Conformational difference in the solid state and in solution of methyl 2,3,4-trideoxy-2,4-di-C-methyl-6-O-trityl-α-d-lyxo-hexopyranoside

The conformational difference of the title compound (1) in the solid state and in solution has been investigated by X-ray crystallography and high-field proton n.m.r. spectrometry. In the solid state, compound 1 adopts the ⁴C₁(d) conformation (1a), whereas 1 exists preferentially in the ¹C₄(d) conformation (1b) in chloroform solution.     

Conformational studies on aldonolactones by n.m.r. spectroscopy. Conformations of d-glucono-1,5-lactone and d-mannono-1,5-lactone in solution

The conformations of d-glucono-1,5-lactone (1) and d-mannono-1,5-lactone (2) in solution were investigated by ¹H- and ¹³C-n.m.r. spectroscopy. Conformational equilibria for 1 and 2 were found to lie strongly in favor of the ⁴H₃(d),gg and B_2,5(d),gg conformations, respectively.     

Reaktionen der glucuronsäure : 7. Mitt. Oxidationen an d-glucofuranosidurono-6,3-lactonen

Methyl α-D- (1) and methyl β-D-glucofuranosidurono-6,3-lactone (5) were oxidized at C-2 or C-5, 1,2-O-isopropylidene-α-D- (10) and 1,2-O-cyclohexylidene-α-D-glucofuranurono-6,3-lactone (11) at C-5 by various methods to the corresponding D-arabino- or D-xylo-hexulofuranosiduronolactones. In contrast to the starting materials 5, 10, and 11, the 5-uloses 15, 17, and 18 do not exhibit reducing power in alkaline Cu²⁺ solutions. Methyl 5-O-benzyl-α-D- and methyl 5-O-benzyl-β-D-arabino-2-hexulofuranosidurono-6,3-lactone reduce Benedict solution at room temperature.     

The synthesis of 5-O-(2-acetamido-2-deoxy-α-D-glucopyranosyl)-β-D-glucofuranose

Condensation of dimeric 3,4,6-tri-O-acetyl-2-deoxy-2-nitroso-α-D-glucopyranosyl chloride (1) with 1,2-O-isopropylidene-α-D-glucofuranurono-6,3-lactone (2) gave 1,2-O-isopropylidene-5-O-(3,4,6-tri-O-acetyl-2-deoxy-2-hydroxyimino-α-D-arabino-hexopyranosyl)-α-D-glucofuranurono-6,3-lactone (3). Benzoylation of the hydroxyimino group with benzoyl cyanide in acetonitrile gave 1,2-O-isopropylidene-5-O-(3,4,6-tri-O-acetyl-2-benzoyloxyimino-2-deoxy-α-D-arabino-hexopyranosyl)-α-D-glucofuranurono-6,3-lactone (4). Compound 4 was reduced with borane in tetrahydrofuran, yielding 5-O-(2-amino-2-deoxy-α-D-glucopyranosyl)-1,2-O-isopropylidene-α-D-glucofuranose (5), which was isolated as the crystalline N-acetyl derivative (6). After removal of the isopropylidene acetal, the pure, crystalline title compound (10) was obtained.     

Synthesis, characterization, crystal structures and photophysical properties of copper(I) complexes containing 1,1′-bis(diphenylphosphino)ferrocene (B-dppf) in doubly-bridged mode

