Structure of SmCl3, DyCl3, and HoCl3 molecules based on the data of synchronous electron diffraction and mass-spectrometric experiment

Saturated vapors of SmCl₃, DyCl₃, and HoCl₃ have been studied in the framework of a synchronous electron diffraction and mass-spectrometric experiment at temperatures 1205 K, 1160 K, and 1148 K, respectively. In vapors of all compounds, along with monomer molecular forms, an insignificant (up to 2 mol.%) amount of dimers was detected. Parameters of the effective configuration of monomer molecules were determined. For molecules SmCl₃, DyCl₃, and HoCl₃ values of internuclear distances r _g(Ln-Cl) were 2.511(5) Å, 2.453(5) Å, and 2.444(5) Å, values of valence angles ∠_g(Cl-Ln-Cl) were 115.6(11)°, 116.8(10)°, and 116.6(10)°, respectively. It is shown that parameters of the r _g-structure are not incompatible with the notion of a planar equilibrium geometrical configuration of molecules SmCl₃, DyCl₃, and HoCl₃. Main tendencies in the change of structural and vibration characteristics in the series of lanthanide trichlorides are considered.     

Dependence of Polymer Chain Entanglements on the Solution Concentration

For the viscometric determination of molecular weights of polymers, sufficiently dilute solutions have to be used so that entanglements of the polymer chain are absent. The concentration of the polymer should be such that the relative viscosity (η_r) lies in the range 1.1–1.5 [1]. Similarly, for molecular weight determination by light scattering, the suggested concentration for polymer with weight-average molecular weight ( M _w ) > 10⁵ is 0.5 wt%; for those with M _w < 10⁵, up to 1% may be used [2].

The limits of polymer concentration for such measurements are not clearly known. On dissolution, the polymer molecules adopt a more or less extended configuration whose shape depends on the structure and molecular weight of the polymer, the properties of the solvent, and the temperature

[3]. The molecules of flexible linear polymers acquire a coiled configuration due to free rotation about the C-C bonds. When a dilute solution satisfies theta conditions, the polymer molecules are free from all kinds of interaction and move freely. Then their solution properties could possibly be related to their end-to-end distance. Based on this concept, our attempt to establish the permissible limits of polymer concentration for dilute solutions of several polymers of different molecular weights is reported here.     

One‐dimensional Salen‐type Chain‐like Lanthanide(III) Coordination Polymers: Syntheses,Crystal Structures,and Fluorescence Properties

Four salen‐type lanthanide(III) coordination polymers [LnH₂L(NO₃)₃(MeOH)_x]_n [Ln = La ( 1 ), Ce ( 2 ), Sm ( 3 ), Gd ( 4 )] were prepared by reaction of Ln(NO₃)₃ · 6H₂O with H₂L [H₂L = N,N′‐bis(salicylidene)‐1,2‐cyclohexanediamine]. Single‐crystal X‐ray diffraction analysis revealed that H₂L effectively functions as a bridging ligand forming a series of 1D chain‐like polymers. The solid‐state fluorescence spectra of polymers 1 and 2 emit single ligand‐centered green fluorescence, whereas 3 exhibits typical red fluorescence of Sm^III ions. The lowest triplet level of ligand H₂L was calculated on the basis of the phosphorescence spectrum of Gd^III complex 4 . The energy transfer mechanisms in the lanthanide polymers were described and discussed.     

The dinuclear scandium(III) cyclooctatetraenyl chloride complex di‐μ‐chlorido‐bis[(η8‐cyclooctatetraene)(tetrahydrofuran‐κO)scandium(III)]

Only a few cyclooctatetraene dianion (COT) π‐complexes of lanthanides have been crystallographically characterized. This first single‐crystal X‐ray diffraction characterization of a scandium(III) COT chloride complex, namely di‐μ‐chlorido‐bis[(η⁸‐cyclooctatetraene)(tetrahydrofuran‐κO )scandium(III)], [Sc₂(C₈H₈)₂Cl₂(C₄H₈O)₂] or [Sc(COT)Cl(THF)]₂ (THF is tetrahydrofuran), (1), reveals a dimeric molecular structure with symmetric chloride bridges [average Sc—Cl = 2.5972 (7) Å] and a η⁸‐bound COT ligand. The COT ring is planar, with an average C—C bond length of 1.399 (3) Å. The Sc—C bond lengths range from 2.417 (2) to 2.438 (2) Å [average 2.427 (2) Å]. Direct comparison of (1) with the known lanthanide (Ln) analogues (La, Ce, Pr, Nd, and Sm) illustrates the effect of metal‐ion (M ) size on molecular structure. Overall, the M —Cl, M —O, and M —C bond lengths in (1) are the shortest in the series. In addition, only one THF molecule completes the coordination environment of the small Sc^III ion, in contrast to the previously reported dinuclear Ln–COT–Cl complexes, which all have two bound THF molecules per metal atom.     

