Effect of lanthanide contraction on the mixed polyamine systems Ln/Sb/Se/(en+dien) and Ln/Sb/Se/(en+trien): Syntheses and characterizations of lanthanide complexes with a tetraelenidoantimonate ligand

Mixed polyamine systems Ln/Sb/Se/(en+dien) and Ln/Sb/Se/(en+trien) (Ln=lanthanide, en=ethylenediamine, dien=diethylenetriamine, trien=triethylenetetramine) were investigated under solvothermal conditions, and novel mixed-coordinated lanthanide(III) complexes [Ln(en)₂(dien)(η²-SbSe₄)] (Ln=Ce(1a), Nd(1b)), [Ln(en)₂(dien)(SbSe₄)] (Ln=Sm(2a), Gd(2b), Dy(2c)), [Ln(en)(trien)(μ-η¹,η²-SbSe₄)]_∞ (Ln=Ce(3a), Nd(3b)) and [Sm(en)(trien)(η²-SbSe₄)] (4a) were prepared. Two structural types of lanthanide selenidoantimonates were obtained across the lanthanide series in both en+dien and en+trien systems. The tetrahedral anion [SbSe₄]³⁻ acts as a monodentate ligand mono-SbSe₄, a bidentate chelating ligand η²-SbSe₄ or a tridentate bridging ligand μ-η¹,η²-SbSe₄ to the lanthanide(III) center depending on the Ln³⁺ ions and the mixed ethylene polyamines, indicating the effect of lanthanide contraction on the structures of the lanthanide(III) selenidoantimonates. The lanthanide selenidoantimonates exhibit semiconducting properties with E_g between 2.08 and 2.51 eV.     

Tetrathiafulvalene-based lanthanide coordination complexes: Synthesis,crystal structure,optical and electrochemical characterization

The explorative lanthanide coordination chemistry of 4′,5′-bis-(propylthio)tetrathiafulvenyl[i]dipyrido[3,2-a:2′,3′-c]phenazine (TTF-dppz) is described. Thereby, four new Ln(III) complexes, [Ln(NO₃)₃(TTF-dppz)₂] with Ln(III) = Nd (1), Eu (2), Gd (3), Tb (4), have been prepared and characterized. An X-ray crystallographic study of [Gd(NO₃)₃(TTF-dppz)₂] (3) shows that the Gd(III) ion is coordinated to six oxygen atoms from three bidentate nitrate ligands and four nitrogen atoms from two bidentate TTF-dppz molecules forming a distorted bicapped square antiprism coordination geometry. The UV-vis spectra of the four Ln(III) complexes show very strong absorption bands in the UV region consistent with ligand centred electronic π-π* transitions and an intense broad absorption band in the visible region corresponding to a spin-allowed electronic π-π* ¹ILCT transition from the TTF-dppz ligand. Upon coordination, the ¹ILCT band of the free TTF-dppz ligand is bathochromically shifted. The electrochemical studies reveal that all complexes undergo two reversible oxidation and one (quasi)reversible reduction processes, ascribed to the successive oxidations of the TTF moiety and the reduction of the dppz unit, respectively. Moreover, the magnetic properties of complexes 3 and 4 are discussed.     

Synthesis,reactivity and structural characterization of lanthanide hydroxides stabilized by a carbon-bridged bis(phenolate) ligand

The synthesis of lanthanide hydroxo complexes stabilized by a carbon-bridged bis(phenolate) ligand 2,2’-methylene-bis(6-tert-butyl-4-methylphenoxo) (MBMP²⁻) was described, and their reactivity toward phenyl isocyanate was explored. Reactions of (MBMP)Ln(C₅H₅)(THF)₂ with a molar equiv. of water in THF at −78 °C afforded the bis(phenolate) lanthanide hydroxides as dimers [{(MBMP)Ln(μ-OH)(THF)₂}₂] [Ln = Nd (1), Yb (2)] in high yields. Complexes 1 and 2 reacted with phenyl isocyanate in THF, after workup, to give the desired O−H addition products, [(MBMP)Ln(μ-η¹:η²-O₂CNHPh)(THF)₂]₂ [Ln = Nd (3), Yb (4)] in excellent isolated yields. These complexes were well characterized, and the molecular structures of complexes 2 to 4 were determined by X-ray crystallography. The ytterbium atom in complex 2 is coordinated to six oxygen atoms to form a distorted octahedral geometry, whereas each metal center in complexes 3 and 4 is seven-coordinated, and the coordination geometry can be best described as a distorted pentagonal bipyramid.     

