Synthesis and reactivity of diphosphino Pt(II) silanolate complexes as molecular models of the interaction of platinum particles with silica

A series of di- and monosubstituted cis-platinum(II) silanolate complexes, Pt(OSiR₃)₂(dppe) (R=Et, 1; R=Me, 2) and Pt(OSiR₃)Cl(dppe) (R=Et, 3; R=ⁱPr, 4) where dppe is 1,2-bis(diphenylphosphino)ethane, have been isolated and characterised spectroscopically. Complex 1 does not react with CO and H₂ under anhydrous conditions, but the complexes Pt{C(O)OCH₃)}₂(dppe) (6) and Pt(CO₃)(dppe) (7) have been isolated bubbling CO in methanol and CO₂ in moist benzene solutions of 1, respectively. The behaviour of 1 towards water or methanol is discussed on the basis of ¹H, and ³¹P{¹H} NMR spectroscopic data. The new complex Pt{S₂C(OSiEt₃)₂}(dppe) (8) has been isolated by reaction of 1 with CS₂ in benzene solution. This reactivity would suggest a high sensitivity towards water, but not towards H₂ or CO, of the bonding of slightly oxidised platinum particles with silanol groups of silica surface.     

Effect of temperature on gas composition and char structural features of pyrolyzed agricultural residues

The gases and chars produced during fast pyrolysis of maize stalk, rice straw, cotton straw and rice husk at temperatures ranging from 600 to 1000 °C were studied by Fourier transform infrared spectroscopy, non-dispersive infrared technique, thermal conductivity detection method, ultimate analysis, X-ray diffraction, helium density measurement and N₂ adsorption method. The gas yield increased by more than 80% from 600 to 1000 °C, while the char and liquid yield decreased. The content of CO₂, CO and CH₄ accounted for more than 86%. The CO and CH₄ content increased with temperature, while the CO₂ content decreased. The hydroxyl, aliphatic CH, carbonyl, olefinic CC and ether groups were lost above 800 °C. Carbon skeleton shrinkage increased by more than 23% when the temperature increased from 600 to 1000 °C. Maximum porosity appeared at 900 °C. This study revealed the relationships between gas composition/char properties and pyrolysis temperature under high heating rate conditions.     

Influence of manure types and pyrolysis conditions on the oxidation behavior of manure char

Livestock manure can be quickly converted into valuable products (H₂, syn-gas and char) by low temperature gasification. Manure char combustion offers energy for the gasification reactions. In the paper, the influence of manure type and pyrolysis conditions on manure char reactivity is addressed. The results show that the oxidation behaviors of manure char are dependent strongly on manure type and pyrolysis conditions employed. The large difference between the oxidation behaviors of pig and hen manure chars can be attributed to the difference in the organic materials and minerals of the samples. High final temperature, flash pyrolysis and water steam atmosphere used for char preparation promote the resultant char reactivity.     

The molecular path to inorganic materials - Zinc oxide and beyond

In the current article, we present a concept for the synthesis of complex nanoscaled materials. The synthetic strategy involves a stepwise assembly of materials starting from special molecular precursors possessing multiple information. Therefore, the article focuses on a strong pervasion of inorganic materials chemistry, solid-state chemistry and molecular chemistry. The concept introduced is finally highlighted by examples from our current research in the field of zinc oxide materials.     

Stability, molecular structures and magnetic properties of dinuclear iron complexes supported by benzoic hydrazide derivative ligands

We report experimental evidences including molecular solid-state structure determinations, magnetic measurements and EPR studies for the formation (in the solid-state) of novel dinuclear (μ-OMe)₂(L)₄ complexes (HL are 2-ylidenhydrazidebenzoic-1,3-dithiolane acid and N′-cyclopentylidene-2-hydroxybenzohydrazide). The two novel dinuclear iron compounds described in the present contribution exhibit antiferromagnetic intra-molecular coupling. Crystal structures of the supporting ligands as well as one mononuclear species have also been determined.     

