Polyaza Macrocycles Research Articles

Self-assembly in Schiff base lanthanide complexes — From supramolecular dimers to coordination polymers

A review is given of the latest contribution of the author’s research group to the coordination chemistry of Schiff base polyaza macrocycles and acyclic salicylaldimines. Focus is placed on the effectiveness of lanthanides in supramolecular self-assembly of the components leading to the formation of compounds with unusual properties and structures.Key words: Schiff base macrocycles, salicylaldimines, lanthanides, self-assembly, template synthesis.

Coordination Features of a Polyaza-Bipyridine-Macrocyclic Ligand toward Co(II) and Cd(II) in Water and Dimethylsulfoxide

The coordination features of a polyaza macrocycle, containing the diverse bipyridine unit 4,4′-(2,5,6,11,14-pentaaza[15]-[15](2,2′)-bipyridylophane (L3), with Co(II) and Cd(II) have been studied in aqueous solution and in the aprotic solvent dimethylsulfoxide (DMSO). The study was carried out at 298 K by means of potentiometric, spectrophotometric and calorimetric techniques. The formation of the dinuclear species M2 L3 is observed for Co(II) both in water and in DMSO, whereas Cd(II) is able to form this type of dinuclear complex only in DMSO. The FT-IR spectra of the mononuclear species ML3, formed in both solvents, provide evidence that the rigid structure of the polyaminic chain prevents metal ions from being coordinated by all of the nitrogens of the macrocyclic cavity, in good agreement with the behavior suggested by the thermodynamic parameters. The results are compared with those for the complexation of Co(II) and Cd(II) with similar polyazamacrocycles containing a bipyridine unit directly inside the cavity. Semi-empirical calculations were also performed to obtain structural information.

Review: Metal Complexes of Polyaza and Polyoxaaza Macrocyclic Ligands: A Look into the Past and Present Work

Review: Metal Complexes of Polyaza and Polyoxaaza Macrocyclic Ligands: A Look into the Past and Present Work

Sol–gel materials with trapped trinuclear class-II mixed-valence macrocyclic complexes that mimic their solution redox behaviour

The redox chemistry of mixed-valence CoIII/FeII/CoIII complexes in solution and trapped in sol–gel matrices has been compared. Whereas the redox S2O82−/OH− reactivity cycling of the complexes [{LnCoIII(µ-NC)}2FeII(CN)4]2+ physically immobilized into the pore network of TEOS-derived xerogels, where Ln represents a polyaza macrocycle, mimic perfectly the reactivity shown in solution without leaching of the complex to the reaction medium, all attempts to immobilize smaller and negatively charged dinuclear [{LnCoIII(µ-NC)}FeII(CN)5]− related complexes have been found unsuccessful. A fine tuning of the pore size of the matrix, the electrostatic interactions between the matrix’s surface and the complexes, as well as possible chemical adduct formation between the OR groups of the matrix and the cyanide ligands, seem to be responsible for the effects observed. The chemical preparation of the mixed-valence complexes inside the sol–gel matrix has also been tried by using a silylated modified Ln ligand with four hydrolysable-Si(OEt)3 groups. Following the anchoring of the ligand to a TEOS-derived matrix, the initial formation of the LnCoIII building block has been achieved, but diffusion of the negatively charged [Fe(CN)6]4− species to the {LnCoIII}3+ centre is severely hindered unless high acidity is used. Nevertheless, under such acidic conditions the mixed-valence [{LnCoIII(µ-NC)}FeII(CN)5]− compounds have been successfully formed inside the matrix and have been characterized by IR and UV-Vis spectroscopy. Despite this fact, the redox S2O82−/OH− reactivity cycling carried out on the latter materials has proved to be much more slow than for xerogels containing the trinuclear [{LnCoIII(µ-NC)}2FeII(CN)4]2+ species physically trapped.

Polyaza metacyclophanes as ditopic anion receptors

Five macrocyclic polyaza metacyclophanes L1-L5 prepared by dipode coupling of the tosylated precursors have been studied. The basicity of the ligands has been measured potentiometrically and their ability to complex halides and perchlorate has been studied in the solid state by X-ray crystallography. The results reveal that the ligands generally act as ditopic halide receptors with even the largest, L5, being too small to envelop the anion. The ligand's basicity behaviour parallels that observed for related para-analogues. Despite the ready crystallisation of fluoride, HF2-, chloride, bromide, iodide and triiodide salts in the solid state, there appears to be little affinity for halides in aqueous solution in the pH range accessible via potentiometry. The results do give a detailed insight into the role of the aryl ring in restricting the conformational flexibility of the ligands and, hence, the ability to chelate perching anions.

