Heterotopic Ligands Research Articles

Structural and Magnetic Properties of the {Cr(pybd)3[Cu(cyclen)]2}(BF4)4 Heteronuclear Complex

Heterotopic ligands containing chemically different binding centers are appealing candidates for obtaining heteronuclear metal complexes. By exploiting this strategy, it is possible to introduce different paramagnetic centers characterized by specific anisotropic magnetic properties that make them distinguishable when weakly magnetically coupled. This molecular approach has great potential to yield multi-spin adducts capable of mimicking logical architectures necessary for quantum information processing (QIP), i.e., quantum logic gates. A possible route for including a single-ion magnetic center within a finite-sized heterometallic compound uses the asymmetric (1-pyridyl)-butane-1,3-dione (pybd) ligand reported in the literature for obtaining Cr3+−Cu2+ metallo-cages. To avoid the formation of cages, we adopted the cyclen (1,4,7,10-tetraazacyclododecane) ligand as a “capping” agent for the Cu2+ ions. We report here the structural and magnetic characterization of the unprecedented adduct {Cr(pybd)3[Cu(cyclen)]2}(BF4)4, whose structure is characterized by a central Cr3+ ion in a distorted octahedral coordination environment and two peripheral Cu2+ ions with square-pyramidal coordination geometries. As highlighted by Continuous Wave Electron Paramagnetic Resonance (EPR) spectroscopy and Direct Current (DC) magnetometry measurements, this adduct shows negligible intramolecular magnetic couplings, and it maintains the characteristic EPR signals of Cr3+ and Cu2+ moieties when diluted in frozen solutions.

Homodinuclear Lanthanide Complexes with the Divergent Heterotopic 4,4′‐Bipyridine N‐Oxide (bipyMO) Ligand

The synthesis of dinuclear molecular complexes [Eu2(dbm)6(bipyMO)2], 1, [Tb2(dbm)6(bipyMO)2], 2, [Eu2(tta)6(bipyMO)2], 3 [Eu2(hfac)6(bipyMO)3], 4, [Tb2(hfac)6(bipyMO)3], 5 is here reported (bipyMO = 4,4′‐bipyridine N‐oxide, Hdbm = dibenzoylmethane, Htta = thenoyltrifluoroacetone, Hhfac = hexafluoroacetylacetone). The products were obtained in mild conditions and with high yields reacting anhydrous lanthanide β‐diketonates and bipyMO in 1:1 or 1.5 molar ratio in toluene. X‐ray single crystal studies on 2, 3, 4 showed that the heterotopic ligands are hypodentate, bridging the two lanthanide centres exclusively through the oxygen atom. Photoluminescence studies show bright red emissions from europium derivatives with absolute quantum yields up to 44 %.

Synthesis and photophysical properties of europium complexes with heterotopic hexadentate ligands based on 2,2’-bipyridyl-6,6’-dicarboxamide

Europium complexes with heterotopic hexadentate ligands based on 2,2’-bipyridyl-6,6’-dicarboxamide exhibit bright long-lived luminescence at 618 nm as well as extremely low solubility (

Silver(I) and rhenium(I) metal complexes of a 2,2'-bipyridine-functionalized third-generation tris(pyrazolyl)methane ligand.

Heterotopic ligands offer the possibility of preparing polynuclear bimetallic complexes. Recent studies of heteroditopic ligands and their metal complexes have focused on novel supramolecular systems, biological activity, and the development of MRI contrast agents. The heteroditopic ligand Bipy-CH2-O-CH2-C(pz)3 (Bipy-L; Bipy is 2,2'-bipyridine and pz is pyrazolyl) reacts with AgBF4 to produce the coordination polymer catena-poly[[silver(I)-(μ-5-{[tris(pyrazol-1-yl)methoxy]methyl-κ2N,N'}-2,2'-bipyridine-κ2N,N')] diethyl ether hemisolvate], {[Ag(C22H20N8O)]BF4·0.5C4H10O}n, and with Re(CO)5Br to form the discrete compound bromidotricarbonyl(5-{[tris(pyrazol-1-yl)methoxy]methyl}-2,2'-bipyridine-κ2N,N')rhenium(I), [ReBr(C22H20N8O)(CO)3]. The silver(I) compound is a one-dimensional coordination polymer, built up by a κ2 coordination mode of the bipyridine group and a κ2-κ0 coordination mode of the -C(pz)3 donor set. In [ReBr(Bipy-L)(CO)3], the ligand coordinates only via the bipyridine end, leaving the -C(pz)3 donor set free for further coordination interactions.