Crystal and Molecular Structure of Bis(η5-methylcyclopentadienyl)titana(IV)-cyclohexasulfane Ti(η5-C5H4CH3)2S5

The crystal and molecular structure of Ti(n⁵-C₅H₄CH₃)₂S₅has been determined by X-ray diffraction studies. The substance crystallizes in the monoclinic crystal system [a = 6.8642(5), b = 16.507(1), c = 13.074(1) Å, β = 82.407(3)°, space group P2₁/n, Z = 4]. The geometry about the titanium atom is a distorted tetrahedron, with a (centroid)-Ti-(centroid) angle of 131.29° and a S? Ti? S angle of 93.38°. The six-membered ring TiS₅ has a cyclohexane-like chair configuration. The structural results are compared to those for similar type titanium complexes.     

Molecular structure of bismuth trichloride from combined electron diffraction and vibrational spectroscopic study

The results of an electron diffraction reanalysis, augmented with a combined electron diffraction and vibrational spectroscopic elucidation, of the molecular structure of BiCl₃ are reported. The principal parameters arer _g (Bi-Cl)=2.424±0.005 å (r =2.417±0.005 å) and <Cl-Bi-Cl=97.5±0.2. They are in excellent agreement with previous electron diffraction analysis [1], utilizing a more limited data range from the same experiment. They are also fully consistent with the expected trends of geometrical variation in the Group V trihalide series. The force fields of BiCl₃, determined by normal coordinate analysis and by combined analysis, agree within experimental error.     

Coordination and recognition of lanthanide cations by a methyl-substituted cucurbit[6]uril derived from 3α-methyl-glycoluril

The interactions between a series of lanthanide cations (Ln³⁺) and a methyl-substituted cucurbit[6]uril derived from 3α-methyl-glycoluril (SHMeQ[6]) in the presence of [CdCl₄]^2 ? as a structure-directing agent in aqueous HCl solutions (6.0 mol·L ^? 1) have been investigated. The formation of ionic radius-dependent complexes, the crystal structures of six of which have been obtained, shows the recognition ability of SHMeQ[6] towards lanthanide cations. For example, SHMeQ[6] forms molecular capsule-like complexes with the two lightest lanthanide cations, La³⁺ and Ce³⁺; molecular pairs with Nd³⁺, Sm³⁺, Eu³⁺ and Gd³⁺, and no solid crystals are formed with the heavier lanthanides.     

Synthesis, characterization and thermal analysis of 1:1 and 2:3 lanthanide(III) citrates

The synthesis and characterization of lanthanide(III) citrates with stoichiometries 1:1 and 2:3; [LnL·xH₂O] and [Ln₂(LH)₃·2H₂O], Ln=La, Ce, Pr, Nd, Sm and Eu are reported. L stands for (C₆O₇H₅)^3? and LH for (C₆O₇H₆)^2?. Infrared absorption spectra of both series evidence coordination of carboxylate groups through symmetric bridges or chelation. X-ray powder patterns show the amorphous character of [LnL·xH₂O]. The compounds [Ln₂LH₃·2H₂O] are crystalline and isomorphous. Emission spectra of Eu compounds suggest C _2v symmetry for the coordination polyhedron of [LnL·xH₂O] and C _4v for [Ln₂(LH)₃·2H₂O]. Thermal analyses (TG-DTG-DTA) were carried out for both series. The thermal analysis patterns of the two series are quite different and both fit in a 4-step model of thermal decomposition, with lanthanide oxides as final products.     

