Interaction of polyamine macrocycles with Zn(II) and ATP in aqueous solution. Binary and ternary systems. A potentiometric,NMR and fluorescence emission study

ATP binding to ligands L1 and L3 and to their Zn(II) complexes has been examined by means of potentiometric and ¹H and ³¹P NMR measurements in aqueous solution. Their coordination features have been compared to those of ligand L2 and its Zn(II) complex. In all the three cases, the Zn(II) complexes proved to be better receptors than free ligands, due to the synergetic action of metal ion and ammonium functions in ATP binding. Among the three complexes, Zn(II) complex with L1 shows the highest equilibrium constant, which can be ascribed to the fact that, being coordinated by the dipyridine nitrogens outside the macrocyclic cavity, it is less saturated by ligand donors. The ³¹P NMR investigation showed that the nucleotide interacts via the P_γ and P_β phosphate groups with both free ligands and complexes, while the ¹H spectra revealed that the binding is reinforced by the presence of π–π interactions. Photophysical studies showed that the fluorescence emission intensity of the Zn(II) complexes is enhanced upon interaction with ATP.     

Solution behaviour of a monooxorhenium(V) complex of 1,4,8,11-tetraazacyclotetradecane

The reaction of ReOCl₃(PPh₃)₂ with cyclam gives a macrocyclic monooxorhenium(V) complex, [ReO(cyclam)(OH₂)]Cl₃ (1). This exist as a monocation in aqueous solution in which the cyclam ligand is doubly deprotonated [ReO(C₁₀H₂₂N₄(OH₂)]⁺ (2), the structure of which has been defined with the aid of NMR, visible spectrophotometric and FAB mass spectrometric methods.     

Dinuclear Ni(II) and Cu(II) complexes with indolecarboxamide ligand: Synthesis, structure and properties

A potential tetradentate indolecarboxamide ligand, H₄L³ is synthesized and investigated for its coordination abilities towards Ni(II) and Cu(II) ions. Two H₄L³ ligands in their tetra-deprotonated form [L³]⁴⁻, were found to coordinate two metal centers resulting in the formation of [Ni₂(L³)₂]⁴⁻ (5) and [Cu₂(L³)₂]⁴⁻ (6) complexes. The crystal structure of 6 displays the formation of a dinuclear structure where two fully deprotonated ligands, [L³]⁴⁻ hold two copper(II) ions together. Even more interesting is the fact that both deprotonated ligands, [L³]⁴⁻ coordinate the copper ions in an identical and symmetrical fashion. The Na⁺ cations present in the complex 6 stitch together the dinuclear units resulting in the formation of a coordination chain polymer. Four sodium ions connect two dinuclear units via interacting with the O_amide groups. Further, Na⁺ cations were found to coordinate several DMF molecules; some of them are terminal and a few are bridging in nature. The solution state structure (determined by the NMR spectral analysis) of the diamagnetic complex 5 also supported the fact that two deprotonated ligands, coordinate two nickel ions in an identical and symmetrical fashion. Absorption spectral studies reveal that the solid-state square-planar geometry is retained in solution and both complexes do not show any tendency to coordinate potential axial ligands. The variable-temperature magnetic measurements and EPR spectra indicate spin-spin exchange between two copper centers in complex 6. The electrochemical results for both complexes show three irreversible oxidative responses that correspond to the oxidation of first and second metal ion followed by the ligand oxidation, respectively.     