Electrochemical and spectroscopic characterization of new cobalt(II) complexes. Catalytic activity in oxidation reactions by molecular oxygen

The synthesis and characterization of some new complexes with tetradentate Schiff bases derived from bis(salicylaldehyde)etylenediimine, H₂Salen are reported in this paper. The Co(II) Schiff bases complexes investigated are: (bis(5-nitro-salicylaldehyde) ethylenediiminato)cobalt(II), (CoNSalen); (bis(-ethyl-salicylaldehyde) ethylenediiminato)cobalt(II) (CoEtSalen); (bis(-ethyl-3,5-diiode-salicylaldehyde) ethylenediiminato) cobalt(II),(CoDIEtSalen); (bis(,5-dimethyl-3-iode-salicylaldehyde)ethylenediiminato)cobalt(II) (CoDMISalen) and (bis(salicylaldehyde)methylene-p,p′-diphenylene)cobalt(II), (CoSalmbfn). The characterization of the complexes was performed by elemental analysis, UV–Vis, FTIR spectroscopy, powder X-ray diffraction and cyclic voltammetry. Pyridine (py), present in the solution of complexes in DMF, coordinates to the metal ion in axial position, inducing a significant decrease of the redox potentials. Significant influences have the substituents grafted on ligands’ molecules. The separated complexes evince catalytic activity in the oxidation reaction of 2,6-di-t-butylphenol with molecular oxygen. These complexes seem capable of forming reversible adducts with molecular oxygen.     

Saccharinate-metal complexes with 1,10-phenanthroline (phen) or 2,2′-bipyridine (bipy) as co-ligands; the synthesis, crystal and molecular structures of five new compounds of divalent metals

Five new saccharinate complexes of divalent metals with either phen or bipy as co-ligands have been synthesised, and fully characterised by single crystal X-ray diffraction at low temperature. The complexes [M(phen)₂(H₂O)₂](sac)₂·H₂O (M = Co or Zn) are isostructural, while [Hg(bipy)₂(sac)₂] is isostructural with the analogous cadmium(II) compound, which has been described previously in the literature. Cadmium(II) complex [Cd(phen)₂(sac)(H₂O)](sac).H₂O has an octahedral cation with the unidentate ligands in cis-positions, while [Hg(phen)₂(sac)](sac)·2.5 H₂O provides a rare example of a distorted tbp structure for the cation, with five nitrogen donors. The structures are compared with those of related saccharinate complexes. In general, the more sterically demanding phen, when compared with bipy, forces more of the saccharinate anions to be uncoordinated, and for smaller ligands such as H₂O to be coordinated to the metal, despite the electrostatic attraction between the positively charged metal and the anion. Intramolecular hydrogen bonding involving saccharinate groups plays an important role in all the hydrated complexes.     

Substitution reaction mechanisms of dihydrido-ruthenium(II) phosphine complexes: hydribe basicity and molecular hydrogen intermediates

Kinetic and activation parameter data for the reactions of cct-Ru(H)₂(CO)₂(PPh₃)₂ (1) (cct = cis, cis, trans) in THF with thiols, CO and PPh₃ to give cct-RuH(SR)(CO)₂(PPh₃)₂, Ru(CO)₃(PPh₃)₂ and Ru(CO)₂(PPh₃)₂, respectively, reveal a common, rate-determining step, the initial dissociation of H₂ from 1; the activated complex probably resembles the corresponding Ru(η²-H₂) species. Reaction of Ru(H)₂(dppm)₂ (2) (as a cis/trans mixture, DPPM = bis(diphenylphosphino)methane) with thiols initially generated cis- and trans- RuH(SR) (dppm)₂ with a rate that depends on both the type and concentration of thiol. The higher basicity of the hydride ligands in 2 (versus 1), which is demonstrated by deuterium exchange with CD₃OD, gives rise in the thiol reaction to an initial protonation step prior to loss of H₂. A species detected in the thiol reaction is possibly [RuH(η²-H₂ (dppm)₂]², the anticipated intermediate for this reaction and for the hydrogen exchange with alcohol. A longer reaction of 2 with PhCH₂SH gives solely cis-Ru(SCH₂Ph)₂(dppm)₂.     