A Sleeping Host Awoken by Its Guest: Recognition and Sensing of Imidazole‐Containing Molecules Based on Double Cu2+ Translocation inside a Polyaza Macrocycle

A Sleeping Host Awoken by Its Guest: Recognition and Sensing of Imidazole‐Containing Molecules Based on Double Cu²⁺ Translocation inside a Polyaza Macrocycle

A sleeping host awoken by its guest: recognition and sensing of imidazole-containing molecules based on double Cu2+ translocation inside a polyaza macrocycle.

pH-driven double Cu2+ ion translocation occurs inside an heteroditopic macrocycle. The movement opens and closes the system allowing or preventing it to function as receptor for bidentate anions. When imidazole is added to a solution buffered at an appropriate pH value, opening of the system and substrate binding can be induced by the substrate itself, which results in a sharp color change (see picture).

Applications for Polyaza Macrocycles with Nitrogen‐Attached Pendant Arms

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of New Macrocyclic Polyaza Compounds Containing 1-Methylpyrazole

New macrocyclic polyaza compoundscontaining the 1-methylpyrazole moiety are synthesizedin high yield by [2+2]dipodal condensation andreduction. The ring contracted structure of the Schiffbase has been elucidated by NMR. Two of thesemacrocycles form dinuclear complexes with copper andsilver. Macrocyclic Schiff base 5a extracts74.5% silver from aqueous to organic phase.

Dissociation Kinetics of Cerium(lll) Complexes of Macrocyclic Polyaza Polycarboxylate Ligands TETA and DOTA

AbstractThe acid‐catalyzed dissociation rate constants of the cerium(III) complexes of 1,4,8,11‐tetraazacyclo‐tetradecane‐1,4,8,11‐tetraacetic acid (TETA) and 1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid (DOTA) have been determined at four different temperatures (i.e., 25.0°C,32.0°C,39.0°C,45.0°C) in aqueous media (μ = 0.10 M, HCl/KCl) to obtain additional kinetic data and to evaluate possible effects of ligand pre‐organization for metal ion complexation. The rates are much faster for Ce(TETA)− than for Ce(DOTA)−, indicating the lower thermodynamic stability of the former. In the presence of excess strong acid, 0.1‐1.0 MHCl, the dissociation reactions follow the rate law: ‐d[ML]T/dt = (kd + kH[H+])[ML]T and ‐d[ML]T/dt = (kH[H+] + kH2[H+]2)[ML]T, respectively, where kd is acid‐independent dissociation reaction rate constant and kH and kH2 are the respective dissociation rate constants for the pathways involving monoprotonated and diprotonated species. The rate activation parameters, ΔH≠, ΔS≠ and ΔG≠, for each dissociation pathway have been obtained and their values are consistent with the proposed mechanisms. In particular, the rate difference between Ce(TETA)−and Ce(DOTA)− for the monoprotonated complex dissociation pathway is mainly due to difference in ΔHH≠. It has been concluded that ligand pre‐organization results in more stable complexes and slower complex dissociation rates.

Photophysics of supercomplexes. A laser-induced optoacoustic study of the adducts between Ru(bpy)(CN) 42− and polyaza macrocycles

In aqueous solution, the energy content of the triplet metal-to-ligand charge transfer ( 3 MLCT ) state, as determined by laser-induced optoacoustic spectroscopy, for both 1:1 supercomplexes {[Ru(bpy)(CN) 4]·[24]ane-[N 6H 6]} 4+ and {[Ru(bpy)(CN) 4]·[32]ane-[N 8H 8]} 6+ are similar to that for free Ru(bpy)(CN) 4 2− (223±8 kJ/mol). The reduction of the structural volume change upon formation of the 3 MLCT state in the order Ru(bpy)(CN) 4 2− (14.9 ml/mol), {[Ru(bpy)(CN) 4]·[32]ane-[N 8H 8]} 6+ (5.2 ml/mol) and {[Ru(bpy)(CN) 4]·[24]ane-[N 6H 6]} 4+ (2.5 ml/mol) is attributed to the rigidity of the macrocycle cavity. The 3 MLCT state lifetime increase from 104 ns for Ru(bpy)(CN) 4 2− to 150 ns for {[Ru(bpy)(CN) 4]·[24]ane-[N 6H 6]} 4+ and 182 ns for {[Ru(bpy)(CN) 4]·[32]ane-[N 8H 8]} 6+ is due to the decrease in the number of CN groups free to form hydrogen bonds with water: four, one, and none, respectively.

