Structural, thermal, and spectral investigations of the lanthanide(III) biphenyl-4,4′-dicarboxylates

The lanthanide biphenyl-4,4′-dicarboxylates (bpdc) series of the general formulae Ln₂(bpdc)₃·nH₂O, where Ln = lanthanides from La(III) to Lu(III); bpdc = C₁₂H₅(COO) ₂ ^2? ; n = 4, 5 or 6 have been obtained by the conventional precipitation method. All prepared complexes were characterized by elemental analysis, simultaneous thermal analyses thermogravimetric-differential scanning calorimetry (TG–DSC) and TG–FT-IR, FT-IR, and FT-Raman spectroscopy as well as X-ray diffraction patterns measurements. In the whole series of analyzed complexes the bpdc^2? ligand is completely deprotonated. In view of that, four carboxylate oxygen atoms are engaged in the coordination of Ln(III) ions. The synthesized compounds are polycrystalline and insoluble in water. They crystallize in the low symmetry crystal systems, like monoclinic and triclinic. Heating in the air atmosphere resulted in the multi-steps decomposition process, namely endothermic dehydration and strong exothermic decomposition processes. The dehydration process leads to the formation of stable anhydrous Ln₂bpdc₃ compounds which subsequently decompose to the corresponding lanthanide oxides.     

Thermal studies of some biologically active oxovanadium(IV) complexes containing 8-hydroxyquinolinate and hydroxamate ligands

The thermal decomposition behaviours of oxovanadium(IV)hydroxamate complexes of composition [VO(Q)_2?n(HL^1,2)_n]: [VO(C₉H₆ON)(C₆H₄(OH)(CO)NHO)] (I), [VO(C₆H₄(OH)(CO)NHO)₂] (II), [VO(C₉H₆ON)(C₆H₄(OH)(5-Cl)(CO)NHO)] (III), and [VO(C₆H₄(OH)(5-Cl)(CO)NHO)₂] (IV) (where Q?=?C₉H₆NO^? 8-hydroxyquinolinate ion; HL¹?=?[C₆H₄(OH)CONHO]^? salicylhydroxamate ion; HL²?=?[C₆H₃(OH)(5-Cl)CONHO]^? 5-chlorosalicylhydroxamate ion; n?=?1 and 2), which are synthesised by the reactions of [VO(Q)₂] with predetermined molar ratios of potassium salicylhydroxamate and potassium 5-chlorosalicylhydroxamate in THF?+?MeOH solvent medium, have been studied by TG and DTA techniques. Thermograms indicate that complexes (I) and (III) undergo single-step decomposition, while complexes (II) and (IV) decompose in two steps to yield VO(HL^1,2) as the likely intermediate and VO₂ as the ultimate product of decomposition. The formation of VO₂ has been authenticated by IR and XRD studies. From the initial decomposition temperatures, the order of thermal stabilities for the complexes has been inferred as III?>?I > II?>?IV.     

Comparison of thermal properties of lanthanide trimellitates prepared by different methods

By diffusion in gel medium new complexes of formulae: Nd(btc)⋅6H₂O, Gd(btc)⋅4.5H₂O and Er(btc)·5H2O (where btc=(C₆H₃(COO)₃ ³⁻) were obtained. Isomorphous compounds were crystallized in the form of globules. During heating in air atmosphere they lose stepwise water molecules and then anhydrous complexes decompose to oxides. Hydrothermally synthesized polycrystalline lanthanide trimellitates form two groups of isomorphous compounds. The light lanthanides form very stable compounds of the formula Ln(btc)⋅nH₂O (where Ln=Ce−Gd and n=0 for Ce; n=1 for Gd; n=1.5 for La, Pr, Nd; n=2 for Eu, Sm). They dehydrate above 250°C and then immediately decomposition process occurs. Heavy lanthanides form complexes of formula Ln(btc)⋅nH₂O (_Ln=Dy−Lu). For mostly complexes, dehydration occurs in one step forming stable in wide range temperature compounds. As the final products of thermal decomposition lanthanide oxides are formed.     

