Host-guest Interactions in Intercalates Zr(HPO4)2·2C2H5OH and VOPO4·2C2H5OH

Molecular mechanics simulations using Cerius² modelling environment combined with vibrational spectroscopy (IR and Raman) have been used to study the host-guest interactions in zirconium and vanadyl phosphate intercalated with ethanole. The strategy of investigation is based on the comparison of vibrational spectra for the host compound, intercalate and guest species. This comparison confirmed the rigidity of VOPO₄- and Zr(HPO₄)₂-layers during the intercalation and provided us with the basis for the strategy of modelling. Molecular mechanics simulations revealed the structure of intercalates and enabled to analyse the host-guest interaction energy and bonding geometry. The bilayer arrangement of ethanole molecules in the interlayer space with two differently bonded ethanole molecules has been found in both intercalates. The average interaction energy ethanole-layer for two differently bonded ethanole molecules is : 127.5 and 135.7 kcal·mol^-1 in Zr(HPO₄)₂·2C₂H₅OH, respectively 94.0 and 104.4 kcal·mol^-1 in VOPO₄·2C₂H₅OH. The Coulombic contribution to the ethanole-layer interaction energy is predominant in all cases, but the hydrogen bonding contribution is much higher in Zr(HPO₄)₂·2C₂H₅OH than in VOPO₄·2C₂H₅OH. Present results of modelling enabled the interpretation of vibrational spectra and explanation of small changes in positions and shapes of spectral bands, in infrared and Raman spectra, proceeding from the host structure to intercalates.     

Hydrogen bonds determine the structures of the ternary heterocyclic complexes C₂H₄O···2HF, C₂H₅N···2HF and C₂H₄S···2HF: density functional theory and topological calculations

A theoretical study of structural, electronic, topological and vibrational parameters of the ternary hydrogen-bonded complexes C₂H₄O···2HF, C₂H₅N···2HF and C₂H₄S···2HF is presented here. Different from binary systems with a single proton donor, the tricomplexes have the property of forming multiple hydrogen bonds, which are analyzed from a structural and vibrational point of view, but verified only by means of the quantum theory of atoms in molecules (QTAIM). As traditionally done in the hydrogen bond theory, the charge transfer between proton donors and acceptors was computed using the CHELPG calculations, which also revealed agreement with dipole moment variation and a cooperative effect on the tricomplexes. Furthermore, redshift events on proton donor bonds were satisfactorily identified, although, in this case, an absence of experimental data led to the use of a theoretical argument to interpret these spectroscopic shifts. It was therefore the use of the QTAIM parameters that enabled all intermolecular vibrational modes to be validated. The most stable tricomplex in terms of energy was identified via the strength of the hydrogen bonds, which were modeled as directional and bifurcated.     

Resonance Raman studies of the peroxotitanate(IV) complexes K2(Ti(O2)(SO4)2)·5H2O and K2(Ti(O2)(C2O4)2)·3H2O

The resonance Raman spectra of K₂(Ti(O₂)(SO₄)₂)·5H₂O and K₂(Ti(O₂)(C₂O₄)₂)·3H₂O are recorded. The results are consistent with the triangular structure of the peroxotitanium unit, Ti(O₂), with C_2ν symmetry. The ν(OO), ν_s(TiO) and ν_as(TiO) are observed around 890, 610 and 535 cm⁻¹, respectively. The resonance effects are shown to be associated with the 425 nm absorption band. This band is assigned to the O₂²⁻ → Ti(IV) charge-transfer transition. The calculated force constant values for the O₂²⁻ and TiO bonds are 320 and 275 N m⁻¹, respectively.     

The structure and properties of tetrakis(tironato)cerate(IV), Na12[Ce(C6H2O2(SO3)2)4]·9H2O·6C3H7NO