Di- and trinuclear Ru(II) complexes of 1,10-phenanthroline and 2,2′-bipyridine derivatives; synthesis, photophysical and electrochemical properties

Three heterotopic ligands L1, L2, and L3 based on 1,10-phenanthroline and 2,2′-bipyridine moieties have been synthesized and characterized. The Ru(II) complexes [{Ru(bpy)2}3(µ3-L1)](PF6)6, [{Ru(bpy)2}3(µ3-L2)](PF6)6, and [{Ru(bpy)2}2(µ2-L3)](PF6)4 (bpy = 2,2′-bipyridine) have been prepared by refluxing Ru(bpy)2Cl2·2H2O with each ligand in ethanol. All three complexes display MLCT absorptions at around 455 nm and emissions at around 618 nm. Electrochemical studies of the complexes reveal one Ru(II)-centered quasi-reversible oxidation at around 1.32 V and three ligand-centered reductions in each case.

Three trinuclear Ru(II) complexes containing 4,5-diazafluorene and 2,2′-bipyridine: synthesis, absorption spectrum, luminescence, and redox behavior

Three heterotopic ligands L1, L2, and L3 have been prepared by the reaction of 4,4′-bis(bromomethyl)-2,2′-bipyridine with 4,5-diazafluoren-9-oxime, 9-(2-hydroxy)phenylimino-4,5-diazafluorene, and 9-(4-hydroxy)phenylimino-4,5-diazafluorene, respectively, in DMF. The three ligands consist of two 4,5-diazafluorene units and one 2,2′-bipyridine unit. Ru(II) complexes [{Ru(bpy)2}3(μ3-L1−3)](PF6)6 (bpy = 2,2′-bipyridine) were prepared by refluxing Ru(bpy)2Cl2·2H2O and the ligands in 2-methoxyethanol. The three Ru(II) complexes display metal-to-ligand charge-transfer absorption at 445–450 nm and one Ru(II)-centered oxidation at 1.32 V in CH3CN solution at room temperature. Upon excitation into the metal-to-ligand charge-transfer band, the emission intensities of [{Ru(bpy)2}3(μ3-L2)]6+ and [{Ru(bpy)2}3(μ3-L3)]6+ are almost equal to that of [{Ru(bpy)2}3(μ3-L1)]6+ in CH3CN solution at room temperature, but weaker than that of [{Ru(bpy)2}3(μ3-L1)]6+ in EtOH–MeOH (4 : 1, v/v) glassy matrix at 77 K.

Construction of three new mixed-ligand Zn(II) coordination polymers based on nitrogen-containing heterotopic ligands and carboxylate co-ligands

Reactions of Zn(II) salts, presynthesized 5-(4-(1H-imidazol-1-yl)phenyl)-1H-tetrazolate (HIPT) and various carboxylate ligands result to three new coordination polymers (CPs), namely, [Zn2[(IPT)2(ox)]}n (H2ox=oxalic acid, 1), [Zn2(IPT)2(mNBDC)]n (H2mNBDC=5-nitroisophthalic acid, 2), and [Zn2(IPT)(CA)(H2O)]n (H3CA=citric acid, 3). Compound 1 can be seen as constructed from 2D [Zn(IPT)]n layers with (6,3) topology and pillared by ox2−. It is a 3D (3,4)-connected framework with InS topology. Compound 2 has 2D bilayer structure based on 2D [Zn(IPT)]n single layer and mNBDC2− linkers. Compound 3 is a 3D pillar-layer framework built by Zn–CA bilayers and IPT− pillars. The results showed that the coordination modes, configurations of IPT−, and the structure of carboxylate co-ligands have great influence on the structures of the final network. The choice of carboxylate can decide the result of CPs in Zn–IPT chains/net subunits plus carboxyl linkers or Zn–carboxylate chains/net subunits plus IPT− linkers. The thermal stabilities and luminescent properties of selected compounds have also been studied.

