Showing papers in "European Journal of Inorganic Chemistry in 2001"

Nanoscopic Metal Particles − Synthetic Methods and Potential Applications

Abstract: Mono- and bimetallic colloidal particles have gained increasing attention in science and application throughout the last several years. In this contribution, we present a synopsis of the wet chemical syntheses of these materials and survey potential applications in catalysis and materials science. Methods for the characterization of these particles and their surfaces are not reviewed here.

Palladacycles − An Old Organometallic Family Revisited: New, Simple, and Efficient Catalyst Precursors for Homogeneous Catalysis

Abstract: Nitrogen-, phosphorus-, and sulfur-containing palladacycles, typically containing four- or six-electron donor anionic metallated ligands, are emerging as a new family of organometallic catalyst precursors. These thermally and air-stable complexes are easy to handle and their synthesis is often straightforward. Palladacycles are now being successfully exploited in catalytic reactions ranging from classical hydrogenations to enantioselective aldol-type condensations. The main recent achievements pertaining to their use in homogeneous organometallic catalysis are outlined herein.

Second‐Order Optical Nonlinearities in Coordination Chemistry: The Case of Bis(salicylaldiminato)metal Schiff Base Complexes

Abstract: Since the mid-1980s, there has been a growth of interest in the search and development of molecular second-order nonlinear optical (NLO) materials that possess various device applications. Beside the most traditional donor-acceptor (“push-pull”) organic chromophores (e.g. the stilbene family), chemists have increasingly extended their field of investigations to newer generations of organic molecules of greater complexity. In recent years, coordination complexes through their unique characteristics such as various redox and magnetic properties, in addition to their great diversity of geometries, have introduced a new dimension to the area. This review attempts to summarize the NLO capabilities of bis(salicylaldiminato)metal Schiff base complexes: (i) chromophores with enhanced hyperpolarizabilities (β) can be obtained by virtue of the coordinated metal center; (ii) the use of chiral substituents allows the engineering of the chromophores into various non-centrosymmetric environments and efficiencies of about 10 times that of urea in second-harmonic generation; (iii) the general trend observed for the high temperature stability in this family of chromophores, while combined with the large β×μ products, makes these systems interesting candidates for their incorporation into poled polymers with high glass transition temperatures (Tg); (iv) the possibility for β modulation induced by magnetic transition is also seen with respect to the concept of molecular switching.

Structure and Magnetism of a Polycrystalline Transition Metal Soap − CoII[OOC(CH2)10COO](H2O)2

Abstract: Diaquacobalt(II) n-dodecane-α,ω-dioate (2) has been synthesized by metathesis of the corresponding potassium soap 1 and has been fully characterized by chemical and spectroscopic analysis. The crystal structure of 2 has been established by X-ray powder diffraction techniques combined with electron diffraction experiments. It crystallizes in a monoclinic cell [P21/a; a = 9.6558(8), b = 7.4793(6), c = 19.8936(2) A, β = 95.648(9)°, V = 1429.7(3) A3; Z = 2] and consists of stacked layers of cobalt(II) ions connected by carboxylato bridges, thus forming chains that extend along the a axis. These layers are separated by alkyl chains arranged quasi-perpendicularly to the polar sheets. Structure analysis reveals a rare anti-anti conformation of the Co−OCO−Co fragments, which is thought to be responsible for the weak antiferromagnetism of the CoII chains. The exchange coupling constant between the magnetic centres has been estimated as J = −2.08 K.

Metallic Palladium in the Heck Reaction: Active Catalyst or Convenient Precursor?

Abstract: Novel experimental evidence is presented pointing out that “heterogeneous” palladium metal catalysts employed in Heck-type reactions mainly act as sources of soluble palladium(II) complexes, which are the true catalytically active species.

Recent Developments in the Reactivity of Allenylidene and Cumulenylidene Complexes

Abstract: Allenylidene and higher cumulenylidene complexes [M]=C(=C)n=CR1R2 (n = 1, 2, 3) have continuously gained significance in the context of transition metal carbene chemistry. Important developments which have been disclosed during the last two years are reviewed. These include a variety of stoichiometric and catalytic reactions of allenylidene complexes and their utility in organic synthesis. The related chemistry of butatrienylidene (n = 2) and pentatetraenylidene (n = 3) complexes as well as theoretical studies are also reviewed.

