Solution state structure and equilibria of lanthanide (fod)3 complexes revisited: A 1 H, 13 C and 19 F nuclear magnetic resonance study of Eu(fod)3.

In a qualitative approach, variable temperature 1 H, 19 F and 13 C nuclear magnetic resonance (NMR) were used to characterize the solution state structure and equilibria of the widely used lanthanide solvent reagent Eu(fod)3 . Despite the fact that the side chain fluorines are far from the coordination site, the 19 F-1 H NMR spectra turned out to be sensitive reporters of self-coordination and/or adduct formation with other ligands. For example, they predict/explain immediately the otherwise hardly predictable magnitude of the expectable paramagnetic effects. The temperature-dependent Fermi-contact effects observed in the 13 C{1 H} spectra were extremely important aides in their assignments. The equilibria could be manipulated by changing the solvent used and/or the reagent/ligand molar ratio. Depending on their coordination ability, the solvents possess a certain control over the adduct life times. Sharpening of the 19 F signals in the presence of associative solvent molecules such as dimethyl sulfoxide (DMSO) or CH3 CN is an indication of changing complex structure (shifting the equilibrium towards the monomeric form). In apolar solvents, relaxation and diffusion data confirmed the oligomerization of the Eu(fod)3 -d27 chelate complexes already at relatively low (≥3.0 mg/0.4 ml) concentration.

Dithallium(III)-Containing 30-Tungsto-4-phosphate, [Tl2Na2(H2O)2(P2W15O56)2]16-: Synthesis, Structural Characterization, and Biological Studies.

Here we report on the synthesis and structural characterization of the dithallium(III)-containing 30-tungsto -4-phosphate [Tl2Na2(H2O)2{P2W15O56}2]16- (1) by a multitude of solid-state and solution techniques. Polyanion 1 comprises two octahedrally coordinated Tl3+ ions sandwiched between two trilacunary {P2W15} Wells-Dawson fragments and represents only the second structurally characterized, discrete thallium-containing polyoxometalate to date. The two outer positions of the central rhombus are occupied by sodium ions. The title polyanion is solution-stable as shown by 31P and 203/205Tl NMR. This was also supported by Tl NMR spectra simulations including several spin systems of isotopologues with half-spin nuclei (203Tl, 205Tl, 31P, 183W). 23Na NMR showed a time-averaged signal of the Na+ counter cations and the structurally bonded Na+ ions. 203/205Tl NMR spectra also showed a minor signal tentatively attributed to the trithallium-containing derivative [Tl3Na(H2O)2(P2W15O56)2]14-, which could also be identified in the solid state by single-crystal X-ray diffraction. The bioactivity of polyanion 1 was also tested against bacteria and Leishmania.

Solid-State NMR Study of Paramagnetic Bis(alaninato-κ(2)N,O)copper(II) and Bis(1-amino(cyclo)alkane-1-carboxylato-κ(2)N,O)copper(II) Complexes: Reflection of Stereoisomerism and Molecular Mobility in (13)C and (2)H Fast Magic Angle Spinning Spectra.

Solid-state stereochemistry and mobility of paramagnetic copper(II) complexes formed by aliphatic amino acids (l-alanine, d,l-alanine, 1-amino-2-methyl-alanine) and 1-amino(cyclo)alkane-1-carboxylic acids (alkane = propane, butane, pentane, hexane) as bidentate ligands has been studied by (13)C and (2)H solid-state fast magic angle spinning (MAS) NMR spectroscopy. We examined the prospective method to characterize solid-state paramagnetic compounds in a routine way. Both (13)C and (2)H MAS spectra can distinguish d,l and l,l diastereomers of natural and polydeuterated bis([Dn]alaninato)copper(II) (n = 0, 2, 8) complexes with axial and/or equatorial methyl positions (conformations) primarily due to different Fermi-contact (FC) contributions. The three-bond hyperfine couplings clearly show Karplus-like dependence on the torsional angles which turned out to be a useful assignment aid. Density functional theory calculations of the FC term and crystal structures were also used to aid the final assignments. The correlations obtained for bis(alaninato-κ(2)N,O)copper(II) complexes were successfully used to characterize other complexes. The usefulness of the (2)H MAS spectra of the deuterated complexes was underlined. Even the spectra of the easily exchangeable amine protons contained essential stereochemical information. In the case of a dimer structure of bis(1-aminohexane-1-carboxylato-κ(2)N,O)copper(II) both the (13)C and (2)H resolutions were good enough to confirm the presence of the cis and trans forms in the asymmetric unit. With regard to the internal solid-state motions in the crystal lattice, the obtained quadrupolar tensor parameters were similar for the d,l- and l,l-alaninato isomers and also for the cis-trans forms suggesting similar crystal packing effects, static amine deuterons involved in hydrogen bonding, and fast rotating methyl groups.

