Showing papers in "European Journal of Inorganic Chemistry in 2003"

Glasses with Medical Applications

Abstract: Bioactive glasses react chemically with the body fluids. The reaction product is an apatite, which, with the intervention of biological drivers, assists the generation of bone matrix and bone growth. The main application of these bioactive glasses in the clinical field is the filling of osseous cavities, manufacture of small parts for middle ear bone replacement and maxilofacial reconstruction and dental applications. Thanks to advances in related medical technologies, bioactive glasses are now undergoing a new stage of development, resulting in different mechanical properties, drug de

Helical Ribbons of Cadmium(II) and Zinc(II) Dicarboxylates with Bipyridyl- Like Chelates Syntheses, Crystal Structures and Photoluminescence

Abstract: Four mixed-ligand complexes of [M(mpa)(phen)]n [M =C d (1 )o r Zn (2) and mpa = m-phthalate and phen = 1,10-phenanthroline) and [M2(mpa)2(2,2-bpy)2]n [M = Zn (3 )o r Cd (4) and 2,2-bpy = 2,2-bipyridine] have been synthesized and their crystal structures have been established by single-crystal X-ray diffraction. They all consist of one-dimensional ribbons featuring dinuclear units. Both 1 and 2 crystallize isomorphously in the monoclinic space group P2/c and feature

Nanoparticulated Gold: Syntheses, Structures, Electronics, and Reactivities

Abstract: This microreview deals mainly with the synthesis and the electronic and chemical properties of gold nanoparticles. Modern synthetic routes, based on physical and on chemical procedures, as well as structural and optical features, are described. The bulk-to-molecule transition is discussed by studying size-controlled quantum-size effects, resulting in the determination of discrete electronic energy levels in Au55 clusters. Conductivity measurements of three- and two-dimensionally organized ligand-protected Au55 clusters are described, as well as the current techniques for the generation of ordered monolayers and artificial patterns of quantum dots. Finally, some aspects of the chemical activity of gold nanoparticles are discussed by considering ligand-exchange processes and, last but not least, the expanding role of gold nanoparticles in catalysis is considered. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Palladium‐Catalyzed Cyanation of Aryl Halides: Recent Developments and Perspectives

Abstract: The palladium-catalyzed cyanation of aryl halides is an elegant method for the preparation of benzonitriles. Since its discovery in 1973, this reaction has been the topic of several investigations. Nevertheless, the general methodology is still somewhat underdeveloped compared to other palladium-catalyzed coupling reactions. Here, we summarize important developments from 1997 until 2003 in this area. Recent contributions from our group include the development of palladium/phosphane/amine catalyst systems for the cyanation of aryl chlorides, the successful cyanation of aryl halides with acetone cyanohydrin and trimethylsilyl cyanide as cyanation reagents, and a general improvement of catalyst efficiency by using a continuous dosage of cyanide sources. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Supramolecular Organisation of Polymeric Coordination Chains into a Three-Dimensional Network with Nanosized Channels that Clathrate Large Organic Molecules

Abstract: Hydrothermal treatment of a mixture of [Zn(MeCO2)2]·H2O, terephthalic acid, and 2,2′-bipyridine resulted in a coordination polymer [Zn(bpy)(tp)](bpy) (1; bpy = 2,2′-bipyridine, H2tp = terephthalic acid) which crystallizes in the monoclinic space group C2/c, Mr = 541.85, a = 15.388(11), b = 21.963(11), c = 7.670(8) A, β = 112.82(2)°, V = 2387(3) A3, Z = 4, Dc = 1.506 g·cm−3. An X-ray single-crystal structural analysis reveals that 1 is a three-dimensional network with nanosized channels constructed from one-dimensional coordination chains via C−H···O hydrogen bonds and aromatic intercalations. TGA and XRPD showed that the porous network of 1 is very stable while the guest 2,2′-bipyridine molecules in the channels are removable. Compound 1 shows a strong ligand-centred emission at room temperature in the solid state. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Developing Remote Metal Binding Sites in Heteropolymolybdates