Metal complexes with two tri-aza,tri-oxa pendant-armed macrocyclic ligands: Synthesis,characterization, crystal structures and fluorescence studies

Metal complexes of two new tri-aza, tri-oxa macrocycles containing ethyl acetate (L¹) or carboxymethyl (H₂L²) pendant arms with hydrated nitrate or perchlorate salts of alkaline earth, post-transition and lanthanide metal ions have been synthesized and characterized by microanalysis FAB MS, conductivity measurements, IR, UV–Vis spectroscopy and fluorescence emission studies. The synthesis and characterization of the Pb(II) complexes with the armless macrocyclic precursors L (Schiff base macrocycle) and L′ (diaminic reduced macrocycle) are also reported. The crystal structures of complexes [PbL(ClO₄)(H₂O)](ClO₄), [PbL′(ClO₄)](ClO₄) and ([Zn₂L²(Cl)(H₂O)](ClO₄))_∞ have been determined. In both lead(II) complexes, the metal ion is located inside the macrocyclic cavity and is coordinated by all N₃O₃ donor atoms in the complex with L′ but only by the nitrogen atoms present in the ligand in the complex with L. In both cases, the coordination sphere of the metal atom is completed with a perchlorate anion or a water molecule in the iminic complex of L. X-ray studies on the Zn(II) complex show the presence of a supramolecular structure that is consistent with a linear polymer formed alternately by an endomacrocyclic metal atom coordinated to a macrocyclic ligand and an exomacrocyclic metal ion in distorted octahedral and tetrahedral environments, respectively. UV–Vis and fluorescent emission studies were carried out on the ligands L¹ and H₂L² and their metal complexes, but only the luminescence spectra of the Eu(III) and Tb(III) complexes with L¹ in aqueous solution at ca. pH 7 show the characteristic visible emission of the metal. The value of the quantum yield determined for the Eu(III) complex is similar to that reported in the literature for other Eu(III) complexes.     

Cd(II) complexes with N8 and N4O4 donor macrocyclic ligands

The coordination capability of the octaaza 24-membered (L¹) and the tetraoxotetraaza 28-membered (L²) macrocycle ligands - with different sizes, nature and number of the donor atoms - has been investigated with nitrate and perchlorate Cd(II) salts. The complexes were prepared in 1:1 and 2:1 Cd:L molar ratio. The characterization by elemental analysis, IR, LSI mass spectrometry, conductivity measurements and ¹H NMR spectroscopy, together with the crystal structure of the complexes [CdL¹](NO₃)₂ · 0.5H₂O, [CdL¹](ClO₄)₂ and [CdL²(CH₃CN)₂](ClO₄)₂ · CH₃CN · H₂O confirms the formation of mononuclear complexes in all cases. The [CdL¹](NO₃)₂ · 0.5H₂O and [CdL¹](ClO₄)₂ present a mononuclear endomacrocyclic structure with the metal ion coordinated by the eight donor nitrogen atoms from the macrocyclic backbone in a square antiprism geometry. The complex [CdL²(CH₃CN)₂](ClO₄)₂ · CH₃CN · H₂O is also mononuclear, but the cadmium ion is in an octahedral environment coordinated by four amine nitrogen atoms from the macrocyclic framework and two nitrogen atoms from two acetonitrile molecules. The ether oxygen atoms from the ligand are not coordinated.     

Synthesis, crystal structure, NMR and ab initio molecular-orbital studies of some magnesium(II) macrocyclic Schiff-base complexes, with two 2-aminoethyl pendant arms

Three new Mg(II) bis(pendant arm) macrocyclic Schiff-base complexes, [MgLⁿ]²⁺(n=5, 6, 7), have been prepared via cyclocondensation of 2,6-diacetylpyridine with branched hexaamines and characterised spectroscopically. In addition, for [MgL⁵](ClO₄)₂ the crystal structure is reported. This is the first X-ray structural determination of an Mg(II) complex coordinated by seven nitrogen atoms. The ligands, L, are 15-, 16- and 17-membered pentaaza macrocycles having two 2-aminoethyl pendant arms [L⁵; 2,13-dimethyl-6,9-bis(aminoethyl)-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18), 2, 12, 14, 16-pentaene, L⁶; 2,14-dimethyl-6,10-bis(aminoethyl)-3,6,10,13,19-pentaazabicyclo[13.3.1]nonadeca-1(19), 2, 13, 15, 17-pentaene and L⁷; 2,15-dimethyl-6,11-bis(aminoethyl)-3,6,11,14,20-pentaazabicyclo[14.3.1]eicosa-1(20),2,14,16,18-pentaene]. The crystal structure of [MgL⁵](ClO₄)₂, was determined by X-ray diffraction and showed that the complex cation that had formed consisted of a pentagonal bipyramidally coordinated Mg(II) ion. All complexes were characterised by IR, ¹H NMR,¹³C NMR, COSY(H,H) and HETCOR(H,C) spectroscopy, and the data indicate that the structure is approximately pentagonal bipyramidal in each case. This structural assignment is also supported by ab initio HF-MO calculations made using the standard 3-21G* basis set.     