Homonuclear SQ-DQ correlations in solids: applications of the broadband BaBa scheme to reveal 31P-31P spatial correlations in two-, three-, four-, and five-spin systems.

In this paper, we report on the use and limitations of the popular double-quantum recoupling sequence back-to-back in studies of (31)P-(31)P spatial proximities in Pd-phosphine complexes at medium field (9.38 T) under the conditions of fast MAS. The effects of internuclear distances in different spin systems and the impact of isotropic chemical shift and chemical shift anisotropy (CSA) offsets on the detectibility of SQ-DQ correlations were of particular interest to us. Selected model compounds with these requirements in mind were synthesized. By optimization of the excitation times of SQ-DQ correlations up to 4.6 Å could be obtained even in four-spin systems; however, certain long-range correlations may be weak or missing. Although under fast MAS, CSA values up to 270 ppm are well tolerated, in multi-spin systems in cases of isotropic chemical shift offsets larger than 50 ppm, the DQ coherences cannot be properly excited.

Sterically-directed consecutive and size-selective self-assembly of palladium diphosphane complexes with an Ar-BIAN ligand: unexpected formation of pentameric and hexameric aggregates.

The coordination properties of N,N'-bis[4-(4-pyridyl)phenyl]acenaphthenequinonediimine (L(1)) and N,N'-bis[4-(2-pyridyl)phenyl]acenaphthenequinonediimine (L(2)) were investigated in self-assembly with palladium diphosphane complexes [Pd(P;P)(H(2)O)(2)](OTf)(2) (OTf = triflate) by using various analytical techniques, including multinuclear ((1)H, (15)N, and (31)P) NMR spectroscopy and mass spectrometry (P;P = dppp, dppf, dppe; dppp = bis(diphenylphosphanyl)propane, dppf = bis(diphenylphosphanyl)ferrocene, and dppe = bis(diphenylphosphanyl)ethane). Beside the expected trimeric and tetrameric species, the interaction of an equimolar mixture of [Pd(dppp)](2+) ions and L(1) also generates pentameric aggregates. Due to the E/Z isomerism of L(1), a dimeric product was also observed. In all of these species, which correspond to the general formula [Pd(dppp)L(1)](n)(OTf)(2n) (n = 2-5), the L(1) ligand is coordinated to the Pd center only through the terminal pyridyl groups. Introduction of a second equivalent of the [Pd(dppp)](2+) tecton results in coordination to the internal, sterically more encumbered chelating site and induces enhancement of the higher nuclearity components. The presence of higher-order aggregates (n = 5, 6), which were unexpected for the interaction of cis-protected palladium corners with linear ditopic bridging ligands, has been demonstrated both by mass-spectrometric and DOSY NMR spectroscopic analysis. The sequential coordination of the [Pd(dppp)](2+) ion is attributed to the dissimilar steric properties of the two coordination sites. In the self-assembled species formed in a 1:1:1 mixture of [Pd(dppp)](2+)/[Pd(dppe)](2+)/L(1), the sterically more demanding [Pd(dppp)](2+) tectons are attached selectively to the pyridyl groups, whereas the more hindered imino nitrogen atoms coordinate the less bulky dppe complexes, thus resulting in a sterically directed, size-selective sorting of the metal tectons. The propensity of the new ligands to incorporate hydrogen-bonded solvent molecules at the chelating site was confirmed by X-ray diffraction studies.

Aminopropyl-Silica Hybrid Particles as Supports for Humic Acids Immobilization.

