Coordination properties of α-hydroxy carboxylic acids. Part I. Binuclear niobium (V) complex acids and some salts

The conditions of dissolution of freshly precipitated niobium (V) oxide in α-hydroxy carboxylic acids glycolic, lactic, malic and tartaric were investigated. The dissolution is a function of the molar ratio α-hydroxy carboxylic acid/hydrated niobium(V) oxide, pH of the solution, temperature and time. From solutions of α-hydroxy monocarboxylic acids at 2 < pH < 3 the binuclear complexes H₃O[Nb₂O₄(C₂H₂O₃)(C₂H₃O₃)]·H₂O and H₃O[Nb₂O₄(C₃H₄O₃)(C₃H₅O₃)]·H₂O were isolated. Colourless, poorly-crystalline complexes are 1:1 electrolytes and, according to i.r. spectral evidence, the binuclearity in their structures is achieved through oxygen bridges. With α-hydroxy dicarboxylic acids crystalline M[Nb₂O₃(C₄H₃O₅)(C₄H₄O₅)]·nH₂O and poorly crystalline complexes, M₂[Nb₂O₂(C₄H₂O₆)₂]·nH₂O, M = H₃O⁺, NH₄⁺ were prepared as 1:1 electrolytes for the former and 1:2 electrolytes for the latter. Analytical, spectral, conductometric and potentiometric titration data give evidence for binuclear malatoniobate(V) and tartratoniobate(V) anions with bridging complex-forming agents.     

Oxoperoxofluoromolybdate(VI) complexes. The first synthesis of oxodiperoxofluoromolybdate(VI) complexes

A number of oxoperoxofluoromolybdate(VI) complexes, viz. M₂[MoO(O₂)F₄] and M₂[MoO(O₂)₂F₂] where M = K and NH₄ and K[MoO(O₂)₂F]·2H₂O have been synthesised by various methods. The infrared spectra suggest that the peroxide groups are bonded to the molybdenum centre in a triangular bidentate manner.     

Peroxo heteroligand vanadates(V): Synthesis,spectra-structure relationships,and stability toward decomposition

Effect of heteroligands (L) on the properties of vanadium peroxides was investigated by preparing a number of peroxovanadium complexes, which were characterized by analysis, IR, UV/V and NMR spectra. X-ray structures for some were obtained. The vanadates(V) contain the cation M(I)=Na, K, NH₄, Rb or Cs. Diperoxo complexes include M(I)[VO(O₂)₂L], where L=dipyridyl, o-phenanthroline; M(I)₃[VO(O₂)₂(C₂O₄)]; K₂[(nicotinic acid) {VO(O₂)₂}₂]H₂O;M(I)₄[O{VO(O₂)₂}₂ cystine]2H₂O; H₄[O{VO(O₂)₂(adenine)₂)₂]2H₂O; and K₂H₂[O{VO(O₂)₂(adenosine)}₂]2H₂O. Monoperoxo vanadates(V) correspond to the formula M(I)₂[VO(O₂)L]₂ for L=citrate and malate; M(I)₂[VO(O₂)L] for L=nitrilotriacetate; M(I)[VO(O₂)L] for L=iminodiacetate, tartrate and EDTA; and [HVO₂(O₂)(adenosine)]2H₂O. Syntheses of these heteroligand peroxovanadium compounds are sensitive to pH, temperature and the concentration of the components. The stability towards decomposition in solid state, mother-liquid and pure water solutions depends upon the heteroligand. Characteristic (V=O) and (O-O) stretching frequency bands in IR can be correlated with the corresponding bond lengths and the [peroxoV(V)] charge transfer bands in UV/V spectra. Intramolecular one-electron transfer in peroxo vanadates(V) can trigger the generation of radicals, and its dependency upon the nature of the heteroligand is discussed.     

