Molecular Ln(III)−H−E(II) Linkages (Ln=Y,Lu; E=Ge,Sn, Pb)

Following the alkane-elimination route, the reaction between tetravalent aryl tintrihydride Ar*SnH₃ and trivalent rare-earth-metallocene alkyls [Cp*₂Ln(CH{SiMe₃}₂)] gave complexes [Cp*₂Ln(μ-H)₂SnAr*] implementing a low-valent tin hydride (Ln=Y, Lu; Ar*=2,6-Trip₂C₆H₃, Trip=2,4,6-triisopropylphenyl). The homologous complexes of germanium and lead, [Cp*₂Ln(μ-H)₂EAr*] (E = Ge, Pb), were accessed via addition of low-valent [(Ar*EH)₂] to the rare-earth-metal hydrides [(Cp*₂LnH)₂]. The lead compounds [Cp*₂Ln(μ-H)₂PbAr*] exhibit H/D exchange in reactions with deuterated solvents or dihydrogen.     

NMR Studies of Mixed-Ligand Lanthanide (III) Complexes. Peculiarities of Molecular Structure, Dynamics and Paramagnetic Properties for Cerium Subgroup Chelates with Crown Ethers

The molecular structure, dynamics and paramagnetic properties of the complex cations [Ln(ptfa)₂ (18-crown-6)]⁺ in deuterated toluene were studied for Ln = La, Ce, Pr and Nd. The activation enthalpy values of 68 ± 5, 55 ± 15 and 60 ± 13 kJ mol^-1 for the 18-crown-6 conformationalinversion processes for the complexcations of Ce, Pr and Nd, respectively,were obtained. Quantitativeinvestigation of the lanthanide-induced chemical shifts shows a monotonic change of a spatial structure and magnetic susceptibility in comparison with the Bleaney predicted dependence. The free energy of molecular inversion activation for 18-crown-6 molecules in the complex cation [Ln(fod)₂(18-crown-6)]⁺ is 74 ± 9 kJ mol^-1 at 363 K, which is a little more than the value of the free energy of activation 64 ± 9 kJ mol^-1 at 363 K in the complex cation [Ln(ptfa)₂(18-crown-6)]⁺.     

Nanosized thermometric NMR sensors based on the paramagnetic complex ion pairs of lanthanides(III) for temperature determinations in low-polar nonaqueous solutions

For temperature determination in solutions it is suggested that the temperature dependence of the paramagnetic lanthanide-induced shifts (LIS) in the NMR spectra on the ligand nuclei be used for [Ln(PTA)₂(18-crown-6)]⁺[Ln(PTA)₄]^? complex ion pairs formed in CCl₄, CDCl₃, CD₂Cl₂, CD₃C₆D₅, and C₂D₃N type low-polar solvents (Ln = La, Ce, Pr, Nd, Eu; PTA is the pivalyltrifluoroacetonato anion). It was found experimentally that the [Ln(PTA)₂(18-crown-6)]⁺ complex cation molecules (Ln = Ce and Pr) proved most suitable for use as nanosized (≈1.1 nm) probes for temperature determinations in nonaqueous solutions. A linear dependence of the LIS on the ¹H nuclei of different groups and the difference between the LIS corresponding to the CH₂ groups of the 18-crown-6 molecules and the CH groups of the PTA anions on the reciprocal temperature (1/T) was found. The LIS of the individual signals of different groups in Ln paramagnetic complexes (relative to the signals of the diamagnetic analogs, e.g., La or Lu) may be used for temperature control in the sample, although the temperature measurement error is smaller (≤ 0.04 K) when the difference between the LIS of the CH₂ and CH groups is used. Due to the high thermodynamic and kinetic stability combined with small sizes of [Ln(PTA)₂(18-crown-6)]⁺[Ln(PTA)₄]^? molecules in nonaqueous solutions, these compounds may be used as thermometric NMR sensors directly in reaction media for in situ control over temperature.     