The title complex, prepared in 1 M NaOH, was crystallized from hot N,N-dimethylformamide/ ethanol solutions to give Na₁₂[Ce(C₆H₂O₂(SO₃)₂)₄]· 9H₂O·6DMF. The purple—brown crystals were examined by X-ray diffraction while inside quartz capillaries filled with DMF, (λ_max 425 nm, ϵ 3664; λ_sh 520 nm, ϵ 2240) and belong to space group Pbca, Z=8 with a=21.846(4), b=17.348(2), c=43.103- (6) Å, V=16.335(7) ų, D_c=1.693 gcm^t−3, D_o=1.725 g cm^t−3. Diffractometer data were collected using Mo Kα radiation to 2θ=43^o. For 7331 independent data with F_o²>3σ(F_o²) full matrix least squares refinement converged to unweighted and weighted R factors of 0.072 and 0.110, respectively, with a mixture of anisotropic and isotropic thermal parameters. The disordered DMF atom parameters were not refined. The structure consists of discrete monomeric Ce(C₆H₂S₂O₈)₄¹²⁻ units with 12 Na⁺ counter cations and 10 H₂O molecules (two with half occupancy), and 6 DMF molecules of solvation filling up spaces between cations and anions. Cerium(IV) is in a general position with a coordination polyhedron close to the trigonal-faced dodecahedron, D_2d, with the angles between the two BAAB trapezoids of 2.3^o and 3.7^o. The average CeO(A) distance, 2.363(9) Å is longer than the average CeO(B) distance, 2.326(15)Å, with the reverse being true for one of the four tironato ligands. The average ring OCeO angle is 67.9(1)^o. The cerium (IV) complex is found by cyclic voltammetry to undergo a quasi-reversible one-electron reduction (in strongly basic solution with excess tiron) with Ef=−497 mV vs. SCE, hence the ratio of the formation constants for tetrakis(tironato)cerate(IV) to that for tetrakis(tironato)cerate(III), K_IV/K_III, is 10³³. Characterization of other tiron salts is reported.     

Platinum(II) complexes of methyl-substituted xanthines: crystal structures of K[Pt(theobromine)Cl3]·H2O,trans-[ Pt(isocaffeine)2Cl2]·H2O and K(isocaffeinium)[PtCl4]·H2O

The preparations of Pt(theophylline)₂Cl₂, K[Pt- (theophylline)Cl₃], K[Pt(theobromine)Cl₃]·H₂O (1), trans-[Pt(isocaffeine)₂Cl₂]·H₂O (2), and K(isocaffeinium)[PtCl₄]·H₂O (3) are reported.Crystals of 1 are monoclinic P2₁/n with a=7.641- (2), b=11.873(3), c=15.868(4) Å, β=90.80(2)°, Z=4. The structure was refined on 1443 reflections to R=0.028. In the planar [Pt(theobromine)Cl₃]⁻ anion Pt-N(9)=2.016(6) Å, Pt-Cl=2.299(2), 2.289(2), and 2.303(2) Å. The imidazole ring is rotated away from the coordination plane by 79.8°. Symmetry related theobromine units pack parallel to each other with a mean inter-ring separation of 3.27 Å.Crystals of 2 are monoclinic P2₁/a with a=7.345- (2), b=20.021(5), c=8.031(2) Å, β=104.18(2)°, Z=2. The structure was refined on 1132 reflections to R=0.029. The Pt-N(7) distance is 2.003(3) Å and Pt-Cl=2.298(1) Å. The imidazole ring is rotated away from the PtCl₂N₂ plane by 76.8°. In this compound, the isocaffeine units do not stack, but form a staggered arrangement within the unit cell.Crystals of 3 are monoclinic P₁/c with a= 7.382- (1), b=14.014(4), c=15.757(4) », β=92.30(2)°, Z=4. The structure was refined on 2057 reflections to R=0.032. The isocaffeine is protonated at N(7). The Pt-Cl distances in the PtCl₄²⁻ anion range between 2.29–2.31 Å. The protonated isocaffeine cations and the PtCl₄²⁻ anions form a very nearly parallel infinitely stacked arrangement with minimum interlayer atomic separations of 3.37 and 3.44 Å.     

A novel vanadium(V) homocitrate complex: synthesis,structure, and biological relevance of [K2(H2O)5][(VO2)2(R,S-homocitrate)2]·H2O

Initial investigations into the possible roles of homocitric acid in the biosynthesis and function of the active site cofactor of nitrogenase resulted in the isolation and characterization of the dinuclear vanadium(V) species [K₂(H₂O)₅][(VO₂)₂(R,S-C₇H₈O₇)₂]·H₂O ( 1). Complex 1 represents the first synthetic structurally characterized transition metal homocitrate complex and may represent an early mobilized precursor in the biosynthesis of VFeco. Compound 1 was characterized by a variety of physical methods, including X-ray crystallography. Crystal data: space group P?* (#2), with a?=?10.292 (3)?Å, b?=?16.663 (3)?Å, c?=?8.343 (1)?Å, α?=?95.93 (1)°, β?=?105.74 (2)°, γ?=?90.86 (2)°, V?=?1386 (1)?ų, and Z?=?2. The homocitrate ligand is coordinated to the vanadium(V) atoms in a bidentate fashion via the deprotonated bridging hydroxyl group and a carboxylate donor. This unique coordination mode accurately mimics the coordination of homocitrate to the cofactor of nitrogenase.     