Synthesis and characterization of bis(guanidinate)lanthanide diisopropylamido complexes: New highly active initiators for the polymerizations of ε-caprolactone and methyl methacrylate

Treatment of LnCl₃ with [(SiMe₃)₂NC(NiPr)₂]Li in 1:2 molar ratio afforded the soluble bis(guanidinate)lanthanide chlorides {[(SiMe₃)₂NC(NiPr)₂]₂Ln(μ-Cl)}₂ (Ln=Y (1), Nd (2)). Amination of 1 and 2 with two equivalents of LiN(iPr)₂ in a mixture solution of toluene and hexane gave [(SiMe₃)₂NC(NiPr)₂]₂LnN(iPr)₂ (Ln=Y (3), Nd (4)) in good isolated yields. The single-crystal structural analyses of 2 and 3 revealed that the coordination geometries of lanthanide metals are best described as a distorted pseudo-octahedron and a pseudo-pyramid, respectively. Complexes 3 and 4 exhibited extremely high activity for the polymerizations of ε-caprolactone and methyl methacrylate (MMA).     

Syntheses and molecular structures of mono(guanidinate) lanthanide borohydrides and their catalytic activity for MMA-polymerization

The mono(guanidinate) lanthanide borohydride complexes of [(Me₃Si)₂NC(NCy)₂]Ln(BH₄)₂(THF)₂ (Ln = Yb (1), Er (2)) have been synthesized by the reactions of corresponding Ln(BH₄)₃(THF)₃ with sodium guanidinate of [(Me₃Si)₂NC(NCy)₂]Na in a 1:1 molar ratio in THF. They were characterized by elemental analysis, infrared spectrum and X-ray diffraction analysis. 1 and 2 have similar structures. The lanthanide ion was bonded by an η²-guanidinate ligand, two η³-BH₄ ligands and two THF molecules as a distorted octahedron. The two BH₄ ligands in a complex are equivalent and cis to each other. The structure of solvated sodium guanidinate of {[(Me₃Si)₂NC(NCy)₂]Na(THF)}₂ (3) was also presented. In a dimeric molecule of 3, each Na atom is bound to three nitrogen atoms from two guanidinate groups and one oxygen atom from the THF molecule. 1 and 2 displayed moderate high catalytic activity for the polymerization of methyl methacrylate. The Er complex is more active than the Yb complex.     

New 3d–4f supramolecular systems constructed by [Fe(bipy)(CN)4] and partially blocked lanthanide cations

