Mixed borohydride-chloride complexes of the rare earth elements

Mixed borohydride-chloride complexes of lanthanum and neodymium having the 2,5-bis{N-(2,6-diisopropylphenyl)iminomethyl}pyrrolyl ligand in the coordination sphere were synthesised by the reaction of potassium 2,5-bis{N-(2,6-diisopropylphenyl)iminomethyl}pyrrolyl [(DIP₂-pyr)K] with a 1:1 mixture of [Ln(BH₄)₃(THF)₃] and LnCl₃ (Ln = La, Nd). Both compounds are dimeric in the solid state. The metal atoms are bridged almost symmetrically by two μ-chlorine atoms. Quantum chemical calculations for the lanthanum compound were performed to obtain a deeper insight into the bonding in the molecule.     

Lanthanide-based hexanuclear complexes usable as molecular precursors for new hybrid materials

Lanthanide containing octahedral hexanuclear complexes with general chemical formula [Ln₆O(OH)₈(NO₃)₆(H₂O)_x].2NO₃.yH₂O where Ln = Ce–Lu (except Pm) or Y, x = 0, 6, 12, 14 or 16 and y = 0, 2, 4 or 5 constitute a great family of polymorphic compounds. The synthesis and the crystal structures of all these compounds are overviewed. The hydration/dehydration processes that allow the structural transitions from one compound to another are described. The crystal structure of compounds with general chemical formula [Ln₆O(OH)₈(NO₃)₆(H₂O)₆].2NO₃ where Ln = Ce–Lu (except Pm) or Y is described. It has been solved on the basis of a powder XRD diagram. The use of such hexanuclear complexes as molecular precursors for new materials is also discussed.     

Insertion of ketenes into lanthanocene n-butylamide and imidazolate complexes

Reaction of Cp₂LnNHⁿBu with 1 equiv. of Ph₂CCO in toluene affords dimeric complexes [Cp₂Ln(OC(CHPh₂)NⁿBu)]₂ [Ln = Yb (1), Dy (2)], derived from a formal insertion of the CC bond of the ketene into the N–H bond. Treatment of CpErCl₂ with 2 equiv. of LiNHⁿBu followed by reacting with Ph₂CCO affords a rearrangement product [Cp₂Er(OC(CHPh₂)NⁿBu)]₂ (3). Treatment of [Cp₂Ln(μ-Im)]₃ (Im = imidazolate) with PhRCCO gives [Cp₂Ln(μ-OC(Im)CPhR)]₂ [R = Et, Ln = Yb (4); R = Ph, Ln = Yb (5), Er (6)]. In contrast to the previous observations that [Cp₂ErNⁱPr₂]₂ and [Cp₂ErNHEt]₂ react with ketenes to give di-insertion products, in the present cases the presence of excess of ketenes has no influence on the final product even with prolonged heating and only monoinsertion products are isolated. All these complexes were characterized by elemental analysis, IR and mass spectroscopies. The structures of complexes 1 and 3–6 were also determined through X-ray single crystal diffraction analysis.     

Synthesis and investigations of mixed-ligand lanthanide complexes with N,N′-dipyrrolidine-N′′-trichloracetylphosphortriamide,dimethyl-N-trichloracetylamidophosphate, 1,10-phenanthroline and 2,2′-bipyrimidine