Self-assembled two-dimensional salicylaldimine lanthanum(III) nitrate coordination polymer

The unprecedented self-assembled formation of a two-dimensional salicylaldimine lanthanum coordination polymer is proved by the X-ray diffraction analysis of new lanthanum(III) nitrate complex containing the N,N′-bis(salicylidene)-1,4-butanediamine ligand L, which was prepared in situ through one-step template [2+1] Schiff base condensation of salicylaldehyde with 1,4-butanediamine in the presence of lanthanum(III) nitrate ion and characterized by spectroscopic (IR, ESI-MS, UV-Vis, and ¹H NMR) data and microanalysis. The complex displays an infinite [La₂L₄(NO₃)₆]_∞ polymeric structure based on networks of ten-coordinated La(III) nodes linked by bridging L ligands. The coordination geometry around the lanthanum is a distorted bicapped dodecahedron. This polymer can be described as composed from the columns of dimers connected into chains, via the flexible chain parts of ligands.     

Complex formation and stability of westiellamide derivatives with copper(II)

The Cu^II coordination chemistry of three synthetic analogues of westiellamide (H₃L^wa) with an [18]azacrown-6 macrocyclic structure and imidazole (H₃L¹), oxazole (H₃L²), or thiazole (H₃L³) heterocyclic donors in addition to the peptide groups, is reported. The N_heterocycle–N_peptide–N_heterocycle binding sites are highly preorganized for the coordination to Cu^II ions. The stability constants of mono- and dinuclear Cu^II complexes of H₃L¹, H₃L², and H₃L³, obtained by isothermal titration microcalorimetry, are reported. EPR and NMR spectroscopy as well as electrospray ionization mass spectrometry (ESI-MS) were used to characterize the complexes formed in solution. The stabilities of the mononuclear and dinuclear Cu^II complexes of the three ligands are in the range of 10⁵ M⁻¹, but there are subtle differences; specifically the oxazole-derived ligand has, in contrast to the other two macrocycles, a negative formation entropy for coordination to the first Cu^II ion and a higher stability for complexation to a second Cu^II center in comparison with the first Cu^II center (cooperativity). Differences between the three ligands are also apparent in terms of the formation mechanism. With the oxazole-based ligand H₃L², NMR spectroscopy, EPR spectroscopy, and ESI-MS indicate the formation of a ligand–Cu^II 2:1 intermediate, and this may explain the differences in the formation entropy as well as the cooperativity.     

Structure, solution equilibria and magnetic properties of copper(II) complexes with new sulfurated triazoline derivatives of α-amino acids

Two new sulfurated triazoline ligands have been synthesized by functionalization of glycine and l-alanine (HL¹ and HL², respectively) at the carboxylate site with retention of chirality in the latter case. The ligands and their copper(II) complexes have been characterized by spectroscopic methods and their structures were determined by X-ray diffraction. The compound [Cu(H₂L²)₂](H₅O₂)(SO₄)₂(HSO₄) presents a very disordered structure with regard to the anionic counterion and a very unusual elongated crystal cell. In all the complexes the ligands are (N,S) coordinated to copper(II), while the amino groups remain protonated and uncoordinated. The ligands have also been studied in solution and their dissociation constants were determined both by potentiometry and ¹H NMR titrations. Potentiometric studies on the complex [Cu(H₂L²)₂](H₅O₂)(SO₄)₂(HSO₄) were performed to determine the dissociation constants of the ligand once coordinated to the metal. The complex [CuCl₂(H₂L¹)]Cl was studied also by magnetic susceptibility measurements, showing an interesting antiferromagnetic behavior at low temperature which has been interpreted on the basis of its crystal packing.     