The reaction of acetonitrile (1–5) and mixed acetonitrile/water 1:1 (6–9) solutions containing the cyanide-bearing [Fe(bipy)(CN)₄]⁻ building block (bipy = 2,2′-bipyridine) and the partially blocked [Ln(bpym)]³⁺ cation (Ln = lanthanide trivalent cation and bpym = 2,2′-bipyrimidine) has afforded two new families of 3d–4f supramolecular assemblies of formula [Ln(bpym)(NO₃)₂(H₂O)₃][Fe(bipy)(CN)₄] · H₂O · CH₃CN [Ln = Sm (1), Gd (2), Tb (3), Dy (4) and Ho (5)] and [Ln(bpym)(NO₃)₂(H₂O)₄][Fe(bipy)(CN)₄] [Ln = Pr (6), Nd (7), Sm (8), Gd (9)]. They crystallize in the P2₁/c (1–5) and P2/c (6–9) space groups and their structures are made up of [Fe(bipy)(CN)₄]⁻ anions (1–9) and [Ln(bpym)(NO₃)₂(H₂O)_n]⁺ cations [n = 3 (1–5) and 4 (6–9)] with uncoordinated water and acetonitrile molecules (1–5) which are interlinked through an extensive network of hydrogen bonds and π–π stacking into three-dimensional motifs. Both families have in common the occurrence of the low-spin iron(III) unit [Fe(bipy)(CN)₄]⁻ where two bipy–nitrogen and four cyanide–carbon atoms build a somewhat distorted octahedral surrounding around the iron atom [Fe–N = 1.980(3)–1.988(3) Å (1–5) and 1.988(2)–1.992(2) Å (6–9); Fe–C = 1.904(5)–1.952(4) Å (1–5) and 1.911(2)–1.948(3) Å (6–9)]. The main structural difference between both families concerns the environment of the lanthanide atom which is nine- (1–5)/10-coordinated (6–9) with a chelating bpym, two bidentate nitrate and three (1–5)/four (6–9) water molecules building distorted monocapped (1–5)/bicapped (6–9) square antiprisms. This different lanthanide environment is at the origin of the different hydrogen bonding pattern of the two families of compounds.     

Synthesis, characterization of homoleptic guanidino lanthanide complexes and their catalytic activity for the ring-opening polymerization of ε-caprolactone

A series of homoleptic lanthanide guanidinate (guan)₃Ln · ((C₂H₅)₂O)_n (Ln=Yb, n=1 guan=(CyN)₂CNiPr₂, (1); Ln=Nd, n=0, guan=(CyN)₂CNiPr₂, (2); (iPrN)₂CNiPr₂, (3); (iPrN)₂CN(CH₂)₅, (4)); (iPr=isopropyl, Cy=Cyclohexyl) were synthesized by the reaction of THF solution of lithium guanidinate with anhydrous lanthanide trichlorides in THF in 3:1 molar ratio. The molecular structures of 2 and 3 were determined to be monomeric in solid state with a six coordinate lanthanide metal ligated by six nitrogens of three guanidinate groups. All the complexes exhibited extremely high activity for the ring-opening polymerization of ε-caprolactone and the polymerization gave the polymers with high molecular weights. The different substituents at guanidino ligands have great effect on the catalytic activity. The mechanism of the polymerization was presented.     

Dimolybdenum complexes containing anions of N,N′-bis(pyrimidine-2-yl)formamidine and N-(2-pyrimidinyl)formamide

The reactions of Mo₂(O₂CCH₃)₄ with different equivalents of N,N′-bis(pyrimidine-2-yl)formamidine (HL1) and N-(2-pyrimidinyl)formamide (HL2) afforded dimolybdenum complexes of the types Mo₂(O₂CCH₃)(L1)₂(L2) (1) trans-Mo₂(L1)₂(L2)₂ (2) cis-Mo₂(L1)₂(L2)₂ (3) and Mo₂(L2)₄ (4). Their UV–Vis and NMR spectra have been recorded and their structures determined by X-ray crystallography. Complexes 2 and 3 establish the first pair of trans and cis forms of dimolybdenum complexes containing formamidinate ligands. The L1 ligands in 1–3 are bridged to the metal centers through two central amine nitrogen atoms, while the L2 ligands in 1–4 are bridged to the metal centers via one pyrimidyl nitrogen atom and the amine nitrogen atom. The Mo–Mo distances of complexes 1 [2.0951(17) Å], 2 [2.103(1) Å] and 3 [2.1017(3) Å], which contain both Mo?N and Mo?O axial interactions, are slightly longer than those of complex 4 [2.0826(12)–2.0866(10) Å] which has only Mo?O interactions.     