Five copper(I) complexes having general formula [Cu₂(μ-X)₂(κ²-P,P-B-dppf)₂] (X = Cl(1), Br(2), I(3), CN(4), and SCN(5)) were prepared starting with CuX and B-dppf in 1:1 molar ratio in DCM-MeOH (50:50 V/V) at room temperature. The complexes have been characterized by elemental analyses, IR, ¹H NMR, ³¹P NMR and electronic spectral studies. Molecular structures for 1, 2 and 4 were determined crystallographically. Complexes 1, 2 and 4 exist as centrosymmetric dimers in which the two copper atoms are bonded to two bridging B-dppf ligands and two bridging (pseudo-)halide groups in a μ-η¹ bonding mode to generate nearly planar Cu₂(μ-η¹-X)₂ framework. Both bridging B-dppf ligands are arranged in antiperiplanar staggered conformation in 1 and 2 (mean value 56.40-56.76°), and twisted from the eclipsed conformation (mean value 78.19°) in 4. The Φ angle value in 4 is relatively larger as compared to 1 and 2. This seems to indicate that the molecular core [Cu₂(μ-η¹-X)₂] in 4 is a sterically demanding system that forces the B-dppf ligand to adopt a relatively strained conformation in comparison to less strained system in 1 and 2. All the complexes exhibit moderately strong luminescence properties in the solution state at ambient temperature.     

Conformational analysis of 1,2:3,4-di-O-isopropylidene-α-d-galacto-octopyranose derivatives: a 1H- and 13C-N.M.R.-spectral and x-ray comparative study

The pyranoid conformations of 7-acetamido-6,7,8-trideoxy-1,2:3,4-di-O-isopropylidene-d-glycero-α-d-galacto-octopyranose (3) and 7-acetamido-7,8-dideoxy-1,2:3,4-di-O-isopropylidene-l-threo-α-d-galacto-octopyranose (4) in solution have been determined by calculation of the dihedral angles from the vicinal, proton-proton coupling-constants, using three modifications of the Karplus equation. Of these, only the equation ³J(HCCH)(φ)  (7.48  0.74 -ΣδE_x)  (2.03  0.17 ΣE_x)cos φ + (4.60  0.23 ΣδE_x)cos 2φ + 0.06 (Σ ± ΔE_x)sin φ + 0.62 (Σ ± ΔE_x)sin 2φ indicates that the pyranoid part of 3 and 4 has the °S₂ conformation, very slightly distorted towards °H₅, in agreement with the conformations determined for the crystalline state. Analysis of the ¹H-n.m.r. data for a series of 1,2:3,4-di-O-isopropyl-idene-α-d-galacto-octopyranose derivatives shows that the pyranoid parts of these compounds adopt the same conformation as that found for 3 and 4.     

Two new pH-controlled metal-organic frameworks based on polynuclear secondary building units with conformation-flexible cyclohexane-1,2,4,5-tetracarboxylate ligand

By regulating the pH values, two new zinc(II) coordination polymers, formulated as [Zn₄(μ₇-CTA^I)(μ₃-OH)(μ₂-OH)₃(H₂O)₂]_n·2n(H₂O) (1), [Zn₂(μ₇-CTA^II)(H₂O)₃]_n (2) have been prepared by a flexible ligand, cyclohexane-1,2,4,5-tetracarboxylic acid (H₄CTA) under hydrothermal conditions. Complex 1 exhibits a two-dimensional binodal (3,6)-connected topological network containing rare octanuclear zinc(II) clusters as the secondary building units (SBU1). Complex 2 displays a three-dimensional binodal (4,8)-connected topological network containing unusual Zn₄(COO)₆ secondary building units (SBU2). And importantly, the conformation of H₄CTA in 1 exhibits (a,e,e,a) fashion and transforms to thermodynamically more stable conformation (e,a,e,e) type in 2 by pH-controlled. In addition, both of the complexes show strong photoluminescence at room temperature, and may be good candidates for potential luminescence materials.     

The conformation of 2,3,4-tri-O-acetyl-D-xylono-l,5-lactone

A conformational analysis of 2,3,4-tri-O-acetyl-D-xylono-1,5-lactone (5) has been performed by using ¹H-n.m.r. spectral data. Evidence is presented that the C-3 and C-4 acetoxyl groups are anti-periplanar. The possible contribution of attractive 1,3- and 1,4-interactions between the electropositive lactone-ring oxygen and the endo-acetoxyl groups at C-3 and C-4 to the conformational stability of 5 is discussed.     