Coordination compounds with general formula [Ln(L¹)₃phen], where Ln = Nd, Eu, Er, Yb, HL¹ = N,N′-dipyrrolidine-N′′-trichloracetylphosphortriamide, phen = 1,10-phenanthroline; [Ln(L¹)₃bpm], where Ln = La, Nd, Eu, Gd, Er, Y, bpm = 2,2′-bipyrimidine and [{Ln(L²)₃}₂(μ-bpm)], where Ln = La, Nd, Eu, Gd, Er, Y, HL² = dimethyl-N-trichloracetylamidophosphate have been synthesized and characterized by means of IR and UV–Vis spectroscopy. Crystal structures of [Nd(L¹)₃phen] (1), [Nd(L¹)₃bpm] (2) and [{Nd(L²)₃}₂(μ-bpm)] (3) have been determined. It was found, that in the deprotonated form the phosphoryl ligands (L¹)^? and (L²)^? are coordinated to the neodymium atoms in a bidentate manner via the oxygen atoms of the phosphoryl and the carbonyl groups with formation of six-membered metallocycles. In the case of compounds 1 and 2 the 1,10-phenanthroline (or 2,2′-bipyrimidine) molecules are coordinated to the metals in a bidentate manner via the nitrogen atoms. In contrast 2,2′-bipyrimidine acts in the bidentate-bridge mode forming binuclear complex 3. Variable-temperature magnetic susceptibility measurements of 3 and [{Gd(L²)₃}₂(μ-bpm)] (4) reveal a weak antiferromagnetic interaction between the two magnetic centres, whereas in the case of [{Eu(L²)₃}₂(μ-bpm)] (5) the presence of spin–orbit coupling leads to a deviation from the Curie and Curie–Weiss laws.     

A family of dodecanuclear Mn11Ln single-molecule magnets

A series of four isostructural dodecanuclear complexes [Mn^III₉Mn^II₂Ln^III(O)₈(OH)(piv)₁₆(NO₃)(CH₃CN)]·xCH₃CN·yC₇H₁₆ (piv = pivalate; x = ½, y = ¾, Ln = Tb (1); x = 2, y = ½, Ln = Dy (2), Ho (3), and Y (4)) has been prepared for which the structural motif described as ‘a lanthanide ion nested in a large manganese shell’ is observed. All compounds show out-of-phase signals in their ac susceptibilities, and their single-molecule magnet behaviour was confirmed by single-crystal micro-SQUID studies of 1-3 which show hysteresis loops of molecular origin at T < 1.0 K. The SMM behaviour observed in compounds 1-3 is more pronounced than that for 4, which contains the diamagnetic Y^III ion. This is principally the result of ferromagnetic coupling between the paramagnetic anisotropic Ln^III ions (Tb^III, Dy^III and Ho^III) and the manganese shell, which enhances the total spin ground state of the complexes.     

Crystal structures,luminescence, and thermal properties of lanthanide complexes with 2,3,4-trimethoxybenzoic acid and 1,10-phenanthroline

The complexes of [Ln(2,3,4-tmoba)₃phen]₂ (Ln = Dy (1), Eu (2), Tb (3); 2,3,4-tmoba = 2,3,4-trimethoxybenzoate; phen = 1,10-phenanthroline) were synthesized and characterized by a series of techniques including the elemental analysis, IR and fluorescent spectra and TG/DSC-FTIR technology. The crystal structures were determined by X-ray crystallography. Each complex include two Ln³⁺ ions, six 2,3,4-tmoBA and two phen molecules forming a binuclear structure, giving the coordination number of nine. The three-dimensional IR accumulation spectra of gaseous products for the complexes 1 to 3 are analyzed and the thermal decomposition processes are further authenticated. Through means of differential scanning calorimeter (DSC), two solid-solid phase transition endothermic peaks were found in the complex 2, which was different from the complexes 1 and 3. The heat capacities of these complexes were measured and fitted to a polynomial equation with the least squares method for each complex on the basis of the reduce temperature x (x = [T − (T_max + T_min)/2]/[(T_max − T_min)/2]) over the range from (256.15 to 476.15) K. Subsequently, the smoothed molar heat capacities and thermodynamic functions (H_T−H_298.15 K), (S_T−S_298.15 K), and (G_T−G_298.15 K) of the complexes 1 to 3 were calculated based on the fitted polynomial of the heat capacities. The fluorescent intensity of the complexes 2 and 3 are markedly improved as well.     