Syntheses,crystal structures,and magnetic and luminescent properties of a series of lanthanide coordination polymers with chelidamic acid ligand

A series of lanthanide(III) complexes with chelidamic acid ligand, [Ln(C₇H₂NO₅)·3H₂O]_n·nH₂O (Ln = La (1), Y (2), Sm (3), and Nd (4)), [Gd₂(C₇H₂NO₅)₃·4H₂O]_n·2nH₂O (5) and [Ce(C₇H₂NO₅)·1.5H₂O]_n (6), have been synthesized by hydrothermal method and structurally characterized by single-crystal X-ray diffraction. Complexes 1–4 are isostructural and possess 2D framework. Complex 5 contains two different Gd(III) ions linked through carboxylate group to form a 2D framework. Complex 6 exhibits a (4⁴) topology 2D network. The variable-temperature magnetic properties of 3 and 5 have been investigated. Furthermore, the photoluminescent properties of 1, 2, 3, and 5 at room temperature were also studied.     

Syntheses, structures, luminescence, and magnetism of four 3D lanthanide 5-sulfosalicylates

Four 3D lanthanide(III) complexes with 5-sulfosalicylic acid (H₃SSA) as bridging ligands, Ln(SSA)(H₂O)₂ [Ln=Ce(III) (1), Pr(III) (2), Nd(III) (3) and Dy(III) (4)], have been synthesized and characterized by elemental analysis, IR, XRD and single-crystal X-ray diffraction. X-ray structural analysis reveals that isostructral complexes 1-4 possess 3D structures with 4⁶6⁴ topology. Complexes 1 and 2 exhibit broad intraligand fluorescent emission bands. Complexes 3 and 4 not only display intraligand fluorescent emission bands, but also present Nd(III) characteristic emission in the near-IR region and sensitized luminescence of Dy(III) ions in the visible region, respectively. Variable-temperature magnetic susceptibility measurements of 2-4 have been studied over the temperature range of 4-300 K.     

Synthesis, structure, solid-state thermal decomposition and magnetic properties of binuclear Nd, Gd and Eu cymantrenecarboxylates

New rare-earth cymantrenecarboxylates [Nd₂(μ₂-OOCCym)₄(OOCCym)₂(THF)₄] (1) and [Ln₂(μ₂-OOCCym)₄(OOCCym)₂(THF)₄]·THF (Ln = Gd (2), Eu (3); Cym = (η⁵-C₅H₄)Mn(CO)₃) were synthesized starting from carboxycymantrene and lanthanide nitrates, and characterized by X-ray diffraction. The crystals of 1-3 consist of isolated binuclear molecules; the Ln atoms are eight-coordinate. The magnetic properties of 2 are indicative of antiferromagnetic coupling between the Gd atoms at liquid helium temperature. The thermal decomposition of complexes 1-3 was studied by differential scanning calorimetry (DSC) and thermogravimetry (TG). According to the X-ray powder diffraction patterns, the thermal decomposition of the complexes in air affords a mixture of LnMn₂O₅ and Mn₂O₃ as the final products.     

Synthesis, crystal structure, and chirality of divalent lanthanide reagents containing tri- and tetraglyme

Six new divalent lanthanide complexes using triglyme (trigly) and tetraglyme (tetgly) as achiral ligands have been prepared, using a facile synthetic method, in search for enantioselective solid-state reagents. The crystal structures of cis-[SmI₂(trigly)thf] (1), trans-[YbI₂(trigly)thf] (2), trans-[SmI₂(trigly)dme] (3), trans-[YbI₂(tetgly)] (4), trans-[EuI₂(tetgly)thf] (5), and [Sm(tetgly)₂][SmI₃(tetgly)]I (6) have been determined. All complexes, except 5, are chiral. The 10-coordinate cation in 6 displays a helical chirality since the two tetraglyme ligands are wrapped around the samarium ion. Since trans-[YbI₂(tetgly)] (4), which has a chiral arrangement of terminal methyl groups, crystallizes as a conglomerate, preferential crystallization and consequent enantioselective reduction of acetophenone was attempted, but resulted in racemic products, possibly on account of racemic twinning in 4.     