Synthesis,crystal structures and properties of three new lanthanide 2,6-pyridinedicarboxylate complexes with zero-dimensional structure

Three new lanthanide dipicolinate complexes with zero-dimensional structure have been synthesized by mild hydrothermal method. In these complexes the lanthanide is surrounded by three dipicolinate groups in the usual tridentate mode. For two of them, (CN₃H₆)₃[La(C₇H₃NO₄)₃] · 3H₂O I and (C₄N₂H₁₂)_1.5[Ce(C₇H₃NO₄)₃] · 7H₂O II, the dipicolinate groups are wholly unprotonated. The resulting molecular entity is three-times negatively charged and the balance charge is insured by the presence of guanidinium or piperazinium ions for the first and second, respectively. For the third complex, [Eu(C₇H₄NO₄)₃]₂ · 2.5H₂O III, one hydrogen atom remains globally on each dipicolinate and so the molecular entities are neutral. For the latter complex, the resulting molecular entities are connected into chains through strong hydrogen bonding. Thermogravimetric analyses and luminescent behaviour of complex III have been carried out.     

Self-assembly of four three-dimensional reduced molybdenum(V) phosphates decorated with transitional metal complexes

Four new three-dimensional materials built from reduced molybdenum(V) phosphates as building blocks and transitional metal (Co, Zn and Cd) complexes as linkers, (Hbpy)₂[Co(bpy)(H₂O)]₂[Co(H₂PO₄)₂ (HPO₄)₆(MoO₂)₁₂(OH)₆] (1), [Co(H₂O)₄]₂[Co(Hbpy)(H₂O)]₂[Co(bpy)][Co(HPO₄)₄(PO₄)₄(MoO₂)₁₂(OH)₆] · 6H₂O (2), Na₂[Zn(Hbpy)(H₂O)₂]₂[Zn(Hbpy)]₂[Zn(HPO₄)₂(PO₄)₆(MoO₂)₁₂(OH)₆] · 4H₂O (3), (H₂bpy)₂[Cd(bpy)(H₂O)]₂[Cd(bpy)(H₂O)₂]₂[Cd(HPO₄)₄(PO₄)₄(MoO₂)₁₂(OH)₆] · 2H₂O (4) (bpy = 4,4′-bipyridine), have been synthesized and characterized by elemental analyses, IR, TG, and single crystal X-ray diffraction. The 3-D framework of 1 is constructed from Co[P₄Mo₆]₂ dimers bonded together with [Co(bpy)]_n coordination polymer chains. In compound 2, the Co[P₄Mo₆]₂ dimers are linked by both [Co(bpy)] complex chains and the cobalt dimers to form a 3-D framework. Compounds 1 and 2 represent the first examples of reduced molybdenum(V) phosphates decorated with transition metal complexes chains. The 3-D framework of 3 is constructed from Zn[P₄Mo₆]₂ dimers bonded together with [Zn(bpy)] coordination complexes and [Zn(bpy)(H₂O)₂] complexes. In compound 4, the Cd[P₄Mo₆]₂ dimers are coordinated with [Cd(bpy)(H₂O)] and [Cd(bpy)(H₂O)₂] complexes to construct a 3-D structure. To our best knowledge, it is the first time that linear ligand 4,4′-bpy molecules have been grafted into the backbone of reduced molybdenum phosphates. Furthermore, the magnetic properties of compounds 1 and 2 are reported.     

Bis(undecatungstogermanate) lanthanates of potassium

The K₁₃[Ln(GeW₁₁O₃₉)₂]·nH₂O (Ln = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Tm, Yb) have been prepared. Some properties of these compounds have been studied. The change of main bands in their IR spectra with reference to α-GeW₁₂O₄₀⁴⁻ is discussed. v_as (W---O_d) is shifted toward low wavenumber and v_as (W---O_b---W), δ(O---Ge---O) each appear as two distinct bands. X-ray powder diffraction shows that the molecular symmetry of K₁₃[Ln(GeW₁₁O₃₉)₂] is lower than that of α-K₈(GeW₁₁O₃₉). XPS determinations reveals that the Ln---O bond has coordination character and that the shifts of W_4f and O_ls are between K₁₃Ln (GeW₁₁O₃₉₂ and α-H₄(GeW₁₂O₄₀). Magnetic measurement confirms that the lanthanide elements are +3 valent in this complexes and the magnetic moments are very close to the values found by Van Vleck.     