Thermal decomposition of dinuclear complexes LM(μ-OOCR)<Subscript>4</Subscript>ML (L is α-substituted pyridine)

The solid-state thermal decomposition of the dinuclear pivalate complexes LM(μ-OOCR)₄ML, both those synthesized earlier (M = Mn^II, Fe^II, or Co^II; L = 2,6-(NH₂)₂C₅H₃N)) and new complexes (M = Cu^II; L = 2,6-(NH₂)₂C₅H₃N or (2-NH₂)(6-CH₃)C₅H₃N), was studied by differential scanning calorimetry and thermogravimetry. The decomposition of the Co^II complexes is accompanied by the aggregation to form the volatile octanuclear complex Co₈(μ₄-O)₂(μ_n-OOCCMe₃)₁₂ (n = 2 or 3), whereas the thermolysis of the Mn^II, Fe^II, and Cu^II complexes is destructive, the phase composition of the decomposition products being substantially dependent on the nature of metal and the α substituent R in the apical organic ligand.     

Mass spectra of organolanthanide complexes

The EI mass spectra of seven 1,1′-(3-oxa-pentamethylene)-dicyclopentadienyl lanthanide and yttrium chlorides ( 1–7 ), and eleven dicyclopentadienyl lanthanide and yttrium chlorides ( 8–18 ) were investigated. Fragmentation patterns of these complexes were studied by using metastable ion measurements. The EI spectra of complexes 1–7 exhibited strong molecular ion peaks, the fragmentation of molecular ions were more complicated. The EI mass spectra of complexes 8–18 supported the dimeric structure under gaseous state. In the spectra of dimers (C₅H₅)₃LN⁺ observed were resulted from the skeletal rearrangement involving the migration of cyclopentadienyl moiety.     

Thermal and luminescence characterization of lanthanide 2,6-naphthalenedicarboxylates series

The lanthanide 2,6-naphthalenedicarboxylates series of the formulas Ln₂(ndc)₃·nH₂O, where Ln = lanthanides from La(III) to Lu(III); ndc - C₁₀H₆(COO)₂²⁻; n = 4, 4.5 or 5 have been prepared by the precipitation method. All obtained products were examined and characterized by elemental analysis, FTIR spectroscopy, simultaneous thermal analyses TG-DSC and TG-FTIR, X-Ray diffraction patterns as well as luminescence measurements. The crystalline compounds form three isostructural groups: Ce-Sm; La and Eu-Dy; Ho-Lu. In all complexes, the ndc²⁻ ligand appears in the deprotonated form. Heating of the complexes resulted in the multi-steps decomposition process. The dehydration process leads to the formation of stable crystalline Ln₂ndc₃ compounds which further decompose to the corresponding lanthanide oxides (air atmosphere). In argon atmosphere they decompose with releasing of water, carbon oxides and naphthalene molecules. The luminescence properties of Eu(III), Nd(III), Tb(III) and Er(III) complexes were investigated. The complexes of Eu(III) and Tb(III) emitted red and green light when excited by ultraviolet light whereas Nd(III) and Er(III) display emissions in the NIR region.     

Influence of the nature of organic ligands on the character of thermal decomposition products of CoII and NiII pivalate complexes with amino derivatives of pyridine

The thermal stability and the solid-state thermal decomposition of the known mononuclear cobalt(II) and nickel(II) complexes [H₂N(C₅H₃N)N(H)C(Me)=NH]M(OOCBu^t)₂, [(NH₂)₂C₆H₂Me₂]₃M(OOCBu^t)₂ and the new compounds L₂M(OOCBu^t)₂ (L = = (2-NH₂)C₅H₃N, (2-NH₂)(6-Me)C₅H₃N), and [(2,6-NH₂)₂C₅H₃N]₂Ni(OOCBu^t)₂ were studied by differential scanning calorimetry and thermogravimetric analysis. Efficient methods were developed for the synthesis of these complexes. The mononuclear complexes are thermally quite stable. The thermal stability of the complexes depends on the nature of the ligand and decreases in the series (2,6-NH₂)₂C₅H₃N > H₂N(C₅H₃N)NHC(Me)=NH > (NH₂)₂C₆H₂Me₂ > (2-NH₂)C₅H₃N > (2-NH₂)(6-Me)C₅H₃N. The nickel(II) complexes are thermally more stable than the related cobalt(II) complexes. The thermolysis (<500 °C) of Co and Ni pivalates is a destructive process. The phase composition of the decomposition products is determined by the nature of metal and coordinated ligands.     