Oligonuclear nickel(II) complexes sustained by intermolecular hydrogen-bonding

Reaction of Ni(OAc)₂ with the symmetric `end-off' compartmental proligand 2,6-[N,N^′-bis(2-hydroxy-phenylmethyl)-N,N^′-bis(2-pyridylmethyl)aminomethyl]-4-methylphenol (H₃L) in the presence of NaPF₆ has been found to generate a homotetranuclear nickel(II) complex [(Ni₄HL)(L)(OAc)₂(H₂O)₂(HOAc)₂]PF₆. The crystal structure of the complex reveals that the complex is donor asymmetric and that the extended supra-ligand periphery is maintained by a tight hydrogen-bond between two pendant phenol/phenoxy groups of adjacent ligands and by further tight hydrogen-bonds between coordinated acetic acid molecules and the remaining pendant phenols of the ligand, generating a double acid salt of the type [CH₃COO?H?LH?L?H?OOCCH₃]⁵⁻. Reaction of H₃L with Ni(OAc)₂ and NaClO₄ in methanol gave the complex [Ni₂(HL)(OAc)₂(OH₂)₂][ClO₄]. The structure was determined by X-ray diffraction and showed that the complex exists as a dimer promoted by intermolecular hydrogen-bonding.     

Synthesis, crystal structure and esterification of a novel iron(III) 18-metallacrown-6 complex

The trianionic heptadentate ligand, (Z)-3-(5′-chlorosalicylhydrazinocarbonyl) propenoic acid, has been synthesized and reacted with FeCl₃·6H₂O, to produce the complex [Fe^III₆(C₁₂H₈N₂O₅Cl)₆(H₂O)₄(CH₃OH)₂]·8H₂O·4CH₃OH. In the self-assembly process the ligand was esterified and transferred into (Z)-methyl 3-(5′-chlorosalicylhydrazinocarbonyl) propenoate. In the crystal structure, the neutral Fe(III) complex contain a 18-membered metallacrown ring consisting of six Fe(III) and six trianionic ligands. The 18-membered metallacrown ring is formed by the succession of six structural moieties of the type [Fe(III)-N-N]. Due to the meridional coordination of the ligands to the Fe³⁺ ions, the ligands enforce the stereochemistry of the Fe³⁺ ions as a propeller configuration with alternating Λ/Δ forms. The metallacrown can be treated with SnCl₂ or Zn powder to obtain purified ester.     

Synthesis, characterization and X-ray crystal structure of [Re(L4)(CO)3]Br · 2CH3OH (L4 = N,N-bis[(2-diphenylphosphino)ethyl]methoxyethylamine): A model compound for novel cationic Tc(I)-tricarbonyl radiotracers useful for heart imaging