Protonated N-heterocycle-templated supramolecular frameworks built of triangular molybdenum(IV) clusters

A series of porous supramolecular complexes (Hoxine)₂ · [Mo₃O₄(C₂O₄)₃(H₂O)₃] · 5H₂O (1),(Hphen)₂ · [Mo₃O₄(C₂O₄)₃(H₂)₃]  · 0.5C₂H₅OH · 7H₂O (2), H₂bpy · [Mo₃O₄(C₂O₄)₃(H₂O)₃] · 2.5H₂O (3), H₂TTD · [Mo₃O₄(C₂O₄)₃(H₂O)₃] · C₂H₅OH · 3H₂O (4), (oxine = 8-hydroxyquinoline, phen = 1,10-phenanthroline, bpy = 4,4′-bipyridine, TTD = triethylene diamine) have been prepared and characterized by single-crystal X-ray crystallography, elemental analysis and infrared spectroscopy. Self-assembly of [Mo₃O₄(C₂O₄)₃(H₂O)₃]²⁻ directed by H-bonding association between the coordination water molecules and oxalate groups forms 2-D host H-bonded single layer in 1, double layer in 2 and 3, and undulated layer in 4 depending on the nature of the guest protonated N-heterocycles. Unlike cis-Hoxine⁺ or Hphen⁺ that employs lattice water molecules H-bonded to them to interconnect the host layers, trans-H₂bpy²⁺ or H₂TTD²⁺ acts a linker between the neighboring host layers to form 3-D supramolecular frameworks with channeled structures wherein the guest protonated cations are located.     

The synthesis of technetium(V) complexes containing sterically bulky thiolate ligands. The molecular structure of tetrabutylammonium oxotetrakis(2,4,6-trimethylbenzenethiolato)technetate(V)

The reactions between [TcOCl₄]⁻ and the sterically bulky thiols ArSH (Ar = 2,4,6-Me₃C₆H₂, 2,4,6- Prⁱ₃C₆H₂ and 2,6-Ph₂C₆H₃) in methanol afford complexes of formula [TcO(SAr)₄]⁻ which may be isolated as salts with bulky organic cations. The molecular structure of [Buⁿ₄N][TcO(2,4,6-Me₃C₆H₂S)₄] was determined by X-ray diffraction methods. The Tc(V) centre was found to adopt the expected square pyramidal geometry in which an oxo group occupies the apical site and the four thiolate sulphurs the basal sites. The TcO distance is 1.659(11) Å and the average TcS distance 2.38(2) Å. The average cis STcS, trans STcS and OTcS angles are respectively 82.7(6)°, 138.4(3)° and 110.8(4)°.     

Kinetics of Inhibition of Rabbit Intestine Alkaline Phosphatase by Heteroligand Peroxo Complexes of Vanadium(V) and Tungsten(VI)

The present work was undertaken to examine and compare some biologically important properties of peroxo compounds of V(V) and W(VI) containing biogenic species as ancillary ligand. New anionic peroxovanadate(V) complex of the type Na[VO(O₂)₂(triglycine)]·3H₂O (pV1) and a molecular peroxotungstate(VI) [WO(O₂)₂(triglycine)]·3H₂O (pW1) were synthesized and characterized for the purpose and their stability in solution was ascertained. Studies on kinetics of inhibition of alkaline phosphatase activity by the newly synthesized compounds and series of dipeptide and amino acid containing peroxo complexes of vanadium and tungsten synthesized previously by us viz., Na[VO(O₂)₂(gly-gly)(H₂O)]·H₂O (gly-gly = glycyl-glycine), Na[VO(O₂)₂(asn)]·H₂O (asn = asparagine), Na[VO(O₂)₂(gln)]·H₂O (gln = glutamine), and [WO(O₂)₂(gly-gly)(H₂O)]·3H₂O, revealed that each of these species is a potent mixed-type inhibitor of the enzyme. Significant difference was noted between the peroxovanadium (pV) and peroxotungsten (pW) compounds in terms of their oxidant activity with reduced glutathione.     

A heteronuclear (Pt,Zn) complex of 1-methyluracil with different coordination geometries (square-planar and square-pyramidal) of the two metals

Reaction of cis-(NH₃)₂Pt(1-MeU)₂ (1-MeU = 1- methyluracil anion, C₅H₅N₂O₂) with ZnSO₄·7H₂O leads to the formation of a dinuclear complex of composition [(NH₃)₂Pt(C₅H₅N₂O₂)₂Zn(H₂O)₃]SO₄· 2H₂O. The compound crystallizes in space group P2₁/c with a = 10.534(1), b = 17.933(2), c = 11.490(1) Å, β=94.61(1)°, Z=4. The structure was refined to R=0.043 and R_w=0.061. In this compound, Pt is coordinated through N3 to the 1-MeU ligand, while Zn is bound through the two O4 oxygens and completes its distorted square-pyramidal coordination sphere by three aqua ligands. The positions of the two metals relative to their basal donor atoms and the shortness of the PtZn separation (2.760(1) Å) suggest a bonding interaction between the two metals. Using ¹H NMR spectroscopy, a formation constant of ca. 114 1 mol^?1 for the Pt, Zn complex has been estimated.     