Abstract: Anderson-type polyoxomolybdates [MMo6O18{(OCH2)3CNH2}2]3− (M = MnIII, FeIII) were prepared and structurally characterized. The tris(alkoxo) ligands are bound to the central heteroatom via their oxygen atoms. The corresponding compounds with M = NiII or ZnII are not accessible since these cations have a preference for the amino functionality. The pendant amino groups of the manganese-containing derivative react with pyridinecarbaldehydes to give the corresponding imines. This provides new mono- and bidentate binding sites for metal cations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Degradation of the Second-Generation Grubbs Metathesis Catalyst with Primary Alcohols and Oxygen - Isomerization and Hydrogenation Activities of Monocarbonyl Complexes.

Abstract: Reaction of the second-generation Grubbs metathesis catalyst [RuCl2(=CHPh)(H2IMes)(PCy3)] (2) (H2IMes = 1,3-dimethyl-4,5-dihydroimidazol-2-ylidene) with primary alcohols in the presence of a base produced the complexes [RuClH(CO)(PCy3)2] (3) and [RuClH(CO)(H2IMes)(PCy3)] (5). When benzyl alcohol was used, the ruthenium phenyl complexes [RuClPh(CO)(PCy3)2] (4) and [RuClPh(CO)(H2IMes)(PCy3)] (7) were formed in addition to 3 and 5. Complex 7, characterised by an X-ray structure analysis, was also formed on exposure of 2 to oxygen. The isomerization and hydrogenation activity of 7 was determined and compared with that of 3 and 4. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Preparation of Rhodium Catalysts Supported on Carbon Nanotubes by a Surface Mediated Organometallic Reaction

Abstract: The dimeric complex [Rh2Cl2(CO)4] was grafted to multi-walled carbon nanotubes (MWNTs) previously oxidised with nitric acid and then treated with sodium carbonate to produce carboxylate groups on their outer surface. The grafting mechanism involves bridge-splitting and substitution of -COO for Cl, as evidenced by the presence of NaCl in the samples. A further reduction/decomposition step under dihydrogen at 573 K afforded highly dispersed rhodium nanoparticles (≈1.5−2.5 nm). This novel rhodium-supported carbon material (Rh/MWNT-COONa) was tested as a catalyst for the hydrogenation of trans-cinnamaldehyde and the hydroformylation of hex-1-ene in the liquid phase: in both cases it was found to be very selective, toward C=C double-bond hydrogenation and the production of linear and branched aldehydes, respectively. A comparison was made between its catalytic activity and that of rhodium supported on pristine MWNTs and on nitric acid-oxidised MWNTs. We observed that these latter catalysts have larger particle sizes and lower activities, thus confirming the efficiency of our grafting procedure. Moreover, the better results obtained when using MWNT-COONa as support with respect to carboxylate-containing activated carbon also point to the important role played by the mesoporous nature of the carbon nanotube support, which can ameliorate transfer processes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Synthesis, Crystal Structure, and Photophysical and Magnetic Properties of Dimeric and Polymeric Lanthanide Complexes with Benzoic Acid and Its Derivatives

Abstract: A new family of lanthanide carboxylate complexes with benzoic acid and its derivatives was synthesised and characterised. The structures of the complexes were established by X-ray crystallography, which revealed that various chelating modes of the carboxylate ligands are present on the metal ion, resulting in the formation of dimeric and polymeric skeletons. The photophysical properties of the Eu and Tb complexes were studied: the complexes exhibited sensitised luminescence in the visible spectral region, but the luminescence intensities and lifetimes were very sensitive to quenching by the OH groups of methanol molecules. The solid-state magnetic properties of the Gd and Tb complexes demonstrated the presence of weak antiferromagnetic exchange interactions at very low temperatures, caused by interaction between the neighbouring ions along the chain. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2003)

Structural Variations and Formation Constants of First-Row Transition Metal Complexes of Biologically Active Aroylhydrazones