N-Substituted Amido Derivatives of Lanthanides

The synthesis of lanthanide amido complexes of the type Ln(CH₃CONR)₃ (I), (OPrⁱ)Ln(C₆H₅CONC₆H₅)₂ (II), and (OBu^t)Ln(C₆H₅CONC₆H₅)₂ (III) [where Ln = La, Pr, Nd; R = C₆H₅, p-NO₂C₆H₄, p-BrC₆H₄] are described. Infrared spectra indicate deprotonation of the secondary amide (anilide). Anion coordination is proposed as chelating bidenate ligands.     

Oxidative degradation of the organometallic iron(II) complex [Fe{bis[3‐(pyridin‐2‐yl)‐1H‐imidazol‐1‐yl]methane}(MeCN)(PMe3)](PF6)2: structure of the ligand decomposition product trapped via coordination to iron(II)

Iron is of interest as a catalyst because of its established use in the Haber–Bosch process and because of its high abundance and low toxicity. Nitrogen‐heterocyclic carbenes (NHC) are important ligands in homogeneous catalysis and iron–NHC complexes have attracted increasing attention in recent years but still face problems in terms of stability under oxidative conditions. The structure of the iron(II) complex [1,1′‐bis(pyridin‐2‐yl)‐2,2‐bi(1H‐imidazole)‐κN³][3,3′‐bis(pyridin‐2‐yl‐κN)‐1,1′‐methanediylbi(1H‐imidazol‐2‐yl‐κC²)](trimethylphosphane‐κP)iron(II) bis(hexafluoridophosphate), [Fe(C₁₇H₁₄N₆)(C₁₆H₁₂N₆)(C₃H₉P)](PF₆)₂, features coordination by an organic decomposition product of a tetradentate NHC ligand in an axial position. The decomposition product, a C—C‐coupled biimidazole, is trapped by coordination to still‐intact iron(II) complexes. Insights into the structural features of the organic decomposition products might help to improve the stability of oxidation catalysts under harsh conditions.     

Kinetic study of thermal degradation of di-, chlorodi- and triorganotin(IV) complexes of 2-[(2,6-dichlorodiphenyl)amino]benzene acetate

The organotin complexes of the general formulae R₂SnL₂, R₂SnLCl and R₃SnL where R = C₄H₉, C₆H₅, and C₇H₇ and L = 2-[(2,6-dichlorodiphenyl)amino]benzene acetate, were subjected to thermal decomposition by thermogravimetric analysis (TGA). The decomposition of these compounds occurs mostly in two steps. Kinetic parameters such as order of reaction (n), activation energy (Ea), enthalpy (ΔH^?) and entropy (ΔS^?) of activation were calculated by using the Coats and Horowitz methods. The calculated values are in good agreement with observed TG values that confirm the structural integrity of the complexes.     

Structural Parameters and Electron Transfer in Ytterbium,Lutetium, and Cerium Compounds with Hydrocarbon Monocycles

The DFT (U)PBE0 method was used to calculate the structural parameters of the C₅H₅Yb·, C₅H₅Lu, C₈H₈Lu·, C₈H₈Yb, (C₅H₅)₂Yb, (C₅H₅)₃Yb, C₅H₅YbC₈H₈, C₅H₅Ce·C₈H₈, C₅H₅LuC₈H₈, (C₈H₈)₂Lu, (C₈H₈)Ce*, (C₈H₈)₂Ce, (C₈H₈LuC₈H₈)₂Yb, and (C₈H₈Ce·C₈H₈)₂Yb molecules. In the (C₈H₈)₂Ce molecule, the oxidation state of the lanthanide is higher than in the quadruple-decker (C₈H₈LnC₈H₈)₂Yb complexes, in the C₅H₅LnC₈H₈ molecules, and in the free radicals (C₈H₈)₂Ce* and (C₈H₈)₂Lu. Oxidation of (C₅H₅)₂Yb with cyclooctatetraene and the binding of the (C₈H₈)₂Ln molecules by ytterbium(II) are exothermic reactions. The atomic charges and the dipole and quadrupole moments are indicative of incomplete transfer of the lanthanide valence electrons to the ligands, i.e., of a significant covalent component of the η⁵ and η⁸ bonds. Lutetium interacts with cyclooctatetraene as a lanthanide, without showing the properties of transition metals.