Synthesis,inhibitory activity and molecular docking studies of two Cu(II) complexes against Helicobacter pylori urease

Two mononuclear copper(II) complexes, [Cu(C₁₅H₁₆NO₂)₂] (1) and [Cu(C₆H₉N₂O₄)₂·3H₂O] (2·3H₂O), were synthesised and structurally characterised by single-crystal X-ray analysis. The copper(II) atom adopts a square-planar environment in complex 1, while the geometry in 2·3H₂O could be described as the distorted square pyramidal. Complexes 1 and 2·3H₂O were evaluated for their inhibitory activities against Helicobacter pylori (H. pylori) urease in vitro. They both were found to have strong inhibitory activities against H. pylori urease comparable to that of acetohydroxamic acid (AHA). A docking simulation was performed to position 2 into the H. pylori urease active site to determine the probable binding conformation.     

pH-specific synthesis,isolation, spectroscopic and structural characterization of a new dimeric assembly of dinuclear vanadium(V)–citrate–peroxo species from aqueous solutions

Outstanding among the plethora of roles of vanadium in biological systems is its ability to act as an insulin mimetic agent, counteracting hyperglycemia. Poised to comprehend the interactions of V(V) with physiological substrates of low molecular mass, research efforts were launched to investigate the aqueous synthetic chemistry of the ternary V(V)–citric acid–H₂O₂ system. In a pH-specific fashion, reaction of VCl₃ with citric acid and H₂O₂ in aqueous ammonia led to the isolation of a unique assembly of ternary dinuclear complexes in (NH₄)₆[V₂O₂(O₂)₂(C₆H₅O₇)₂] · [V₂O₂(O₂)₂(C₆H₆O₇)₂] · 6H₂O (1). This unique assembly of dinuclear species was characterized by elemental analysis, FT-IR spectroscopy and X-ray crystallography. The structure of 1 reveals two dinuclear V₂O₂ core complexes, bearing peroxo moieties and bound citrates of variable deprotonation state and coordination mode. The physicochemical data: (a) present an unusual “instant picture” of the pH-specific aqueous speciation of the investigated system, attest to the presence of known species and clearly suggest the existence of a new discrete species in the aqueous structural speciation of the ternary system, (b) exemplify the usefulness of the synthetic strategy in the discovery of new discrete V(V)–citrate–peroxo species, and (c) offer insight into the ternary interactions of V(V) toward O-containing substrates relevant to insulin mimetic activity.     

Croconato-containing M(III) (M = Ga, Er) complexes as potential building blocks for mono/multifunctional molecular materials

The one-pot synthesis and structural characterization of two new complexes of the croconato ligand (C₅O₅)²⁻ with the Ga(III) and Er(III) metal ions are reported. The mononuclear tris-chelated (n-Bu₄N)₃[Ga(C₅O₅)₃], 1, which exhibits an octahedral geometry, is present as Δ and Λ enantiomers in equal amounts; the K₂[Er(C₅O₅)(μ-SO₄)(OH₂)₄]₂ complex, 2, shows dinuclear erbium moieties with bridging sulfate anions and interposed K(I) cations with a capped trigonal prismatic coordination geometry. 2 shows paramagnetic behavior in the 2-300 K range typical of two isolated Er(III) ions. Vibrational (FT-IR and FT-Raman) and electronic spectroscopies have shown to be a reliable diagnostic tool in distinguishing different molecular arrangements of the croconato ligand in different complexes. The analogies of the gallium complex with the corresponding [M(C₂O₄)₃]³⁻ tris-chelated complexes which have been used as chiral building blocks of molecular conductors are pointed out.     