Synthesis and single crystal X-ray structure of the first cationic Pd(ii) complex of a tellurium-containing polyaza macrocycle: contrasting reactions of Pd(ii) and Pt(ii) with a 22-membered macrocyclic Schiff base

The reaction of the tellurium containing macrocyclic Schiff base 1 with Pd(PhCN)2Cl2 and NH4PF6 gives the expected cationic complex [PdII1][PF6]2; by contrast the reaction of 1 with Pt(cod)Cl2 proceeds via novel transmetallation to yield an organoplatinum complex.

Synthesis and Protonation Behavior of 26-Membered Oxaaza and Polyaza Macrocycles Containing Two Heteroaromatic Units of 3,5-Disubstituted Pyrazole or 1-Benzylpyrazole. A Potentiometric and1H and13C NMR Study

The synthesis and acid−base behavior of two series of 26-membered dioxatetraamine and hexaamine heterocyclophanes containing two nuclei of either pyrazole (4a and 6a) or 1-benzylpyrazole (4b and 6b), respectively, are reported. Dipodal (2 + 2) condensations of 3,5-pyrazoledicarbaldehyde 2a or its 1-benzyl derivative 2b with 1,5-diamino-3-oxapentane afford in both cases the stable Schiff bases 3a,b in 90% yield, which after reduction with NaBH4 gave 4a,b in 75% and 84% yield, respectively. Condensation of 2a with diethylenetriamine leads to a complex mixture containing imidazolidine isomers, which was reduced in situ to afford 6a in 30% yield. Condensation of 2b with the same amine gave the stable diimidazolidine derivative 5b, which after crystallization was isolated as a pure compound in 80% yield and fully identified from analytical and 1H and 13C NMR data as a constitutional isomer with both imidazolidine rings located at the side of the pyrazole closer to the benzylic substituents. Reduction of 5b wit...

Spectral Discrimination of Chiral Macrocyclic Paramagnetic Metal Complexes by NMR Techniques≠

Axially symmetric macrocyclic polyaza complexes of lanthanide(III) ions are present in aqueous solution as a racemic mixture of two enantiomers in slow exchange at room temperature. Chiral resolution of an anionic paramagnetic complex has been achieved by exploiting multisite electrostatic and hydrogen-bonding interactions with an optically active organic base, and revealed by NMR techniques as illustrated. The bonding of the optically active substrate to the complex has been elucidated.

ChemInform Abstract: Synthetic and Structural Aspects of the Chemistry of Saturated Polyaza Macrocyclic Ligands Bearing Pendant Coordinating Groups Attached to Nitrogen

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Interaction of mono- and triphosphate anions with a protonated polyaza macrocycle and its Cu(II) complexes

The reactions of monophosphate (Mp) and triphosphate (Tp) with the protonated hexaaza macrocyclic ligand 3,6,9,16,19,22-hexaaza-27,28-dioxatricyclo[22.2.1.1 11,14]octacosa-1 (26),11,13,24-tetraene (BFBD) and its mono- and dinuclear copper(II) complexes, have been investigated. Potentiometric studies show that Tp is bound to protonated BFBD and Cu(II) complexes of this ligand more strongly than is MP. The crystal structures of two new binary complexes of Mp and Tp with this ligand are reported. Both of them crystallize in the triclinic system with space group P1. The binary complex 1 has lattice parameters a = 12.630, b = 13.152, c = 12.561 Å, α = 96.359(1), β = 98.02(2), γ = 117.85(1)° and Z = 2. It contains the BFBD-Mp binary cation. The binary complex 2 has lattice parameters a = 12.717(4), b = 14.331(7), c = 19.687(7) Å, α = 96.66(3), β = 107.68(2), γ = 93.11(3)° and Z = 2. It consists of the BFBD-Tp cation and the BFBD-2Tp anion. Electrostatic attractive forces and hydrogen bonds play major roles in the formation of these binary complexes.

ChemInform Abstract: pH‐Controlled Selective Protection of Polyaza Macrocycles.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

PH-Controlled Selective Protection of Polyaza Macrocycles

pH-Controlled Selective Protection of Polyaza Macrocycles

ChemInform Abstract: A Convenient, Novel Approach for the Synthesis of Polyaza Macrocyclic Bifunctional Chelating Agents.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Polyaza Macrocycles Containing the Piperazine Ring as a Semi‐Flexible Moiety

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.