A non-platonic M4L4 complex constructed using heterotopic ligands

An unusual, chloride-capped M4L4 complex has been prepared using heterotopic ligands with carboxylate and dipyridyl coordinating sites.

Effect of Ligand Spacer on Metallosupramolecular Architectures: From a Dinuclear Copper(II) Double Helicate to a Tetranuclear Copper(II) Complex

AbstractTwo new bis(N,O‐bidentate) Schiff base ligands with asymmetric spacers between the donor sites have been synthesized. The asymmetric ligand H2L1 self‐assembles with copper(II) ions to give rise to a dinuclear copper(II) complex [Cu2L12] (1), while a more flexible ligand H2L2, having an additional methylene group in the spacer, forms a tetranuclear copper(II) cluster [Cu4L24] (2). Both complexes have been characterized by different analytical and spectroscopic techniques. Single‐crystal X‐ray diffraction study of 1 shows a dinuclear copper(II) double‐stranded helicate with the two heterotopic ligands oriented head‐to‐head (HH), with a separation of 7.687(3) Å between the distorted tetrahedral copper(II) centers. The bis(bidentate) ligand strands wrap around the copper centers with a similar relative orientation (HH) to give rise to a double‐helical structure. The intramolecular face‐to‐face π–π interaction stabilizes the double‐helical structure of the molecule. In the tetranuclear complex 2, the four copper(II) centers, separated by 7.288(2)–8.239(2) Å, define a slightly distorted tetrahedron.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Luminescense properties of new complexes of Eu(III) and Tb(III) with heterotopic ligands

As a result of coordination between ligands L and L′ and europium(III) and terbium(III) ions, the new architectures were formed. The formulae of the complexes have been assigned on the basis of the spectroscopic data in solution and microanalyses. The europium complexes show excellent luminescence properties with high quantum yield ( 1b-Eu 3 L 2) and effective intramolecular energy transfer from the ligand to the Eu(III) ions.

Preparation of new heterotopic ligands

A six-step synthesis of two new heterotopic ligands, each possessing two unusual N,N,N,O tetradentate binding subunits, has been developed. This work presents a particularly facile and rapid synthetic protocol for the preparation of these ligands, which one expected to act as useful components in inorganic self-assembly for the preparation of various types of complexes.

Selective Self-Assembly of a Sequential Bipyridine−Bipyrazine Ligand Strand into a Double-Stranded CuI Helicate

In this paper new aspects on the self-assembly processes of didentate coordinating ligands leading to a double-stranded helicate are described. It was reported, that directionality in the self-recognition of CuI ions could be driven by factors relating to the electronic configuration of heterocycles in carefully designed heterotopic ligands. If the sequential bipyrazine−bipyridine ligand strand 4 reacts with 1 equiv. of CuI the dimetallic complex [Cu2(L4)2][PF6]2 is formed in a cooperative process. In this coordination compound the two strands are oriented in opposite directions (HT) as illustrated by the X-ray structure of [Cu2(L4)2][PF6]2. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Synthesis of 1-methyl-2-diphenylphosphino-3-(1′-isoquinolyl)indole; an easily racemised ligand giving insights into catalytic asymmetric allylation

Abstract The synthesis of the title compound is described, involving 2-lithiation and phosphinylation of the coupled heterocycle in the final step. Attempts to resolve the phosphine by previously described methods led to its immediate racemisation, also observed more slowly in the PdCl2 complex, for which the X-ray structure is described. The phosphinamine formed a cationic Pd(1,3-diphenylallyl) complex with high diastereoselectivity. By analysis of the solution stucture using NMR techniques, in comparison with the X-ray structure, some inferences about the mechanism of allylic alkylation with related heterotopic ligands can be drawn.