Synthesis,Crystal Structures,and Spectroscopic Properties of Novel Gadolinium and Erbium Triphenylsiloxide Coordination Entities

In alkali metal and lanthanide coordination chemistry, triphenylsiloxides seem to be unduly underappreciated ligands. This is as surprising as that such substituents play a crucial role, among others, in stabilizing rare oxidation states of lanthanide ions, taking a part of intramolecular and molecular interactions stabilizing metal-oxygen cores and many others. This paper reports the synthesis and characterization of new lithium [Li₄(OSiPh₃)₄(THF)₂] (1), and sodium [Na₄(OSiPh₃)₄] (2) species, which were later used in obtaining novel gadolinium [Gd(OSiPh₃)₃(THF)₃]·THF (3), and erbium [Er(OSiPh₃)₃(THF)₃]·THF (4) configuration, it can result in res were determined for all 1–4 compounds, and in addition, IR, Raman, absorption spectroscopy studies were conducted for 3 and 4 lanthanide compounds. Furthermore, direct current (dc) variable-temperature magnetic susceptibility measurements on polycrystalline samples of 3 and 4 were carried out in the temperature range 1.8–300 K. The 3 shows behavior characteristics for the paramagnetism of the Gd³⁺ ion. In contrast, the magnetic properties of 4 are dominated by the crystal field effect on the Er³⁺ ion, masking the magnetic interaction between magnetic centers of neighboring molecules.     

Synthesis and structure of lanthanide complexes with large-bite diphosphine dioxide ligands

Three large-bite diphosphine dioxide ligands were reacted with lanthanide salts to yield either molecular or polymeric complexes. The two flexible ligands gave bischelate complexes of general formulae [Ln(dppfO₂)₂Cl_x(NO₃)_2−x][FeCl₄] and [Ln(dppdO₂)₂(NO₃)₂]NO₃, where dppfO₂ and dppdO₂ are bis(diphenylphosphoryl)ferrocene and bis(diphenylphosphoryl)diphenyl ether, respectively. Reactions of the rigid bis(diphenylphosphoryl)benzene (dppbO₂) with lanthanide salts yielded linear coordination polymers of a 1:1.5 metal-to-ligand stoichiometry. The compounds were studied by single crystal X-ray diffraction, IR spectroscopy, mass spectrometry, and TG/DSC techniques.     

Ligand Recognition Processes in the Formation of Homochiral C3‐Symmetric LnL3 Complexes of a Chiral Alkoxide

The reaction of a chiral racemic bidentate ligand HL¹ (tBu₂P(O)CH₂CH(tBu)OH) with mid to late trivalent lanthanide cations affords predominantly homochiral lanthanide complexes (RRR)‐[Ln(L¹)₃] and (SSS)‐[Ln(L¹)₃]. A series of reactions are reported that demonstrate that the syntheses are under thermodynamic control, and driven by a ligand ‘self‐recognition’ process, in which the large asymmetric bidentate L¹ ligands pack most favourably in a C₃ geometry around the lanthanide cation. The synthesis of bis(L¹) adducts [Ln(L¹)₂X] (X=N(SiMe₃)₂, OC₆H₃tBu‐2,6) is also reported. Analysis of the diastereomer mixtures shows that homochiral (L¹)₂ complexes are favoured but to a lesser extent. The complexes Ln(L¹)₃ and [Ln(L¹)₂(OC₆H₃tBu‐2,6)] have been studied as initiators for the polymerization of ε‐caprolactone and its copolymer with lactide, glycolide and its copolymer with lactide, and ε‐caprolactam.     

Molecular Structure of PrBr3 and HoBr3 According to Simultaneous Electron Diffraction and Mass Spectrometry Experiment

The saturated vapors of praseodymium and holmium tribromides were investigated for the first time by electron diffraction with mass spectral monitoring at 1100(10) and 991(10) K. It is established that the molecules have a pyramidal effective configuration with bond angles Br–Pr–Br = 114.7(10)° and Br–Ho–Br = 115.3(11)°. Given the low deformation vibration frequencies of lanthanide tribromide molecules, the insignificant pyramidality of the r_g configuration may correspond to the planar equilibrium geometry of D_3h symmetry for the molecules. The internuclear distances r_g(Pr–Br) = 2.696(6) and r_g(Ho–Br) = 2.594(5) point to the lanthanide compression effect. The vibration frequencies of PrBr₃ and HoBr₃ molecules were estimated from electron diffraction data.     

