Optically active zwitterionic lambda(5)Si,lambda(5)Si'-disilicates: syntheses, crystal structures, and behavior in aqueous solution

The zwitterionic lambda(5)Si,lambda(5)Si'-disilicates 1-8 were synthesized and characterized by solid-state and solution NMR spectroscopy. In addition, compounds 26 H(2)O, 32 CH(3)CN, 45/2 CH(3)CN, 6CH(3)OH, 7, and 8CH(3)OHCH(3)CN were studied by single-crystal X-ray diffraction. The optically active (Delta,Delta,R,R,R,R)-configured compounds 1-8 contain two pentacoordinate (formally negatively charged) silicon atoms and two tetracoordinate (formally positively charged) nitrogen atoms. One (ammonio)alkyl group is bound to each of the two silicon centers, and two tetradentate (R,R)-tartrato(4-) ligands bridge the silicon atoms. Although these lambda(5)Si,lambda(5)Si'-disilicates contain SiO(4)C skeletons, some of them display a remarkable stability in aqueous solution as shown by NMR spectroscopy and ESI mass spectrometry.     

Dianionic complexes with hexacoordinate silicon(IV) or germanium(IV) and three bidentate ligands of the hydroximato(2-) type: syntheses and structural characterization in the solid state

Reaction of Si(OMe)(4) with acetohydroxamic acid or benzohydroxamic acid and HNMe(2) (molar ratio 1:3:2) in MeCN yielded dimethylammonium fac-tris[acetohydroximato(2-)]silicate (fac-5) and N,N-dimethylacetamidinium fac-tris[benzohydroximato(2-)]silicate (fac-8), respectively. Reaction of Si(OMe)(4) with benzohydroxamic acid and HNMe(2) (molar ratio 1:3:2) or ethane-1,2-diamine (molar ratio 1:3:1) in MeOH gave dimethylammonium fac-tris[benzohydroximato(2-)]silicate-methanol (fac-6.MeOH) and ethane-1,2-diammonium mer-tris[benzohydroximato(2-)]silicate-dimethanol (mer-9.2MeOH), respectively. Reaction of Ge(OMe)(4) with benzohydroxamic acid and HNMe(2) (molar ratio 1:3:2) in MeOH resulted in the formation of dimethylammonium fac-tris[benzohydroximato(2-)]germanate-methanol (fac-7.MeOH). Single-crystal X-ray diffraction studies showed that the Si(Ge)-coordination polyhedra of the racemic hexacoordinate silicon (germanium) compounds fac-5, fac-6.MeOH, fac-7.MeOH, fac-8, and mer-9.2MeOH are distorted octahedra. All compounds were additionally characterized by solid-state VACP/MAS NMR studies ((13)C, (15)N, (29)Si). The structural investigations were complemented by computational studies of the dianions of fac-5 and mer-5.     

Spirocyclic zwitterionic lambda5Si-silicates with two bidentate ligands derived from alpha-amino acids or alpha-hydroxycarboxylic acids: synthesis, structure, and stereodynamics

A series of zwitterionic lambda(5)Si-silicates with a (2,2,6,6-tetramethylpiperidinio)methyl group and two identical bidentate ligands derived from glycine, (S)-alanine, (S)-phenylalanine, glycolic acid, (S)-lactic acid, (S)-3-phenyllactic acid, or (S)-mandelic acid were synthesized and structurally characterized (solution and solid-state NMR spectroscopy; single-crystal X-ray diffraction). The chiral lambda(5)Si-silicates with ligands derived from optically active alpha-amino acids or alpha-hydroxycarboxylic acids were isolated as enantiomerically and diastereomerically pure compounds that undergo a (Lambda)/(Delta)-epimerization in solution.     

Spectroscopic and structural characterization of the CyNHC adduct of B2pin2 in solution and in the solid state

The Lewis base adduct of B(2)pin(2) and the NHC (1,3-bis(cyclohexyl)imidazol-2-ylidene), which was proposed to act as a source of nucleophilic boryl groups in the β-borylation of α,β-unsaturated ketones, has been isolated, and its solid state structure and solution behavior was studied. In solution, the binding is weak, and NMR spectroscopy reveals a rapid exchange of the NHC between the two boron centers. DFT calculations reveal that the exchange involves dissociation and reassociation of NHC rather than an intramolecular process.     