Delving into the complex picture of Ti(IV)-citrate speciation in aqueous media: Synthetic, structural, and electrochemical considerations in mononuclear Ti(IV) complexes containing variably deprotonated citrate ligands

The aqueous reaction of TiCl₄ with citric acid at pH ∼ 4 (KOH), led to the surprising isolation of a species assembly K₃[Ti(C₆H₆O₇)₂(C₆H₅O₇)] · K₄[Ti(C₆H₅O₇)₂(C₆H₆O₇)] · 10H₂O (1). The same system at pH ∼ 3 (neocuproine), led to the crystalline material (C₁₄H₁₃N₂)₂[Ti(C₆H₆O₇)₃] · 5H₂O (2), while at pH 5.0 (NaOH), afforded Na₃[Ti(C₆H₆O₇)₂(C₆H₅O₇)] · 9H₂O (3). Analytical, spectroscopic and structural characterization of 1, 2 and 3 revealed their distinct nature exemplified by mononuclear complexes bearing variably deprotonated citrates bound to Ti(IV). Solid-state ¹³C MAS NMR spectroscopy in concert with solution ¹³C and ¹H NMR on 3 provided ample evidence for the existence of bound citrates of distinct coordination mode to the metal ion. Cyclic voltammetry defined the electrochemical signature of complex 2, thereby projecting the physicochemical profile of the species formulated by the aforementioned properties. Comparison of cyclic voltammetric data on available discrete Ti(IV)-citrate species depicts the electrochemical profile and an E_1/2 value trend of the species in that binary system’s aqueous speciation, further substantiating the redox behavior of mononuclear Ti(IV)-citrate species in a pH-sensitive fashion. Collectively, the well-defined discrete species in 1-3 reflect and corroborate a synthetically challenging yet complex pH-specific picture of the aqueous Ti(IV) chemistry with the physiological citric acid, and shed light on the pH-dependent speciation in the binary Ti(IV)-citrate system.     

Synthesis and coordination chemistry of tripodal dialkyl[1,2-bis(diethylcarbamoyl)ethyl]phosphonates with lanthanide nitrates

Trifunctional dialkyl [1,2-bis(diethylcarbamoyl)- ethyl] phosphonates, (RO)₂P(O)CH[C(O)N(C₂H₅)₂]- [CH₂C(O)N(C₂H₅)₂] R  CH₃, C₂H₅, i-C₃H₇, n-C₆H₁₃ were prepared from the respective sodium salts, Na[(RO)₂P(O)CHC(O)N(C₂H₅)₂] and N,N- diethylchloroacetamide, and they were characterized by elemental analysis, mass, infrared and NMR spectroscopy. The molecular structure of (i-C₃H₇O)₂- P(O)CH[C(O)N(C₂H₅)₂][CH₂C(O)N(C₂H₅)₂] was determined by single crystal X-ray diffraction analysis and found to crystallize in the monoclinic space group P2₁/c with a=15.589(6), b=9.783(4), c= 16.283(7) Å, β = 110.90(3)°, Z = 4 and V= 2320(2) ų. The structure was solved by direct methods and blocked least-squares refinement converged with Rf = 5.7% and R_wF= 4.4% on 2266 unique data with F>4σ(F). Important bond distances include PO 1.459(3) Å, CHCO 1.228(3) Å and CHCH₂CO 1.223(3) Å. The coordination chemistry of the ligand with several lanthanides was examined, and the structure of the complex Gd(NO₃)₃{[(i-C₃H₇O)₂P(O)CH[C(O)N(C₂H₅)₂][CH₂C(O)N(C₂H₅)₂]}₂·H₂O was determined. The complex crystallized in the monoclinic space group P2₁/n with a = 13.524(5), b = 22.033(4), c = 19.604(4) Å β = 106.22(2)°, Z = 4 and V= 5609(3) ų. The structure was solved by heavy atom techniques and blocked least-squares refinement converged with R_F = 5.9% and R_wF = 4.1% on 5275 reflections with F > 4σ(F). Both trifunctional ligands were found to bond to Gd(III) through only the phosphoryl oxygen atoms. The remainder of the Gd coordination sphere was composed of three bidentate nitrate oxygen atoms and an oxygen bonded water molecule. Several important bond distances include GdO(phosphoryl)_av = 2.343(5) Å, GdO(nitrate)_av = 2.475(7) Å, GdO(water) = 2.354(5) Å, PO(phosphoryl)_av = 1.467(6) Å, CHCO_av = 1.242(10) Å and CHCH₂CO_av = 1.209(11) Å.     