Monoanionic N,N,O‐Scorpionate Ligands and their Iron(II) and Zinc(II) Complexes: Models for Mononuclear Active Sites of Non‐Heme Iron Oxidases and Zinc Enzymes

Abstract: The chemical behavior of two bis(3,5-dialkylpyrazol-1-yl)acetic acids and their coordination properties towards ZnCl2 and FeCl2 was studied. Reaction of bis(3,5-dimethylpyrazol-1-yl)acetic acid (bdmpza) (1) with ZnCl2 and FeCl2 gave the 2:1 complexes [(bdmpza)2Zn] (4) and [(bdmpza)2Fe] (5). Crystal structures of both complexes were obtained. In contrast, the sterically more hindered ligand bis(3,5-di-tert-butylpyrazol-1-yl)acetic acid (bdtbpza) (3) coordinates only once to zinc(II) resulting in the complex [(bdtbpza)ZnCl] (6). This provides a structural model complex for the active sites of zinc enzymes such as thermolysin or carboxypeptidase. The good agreement with these active sites was demonstrated by a crystal structure of 6. To the best of our knowledge, this is the first report of zinc complexes with a monoanionic N,N,O-tridentate ligand using a carboxylate O-donor. Substitution of benzylthiolate for the chloride ligand 6 yielded [(bdtbpza)Zn(SCH2Ph)] (8) indicating that the bulky tert-butyl groups do not prevent access to the zinc atom. Reaction of bdtbpza (3) with FeCl2 led to [(bdtbpza)FeCl] (7), which might serve as a structural model complex for the active sites of mononuclear non-heme iron oxidases and oxygenases such as IPNS, DAOCS or CAS.

Dioxo- and Oxovanadium(V) Complexes of Biomimetic Hydrazone ONO Donor Ligands: Synthesis, Characterisation, and Reactivity

Abstract: The dioxovanadium(V) complexes M[VO2(L)solv] (2, 5, 6) have been isolated along with dimeric, oxo-bridged monooxovanadium complexes with the formula [{VOL}2µ-O] (1, 4), and characterised by their spectral and thermogravimetric properties and reactivity patterns. H2L is the hydrazone H2{(R-sal)-iNH} [sal derives from salicylaldehyde (R = H) or p-Cl-salicylaldehyde (R = Cl)] or H2hap-iNH, where hap is the o-hydroxyacetophenone moiety, and iNH stands for isonicotinic acid hydrazide. In the isolated potassium (M = K) complexes 2a, 5 and 6, solv is a water molecule, which was exchanged for methanol or DMSO in the respective solutions as shown by 51V NMR. Treatment of the dimeric (1 and 4) or anionic complexes (2a and 5) with H2O2 yielded (unstable) oxoperoxovanadium complexes K[VO(O2)L] (7, 8). Acidification of 1 and 4 afforded oxohydroxo complexes. When compound 2a is dissolved in methanol, it is partly deoxygenated to form [VO(OMe)(HOMe)L] (9), the crystal and molecular structures of which have been determined, confirming the ONO binding mode of L in its enolate form.

Dinuclear Cobalt(II) Complexes of an Acyclic Phenol-Based Dinucleating Ligand with Four Methoxyethyl Chelating Arms − First Magnetic Analyses in an Axially Distorted Octahedral Field

Abstract: An end-off type acyclic ligand with four methoxyethyl chelating arms, 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-methylphenol [H(bomp)], formed dinuclear cobalt(II) complexes [Co2(bomp)(MeCO2)2]BPh4 (1) and [Co2(bomp)(PhCO2)2]BPh4 (2). X-ray analysis revealed that complex 1·CHCl3 contains two cobalt ions bridged by a phenolic oxygen and two acetate groups, forming a μ-phenoxo-bis(μ-acetato)dicobalt(II) core. Magnetic susceptibility was measured for 1 and 2 over the temperature range 1.8−300 K. The data were successfully analyzed using a new theoretical method assuming an axially distorted octahedral field (Δ = 753 and 775 cm−1, respectively) for each cobalt(II) ion to reveal weak antiferromagnetic interactions (J = −0.96 and −1.74 cm−1, respectively).

Hydrothermal Synthesis of a Two-Dimensional Coordination Polymer [Fe(phen)(μ6-bta)1/2]n (bta = Benzene-1,2,4,5-tetracarboxylate, phen = 1,10-Phenanthroline)

Abstract: A metal-ligand complex [Fe(phen)(μ6-bta)1/2]n (phen = 1,10-phelanthroline; bta = benzene-1,2,4,5-tetracarboxylate ligand) has been hydrothermally synthesized and structurally characterized by single crystal X-ray crystallography, showing that it possesses a novel, two-dimensional polymeric structure.