VO(ReO4)2: solid state and structural chemistry

VO(ReO₄)₂ was prepared by an oxido-reduction reaction between V₂O₅ and ReO₃ oxides at 700°C. It appears as green micro-crystalline powder and single crystals. It crystallizes in the orthorhombic system, space group Cmc2₁, with cell parameters a=5.7110(4), b=14.699(1), c=8.8230(4) Å and four formula units in the cell. The structure investigation provided the formula supported by a low R value of 0.038 from 1094 independent hkl reflections. The presence of V+IV is confirmed by magnetic measurement, but clearly enlightened by the structural features with the presence of a VO²⁺ vanadyl group. Re(VII) occupy two independent tetrahedra sharing corners with the VO₅ square pyramid forming infinite [VO(ReO₄)₂]_n ribbons along the [100] direction. These ribbons are linked together by a sixth longer VO interaction (2.29 Å), thus building a distorted VO₆ octahedron and defining layers parallel to (021) plane. The layers are held together by a Van der Waals interaction. VO(ReO₄)₂ is obviously the right formula of the early reported phase ‘V₂Re₂O₁₁’, the chemistry and structural determination being revisited.     

Manganese(I) poly(mercaptoimidazolyl)borate complexes: spectroscopic and structural characterization of Mn...H-B interactions in solution and in the solid state

The manganese(I) tricarbonyl complexes (Bm(R))Mn(CO)3(R = Me, Bz, But, p-Tol) and (PhBmMe)Mn(CO)3, the first bis(mercaptoimidazolyl)borate derivatives for this metal, have been readily prepared and fully characterized. In particular, the presence of three-center-two-electron Mn...H-B interactions in these species, both in solution and in the solid state, has been investigated using a combination of IR and NMR spectroscopies and, in the case of the methyl-, tert-butyl- and para-tolyl-substituted derivatives, by X-ray crystallography. To complement these synthetic and structural studies, the tris(mercaptoimidazolyl)borate complexes (TmMe)Mn(CO)3(R = Me, Bz, But, p-Tol) and (PhTm(Me))Mn(CO)3, as well as the related pyrazolylbis(mercaptoimidazolyl)borate (pzBmMe)Mn(CO)3, have also been synthesized and characterized by a combination of analytical and spectroscopic techniques.     

Synthesis and structural characterization of lanthanide(III) nitrate complexes of a tetraiminodiphenol macrocycle in the solid state and in solution

The lanthanide(III) complexes [Ln(LH2)(NO3)3] 1-11(La-Er), 15(Y) and [Ln(LH2)(NO3)2(H2O)](NO3) 12-14 (Tm-Lu) of the tetraiminodiphenolate macrocycle L2- have been prepared by the transmetallation reaction between [Pb(LH2)(NO3)2] and Ln(NO3)3.nH2O. In these compounds, the uncoordinated imino nitrogens are protonated and are hydrogen bonded to the phenolate oxygens. The X-ray crystal structures of the La (1), Ho (10) and Lu (14) compounds have been determined. Compounds 1 and 10, in which all the three nitrates are bound in bidentate fashion, are isostructural with distorted bicapped square antiprism geometry for the metal centre. In [Lu(LH2)(NO3)2(H2O)](NO3) 14, of the two metal bound nitrates one is bidentate and the other is unidentate, while the metal centre obtains a distorted square antiprism coordination environment. Proton NMR spectra of the paramagnetic lanthanide complexes have been studied in detail. Contributions of contact and pseudo-contact shifts to the lanthanide induced isotropic shifts (LIS) of the macrocycle protons have been separated and good agreement has been obtained between the calculated LIS values and the experimentally observed values. Analysis of the NMR data has led us to conclude that all the complexes in dimethyl sulfoxide solution attain similar configurations. The absorption and emission spectral characteristic of several compounds have been investigated. The complexes of samarium (5) and europium (6) on photoexcitation at 400 nm exhibit well-resolved luminescence spectra at 77 K both in the solid state and a methanol-ethanol (1 : 4) glassy matrix. For the terbium (8) and dysprosium (9) complexes, however, the observed luminescence peaks are less resolved and weak in intensity.     