Chemical speciation of oxalato complexes of indium(III)

Abstract

Chemical speciation of binary complexes of indium(III) with oxalic acid has been investigated pH metrically at 303 K and at an ionic strength of 0.2 mol dm^?3. The approximate formation constants have been calculated with the computer program SCPHD utilizing the experimental data obtained by monitoring H⁺ ion concentration. The formation constants thus obtained are refined with the computer program, MINIQUAD75 using primary alkalimetric data. The selection of the best-fit chemical model is based on the statistical parameters and residual analysis. The major complexes formed are In(C₂O₄)₂^?, In(C₂O₄)₃^3?, [In(C₂O₄)₂OH]^2? and [In(C₂O₄)₂ (OH)₂]^3?. The distribution patterns of the different species with the pH values showed that In(C₂O₄)₂^? is the predominant species.     

Synthesis and characterisation of dinuclear oxomolybdenum(V) complexes with thienyl carboxylate ligands

The first structurally characterised oxomolybdenum(V) complexes with thienyl carboxylate ligands were prepared by the reaction of [Mo₂O₃(C₅H₇O₂)₄] or (NH₄)₂[MoOCl₅] with the corresponding acid (2-thiophenecarboxylic, 5-methyl-2-thiophenecarboxylic or 3-(3-thienyl)acrylic acid). Complexes [Mo₂O₃(μ-OC₂H₅)(μ-O₂CR)(C₅H₇O₂)₂](R = -C₄H₃S (1), -C₄H₂S(CH₃) (2) or -CHCHC₄H₃S (3)) were obtained upon substitution of two acetylacetonate ligands from [Mo₂O₃(C₅H₇O₂)₄] with RCOO⁻ in dry ethanol. Reactions of (NH₄)₂[MoOCl₅] with the corresponding thienyl carboxylic acid in the presence of γ-picoline (C₆H₇N) yielded complexes (C₆H₇NH)[Mo₂O₄(μ-O₂CR)Cl₂(C₆H₇N)₂] (R = -C₄H₃S (4), -C₄H₂S(CH₃) (5) or -CHCHC₄H₃S (6)). All of the six new complexes were characterised as dinuclear. The molecular structures of 1, 3, 4·0.5CH₃CN and 5 were determined by the single crystal X-ray diffraction method. In the complexes the two molybdenum atoms are doubly bridged either by one oxygen and one ethoxy-oxygen, or alternatively by two oxo-oxygens, and are additionally bridged by the thienyl carboxylate ion in a didentate bridging manner. All complexes were further characterised by means of chemical analysis, IR spectroscopy, TG and in some cases by the one and two-dimensional NMR method.     

Platinum(II) complexes with aryl tellurols and diaryl ditellurides: Syntheses and spectral investigations

Arytellurol complexes [PtCl(TeAr)(PPh₃)₂] (I) and [Pt(TeAr)₂(PPh₃)₂] (II) are readily obtained from cis-[PtCl₂(PPh)₃)₂] and NaTeAr (Ar = C₆H₅, 4-CH₃OC₆H₄ and 4-CH₃CH₂OC₆H₄) in ethanolbenzene at room temperature. ³¹P NMR spectra of (I) and (II) indicate their trans configuration in solution. Metathetical reactions between I (Ar = 4-CH₃OC₆H₄) and NaX (X = I, Br, SCN) occur in methanol to give [Pt(X)(TeC₆H₄OCH₃-4)(PPh₃)₂]. ¹H NMR shows that equimolar proportions of NaTeC₆H₅, NaTeC₆H₄OCH₂CH₃-4 and cis-[PtCl₂(PPh₃)₂] give a mixture of three complexes: II, Ar = C₆H₅; II, Ar = 4-CH₃CH₂OC₆H₄; and [Pt(TeC₆H₅)(TeC₆H₄OCH₂CH₃-4)(PPh₃)₂]. Polymeric complexes [PtCl(TeAr)]_n (III) and [Pt(TeAr)₂]_n (IV) result from reaction between K₂[PtCl₄] and NaTeAr in aqueaous ethanol. They react with excess of PPh₃ in CDCl₃ to yield monomeric complexes I and II respectively which were characterized in situ by ¹H and ³¹P NMR of the reaction mixtures. IR spectra indicate the presence of bridging chloride ligands in III. An alternating chloride and tellurol bridged chain structure for III and a tellurol bridged for IV have been proposed. Reaction between equimolar amounts of III and PPh₃ in dichloromethane yielded a tellurol bridged dimeric complex [PtCl(μ-TeAr)(PPh₃)]₂ (V) with terminal chloride ligand as suggested by IR study. Ethanolic solutions of diarylditellurides also react readily with an aqueous solution of K₂[PtCl₄] at 10 °C to give complexes for which the structure trans-[PtCl₂(ArTeTeAr)₂] (VI) is suggested from their elemental analyses, IR, Raman (in one case only), ¹H, ¹²⁵Te (in one case only), and ¹⁹⁵Pt NMR spectra and reactions with triphenylphosphine which liberated free ditellurides. At 40 °C or above the same ditellurides form polymeric complexes III with K₂[PtCl₄] in aquaeous ethanol.     

