Synthesis, characterization, and fluorescence behavior of four novel macrocyclic emissive ligands containing a flexible 8-hydroxyquinoline unit

Four emissive macrocyclic ligands mono-substituted with an 8-hydroxyquinoline pendant arm are presented. The new compounds have been used for metal-ion detection, which results from the competition between PET (photo-induced electron transfer) and PPT (photo-induced proton transfer) mechanisms. Solid metal complexes with divalent Cu(II), Zn(II), and Cd(II), and trivalent metal ions Al(III) and Cr(III) have been also synthesized and characterized. The compounds have been isolated as mononuclear or dinuclear (Cu(II)) complexes, confirming the stoichiometry observed in solution.     

Novel polyamides with acyclic and cyclic bipyridinediyl diamino structures in the polymer backbone: Synthesis and complexation with transition metals

The synthesis of two novel polyamide ligands 3 and 4 , containing 2,17-diaza[3.3](6,6′)-2,2′-bipyridinophane or 6,6′-bis(2-picolylaminomethyl)-2,2′-bipyridine units as part of the polymer backbone, respectively, and of the appropriate diamide model compounds 1c and 2c is described. ¹H-NMR and IR spectral data support the ligand structures; furthermore, ¹H-VTNMR analysis on macrocyclic diamide 1c indicates a restricted rotation of the amide bonds at ambient temperature and suggests for this molecule a fixed syn conformation in solution, with a “face to face” arrangement of the dipyridinyl moieties. Model compound 2c and polyamide 4 form stable 1:1 complexes with transition metals Co(II), Ni(II), and Cu(II). Conversely, macrocyclic model 1c and polyamide 3 exhibit the unique property to specifically complex Cu(II), even in the presence of sizeable amounts of Co(II) and Ni(II). The IR spectral changes related to the ligands upon complexation are briefly discussed.     

NICKEL(II) COMPLEXES OF NOVEL MACROCYCLIC LIGANDS CONTAINING PENDANT NITRO GROUPS

Abstract

The addition of nitromethane anion to the C=N group of polyalkyl-1,4,8,11-tetraazacyclotetradeca-4, 11-dienenickel(II) diperchlorate gave Ni(II) complexes of new macrocyclic ligands containing a pendant 5-nitromethyl group. Variable temperature (80–290 K) magnetic susceptibilities were determined for the paramagnetic monoperchlorates and the diamagnetic square-planar diperchlorates. Conformations of the nitromethyl groups in the macrocyclic ligands were established on the basis of ¹H NMR evidence.     

Design of phenanthrimidazole-pendant cyclam and cyclen macrocyclic complex ligands as inorganic hosts: Photophysics,electrochemistry, and bimetallic complex formation

Novel ruthenium(II)bpy complexes of the phenanthrimidazole-pendant cyclen and cyclam macrocyclic ligands were synthesized as inorganic host molecules. Inorganic host design was planned as a “complex ligand” form because of its tetraaza macrocyclic unit, which has the ability to coordinate to the metals. Photophysical properties and metal selectivity of inorganic hosts RuL1A and RuL2 complex ligands were investigated by UV-vis and fluorescence spectroscopy in aqueous medium. Among Ag(I), Li(I), Na(I), K(I), Cd(II), Cr(II), Fe(II), Hg(II), Ni(II), Pb(II), Zn(II), Cu(II), Mn(III), and Co(III) metal ions, Fe(II) addition causes spectral changes for both RuL1A and RuL2 complex ligands. Electrochemical studies were performed for RuL1B and also for cis-[Ru(bpy) ₂ Cl ₂ ] . Bimetallic complexes [[Ru(bpy)₂([Ni(2-(4-((1,4,8,11-tetraazacyclotetradecan-1-yl)methyl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline])](ClO₄)₄, RuL1-NiA and [Ru(bpy)₂([Ni(2-(4-((1,4,8,11-tetraazacyclotetradecan-1-yl)methyl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline])]Cl₄, RuL1-NiB solid complexes were also obtained by the reaction of the RuL1B and Nickel(II).     