Structure and electrochemistry of the bridging-ligand mono-substituted diruthenium compound, [Ru2(II,III)(O2CCH3)3(admpym)(Cl)(MeOH)] (Hadmpym=2-amino-4,6-dimethylpyrimidine)

The ligand substitution reaction of Ru₂(O₂CCH₃)₄Cl with 2-amino-4,6-dimethylpyrimidine (Hadmpym) under gentle refluxing conditions in methanol led to the formation of a bridging-ligand mono-substituted compound, [Ru₂(O₂CCH₃)₃(admpym)(Cl)(MeOH)] (1). Compound 1 crystallized in monoclinic space group P2₁/n (no. 14) with a=8.3074(8) Å, b=12.3722(8) Å, c=18.913(1) Å, β=95.559(3)°, V=1934.8(3) ų, and Z=4. Temperature dependence of the magnetic susceptibility of 1 revealed it to be in a spin ground state S=3/2 arising from the electronic configuration of σ²π⁴δ²(δ*π*)³. Compound 1 undergoes three metal-centered redox reactions in electrochemistry: E_1/2 ^(ox)=+0.72 V (I_a/I_c<1, ΔE_p=0.17 V); E_1/2 ^(1,red)=−0.65 V (I_a/I_c≈1, ΔE_p=0.10 V); and E_1/2 ^(2,red)=−1.80 V (I_a/I_c?1, ΔE_p=0.16 V). Then, the redox species produced by electrolysis were characterized by spectroscopic studies.     

Crystal and molecular structures of substituted α-d-glucopyranosides

The crystal and molecular structures of methyl 2,4,6-tri-O-pivaloyl-α-d-glucopyranoside (1), methyl 4,6-O-(R)-benzylidene-2-O-pivaloyl-α-d-glucopyranoside (2), and methyl 4,6-O-(R)-benzylidene-2,3-di-O-pivaloyl-α-d-glucopyranoside (3) were determined by X-ray analysis. Crystals of 1 are orthorhombic, space group P2₁2₁2₁ with the unit cell a = 13.026(2), b = 16.832, c = 11.929(2) Å, Z = 4. Crystals of 2 are monoclinic, space group P2₁. The unit-cell parameters are a = 6.519(1), b = 14.664(4), c = 10.635(4) Å, β = 93.18(1)°, Z = 2. Crystals of 3 are orthorhombic, space group P2₁2₁2₁ with a = 10.006(3), b = 13.874(3), c = 18.527(5) Å, Z = 4. The structures were solved by MULTAN and refined by a full-matrix procedure to final values of R = 0.084 (1), 0.048 (2), and 0.069 (3). The pyranose ring in each compound adopts the ⁴C₁ conformation. The 1,3-dioxane rings in 2 and 3 show a chair conformation. The molecular packing in 1 is through the hydrogen bonds involving HO-3 and the 6-O-pivaloyl carbonyl group [HO-3 ⋯ O-9, 2.855(8) Å], which connect the molecules into a chain along

. The endocyclic oxygen atom is involved in an intermolecular hydrogen-bond with HO-3 [2.848(4) Å], joining molecules of 2 into the chains along

. There are no free hydroxyl groups in 3 and molecular packing reflects van der Waals interactions only.     

Synthesis and characterisation of pyrazolic palladium compounds containing alcohol functionality:: rotation around the Pd-N bond

The ligands 1-hydroxymethylpyrazole (hl¹), 1-(2-hydroxyethyl)pyrazole (hl²) and 1-(3-hydroxypropyl)pyrazole (hl³) react with [PdCl₂(CH₃CN)₂] to give trans-[PdCl₂(hl)₂] compounds. Due to a hindered rotation around the Pd-bond, these compounds present two different conformations in solution: anti and syn. The conformation presented depends on the relative disposition of the hydroxyalkylic chains of the two pyrazolic ligands. The present study was carried out on the basis of NMR experiments. The present paper reports the crystal structure of trans-[PdCl₂(hl²)₂]. The synthesis and characterisation of compounds [Pd(hl)₄](BF₄)₂ (hl = hl¹, hl² and hl³) starting from [Pd(CH₃CN)₄](BF₄)₂ and the corresponding chlorocomplexes trans-[PdCl₂(hl)₂] are also described.     

