Transition metal bonding functions and their applications in catalytic adsorptions and reactions: Part III. Effect of metal valence band and periodic trend of CO σ-π bonding functions on transition metals

Our model of metal valence band and our new concept of σ-π coordination are further discussed and confirmed in this paper.The infrared stretching frequencies of C-O decrease in the order 2056, 1886 and 1786 cm⁻¹ in Ni(CO)₄, Co(CO)₄⁻¹ and Fe(CO)₄⁻², which parallels the increase in d electron back-donation functions (B metal bonding functions) from 1.539, 2.121 to 2.895 on Ni, Co and Fe metals, respectively. On the other hand, the M-C bond orders increase from 1.33, 1.89 to 2.16 for Ni(CO)₄, Co(CO)₄⁻¹ and Fe(CO)₄⁻², which parallel the increase in A(CO5σ-Mσ)-B(CO2π-Mπ) metal bonding functions from 24.61, 30.01 to 33.19, respectively. They are in agreement with our new concept of σ-π coordination proposed in the previous paper. This new concept has also been used to analyze the mechanism of the formation of Ni(CO)₄, Co(CO)₄⁻¹ and Fe(CO)₄⁻², and to explain why they can automotively hybridize each other despite the energy differences between 3d and 4s, 4p, which are very large.The effects of metal valence bands have been accounted for on all transition metals (d¹ to d⁸), and it is demonstrated that d orbitals increase from the Vd band upward to the Vs band, and s orbitals from the Vs band downward to the Vd band, which is equivalent to a change in orbital potential, and would modify their orbital overlap integrals with the adsorbate M.O.s and the A, B metal bonding functions significantly. The effective potentials and the percentage s, d functions of Vs, Vd and d_occ bands are the most important factors for determining the effect of the metal valence band. The effects of promoter and support are also altered by changes in the above factors. For Group VIII metals, the valence band provides various s and d orbitals at various potentials, in which a certain number of s and d orbitals can match better with CO adsorbate M.O.s, which explains why CO adsorbed species on Group VIII metals are all stable and adsorption rates are all relatively rapid.The periodic trends of metal A, B, AB and D_c bonding functions depend on the structures of the metal valence band, i.e. the potential levels and s, d percentage functions of Vs, Vd and d_occ bands. For 4d and 5d metals, the potential levels of the Vs band are high, which cannot form a strong CO 5σ-M σ bond, but the potential levels of Vd band are higher and the width of the d band is wider than those of 3d metal, so their B bonding functions are larger, and they can be used to activate saturated and unsaturated hydrocarbons. In contrast, for 3d metals, the potentials of the Vs band are lower, which favour formation of strong CO 5σ-M σ and M-C bonds, i.e. their A and D_c bonding functions are larger, which can promote coke formation. While ABD_cD_o can be used to characterize CO dissociation, B/A can be used to characterize C-C formation.The characteristics of various metal bonding functions on each transition metal are useful for designing catalyst composition. A typical example has been illustrated, using the possibility to select non-noble metals instead of noble metals in hydrocarbon reactions.     

Synthesis of platinum complexes containing (+)-bornyl- and (−)-menthylammonium in the outer coordination sphere and their catalytic activity in hydrosilylation reactions

Optically active (+)-bornyl- and (−)-menthylammonium platinates were synthesized starting from H₂[PtCl₆] · 4H₂O and hydrochlorides of the corresponding amines. Catalytic activity of the complexes in the hydrosilylation reactions of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane with 1,1,3,3-tetramethyldisiloxane and acetophenone with diphenylsilane was studied. The addition of the siloxanes leads to a predominant formation of β-adduct. Activity of the catalysts, evaluated on the 50% conversion of the substrate, decreases in the following sequence: (−)-(menthylNH₃)₂[PtCl₆] > (Et₃NH)₂[PtCl₆] > (+)-(bornylNH₃)₂[PtCl₄] > (+)-(bornylNH₃)₂[PtCl₆]. Asymmetric induction is observed in the hydrosilylation of aceto-phenone in the presence of (+)-(bornylNH₃)₂[PtCl _n ] (n = 4, 6); (+)-(bornylNH₃)₂[PtCl₆] showed the highest catalytic activity and selectivity. The hydrosilylation of acetophenone gave 1-phenylethoxy(diphenyl)silane, 1-phenylvinyloxy(diphenyl)silane, and 2-phenylethyl-2-diphenylsiloxy(diphenyl)silane as the products. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 341–349, February, 2008.     