Structure and magnetic properties of 3d–4f heterometallic complexes containing di-2-pyridyl ketoximate: An approach to single-molecule magnets

[{Ln(hfac)₃}₂{Ni(dpk)₂(phen)}] (1Ln) and [{Ln(hfac)₃}₂{Ni(dpk)₂(py)₂}] (2Ln) were synthesized and characterized, where dpk = di-2-pyridyl ketoxmate and Ln = La, Tb, Dy, Ho, Er. The N–O groups from dpk bridged the central nickel(II) ion and terminal lanthanide(III) ions, giving a linear trinuclear array. Dc magnetic susceptibility measurements revealed that they did not possess appreciable intramolecular ferromagnetic or ferrimagnetic interaction. Ac magnetic susceptibility measurements clarified that frequency dependence of out-of-phase ac susceptibility was observed only for Dy derivatives 1Dy and 2Dy, which is regarded as an indication of single-molecule magnets.     

DFT study of group 8 catalysts for the hydrophenylation of ethylene: Influence of ancillary ligands and metal identity

Computational methods are used to investigate catalytic hydrophenylation of ethylene using complexes of the type [(Y)M(L)(CH₃)(NCMe)]ⁿ⁺ [Y = Mp, n = 1; Y = Tp, n = 0; M = Ru or Os; L = PMe₃, PF₃, or CO; Mp = tris(pyrazolyl)methane; Tp = hydrido-tris(pyrazolyl)borate]. The conversion of ethylene and benzene to ethylbenzene with [(Y)M(L)(Ph)]ⁿ⁺ as catalyst involves four steps: (1) ethylene coordination, (2) ethylene insertion into the M–Ph bond, (3) benzene coordination, and (4) benzene C–H activation. DFT calculations form the basis to compare stoichiometric benzene C–H activation by [(Y)M(L)(CH₃)(NCMe)]ⁿ⁺ complexes to yield methane and [(Y)M(L)(Ph)(NCMe)]ⁿ⁺. In addition, starting from the 16-electron species [(Y)M(L)(Ph)]ⁿ⁺, potential energy surfaces for the formation of ethylbenzene are calculated to reveal the impact of modifications to the scorpionate ligand (Mp or Tp), co-ligand (L) and metal center (M).     

In search for mixed transition metal/lanthanide single-molecule magnets: Synthetic routes to NiII/TbIII and NiII/DyIII clusters featuring a 2-pyridyl oximate ligand

Employing the mononuclear complex [Ni{(py)C(Me)NO}₂{(py)C(Me)NOH}] (1) as ‘ligand’ [(py)C(Me)NOH = methyl 2-pyridyl ketone oxime], the use of the ‘metal complexes as ligands’ approach has led to the synthesis of the mixed Ni^II/Ln^III complexes [NiTb{(py)C(Me)NO}₂(NO₃)₃{(py)C(Me)NOH}] (2), [Ni₂Ln₂{(py)C(Me)NO}₆(NO₃)₄] (Ln = Dy, 3; Ln = Tb, 4) and [Ni₂Tb{(py)C(Me)NO}₆](NO₃) (5). The structures of 2, 3, and 5, and the magnetic properties of 2 and 5 are briefly discussed.     

Crystal growth of inter-lanthanide LaLn′O3 (Ln′ = Y,Ho–Lu) perovskites from hydroxide fluxes

In this article, we report the growth of single crystals of the inter-lanthanide series LaLn′O₃ (Ln′ = Y, Ho–Lu) using molten hydroxide fluxes. Inter-lanthanide oxides, LnLn′O₃ (where Ln and Ln′ = lanthanides) typically crystallize in the A-, B- or C-Ln₂O₃ or in the ABO₃ perovskite structure types, depending on the relative sizes of the lanthanide cations involved. The inter-lanthanide oxides, LaLn′O₃ (Ln′ = Y, Ho–Lu), reported herein were determined to crystallize in the orthorhombic (Pnma) perovskite-type structure. A discussion on the effect of cation radii on the resultant crystal structure for LaLn′O₃ (Ln′ = Y, Ho–Lu) and other reported inter-lanthanide oxides is presented herein.     

