possible consequences for hydrogen bonding with the complementary bases thymine or uracil are discussed briefly. Protonation of the OH groups in the Pt(IV) complexes has been shown not to occur above pH 1.     

Coatline A and B,two C-glucosyl-α-hydroxydihydrochalcones from Eysenhardtia polystachya

The first two examples of naturally occurring C-glucosyl-α-hydroxydihydrochalcones have been isolated from Eysenhardtia polystachya, a Mexica     

Photochemical reactions of bis(bistrimethylsilylamido)tin(II) with; Hexacarbonylmolybdenum and tungsten

Irradiation of M(CO)₆ (M = Mo. W) and Sn[N(SiMe₃)₂]₂ in hexane with UV light results in carbonyl substitution to form both M(CO)₅Sn[N(SiMe₃)₂]₂ and M(CO)₄Sn[N(SiMe₃)₂]₂)₂ complexes. The M(CO)₄L₂ species present the first examples in which both cis and trans isomers have been observed upon substitution of bulky divalent main group IV ligands. The highly air-sensitive W(CO)₅L and W(CO)₄L₂ complexes have been isolated.     

Uranyl(VI), copper(II) and nickel(II) complexes derived from a new compartmental ligand

A new heptadentate compartmental ligand has been synthesized by condensation of 3-formylsalicylic acid and 1,5-diamino-3-thiapentane in methanol (H₄L_a). This Schiff base contains an inner N₂SO₂ and an outer O₂O₂ site and gives, by reaction with copper(II), nickel(II) and uranyl(VI) diacetate, mononuclear, homo- and heterobinuclear complexes. In the mononuclear copper and nickel complexes, the metal ion is in the inner N₂SO₂ site, while it is in the outer O₂O₂ for uranyl; a solvent molecule fills the fifth equatorial coordination position in this last complex. The physico-chemical properties of the compounds are discusscd on the basis of infrared, electronic and magnetic data and by comparison with the analogous complexes with the ligand obtained by reaction of 3- formylsalicylic acid and diethylenetriamine (H₄L_b). The mononuclear copper and the heterodinuclear copper-uranyl complexes show anomalously low magnetic moments.