Electrochemistry of macrocyclic complexes of alkaline cations: Part IV. Reduction of (mnp,K)+ cryptates

The reductions of five macrobicyclic potassium cryptates (ligands (322), (222), (221), (22 C₈), (211)) and two macromonocyclic potassium complexes (ligands (22) and (18 crown 6)) are studied by polarography, coulometry and cyclic voltammetry in propylene carbonate (PC). The mechanism and the parameters of the electrochemical reduction are discussed in terms of dependence upon three important features of the macrocyclic ligands: the size of the intramolecular cavity, the number of oxygen heteroatoms in the ligand, and the number of “branches” in the ligand (cryptate effect). The electrochemical results are consistent with the other known physicochemical parameters of these complexes. The electroreduction behaviour might allow the structure and the stability constant of alkaline cryptates in a given medium (PC) to be approximated. Reciprocally, these physicochemical characteristics may lead to a rather precise prediction of the electrochemical behaviour of the corresponding macrocyclic complexes.     

THE AROMATICITY OF TRANSITION METAL COMPLEXES DERIVED FROM 1,2- AND 1,3-DITHIO-DIKETONES

Abstract

Fully conjugated cyclic transition metal complexes are potential aromatic species, showing complete cyclic delocalization of the p- and d-electrons. It was proposed earlier that such aromaticity could only be found in complexes with “even-numbered” ligands (type I), while complexes containing “odd” ligands (type II) should not show full delocalization and hence be classified as non-aromatic.     

Coordination chemistry of N-aminopropyl pendant arm derivatives of mixed N/S-, and N/S/O-donor macrocycles, and construction of selective fluorimetric chemosensors for heavy metal ions

The coordination chemistry of the N-aminopropyl pendant arm derivatives (L1c-4c) of the mixed donor macrocyclic ligands [12]aneNS2O, [12]aneNS3, [12]aneN2SO, and [15]aneNS2O2(L1a-4a) towards Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II) in aqueous solution has been investigated. The protonation and stability constants with the aforementioned metal ions were determined potentiometrically and compared, where possible, with those of the unfunctionalised macrocycles. The measured values show that Hg(II) and Cu(II) in water have the highest affinity for all ligands considered, with the N-aminopropyl pendant arm weakly coordinating the metal centres. Crystals suitable for X-ray diffraction analysis were grown for the perchlorate salt (H2L1c)(ClO4)2.dmf, and for the 1 : 1 complexes [Cd(L3a)(NO3)2](1), [Cu(L4a)dmf](ClO4)2(2), [Zn(L1c)(ClO4)]ClO4(3), [Cd(L1c)(NO3)]NO3(4), and [Hg(L2c)](ClO4)2(5). Their structures show the macrocyclic ligands adopting a folded conformation, which for the 12-membered systems can be either [2424] or [3333] depending on the nature of the metal ion. L1c-4c were also functionalised at the primary amino pendant group with different fluorogenic subunits. In particular the N-dansylamidopropyl (Lnd, n= 1-4), and the N-(9-anthracenylmethyl)aminopropyl (Lne, n= 1, 2, 4, ) pendant arm derivatives of L1a-4a were synthesised and their optical responses to the above mentioned metal ions were investigated in MeCN/H2O (4 : 1 v/v) solutions.     

A new pyridine-based 12-membered macrocycle functionalised with different fluorescent subunits; coordination chemistry towards Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II)

The coordination chemistry of the new pyridine-based, N2S2-donating 12-membered macrocycle 2,8-dithia-5-aza-2,6-pyridinophane (L1) towards Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II) has been investigated both in aqueous solution and in the solid state. The protonation constants for L1 and stability constants with the aforementioned metal ions have been determined potentiometrically and compared with those of ligand L2, which contains a N-aminopropyl side arm. The measured values show that Hg(II) in water has the highest affinity for both ligands followed by Cu(II), Cd(II), Pb(II), and Zn(II). For each metal ion considered, 1:1 complexes with L1 have also been isolated in the solid state, those of Cu(II) and Zn(II) having also been characterised by X-ray crystallography. In both complexes L1 adopts a folded conformation and the coordination environments around the two metal centres are very similar: four positions of a distorted octahedral coordination sphere are occupied by the donor atoms of the macrocyclic ligand, and the two mutually cis-positions unoccupied by L1 accommodate monodentate NO3- ligands. The macrocycle L1 has then been functionalised with different fluorogenic subunits. In particular, the N-dansylamidopropyl (L3), N-(9-anthracenyl)methyl (L4), and N-(8-hydroxy-2-quinolinyl)methyl (L5) pendant arm derivatives of L1 have been synthesised and their optical response to the above mentioned metal ions investigated in MeCN/H2O (4:1 v/v) solutions.     