Cyclodextrin solubilization of celecoxib: solid and solution state characterization

The low aqueous solubility of celecoxib (CCB) hampers its oral bioavailability and permeation from aqueous environment through biological membranes. The aim of this study was to enhance the aqueous solubility of CCB by complexation with cyclodextrin (CD) in the presence of water-soluble polymer. The effects of different CDs (αCD, βCD, γCD, 2-hydroxypropyl-β-cyclodextrin and randomly methylated β-cyclodextrin (RMβCD)) and mucoadhesive, water-soluble polymers (hydroxypropyl methylcellulose (HPMC), chitosan and hyaluronic acid) were investigated. The phase solubility profiles and CCB/CD complex characteristics were determined. RMβCD exhibited the greatest solubilizing effect of the two CDs tested. However, γCD was also selected for further investigations due to its safety profile. Addition of polymer to the aqueous CD solutions enhanced the CD solubilization. Formation of CCB/RMβCD/HPMC and CCB/γCD/HPMC ternary complexes resulted in 11 and 19-fold enhancement in the apparent complexation efficiency in comparison to their CCB/CD binary complex, respectively. The size of ternary complex aggregates in solution were determined to be from about 250 to about 350 nm. The data obtained from Fourier transform infra-red, differential scanning calorimetry and powder X-ray diffraction indicated presence of CCB/CD inclusion complexes in the solid state. Proton nuclear magnetic resonance data demonstrated that CCB was partially and totally inserted into the hydrophobic central cavities of RMβCD and γCD.     

Synthesis of stannic(IV) complexes: Their structural elucidation in solid and solution state and antimicrobial activity

A series of organotin(IV) thiocarboxylates have been synthesized with the general formula R₂SnL₂ and R₃SnL (R = Ph₂(I), Me₃(II), n‐Bu₃(III), Ph₃(IV), Cy₃(V), Me₂(VI), n‐Bu₂(VII), and L = piperidine‐1‐thiocarboxylic acid) in anhydrous toluene under the reflux conditions. The complexes were characterized by microanalysis, IR, ¹H and ¹³C NMR, mass spectrometry, and XRD. NMR data revealed that thiocarboxylic acid acts as bidentate, and complexes exhibit the four‐coordinated geometry in solution state. In solid state, diorganotin complexes exhibit the hexa‐coordinated geometry whereas the triorganotin(IV) compounds show the five‐coordinated geometry. These complexes were also tested for their antimicrobial activity along with the ligand against different animals, plant pathogens, and Artemia salina. All complexes with few exceptions show high activity as compared to the ligand. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:664–674, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20380     

Four triarylantimony(V) carboxylates: syntheses,structural characterization and in vitro cytotoxicities

Four new organoantimony carboxylates, (R–COO)₂SbR′₃ [R–COOH = (±)-2-phenoxypropionic acid and R′ = phenyl (1), 4-fluorophenyl (2), 3-fluorophenyl (3), 3,4,5-trifluorophenyl (4)], were synthesized and structurally characterized by elemental analysis, ¹H, ¹³C NMR, IR and X-ray single crystal diffraction. Structural analyses reveal that 1–3 show similar five-coordinate trigonal bipyramidal geometries, binding with three aryl groups and two deprotonated unidentate ligands. Unexpectedly, 4 exhibits pentagonal bipyramidal arrangement accompanied by two Sb–O (carbonyl) coordination bonds. In vitro cytotoxic activities of 1–4 have been determined by the MTT method against four cancer cell lines. Studies reveal that 1–4 have an activity similar to cisplatin on lung cancer cell line A549 and but also exhibit excellent cytotoxicity against cisplatin-insensitive colon cancer cell lines HCT-116, Caco-2 and human promyelocytic leukemia cell line HL-60. Additionally, the results showed that most of these triarylantimony(V) complexes exhibited enhanced cytotoxicity compared with the ligand and four triarylantimony dichloride precursors, which clearly implied a positive synergistic effect. Also interestingly, it was found that 3- or 4- mono-fluoro-substituted triphenylantimony, compounds 2 and 3, exhibit higher in vitro cytotoxicities toward the four cancer cell lines than the tri-3,4,5-trifluoro-substituted and without-fluoro-substituted triphenylantimony complexes. The structure-activity relationship of the cytotoxicity of 1–4 is discussed.     

