Bi-O Bonds Research Articles

Sol-Gel Synthesis, Crystal Structure and Electronic Properties in Bi2+xAlxNi4-3xO7+δ (0.0 ≤ x ≤ 0.75) Composite Oxides

Sol-gel synthesis of Bi2+xAlxNi4-3xO7+δ (A1-A4: x = 0.0, 0.25, 0.50, 0.75) composite oxides were performed via nitrate-citrate route. Analysis of the powder XRD patterns by Fullprof shows cubic unit cell with lattice parameters in A1-A4: a = 10.2678, 10.1197, 10.1183, 10.1134 A; Z= 4 and space group Pm3n. Average crystallite sizes in A1-A4 determined by Scherrer’s relation are found to be in the range ~ 42-61 nm. The differential thermal analysis (DTA)/ thermogravimetric (TG) results show no phase transitions in the range 25-800 oC. The morphology of the samples characterized by scanning electron microscopy (SEM) show similar results with respect to the particle sizes and shapes. Rietveld refinement of the unit cell structure shows appreciably lowered agreement factors Rp, Rwp and Rexp for all the samples. The Bi-O and Ni-O bonds of different sites show marginal variations in the samples. Circular electron density contours around Ni and O due to valence orbitals shows the partial ionic character of Ni-O bonds. The plane-wave Density Functional Theory (DFT) calculations on crystal of structure of A1-A4 for band structure and density of states (DOS) using a CASTEP programme package show the valence band (VB) located at -8.0 to ~ 0.0 eV (Fermi level) predominantly comprised of O 2p orbitals overlapping with in-phase with Ni t2g , and the Bi 6s orbitals to form Ni-O-Bi bonds, and O 2p orbitals overlapping with Ni t2g or Bi 6s forming O-Ni-O or Bi-O-Bi bonds. The conduction band (CB) is composed of Ni eg orbitals, which narrows down with complete smearing of ~ 2.0 to 3.0 eV CB as in A1 in A2-A4 due to the absence of Al 3+ d orbitals. This result shows the transition of semiconductor-like as in A1 to metallic character with the Ni eg band predominantly crossing the Fermi level, in A2-A4. Research Article

Electronic structure of multiferroicBiFeO3and related compounds: Electron energy loss spectroscopy and density functional study

The electronic structure of complex oxides is important for the understanding of their functional properties. In this paper, the electronic structures of the multiferroic perovskite bismuth ferrite $({\text{BiFeO}}_{3})$ and the related isostructural compounds ${\text{Bi}}_{0.9}{\text{La}}_{0.1}{\text{FeO}}_{3}$ and ${\text{BiFe}}_{0.7}{\text{Mn}}_{0.3}{\text{O}}_{3}$ are investigated through experiments and modeling. Using electron energy loss spectroscopy the oxygen $K$ edge, i.e., the unoccupied $\text{O}\text{ }p$ density of states, is probed. As these states participate in covalent bonding with both Bi and Fe states, insight into the bonding in the materials is obtained. By substituting on both cation sites, it is possible to connect features in the spectrum to chemical bonds to the cations. We compare the experimental results of substituted and unsubstituted ${\text{BiFeO}}_{3}$ and apply a multiple-scattering approach as well as density functional theory to interpret the differences in terms of changes in electronic structure and density of states. Specifically, we show that although mainly ionic, both Bi-O and Fe-O bonds have some covalent character, and that Mn substitution on Fe sites is found to alter the Bi-O bonds and reduce the anisotropy of the system. Upon introduction of La on Bi sites, the covalent character of the material is reduced and the ionic interaction increases as the La-O bond is higher in energy and mediated through other cation orbitals ($\text{La}\text{ }d$ orbitals) than the Bi-O bond ($\text{Bi}\text{ }p$ orbitals). Also, La substitution is found to influence the Fe electronic structure, showing that the $A$ and $B$ site cations are more coupled than commonly recognized. Thus, we use the electronic structure to confirm that $B$ site cation substitution can influence the ferroelectricity, which is usually almost exclusively attributed to $A$ site cation anisotropy.