Abstract: Iron chelators of the 2-pyridinecarbaldehyde isonicotinoylhydrazone (HPCIH) class show high potential for the treatment of iron overload diseases. In the present study, selected first-row transition metal (from Mn to Zn) complexes with HPCIH and 2-pyridinecarbaldehyde (4'-aminobenzoyl)hydrazone (HPCAH) were synthesised and characterised. Crystallography reveals that HPCAH exclusively forms bis complexes with divalent transition metals, with each ligand coordinating meridionally through its pyridine-N, imine-N and carbonyl-O atoms, forming distorted octahedral cis-MN4O2 complexes. Complexes of HPCIH were more varied and unpredictable, with metal/ligand ratios of 1:1, 1:2, 2:2 and 3:2 obtained with different metal ions. The isonicotinoyl ring N-atom in HPCIH was found to be an effective ligand, and this resulted in the varied metal/ligand ratios observed. The formation constants of divalent metal complexes with HPCIH were determined by potentiometric titrations and the values obtained were consistent with similar tridentate ligands and with the Irving-Williams order. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).

Oligomerisation of Ethylene to Linear α‐Olefins by new Cs‐ and C1‐Symmetric [2,6‐Bis(imino)pyridyl]iron and ‐cobalt Dichloride Complexes

Abstract: A new family of Cs- and C1-symmetric 2,6-bis(imino)pyridyl ligands has been synthesised. These ligands, which differ from their known counterparts in the contemporaneous presence of alkyl and aryl substituent at the ketimine nitrogen atoms, form stable, five-coordinate complexes with FeCl2 and CoCl2. All ligands and catalysts have been fully characterised both in the solid state and in solution. A single-crystal X-ray analysis of [CoCl2{2-[CMe=N−(2,6-dimethylphenyl)]-6-(CMe=N−C6H11)C5H3N}]·H2O shows the metal centre to adopt a highly distorted square-pyramidal geometry. In combination with methylaluminoxane (MAO), both iron and cobalt compounds act as effective and selective (> 99%) catalysts for the oligomerisation of ethylene to a Schulz−Flory distribution of α-olefins, with the α factor ranging from 0.61 to 0.91. The iron catalysts exhibit TOFs as high as 7·105 mol C2H4 (mol of cat × h)−1 and are much more active than their cobalt analogues. Experiments at different ethylene pressures with the iron catalysts showed that both the propagation rate and the chain transfer rate are first order in ethylene pressure. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2003)

Synthesis, Crystal Structure and Fluorescence of Two Novel Mixed‐Ligand Cadmium Coordination Polymers with Different Structural Motifs

Abstract: Two novel cadmium(II) coordination compounds, [Cd(bpe)1.5(NO2-BDC)]·0.25H2O (1) and [Cd(bpp)(NO2-BDC)(H2O)]·0.25H2O (2) [NO2-BDCH2 = 5-nitro-1,3-benzenedicarboxylic acid, bpe = 1,2-bis(4-pyridyl)ethane, bpp = 1,3-bis(4-pyridyl)propane] have been hydrothermally synthesized by reaction of cadmium chloride and NO2-BDC with the homologous ligands bpe and bpp, respectively. The former compound displays a remarkable three-dimensional architecture sustained by the catenation of 2D bilayers, while the latter exhibits a unique twofold interpenetrating three-dimensional architecture. The thermal and fluorescence properties associated with their crystal structures have been measured. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Synthesis, Reactivity, Crystal Structures and Catalytic Activity of New Chelating Bisimidazolium‐Carbene Complexes of Rh

Abstract: A series of new bridging, chelating and pincer N-heterocyclic carbenes of RhI and RhIII have been obtained under mild conditions. The compounds have been fully characterised and their crystal structures determined. The chelate-pincer coordination of the ligands means that the stability of these compounds is significantly greater than other carbene complexes of Rh. The compounds have been tested in catalytic reactions such as hydrogen transfer from alcohols to ketones, and hydrosilylation of terminal olefins and alkynes; they show a high activity for both processes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Single-Atom O-Bridged Urea in a Dinickel(II) Complex together with NiII4, CuII2 and CuII4 Complexes of a Pentadentate Phenol-Containing Schiff Base with (O,N,O,N,O)-Donor Atoms