     

A comparative study on the thermal decomposition of lanthanide biscitrato chromate(III) hydrates, Ln[CrC6(H5O7)2]·nH2O

The thermal decomposition of lanthanide biscitrato chromate (III) hydrates, [Ln(Cr(C₆H₅O₇)₂] nH₂O whereLn=Pr, Nd, Dy and Ho have been carried out in static air and flowing argon atmospheres and thereby compared the decomposition nature with that of the lanthanum biscitrato chromate(III) dihydrate reported earlier. The precursor complexes decompose in four major steps. Stable oxycarbonates and chromates(V) have been isolated as intermediates. It has been found that for heavier lanthanide complexes all the decomposition steps are pushed to higher temperature ranges. Moreover, the thermal stability range of chromates(V) is much lesser compared to that of LaCrO₄. Based on the observed experimental results a general scheme for the decomposition of lanthanide biscitrato chromate(III) hydrates is proposed.     

Synthese und NMR.-Spektren von neuartigen Lanthanoid-Kobalt-Sandwichkomplexen

Synthesis and NMR. Spectra of Novel Lanthanide-Cobalt Sandwich Compounds The reaction of [(C₅H₅)Co{P(O)(OR)₂}₂{P(OH)(OR)₂}] ( 3 , R = CH₃, C₂H₅) with lanthanide(III) compounds yields the cationic trinuclear complexes [{(C₅H₅)Co[P(O)(OR)₂]₃}₂Ln]^⊕X^? ( 2 , R = CH₃, C₂H₅; Ln = La, Eu, Pr; X = BF₄, BPh₄). According to thermogravimetric and NMR. studies these compounds do not contain additional coordinated water molecules. It is therefore supposed that the central lanthanide ion has a regular sixfold coordination of phosphoryl ligands. The ³¹P- and ¹H-NMR. spectra of 2 (R = CH₃; Ln = La, Eu, Pr) and 3 are discussed. It can be shown that the Fermi contact shift as well as the coordination shift make significant contributions to the observed lanthanide induced shift of the cyclopentadienyl signal.The dominating influence of the Fermi contact interaction on the ³¹P chemical shift is in accord with theoretical considerations and comparable experimental values. The temperature dependence of the proton chemical shifts of 2 (R = CH₃; Ln = Eu) is also discussed.     

A thermal behaviour and structural study of bis(hydroxamato)oxovanadium(IV) complexes

The bis(hydroxamato)oxovanadium(IV) complexes of composition [VO(IAH)₂)] (I), [VO(IBH)₂)] (II) and [VO(ICH)₂)] (III) (where IAH = indole-3-acetohydroxamate; (C₉H₈NCONHO^?); IBH = indole-3-butyrohydroxamate; (C₁₁H₁₂NCONHO^?); ICH = indole-2-carbohydroxamate; (C₈H₆NCONHO^?)) synthesized form the reactions of VOSO₄·5H₂O with bi-molar amounts of potassium salts of the respective hydroxamic acids in methanol have been characterised by elemental analyses, magnetic moment measurements and IR spectral studies. The thermal behaviour of complexes has been studied by TG and DTA techniques. Thermograms indicated that all complexes decompose in two steps yielding [VO(IAH)], [VO(IBH)] and [VO(ICH)] as intermediate of respective complexes and VO₂ as the final product of decomposition in each case. From the initial decomposition temperatures (IDT), the order of thermal stability for the complexes has been inferred as II > I > III.     