The approach to 4d/4f-polyphosphides

The first 4d/4f polyphosphides were obtained by reaction of the divalent metallocenes [Cp*₂Ln(thf)₂] (Ln = Sm, Yb) with [{CpMo(CO)₂}₂(μ,η^2:2-P₂)] or [Cp*Mo(CO)₂(η³-P₃)]. Treatment of [Cp*₂Ln(thf)₂] (Ln = Sm, Yb) with [{CpMo(CO)₂}₂(μ,η^2:2-P₂)] gave the 16-membered bicyclic compounds [(Cp₂*Ln)₂P₂(CpMo(CO)₂)₄] (Ln = Sm, Yb) as the major products. From the reaction involving samarocene, the cyclic P₄ complex [(Cp*₂Sm)₂P₄(CpMo(CO)₂)₂] and the cyclic P₅ complex [(Cp*₂Sm)₃P₅(CpMo(CO)₂)₃] were also obtained as minor products. In each reaction, the P₂ unit is reduced and a rearrangement occurred. In dedicated cases, a P–P bond formation takes place, which results in a new aggregation of the central phosphorus scaffold. In the reactions of [Cp*₂Ln(thf)₂] (Ln = Sm, Yb) with [Cp*Mo(CO)₂P₃] a new P–P bond is formed by reductive dimerization and the 4d/4f hexaphosphides [(Cp*₂Ln)₂P₆(Cp*Mo(CO)₂)₂] (Ln = Sm, Yb) were obtained.     

Molecular Polyarsenides of the Rare‐Earth Elements

Reduction of [Cp*Fe(η⁵‐As₅)] with [Cp′′₂Sm(thf)] (Cp′′=η⁵‐1,3‐(tBu)₂C₅H₃) under various conditions led to [(Cp′′₂Sm)(μ,η⁴:η⁴‐As₄)(Cp*Fe)] and [(Cp′′₂Sm)₂As₇(Cp*Fe)]. Both compounds are the first polyarsenides of the rare‐earth metals. [(Cp′′₂Sm)(μ,η⁴:η⁴‐As₄)(Cp*Fe)] is also the first d/f‐triple decker sandwich complex with a purely inorganic planar middle deck. The central As₄^2? unit is isolobal with the 6π‐aromatic cyclobutadiene dianion (CH)₄^2?. [(Cp′′₂Sm)₂As₇(Cp*Fe)] contains an As₇^3? cage, which has a norbornadiene‐like structure with two short As?As bonds in the scaffold. DFT calculations confirm all the structural observations. The As?As bond order inside the cyclo As₄ ligand in [(Cp′′₂Sm)(μ,η⁴:η⁴‐As₄)(Cp*Fe)] was estimated to be in between an As?As single bond and a formally aromatic As₄^2? system.     

First Homoleptic Rare Earth Carbazolates: Synthesis,Crystal Structures,Spectroscopic and Thermal Investigations of Divalent 1[Ln(NC12H8)2] with Ln = Europium and Ytterbium

The compounds [Ln(NC₁₂H₈)₂], Ln = Eu and Yb, were obtained in solvent free reactions of the rare earth elements europium and ytterbium with the amine carbazole. Single crystals of both compounds were grown from the melt syntheses, no recrystallization from solvents was necessary. The new compounds are the first examples of homoleptic carbazolates of the rare earth elements furthermore exhibiting divalent lanthanides. In absence of any solvent, carbazole as the sole coordination partner shows η⁶‐π‐coordination in addition to the μ₁‐ and μ₂‐coordination of the nitrogen atoms. This results in a one‐dimensional chain structure of dimers with a formal C.N. of 6 for the rare earth elements and thus being low for divalent lanthanides. The products were investigated by X‐ray single crystal and powder diffraction, Mid IR, Far IR and Raman spectroscopy, and with DTA/TG regarding their thermal behaviour. Both compounds [Ln(NC₁₂H₈)₂], Ln = Eu (1) and Yb (2) , crystallize isotypic in the triclinic space group P1.     

Zur Elektronenstruktur metallorganischer Komplexe der f‐Elemente. 64 Äußert sich die zwitterionische Natur des Triphenylphosphanoxid‐Liganden auch in seinen spektrochemischen Eigenschaften?

Electronic Structures of Organometallic Compounds of f Elements. 64 Does the Zwitterionic Nature of the Triphenylphosphine Oxide Ligand Manifest itself in its Spectrochemical Properties? The triphenylphosphine oxide mono adducts of the moiety tris(η⁵‐cyclopentadienyl)lanthanide(III) (Ln(Cp)₃; Ln = Pr ( 1 ), La ( 2 )) were synthesized and structurally characterized. The Ln–O distances of these compounds are noticeably shorter than those of the corresponding THF adducts. A crystal field (CF) analysis of the optical spectra of 1 leads to a low absolute value of the quadratic CF parameter which is comparable with those of [Pr(Cp)₃(L)]^? adducts with anionic bases but not with [Pr(Cp)₃(MeTHF)]. Reasons for the latter finding are presented.     