Factors affecting nucleolytic efficiency of some ternary metal complexes with DNA binding and recognition domains. Crystal and molecular structure of Zn(phen)(edda)

The binding selectivity of the M(phen)(edda) (M = Cu, Co, Ni, Zn; phen = 1,10-phenanthroline, edda = ethylenediaminediacetic acid) complexes towards ds(CG)₆, ds(AT)₆ and ds(CGCGAATTCGCG) B-form oligonucleotide duplexes were studied by CD spectroscopy and molecular modeling. The binding mode is intercalation and there is selectivity towards AT-sequence and stacking preference for A/A parallel or diagonal adjacent base steps in their intercalation. The nucleolytic properties of these complexes were investigated and the factors affecting the extent of cleavage were determined to be: concentration of complex, the nature of metal(II) ion, type of buffer, pH of buffer, incubation time, incubation temperature, and the presence of hydrogen peroxide or ascorbic acid as exogenous reagents. The fluorescence property of these complexes and its origin were also investigated. The crystal structure of the Zn(phen)(edda) complex is reported in which the zinc atom displays a distorted trans-N₄O₂ octahedral geometry; the crystal packing features double layers of complex molecules held together by extensive hydrogen bonding that inter-digitate with adjacent double layers via π…π interactions between 1,10-phenanthroline residues. The structure is compared with that of the recently described copper(II) analogue and, with the latter, included in molecular modeling.     

Supramolecular recognition: association of palladium molecular clefts with planar platinum complexes

The crystal structures of two new molecular recognition adducts formed between a dicationic, di-terpyridyl-Pd-Cl molecular cleft and two square planar platinum complexes are reported. In both structures, the planar platinum-containing guests are located within the molecular cleft formed by the two parallel disposed terpyridyl-Pd-Cl⁺ units of the receptor. The crystal structure of the adduct formed between the molecular cleft and a neutral platinum complex has interplanar distances between the host and guest of 3.24 Å, a distance shorter than that usually ascribed to π-stacking interaction (∼3.45 Å). The short distance is likely the result of metal-metal interaction between the host and guest. The second adduct, that between the dicationic molecular receptor and an anionic platinum complex, also bears the guest within the molecular cleft. The interplanar distances between the cationic terpyridyl-Pd-Cl units of the host and the anionic guest (3.21 and 3.29 Å) are also shorter than typical π-stacking distances but no metal-metal interaction is present. Coulombic attraction between the host and guest is believed to be responsible for the short interplanar separation. These data are discussed in relation to analogous systems that associate through π-π and metal-metal interaction.     

Molecular modeling studies of the intramolecular twist mechanisms of racemization for tris chelate complexes

The preferred mechanisms of racemization for three tris chelate complexes, Co(acac)₃, Fe(phen)₃ ³⁺ and Fe[S₂CN(CH₂)₄]₃, were investigated by molecular modeling. The transition states for both a Bailar twist and a Rây-Dutt twist were considered; semi-empirical calculations (PM3) yielded activation energies. The preferred mechanism was the Bailar twist for Co(acac)₃ and Fe[S₂CN(CH₂)₄]₃ with activation energies of 83.2 and 7.3 kcal mol⁻¹, respectively, and the Rây-Dutt twist for Fe(phen)₃ ³⁺ with an activation energy of 114.4 kcal mol⁻¹. These results are compared with those of geometrical models.     

A click procedure with heterogeneous copper to tether technetium-99m chelating agents and rhenium complexes. Evaluation of the chelating properties and biodistribution of the new radiolabelled glucose conjugates

An efficient protocol was developed to tether chelating agents and rhenium complexes onto a glucoside scaffold with a heterogeneous copper catalyst via click chemistry. The supported catalyst avoids the formation of unwanted copper complexes during the cyclisation step. The possibility to graft a pre-chelated M(CO)₃ core by click chemistry onto a biomolecule was highlighted for the first time. ^99mTc(CO)₃-glucoconjugates displayed excellent in vitro stability, a fast in vivo blood clearance and a low specific organ uptake or long-term retention in spleen and stomach.     