Thermal investigation and infrared evolved gas analysis of light lanthanide(III) complexes with pyridine-3,5-dicarboxylic acid

The characterisation of light lanthanide(III) complexes with pyridine-3,5-dicarboxylic acid of the formula Ln₂pdc₃·nH₂O where Ln denotes lanthanides from La to Gd, pdc = C₇H₅NO₄²⁻; n = 6 for Ce(III), n = 7 for Pr(III) and Sm(III), n = 8 for La and n = 13 for Nd(III), Eu(III) and Gd(III) was performed by the thermal analysis TG-DTA and the simultaneous infrared evolved gas analysis TG-FTIR. Heating of the crystalline complexes resulted in the dehydration process at first. Next, dehydrated compounds decompose releasing of CO₂, CO, CH₄ and hydrocarbons. Free pyridine molecules were detected only in the gaseous products of lanthanum(III) complex decomposition.     

Lanthanide complexes derived from hexadentate macrocyclic ligand: Synthesis,spectroscopic and thermal investigation

The lanthanide complexes derived from (3,5,13,15-tetramethyl 2,6,12,16,21-22-hexaazatricyclo[15.3.I^1-17I^7-11]cosa-1(21),2,5,7,9,11(22),12,15,17,19-decane) were synthesized. The complexes were found to have general composition [Ln(L)X₂·H₂O]X, where Ln = La³⁺, Ce³⁺, Nd³⁺, Sm³⁺ and Eu³⁺ and X = NO₃^? and Cl^?. The ligand was characterized by elemental analyses, IR, Mass, and ¹H NMR spectral studies. All the complexes were characterized by elemental analyses, molar conductance measurements, magnetic susceptibility measurements, IR, Mass, electronic spectral techniques and thermal studies. The ligand acts as a hexadentate and coordinates through four nitrogen atoms of azomethine groups and two nitrogen of pyridine ring. The lanthanum complexes are diamagnetic while the other Ln(III) complexes are paramagnetic. The spectral parameters i.e. nephelauxetic ratio (β), covalency factor (b^1/2), Sinha parameter (δ%) and covalency angular overlap parameter (η) have been calculated from absorption spectra of Nd(III) and Sm(III) complexes. These parameters suggest the metal–ligand covalent bonding. In the present study, the complexes were found to have coordination number nine.     

Magnetic properties and exchange couplings of one-dimensionally arrayed 4f−3d heterometallic [Ln2Cu2]n compounds

Heterometallic polymeric coordination compounds [{Ln(hfac)₂(CH₃OH)}₂{Cu(dmg)(Hdmg)}₂]_n ([Ln₂Cu₂]_n; Ln = Tb, Ho, and Er; H₂dmg = dimethylglyoxime; Hhfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione) were synthesized, and the X-ray crystallographic analysis shows that their structures are isomorphous to those of the known ferrimagnetic [Gd₂Cu₂]_n and [Dy₂Cu₂]_n analogs. The exchange couplings in [Tb₂Cu₂]_n, [Ho₂Cu₂]_n, and [Er₂Cu₂]_n were precisely evaluated by high-frequency EPR and pulsed-field magnetization studies, giving J_Tb?Cu/k_B = ?0.77(2) K, J_Ho?Cu/k_B = ?0.250(12) K and J_Er?Cu/k_B = ?0.149(15) K. They were comparable to those of the Gd and Dy analogs. The absolute value of the exchange coupling parameter monotonically decreases in the order of Gd, Tb, Dy, Ho, and Er.     

Heterometallic 3d–4f coordination polymers: Synthesis,characterization and magnetic properties of 1D zigzag chains containing samarium and terbium

Reaction of the copper precursor [Cu(MeOsaltn)(H₂O)] (H₂MeOsaltn = N,N′-bis(3-methoxysalicylidene)-1,3-diaminopropane) with Ln(NO₃)₃·6H₂O (Ln = Sm and Tb) and pyrazine-2,3-dicarboxylic acid (H₂pyrdic) results in the formation of 1D zigzag chains with the general formula of [Cu(MeOsaltn)Ln(NO₃)(pyrdic)]_n·nDMF. X-ray crystal structures reveal that the samarium and terbium compounds are isostructural and crystalize in the orthorhombic space group Pbcn. The chains are composed of heterodinuclear copper–lanthanide building blocks which are linked by the pyrazine-2,3-dicarboxylate bridging units. Temperature-dependent susceptibility measurements indicate antiferromagnetic exchange interactions for the samarium–copper chain whereas for the terbium–copper compound ferromagnetic interactions are observed.     