Transition metal chemistry of cyclodiphosphanes containing phosphine and amide-phosphine functionalities: formation of a stable dipalladium(II) complex containing a Pd-P σ-bond

Cyclodiphosphazanes containing phosphine or phosphine plus amide functionalities {((t)BuNP(OC(6)H(4)PPh(2)-o)}(2) (3), {(t)BuNP(OCH(2)CH(2)PPh(2))}(2) (4), {(t)BuHN((t)BuNP)(2)OC(6)H(4)PPh(2)-o} (5), and {(t)BuHN((t)BuNP)(2)OCH(2)CH(2)PPh(2)} (6) were synthesized by reacting cis-{(t)BuNPCl}(2) (1) and cis-[(t)BuHN((t)BuNP)(2)Cl] (2) with corresponding phosphine substituted nucleophiles. The reactions of 3 and 5 with excess of elemental sulfur or selenium produce the corresponding tetra and trichalcogenides, {((t)BuNP(E)(OC(6)H(4)P(E)Ph(2)-o)}(2) (7, E = S; 8, E = Se) and {(t)BuHN((t)BuNP)(2)OC(6)H(4)P(E)Ph(2)-o} (9, E = S; 10, E = Se), respectively, in quantitative yields. The reactions between 3 and [Rh(COD)Cl](2) or [M(COD)Cl](2) (M = Pd or Pt) afford bischelated complexes [Rh(CO)Cl{(t)BuNP(OC(6)H(4)PPh(2)-o)}](2) (11), and [MCl(2){(t)BuNP(OC(6)H(4)PPh(2)-o)}](2) (12, M = Pd; 13, M = Pt) in good yield. The 1 : 2 reaction between 3 and [PdCl(η(3)-C(3)H(5))](2) in dichloromethane resulted initially in the formation of a tripalladium complex of the type [Pd(3)Cl(4)(η(3)-C(3)H(5))(2){(t)BuNPOC(6)H(4)PPh(2)}(2)] (14a) which readily reacts with moisture to form an interesting binuclear complex, [Cl(2)Pd{μ-(PPh(2)C(6)H(4)OP(μ-(t)BuN)(2)P(O)}(μ-Cl)Pd(OC(6)H(4)PPh(2))] (14b). One of the palladium(II) atoms forms a simple six-membered chelate ring, whereas the other palladium(II) atom facilitates the moisture assisted cleavage of one of the endocyclic P-O bonds followed by the oxidation of P(III) to P(V) thus forming a Pd-P σ-bond. The broken ortho-phosphine substituted phenoxide ion forms a five-membered palladacycle with the same palladium(II) atom. Similar reaction of 5 with [PdCl(η(3)-C(3)H(5))](2) also affords a binuclear complex [{PdCl(η(3)-C(3)H(5))}(t)BuNH{(t)BuNP}(2)OC(6)H(4)PPh(2){PdCl(2)}] (15) containing a PdCl(2) moiety which forms a six-membered chelate ring via ring-phosphorus and PPh(2) moieties on one side and a PdCl(η(3)-C(3)H(5)) fragment coordinating to amide bound phosphorus atom on the other side of the ring. Treatment of 3 with four equivalents of AuCl(SMe(2)) produces a tetranuclear complex, [(AuCl)(4){(t)BuNP(OC(6)H(4)PPh(2))}(2)] (16), whereas a 1 : 3 reaction between 5 and AuCl(SMe(2)) leads to the formation of a trinuclear complex, [(t)BuNH{(t)BuNP(AuCl)}(2)OC(6)H(4)P(AuCl)Ph(2)] (17). The crystal structures of 3, 5, 9-11 and 13-17 are reported.     

Ortho-hydroxyphenylhydrazo-β-diketones: tautomery, coordination ability, and catalytic activity of their copper(II) complexes toward oxidation of cyclohexane and benzylic alcohols