Affinity and nuclease activity of macrocyclic polyamines and their CuII complexes

The stability constants of Cu(II) complexes that consist of either an oxaaza macrocycle with two triamine moieties linked by dioxa chains, or two macrocyclic ligands with a polyamine chain which are connecting the 2 and 9 positions of phenanthroline, have been determined by means of potentiometric measurements. The results are compared to those reported for other ligands with a similar molecular architecture. Of the complexes that contain phenanthroline in their macrocycle, the Cu(II) ion of the complex with the smallest and most rigid macrocycle (L3) has an unsaturated coordination sphere, while in the complex with the largest macrocycle (L5) the Cu(II) ion is coordinatively almost saturated. These results are corroborated by the crystal structure of the [CuL5](ClO4)2 complex. The affinity of the ligands and the complexes towards nucleic acids was studied by measuring the changes in the melting temperature, which showed that the affinity of the macrocyclic ligands towards double-stranded DNA or RNA is generally smaller than that of their linear analogues that bear a similar charge, with a strong preference for polyA-polyU, a model for RNA. However, the complexes of two of the changed macrocyclic ligands which contain a phenanthroline unit (L4, L5) showed a distinctly larger increase in their melting temperature deltaTm with DNA (polydA-polydT), which is reversed again in favor of RNA upon metallation to the dinuclear copper complex with L5. Experiments with supercoiled plasmid DNA showed a particularly effective cleavage with a mononuclear Cu(II) complex that contains a phenanthroline unit (L6). Related ligands showed less activity towards DNA, but not so towards the biocidic bis(p-nitrophenyl)phosphate (BNPP). In both cases (with DNA and BNPP) the activity seemed to increase with decrease of coordinative saturation of the Cu(II) ion, with the exception of one particular ligand (L6). Experiments with radical scavengers in the DNA experiments showed some decrease in cleavage, which indicates the participation of redox processes.     

Quantum-chemical models of the molecular structures of open-chain and macrocyclic <Emphasis Type="Italic">d</Emphasis>-metal chelates with (N,O)- and (N,S)-donor polydentate ligands

The results of quantum-chemical calculations of the molecular structures of d-metal chelate complexes with compartmental and macrocyclic ligands arising as a result of “self-assembly” processes (template synthesis) to form so-called open and closed contours around the complexing agent have been systematized and generalized. In general, for compounds of both the first and second groups, molecular structures with noncoplanar chelate cores and macrocyclic moieties are more characteristic than coplanar ones. The review covers the works of the author and other researchers carried out mainly over the past 20 years     

Spin-State Variations of Iron(III) Complexes with Tetracarbene Macrocycles

Starting from their six-coordinate iron(II) precursor complexes [L^8RFe(MeCN)]²⁺, a series of iron(III) complexes of the known macrocyclic tetracarbene ligand L^8H and its new octamethylated derivative L^8Me, both providing four imidazol-2-yliden donors, were synthesized. Several five- and six-coordinate iron(III) complexes with different axial ligands (Cl⁻, OTf⁻, MeCN) were structurally characterized by X-ray diffraction and analyzed in detail with respect to their spin state variations, using a bouquet of spectroscopic methods (NMR, UV/Vis, EPR, and ⁵⁷Fe Mößbauer). Depending on the axial ligands, either low-spin (S=1/2) or intermediate-spin (S=3/2) states were observed, whereas high-spin (S=5/2) states were inaccessible because of the extremely strong in-plane σ-donor character of the macrocyclic tetracarbene ligands. These findings are reminiscent of the spin state patterns of topologically related ferric porphyrin complexes. The ring conformations and dynamics of the macrocyclic tetracarbene ligands in their iron(II), iron(III) and μ-oxo diiron(III) complexes were also studied.     

Dinuclear macrocyclic palladium complexes having pincer coordinating groups and their catalytic properties in Mizoroki-Heck reactions

An improved synthetic method of palladium(II) dinuclear macrocyclic complexes have been described. Each of the two isomers of the complexes [Pd₂LBr₂] has a macrocyclic ligand L in which two 2,6-bis(diaminomethyl)phenyl units coordinate to the Pd(II) centers with N, C, N donor atoms. Substitution of the bromo ligands of one of the isomer of the complexes with acetonitrile ligands affords a new dinuclear complex. Catalytic activities of these complexes were studied for the Mizoroki-Heck type reactions of iodobenzene and styrene. High turnover number up to 30,000 was achieved using one of the isomer of the complexes.     