Investigation of a BiB3O6crystal growth mechanism by high-temperature Raman spectroscopy

High-temperature Raman spectroscopy has been applied to investigate the melt structure near the BiB3O6 (BIBO) crystal–melt interface. Based on the experimental results, the crystal growth mechanism was proposed. (BOO)n (O = bridging oxygen atom) chains and free Bi3+ cations present in the BIBO bulk melt act as the crystal growth units. Bi-O bonds and [BO4]-tetrahedra were found near the BIBO crystal–melt interface. Two neighboring oxygen atoms in a (BOO)n chain or in two different (BOO)n chains are connected by the Bi3+ cations to form the structural prototype of BIBO crystal. Two adjacent (BOO)n chains are further connected to each other through the [BO4] tetrahedra to form the BIBO crystal structure. The predicted growth habit of the BIBO crystal is consistent with the observed one based on the mechanism.

Ab initiomolecular dynamics simulations of oxide-ion disorder in theδ-Bi2O3

We study in detail the structural, dynamical, and electronic properties of the $\ensuremath{\beta}$ and $\ensuremath{\delta}$ phases of ${\text{Bi}}_{2}{\text{O}}_{3}$ using Born-Oppenheimer molecular dynamics together with extensive lattice static simulations at the level of gradient-corrected density-functional theory. The short Bi-O bonds of $\ensuremath{\sim}2.1--2.2\text{ }\text{\AA{}}$ and the broad peak in the O-Bi-O angular distribution function at $\ensuremath{\sim}70\ifmmode^\circ\else\textdegree\fi{}$ of $\ensuremath{\delta}{\text{-Bi}}_{2}{\text{O}}_{3}$ are in good agreement with those from neutron diffraction, locally resembling the distorted structures of many fully ordered oxides of bismuth under ambient conditions. This places some doubt on structural models where the oxygen vacancies are either distributed at random over a set of ``ideal'' anion lattice sites or preferentially aligned in pairs at these positions. The irregular local structure of $\ensuremath{\delta}{\text{-Bi}}_{2}{\text{O}}_{3}$ is intimately connected to the pronounced electron density around bismuth, providing evidence for the presence of a sterochemically active ``lone pair.'' The dominant influence of the anion $2p$ orbital on this asymmetry mirrors recent findings for many ordered post-transition-metal oxides and contrasts that of the conventional ``$n{s}^{2}$ lone-pair model.'' The markedly curved diffusion trajectories and an unusually high occurrence of short residence times show that the oxygen diffusion is strongly influenced by the local distortions of the immobile lattice. In contrast, we find little evidence for collective diffusion of oxygens.

Charge transfer transitions in multiferroicBiFeO3and related ferrite insulators

The optical response of the technologically interesting multiferroic ${\text{BiFeO}}_{3}$ and related complex iron oxides, having high N\'eel or Curie temperature, is studied in the wide spectral range from 0.6 up to 5.8 eV by means of spectroscopic ellipsometry. The investigated iron oxides have different crystal symmetry with ${\text{FeO}}_{6}$ octahedral and ${\text{FeO}}_{4}$ tetrahedral centers distorted to a certain degree. One of the two groups of materials includes ${\text{BiFeO}}_{3}$, ${\text{ErFeO}}_{3}$, ${\text{Y}}_{.95}{\text{Bi}}_{.05}{\text{FeO}}_{3}$, $\ensuremath{\alpha}{\text{-Fe}}_{2}{\text{O}}_{3}$, ${\text{Fe}}_{2\ensuremath{-}x}{\text{Ga}}_{x}{\text{O}}_{3}$, and ${\text{Fe}}_{3}{\text{BO}}_{6}$ in which iron ${\text{Fe}}^{3+}$ ions occupy only octahedral centrosymmetric or noncentrosymmetric positions and distortions range of 1--20 %. The second group includes ${\text{LiFe}}_{5}{\text{O}}_{8}$, ${\text{BaFe}}_{12}{\text{O}}_{19}$, ${\text{Sm}}_{3}{\text{Fe}}_{5}{\text{O}}_{12}$, and ${\text{Ca}}_{2}{\text{Fe}}_{2}{\text{O}}_{5}$ in which ${\text{Fe}}^{3+}$ ions occupy both octahedral and tetrahedral positions with a rising tetra/ortho ratio. We show that in the spectral range up to $\ensuremath{\sim}3.7\text{ }\text{eV}$, the optical response is dominated by $p\text{\ensuremath{-}}d$ charge transfer (CT) transitions, while at $Eg3.7\text{ }\text{eV}$ both $p\text{\ensuremath{-}}d$ and $d\text{\ensuremath{-}}d$ CT transitions are revealed. At variance with several previous investigations, we present a correct and unified assignment of different dipole-allowed and dipole-forbidden CT transitions. All the ferrites investigated are CT insulators with the band gap determined by a dipole-forbidden $p\text{\ensuremath{-}}d$ CT transition ${t}_{1g}\ensuremath{\rightarrow}{t}_{2g}$, forming a $\ensuremath{\sim}2.5\text{ }\text{eV}$ band on the tail of a strong 3.0 eV band assigned to dipole-allowed $p\text{\ensuremath{-}}d$ CT transitions ${t}_{2u}(\ensuremath{\pi})\ensuremath{\rightarrow}{t}_{2g}$ in octahedral ${\text{FeO}}_{6}$ centers. A noticeable enhancement of the optical response in ${\text{BiFeO}}_{3}$ at $\ensuremath{\sim}4\text{ }\text{eV}$ as compared with other related iron oxides is attributed to CT transitions within the Bi-O bonds. We report an observation of unexpected midinfrared CT bands in calcium ferrite ${\text{Ca}}_{2}{\text{Fe}}_{2}{\text{O}}_{5}$ and an enhanced structureless spectral weight in a wide range below the main CT bands in ${\text{BiFeO}}_{3}$ with a remarkable smearing of the fundamental absorption edge. All these anomalies are assigned to CT instabilities accompanied by a self-trapping of $p\text{\ensuremath{-}}d$ CT excitons and nucleation of electron-hole droplets. The optical detection of this CT instability agrees with the observation of a metal-insulator transition in bismuth ferrite.