Alpha-glucosidase inhibitory effect of anti-diabetic metal ions and their complexes

We found alpha-glucosidase inhibitory (α-GI) effect of metal ions and their complexes which showed the high blood glucose lowering effect in diabetic model animals. The Cu(II) ion and its complexes showed strong α-GI activity greater than clinically used acarbose in in vitro studies. Furthermore, in in vivo experiments, α-GI action was newly discovered in normal ddy mice. These results suggested that one of action mechanisms of the anti-diabetic metal ions and complexes is related to the α-GI effects.     

Metal complexes of modified cyclen as catalysts for hydrolytic restriction of plasmid DNA

Simple and novel nuclease models have been synthesized. These involve metal-binding ligand 1,4,7,10-tetraazlcyclododecane (cyclen) tethered to an acridine ring (a DNA-binding group) by amide linkers of various lengths. Binding of these probes to DNA was studied by monitoring changes in their UV-visible spectra affected by the presence of DNA. Titration of these compounds with increasing amounts of pBR322 DNA caused hypochromic effects and shifted the acridine absorption at 360 nm to a longer wavelength. Under biologically relevant conditions (37 °C and pH 7.4), specific transition metal complexes of these compounds are found to be highly effective catalysts toward the hydrolysis of plasmid DNA. This is demonstrated by their ability to convert the super-coiled DNA (form I) to open-circular DNA (form II). Structure-activity correlation studies show that hydrolytic activity depends on both the structure of ligand (L₁ > L₂ > L₃) and the nature of metal ion cofactor (Co³⁺ > Zn²⁺ > Cr²⁺ > Ni²⁺ > Cu²⁺ > Fe³⁺).     

Synthesis, characterization, and distortion properties of vanadyl complexes of octaphenylporphyrin and dodecaphenylporphyrin

In order to investigate the influence of ligand distortion on metal centers of porphyrin complexes, distorted vanadyl porphyrin complexes, VO(OPP) (OPP = 2,3,5,10,12,13,15,20-octaphenylporphinato) and VO(DPP) (DPP = 2,3,5,7,8,10,12,13,15,17,18,20-dodecaphenylporphinato), have been prepared. In the crystal structures, VO(OPP) and VO(DPP) had a ruffled structure and a saddle-shaped structure, respectively. In addition, these complexes exhibited red shift and broadening of the absorption bands in the UV-Vis spectra and significant negative shifts of oxidation potentials of the porphyrin ligands in the cyclic voltammograms compared with those of the planar VO(TPP) (TPP = tetraphenylporphinato). These results indicate that the OPP and DPP complexes have the distorted structures both in solids and in solutions. The VO bond characters of VO(TPP), VO(OPP), and VO(DPP) do not show the significant difference in their crystal structures and resonance Raman spectra. This suggests that the distortion of porphyrin ligand little affects the Lewis acidity of the metal center. The non-planar porphyrin distortion gives the change of HOMO-LUMO gap.     

Imidazole-based nickel(II) and cobalt(II) coordination complexes for potential use as models for histidine containing metalloproteins

It has been established that small molecule model complexes have been useful in studying more complex biological systems of metalloproteins. Because many metalloproteins have active sites that contain multiple histidine residues bound to a metal center, a series of imidazole-containing scorpionate ligands and the associated Co and Ni complexes have been developed to investigate the bonding parameters of histidine containing active sites. The tris(2-imidazolyl) carbinol (2-TIC, 6) and tris[2-(N-methylimidazolyl)] carbinol (2-^MeTIC, 7) complexes of Ni²⁺ and Co²⁺, namely [Co(2-^MeTIC)₂]Cl₂ (8), [Co(2-^MeTIC)₂](NO₃)₂ (9), [Ni(2-^MeTIC)₂]Cl₂ (10), [Ni(2-^MeTIC)₂](NO₃)₂ (11), [Co(2-TIC)₂](NO₃)₂ (12), and [Ni(2-TIC)₂](NO₃)₂ (13), have been prepared from the reaction of the appropriate ligand and appropriate metal salt in polar solvent. These complexes have been characterized by single crystal X-ray diffraction, spectroscopic techniques, and magnetic susceptibility. In each solid-state structure the metal center in the cation coordinates to three N atoms from two ligands and adopts a pseudo-octahedral coordination geometry. The X-ray characterization of tris[2-(N-methylimidazolyl)] carbinol is also reported.     