Exploring the coordination chemistry and reactivity of hemilabile N-alkylaminopyrazole ligands towards Pd(II)

Reaction of the N-alkylaminopyrazole (NN′N) ligands bis[(3,5-dimethyl-1-pyrazolyl)methyl]ethylamine (bdmae) and bis[(3,5-dimethyl-1-pyrazolyl)methyl]isopropylamine (bdmai) with [PdCl₂(CH₃CN)₂] in a 1:1 M/L ratio in CH₂Cl₂ produces cis-[PdCl₂(NN′N)] (NN′N = bdmae (1), bdmai (2)). The solid state structure of complex 1 was determined by X-ray diffraction studies. The bdmae ligand is coordinated through the two N_pz atoms to the metal atom, which completes its coordination with two chlorine atoms in a cis disposition.Treatment of the corresponding ligand with [PdCl₂(CH₃CN)₂] in 1:1 M/L ratio in the presence of AgBF₄ and metathesis with NaBPh₄ in CH₂Cl₂/CH₃OH (3:1) gave [PdCl(bdmae)](BPh₄) (3), and in the presence of NaBPh₄ in CH₂Cl₂/CH₃CN (3:1) gave [PdCl(bdmai)](BPh₄) (4). Complexes 1 and 2 were again obtained when complexes 3 and 4 were heated under reflux in a solution of Et₄NCl in acetonitrile. These Pd(II) compounds were characterised by elemental analyses, conductivity measurements, IR, ¹H and ¹³C{¹H} NMR, HMQC and NOESY spectroscopies. The NMR studies of the complexes prove the rigid conformation of the ligands when they are complexed.     

Dimolybdenum complexes with mixed formamidinate ligands

A series of dimolybdenum complexes containing mixed formamidinate ligand are discussed. The reactions of trans-Mo₂(O₂CCH₃)₂(o-DMophF)₂ [o-HDMophF=N,N^′-di(2-methoxyphenyl)formamidine] with N,N^′-di(2-pyridyl)formamidine (HDpyF), N,N^′-di(2-pyrimidyl)formamidine (HDpmF) and N,N^′-di(6-methyl-2-pyridyl)formamidine (HDMepyF), in refluxing CH₂Cl₂ afforded the complexes, trans-Mo₂(O₂CCH₃)(DpyF)(o-DMophF)₂ (1), trans-Mo₂(O₂CCH₃)(DpmF)(o-DMophF)₂ (2), and trans-Mo₂(O₂CCH₃)(DMepyF)(o-DMophF)₂ (3), respectively. The o-DMophF⁻ and DMepyF⁻ ligands in these complexes adopt the s-cis, s-trans conformation, resulting in Mo-O short distances [2.889 (3) and 2.861(2) Å for 1; 2.880(3) and 3.024(4) Å for 2], while the DpyF⁻ ligand adopts the s-cis, s-trans conformation, resulting in a Mo-N [3.208(4) Å] and a Mo-H [2.90 (3) Å] short distances. The reactions of trans-Mo₂(O₂CCH₃)₂(o-DMophF)₂ with HDMepyF in CH₃CN gave complexes 3, trans-Mo₂(O₂CCH₃)(DMepyF)₂(o-DMophF) (4), and trans-Mo₂(DMepyF)₂(o-DMophF)₂ (5). The o-DMophF⁻ ligands in 4 and 5 adopt the s-cis, s-cis conformation while DMepyF⁻ assumes an s-cis, s-trans conformation. Complexes 1-5 are the first dimolybdenum complexes containing mixed formamidinate ligands.     

