Risto S. Laitinen

The oxidative addition of diphenyl diselenide and ditelluride to tetrakis(triphenylphosphine)palladium

Abstract The oxidative addition of diphenyl diselenide to [Pd(PPh3)4] in dichloromethane results in the formation of a dinuclear complex [Pd2(SePh)4(PPh3)2] (1) and a mononuclear complex [PdCl(SePh)(PPh3)2] (2) that have been identified and characterized structurally by X-ray crystallography and 31P-NMR spectroscopy. The analogous reaction involving diphenyl ditelluride leads to a mixture of products. [Pd6Cl2Te4(TePh)2(PPh3)6]·1/2CH2Cl2 (3) can be isolated and its X-ray structure determined. While the oxidative addition of Ph2Se2 mainly involves the clevage of the Se–Se bond, that of Ph2Te2 indicates the rupture of both Te–Te and C–Te. Cumulative evidence shows that the choice of the central atom and the solvent also plays an important role in the oxidative addition. The final polynuclear complexes can be conceived to be formed from the mononuclear addition products by sequential condensation steps.

The NMR spectroscopic and X-ray crystallographic study of the oxidative addition of bis(2-thienyl) diselenide to zerovalent palladium and platinum centers

Abstract The pathway of the reaction of dithienyl diselenide with tetrakis(triphenylphosphine)palladium(0) and -platinum(0) has been explored by the use of NMR spectroscopy and X-ray diffraction. The oxidative addition of dithienyl diselenide to [Pd(PPh 3 ) 4 ] mainly results in the formation of two isomers of dinuclear [Pd 2 (SeTh) 4 (PPh 3 ) 2 ] (Th=2-thienyl, C 4 H 3 S) complex. The workup of the solution produced X-ray-quality crystals of trans -[Pd 2 (SeTh) 4 (PPh 3 ) 2 ]. The corresponding reaction with [Pt(PPh 3 ) 4 ], however, affords isomers of mononuclear [Pt(SeTh) 2 (PPh 3 ) 2 ]. Upon recrystallization from dichloromethane a small amount of crystals of dinuclear [Pt 2 (SeTh) 4 (PPh 3 ) 2 ] is obtained together with those of trans -[Pt(SeTh) 2 (PPh 3 ) 2 ]. While the products from both reactions imply that the oxidative addition takes place with the cleavage of the SeSe bond, a small amount of trans -[PdCl(Th)(PPh 3 ) 2 ] is formed in the reaction of [Pd(PPh 3 ) 4 ] and Th 2 Se 2 in dichloromethane indicating that CSe cleavage may also take place during the oxidative addition.

Homo- and heteroatomic chalcogen rings

Abstract This review describes recent progress in the chemistry of homo- and heterocyclic chalcogen species summarizing their preparation, structural characterization, bonding, and spectroscopic properties. Although it is possible to prepare stoichiometrically pure chalcogen rings, many reactions result in the formation of complicated mixtures. The crystal and molecular structures of many homocyclic rings are known. All heterocyclic rings, however, are disordered and therefore it has not been possible to determine accurate bond parameters for them. The identification of individual molecular species and the composition of mixtures of chalcogen ring molecules have been studied successfully with HPLC and Raman spectroscopy, as well as with 77 Se and 125 Te NMR spectroscopy. With development of computing techniques, it has been possible to perform MO calculations with increasing sophistication. They have yielded reliable predictions on ground state geometries and electronic structures of different chalcogen rings. The emphasis of research in recent years has shifted from purely structural studies towards understanding the facile interconversion reactions that take place between the different chalcogen rings. The experimental and theoretical evidence on the mechanism of these ring interconversion pathways are discussed.

The X-ray crystallographic study of the reaction of bis(2-thienyl)ditelluride with tetrakis(triphenylphosphine)platinum or -palladium

Abstract The oxidative addition of dithienyl ditelluride to [Pt(PPh3)4] in dichloromethane results in the formation of a trinuclear complex [Pt3Te2(Th)(PPh3)5]Cl (Th=2-thienyl, C4H3S) (1) as well as a mononuclear complex [PtCl(Th)(PPh3)2] that have been identified and structurally characterized by X-ray crystallography and 31P-NMR spectroscopy. The analogous reaction involving [Pd(PPh3)4] forms a mixture of several products. In dichloromethane [Pd6Cl2Te4(TeTh)2(PPh3)6] (2) can be isolated and its X-ray structure determined. In toluene [Pd6Te4(TeTh)4(PPh3)6] (3) is formed. Both 2 and 3 have a similar hexanuclear framework which has previously been reported for [Pd6Te6(PEt3)8] in the literature. These products indicate that the cleavage of both TeTe and CTe bonds as well as the choice of the solvent play an important role in the oxidative addition. The trinuclear and hexanuclear complexes can be considered to be formed from an initial mononuclear addition product. The reaction pathways are compared to those involved in the reaction of Th2Se2 and [M(PPh3)4] (M=Pt, Pd).

Isomerism in bis(phenylselenolato)bis(triphenylphosphine)platinum(II): the crystal and molecular structures of cis- and trans-[Pt(SePh)2(PPh3)2]

Abstract The reaction of cis-[PtCl2(PPh3)2] and NaSePh in benzene produces a mixture of cis- and trans-isomers of the monomeric platinum complex [Pt(SePh)2(PPh3)2]. The low-temperature X-ray structures of both isomers are reported. The structure of cis-[Pt(SePh)2(PPh3)2] is the first crystallographic characterized cis-isomer of mononuclear platinum(II) complex containing only non-chelating organoselenolato and phosphine ligands.