Synthesis and structures of porphyrin complexes of scandium: ClSc(TTP)·2(C 10H 7Cl) and O[Sc(TTP)] 2·6THF

A facile, high yield metallation procedure is reported for the insertion of Sc into H ₂(TTP) (TTP= dianion of meso-tetratolylporphyrin) using anhydrous ScCl ₃. Single crystal X-ray structures are reported for ClSc(TPP)·2(C ₁₀H ₇Cl) ( 1) and O[Sc(TTP)] ₂·6THF ( 2). Compound 1: space group P2 ₁/c with a = 19.850(17), b = 28.822(24), c = 9.954(9)Å, β = 95.71(7)°, Z = 4; 2: space group P2/n, a = 16.952(9), b = 16.737(5), c = 19.93(1)Å, β = 112.56(5)°, Z = 4. Compounds 1 and 2 both had large amounts of poorly ordered solvents in the lattice which resulted in rather high R factors in the range of 12–14%. In 1, the Sc is five-coordinate (4N and 1Cl) and is centered 0.68Åabove the plane defined by the four porphyrin nitrogens. For 2, the Sc is 0.82Åfrom the plane and contains a non-linear μ-oxide bridge with a ScO Sc angle of 109(3)°, but with essentially coplanar porphyrin rings.     

Hydrothermal synthesis and structural characterization of an organic–inorganic hybrid material: (H2tptz)2[δ-Mo8O26]·2H2O (tptz=2,4,6-tripyridyltriazine)

The reaction of MoO₃ and 2,4,6-tripyridyltriazine (tptz) in water at 180°C for 48 h and pH 5.5 produces (H₂tptz)₂[Mo₈O₂₆]·2H₂O in 70% yield. The structure is constructed from δ-Mo₈O₂₆ ⁴⁻ clusters, H₂tptz²⁺ and H₃O⁺ cations linked through hydrogen bonding into a network. Crystal data: C₁₈H₁₆Mo₄N₆O₁₄; monoclinic P2₁/n; a=10.2225(5) Å, b=14.0072(6) Å, c=18.1154(8) Å, β=93.896(1)°, V=2587.9(2) Å³, Z=4, D_calc=2.372 g cm⁻³; R₁=0.0271 based on 3212 reflections.     

Preparation of (±)-2-(2,3-2H2)Jasmonic Acid and Its Methyl Ester,Methyl (±)-2-(2,3-2H2)Jasmonate

For use as the internal standards in a quantitative analysis of natural jasmonic acid (JA) and methyl jasmonate (JAMe) by gas chromatography-mass spectrometry-selected ion monitoring, (±)-2-(2,3–²H₂)JA and its methyl ester, (±)-2-(2,3–²H₂)JAMe, were efficiently prepared from 2-(2–pentyl)-2-cyclopentenone through catalytic semi-deuteriogenation of acetylenic intermediates with deuterium gas in pyridine.     

Further studies on the copper(II) complexes of lysine: [Cu(II)(H3N·C5H10·CH·NH2·COO)2] [HgI3]2

Spontaneous resolution in the formation of the [HgI₃]⁻ salts of the copper complex of racemic lysine was previously reported. X-ray and IR studies were used to support this conclusion. Gas chromatographic studies using a chiral phase on the crystals originally studied, and on newly formed crystals using D,L-lysine, do not substantiate the suggestion that spontaneous resolution occurs.     

Theoretical investigations of the H···π and X (X = F,Cl, Br,I)···π complexes between hypohalous acids and benzene

The H···π and X (X = F, Cl, Br, I)···π interactions between hypohalous acids and benzene are investigated at the MP2/6-311++G(2d,2p) level. Four hydrogen-bonded and three halogen-bonded complexes were obtained. Ab initio calculations indicate that the X···π interaction between HOX and C₆H₆ is mainly electrostatically driven, and there is nearly an equal contribution from both electrostatic and dispersive energies in the case of XOH–C₆H₆ complexes. Natural bond orbital (NBO) analysis reveals that there exists charge transfer from benzene to hypohalous acids. Atom in molecules (AIM) analysis locates bond critical points (BCP) linking the hydrogen or halogen atom and carbon atom in benzene.     

Rhodium(III) cis-dihydrido complexes with 3,6-bis(2′-pyridyl)pyridazine (dppn) and bidiazines. Crystal and molecular structure of [Rh(H)2(dppn)(PPh3)2]PF6· CH2Cl2

The acetone complex [Rh(H)₂(acetone)₂(PPh₃)₂]- PF₆ reacts with bidiazines and 3,6-bis(2′-pyridyl)- pyridazine (dppn) giving the air stable cis-dihydrido rhodium(III) [Rh(H)₂(L)(PPh₃)₂]PF₆ complexes. The structure of the dichloromethane solvate of [Rh(H)₂(dppn)(PPh₃)₂]PF₆ has been determined by X-ray crystal structure analysis. Crystals are monoclinic, space group P2₁/a, with a = 18.629(6), b = 15.339(5), c = 17.146(5) Å, β = 101.02(3)° and Z = 4. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by block-matrix least-squares to R = 0.076 for 6225 observed reflections. In the structure discrete [Rh(H)₂(dppn)(PPh₃)₂]⁺ cationic complexes, PF₆⁻ anions and dichloromethane solvent molecules are present. The Rh atom is octahedrally surrounded by two cis hydride ligands and by two cis nitrogen atoms from a dppn molecule acting as a bidentate chelating ligand through two neighbouring pyridyl and pyridazinyl nitrogen atoms. Two P atoms from PPh₃, ligands in trans apical positions complete to octahedral the coordination of Rh.     