Magnetic properties and circular dichroism of 1D chains built from chiral mononuclear and non-chiral trinuclear Cu(II) complexes with α-aminocarboxylates

Coordination polymers Cu(l-Pro)(ClO₄)(H₂O)₂ (1) and Cu₃(Gly)₄(H₂O)₂(NO₃)₂ (2) were synthesized and characterized structurally. Compound 1 possesses the structure of 1D chain, where Cu(II) ions are linked by carboxyl-group in syn-anti conformation in equatorial-equatorial mode. Compound 2 is polymeric chain, consisting from trinuclear blocks Cu₃(Gly)₄(H₂O)₂²⁺. In each of these units Cu(II) ions are linked by carboxyl-group in the same way as in 1, while trinuclear units Cu₃(Gly)₄(H₂O)₂²⁺ are linked by NO₃⁻ ions, acting as the bridges between Cu(II) ions of neighboring trinuclear units. Circular dichroism properties of 1 were studied in solid state and solution. Magnetic measurements revealed that there were ferromagnetic exchange interactions between Cu(II) ions in 1 (J = +1.22(1) cm^-1 for Hamiltonian ) and 2 (J = +1.17(2) cm^-1 for Hamiltonian ).     

Syntheses and crystal structures of three Mn(II) complexes with 2-hydroxynicotinate

Three new Mn(II) complexes [Mn(HnicO)₂(H₂O)₂] (1), [Mn₂(HnicO)₂SO₄(H₂O)₂]_n (2), and [NaMn(HnicO)₃]_n (3) (H₂nicO = 2-hydroxynicotinic acid) have been synthesized and determined by X-ray diffraction. For complex 1, the mononuclear units with two bidentate HnicO⁻ ions and two water molecules are assembled into a 3D architecture via hydrogen bonding and π-π interactions. For 2, Mn(II) ions are connected by μ₃-HnicO⁻ and bridging ligands, producing a 2D (6,3) coordination network. For 3, binuclear Na(I)-Mn(II) units with three carbonyl oxygen bridges are interlinked by carboxylate groups, resulting in a 3D 6-connected coordination network with distorted α-Po topology. The magnetic properties of 2 are discussed.     

Synthesis and characterization of cobalt(II)-salicylate complexes derived from N4-donor ligands: Stabilization of a hexameric water cluster in the lattice host of a cobalt(III)-salicylate complex

The syntheses and structural characterization of four cobalt(II)-salicylate complexes, [(TPA)Co^II(HSA)](ClO₄) (1), [(isoBPMEN)Co^II(HSA)](BPh₄) (2), [(TPzA)Co^II(HSA)](ClO₄) (3) and [(6Me₃TPA)Co^II(HSA)](BPh₄) (4) [TPA = tris(2-pyridylmethyl)amine, isoBPMEN = N¹,N¹-dimethyl-N²,N²-bis(2-pyridylmethyl)ethane-1,2-diamine, TPzA = tris((3,5-dimethyl-1H-pyrazole-1-yl)methyl)amine and 6Me₃TPA = tris(6-methyl-2-pyridylmethyl)amine] are described. While 2, 3 and 4 are unreactive towards dioxygen, 1 reacts slowly with molecular oxygen to a cobalt(III)-salicylate complex, [(TPA)Co^III(SA)](ClO₄) (1a). Two different crystalline forms, 1a and 1a·4H₂O were isolated depending upon the condition of oxidation and crystallization. The solid-state structures of cobalt(III)-salicylate unit in both 1a and 1a·4H₂O show a six-coordinate distorted octahedral coordination geometry at the cobalt(III) center ligated by the tetradentate ligand (TPA) where the dianionic salicylate (SA) binds in a bidentate fashion through one carboxylate and one phenolate oxygen. The hydrated form 1a·4H₂O reveals a hexameric water cluster formation in the inorganic lattice host. The complex cation and the perchlorate counterion are involved in stabilizing the (H₂O)₆ cluster in a rare ‘pentamer planar+1’ conformation. A one-dimensional water tape consisting of edge-shared water hexamers is observed. The water tape represents a subunit of ice structure.     