Low‐Coordinate Single‐Ion Magnets by Intercalation of Lanthanides into a Phenol Matrix

It is very challenging to synthesize stable trivalent rare‐earth complexes in which the coordination number is lower than 3 for the high oxidation state, there is a large ion radius and nearly non‐bonding character of trivalent lanthanide ions. The bulky phenol ligand ArOH (Ar=2,6‐Dipp₂C₆H₃, Dipp=2,6‐diisopropylphenyl) was utilized to construct low‐coordinate lanthanide compound [(ArO)Ln(OAr′)] (Ar′=6‐Dipp‐2‐(2′‐ⁱPr‐6′‐CHMe(CH₂^?)C₆H₃)C₆H₃O^?; Ln=Tb, Dy, Ho, Er, Tm). These complexes and the free ligand ArOH were isostructural. Magnetic measurements and theoretical studies demonstrated that both the oblate‐type dysprosium and prolate‐type erbium analogues exhibited single‐ion magnet (SIM) behavior. The bulky phenol ligands provided strong uniaxial ligand field, making the dysprosium SIM possessing blocking barrier up to 961 K.     

Evaluation of AM1-calculated radical cation ion-neutral complexes

AM1 semiempirical molecular orbital calculations are reported for 20 ion-neutral complexes, including hydrogen-bonded complexes, presumably involved in the gas-phase unimolecular decomposition of simple organic radical cations. The systems investigated are [C₂H₄O₂]^˙+, [C₂H₅NO]^˙+, [C₂H₆O]^˙+, [C₂H₆O₂]^˙+, [C₃H₆O]^˙+, [C₃H₆O₂]^˙+, [C₃H₈O]^˙+, and [C₃H₈O₂]^˙+. The AM1 results are compared with ab initio molecular orbital calculations at different levels of theory up to MP3/6-31G(d, p)//SCF/6-31G(d) + ZPVE and the available experimental data. AM1 fails to predict some local minima and the equilibrium geometries calculated for several complexes are found to be qualitatively different from those predicted by the ab initio calculations. However, reasonable agreement is generally found for the stabilization energies of the complexes toward dissociation into their loosely bound components. © John Wiley & Sons, Inc.     

Syntheses,structures, thermal stabilities and bacteriostatic activities of four lanthanide complexes

Four lanthanide complexes, [La₂(2,4-DClBA)₆(5,5′-DM-2,2′-bipy)₂(H₂O)₂]·2C₂H₅OH (1) and [Ln(2,4-DClBA)₃(5,5′-DM-2,2′-bipy)(C₂H₅OH)]₂ (Ln = Pr(2), Sm(3), Gd(4); 2,4-DClBA = 2,4-dichlorobenzoate; 5,5′-DM-2,2′-bipy = 5,5′-dimethyl-2,2′-bipyridine), were synthesized and characterized via elemental analysis, infrared spectra and thermogravimetric analysis (TG). The crystal structures of 1 and 2–4 are different; Each La³⁺ is nine-coordinate adopting a distorted mono-capped square antiprism, while the Ln³⁺ ions of 2–4 are all eight-coordinate with a distorted square antiprismatic molecular geometry. There are subtle changes in the local coordination geometry of the lanthanide–5,5′-DM-2,2′-bipy complexes. Binuclear 1 complexes are stitched together via two kinds of hydrogen bonding interactions (OH?O and CH?O) to form 1-D chains along the y axis, while the units of 2–4 are stitched together via CH?O to form 1-D chains along the x axis. TG analysis revealed thermal decomposition processes and thermal stabilities of the complexes. The bacteriostatic activities of the complexes were evaluated against Candida albicans, Escherichia coli, and Staphylococcus aureus.     