Synthesis, X-ray characterization, NMR and ab initio molecular-orbital studies of some cadmium(II) macrocyclic Schiff-base complexes with two 2-aminoethyl pendant arms

Three new pendant arm Schiff-base macrocyclic complexes, [CdLⁿ]²⁺ (n = 5, 6, 7), have been prepared via cyclocondensation of 2,6-diacetylpyridine with three different branched hexaamines in the presence of Cd(II). The ligands 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]. All complexes were investigated by IR, ¹H and ¹³C NMR, COSY(H,H) and HETCOR(H,C) spectroscopy and X-ray diffraction. In the solid state structure of each complex the Cd(II) ion is situated centrally within an approximately planar pentaaza macrocyclic ring, binding to the five nitrogen atoms, and also to the two pendant amines which are located on opposite sides of the macrocyclic plane. ab initio HF-MO calculations using a standard 3-21G* basis set have been used to verify that these similar basic structures correspond to energy minima in the gas phase.     

Molecular structures of metal macrocyclic compounds with nitrogen,oxygen, and sulfur atoms in macrocycles arising in “self-assembly” processes: quantum-chemical modeling

The results of quantum-chemical calculations of the molecular structures of d-metal macrocyclic chelate complexes with compartmental and macrocyclic (N,O)- and (N,S) donor atomic ligands arising as a result of “self-assembly” process have been systematized and generalized. It has been noticed that, generally, for such coordination compounds, molecular structures with noncoplanar chelate nodes and noncoplanar macrocycles are more typical than those with coplanar ones. The review covers the works of the author and other researchers carried out mainly over the past 20 years.     

Complexes of pendant-armed cyclam derivatives with copper(II) perchlorate: Synthesis and crystal structures

A designed series of cyclam type macrocyclic ligands 1–3 that feature a different degree of saturation and number of functional appendages of the macroring, including preparation of the respective Cu(II) perchlorate complexes 1a–3a, was synthesized. Comparative discussion of the X-ray crystal structures of the free ligands and the corresponding complexes shows that dependent on the structure of the compound, transanular, pendant arm and anion involving conventional and weaker H bond contacts are operating. In the complexes, the coordination environment around the Cu(II) cation is distorted octahedral with the nitrogens of the macroring defining the equatorial sites and either two oxygens, each of a perchlorate anion, or the lateral pyridine nitrogens in apical positions. Thus, only the pyridine containing pendants in 3a proved effective in metal ion coordination while the anisyl groups are engaged in H bonding, respectively. The uncomplexed macrocycle 3 yielded an inclusion compound with chloroform, also indicating a special ability relating to this series of compounds.     

Correction to: A kinetic investigation of mononuclear trans-platinum(II) complexes with mixed amine ligands

Transition Metal Chemistry - The article “A kinetic investigation of mononuclear trans-platinum(II) complexes with mixed amine ligands”, written by “Moses Ariyo Olusegun, Desigan...     

Interaction of Co(II), Ni(II) and Cu(II) with dibenzo-substituted macrocyclic ligands incorporating both symmetrically and unsymmetrically arranged N, O and S donors

The synthesis and characterisation of four 17-membered, dibenzo-substituted macrocyclic ligands incorporating unsymmetrical arrangements of their N(3)S(2), N(3)O(2) and N(3)OS (two ligands) donor atoms are described; these rings complete the matrix of related macrocyclic systems incorporating both symmetric and unsymmetric donor sets reported previously. The X-ray structures of three of the new macrocycles are reported. In two of the Cu(II) structures only three of the possible five donor atoms present in the corresponding macrocyclic ligand bind to the Cu(II) site, whereas all five donors are coordinated in each of the remaining complexes. The interaction of Co(II), Ni(II) and Cu(II) with the unsymmetric macrocycle series has been investigated by potentiometric (pH) titration in 95% methanol; X-ray structures of two nickel and three copper complexes of these ligands, each exhibiting 1:1 (M:L) ratios, have been obtained. The results are discussed in the context of previous results for these metals with the analogous 17-membered ring systems incorporating symmetrical arrangements of their donor atoms, with emphasis being given to both the influence of the donor atom set, as well as the donor atom sequence, on the nature of the resulting complexes.     