2,4-Bis(diphenylphosphorylmethyl)mesitylene: Synthesis and complex formation with lanthanide nitrates. Crystal structure of [Nd(L1(NO3)3 · Me2CO]

A new bisphosphoryl ligand, 2,4-bis(diphenylphosphorylmethyl)mesitylene (L¹), has been synthesized. Upon the interaction of L¹ with lanthanide nitrates, stable mononuclear chelates [Ln(L¹) _n (NO₃)₃] (Ln = Ce(III), Nd(III), Er(III); n = 1, 2) were obtained. The structure of the complexes in solid state and in solution was studied by vibrational (IR and Raman) spectroscopy, X-ray diffraction, and conformational (molecular mechanics) analysis.     

Cadmium(II) complexes with monoiodo- and dibromodipyrromethenes: synthesis,molecular structure,spectral-luminescent properties,and stability in solutions

Cadmium(II) chelates with 4-iodo-, 5,5´-, and 4,4´-dibromo-2,2´-dipyrromethenes (HL¹, HL², and HL³, respectively) with the composition of [CdL₂] were synthesized. The influence of structural features of their molecules and properties of the medium on the characteristics of absorption and fluorescence spectra, and also on the thermodynamic stability constants in solutions was evaluated. The results of quantum chemical calculations revealed that the additional coordination interactions between the bromine atoms at the α-positions of dipyrromethene ligands and the complexing atom are possible in the molecular structure of α,α´- dibromosubstituted dipyrromethenate [Cd(L²)₂] in contrast with β-halogenated analogues [Cd(L¹)₂] and [Cd(L³)₂].     

Adducts of aqua complexes of Ln3+ with a symmetrical octamethyl-substituted cucurbituril: potential applications for isolation of heavier lanthanides

Interaction of a series of lanthanide cations (Ln³⁺) with a symmetrical octamethyl-substituted cucurbituril (OMeQ[6]) has been investigated. X-ray single-crystal diffraction analysis has revealed that the interaction results in the formation of adducts of OMeQ[6] with aqua complexes of lanthanide cations ([Ln(H₂O)₈]³⁺), Ln = Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb in OMeQ[6]–Ln(NO₃)₃–H₂O systems. However, no solid crystals were obtained from systems containing La, Ce, Pr, Nd and Sm. X-ray diffraction analysis has revealed that although the solid adducts fall into two isomorphous groups, there are no significant differences in the interactions between OMeQ[6] and [Ln(H₂O)₈]³⁺ complexes and in the corresponding supramolecular assemblies. Thermodynamic parameters for the interaction between OMeQ[6] and [Ln(H₂O)₈]³⁺ complexes based on isothermal titration calorimetry experiments show two periods corresponding to the above two systems, with the lighter lanthanide cations preferring to remain in solution and the heavier lanthanide cations forming crystalline solids. Electron spectroscopy has shown that interaction of OMeQ[6] with lanthanide cations could provide a means of isolating heavier lanthanide cations from their lighter counterparts.     

The molecular structure of PrI3 and GdI3 as determined by synchronous gas-phase electron diffraction and mass spectrometric experiment assisted by quantum chemical calculations

A gas electron diffraction study of PrI₃ and GdI₃ has been carried out in combination with mass spectrometric vapour monitoring at 1110(10) K and 1100(10) K, respectively. Up to 3 mol.% of dimeric species was observed in addition to the dominating monomeric molecules. The change of the thermal-averaged r _g configuration parameters of the molecules in the series LaI₃ → LuI₃ reflects the lanthanide contraction. A low value of the shrinkage δ(I···I) even at such a high temperatures may be considered due to vibration effects in molecule whose equilibrium geometric nuclear structure is planar and which correspond to configurationally averaged 4f ⁿ electronic state. B3LYP calculations performed in this study with large core potential for lanthanide atoms also resulted in equilibrium geometry of D _3h symmetry. According to the quantum chemical calculations, the potential function the non-planar vibration is essentially anharmonic, which is therefore to be taken into account to correctly describe nuclear dynamics in molecules such as LnI₃.     