Gemischte Sandwichkomplexe der 4 f‐Elemente: Enantiomerenreine Cyclooctatetraenyl‐Cyclopentadienyl‐Komplexe des Samariums und Lutetiums mit donorfunktionalisierten Cyclopentadienylliganden

Organometallic Compounds of the Lanthanides. 139 Mixed Sandwich Complexes of the 4 f Elements: Enantiomerically Pure Cyclooctatetraenyl Cyclopentadienyl Complexes of Samarium and Lutetium with Donor‐Functionalized Cyclopentadienyl Ligands The reactions of [K{(S)‐C₅H₄CH₂CH(Me)OMe}], [K{(S)‐C₅H₄CH₂CH(Me)NMe₂}] and [K{(S)‐C₅H₄CH(Ph)CH₂NMe₂}] with the cyclooctatetraenyl lanthanide chlorides [(η⁸‐C₈H₈)Ln(μ‐Cl)(THF)]₂ (Ln = Sm, Lu) yield the mixed cyclooctatetraenyl cyclopentadienyl lanthanide complexes [(η⁸‐C₈H₈)Sm{(S)‐η⁵ : η¹‐C₅H₄CH₂CH(Me)OMe}] ( 1 a ), [(η⁸‐C₈H₈)Ln{(S)‐η⁵ : η¹‐C₅H₄CH₂CH(Me)NMe₂}] (Ln = Sm ( 2 a ), Lu ( 2 b )) and [(η⁸‐C₈H₈)Ln{(S)‐η⁵ : η¹‐C₅H₄CH(Ph)CH₂NMe₂}] (Ln = Sm ( 3 a ), Lu ( 3 b )). For comparison, the achiral compounds [(η⁸‐C₈H₈)Ln{η⁵ : η¹‐C₅H₄CH₂CH₂NMe₂}] (Ln = Sm ( 4 a ), Lu ( 4 b )) are synthesized in an analogous manner. ¹H‐, ¹³C‐NMR‐, and mass spectra of all new compounds as well as the X‐ray crystal structures of 3 b and 4 b are discussed.     

Effect of Inorganic Components on Thermal Stability of Methylsiloxane-Based Inorganic/Orgnaic Hybrids

The thermal decomposition behavior of methylsiloxane-based inorganic/organic hybrids containing an inorganic component derived from metal alkoxides such as Si(OCH₃)₄, Al(O^sC₄H₉)₃, Ti(OⁱC₃H₇)₄ and Nb(OC₂H₅)₅ was investigated by means of thermogravimetric and differential thermal analysis (TG-DTA), Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. The decomposition temperature of methyl groups in methylsiloxane-based inorganic/organic hybrids containing an inorganic component derived from metal alkoxides was higher than that in the methylsiloxane-based inorganic/organic hybrid prepared from only CH₃Si(OC₂H₅)₃. In particular, when incorporating Nb and Ti inorganic components, methyl groups in methylsiloxane-based inorganic/organic hybrids decomposed at about 100 and 200^∘C higher temperatures, respectively, than those in the methylsiloxane-based inorganic/organic hybrid prepared from only CH₃Si(OC₂H₅)₃. The incorporation of an inorganic component other than siloxane into methylsiloxane-based inorganic/organic hybrids was found to thermally stabilize the methyl groups of methylsiloxane networks.     

Spectral and biological investigation of 5-hydroxyl-3-oxopyrazoline 1-carbothiohydrazide and its transition metal complexes

Mononuclear complexes of 5-hydroxyl-3-oxopyrazoline-1-carbothiohydrazide, H₃HOC, with VO²⁺, Co(II), Ni(II), Cu(II) and Cd(II) have been isolated. The elemental analyses, magnetic, spectral [u.v.–vis., i.r., e.s.r. ¹H n.m.r. and mass] with thermal analysis have been used to characterize the isolated complexes. The ligand behaves as a mononegative tridentate with Ni(II) and Co(II) ions and neutral bidentate in [Cu(H₃HOC)(NO₃)₂]0.5 H₂O, [VO(H₃HOC)SO₄] and [Cd(H₃HOC)Cl₂C₂H₅OH]C₂H₅OH complexes. The octahedral structure was suggested for all the isolated complexes except VO²⁺. The TG analyses recorded different decomposition steps started at a temperature, indicating thermally unstable complexes. Screening showed antimicrobial activity for Cd(II) and Ni(II) complexes against the investigated bacteria as well as a significant adverse effects on DNA but a moderate effect is displayed with the other complexes.