Defective Double-Cubane, Tetranuclear Manganese(II) and Cobalt(II) Complexes with Simultaneous μ1,1-Azido and μ-O Bridges

Abstract: The reactions of M(O2CCH3)2·4H2O (M= Mn, Co) with di-2-pyridyl ketone, (py)2CO, and NaN3 in CH3OH or CH3OH/H2O allow isolation of the tetranuclear compounds [Mn4(μ1,1-N3)2(N3)2{(py)2C(OH)O}2{(py)2C(OCH3)O}2] (1) and [Co4(μ1,1-N3)2(N3)2{(py)2C(OH)O}2{(py)2C(OCH3)O}2]·2H2O (2). X-ray diffraction analysis reveals defective double-cubane tetrameric entities in which the MnII or CoII atoms are linked by μ1,1-N3 bridges and two kinds of O-bridges. The molar magnetic susceptibility measurements of 1 and 2 in the 2−300 K range indicate weak antiferromagnetic coupling for 1 and clear bulk ferromagnetic coupling for 2.

Stability of the Metal Configuration in Chiral-at-Metal Half-Sandwich Compounds

Abstract: Half-sandwich compounds with a three-legged piano-stool geometry are prominent examples of optically active chiral-at-metal complexes. In these compounds, the configuration at the metal atom may be stable or labile in solution. Configurationally stable compounds can be used for the elucidation of the stereochemical course of substitution reactions and for organic synthesis in ligand transformation reactions. With configurationally labile compounds, the rate of change of the metal configuration can be measured, which sets an upper limit with regard to the handling of the compounds in solution. Surprisingly, in a number of recent papers the lability of the metal configuration has been overlooked resulting in misinterpretations and wrong conclusions.

On the Mechanism of the Hydroxycarbonylation of Styrene with Palladium Systems

Abstract: We present a review concerning the mechanism involved in the hydroxycarbonylation of styrene. We discuss the intermediates proposed in the literature, the effect of the acidic medium, the reactivity and kinetics, as well as the results of theoretical calculations on hydroxycarbonylation and related reactions. We have performed an in situ high-pressure NMR study to obtain more insight into the mechanisms that control the regioselectivity and have assessed how this is affected by the phosphorus ligand and the catalyst precursor. We observed palladium hydride and palladium acyl species and we suggest a catalytic cycle involving palladium hydride, palladium alkyl, and palladium acyl intermediates.

Fluorine Route Synthesis of Montmorillonites Containing Mg or Zn and Characterization by XRD, Thermal Analysis, MAS NMR, and EXAFS Spectroscopy

Abstract: EXAFS spectroscopy, combined with X-ray powder diffraction, chemical and thermal analysis, scanning electronic microscopy, 29Si, 27Al, and 19F MAS NMR spectroscopy, are used in the structural analysis of montmorillonites, synthesised in an acidic fluoride medium. Hydrothermal synthesis performed under mild conditions (493 K, autogenous pressure) enables the formation of montmorillonite clays, containing Al and Zn or Mg in the octahedral sheet. It is shown that montmorillonites can only be synthesized in a narrow range of compositions. An accurate value of the Al for Si substitution rate in the tetrahedral sheet is determined by using 27Al MAS NMR spectroscopy performed under definite conditions. Some interatomic distances are determined by EXAFS spectroscopy (RMg−O = 2.11 A, RZn−O = 2.08 A, RZn−Al = 2.98 A, RZn−Zn = 3.11 A) which reveals strong local distortions in the octahedral sheet with respect to the ideal montmorillonite structure. Lengthening of the out-of-plane Zn−Si(Al) distances also shows the swelling of the whole layer in the neighbourhood of Zn. Moreover, the combination of EXAFS and 19F MAS NMR spectroscopic data reveals a clustering of the divalent elements of the octahedral sheet, which is related to a possible local trioctahedral character of these materials.