From a nanoparticular solid-state material to molecular organo-f-element-polyarsenides

A convenient pathway to new molecular organo-lanthanide-polyarsenides in general and to a f-element complex with the largest polyarsenide ligand in detail is reported. For this purpose, the activation of the solid state material As⁰_nano (nanoscale gray arsenic) by the multi electron reducing agents [K(18-crown-6)][(Ln^+II)₂(μ-η⁶:η⁶-C₆H₆)] (Ln = La, Ce, Cp′′ = 1,3-bis(trimethylsilyl)cyclopentadienyl anion) and [K(18-crown-6)]₂[(Ln^+II)₂(μ-η⁶:η⁶-C₆H₆)] (Ln = Ce, Nd) is shown. These non-classical divalent lanthanide compounds were used as three and four electron reducing agents where the product formation can be directed by variation of the applied reactant. The obtained Zintl anions As₃³⁻, As₇³⁻, and As₁₄⁴⁻ were previously not accessible in molecular 4f-element chemistry. Additionally, the corresponding compounds with As₁₄⁴⁻-moieties represent the largest organo-lanthanide-polyarsenides known to date.

Reaction of non-classical divalent lanthanide compounds with nanoparticulate gray arsenic via three- and four-electron reduction led to a series of new f-element polyarsenides, including the largest f-element polyarsenide known to date.     

Ln3UO6Cl3 (Ln=La,Pr, Nd) -. Die ersten Oxochlorouranate der Seltenen Erden

Ln₃UO₆Cl₃ (Ln=La, Pr, Nd) — The First Oxochlorouranates of the Rare Earths . The new compounds Ln₃UO₆Cl₃ (Ln=La, Pr, Nd) were prepared by heating stoichiometric amounts of LnOCl/Ln₂O₃/U₃O₈ (7 : 1 : 1) (Ln=La, Nd) and PrOCl/Pr₆O₁₁/U₃O₈ (12 : 1 : 2) in silica ampoules (5 d, 1000°C, Ln=La; 9 d 800°C, Ln=Pr, Nd) in the presence of an excess of chlorine [p(Cl₂, 25°C)=1 atm]. Single crystals were obtained by chemical transport reactions using chlorine [p(Cl₂, 25°C)=1 atm] as transport agent [T₂=1000°C→T₁=900°C (Ln=La); T₂=840°C→T₁=780°C (Ln=Pr, Nd)]. Crystals of Ln₃UO₆Cl₃ (Ln=La, Pr, Nd) were investigated by X-ray diffraction methods and La₃UO₆Cl₃ additionally by high resolution electron microscopy. The compounds Ln₃UO₆Cl₃ crystallize in the hexagonal spacegroup P6₃/m (No. 176) with Z=2 formula units per unit cell. Isotypical structure refinements resulted in R=3.04% respectively R_w=1.91% (Ln=La), R=4.72% respectively R_w=3.80% (Ln=Pr) and R=3.99% respectively R_w=2.49% (Ln=Nd). Uranium is coordinated with six oxygen atoms forming a trigonal prism. Lanthanide ions are 10-coordinated (6 oxygen atoms, 4 chlorine atoms).     

Complexes of the Lighter Lanthanoid Nitrates with 15-crown-5 and 18-crown-6 ethers: Synthesis and characterization

Complexes of lanthanoid trinitrates Ln(NO₃)₃ with 15-crown-5 ether 1 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd) and with 18-crown-6 ether 2 (Ln = La, Ce, Pr, Nd) having a 1:1 stoichiometry as well as 4:3 complexes with 2 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd) have been synthesized and characterized. All the isolated complexes are solvent free. At 170–220° the 1:1 complexes of 2 are quantitatively transformed into 4:3 complexes. X-Ray powder diagrams of the neodymium complexes with 2 indicate that both the 1:1 and 4:3 complexes are genuine compounds. All the 1:1 complexes show a characteristic IR. absorption band at 875–880 cm^?1 absent from both the spectra of the free ligands and of the 4:3 complexes. The spectroscopic properties (IR. and electronic spectra, fluorescence lifetimes) of the complexes and the low magnetic moments of the Ln(III) ions in the complexes with Ln = Ce-Eu are indicative of a strong interaction between the lanthanoid ions and the crown ethers 1 and 2 .     