New hydrazone o-HO-phenylhydrazo-β-diketones (OHADB), R(1)NHN═CR(2)R(3) [R(1) = HO-2-C(6)H(4), R(2) = R(3) = COMe (H(2)L(1), 1), R(2)R(3) = COCH(2)C(Me)(2)CH(2)CO (H(2)L(2), 2), R(2) = COMe, R(3) = COOEt (H(2)L(4), 4); R(1) = HO-2-O(2)N-4-C(6)H(3), R(2)R(3) = COCH(2)C(Me)(2)CH(2)CO (H(2)L(3), 3), R(2) = COMe, R(3) = COOEt (H(2)L(5), 5), R(2)R(3) = COMe (H(2)L(6), 6A)], and their Cu(II) complexes [Cu(2)(CH(3)OH)(2)(μ-L(1))(2)] 7, [Cu(2)(H(2)O)(2)(μ-L(2))(2)] 8, [Cu(H(2)O)(L(3))] 9, [Cu(2)(μ-L(4))(2)](n) 10, [Cu(H(2)O)(L(5))] 11, [Cu(2)(H(2)O)(2)(μ-L(6))(2)] 12A and [Cu(H(2)O)(2)(L(6))] 12B were synthesized and fully characterized, namely, by X-ray analysis (4, 5, 7-12B). Reaction of 6A, Cu(NO(3))(2) and ethylenediamine (en) leads, via Schiff-base condensation, to [Cu{H(2)NCH(2)CH(2)N═C(Me)C(COMe)═NNC(6)H(3)-2-O-4-NO(2)}] (13), and reactions of 12A and 12B with en give the Schiff-base polymer [Cu{H(2)NCH(2)CH(2)N═C(Me)C(COMe)═NNC(6)H(3)-2-O-4-NO(2)}](n) 14. The dependence of the OHADB tautomeric equilibria on temperature, electronic properties of functional groups, and solvent polarity was studied. The OHADB from unsymmetrical β-diketones exist in solution as a mixture of enol-azo and hydrazo tautomeric forms, while in the solid state all the free and coordinated OHADB crystallize in the hydrazo form. The relative stabilities of various tautomers were studied by density functional theory (DFT). 7-14 show catalytic activities for peroxidative oxidation (in MeCN/H(2)O) of cyclohexane to cyclohexanol and cyclohexanone, for selective aerobic oxidation of benzyl alcohols to benzaldehydes in aq. solution, mediated by TEMPO radical, under mild conditions and for the MW-assisted solvent-free synthesis of ketones from secondary alcohols with tert-butylhydroperoxide as oxidant.     

The first metals in Mendeleiev’s Table: Part II. A new argument against the placement of hydrogen atop the alkali metal column

Every so often an experiment trying to give reliable evidence for a metallic hydrogen solid is reported. Such evidence is, however, not too convincing. As Eric Scerri has recently reiterated, “the jury is still out on that issue” (Scerri 2012). This search stems from the common spectroscopy shared by the hydrogen atom and all the alkali metal atoms, and perhaps is guided by a desire to place hydrogen atop the alkali metals, in Mendeleiev’s Table, reinforced by the fact pointed out by Scerri (The Periodic Table, its story and its significance, Oxford University Press, Oxford, 2007, 2012) that there is no other obvious place for hydrogen in said Table. But H₂ is a light gas at room temperature, while Li, Na, K and the other alkali elements form solid metal crystals. At very low temperatures, of course, hydrogen solidifies, but it is formed by H₂ molecules (see for example, Van Kranendonk in Solid hydrogen, Plenum Press, New York, 1983). Our purpose here is to use a new argument to break this impasse: “should H be grouped with the alkali metals with which it shares a common spectroscopy, but which solidifies in a completely different fashion?” This argument has been proposed before in a couple of papers in this journal to establish a similar question for He and the alkaline earths (Novaro in Found Chem 10:4, 2008, Ramírez-Solís and Novaro in Found Chem, 2012), as is discussed in “Precedents” section.     

An updated review of metal–organic framework materials in photo(electro)catalytic applications: From CO2 reduction to wastewater treatments

This review summarizes recent advances in the development of metal–organic framework (MOF) materials, focusing on their photocatalytic and photoelectrocatalytic activities for different applications, such as CO₂ reduction, water splitting, elimination of inorganic contaminants, and degradation of organic pollutants. In each section, the first applications described focus on the photocatalysts developed using MOF materials. Meanwhile, the latest are centered on photoelectrode applications using these materials. The last advances in the synthesis process are discussed in terms of improvement in electron transfer and charge separation, which enhance the activity of the photo (electro)catalysts. Finally, some insights about the upcoming applications of MOF materials are provided.     