Uric acid salts of magnesium: crystal and molecular structures and thermal analysis of two phases of Mg(C5H3N4O3)2 · 8H2O

Two structurally different phases of a uric acid salt of magnesium, Mg(hydrogenurate)₂ · 8H₂O, have been prepared by crystallization from solution at pH = 7.5–8.0 and were investigated by x-ray crystallography, thermal analysis, and ir spectroscopy. Both phases are monoclinic, space group P2₁/c with a = 9.573(2), b = 14.627(3), c = 7.170(1) Å, β = 101.91(1)° (phase I) and a = 10.397(2), b = 14.306(3), c = 6.732(1) Å, β = 104.64(2)° (phase II). The crystal structures of both phases (R = 0.053 and 0.051, respectively) contain isolated octahedral [Mg(H₂O)₆]²⁺ cations, hydrogenurate monoanions, and two molecules of water of crystallization per formula unit. The structural formula representing these facts is [Mg(H₂O)₆] (hydrogenura-te)₂·2H₂O. The tautomeric form of the hydrogenurate molecule corresponds to the tri-keto form of uric acid deprotonated at N(3). Differences in bond length between uric acid and the hydrogenurate molecule may be described in terms of three additional resonance structures distributing the formal negative charge at N(3) within the pyrimidine (but not the imidazole) ring. Deprotonation at N(3) significantly decreases the internal C-N-C angle at N(3). Alternating pairs of medium-strong intermolecular N-HO hydrogen bonds lead to infinite chains of hydrogenurate molecules extending along the b axis of the unit cells in both phases. The main difference between the two phases lies in their stacking pattern of the hydrogenurate molecules. Infrared data confirm the hydrogen bonding characteristics resulting from the crystal structure analysis. Thermogravimetric measurements and differential scanning calorimetry data show that the dehydration of both phases occurs in two distinct steps with Mg(hydrogenurate)₂.6H₂O as an intermediate phase. The first dehydration step (−2H₂O) is a topotactic reaction with three-dimensional preservation of the main structure elements of the octahydrate in the structure of the hexahydrate.     

Structure and magnetic properties of LnIII[Ru2(CO3)4] · 8H2O

Ln^III[Ru₂(CO₃)₄] · 8H₂O (Ln = Gd, Nd, Ho, Yb) is formed from the reaction of Ln^III and [Ru₂(CO₃)₄]^3? in water. These Ln^III materials have a 3D network structure composed of linked chains and μ_n-CO₃ linkages to both Ru and Ln^III sites, and are best described as Ln^III(OH₂)₄[Ru₂(CO₃)₄]_1/2[Ru₂(CO₃)₄(OH₂)₂]_1/2 · 3H₂O. Complete characterization of the Gd^III species is presented, as the other Ln^III are isostructural and exhibit large spin–orbit coupling leading to complex magnetic behavior. Magnetic ordering is not observed above 2 K.     

Crystal structure,magnetic and thermal properties of the one-dimensional complex [Nd(pzam)3(H2O)Mo(CN)8] · H2O

The new d–f cyanido-bridged 1D assembly [Nd(pzam)₃(H₂O)Mo(CN)₈] · H₂O was prepared by self-assembly of pyrazine-2-carboxamide (pzam), Nd(NO₃) · nH₂O and (Bu₃NH)₃[Mo(CN)₈] · 4H₂O in acetonitrile. X-ray crystallographic studies indicate that the complex comprises chains of alternating, cyanido-bridged [Nd(pzam)₃(H₂O)]³⁺ and Mo(CN)₈]^3? fragments. The magneto-structural properties have been studied by field-dependent magnetization and specific heat measurements at low temperatures (?0.3 K). Below ≈10 K the Nd(III) moment is well approximated by an effective spin S = 1/2, with anisotropic g-tensor. The exchange coupling between the Nd(III) and the Mo(V) spins S = 1/2 along the structural chains is found to be ferromagnetic, with J/k_B = 1.8 ± 0.2 K and approximately XY (planar) anisotropy. No evidence for 3D interchain magnetic ordering is found. A comparison with magneto-structural data of other cyanido-bridged complexes involving the Nd(III) ion is presented.