The tautomerism of 1H-pyrazole-3(5)-(N-tert-butyl)carboxamide in the solid state and in solution

The X-ray crystal structure of 1H-pyrazole-3-(N-tert-butyl)-carboxamide was determined. In the solid state, the 13C and 15N CP/MAS NMR spectra correspond to this tautomer. In solution, both tautomers are present in a ratio that depends on the temperature (at 293 K, 90% 3-substituted/10% 5-substituted). Some unusual 1H, 1H couplings involving the NH proton were observed. DFT (GIAO) calculations were carried out.     

Physicochemical characterization of terbinafine-cyclodextrin complexes in solution and in the solid state

Terbinafine (TB) is an allylamine derivative used as oral and topical antifungal agent. The physicochemical properties of the complexes between TB and different cyclodextrins (CDs): α-CD, β-CD, hydroxypropylβ-CD, methylβ-CD and γ-CD, have been studied in pH 12 aqueous solutions at 25 °C and in the solid state. Different phase solubility profiles of TB in the presence of CDs have been obtained: A_L type for TB with hydroxypropylβ-CD and γ-CD, A_P type for the complexes with methylβ-CD and α-CD, while a B_S profile was found for TB-β-CD. The apparent stability constants of the complexes were calculated at 25 °C from the phase solubility diagrams. The higher increase of TB solubility, up to 200-fold, together with the higher value of the stability constant were found for the complex with methylβ-CD. Solid systems of 1:1 drug:CD molar ratio were prepared and characterised using X-ray diffraction patterns, thermal analysis and FTIR spectroscopy. The coevaporation method can be considered the best method in preparing these solid complexes. The complexes of TB with natural CDs, except with α-CD, were crystalline, whereas the methyl and hydroxypropyl derivatives gave rise to amorphous phases. Dissolution rate studies have been performed with TB-β-CD and TB-HPβ-CD complexes, showing a positive influence of complexation on the drug dissolution.     

Vibrational spectra of alpha-amino acids in the zwitterionic state in aqueous solution and the solid state: DFT calculations and the influence of hydrogen bonding

The zwitterionic forms of the two simplest alpha-amino acids, glycine and l-alanine, in aqueous solution and the solid state have been modeled by DFT calculations. Calculations of the structures in the solid state, using PW91 or PBE functionals, are in good agreement with the reported crystal structures, and the vibrational spectra computed at the optimized geometries provide a good fit to the observed IR and Raman spectra in the solid state. DFT calculations of the structures and vibrational spectra of the zwitterions in aqueous solution at the B3-LYP/cc-pVDZ level were found to require both explicit and implicit solvation models. Explicit solvation was modeled by inclusion of five hydrogen-bonded water molecules attached to each of the five possible hydrogen-bonding sites in the zwitterion and the integration equation formalism polarizable continuum model (IEF-PCM) was employed, providing a satisfactory fit to observed IR and Raman spectra. Band assignments are reported in terms of potential-energy distributions, which differ in some respects to those previously reported for glycine and l-alanine.     

Np(V) carbonates in solid state and aqueous solution

The solubility of NaNpO₂CO₃(s) in 0.1M perchlorate solution at 25°C in equilibrium with 1.0% CO₂/N₂ atmosphere has been investigated as a function of pH/lg [CO₃ ^2-]. The solid phase was found hexagonal with a=1008.1±0.3 pm and c=991.1±0.2 pm. A solubility product of lg Ksp(NaNpO₂CO₃)=–10.22±0.02 and a formation constant of the first Np(V) carbonato species of lg ß₀₁ = 4.52±0.02 was evaluated. For the dicarbonato species an upper limit of lg lg ß₀₂ < 6.6 was derived. Comparison of the present data with solubility values of Np(V) in equilibrium with 0.03% CO₂ partial pressure gave evidence that carbonato species are prevailing in solutions at both 1% and 0.03% CO₂ partial pressures.     