Solution-phase disproportionation equilibria for monosubstituted Pentakis- (arylisocyanide)cobalt(I) complexes by proton-NMR studies

Equilibrium constants, K_dis, for the solvent- dependent, solution-phase disproportionation equilibria of monosubstituted pentakis(arlisocyanide)cobalt(I) complexes: 2[Co(CNR)₄L]⁺?[Co(CNR)₃L₂]⁺ + [Co(CNR)₅]⁺, K_dis = $\text{[Co(CNR)}{}_3\text{L}{}_2\text{][Co(CNR)}{}_5\text{]}\text{[Co(CNR)}{}_4\text{L]}{}^2$ are measured by planimeter-integration of proton- NMR spectra at ambient temperature. The complexes, [Co(CNR)₄L]ClO₄, R = 2,6-Me₂C₆H₃, L = P(C₆H₅)₃, P(C₆H₄Cl-p)₃, P(OC₆H₅)₃, P(OC₆H₄Cl-p)₃; R = o-MeC₆H₄, L = P(C₆H₄Cl-p)₃, P(OC₆H₅)₃, P(OC₆H₄Cl-p)₃; R = 2,4,6-Me₃C₆H₂, L = P(C₆H₅)₃; R = 2,6-Et₂C₆H₃, L = P(C₆H₅)₃; are investigated in the deuterated solvents, CDCl₃, CD₃CN, (CD₃)₂CO, C₅D₅N, CD₃NO₂, and (CD₃)₂SO. Disproportionation seems to occur in all [Co(CNR)₄L]⁺, but NMR study is facilitated by utilizing equivalent alkyl protons (i.e., Me-groups) on the RNC ligands.Correlation of K_dis values with steric-hindrance of the RNC in sets of complexes with the same P-ligand is evident in all solvents: K_dis decreases with increased steric-hindrance in RNC. The K_dis values for complexes with the same RNC and analogous triarylphosphine, triarylphosphite ligands (i.e., PR₃, P(OR)₃, same R) are approximately equal. The K_dis values for complexes of P-ligands with Cl-substituent are significantly larger than K_dis values for complexes with the corresponding unsubstituted P-ligands (e.g., [Co(CNR)₄P(C₆H₄Clp)₃]ClO₄vs. [Co(CNR)₄P(C₆H₅)₃]ClO₄) in (CD₃)₂CO and C₅D₅N solution, but are smaller in CDCl₃ and CD₃CN, and approximately equal in CD₃NO₂ and (CD₃)₂SO. Properties of the solvents are also considered.     

N-substituted ethylcarbamate complexes of thorium(IV) and lanthanum(III) nitrates

N-substituted ethylcarbamates form with thorium nitrate the complexes Th(NO₃)₄·3RHNC(O)OC₂H₅ (where R = CH₃, C₂H₅, C₆H₅(CH₃)CH) and with lanthanum nitrate the complexes La(NO₃)₃· 2RR′NC(O)OC₂H₅·3H₂O (where R = CH₃, C₂H₅, C₆H₅(CH₃)CH; R′ = H and R = CH₃, C₆H₅; R′ = C₂H₅ or R = R′ = CH₃). In addition the anhydrous La(NO₃)₃·3(C₂H₅)₂NC(O)OC₂H₅ has been isolated. From the IR spectra it is deduced that the carbamates coordinate the metal through the carbonyl oxygen atom and that the nitrato groups act as chelated ligands. ¹H nmr spectral data of the complexes are reported and discussed.