Electronic Structure of Thiolate‐bridged Diiron Complexes and a Single‐electron Oxidation Reaction: A Combination of Experimental and Computational Studies

Single‐electron oxidation of a diiron‐sulfur complex [Cp*Fe(μ‐bdt)FeCp*] ( 1 , Cp*=η⁵‐C₅Me₅; bdt=benzene‐1,2‐dithiolate) to [Cp*Fe(μ‐bdt)FeCp*]⁺ ( 2 ) has been experimentally conducted. The bdt ligand with redox‐active character has been computationally proposed to be a dianion (bdt^2?) rather than previously proposed monoanion (bdt^·?) radical in 1 though it has un‐equidistant aromatic C? C bond lengths. The ground state of 1 is predicted to be two low‐spin ferrous ions (S_Fe=0) and 2 has a medium‐spin ferric ion (S_Fe=1/2) and a low‐spin ferrous center (S_Fe=0), and the oxidation of 1 to 2 is calculated to be a single‐metal‐based process. Both complexes have no significant antiferromagnetic coupling character.     

Half-sandwich bis(tetramethylaluminate) complexes of the rare-earth metals: synthesis, structural chemistry, and performance in isoprene polymerization

The protonolysis reaction of [Ln(AlMe(4))(3)] with various substituted cyclopentadienyl derivatives HCp(R) gives access to a series of half-sandwich complexes [Ln(AlMe(4))(2)(Cp(R))]. Whereas bis(tetramethylaluminate) complexes with [1,3-(Me(3)Si)(2)C(5)H(3)] and [C(5)Me(4)SiMe(3)] ancillary ligands form easily at ambient temperature for the entire Ln(III) cation size range (Ln=Lu, Y, Sm, Nd, La), exchange with the less reactive [1,2,4-(Me(3)C)(3)C(5)H(3)] was only obtained at elevated temperatures and for the larger metal centers Sm, Nd, and La. X-ray structure analyses of seven representative complexes of the type [Ln(AlMe(4))(2)(Cp(R))] reveal a similar distinct [AlMe(4)] coordination (one eta(2), one bent eta(2)). Treatment with Me(2)AlCl leads to [AlMe(4)] --> [Cl] exchange and, depending on the Al/Ln ratio and the Cp(R) ligand, varying amounts of partially and fully exchanged products [{Ln(AlMe(4))(mu-Cl)(Cp(R))}(2)] and [{Ln(mu-Cl)(2)(Cp(R))}(n)], respectively, have been identified. Complexes [{Y(AlMe(4))(mu-Cl)(C(5)Me(4)SiMe(3))}(2)] and [{Nd(AlMe(4))(mu-Cl){1,2,4-(Me(3)C)(3)C(5)H(2)}}(2)] have been characterized by X-ray structure analysis. All of the chlorinated half-sandwich complexes are inactive in isoprene polymerization. However, activation of the complexes [Ln(AlMe(4))(2)(Cp(R))] with boron-containing cocatalysts, such as [Ph(3)C][B(C(6)F(5))(4)], [PhNMe(2)H][B(C(6)F(5))(4)], or B(C(6)F(5))(3), produces initiators for the fabrication of trans-1,4-polyisoprene. The choice of rare-earth metal cation size, Cp(R) ancillary ligand, and type of boron cocatalyst crucially affects the polymerization performance, including activity, catalyst efficiency, living character, and polymer stereoregularity. The highest stereoselectivities were observed for the precatalyst/cocatalyst systems [La(AlMe(4))(2)(C(5)Me(4)SiMe(3))]/B(C(6)F(5))(3) (trans-1,4 content: 95.6 %, M(w)/M(n)=1.26) and [La(AlMe(4))(2)(C(5)Me(5))]/B(C(6)F(5))(3) (trans-1,4 content: 99.5 %, M(w)/M(n)=1.18).     