Solid state NMR characterization of individual compounds and solid solutions formed in Sc(2)O(3)--V(2)O(5)--Nb(2)O(5)--Ta(2)O(5) system

In this study, (51)V, (45)Sc and (93)Nb MAS NMR combined with satellite transition spectroscopy analysis were used to characterize the complex solid mixtures: VNb(9(1-x))Ta(9x)O(25), ScNb((1-x))Ta(x)O(4) and ScNb(2(1-x))Ta(2x)VO(9) (x = 0, 0.3, 0.5, 0.7, 1.0). This led us to describe the structures of Sc and V sites. The conclusions were based on accurate values for (51)V quadrupole coupling and chemical shift tensors obtained with (51)V MAS NMR/SATRAS for VNb(9)O(25), VTa(9)O(25) and ScVO(4). The (45)Sc NMR parameters have been obtained for Sc(2)O(3), ScVO(4), ScNbO(4) and ScTaO(4). On the basis of (45)Sc NMR and data available from literature, the ranges of the (45)Sc chemical shift have been established for ScO(6) and ScO(8). The gradual change of the (45)Sc and (51)V NMR parameters with x confirms the formation of solid solutions in the process of synthesis of VNb(9(1-x))Ta(9x)O(25) and ScNb((1-x))Ta(x)O(4), in contrast to ScNb(2(1-x))Ta(2x)VO(9). The cation sublattice of ScNb((1-x))Ta(x)O(4) is found to be in octahedral coordination. The V sites in VNb(9(1-x))Ta(9x)O(25) are present in the form of slightly distorted tetrahedra. The (93)Nb NMR parameters have been obtained for VNb(9)O(25).     

Zinc(II) and mercury(II) complexes with Schiff bases: syntheses,spectral, and structural characterization

Schiff bases o-vanilidene-1-aminobenzene (HL¹) and o-vanilidene-2-methyl-1-aminobenzene (HL²) lead to the formation of mono- and bis-[(Cl)Zn(L¹)] (1), [(Cl)Zn(L²)] (2), [(Cl)Hg(L¹)] (3), [(Cl)Hg(L²)] (4), [Zn(L¹)₂] (5), [Zn(L²)₂] (6), [Hg(L¹)₂] (7), and [Hg(L²)₂] (8) complexes by reactions of zinc(II) and mercury(II) chlorides in different mole ratio(s). Complexes 1–8 have been characterized by elemental analyses (Zn, Hg, C, H, Cl, and N), melting point and spectral (IR, ¹H-NMR), PXRD, molar conductivity measurement, and TGA. Conductivity measurements suggest non-electrolytes. Structural compositions have been assigned by mass spectral studies. Four-coordinate geometry may be assigned to these complexes tentatively. Structural study reveals that in 1–4 two metal centers are held together by two bridged (μ₂-Cl) chlorides, whereas 5–8 contain two bidentate Schiff-base ligands around one metal-producing monomers.     

Nickel(II) and copper(II) complexes of 5-o-tolyl-[1,3,4]-oxadiazole-2-thione and ethylenediamine: syntheses,spectral, and structural characterization

The reaction of potassium [N′-(2-methyl-benzoyl)-hydrazinecarbodithioate [K⁺(H₂L)^?] with metal acetate yielded M(H₂L)₂ (M = Ni, Cu), which on reaction with excess ethylenediamine (en) formed mononuclear mixed ligand complexes [Ni(en)₂(tot)₂] (1) and [Cu(en)₂](tot)₂ (2). The complexes have been characterized by elemental analyses, IR, magnetic susceptibility, and electronic spectral studies. Molecular structures of [Ni(en)₂(tot)₂] (1) and [Cu(en)₂](tot)₂ (2) showed 5-(o-tolyl)-[1,3,4]-oxadiazole-2-thione coordinated through oxadiazole nitrogen in 1 and ionically bonded via thiol sulfur in 2.