Lanthanide complexes of the monovacant Dawson polyoxotungstate [α2-As2W17O61] with 1D chain: Synthesis, structures, and photoluminescence properties

Six new lanthanide complexes, (H₃O)[Ln₃(H₂O)₁₇(α₂-As₂W₁₇O₆₁)]·nH₂O ((1) Ln=Ce^III and n≈13; (2) Ln=Pr^III and n≈9; (3) Ln=Nd^III and n≈14; (4) Ln=Sm^III and n≈8; (5) Ln=Eu^III and n≈4; (6) Ln=Gd^III and n≈7), have been isolated by conventional solution method and characterized by elemental analysis, IR spectroscopy and single crystal X-ray diffraction. All the complexes are isomorphic and crystallize in the triclinic space group P-1. These complexes are 1D chain-like structures constructed by lanthanide cations and monovacant Dawson-type [α₂-As₂W₁₇O₆₁]¹⁰⁻ polyoxoanions. The striking feature of the structures is that there are three kinds of coordination environments for lanthanide cations, which are responsible for the formation of polymeric structures. Photoluminescence measurements reveal that 4 and 5 exhibit orange and red fluorescent emission at room temperature, respectively.     

Rare earth metal bis(alkyl) complexes bearing amino phosphine ligands: Synthesis and catalytic activity toward ethylene polymerization

Reactions of neutral amino phosphine compounds HL^1-3 with rare earth metal tris(alkyl)s, Ln(CH₂SiMe₃)₃(THF)₂, afforded a new family of organolanthanide complexes, the molecular structures of which are strongly dependent on the ligand framework. Alkane elimination reactions between 2-(CH₃NH)-C₆H₄P(Ph)₂ (HL¹) and Lu(CH₂SiMe₃)₃(THF)₂ at room temperature for 3 h generated mono(alkyl) complex (L¹)₂Lu(CH₂SiMe₃)(THF) (1). Similarly, treatment of 2-(C₆H₅CH₂NH)-C₆H₄P(Ph)₂ (HL²) with Lu(CH₂SiMe₃)₃(THF)₂ afforded (L²)₂Lu(CH₂SiMe₃)(THF) (2), selectively, which gradually deproportionated to a homoleptic complex (L²)₃Lu (3) at room temperature within a week. Strikingly, under the same condition, 2-(2,6-Me₂C₆H₃NH)-C₆H₄P(Ph)₂ (HL³) swiftly reacted with Ln(CH₂SiMe₃)₃(THF)₂ at room temperature for 3 h to yield the corresponding lanthanide bis(alkyl) complexes L³Ln(CH₂SiMe₃)₂(THF)_n (4a: Ln = Y, n = 2; 4b: Ln = Sc, n = 1; 4c: Ln = Lu, n = 1; 4d: Ln = Yb, n = 1; 4e: Ln = Tm, n = 1) in high yields. All complexes have been well defined and the molecular structures of complexes 1, 2, 3 and 4b-e were confirmed by X-ray diffraction analysis. The scandium bis(alkyl) complex activated by AlEt₃ and [Ph₃C][B(C₆F₅)₄], was able to catalyze the polymerization of ethylene to afford linear polyethylene.     

Synthesis, crystal structures and photoluminescent properties of lanthanide supramolecular complexes with 4-oxo-1(4H)-quinolineacetate

Five new lanthanide supramolecular complexes, namely, [Sm(oqa)₂(H₂O)₄]₂ (ClO₄)₂·(bpy)₂ (1), [Ln(oqa)₃]·2H₂O [Ln=Sm(2), Gd(3)] and [Ln(oqa)₂(NO₃)(H₂O)] [Ln=Pr(4), Eu(5)] (oqa=4-oxo-1(4H)-quinolineacetate, bpy=4,4′-bipyridine), have been synthesized under hydrothermal conditions. These complexes exhibit three typical structure features. Complex 1 possesses a dimeric structure, which is further connected together through hydrogen bonds and π-π attractions, forming a 3D supramolecular framework. Compounds 2-3 are isomorphous and contain 1D ring-like chains, which are further interconnected by the oqa ligands into 2D sheet-like structures. 4 and 5 exhibit eight-connected 3D network of 4²⁴·6⁴-bcu topology. The various coordination modes of carboxylate ligands and the selection of the counterions have clearly affected the topological structures. Furthermore, the solid-state luminescent properties of complexes 1, 2 and 5 were investigated at room temperature and they show intense, characteristic emissions in the visible region.     