Equilibria of the anomeric and ring forms of ammonium 3-deoxy-d-manno-octulosonate in deuterium oxide

The tautomeric composition of a solution of ammonium 3-deoxy-d-manno-octulosonate (KDO, 1a) in D₂O at 28° was assessed by means of ¹³ C-F.t.-n.m.r. spectroscopy. The results revealed the presence of 6?0 and 11 % of the α and β anomers of the pyranose, and 20 and 9 % of the two furanoses, and suggested, but did not unequivocally prove, that the major furanose form is the α anomer. To facilitate interpretation of the spectral results for 1, ammonium 3,5-dideoxy-d-arabino(or ribo)-octulosonate (3a) was prepared by the reaction of 5-deoxy-d-erythro-pentose with sodium oxalacetate at pH 11. A chromatographically homogeneous, noncrystalline sample of 3 was obtained by lyophilization, and characterized as its (4-nitrophenyl)hydrazone (m.p. 162-163°). The ¹³C-n.m.r. spectrum of a solution of 3a in D₂O revealed it to be substantially all in the α-pyranose form. No signals were obtained for the possible 1,4-lactone of 3. As the 1,5-lactone and furanose forms are impossible for 3, it exhibited no signals analogous to those attributed to furanoid 1. On the basis of these results for 3, the two lactone forms of 1 were excluded from consideration, and the three pairs of ¹³C-n.m.r. signals observed at ≈45, 86, and 104 p.p.m. were assigned to the furanose forms of 1.     

Binuclear manganese(III) complexes of an unsymmetric pyrazolate-based compartmental ligand with hard donor set

The synthesis, crystal structure and magnetic properties of manganese(III) binuclear complexes [Mn^III₂(L-3Н)₂(CH₃ОH)₄]·2CH₃ОH (1) and [Mn^III₂(L-3Н)₂(Py)₄]·2Py (2) (L = 3-[(1E)-N-hydroxyethanimidoyl]-4-methyl-1H-pyrazole-5-carboxylic acid) are reported. The ligand contains two distinct donor compartments formed by the pyrazolate-N and the oxime or the carboxylic groups. The complexes were characterized by X-ray single crystal diffraction, revealing that both 1 and 2 consist of dinuclear units in which the two metal ions are linked by double pyrazolate bridges with a planar {Mn₂N₄} core. Cryomagnetic measurements show antiferromagnetic interaction with g = 1.99, J = −3.6 cm⁻¹, Θ = −2.02 K for 1 and g = 2.00, J = −3.7 cm⁻¹, Θ = 1.43 K for 2.     

Synthesis, structures and conductivity properties of silver 3-sulfobenzoate coordination polymers

Four coordination polymers based on Ag^I/3-sulfobenzoate/N-donor ligands, [Ag₂Na₂(3-sb)₂(H₂O)₇]_n (1), {[Ag₂(3-sb)(apy)]·(H₂O)}_n (2), {[Ag₂(4,4′-bipy)₂(H₂O)₃]·[Ag₂(4,4′-bipy)₂(H₂O)₂]·2(3-sb)·4(H₂O)}_n (3) and {[Ag(3-sb)(bpe)(H₂O)][Ag(bpe)(H₂O)]·3(H₂O)}_n (4) where 3-sb is 3-sulfobenzoate, apy is 2-aminopyridine, bipy is 4,4′-bipyridine and bpe is 1,2-bis(4-pyridyl)ethylene, were prepared and characterized, and their fluorescence and electric conductivity properties were studied. Complex 1 is a 3D architecture in which 3-sb ligands exhibit μ₄-κ¹(O1,O2-Ag): κ¹(O3,O5-Na) trans-trans coordination mode. The molecular structure of 2 is a 2D layer. Complexes 3 and 4 are cation-anion species and 1D polymers. In these complexes hydrogen bonds provide additional assembly forces, giving 3D hydrogen bonding networks for 1 and 3, and 2D layers for 2 and 4. Abundant weak interactions, such as Ag-Ag interactions in 1-3, Ag-π interactions in 1-4, π-π interactions in 1, 3-4, and C-H···π interactions in 3-4, also can be found. The weak interactions are strongly related to the fluorescence and electric conductivity properties, providing the way for understanding the relationship between structures and properties.