Syntheses and characterization of η-hexamethylbenzeneruthenium(II)-β-diketone complexes: their reactions with mono- and bidentate neutral ligands

The complex [(η⁶-C₆Me₆)Ru(μ-Cl)Cl]₂1 react with sodium salts of β-diketonato ligands in methanol to afford the oxygen bonded neutral complexes of the type [(η⁶-C₆Me₆)Ru(κ²-O,O′-R¹COCHCOR²)Cl] {R¹, R² = CH₃ (2), CH₃, C₆H₅ (3), C₆H₅ (4), OCH₃ (5), OC₂H₅ (6)}. Complex 4 with AgBF₄ yields the γ-carbon bonded ruthenium dimeric complex 7. Complex 4 also reacts with tertiary phosphines and bridging ligands to yield complexes of the type [(η⁶-C₆Me₆)Ru(κ²-O,O′-C₆H₅COCHCOC₆H₅)(L)]⁺ (L = PPh₃ (8), PMe₂Ph (9)) and [{η⁶-C₆Me₆)Ru(κ²-O,O′-C₆H₅COCHCOC₆H₅)}₂(μ-L)] L = 4,4′-bipyridine (4,4′-bipy) (11), 1,4-dicyanobenzene (DCB) (12) and pyrazine (Pz) (13). Complexes 2-4 react with sodium azide to yield neutral complexes [(η⁶-C₆Me₆)Ru(κ²-O,O′-R¹COCHCOR²)N₃] {R¹, R² = CH₃ (10a), CH₃, C₆H₅ (10b), C₆H₅ (10c). All these complexes were characterized by FT-IR and FT-NMR spectroscopy as well as analytical data. The molecular structures of complexes [(η⁶-C₆Me₆)Ru(κ²-O,O′CH₃COCH-COC₆H₅)Cl] (3) and [(η⁶-C₆Me₆)Ru(κ²-O,O′-C₆H₅COCHCOC₆H₅] (4) were established by single crystal X-ray diffraction studies. The complex 3 crystallizes in the triclinic space group, [a = 7.9517(4), b = 9.0582(4) and c = 14.2373(8) Å, α = 88.442(3)°, β = 76.6.8(3)° and γ = 81.715(3)°. V = 987.17(9) ų, Z = 2]. Complex 4 crystallizes in the monoclinic space group, P2₁/c [a = 7.5894(8), b = 20.708(2) and c = 29.208(3) Å,β = 92.059(3)° V = 4587.5(9) ų, Z = 8].     

Reactions of dl-homocystine and 3,3′-dithiodipropionic acid with Pd(II) in aqueous hydrochloric solutions. Part I: coordination model

Stoichiometry of Pd(II) interactions with dl-homocystine and 3,3′-dithiodipropionic acid were investigated spectrophotometrically in strong hydrochloric acidic media. It was established that thiolate and sulfinate complexes are products of a disulfide bond cleavage. It is shown that formation of S,S′-binuclear complexes is necessary for the disproportionation reaction. A multi-spectroscopic (UV-Vis, Raman, NMR, EXAFS) investigation on a disulfide bond state in organic disulfides in complexation processes with Pd(II) was developed. A DFT study on geometry of forming complex species was performed.     

Single-turn helix-coil strands stabilized by metal···metal and π-π interactions of the alkynylplatinum(II) terpyridyl moieties in meta-phenylene ethynylene foldamers

Dinuclear alkynylplatinum(II) terpyridyl complexes with oligomeric bridge consisting of five repeating meta-phenylene ethynylene (mPE) units have been found to exhibit a strong tendency to fold back onto themselves to form short helical strands through the stabilization of Pt···Pt and π-π interactions. The steric bulk of the terpyridine ligands and the length of the oligomeric bridge have been found to affect the extent of the intramolecular Pt···Pt interaction that governs the stabilization of the short helical strand in solution. Their folding properties via Pt···Pt and π-π stacking interactions have been studied by (1)H NMR, 2D ROESY NMR, electronic absorption, and emission spectroscopies.     

The metal complexes of heterocyclic β-diketones and their derivatives—VI. The synthesis,structure and i.r. spectral studies of some new metal(II) complexes of 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 (HPMBP)

The monovalent metal complex of Na and the divalent metal complexes of Be, Mn, Co, Ni, Cu, Zn, Mg, Ba, Hg and Pb with 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 (HPMBP), have been synthesized. It is shown that HPMBP behaves like a bidentate enol forming neutral metal chelates through the carbonyl and enolic hydroxyl groups. Characterization of the complexes were by means of elemental analyses, conductivity measurements, i.r. and proton NMR spectroscopy. The i.r. spectra were recorded between 4000 and 200 cm⁻¹ and assignments are proposed for the observed frequencies. Replacement of the methyl group of the 4-acetyl moiety by the phenyl group in the metal chelates of 1-phenyl-3-methyl-4-acetyl-pyrazolone-5 (HPMAP), is found to decrease the C

O, C

C and MO stretching frequencies of the chelate ring. The magnitudes of the MO stretching frequencies for the transition metals show good agreement with the Irving—Williams stability order Cu>Ni>Co>Zn>Mn.     