Mixed-Ligand Copper(II) Complexes with the Rigid Bidentate Bis(N-arylimino)acenaphthene Ligand: Synthesis, Spectroscopic-, and X-ray Structural Characterization

Abstract: Reported are the synthesis, characterization, and crystal structures of two mixed-ligand copper(II) complexes containing bis[N-(2,6-diisopropylphenyl)imino]acenaphthene (o,o′-iPr2C6H3-BIAN). In both complexes, namely [Cu(AcOH)(o,o′-iPr2C6H3-BIAN)Cl2] (1) and [Cu(acac)(AcOH)(o,o′-iPr2C6H3-BIAN)](ClO4) (2) (acac = acetylacetonate and AcOH = acetic acid), the copper ions are in a distorted square-pyramidal coordination environment with an acetic acid molecule in each apical position. The two imine nitrogen atoms of o,o′-iPr2C6H3-BIAN occupy the basal plane with the two chloride atoms and the two oxygen atoms of acac in complexes 1 and 2, respectively. Complex formation results in certain structural changes inside the rigid N−N ligand. Such changes led to an increased planarity of the o,o′-iPr2C6H3-BIAN backbone, and produced a nearly perpendicular angle between the naphthalene and the aromatic imine planes. In complex 2, the more perpendicular arrangement of the o,o′-diisopropylphenyl groups shielding the copper centre was structurally allowed by the elongation of one of the metal-to-ligand bonds and by the relatively larger N−Cu−N bite angle. Also discussed are IR, magnetic, and UV/Vis measurements.

Tuning the Reversible Binding of NO to Iron(II) Aminocarboxylate and Related Complexes in Aqueous Solution

Abstract: Chelate complexes of FeII were investigated with respect to their reactivity against nitric oxide and dioxygen. Through a systematic variation of the structure of the polyaminocarboxylate EDTA, a series of 38 potential chelate ligands were selected for FeII. The nitrosyl complexes were prepared from the FeII chelates with NO gas and examined spectroscopically by UV/Vis and ATR-IR techniques, and themodynamically by determining the overall binding constants for NO. In addition, the reversibility of NO binding to these FeII chelates and the rate of the competing oxidation by dioxygen were studied qualitatively. Whereas the studied complexes all form more or less stable nitrosyl complexes with a characteristic band pattern in the UV/Vis spectra and only slightly diverging frequencies for the NO stretching vibration in the IR spectra, they differ considerably in the reversibility of NO binding, the overall NO binding constants and the sensitivity towards dioxygen. It was found that an increasing number of donor groups on the chelate ligand causes a stronger coordination to FeII, and increases the tendency of the FeII chelates to transfer electron density from iron to substrates like dioxygen or nitric oxide. This results in an accelerated oxidation of FeII to FeIII by dioxygen and a more pronounced tendency of the corresponding nitrosyl complexes to slowly decompose to FeIII and N2O. In addition, the overall binding constant for NO (KNO), which spans a range from 1·103 to 2·107M−1, increases in the same direction as a result of the inductive effect of the chelate ligand.

Imine Versus Amine Donors in Iron‐Based Ethylene Polymerisation Catalysts

Abstract: The synthesis and characterisation of iron(II) dichloro complexes containing neutral tridentate nitrogen ligands of the type 2-arylaminoalkyl-6-aryliminoalkylpyridine [2-ArNHCR(Me)-6-ArN=CR]C5H3N (R = H, Ar = 2,6-iPr2C6H3 or 2,4,6-Me3C6H2; R = Me, Ar = 2,6-iPr2C6H3)] and 2,6-bis(arylaminomethyl)pyridine [2,6-(ArNHCH2)2]C5H3N (Ar = 2,6-iPr2C6H3) are described and their activity in ethylene polymerisation is compared with their 2,6-bis(aryliminoalkyl)pyridine analogues.

Synthesis, Structures and Ethylene Polymerisation Behaviour of Low Valent β-Diketiminato Chromium Complexes