Trends in the structure and bonding of [MCl2{(C4H3S)ECH3}2] (M=Pd, Pt; E=Te, Se)

Abstract The complex formation of (C 4 H 3 E)E′Me (E=S, O; E′=Te, Se) ( 1 – 4 ) with palladium and platinum has been explored by use of NMR spectroscopy and X-ray diffraction. Whereas the 125 Te-NMR spectra of [PdCl 2 {(C 4 H 3 E)TeMe} 2 ] [E=S ( 5 ), E=O ( 6 )] show the existence of both cis - and trans -isomers in solution the spectroscopic information of [MCl 2 {(C 4 H 3 E)SeMe} 2 ] (M=Pd, Pt, E=S, O; 8 – 10 ) indicates the presence of only one isomer. The crystal structure determinations have shown that 5 and 6 are isomorphous and crystallize as cis -isomers forming dimers with close chalcogen–halogen contacts. In contrast, 8 and 10 have turned out to be trans -isomers and form skewed stacks that are bound together in a helical arrangement by weak hydrogen bonds. The structural data indicate that back donation may weakly contribute to the palladium–tellurium bonding in 5 and 6 . In 8 and 10 the effects of the back bonding are negligible.

An experimental and theoretical study of the isomerization of mononuclear bis(arylselenolato)bis(triphenylphosphine)platinum complexes [Pt(SeR)2(PPh3)2]

Mononuclear bis(thienylselenolato)bis(triphenylphosphine)platinum [Pt(SeTh) 2 (PPh 3 ) 2 ] (Th=2-thienyl, C 4 H 3 S) has been prepared by the treatment of cis -[PtCl 2 (PPh 3 ) 2 ] with NaSeTh. The 31 P-NMR spectroscopic information indicates that cis -[Pt(SeTh) 2 (PPh 3 ) 2 ] is initially formed in the reaction. Upon prolonged standing in solution it isomerizes to trans -[Pt(SeTh) 2 (PPh 3 ) 2 ] . The reaction of cis -[PtCl 2 (PPh 3 ) 2 ] with LiSeFu (Fu=2-furyl, C 4 H 3 O) affords immediately a mixture of cis - and trans -isomers of [Pt(SeFu) 2 (PPh 3 ) 2 ] with the relative amount of the trans -isomer increasing with time. The recrystallization of the two reaction mixtures yielded cis , anti - and trans , syn -isomers of [Pt(SeTh) 2 (PPh 3 ) 2 ] as well as cis,syn - and trans , anti -isomers of [Pt(SeFu) 2 (PPh 3 ) 2 ]. Their structures were compared with those of cis , anti - and trans , anti -isomers of [Pt(SePh) 2 (PPh 3 ) 2 ]. The geometries and relative stabilities of all isomers of [Pt(SeTh) 2 (PH 3 ) 2 ], [Pt(SeFu) 2 (PH 3 ) 2 ] and [Pt(SePh) 2 (PH 3 ) 2 ] were studied by the use of ab initio molecular orbital techniques in order to model the structures and isomerization of the observed mononuclear selenolato complexes.

Halogenation of tellurium by SO2Cl2. Formation and crystal structures of (H3O)[Te3Cl13]·1/2SO2, [(C4H8O)2H][TeCl5]·(C4H8O), [(Me2SO)2H]2[TeCl6], and [Ni(NCCH3)6][Te2Cl10]

Abstract The halogenation of elemental tellurium with SO2Cl2 in various solvents has been investigated. (H3O)[Te3Cl13]·1/2SO2 (1) and [(C4H8O)2H][TeCl5]·(C4H8O) (2) were obtained in CS2 and THF, respectively. When DMSO is added into the THF solution of tellurium and SO2Cl2, [(Me2SO)2H]2[TeCl6] (3) is formed. In the acetonitrile solution tellurium and SO2Cl2 form [Ni(NCCH3)6][Te2Cl10] (4) in the presence of metallic nickel. All compounds 1–4 were characterized by 125Te NMR and by X-ray crystallography. The formation of the anions has been discussed.

Slagging tendency of peat ash

The combustion of peat in power plant boilers has increased in recent years in Finland. Whereas the operation of such power plants is generally smooth, the slagging of peat ash can, in some cases, lead to a plant shutdown, thus causing significant economic losses to the entire energy-production chain. It is therefore important to predict the slagging tendency of ash in a given peat type prior to combustion. In this work we discuss the factors involved in the slag formation of peat samples. The work centers both on standard peat ash and on the samples collected from an actual power-plant boiler. The formation and properties of ash particles have been studied with scanning electron microscopy combined with automatic image analysis. X-ray powder diffraction data complement the microscopic studies.

Colloidal surfaces and oligomeric species generated by water treatment chemicals

Abstract Properties of water treatment chemicals were investigated by a novel combination of analytical methods. Oligomer distribution, total surface charge, zeta potential and conductivity were evaluated in simulated systems containing highly and moderately basic polyaluminium chlorides, aluminium sulfate (alum), ferric chloride and ferric sulfate. Species were quantified on the basis of mass spectro-metric results. Polyaluminium chemicals gave rise to an intensive and completely cationic distribution of mainly Al13-based oligomers and high surface charges. Both cationic distribution and charge decreased with increase of pH and increased with concentration of the chemical. The other chemicals produced a wider oligomeric distribution of smaller species, including anions. The dimeric form was typical for iron. In the case of the sulfate-containing chemicals, sulfate was present in the majority of oligomers and zeta potentials were stable. For the chemicals without sulfate, pH values needed to be high enough to provide high zeta values. The results can be utilized in the improvement of coagulation and flocculation mechanisms aimed at the removal of bacteria, viruses and other micro organisms, as well as at humic and mineral particles. In addition, semi quantitative information about oligomeric species may be helpful in breaking down cell membranes to support disinfection.