Cationic rhodium(I) complexes containing 4,4′-disubstituted 2,2′-bipyridines: A systematic variation on electron density over the metal centre

A series of [Rh(COD)(X₂-bipy)]BF₄ complexes (COD = 1,5-cyclooctadiene; X₂-bipy = 4,4′-disubstituted 2,2′-bipyridines; X = OCH₃, CH₃, H, Cl or NO₂) has been prepared from [Rh(COD)Cl]₂. The complexes for X = OCH₃, Cl and NO₂ have not been described previously in the literature. All complexes have been characterised by elemental analysis, IR, ¹H NMR and UV-Vis spectrometry. This series of complexes presents a wide variation on electron density over the metal centre with virtually no variation on its steric environment which discloses interesting possibilities for catalytic and electro-catalytic studies. A preliminary evaluation of these complexes on the hydroformylation of camphene and β-pinene showed that under the rather drastic conditions employed the complexes acted as a precursor for [Rh(CO)₃H], which accounts for most of the catalytic activity.     

Isomorphous La,Nd, and Gd-PCPA-based polymers

An isomorphous series of three novel lanthanide coordination polymers [Ln(PCPA)₃(glycol)] _n , [where, Ln?=?La(1); Nd(2); Gd(3); PCPA?=?p-chlorophenoxyacetate] have been synthesized under hydrothermal conditions and characterized by elemental analyses, IR spectra, TG analysis, fluorescence spectra and single crystal X-ray diffraction analysis. The results reveal that all of them form a chain-like one-dimensional structure. Photoluminescent properties for the complexes are also reported.     

A Series of Three‐Dimensional Rare Earth Coordination Polymers with Two Binary Carboxylate as Mixed‐Ligand: Syntheses,Structures, Properties of [LnIII(mal)(ox)0.5(H2O)2]·2H2O (Ln = Pr,Nd, and La)

A series of lanthanide coordination polymers, [Ln^III(mal)(ox)_0.5(H₂O)₂]·2H₂O (Ln = Pr ( 1 ), Nd ( 2 ), and La ( 3 ); H₂mal= maleic acid; H₂ox = oxalic acid), were synthesized firstly by the reaction of Ln^III nitrate salts with maleic anhydrid and oxalic acid under hydrothermal conditions and were characterized by elemental analysis, IR spectroscopy, and single‐crystal X‐ray diffraction. X‐ray diffraction analyses reveal that they are crystallized in orthorhombic space group Fddd. Lanthanide metal center atom (Ln) and its corresponding centrosymmtric atom link through two chelating/bridging bidentate carboxyl groups of maleic acid ligands to form an infinite inorganic rod‐shaped building unit. These rod‐shaped building units were linked to each other through the carbon atoms of the maleate anions on the [110] plane to form lanthanide‐maleic acid layers. The oxalic acid pillared lanthanide‐maleic acid layers with intersected channels by free water molecules consist of a 3D framework structure. The thermogravimetric analyses of 1 – 3 were discussed in detail. The courses of the thermal decomposition of complexes are similar.     

Synthesis of ferrocene‐containing N‐aryloxo β‐ketoiminate lanthanide complexes and polymerization of ε‐caprolactone

The synthesis, characterization and ε‐caprolactone polymerization behavior of lanthanide amido complexes stabilized by ferrocene‐containing N‐aryloxo functionalized β‐ketoiminate ligand FcCOCH₂C(Me)N(2‐HO‐5‐Bu^t‐C₆H₃) (LH₂, Fc = ferrocenyl) are described. The lanthanide amido complexes [LLnN(SiMe₃)₂(THF)]₂ [Ln = Nd ( 1 ), Sm ( 2 ), Yb ( 3 ), Y ( 4 )] were synthesized in good yields by the amine elimination reactions of LH₂ with Ln[N(SiMe₃)₂]₃(µ‐Cl)Li(THF)₃ in a 1:1 molar ratio in THF. These complexes were characterized by IR spectroscopy and elemental analysis, and ¹H NMR spectroscopy was added for the analysis of complex 4 . The definitive molecular structures of complexes 1 and 3 were determined by X‐ray diffraction studies. Complexes 1 – 4 can initiate the ring‐opening polymerization of ε‐caprolactone with moderate activity. Copyright © 2011 John Wiley & Sons, Ltd.