This report describes synthesis and evaluation of cationic complexes, [^99mTc(CO)₃(L)]⁺ (L = N-methoxyethyl-N,N-bis[2-(bis(3-ethoxypropyl)phosphino)ethyl]amine (L1), N-[(15-crown-5)-2-yl]-N,N-bis[2-(bis(3-ethoxypropyl)phosphino)ethyl]amine (L2) and N-[(18-crown-6)-2-yl]-N,N-bis[2-(bis(3-ethoxypropyl)phosphino)ethyl]amine (L3)) as potential radiotracers for heart imaging. Preliminary results from biodistribution studies in female adult BALB-c mice indicated that the cationic ^99mTc(I)-tricarbonyl complex, [^99mTc(CO)₃(L2)]⁺, has a significant localization in the heart at 60 min post-injection. To understand the coordination chemistry of these bisphosphine ligands with the ^99mTc(I)-tricarbonyl core, we prepared [Re(CO)₃(L4)]Br (L4: N,N-bis[(2-diphenylphosphino)ethyl]methoxyethylamine) as a model compound. [Re(CO)₃(L4)]Br has been characterized by elemental analysis, IR, ESI-MS, NMR (¹H, ¹³C, ¹H-¹H COSY, and ¹H-¹³C HMQC) methods, and X-ray crystallography. In solid state, [Re(CO)₃(L4)]⁺ has a distorted octahedron coordination geometry with PNP occupying one facial plane. The chelator backbone adopts a “chair” conformation with phosphine-P atoms at equatorial positions and the amine-N at the apical site. In solution, [Re(CO)₃(L4)]⁺ is able to maintain its cationic nature with no dissociation of carbonyl ligands or any of the three PNP donors.     

Structure and dynamic behaviour of lanthanide nitrate complexes with bis(diphenylphosphorylmethyl)mesitylene in solutions: The nature of unexpected P NMR spectra

The solution structures of the lanthanide complexes, [Ln(L)(NO₃)₃] and [Ln(L)₂(NO₃)₃], where L = bis(diphenylphosphorylmethyl)mesitylene and Ln = La, Ce, Nd, Er, were investigated by ³¹P NMR and IR spectroscopy, conductivity and sedimentation analysis. Variable-temperature ³¹P{¹H} NMR spectroscopy was used to identify species present in solution and to monitor their interconversions. The results indicate that equilibrium between molecular complexes [Ln(L)_n(NO₃)₃]⁰ and cationic species (as ion pairs [Ln(L)_n(NO₃)₂]⁺ · (NO₃)⁻ and as free ions [Ln(L)_n(NO₃)₂]⁺, throughout n = 1, 2) in solutions can be observed by ³¹P{¹H} NMR spectroscopy due to separate detection of the molecular complexes and cationic species. The chelate coordination of the ligand and nitrate ions is retained in all complex species at ambient temperature except for [Er(L)₂(NO₃)₃]. The crystal structure of [Nd(L)(NO₃)₃(MeCN)]MeCN was determined by X-ray diffraction.     

Influence of Pt and Pd coordination on the equilibrium of 2,2′-dipyridylketone (dpk) with its hydrated gem-diol form (dpk·H2O)

2,2′-Dipyridylketone (dpk), when acting as a chelating ligand for Pd^II or Pt^II, is in slow equilibrium with its corresponding gem-diol form (dpk·H₂O). In D₂O, equilibrium constants K = (dpk·H₂O)/(dpk) change from ca. 0.04 for the free ligand to ca. 3 in the corresponding complexes with cis-[Pt(H₂O)₂]²⁺. In solution, species of both ligands can be identified and differentiated by ¹H NMR spectroscopy, and in the trinuclear μ-OH bridged Pt^II complex [Pt₃(μ-OH)₃(dpk·H₂O)₂(dpk)](NO₃)₃·4.5H₂O (4), both types of ligands are present simultaneously in a ratio of (dpk·H₂O):(dpk) = 2. As demonstrated with a series of Pd^II complexes containing dpk·H₂O and dpk ligands, a straightforward differentiation is possible when DMSO-d₆ is used as solvent, because then also the OH protons of dpk·H₂O are observable. It is also shown that monocrystalline [PdCl₂(dpk·H₂O)] (1), when dissolved in DMSO-d₆, partially converts, with loss of H₂O, to [PdCl₂(dpk)].     