A series of aminopropyl-functionalized silica nanoparticles were prepared through a basic two step sol-gel process in water. Prior to being aminopropyl-functionalized, silica particles with an average diameter of 549 nm were prepared from tetraethyl orthosilicate (TEOS), using a Stöber method. In a second step, aminopropyl-silica particles were prepared by silanization with 3-aminopropyltriethoxysilane (APTES), added drop by drop to the sol-gel mixture. The synthesized amino-functionalized silica particles are intended to be used as supports for immobilization of humic acids (HA), through electrostatic bonds. Furthermore, by inserting beside APTES, unhydrolysable mono-, di- or trifunctional alkylsilanes (methyltriethoxy silane (MeTES), trimethylethoxysilane (Me3ES), diethoxydimethylsilane (Me2DES) and 1,2-bis(triethoxysilyl)ethane (BETES)) onto silica particles surface, the spacing of the free amino groups was intended in order to facilitate their interaction with HA large molecules. Two sorts of HA were used for evaluating the immobilization capacity of the novel aminosilane supports. The results proved the efficient functionalization of silica nanoparticles with amino groups and showed that the immobilization of the two tested types of humic acid substances was well achieved for all the TEOS/APTES = 20/1 (molar ratio) silica hybrids having or not having the amino functions spaced by alkyl groups. It was shown that the density of aminopropyl functions is low enough at this low APTES fraction and do not require a further spacing by alkyl groups. Moreover, all the hybrids having negative zeta potential values exhibited low interaction with HA molecules.

Phospholes with Reduced Pyramidal Character from Steric Crowding. 1. Synthesis and NMR Characterization of 1-(2,4-Di-tert-butyl-6-methylphenyl)-3-methylphosphole.

The sterically crowded 1-(2,4-di-tert-butyl-6-methylphenyl)-3-methylphosphole was synthesized by dehydrohalogenation of the corresponding 3,4-dibromophospholane, in order to probe the possibility that the steric congestion would cause some flattening of the phosphorus pyramid and an increase in electron delocalization. The phosphole was a recrystallizable solid with (31)P NMR delta 1.8. Semiempirical calculations indicated that the pyramidal shape was retained but was noticeably flatter than in 1-phenylphosphole. In the low energy conformation, the phosphole and phenyl ring planes are approximately orthogonal, with the 2-tert-butyl group in the less crowded position that is syn to the lone pair on phosphorus. The 6-methyl group is positioned under the phosphole ring. This conformational prediction was amply confirmed by several chemical shift and coupling effects in the (13)C NMR spectrum. The (1)H NMR spectrum displayed an unusually large four-bond coupling (6 Hz) of (31)P to the m-phenyl proton syn to the lone pair (and none to the anti-meta proton), consistent with the orthogonal conformation. The oxide of the phosphole showed more stability than that of less crowded phospholes and gave a (31)P NMR signal that was detectable over a several hour period at room temperature. The oxide proceeded to give the usual Diels-Alder dimer and also formed a cycloadduct with N-phenylmaleimide. The phosphoryl group of the latter was reduced with trichlorosilane to give the phosphine. This new 7-phosphanorbornene derivative gave the most downfield (31)P NMR shift (delta 153.3) of any member of this family, all of which are characterized by remarkable deshielding in the syn isomer.

Selective ring-opening carbonylation of epoxy-steroids.

Ring-opening alkoxycarbonylation of epoxy-steroids has been carried out with a Co2(CO)8/3-hydroxypyridine catalytic system. High chemo- and regioselectivities were obtained under the reaction conditions applied. Structural analysis of the products proved their high stereochemical purity in each case, accompanied by inversion of the original configuration. No carbonylation took place for sterically hindered steranic epoxides.

Equilibria of mononuclear oxomolybdenum(VI) complexes of triethanolamine. A multinuclear dynamic magnetic resonance study of structure and exchange mechanisms.

1D and 2D 1H and 13C NMR spectra of the assumed [MoO(4)(TEA)](2-) complex recorded in DMSO at variable temperatures clearly indicate one free and two bound hydroxyethyl arms. The free arm of the ligand readily exchanges with the two metal-bound arms. Under such conditions the triethanolamine (TEA) acts as a bidentate ligand. The presence of water accelerates the exchange, which at higher water content involves the free ligand too. In organic solvents the binding strength of the hydroxo groups to the molybdenum is weaker than that of the water molecules. A plausible structure is confirmed by 14N, 17O and 95Mo measurements and an exchange mechanism based on the existence of an eight-membered relatively rigid chelate ring is suggested.

Comparative analysis of zaleplon complexation with cyclodextrins and hydrophilic polymers in solution and in solid state.