Abstract: The preparation, reaction chemistry and ethylene polymerisation behaviour of low valent β-diketiminato chromium complexes are described. [(DDP)CrCl(µ-Cl)]2 (1) [DDPH = 2-{(2,6diisopropylphenyl)amino}-4-{(2,6-diisopropylphenyl)imino}pent-2-ene] is formed by treatment of CrCl3(THF)3 with LiDDP. Alkylation of 1 with AlMe3 results in the formation of the binuclear dimethyl complex [(DDP)CrMe(µ-Cl)]2 (2). In contrast, the attempted alkylation of 1 with benzylmagnesium chloride results in reduction to form the dichromium(II) complex [(DDP)Cr(µ-Cl)]2 (3). Depending on the conditions of crystallisation, 3 can be obtained as the THF adduct [3(THF)2·THF] or co-crystallised with a molecule of dibenzyl [3·Bz-Bz]. Cleavage of the dimeric unit in 1 can be achieved by the addition of carboxylates or β-diketonates to give [(DDP)CrCl(O2CR)(THF)] (R = Me 4a, Ph 4b) and [(DDP)CrCl({O(R)C}2CH)] (R = Me 5a, Ph 5b), respectively. Single crystal X-ray diffraction studies have been performed on 1, 2, 3(THF)2·THF, 3·Bz-Bz, 4a, and 5b. Complexes 1, 2 and 3(THF)2·THF are dimeric and have molecular C2h symmetry. Complex 3·Bz Bz is also dimeric but has its potential C2h symmetry removed by a significant tetrahedral distortion of the chromium coordination geometry. Compound 4a has an octahedral chromium centre coordinated to a single bidentate diketiminate ligand, a bidentate acetate, a chloride and a THF molecule. Complex 5b has a square pyramidal chromium with apical chloride and basal η2 diketiminate and diketonate ligands. The complex contains strong intramolecular C−H···π stabilising interactions. All the complexes are active in ethylene polymerisation on treatment with suitable aluminium activators, affording high molecular weight polyethylene.

The Hydrothermal Synthesis, Crystal Structures and Thermal Stability of the Novel One- and Two-Dimensional Thioantimonate(III) Compounds [Co(tren)]Sb2S4 and [Ni(tren)]Sb2S4

Abstract: Two novel thioantimonate(III) compounds [Co(C6H18N4)]Sb2S4 (1) and [Ni(C6H18N4)]Sb2S4 (2) were synthesised under solvothermal conditions by reacting the transition metal, Sb and S in a 50% solution of tris(2-aminoethyl)amine (tren). The use of a tetradentate amine yields incompletely shielded transition metal cations which in turn are able to form bonds to the sulfur atoms of thioantimonate(III) anions. Compound 1 crystallises in the orthorhombic space group Pbca, a = 13.886(3) A, b = 11.452(2) A, c = 20.549(4) A, V = 3268(1) A3, Z = 8 and compound 2 crystallises in the monoclinic space group P21/n, a = 6.906(1) A, b = 22.822(5) A, c = 10.347(2) A, β = 103.17(3)°, V = 1587.9(6) A3, Z = 4. The 2∝[Sb2S42−] anion in compound 1 is formed by an SbS3 and an SbS4 unit sharing a common corner. Two SbS4 units have a common edge to form an Sb2S2 heterocycle. Four such Sb2S2 rings are at the corners of a two-dimensional square-like net. Interconnection of the rings by SbS3 pyramids yields Sb10S10 rings with pores measuring 10·8.4 A in diameter. The pores are filled by the [Co(tren)]2+ cations. The [Co]2+ cation is in a trigonal bipyramidal environment of four N atoms of the tren ligand and one S atom of the SbS3 pyramid. The one-dimensional 1∝[Sb2S42−] chain anion in 2 is built by two corner-sharing SbS3 units. The [Ni]2+ cation is in an octahedral environment consisting of four N atoms of the tren ligand and two S atoms of the anion. An NiSb2S3 heteroring in a twist conformation is formed with an unusually large Ni−S(1)−Sb(1) angle of 121.73(3)°. For the [Co]2+ (d7) cation no significant energy differences can be expected for the trigonal bipyramidal and octahedral coordination, and due to the geometrical requirements of the tetradentate ligand the former environment is preferred. In contrast, for [Ni]2+ (d8) an octahedral environment is energetically favoured over the trigonal bipyramidal arrangement. Both compounds start to decompose under an Ar atmosphere at about 250 °C. For 1 two not well resolved steps are observed, whereas 2 decomposes in one step. In the X-ray powder patterns of the grey products Sb2S3, Co/NiSbS and Co/NiS could be identified.