An unusual 2D → 3D parallel interpenetration: synthesis and X-ray structure of compound [Ag2(titmb)2][Hsal]2 · 3H2O (titmb=1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene and H2sal=salicylic acid)

The reaction between 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene (titmb) and [Ag(NH₃)₂][Hsal] (H₂sal=salicylic acid) produces novel complex [Ag₂(titmb)₂][Hsal]₂ · 3H₂O (1). There are two unique silver centers in complex 1 with one serving as a trigonal node and the other one as a linear node. Interestingly, there are two sorts of titmb ligands in complex 1, one acting as a three-connecting ligand and the other one as a two-connecting (bridging) ligand. The silver centers are linked by titmb ligand to form 2D puckered layers containing M₅(titmb)₅ macrocyclic motifs, which is large enough to allow the bridging titmb ligands from the neighboring layers to be completely enclosed in. Namely, two neighboring independent layers interpenetrated each other in a parallel fashion without the occurrence of catenation to give a 3D structure.     

Synthesis and characterization of Cr,Mo and W carbonyl complexes of bis(2-(diphenylphosphino)ethyl)benzylamine

Various Cr, Mo and W carbonyl complexes of a tridentate ligand containing N and P as donor atoms, bis(2-(diphenylphosphino)ethyl)benzylamine (DPBA), have been synthesized. Reaction of M(CO)₆ (M = Cr, Mo and W) with DPBA in a 1:1 mole ratio in toluene or xylene, resulted in the formation of facial and meridional complexes of the type [M(CO)₃(DPBA)] (M = Cr, Mo and W). Interaction of Cr(CO)₆ or Mo(CO)₆ with DPBA and PPh₃ in toluene yielded complexes of the composition [Cr(CO)₃(DPBA)(PPh₃)] and [Mo(CO)₂(DPBA)(PPh₃)], respectively. However reaction of W(CO)₆ with DPBA and PPh₃ yielded only [W(CO)₃(DPBA)]. Reaction of Cr(CO)₆ with DPBA and 1,2-bis(diphenylphosphino)ethane(diphos) in toluene for 24 h resulted in the formation of a mixed ligand complex, [Cr(CO)₄(DPBA)(diphos)] where both the ligands coordinate to the metal atom through only one of their donor atoms. A unique binuclear complex of the composition [Mo(CO)₂(DPBA)(diphos)]₂ resulted, with the tridentate ligand DPBA acting as a bidentate bridging ligand, by the reaction of Mo(CO)₆ with DPBA and diphos in refluxing xylene for 24 h. All the complexes are characterized by elemental analysis and infrared spectra. The ³¹P{¹H} and ¹H NMR spectral data of the complexes gave valuable information in elucidating the structures of the complexes. The ligand DPBA has found to behave in a triligate monometallic, biligate monometallic, monoligate monometallic and biligate bimetallic manner.     

Chromium(III) complexes and their relationship to the glucose tolerance factor. Part II. Structure and biological activity of amino acid complexes

A number of octahedral chromium complexes with amino acids are ligands have been prepared and their structures assigned on the basis of their chromatographic and spectral properties. These include complexes with the general structure Cr(AA)₂(H₂O)₂ where the amino acids glycine, glutamic acid and glutamine act as bidentate ligands. The analogous compound with cysteine as ligand is stable at low pH, but at high pH a terdentate cysteine complex, Cr(cysteine)₂^?, is formed. These complexes, as well as a solution of monodentate glycine aquo complexes, and Cr-nicotinic acid-glycine and Cr-nicotinic acid-cysteine complexes of undetermined structure, have been assayed for glucose tolerance factor activity using a yeast assay. Only Cr(glutamine)₂- (H₂O)₂⁺, Cr-nicotinic acid-glycine and the mixture of complexes Cr(glycine)_n(H₂O)_6-n⁺³ showed significant activity. It is proposed that a trans arrangement of the non-coordinated nitrogen atoms in the ligands of these complexes can mimic the structural features of the glucose tolerance factor which are essential for biological activity.     