Addition of Dimethylaminobismuth to Aldehydes, Ketones, Alkenes, and Alkynes

Bi-O chemistry: A direct regioselective route to bismuth bis(amino)naphthalene compounds, incorporating Bi-O and Bi-C bonds is described, in which an amide precursor is treated with aldehydes, ketones, alkenes, and alkynes, leading to insertion into the Bi-NMe(2) bond.

Structure of bismuth oxoborate Bi4B2O9 at 20, 200, and 450°C

Single crystals of bismuth oxoborate Bi4B2O9 have been grown by slowly cooling the melt of a stoichiometric Bi2O3 + H3BO3 mixture. The structure of the borate (monoclinic space group P21/c, a = 11.107 A, b = 6.629 A, c = 11.044 A, β = 91.04°, Z = 4) has been studied at 20, 200, and 450°C. The structure is described not only in terms of full BiO6− and BiO7 polyhedra but also in terms of truncated BiO3− and BiO4− polyhedra and BO3 triangles, as well as oxo-centered OBi3 triangles and OBi4 tetrahedra. It is shown that both the B-O and Bi-O bond lengths are practically unaffected by temperature. Only the angles between polyhedra change with temperature, being responsible for the strong anisotropy of Bi4B2O6 thermal expansion, which was measured by high-temperature powder X-ray diffraction: α11 = 20, α22 = 15, α33 = 6 × 10−6 °C−1, and μ = (c, α33) = −19°.

Synthesis and structures of triphenylbismuth diaroxides Ph3Bi(OAr)2, Ar = C6H3(Br2-2,4), C6H2(Br2-2,6)(NO2-4), and C6H2[(NO2)3-2,4,6

Triphenylbismuth diaroxides Ph3Bi(OAr)2 (Ar = C6H3(Br2-2,4) (I), C6H2(Br2-2,6)(NO2-4) (II), and C6H2[(NO2)3-2,4,6] (III) are synthesized in yields up to 74% by the reaction of triphenylbismuth with phenols in the presence of hydrogen peroxide (taken at a molar ratio 1: 2: 1, respectively) in ether. According to X-ray diffraction data, the bismuth atoms in compounds I-III have distorted trigonal-bipyramidal coordination with the aroxyl substituents in the axial positions; the Bi-C, Bi-O bond lengths and the OBiO, CBiC angles vary in the intervals 2.162–2.204, 2.150–2.299 A and 172.4°–176.1°, 109.6°–139.9°, respectively. Compound II exhibits intramolecular contacts between the central atom and ortho-Br atoms (3.924, 4.101 A), and compound III has similar contacts of the Bi atom with the O atoms of the ortho-nitro groups (3.114, 3.313 A).