Improved Preparations of Molybdenum Coordination Compounds from Tetrachlorobis(diethyl ether)molybdenum(IV)

Abstract: The reduction of MoCl5 with metallic tin in diethyl ether provides a rapid and convenient entry to [MoCl4(OEt2)2] This compound can be transformed easily and in high yields into a variety of other useful synthons The loss of ether in the solid state affords a new and reactive form of MoCl4 Treatment with THF, PMe3 or LiOtBu affords [MoCl4(THF)2], [MoCl4(PMe3)3] or [Mo(OtBu)4] in high isolated yields Treatment with metallic tin in THF affords [MoCl3(THF)3] All of these reactions can be carried out under simple experimental conditions and represent significant improvements relative to previously reported syntheses of the same compounds

Versatility of the Nature of the Magnetic Gadolinium(III)−Vanadium(IV) Interaction − Structure and Magnetic Properties of Two Heterobinuclear [Gd, V(O)] Complexes

Abstract: It has been known for a long time that the magnetic exchange interaction between copper and gadolinium ions is always ferromagnetic. Very recently, three exceptions to this general trend were revealed. They involve complexes associating a gadolinium(III) ion with a copper(II) ion or with radicals of the nitroxide or semiquinone types. We want to show that this trend is more general than expected, for such a behavior can also be observed in heterobinuclear vanadyl-gadolinium complexes.

A Facile Route to Carbonylhalogenometal Complexes (M = Rh, Ir, Ru, Pt) by Dimethylformamide Decarbonylation

Abstract: Dimethyl formamide (DMF) can be a convenient source of the carbonyl ligand in the coordination chemistry of rhodium, ruthenium, iridium, and platinum. We have undertaken a thorough study concerning the course of this reaction. In a first step, DMF-containing complexes are produced, which is usually accompanied by chloride redistribution. Then, upon refluxing, carbonyl species in the same oxidation state are obtained, presumably as a result of HCl-mediated DMF decomposition. Provided that water levels are kept low, reduction can occur to provide the complexes [NH2(CH3)2][RhCl2(CO)2], [NH2(CH3)2][RuCl3(CO)2(DMF)], [RuCl2(CO)2(DMF)2], and [NH2(CH3)2][IrCl2(CO)2]. In the case of platinum, reduction is not effective and [NH2(CH3)2][PtCl3(CO)] is obtained. No carbonylpalladium species can be synthesized in this way, the reaction producing copious amounts of colloidal metal. Adding phosphanes to these chlorocarbonyl-containing solutions allows easy, one-step syntheses of a variety of complexes.

Covalently Linked Ruthenium(II)−Manganese(II) Complexes: Distance Dependence of Quenching and Electron Transfer

Abstract: Continuing our development of artificial models for photosystem II in green plants, a series of compounds have been prepared in which a RU(bpy)(3)(2+) photosensitizer is covalently Linked to a mang ...

Complexes of Manganese, Iron, Zinc, and Molybdenum with a Superbasic Tris(guanidine) Derivative of Tris(2-ethylamino)amine (Tren) as a Tripod Ligand

Abstract: The synthesis of the novel tripod ligand N[CH2CH2N=C(NMe2)2]3, based on the tris(2-ethylamino)amine (tren) backbone and having a set of three superbasic tetramethylguanidine (TMG) donor atoms instead of the primary amine functionalities, is described. This ligand has been prepared by treating tren with the Vilsmeyer salt [(Me2N)2CCl]Cl in the presence of triethylamine as an auxiliary base and NaOH. Complexes of manganese(II), iron(II), and zinc(II) as biologically relevant transition metal ions as well as of molybdenum(0) have been synthesized and spectroscopically and structurally characterized. The electrochemical properties of selected complexes have been studied.

Two‐Level Self‐Organisation of Arrays of [2×2] Grid‐Type Tetranuclear Metal Complexes by Hydrogen Bonding

Abstract: Here we report on the synthesis and characterisation of four new complexes of the [2×2] M4II grid-type (M = Co, Fe, Zn) with oligopyridine-derived ligands. The presence of aminopyrazine and aminopyrimidine moieties at the edge of the ligands potentially enables the formation of infinite hydrogen-bonded multi-grid networks. The ligands were synthesised by subsequent stannylations and Stille-type coupling reactions. The complexes were obtained by self-assembly of the ligand with the metal salt. The single-crystal X-ray structure was determined for the Co complex 7 containing aminopyrimidine as the hydrogen-bonding moiety [P1¯; a = 15.4976(4), b = 18.2114(6), c = 31.9538(10) A, α = 86.9809(13), β = 83.4137(18), γ = 67.2828(16)°]. The crystal structure reveals hydrogen bonding in one direction, thus forming infinite chains of grids, whereas in the second direction of a layer, only weak attractive interactions are found. Anions and solvent molecules are situated between the layers, thus inhibiting any direct interaction between them. Cocrystallisation of the complementary complexes should enable the recognition-controlled alternating arrangement of grids incorporating different metal ions in a chessboard-like manner.