Bridged bis(amidinate) lanthanide complexes: Synthesis,molecular structure and reactivity

The yttrium chloride with the bridged bis(amidinate) L (L = Me₃SiNC(Ph)N(CH₂)₃NC(Ph)NSiMe₃) LYCl(DME) (2) was synthesized and structurally characterized. Treatment of LLnCl(sol)_x (Ln = Yb, sol = THF, x = 2 1; Ln = Y, sol = DME, x = 1 2) with the dilithium salt Li₂L(THF)_0.5 afforded the novel bimetallic lanthanide complexes supported by three ligands, Ln₂(μ₂-L)₃ · DME (Ln = Yb 3, Y 4; DME = dimethylether), instead of the designed complex LLn(μ₂-L)LnL via the ligand redistribution reaction. Complexes 3 and 4 were fully characterized including X-ray analysis and ¹H NMR spectrum for 4. Reaction of LnCl₃ (Ln = Yb, Y) with 2 equiv. of Li₂L(THF)_0.5 gave the anionic complexes [Li(DME)₃][L₂Ln] (Ln = Yb 5, Y 6), which were confirmed by a crystal structure determination. The further study indicated that complexes 3 and 4 can also be synthesized by reaction of LnCl₃ (Ln = Yb, Y) with 1.5 equiv. of Li₂L(THF)_0.5 or reaction of 1 and 2 with anionic complexes 5 and 6. Complexes 3, 4, 5 and 6 were found to be high active catalysts for ring-opening polymerization of ε-caprolactone (CL).     

Ferrocenylpyrazole—A versatile building block for hydrogen-bonded organometallic supramolecular assemblies

The crystal architectures of 5-ferrocenylpyrazole (1) and its metal complexes were investigated. Compound 1 can form non-solvated and chloroform-solvated crystals. In both cases, 1 forms a zigzag one-dimensional architecture via NH?N hydrogen bonds. The hydrogen bond exhibits a twofold disorder, which was shown to be static by solid-state ¹³C NMR. In the solvated crystal, the chloroform is released at 415 K, associated with melting of the crystal. The reaction of 1 with metal salts provided metal-centered ferrocenyl clusters [Zn(NO₃)₂(1)₄] (4), [Co(NO₃)₂(1)₄] (5), [CoCl₂(1)₄] (6), [Zn(NCS)₂(1)₂] (7), cis-[Pt(NH₃)₂(1)₂](PF₆)₂ (8), and trans-[Pt(NH₃)₂(1)₄](PF₆)₂ (9). In all of these complexes, 1 acts as a monodentate ligand. In 4, 5, and 7, the multinuclear units are joined via hydrogen bonds to form supramolecular chains. Two polymorphs were found for the crystals of 4. Both are composed of the same hydrogen-bonded chains, but their arrangements are different. 5-Ferrocenyl-1-tritylpyrazole (2) and 4-ferrocenyl-1-methylpyrazole (3) were also crystallographically characterized.     

Synthesis, structure, and catalytic activity of organolanthanides with chiral biphenyl-based tridentate amidate ligands