Synthesis,characterization and properties of microporous lanthanide silicates: K8Ln3Si12O32NO3·H2O (Ln = Eu,Tb, Gd,Sm)

A family of microporous lanthanide silicates, K₈Ln₃Si₁₂O₃₂NO₃·H₂O (denoted LnSiO-CJ3, Ln = Eu, Tb, Gd, Sm), was synthesized under mild hydrothermal conditions at 503 K. The X-ray powder diffraction patterns of these compounds reveal that they are isostructural. The structure of EuSiO-CJ3 was determined by single-crystal X-ray diffraction analysis. It crystallizes in triclinic space group P-1 (No. 2) with a = 11.599(2) Å, b = 12.225(2) Å, c = 13.829(3) Å, α = 112.99(3)°, β = 92.05(3)°, γ = 90.57(3)°. The structure is based on [Si₃O₈]_n^4n? layers with 6-, 8-, 12-rings that are connected by EuO₆ octahedra to form a 3-D framework with 8-ring channels along the [001] direction. Charge neutrality is achieved by the K⁺ and NO₃^? ions located in the channels. The framework of EuSiO-CJ3 shows good thermal stability, which can be stable up to 1273 K. Ion-exchange capacity of EuSiO-CJ3 was investigated by the exchange of NO₃^? ions with halide ions (F^?, Cl^?, Br^?). The peaks in the emission spectra of LnSiO-CJ3 (Ln = Eu, Tb) belong to the characteristic transitions of Ln³⁺ (Ln = Eu, Tb) respectively. The lifetime measurements of LnSiO-CJ3 (Ln = Eu, Tb) suggest the presence of three Ln³⁺ (Ln = Eu, Tb) environments, which are consistent with the crystallographic results.     

Synthesis,crystal, molecular and electronic structures of thiocyanate ruthenium complexes with pyridine and its derivatives as ligands

The complexes [Ru(SCN)₂(PPh₃)₂(L)₂], where L = py and γ-pic, and [Ru(SCN)₂(PPh₃)₂(L)], where L = py-2-CH₂NH₂ and py-2-CH₂O, have been prepared and studied by IR, NMR, EPR, UV–Vis spectroscopy and X-ray crystallography. The complexes were prepared in the reactions of [RuCl₂(PPh₃)₃] with pyridine, γ-picoline, 2-(aminomethyl)pyridine and 2-(hydroxymethyl)pyridine in methanol solutions. The electronic structures of the obtained compounds have been calculated using the DFT/TD-DFT method.     

3D pillar-layered coordination polymers based on 4d–4f heterometallic assembly

By control of mixed ligands with particular coordination sites, heterometallic coordination polymers, [Ln₂(H₂O)₂Ag(C₂O₄)₂(ina)₃]_n (Ln = Eu (1), Dy (2), Hina = isonicotinic acid) and {[LnAg(C₂O₄)(na)₂]·2H₂O}_n (Ln = La (3), Tb (4), Hna = nicotinic acid), have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR, thermogravimetric analysis (TGA), and single-crystal X-ray diffraction. These coordination polymers feature 3D pillar-layered coordination frameworks constructed from two-dimensional (2D) lanthanide–carboxylate layers and Ag(ina) or Ag(na) pillars. It is interesting that the in situ decarboxylation of pyridine-2,3-dicarboxylic acid into nicotinic acid was observed. The luminescent properties of 1 and 4 were also studied.     