Indenyl Crown Ethers: Heterotopic Ligands with π- and σ-Faces and the Synthesis of Cymantrene and Cobaltocene Crown Ethers and Their Alkaline Metal Ion Complexes

2-Indanone reacts with aza-12-crown-4, aza-15-crown-5, aza-18-crown-6 and diaza-18-crown-6 to give the corresponding enamine 2-indenyl crown ethers 1−4 in almost quantitative yields. The indene subunits of 1−3 can be deprotonated with n-BuLi and reacted with Co(THF)3Br2 to yieldafter oxidationthe cobaltocenium salts 5−7. Four oxidation states of the cobaltocene 5 are readily accessible in the CV experiment: E1/2 = −1.99 V (−I/0, quasireversible), −0.94 V (0/+I), and +0.97 V (+I/+II), with the +I/+II oxidation occurring at an unusually low potential. Addition of LiClO4 or NaClO4 to 5 results in anodic shifts of the 0/+I redox wave of up to +190 mV, whereas the +I/+II redox pair is not at all influenced. The reaction of lithiated 2 with BrMn(CO)3(py)2 gives the corresponding cymantrene crown ether 8. The X-ray crystal structure of 8 displays a very short indenyl−nitrogen bond distance of 136.2(4) pm. Complexation of Li+ and Na+ by 8 [E1/2(0/+I) = +0.91 V] leads to anodic shifts of the redox potential of +1...

Mechanisms Regulating the Reactions of Human Hemoglobin With Oxygen and Carbon Monoxide

The reactions of hemoglobin with oxygen and carbon monoxide are subject to regulation by the heme and the residues surrounding it and by the effectors, also known as heterotopic ligands (H+, Cl-, CO2, and 2,3-diphosphoglycerate), that regulate the equilibrium between its two forms, the oxy or R-structure with high and the deoxy or T-structure with low oxygen affinity. The stereochemical mechanisms of regulation have been studied for many years using a variety of methods. What is new since the subject was last surveyed [1] is determination of the crystal structures at resolutions sufficient to resolve individual atoms of the heme and its surroundings; such structures have now been determined for deoxy, oxy, and carbon monoxyhemoglobin, and for several analogues of transition states in the reaction with oxygen and carbon monoxide. In the past much useful information about the stereochemical mechanism of hemoglobin has come from the study of abnormal human hemoglobins. Now that the genes for the α and s chains of hemoglobin and for the single chain of myoglobin have been cloned in E. coli, directed mutagenesis has provided new tools for probing the reactions of these proteins with ligands. Finally, an (unsuccessful) search for possible antisickling drugs has led to the discovery of a family of compounds which are more powerful allosteric effectors than the natural one, 2,3-diphosphoglycerate, and combine with sites that are far removed from the diphosphoglycerate binding site.

Stereoselective Synthesis and Complexation of a New Chiral Hybrid Phosphine-Phosphine Oxide Ligand from (S)-(+)-Prolinol

Abstract The synthesis and the complex formation of chiral heterotopic ligands with two different binding sites each capable of bonding a different type of metal are described. The action of bis(dimethylamino) aryl phosphine on (S)-(+)-prolinol gives rise to the kinetic stereoisomer (2S,4S)-2-phenyl-1,3,2-oxazaphospholidine 1 and the thermodynamic stereoisomer (2R,4S)-2-phenyl-1,3,2-oxazaphospholidine 2. 1 is then totally converted into 2 at the end of the reaction. The Michaelis Arbuzov reaction of 2 with benzylbromide affords (Rp)-benzylaryl-(2-(S)-bromomethyl pyrrolidine-1-yl) phosphine oxide 3 in 80% yield. Compound 3 is an ideal chiral precursor for the synthesis of chiral hybrid phosphine-phosphine oxide ligands. The bromide atom is smoothly displaced by lithium diphenylphosphide to afford in 80% yield (Rp)-benzylaryl-(2-(S)-diphenylphosphinomethylpyrrolidine-1-yl) phosphine oxide 5. These reaction are proved to be totally stereoselective : the Michaelis Arbuzov reaction does not change the configur...

Heterotopic ligands:synthesis and complexation properties of phosphine-functionalized dipodal macrocycles

The synthesis of a series of phosphine-functionalized dipodal macrocycles is described; prior co-ordination of a cation within the macrocyclic cavity regulates the ligand structure aiding fotmation of heterodinuclear complexes.