稀土冠醚配合物的研究 XI: 稀土(III)硝酸盐与戊二酰双(苯并-15-冠-5)配合物的合成和性质研究

本工作合成了十五个新的镧系、钇的硝酸盐和戊二酰双(苯并-15-冠-5)的配合物,并进行了元素分析、紫外光谱、红外光谱、激光拉曼光谱、差热和热重等性质研究, 对这一系列稀土配合物的性质作了比较。     

Extraction of Lanthanide(III) and Yttrium(III) Nitrates with a Toluene Solution of Trialkylbenzylammonium Naphthenate

Extraction of lanthanides(III) [La(III)-Lu(III)] and yttrium(III) with toluene solution of trialkylbenzylammonium naphthenate mixture was studied. The equations of extraction isotherms taking into account formation of the extractable complexes (R₄N)₂[Ln(NO₃)₃A₂] (A is naphthenate anion) were obtained. The extraction constants of lanthanides [La(III)-Lu(III] and yttrium(III) were calculated.     

Erste Pyridylbenzimidazolate der Lanthanide: Synthese,Kristallstruktur und thermischer Abbau von NH4[Ln(N3C12H8)4] mit Ln = Nd,Yb

The First Pyridylbenzimidazolates of the Lanthanides: Syntheses, Crystal Structure and Thermal Decomposition of NH₄[Ln(N₃C₁₂H₈)₄] with Ln = Nd, Yb Transparent yellow crystals of the compounds NH₄ [Ln^III (N₃C₁₂H₈)₄] with Ln = Nd, Yb were obtained by solvent‐free reactions of the lanthanides neodymium and ytterbium with 2‐(2‐Pyridyl)‐benzimidazole. The bulk syntheses lead to isotypic compounds despite the different ionic radii of Nd^III and Yb^III exhibiting nitrogen coordination of the lanthanides only. Both compounds were investigated IR‐ and Raman‐spectroscopically and in regard to their thermal behaviour. They are the first examples of completely solvent‐free (coordinating and non‐coordinating) compounds of the lanthanides with a complete N‐coordination that were obtained via a solid‐state reaction method.     

Hetero-bimetallic Lanthanide-Coinage Metal Compounds Featuring Possible Metal-Metal Interactions in the Excited State

Heterometallic complexes, combining metals of the outer rims of the d-block, for example lanthanides(III) (Ln) and coinage metals(I) (M) are scarcely reported, synthetically challenging and highly interesting in terms of their interactions. In this context, we synthesized hetero-bimetallic Ln−M compounds ligated by the phosphine functionalized amidinate system (N,N’-bis[(2-diphenylphosphino)phenyl]formamidinate, “dpfam”). The resulting compounds [dpfam₃LnM][OTf] (Ln = La, Nd and M = Ag, Au) feature a close proximity of the two metal centres and were investigated experimentally by photoluminescence spectroscopy and quantum chemical calculations. The latter showed rare La−Au interactions for the first excited state.     

Heterometallic Polyhydride Complexes Containing Yttrium Hydrides with Different Cp Ligands: Synthesis,Structure, and Hydrogen‐Uptake/Release Properties