New macrocyclic Schiff base complexes incorporating a phenanthroline unit: Part 1; Template synthesis of three cadmium(II) complexes and crystal structure, NMR and ab initio studies

Complexes of three Cd(II)-containing macrocyclic Schiff base complexes containing a phenanthroline ligand (L) of the type [CdLⁿ(Cl)]⁺ (n=2,3,4), have been prepared via [1+1] cyclocondensation of 2,9-dicarboxaldehyde-1,10-phenanthroline and a number of linear triamines via a metal-templated reaction and coordination features have been examined. The ligands, L, are 16-, 17-, and 18-membered pentaaza macrocycles and all the complexes incorporate a 1,10-phenanthroline unit as an integral part of their cyclic structure. The complexes have been characterized by a variety of methods including IR, ¹H, ¹³C, DEPT, COSY(H,H) and HMQC(H,C) NMR studies and MALDI mass spectrometry. The polymeric structure of was determined by X-ray crystallography, which showed that the complex cation consisted of a pentagonal bipyramidally coordinated Cd(II) ion. The seven-coordinated Cd(II) ion is ligated by the five nitrogen atoms of the macrocycle in the equatorial plane and has two bridging chloride ligands in the axial positions resulting in a ribbon of such complex ions. Supporting ab initio HF-MO calculations have been undertaken using the standard 3-21G^∗ and 6-31G^∗ basis sets.     

Synthesis and photophysical studies of tetrazolate‐based Eu(III) photoluminescent ternary complexes containing N‐heterocyclic phosphine oxides auxiliary co‐ligands

Two new ternary tetrazolate Eu(III) complexes with phosphine oxide co‐ligands Eu(PTO)₃·(P1/P2) [PTO = 5‐(2‐pyridyl‐1‐oxide)tetrazole, P1 = diphenylphosphorylamino‐phenylphosphoryl‐benzene, P2 = diphenylphosphorylpyridine)‐bis‐isobutyricphosphoryl] were synthesized and characterized using UV, fluorescence, IR and ¹H NMR spectroscopic techniques. The analytical data prove that the complexes are mononuclear in nature and the central Eu(III) ion is coordinated by three N and three O atoms of tetrazolate, and two O atoms of the corresponding bidentate phosphine oxide ligands. The ancillary ligand increased the photoluminescence efficiency of Eu(PTO)₃·P1 (complex 3) by twofold compared with our previously reported Eu(PTO)₃ complex (complex 1). Copyright © 2015 John Wiley & Sons, Ltd.     

Efficient synthetic route to anhydrous mononuclear tris(8-quinolinolato)lanthanoid complexes for organic light-emitting devices

A new lanthanoid 8-quinilinolates type structure was found for lanthanum complex La₃(q^Me)₉(H)(NO₃) (1) formed in the reaction of La(NO₃)₃ · 6H₂O with 2-methyl-8-hydroxyquinoline (Hq^Me) and aqueous ammonia in methanol. The molecule of 1 contains three La atoms connected by six bridging quinolinolate ligands, two terminated η²-coordinated q^Me ligands, one terminated η¹-coordinated q^Me ligand and one terminated NO₃ group. The geometry and ¹H NMR spectrum of the complex suggest that it is bearing −1 charge balanced by proton, which was localized objectively. The arrangement of the compound in crystalline state and in pyridine solution is discussed. Syntheses of water- and acid residual-free mononuclear lanthanoid quinolinolates La(q^Me)₃(py)₂ (2) and Lnq₃(py)₂, (Ln = Y (3), La (4), Sm (5), Eu (6), Tb (7), Er (8), Tm (9); q = 8-quinolinolate, py = pyridine) by the reaction of appropriate amido complexes Ln[N(SMe₃)₂]₃ with 3 equiv. of 2-methyl-8-hydroxyquinoline or 8-hydroxyquinoline in pyridine solution is also described. The complex Laq₃(Ph₃PO)₂ (10) was prepared by treatment of 4 with triphenylphosphine oxide in pyridine solution. Lanthanum 2 complex revealed photoluminescence intensity ca. 3 × 10³ times higher than that of the compound 1 prepared by the traditional way in water-alcohol medium. These data give a ground to consider the Lnq₃(py)₂ complexes as promising material for design of light-emitting devices.