Open-Chain Polyamine Ligands Bearing an Anthracene Unit − Chemosensors for Logic Operations at the Molecular Level

Abstract: In this work the absorption and the fluorescence emission properties as well as the protonation sequence of three open chain polyamine ligands of different dimensions bearing an anthracene unit were studied. The protonation and stability constants with Ni2+, Cu2+, Zn2+, and Cd2+ have been determined in 0.15 mol·dm−3 NaCl at 298.1 ± 0.1 K. The values of both protonation and stability constants follow the expected trends according to the number of nitrogen donors, sequence of chelate rings and hydrophilic−hydrophobic balance. Chelation enhancement of the fluorescence emission (CHEF) was observed for some complexes of these ligands with Zn2+ and Cd2+. In contrast the analog complexes containing Cu2+and Ni2+ exhibit a chelation enhancement of the quenching (CHEQ) except for the complexes with the largest chain where some protonated metal complexes are emissive. These systems are explored from the point of view of chemosensors for logic operations at the molecular level.

Heterocyclopentadienyl Complexes of Group‐3 Metals

Abstract: Heterocyclopentadienyl complexes of group-3 metals (scandium, yttrium, lanthanum and the lanthanides, and uranium) are compounds in which one or more −CH units of a cyclopentadienyl-like ligand have been replaced by a heteroelement (nitrogen, phosphorus, arsenic, or antimony). These ligands can have very diverse substitution patterns, notably with bridged and cavitand-like structures. In addition to the classical η5-coordination behaviour, the heterocyclopentadienyl ligand can adopt a very large array of coordination patterns. Some complexes have a very promising chemistry since they have been found to activate small molecules such as nitrogen and ethylene.

Dinuclear Zinc(II)−Iron(III) and Iron(II)−Iron(III) Complexes as Models for Purple Acid Phosphatases

Abstract: The heterodinuclear ZnIIFeIII complex 1 and the isostructural FeIIFeIII complex 2 with the dinucleating ligand from 2,6-bis[{bis(2-pyridylmethyl)amino}methyl]-4-methoxyphenol (HBPMOP, 3) were prepared and characterized by X-ray crystallography. Solution studies (UV/Vis spectroscopy; electrochemistry) are described. A pH-induced change in the coordination spheres of the metal centers is seen. These complexes serve as models for the mixed-valence oxidation state in purple acid phosphatases. The cleavage acceleration of the activated phosphodiester 2-hydroxypropyl p-nitrophenyl phosphate (HPNP) was investigated in acetonitrile/water (1:1) in the presence of complexes of the ligand BPMOP and its methyl analogue BPMP with regards to its dependence on the pH value. At the optimum pH value (8.5 ± 0.2), the ZnIIFeIII complex from BPMOP shows a 2-fold higher rate acceleration compared with that of the complex containing BPMP. The diiron complex from BPMOP is 4-fold more reactive than the homologous complex from BPMP. The heterodinuclear ZnIIFeIII catalysts are at least 10-fold more reactive than the homonuclear FeIIFeIII catalysts.

Structure, Magnetic Properties and Magnetic Phase Diagram of a Layered, Bimetallic, Cyanide‐Bridged CrIII‐NiII Metamagnet

Abstract: The reaction of hexacyanochromate(III) with Ni(tmc)2+ (tmc = tetramethylcyclam) leads to the formation of the layered compound [Ni(tmc)]3[Cr(CN)6]2·18H2O displaying a corrugated sheet structure. Within each layer, the Ni(tmc) units are surrounded by two Cr(CN)6 complexes in a trans fashion while the Cr(CN)6 units are linked to three Ni(tmc) molecules in facial positions. The magnetic studies show ferromagnetic interaction for a NiII(d8, t2g6eg2)−CN−CrIII(d3, t2g3) system within the layers. Below a critical temperature (TN = 14 K), a bulk antiferromagnetic order is observed due to a small interlayer antiferromagnetic interaction. An antiferromagnetic ferromagnetic phase transition occurs for an applied field HC of 1200 Oe expressing the metamagnetic behavior of the compound. The phase diagram of the compound was constructed and the antiferromagnetic interlayer magnetic energy was estimated to be equal to 0.1 cm−1.