Spectral studies, cyclic voltammetry and synthesis of cobalt(II) and ruthenium(III) complexes with symmetric and asymmetric ring containing membered N2S2, N4, and N5 donor macrocyclic ligands

Reaction of divalent cobalt(II) and trivalent ruthenium(III) salts (NO3, SCN and SO4) with macrocyclic ligands L1, L2 and L3 having N2S2, N4 and N5 core, have been designed and carry out. All these three macrocyclic ligands and their complexes were obtained in pure form. Their structures were investigated by using microanalytical analyses, IR, mass, magnetic moments, electronic and EPR spectral studies. The redox properties of the complexes were also examined by cyclic voltammetry. An interesting feature of complexes is that the relatively large rings of macrocyclic ligands prevent the macrocyclic rings from approaching the metal center as closely as they would, if they were not constrained. So the Ru-N distances are longer than expected due to ring size. Electrochemical studies show that the macrocyclic ligand L1 is more effective electron donors to ruthenium than of L2 and L3. Electronic spectral properties also show that the sulphur donor atom of L1 weakens the ligand field with respect to ligand-to-metal charge-transfer band. However it is expected that second-row transition metal-ligand bonds tend to be weaker than third-row transition metal-ligand bonds. There are well-established examples of reactions in which decreased of reactivity down a triad of transition metals is not observed. These novelties are usually attributed to pi-bonding effects for ligands such as carbon monoxide, solvent effects, or a change in mechanism.     

Structures of Nickel(II) and Copper(II) Complexes of 14-Membered Macrocyclic Quadridentate Ligands

The structures of 41 Ni(II) and 17 Cu(II) complexes of macrocyclic quadridentate ligands have been analyzed, and are discussed about bond lengths, bond angles, conformations, and configurations, upon which many conclusions are formed. The inter- or intra-molecular hydrogen bonds exist among ligands and hydrates in many compounds and play an important role in the structures. There are exhibited two distinct peaks on the histogram of the average Ni-N distances, corresponding to four coordination and six coordination; these average Ni-N distances are 1.95(4) Å and 2.10(5) Å, respectively. The most probable structures of Ni(II) macrocyclic compounds have coordination number six for the metal ion, chair forms for six-membered rings, planar structure for the metal ion and the four donor atoms of the quadridentate ligand and an inversion center at the central metal ion.     

Formation and dissociation kinetics and crystal structures of nickel(II)-macrocyclic tetrathiaether complexes in acetonitrile. Comparison to nickel(II)-macrocyclic tetramines

Complex formation and dissociation rate constants have been independently determined for solvated nickel(II) ion reacting with eight macrocyclic tetrathiaether ligands and one acyclic analogue in acetonitrile at 25 degrees C, mu = 0.15 M. The macrocyclic ligands include 1,4,8,11-tetrathiacyclotetradecane ([14]aneS4) and seven derivatives in which one or both ethylene bridges have been substituted by cis- or trans-1,2-cyclohexane, while the acyclic ligand is 2,5,9,12-tetrathiatridecane (Me2-2,3,2-S4). In contrast to similar complex formation kinetic studies on Ni(II) reacting with corresponding macrocyclic tetramines in acetonitrile and N,N-dimethylformamide (DMF), the kinetics of complex formation with the macrocyclic tetrathiaethers show no evidence of slow conformational changes following the initial coordination process. The differing behavior is ascribed to the fact that such conformational changes require donor atom inversion, which is readily accommodated by thiaether sulfurs but requires abstraction of a hydrogen from a nitrogen (to form a temporary amide). The latter process is not facilitated in solvents of low protophilicity. The rate-determining step in the formation reactions appears to be at the point of first-bond formation for the acyclic tetrathiaether but shifts to the point of chelate ring closure (i.e., second-bond formation) for the macrocyclic tetrathiaether complexes. The formation rate constants for Ni(II) with the macrocyclic tetrathiaethers parallel those previously obtained for Cu(II) reacting with the same ligands in 80% methanol-20% water (w/w). By contrast, the Ni(II) dissociation rate constants show significant variations from the trends in the Cu(II) behavior. Crystal structures are reported for the Ni(II) complexes formed with all five dicyclohexanediyl-substituted macrocyclic tetrathiaethers. All but one are low-spin species.