A new family of Y₄/M₂ and Y₅/M heterobimetallic rare‐earth‐metal/d‐block‐transition‐metal? polyhydride complexes has been synthesized. The reactions of the tetranuclear yttrium? octahydride complex [{Cp′′Y(μ‐H)₂}₄(thf)₄] (Cp′′=C₅Me₄H, 1‐C₅Me₄H ) with one equivalent of Group‐6‐metal? pentahydride complexes [Cp*M(PMe₃)H₅] (M=Mo, W; Cp*=C₅Me₅) afforded pentanuclear heterobimetallic Y₄/M? polyhydride complexes [{(Cp′′Y)₄(μ‐H)₇}(μ‐H)₄MCp*(PMe₃)] (M=Mo ( 2 a ), W ( 2 b )). UV irradiation of compounds 2 a , b in THF gave PMe₃‐free complexes [{(Cp′′Y)₄(μ‐H)₆(thf)₂}(μ‐H)₅MCp*] (M=Mo ( 3 a ), W ( 3 b )). Compounds 3 a , b reacted with one equivalent of [Cp*M(PMe₃)H₅] to afford hexanuclear Y₄/M₂ complexes [{Cp*M(μ‐H)₅}{(Cp′′Y)₄(μ‐H)₅}{(μ‐H)₄MCp*(PMe₃)}] (M=Mo ( 4 a ), W ( 4 b )). UV irradiation of compounds 4 a , b provided the PMe₃‐free complexes [(Cp′′Y)₄(μ‐H)₄{(μ‐H)₅MCp*}₂] (M=Mo ( 5 a ), W ( 5 b )). C₅Me₄Et‐ligated analogue [(Cp′′Y)₄(μ‐H)₄{(μ‐H)₅Mo(C₅Me₄Et)}₂] ( 5 a′ ) was obtained from the reaction of 1‐C₅Me₄H with [(C₅Me₄Et)Mo(PMe₃)H₅]. On the other hand, the reaction of pentanuclear yttrium? decahydride complex [{(C₅Me₄R)Y(μ‐H)₂}₅(thf)₂] ( 1‐C₅Me₅ : R=Me; 1‐C₅Me₄Et : R=Et) with [Cp*M(PMe₃)H₅] gave the hexanuclear heterobimetallic Y₅/M? polyhydride complexes [({(C₅Me₄R)Y}₅(μ‐H)₈)(μ‐H)₅MCp*] ( 6 a : M=Mo, R=Me; 6 a′ : M=Mo, R=Et; 6 b : M=W, R=Me). Compound 5 a released two molecules of H₂ under vacuum to give [(Cp′′Y)₄(μ‐H)₂{(μ‐H)₄MoCp*}₂] ( 7 ). In contrast, compound 6 a lost one molecule of H₂ under vacuum to yield [{(Cp*Y)₅(μ‐H)₇}(μ‐H)₄MoCp*] ( 8 ). Both compounds 7 and 8 readily reacted with H₂ to regenerate compounds 5 a and 6 a , respectively. The structures of compounds 4 a , 5 a′ , 6 a′ , 7 , and 8 were determined by single‐crystal X‐ray diffraction.     

Selective one-step synthesis of triple-decker (porphyrinato)(phthalocyaninato) early lanthanides: the balance of concurrent processes

An effective one-step approach for the preparation of (porphyrinato)(phthalocyaninato) early lanthanides of type [Br(4)TPP]Ln[(15C5)(4)Pc]Ln[Br(4)TPP], where Br(4)TPP = 5,10,15,20-tetrakis-(4-bromophenyl)-porphyrinato-ligand, (15C5)(4)Pc = tetrakis-(15-crown-5)-phthalocyaninato-ligand and Ln = La, Pr, Nd or Eu, is developed. The influence of various factors on the reaction pathway and yields of the complexes is investigated in detail. The developed protocol is found to be general for the early lanthanide subgroup. Variation of the synthetic conditions allowed the determination and isolation of possible side-products, namely heteroleptic double-deckers [Br(4)TPP]Ln[(15C5)(4)Pc] (Ln = Nd, Eu) and triple-decker [Br(4)TPP]Nd[(15C5)(4)Pc]Nd[(15C5)(4)Pc]. The peculiarities of the NMR lanthanide-induced shifts (LIS) of resonances of the synthesized triple-decker complexes are precisely investigated. The isostructurality of the synthesized complexes within the series as well as isostructurality with previously synthesized compounds is demonstrated in terms of two-nuclei analysis of LIS.     

Darstellung und elektronenmikroskopische Untersuchung neuer Verbindungen des Typs Ln3MO4Cl5 (Ln = La?Nd; M = Ge,V)

Preparation and Electronmicroscopic Investigation of New Compounds Ln₃MO₄Cl₅ (Ln = La? Nd; M = Ge, V) By heating mixtures of LnOCl, LnCl₃ und GeO₂ (2:1:1) in evacuated silica tubes (Pt-shells inside) the compounds Ln₃GeO₄Cl₅ (Ln = La? Nd) were prepared. The case that the temperature of preparation (La: T = 900°C, 8d; Ce: T = 800°C, 9d; Pr, Nd: T = 650°C, 13 d) had to be reduced from Ln = La to Ln = Nd indicates a decreasing thermodynamic stability in this direction. The compound La₃VO₄Cl₅ was prepared by heating (900°C, 8d) a mixture (2:1:1) of LaOCl, LaCl₃ and VO₂ and was investigated by electronmicroscopic techniques.