Synthesis,characterization, and catalytic activity of a new series of Ni(II), Cu(II), and Zn(II) complexes of N,N-O,O mixed-bidentate ligands for C–C cross-coupling reactions

Abstract

A new series of air stable transition metal(II) complexes [M(II)(L)(Phen)], [M(II)(L)(Pip)] (M?=?Ni, Cu, and Zn) (H₂L = 2,2′-methylenebis(4-nitrophenol)) (Phen =1,10-phenanthroline) (Pip?=?Piperazine) has been synthesized by incorporating the metal ion with bisphenol and 1,10-phenanthroline/piperazine ligands. The prepared metal complexes were characterized by FT-IR, UV–vis, ¹H NMR, EPR, and mass spectrometry. The metal(II) complexes were potent catalysts for Suzuki–Miyaura and Kumada–Corriu coupling of various aryl halides under optimized conditions.     

A convenient synthesis of new thiaazacrown ethers and study of their complexation reactions with some transition metal cations in binary acetonitrile–chloroform mixture using the conductometric method

Three novel thiaazacrown ethers 1, 2 and 3 were synthesized in a simple way and in high yield. The complex formation between Ag⁺, Cu²⁺, Zn²⁺, Pb²⁺, Hg²⁺ and Cd²⁺ metal cations with thiaazacrown ethers 1, 2 and 3 have been studied in acetonitrile:chloroform (1:1) binary solvent system using conductometric technique. The conductance data show that the stochiometry of the complexes with Ag⁺, Cu²⁺ and Zn²⁺ cations is 1:1 (L:M), but in the case of Pb²⁺ and Hg²⁺ cations, a 1:2 (L:M) complex is formed in solutions. The formation constants of the resulting 1:1 complexes were determined from the molar conductance-mole ratio data at 25 °C. It was found that the stability constants of 1-Ag²⁺, 2-Ag⁺ and 3-Ag⁺ complexes are higher than those of their corresponding Zn²⁺ and Cu²⁺ complexes and found to vary in order 3 > 1 > 2 for Ag⁺.     

Associative combination of lone pair-π, π-π and anion-π interactions observed in a ternary system comprising Mg(II)-malonate-2-aminopyridine-hexafluoridophosphate

One Mg(II) malonate complex with protonated 2-aminopyridine and hexafluoridophosphate as counterions, (C₅H₇N₂)₄[Mg(C₃H₂O₄)₂(H₂O)₂](PF₆)₂ (1) [C₅H₇N₂ = protonated 2-aminopyridine, C₃H₄O₄ = malonic acid] has been synthesized from purely aqueous media just by mixing the reactants in their stoichiometric proportion and its crystal structure has been determined by single-crystal X-ray diffraction. The role of weak forces like lone pair?π and anion?π interactions in influencing the self-assembly process appears to be of importance. A rare combination of lone pair?π and anion?π interactions in 1, of the type lone pair?π/π?π/π?anion, is observed, and this unusual supramolecular network is fully described here.     

Preparation and characterization of (η5-C5H5Co)2- (μ-PPh2)B2H5: evidence for multicenter cluster bonding in σ-π vinyl transition metal complexes

The structural and spectroscopic properties of the new cobaltaborane,Cp₂Co₂(PPh₂)B₂H₅ show that this compound, a formal analogue of a dinuclear transition metal complex containing a C₂H₃ ligand in σ-π bonding mode,exhibits a geometry characteristic of an arachno tetranuclear cluster framework. Comparison with analogous σ-π vinyl complexes suggests a significant component of multicenter cluster bonding character in the carbon-metal interaction in the organometallic compounds.     