Coordination complexes as molecular glue for immobilization of antibodies on cyclic olefin copolymer surfaces

A novel metal-based chelating method has been used to provide an order of magnitude increase in immunoassay performance on cyclic olefin copolymer (COC) plastics compared with passive binding. COCs are hydrophobic, and without surface modification they are often unsuitable for applications where protein adhesion is desired. When interacting with the bare plastic, the majority of the bound proteins will be denatured and become nonfunctional. Many of the surface modification techniques reported to date require costly equipment setup or the use of harsh reaction conditions. Here, we have successfully demonstrated the use of a simple and quick metal chelation method to increase the sensitivity, activity, and efficiency of protein binding to COC surfaces. A detailed analysis of the COC surfaces after activation with the metal complexes is presented, and the immunoassay performance was studied using three different antibody pairs.     

The synthesis, crystal and molecular structures of two saccharinate-metal complexes with dipyridylamine (dipyr) as a co-ligand

The complexes [Cd(dipyr)₂(sac)(H₂O)] sac·H₂O 1 and [Hg(dipyr)(sac)₂] 2, where dipyr = dipyridylamine and sac = saccharinate, have been synthesised, and fully characterised by single-crystal X-ray diffraction at 120 K. The geometry around Cd in 1 is approximately octahedral, with the metal coordinated by two bidentate dipyr ligands, one N-bonded sac and one H₂O molecule; the second sac forms the counter-ion, and there is also a water of crystallisation. An extensive H-bonded network is formed. In the anhydrous Hg complex 2, the metal has approximately tetrahedral geometry, with coordination from a bidentate dipyr ligand and two N-bonded sac groups. H-bonding interactions are again extensive, even without the presence of H₂O molecules in the structure, leading to chains along the a-axis.     

Synthesis, immobilization and catalytic activity of some silylated cyclopentadienyl rhodium(I) complexes

The mixture of isomers of silylated cyclopentadiene derivative C₅H₅CH₂CH₂Si(OMe)₃ (1) has been used for the syntheses of the mononuclear Rh(I) complexes [η⁵-C₅H₄(CH₂)₂Si(OMe)₃]Rh(CO)₂ (3). [η⁵-C₅H₄(CH₂)₂Si(OMe)₃]Rh(COD) (4) and [η⁵-C₅H₄(CH₂)₂Si(OMe)₃]Rh(CO)(PPh₃) (5). Upon entrapment of 3–5 in silica sol-gel matrices, air stable, leach-proof and recyclable catalysts 6–8 resulted. Their catalytic activities in some hydrogenation processes were compared with those of the non-immobilized complexes 3–5, as well as with those of homogeneous and heterogenized non-silylated analogs, 9–14.     

Fluoro-hydrido-oxo and other fluoro-oxo complexes of rhenium (V) containing a triphosphine ligand

The fluoro-hydrido-oxo complex [Re(F)(H)(O)Cyttp]⁺ (3, Cyttp = PhP(CH₂CH₂CH₂PCy₂)₂) was prepared in high yield from [Re(H₂)H₄Cyttp]SbF₆ (1(SbF₆), NaSbF₆ and acetone in toluene at reflux. Reaction chemistry of 3 has been studied and, where appropriate, compared with that of the related dihydrido-oxo complex [ReH₂(O)Cyttp]⁺ (2). Unlike 2, which readily reacts with both CO and SO₂, 3 was found to be inert to these reagents under comparable conditions. However, 3(SbF₆) reacts with NaSbF₆ at elevated temperature to afford the difluoro-oxo complex [ReF₂(O)Cyttp]⁺ (4). 4 undergoes fluoride substitution by Cl⁻ or Br⁻ to yield [Re(X)(F)(O)Cyttp]⁺ (X = Cl (5, Br (6)). 5 can also be obtained by treatment of 6(BPh₄) with LiCl. All of these complexes contain mer-Cyttp, and 3–6 contain trans fluoride and oxide ligands as inferred from spectroscopic data.