The aim of this work was to investigate the potential synergistic effect of water-soluble polymers (hypromellose, HPMC and polyvinylpyrrolidone, PVP) on zaleplon (ZAL) complexation with parent ß-cyclodextrin (ßCD) and its randomly methylated derivative (RAMEB) in solution and in solid state. The addition of HPMC to the complexation medium improved ZAL complexation and solubilization with RAMEB (K(ZAL/RAMEB)=156±5M(-1) and K(ZAL/RAMEB/HPMC)=189±8M(-1); p<0.01), while such effect was not observed for ßCD (K(ZAL/ßCD)=112±2M(-1) and K(ZAL/ßCD/HPMC)=119±8M(-1); p>0.05). Although PVP increased the ZAL aqueous solubility from 0.22 to 0.27mg/mL, it did not show any synergistic effects on ZAL solubilization with the cyclodextrins tested. Binary and ternary systems of ZAL with ßCD, RAMEB and HPMC were prepared by spray-drying. Differential scanning calorimetry, X-ray powder diffraction and scanning electron microscopy demonstrated a partial ZAL amorphization in spray-dried binary and ternary systems with ßCD, while the drug was completely amorphous in all samples with RAMEB. Furthermore, inclusion complex formation in all systems prepared was confirmed by solid-state NMR spectroscopy. The in vitro dissolution rate followed the rank order ZAL/RAMEB/HPMC>ZAL/RAMEB=ZAL/ßCD/HPMC>ZAL/ßCD≫ZAL, clearly demonstrating the superior performance of RAMEB on ZAL complexation in the solid state and its synergistic effect with HPMC on drug solubility. Surprisingly, when loaded into tablets made with insoluble microcrystalline cellulose, RAMEB complexes had no positive effect on drug dissolution, because HPMC and RAMEB acted as a binders inside the tablets, prolonging their disintegration. Oppositely, the formulation with mannitol, a soluble excipient, containing a ternary RAMEB system, released the complete drug-dose in only 5min, clearly demonstrating its suitability for the development of immediate-release oral formulation of ZAL.

Distinction of tris(diimine)ruthenium(II) enantiomers chiral by virtue of helical chirality: temperature-dependent deuterium NMR spectroscopy in partially oriented phases.

2H NMR spectra of perdeuterated tris(diimine)ruthenium(II) complexes have been recorded in lyotropic liquid crystalline phase formed by the chiral polypeptide, poly-gamma-benzyl-L-glutamate (PBLG) and co-solvents. It is demonstrated that the left- and right-rotation isomers of these octahedral metal complexes with D3 symmetry can be distinguished. The effects of temperature and ligand size on spectral resolution were also studied. Although in the case of free bipyridine ligands excellent optical resolution could be obtained at room temperature in the complexes studied, the increase in ligand size has a detrimental effect on the resolution. This can be compensated to some extent by elevating the sample temperature and decreasing the deuterium relaxation rates, but the available temperature range and therefore the applicability of the technique are limited.

N-benzoylimido complexes of palladium. Synthesis, structural characterisation and structure-reactivity relationship.

Benzoyl azides, ArC(O)N3, 2, (Ar = phenyl or substituted phenyl), react with [Pd2Cl2(dppm)2], 1, [dppm = bis(diphenylphosphino)methane] with the formation of novel [Pd2Cl2(mu-NC(O)Ar)(dppm)2], 3, benzoylnitrene complexes that were structurally characterised by multinuclear magnetic resonance and IR spectroscopy and, in several instances, by single crystal X-ray diffraction. As shown by crystallographic studies, the C2P4Pd2 rings adopt extended twist-boat conformations with methylene groups bending towards the bridging benzoylimido moieties. X-ray diffraction studies have revealed the chiral nature of the imido complexes, the chiral element being the propeller-like C2P4Pd2 ring. Structural data accumulated on complexes 3 such as short C-N distances (1.32 A), elongated C=O bonds (1.30 A) as well as the outstandingly high barrier to internal rotation around the N-C(O) linkage (88.3 kJ mol(-1)) are in line with extensive ppi-ppi interaction between the bridging nitrogen and the carbonyl carbon atoms. Theoretical calculations indicate an electron shift from the dimer towards the apical nitrogen atom, which, in turn, facilitates the donation of electrons towards the carbonyl moiety. To elucidate the structure-reactivity relationship of benzoyl azides towards 1, crystallographic and solution IR spectroscopic studies were carried out on a series of para-substituted benzoyl azides. The reaction obeys the Hammett equation. The large positive value of the reaction constant indicates that the azides act as electrophiles in the reaction studied. The enhanced reactivity of 2-nitrobenzoyl azide has been attributed to a decreased conjugation of the phenyl and carbonyl moieties in this reagent.