Synthesis and crystal structure of KBi(C6H4O7) · 3.5H2O

A novel compound, KBi(C6H4O7) · 3.5H2O (I), has been synthesized in the Bi(NO3)2-K3(HCit) system (HCit3− is an anion of citric acid C6H8O7) at a component ratio (n) of 8 in a water-glycerol mixture, and its crystal structure has been determined. The crystals are unstable in air. The crystals are triclinic: a = 7.462 A, b = 10.064 A, c = 17.582 A, α = 100.27°, β = 99.31°, γ = 105.48°, V = 1221.2 A3, Z = 2, space group % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqipu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamiuaiqaig% dagaqeaaaa!3775! $$P\bar 1$$ . In the structure of I, asymmetric binuclear fragments [Bi2(Cit4−)2(H2O)2]2− are linked through inversion centers into polymeric chain anions. Ions K+ and crystal water molecules are arranged in channels between the chains. The Bi(1)...Bi(2) distances in the binuclear fragment are 4.62 A, and the Bi(1)...Bi(1) and Bi(2)...Bi(2) distances between bismuth atoms in the chain are 5.83 and 5.95 A, respectively. The chains are linked through bridging oxygen atoms of the ligands Cit to form layers. In the centrosymmetric four-membered chelate ring Bi2O2 formed through Bi-O(Cit) bonds, the distances Bi(1)-Bi(1) are equal to 4.55 A, and Bi(1)-O are 2.66 and 2.84 A. The Bi-O bond lengths in I are in the range 2.12–3.16 A. The Cit ligands act as hexadentate chelating/bridging ligands.

Oxygen Electroreduction through a Superoxide Intermediate on Bi-Modified Au Surfaces

The mechanism of the electroreduction of oxygen on bare and Bi-submonolayer-modified Au(111) surfaces is examined using surface enhanced Raman scattering (SERS) measurements along with detailed density functional theory (DFT) calculations. The spectroscopy reveals the presence of superoxide-level species at potentials where oxygen is reduced. These species are not present in solutions absent either oxygen or Bi at these potentials. The spectroscopy also reveals the presence of Bi-OH species which are associated with peroxide reduction. Detailed calculations show oxygen associates much more strongly with Bi in the (2 x 2) configuration on Au(111) relative to the bare Au surface. Additionally, the O-O bond is elongated following O2 association, which follows as a consequence of Bi-O bond formation and partial oxidation of the Bi adatom. These results show for the first time that the four-electron electroreduction of oxygen electroreduction occurs via a series pathway on the Bi-modified surface in acid solution.

Synthesis and structure of 2,4,6-tribromophenoxytetraphenylbismuth

Four new complexes of pentavalent bismuth are synthesized: Ph3Bi[OC6H2(Br3-2,4,6)]2, Ph3Bi[OC6H2(Cl3-2,4,6)]2, Ph4BiOC6H2(Br3-2,4,6), and Ph4BiOC6H2(Cl3-2,4,6). Tetraphenylbismuth aroxides are produced by the disproportionation reaction of ligands from pentaphenylbismuth and triphenylbismuth diaroxides in toluene or from pentaphenylbismuth and phenol. Triphenylbismuth diaroxides are synthesized from phenol, triphenylbismuth, and hydrogen peroxide taken at a molar ratio of 2 : 1 : 1, respectively, in diethyl ether. According to the X-ray diffraction data, the bismuth atom surrounding in 2,4,6-tribromophenoxytetraphenylbismuth has the configuration of a trigonal bipyramid with the aroxyl ligand in the axial position. The Bi-C and Bi-O bond lengths are 2,184, 2.190, 2.234, and 2.514 A, respectively, and the equatorial CSbC angles are equal to 111.4°, 121.3°, and 121.3°.

Synthesis and Structure of Bismuth Tris(3-Methylbenzoate) [Bi(O2CC6H4CH3-3)3] and Phenylbismuth Bis(3,4,5-Trifluorobenzoate) [PhBi(μ-O2CC6H2F3-3,4,5)(O2CC6H2F3-3,4,5)]2

Bismuth tris(3-methylbenzoate) [Bi(O2CC6H4CH3-3)3]∞ (I) and phenylbismuth bis(3,4,5-trifluorobenzoate) [PhBi(μ-O2CC6H2F3-3,4,5)(O2CC6H2F3-3,4,5)]2 (II) were synthesized by reacting triphenylbismuth with 3-methylbenzoic and 3,4,5-trifluorobenzoic acids. Coordination numbers of bismuth atoms in I and II are 9 and 6, respectively; carboxylate ligands function as bi- and tridentate ligands. The Bi-O distances in compound I vary in the range of 2.218(3)-3.202(4) A. The Bi-O and Bi-C bond lengths in II are 2.301(2)-2.674(2) and 2.223(3) A, respectively.