Preparation and thermal properties of lanthanide complexes with 2,3-dichlorobenzoic acid and 1,10-phenanthroline

Three lanthanide complexes with a general formula [Ln(2,3-DClBA)₃phen]₂ (Ln(III) = Eu(1), Tb(2), Ho(3); 2,3-DClBA = 2,3-dichlorobenzoate; phen = 1,10-phenanthroline) were synthesized and characterized by elemental analysis, molar conductance, infrared and ultraviolet spectra and powder X-ray diffraction (XRD). The luminescent properties of the complexes 1 and 2 were studied. The thermal behaviors of the complexes were also discussed by thermogravimetric (TG), differential thermogravimetric (DTG) and infrared spectra (IR) techniques. The heat capacities of the complexes were measured from 259.15 to 493.02 K by means of Differential scanning calorimeter (DSC). The dependence of heat capacity on the reduce temperature x (x = [T ? (T_max + T_min)/2]/[(T_max ? T_min)/2]) was fitted to a polynomial equation with the least squares method for each complex. Furthermore, based on the fitted polynomial, the smoothed heat capacities and the derived thermodynamic functions (H_T ? H_298.15 K), (S_T ? S_298.15 K) and (G_T ? G_298.15 K) in the measured temperature range were obtained with an interval of 10 K.     

Using pendant ferrocenyl group(s) as an intramolecular standard to probe the reduction of diiron hexacarbonyl model complexes for the sub-unit of [FeFe]-hydrogenase

The synthesis and characterisation of two diiron hexacarbonyl complexes [Fe₂(SXS)(CO)₆], 1 (SXS = ((^?SCH₂)₂C(CH₃)CH₂OCOFc, Fc = ferrocenyl group) and 2 (SXS = (^?SCH₂CH₂NHCOFc)₂), were described. By using intramolecularly integrated ferrocenyl group(s) in the complexes as an internal standard, the nature of two stepwise one-electron processes of the complexes coupled with a chemical reaction was clearly demonstrated. Examining how the reduction transformed into sole one-electron process with both increasing scanning rate under Ar/CO atmosphere and lowering temperature indicated conclusively that the reduction of both complexes couples to a chemical reaction which involves CO-loss.     

Crystal structures and thermodynamic properties of lanthanide complexes with 2-chloro-4,5-difluorobenzoate and 1,10-phenanthroline

A series of lanthanide complexes with the 2-chloro-4,5-difluorobenzoate (2-cl-4,5-dfba) and 1,10-phenanthroline (phen), have been synthesized with the formulae of [La(2-cl-4,5-dfba)₃phen]_n·nH₂O (1), [Nd(2-cl-4,5-dfba)₃phenH₂O]₂ (2), [Ln(2-cl-4,5-dfba)₃phen]₂ (Ln = Eu (3), Ho (4)). The complexes are characterized by elemental analysis, infrared and fluorescent spectra and X-ray single-crystal diffraction. The structures of the four complexes are very different. Complex 1 is an infinite 1D chain polymeric structure formed by the asymmetric units with the mirror growth pattern. Each La³⁺ ion is coordinated to four bridging carboxylic groups, two tridentate chelating–bridging carboxylic groups, simultaneous with one phen molecule, giving the coordination number of nine. In the molecular structures of complexes 2 and 3, two Ln³⁺ ions are linked by four carboxyl groups, forming two binuclear molecules. In addition, each Nd³⁺ ion in complex 2 is bonded to one H₂O molecule and one carboxyl group by monodentate mode, one phen molecule by bidentate chelating, and each Eu³⁺ ion is also chelated to one phen molecule and one carboxyl group in complex 3. And in complex 4, the Ho³⁺ ion yields a eight-coordinated distorted square anti-prism coordination geometry. The three-dimensional IR accumulation spectra of gaseous products for complexes 1 to 4 are analyzed and further authenticated the thermal decomposition processes with TG-DTG curves. The heat capacities of complexes 2 to 4 are measured and fitted to a polynomial equation by the least squares method on the basis of the reduced temperature x (x = [T−(T_max + T_min)/2]/[(T_max − T_min)/2]). Then the smoothed molar heat capacities and thermodynamic functions of complexes 2 to 4 are calculated. The fluorescence intensity of complex 3 is markedly improved as well.