The metal complexes of some azo and azomethine dyestuffs : Part I. Spectra in water,and in dioxan/water in the wavelength range 320-600 mμ

The visible, spectra of the highly sensitive colorimetric reagent 4-(2-pyridylazo)-resorcinol (I), and of the coloured cpmplexes formed with copper(II), nickel(II), cobalt(II), lead(II), and uranium(VI) were obtained in water and in aqueous dioxan. The structures of these complexes were determined by spectrophotometric methods, and chelation by (I) established as essentially terdentate. Comparison is made with the visible spectra of salicylidene-2-aminopyridine (II), 2-(o-hydroxy-phenyl-imino-methyl)-pyridine (III), and benzeneazoresorcinol (IV), and of the metal complexes of (II) (III) and (IV). The red coloration obtained with 4-(2-pyridylazo)-resorcinol is explained by the presence of a pseudo-phenanthroline system and an o-o'-disubstituted azo system, the active groups in chelation being the pyridine nitrogen atom, the azo nitrogen farthest from the heterocycle, and the o-hydroxyl group.     

Ligand exchange reactions between Cu(II), Pb(II), Al(III), and Cr(III) acetylacetonates and dipivaloylmethanates: The possibility of using exchange reactions in estimation of standard enthalpies of formation of metal β-diketonates

Ligand exchange reactions between Cu(II), Pb(II), Al(III), and Cr(III) acetylacetonates and dipivaloylmethanates were studied by mass spectrometry with sample evaporation from an analog of the Knudsen effusion cell (direct inlet probe). It was shown that exchange reactions can be used to estimate the standard enthalpies of formation of metal β-diketonates.     

Transition metal promoted reactions: XVI. Activation of CS bonds in complexed thiolato ligands. Reduction of the CS bond in Cp2Ni2(μ-SR)2

The carbon-sulfur bond in Cp₂Ni₂(μ-SR)₂ is reductively cleaved by treatment with lithium aluminium hydride to give the corresponding carbonhydrogen bond. Preliminary examination of the reaction mechanism is described.     

Photochemical reactions of [W(CO)4(η-nbd)] with hydrosilanes: Generation of new hydrido complexes of tungsten and their reactivity

Photolysis of the norbornadiene (nbd) complex [W(CO)₄(η⁴-nbd)] (1) creates a coordinatively unsaturated d⁶ species which interacts with the Si-H bond of tertiary and secondary silanes (Cl₃SiH, Et₃SiH, Et₂SiH₂, Ph₂SiH₂) to yield hydride complexes of varying stability. In reaction of complex 1 with Cl₃SiH, oxidative addition of the Si-H bond to the tungsten(0) center gives the seven-coordinate tungsten(II) complex [WH(SiCl₃)(CO)₃(η⁴-nbd)], which has been fully characterized by NMR spectroscopic methods (¹H, ¹³C{¹H}, 2D ¹H-¹H COSY, 2D ¹³C-¹H HMQC and ²⁹Si{¹H}). Reaction of 1 with Et₃SiH leads to the hydrosilylation of the η⁴-nbd ligand to selectively yield endo-2-triethylsilylnorbornene (nbeSiEt₃). The latter silicon-substituted norbornene gives the unstable pentacarbonyl complex [W(CO)₅(η²-nbeSiEt₃)], whose conversion leads to the initiation of ring-opening metathesis polymerization (ROMP). Reaction of secondary silanes (Et₂SiH₂ and Ph₂SiH₂) with 1 leads to the hydrosilylation and hydrogenation of nbd and the formation of bis(silyl)norbornane and silylnorbornane as the major products. In reaction of 1 and Et₂SiH₂, the intermediate dihydride complex [WH(μ-H-SiEt₂)(CO)_x(η⁴-nbd)] was detected by ¹H and ¹³C NMR spectroscopy. As one of the products formed in photochemical reaction of W(CO)₆ with Ph₂SiH₂, the dinuclear complex [{W(μ-η²-H-SiPh₂)(CO)₄}₂] was identified by NMR spectroscopic methods.     

The role of the activity coefficients of surface groups in the formation of surface charge of oxides. Part II: Ion exchange and ζ potentials

A new method is developed to calculate the surface charge densities and potentials of oxides in contact with electrolyte solution as functions of pH and ionic strength. For low ionic strength and not too far from p.z.c. (up to 3 pH units for 10^–3 mol dm^–3 NaCl) the previous model (Kosmulski, 1992) neglecting the ion exchange can be used but farther from p.z.c., correction for the ion exchange is necessary for some systems. This correction leads to increase of the calculated titration charge (that is not necessarily equal to the surface charge), but does not affect the diffuse charge and potential.