Synthesis and Characterization of AgBiO3 with the Cubic KSbO3 Structure.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Two bismuth oxalate hydrates and revision of their chemical formulae.

The crystal structures of two bismuth(III) oxalate hydrates, previously described as 'Bi(2)(C(2)O(4))(3).H(2)C(2)O(4)' and 'Bi(2)(C(2)O(4))(3).7H(2)O', were solved and refined from single-crystal X-ray diffraction data. The results led to the revised chemical formulae Bi(2)(C(2)O(4))(3).6H(2)O and Bi(2)(C(2)O(4))(3).8H(2)O, respectively. Both dibismuth(III) trioxalate hexahydrate (tetraaquatri-micro-oxalato-dibismuth(III) dihydrate, [[Bi(2)(C(2)O(4))(3)(H(2)O)(4)].2H(2)O](n)) and dibismuth(III) trioxalate octahydrate (tetraaquatri-micro-oxalato-dibismuth(III) tetrahydrate [[Bi(2)(C(2)O(4))(3)(H(2)O)(4)].4H(2)O](n)) are characterized by a three-dimensional network of Bi atoms connected by tetradentate oxalate groups. All ligand and 'free' water molecules are located in channels and voids. The mean Bi-O bond lengths are approximately 2.51 A. The lone electron pairs on all Bi(3+) cations are stereochemically inactive.

Orbital hybridization and covalency in paraelectric and ferroelectricSrBi2Nb2O9

Electron-density distributions of paraelectric and ferroelectric ${\mathrm{SrBi}}_{2}{\mathrm{Nb}}_{2}{\mathrm{O}}_{9}$ were analyzed by means of synchrotron x-ray diffraction. The obtained electron-density distributions well reproduced the atomic arrangements of the material. Bonding electrons due to hybridization of orbitals were clearly seen in the Nb-O bonds in the octahedron and in the Bi-O bonds in the ${\mathrm{Bi}}_{2}{\mathrm{O}}_{2}$ layer. The hybridization between $\mathrm{Nb}(4d)$ and $\mathrm{O}(2p)$ orbitals was enhanced in the ferroelectric phase, and one of the Nb-O bonds showed a strong covalent character below the ferroelectric Curie temperature. Weak hybridization of the $\mathrm{Sr}(5s)$ with $\mathrm{O}(2p)$ orbitals appears to play an important role in structural distortion and ferroelectric polarization. The changes in the electron-density distribution through the ferroelectric phase transition are similar to those observed in ferroelectric ${\mathrm{PbTiO}}_{3}$ perovskite.

Evidence for an Unstable Bi(II) Radical from Bi−O Bond Homolysis. Implications in the Rate-Determining Step of the SOHIO Process

The reaction of BiCl(3) with the lithium salt of o-di-tert-butylphenol under nitrogen forms organic oxidation products rather than the expected Bi(OAr)(3) complex, and bismuth disproportionation products. Likewise, the decomposition of Bi(III) aryloxides Bi(O-2,6-(i)Pr(2)C(6)H(3))(3) and ClBi(O-2,4,6-(t)Bu(3)C(6)H(2))(3) leads to corresponding organic oxidation products. These reactions can be explained by Bi-O bond homolysis to form unstable Bi(II) radicals, analogous to a fundamental step suggested to intervene in the SOHIO process.

Reactions of triarylbismuth bis(arenesulfonates)

Reactions of triphenylbismuth with sodium salts, acids, alkalies, and zinc are studied. In the first three cases Bi-O bond cleavage takes place, while zinc reduces the starting bismuth compounds to triphenylbismuth.