Four new chiral organolanthanide amidate complexes have been readily prepared in good yields via silylamine elimination reaction between Ln[N(SiMe₃)₂]₃ (Ln = Sm, Y, Yb) and chiral amidate ligands, (R)-2-(mesitoylamino)-2′-methoxy-6,6′-dimethyl-1,1′-biphenyl (1H) and (R)-2-(mesitoylamino)-2′-dimethylamino-6,6′-dimethyl-1,1′-biphenyl (2H). The steric effect of the ligand coupled with the size effect of the lanthanide ion plays an important role in complex formation. For example, treatment of 1H with half equiv of Sm[N(SiMe₃)₂]₃ gives the C₂-symmetric bis-ligated amidate complex (σOMe:κO:κN-1)₂SmN(SiMe₃)₂ (3) in 75% yield, while reaction of 1H or 2H with half equiv of Ln[N(SiMe₃)₂]₃ (Ln = Y, Yb) affords the C₁-symmetric bis-ligated amidate complexes [(κO:κN-1)(σOMe:κO:κN-1)]LnN(SiMe₃)₂ (Ln = Y (4), Yb (5) and the C₁-symmetric mono-ligated amidate complex (σNMe₂:κO:κN-2)Y[N(SiMe₃)₂]₂ (6), respectively, in good yields. These organolanthanide amidate complexes have been characterized by various spectroscopic techniques, elemental analyses, and X-ray diffraction analyses. They are active catalysts for asymmetric hydroamination/cyclization of aminoalkenes and ring-opening polymerization of rac-lactide, affording cyclic amines in excellent conversions with good ee values and isotactic-rich polylactides, respectively.     

Synthesis and structural characterization of enantiopure exo and endo six-membered oxazoline-derived palladacycles

Direct palladation of (S)-4-benzyl-2-methyl-2-oxazoline (1) and (S)-2-benzyl-4-tert-butyl-2-oxazoline (2) using Pd(OAc)₂ in MeCN afforded the corresponding μ-acetato-dimeric complexes with six-membered exo and endo palladacycles, respectively. The same complexes were obtained by reacting coordination complexes Pd(1)₂(OAc)₂ and Pd(2)₂(OAc)₂ with Pd(OAc)₂ in MeCN. Metalation of (S)-2,4-dibenzyl-2-oxazoline (3) with Pd(OAc)₂ in AcOH, MeCN or CH₂Cl₂ resulted in the regiospecific formation of the six-membered endo palladacycle. The obtained μ-acetato-dimeric complexes were converted to the corresponding μ-chloro-dimeric derivatives 7, 11 and 13 by treatment with LiCl in acetone. The mononuclear PPh₃ adducts 8, 12 and 14 were obtained by reacting dimers 7, 11 and 13 with PPh₃ in benzene. NMR spectroscopy data supported the proposed structures of all complexes and suggested that exo and endo palladacycles in 8 and 12 have rigid boat conformations in CHCl₃. The X-ray crystal structures of the μ-acetato dimer 6 with the exo palladacycle and the PPh₃ adduct 14 with the endo metalacycle revealed boat conformation of both palladacycles and chiral twisted conformations δ(S) and λ(S), respectively, of the oxazoline rings in the solid state.     

Self-assembly of a tridentate Schiff-base ligand with Zn(II) in the presence of lanthanides: Novel crystal structures and spectroscopic properties

Condensation of picolinaldehyde with methyl 4-amino-3-hydroxy-benzoate resulted in the acquisition of a tridentate Schiff-base ligand (HL) which contains a structural moiety typical of octahedrally cored grid-type analogs. Reactions of HL with Zn(NO₃)₂ in the presence of Ln(NO₃)₃ [Ln = Sm(III), Tb(III) and Yb(III)] result in two types of complexes, viz. [Zn(HL)(L)]₂[Ln(NO₃)₅] [Sm(III), 1a and Tb(III), 1b] and [Zn(HL)L]₂[Yb(NO₃)₅]·C₃H₆O (1c). Despite applying two different synthetic protocols, the transition metal ion displayed a greater propensity towards the meridional tridentate pocket, which is reflected by XRD analysis, the ESI-MS technique and further supported by elemental analysis and IR characterization of each compound. In addition, we have compared the luminescence properties of 1a, 1b and 1c with the previously synthesized [Zn(HL)(L)]₂[Zn(NO₃)₄] (1d) to investigate whether a different metal in the outer coordination sphere could somehow tune the compounds’ spectral behavior.