The crystal structure of namibite, Cu(BiO)2VO4(OH), and revision of its symmetry

The crystal structure of namibite, Cu(BiO)2VO4(OH) [triclinic, space group P1̄, a = 6.210(1), b = 7.398(1), c = 7.471(1) Å, α = 90.10(1), β = 108.73(1), γ = 107.47(1)°, V = 308.22(8) Å3, Z = 2] was determined using single-crystal X-ray diffraction data. The refinement, based on 2140 unique reflections with Fo > 4σ(Fo), gave R1 = 3.61%. The structure determination showed namibite to be triclinic-pseudomonoclinic; the previously reported C-centered monoclinic cell is a pseudocell. The structure contains two unique Bi atoms, with nine Bi-O bonds between 2.17 and 3.39 Å. The Bi coordinations show some stereochemical influence of the lone pair of electrons on Bi3+. A threedimensional network is formed by linkages of Bi-O polyhedra to one slightly distorted V5+O4 tetrahedron that decorates chains of corner-sharing CuO6 polyhedra extending parallel to the b axis. The CuO6 polyhedra show the Jahn-Teller-distorted [4+2]-coordination of Cu2+. Layers of Bi atoms parallel to (100) alternate with layers of parallel heteropolyhedral [Cu(VO4)O2(OH)] chains. According to bond-valence calculations and geometrical considerations, the H atom of the OH group is probably involved in disordered or trifurcated H bonding. The structure of namibite represents a slightly distorted ordered variant of the monoclinic structure of brendelite, (Bi,Pb)2(Fe3+,Fe2+)O2(OH)(PO4). Further relations to synthetic Cu3Bi4V2O14, to the 7 Å chain-structure phosphates and sulfates, and to linarite are outlined.

Solvation of the bismuth(III) ion by water, dimethyl sulfoxide, N,N'-dimethylpropyleneurea, and N,N-dimethylthioformamide. An EXAFS, large-angle X-ray scattering, and crystallographic structural study.

The structure of the solvated bismuth(III) ion in aqueous, dimethyl sulfoxide, N,N'-dimethylpropyleneurea, and N,N-dimethylthioformamide solution has been studied by means of EXAFS and large-angle X-ray scattering (LAXS). The crystal structures of the solid compounds octakis(dimethyl sulfoxide)bismuth(III) perchlorate, [Bi(OS(CH3)2)8](ClO4)3, hexakis(N,N'-dimethylpropyleneurea)bismuth(III) perchlorate, [Bi(OCN2(CH2)3(CH3)2)6](ClO4)3, and nonaaquabismuth(III) trifluoromethanesulfonate, [Bi(H2O)9](CF3SO3)3 (redetermination), have been determined. The aqueous solutions must be strongly acidic, since the hydrated bismuth(III) ion starts to hydrolyze into Bi6O4(OH)4(6+) complexes already at an excess of strong acid at 1.0 mol.dm-3. For very acidic aqueous perchlorate solutions, the LAXS and EXAFS data gave a satisfactory fit for eight-coordination of the bismuth(III) ion, with a mean Bi-O bond distance of 2.41(1) A. The crystal structure of octakis(dimethyl sulfoxide)bismuth(III) perchlorate shows that the bismuth(III) ion coordinates eight dimethyl sulfoxide molecules via the oxygen atoms in a distorted square antiprismatic configuration. The mean Bi-O bond distance is 2.43 A and the mean Bi...S distance 3.56 A. For the dimethyl sulfoxide solution, the corresponding mean distances were found to be 2.411(6) and 3.535(12) A. The N,N'-dimethylpropyleneurea-solvated bismuth(III) ion is octahedrally coordinated in both solid state and solution with the Bi-O bond distances of 2.324(5) and 2.322(3) A, respectively. The bismuth(III) ion is six-coordinated in the sulfur donor solvent N,N-dimethylthioformamide with a mean Bi-S bond distance of 2.794(8) A. A comparison with the structure of the solvated lanthanum(III) ion shows that the bismuth(III) ion is smaller for all coordination numbers. New effective ionic radii for the bismuth(III) ion in different coordination numbers are proposed, based on results in this study and in the literature.

EPR, IR and DC conductivity studies ofxCuO-(100-x) Bi2O3 glasses

Glass systemxCuO-(100-x) Bi2O3 in the composition range 30–60 mol% of CuO is prepared by melt-quenching technique. The ESR spectra show no hyperfine splittings in parallel part but the peak to peak field width is found to vary with CuO content. The observedg effective values are found to vary with copper oxide. The absence of hyperfine splittings is due to inhomogeneous broadening. The observed IR spectra suggest the presence of Bi-O bonds. The structure is changing from [BiO6] octahedral to [BiO3] pyramidal units with increasing CuO concentration. D.C. electrical conductivity results indicate that the conduction is electron in nature and arises out of adiabatic hopping of polarons. The activation energy is found to be concentration and temperature dependent.