Abstract: A pentadentate phenol-containing ligand (H3L) with N2O3 donor atoms yields NiII2 (1), NiII4 (2), CuII2 (3) and CuII4 (4) complexes, which have been structurally characterized by X-ray diffraction. Complex 1 contains a single-atom O-bridged urea. The compounds were characterized by IR, UV/Vis, mass spectrometry, electrochemistry and variable-temperature (2−295 K) magnetic susceptibility measurements. Analysis of the susceptibility data shows antiferromagnetic interactions between the metal centers indicating a diamagnetic ground state for complexes 1, 3 and 4, whereas complex 2, a tetranuclear NiII cubane, has a complicated low-lying magnetic structure with a non-diamagnetic ground state. A plot of J vs. Ni−O−Ni angles for all structurally characterized Ni4O4 cubane cores, including 2, irrespective of their symmetry exhibits a large variation of J values within a small range of Ni−O−Ni angles. The electrochemistry of all complexes was investigated in detail and the ligand-centered oxidation to a radical-ligand is inferred from the occurrence of oxidation processes at potentials which are similar. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Synthesis, Structure, and Reactivity of a New Mononuclear Molybdenum(VI) Complex Resembling the Active Center of Molybdenum Oxotransferases

Abstract: The design, synthesis, and structure determination of a pentacoordinate square-pyramidal molybdenum(VI) complex MoO2L (where LH2 is a diacidic tridentate ONO donor ligand) is reported. The substrate binding capacity of MoO2L has been demonstrated by the formation and isolation of six-coordinate octahedral complexes [MoO2L(B)] (where B = imidazole, 1-methylimidazole, pyridine, or γ-picoline) and the structures of [MoO2L(Imz)] and [MoO2L(Py)] have been solved by X-ray crystallography. Oxo transfer of MoO2L to the substrate PPh3 has been demonstrated by the formation of MoOL and [MoOL(bipy)]. Thus, the complex MoO2L behaves as a model for the active center of oxotransfer molybdoenzymes and is of interest in bioinorganic chemistry. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

General Synthesis and Characterization of Monocrystalline Lanthanide Orthophosphate Nanowires

Abstract: Monocrystalline LnPO4 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb) nanowires have been prepared in bulk quantities by a simple, facile, and clean solution-based hydrothermal method at 220−240 °C by finely tuning the acidity of the stock solutions. The length and width of the nanowires were in the range of 1−10 μm and 10−200 nm, respectively. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Blue to Red Fluorescent Emission Tuning of a Cadmium Coordination Polymer by Conjugated Ligands

Abstract: The hydrothermal hydrolysis reactions of Cd(ClO4)2·(6H2O) with 4-[2-(2-pyridyl)ethenyl]benzonitrile (2-PEBN) and 2-[2-(4-cyanophenyl)ethenyl]-8-quinolinol (2-CEQH) afforded two coordination polymers aquabis{4-[2-(2-pyridyl)ethenyl]benzoate}cadmium(II) (1) and 2-[2-(4-carboxylatophenyl)ethenyl]-8-quinolinolate(pyridine)cadmium(II) (2), respectively. Complexes 1 and 2 display strong blue and red fluorescent emission, respectively. Both 1 and 2 have a 2-D grid framework containing a dimer as the corner unit. Crystal data for 1: monoclinic, P21/c, a = 15.2411(2), b = 19.8651(2), c = 15.6929(1) A, α = β = 90, γ = 96.961(1)°; for 2: monoclinic, P21/c, a = 11.9219(1), b = 8.9515(1), c = 18.8204(1)A, α = γ = 90.00, β = 104.372(1)°. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Heterodimetallic Chalcogen‐Bridged Cubane‐Type Clusters of Molybdenum and Tungsten Containing First‐Row Transition Metals

Abstract: Transition metal cluster chalcogenides with cubane-type structures are relevant to our understanding of several industrial and biological catalytic processes. Recent advances in cluster chemistry owe much to the development of rational synthetic approaches, an aspect that is emphasised in this review which focuses on cuboidal clusters of molybdenum and tungsten (M) with M2M′2S4 and M3M′Q4 (Q = S, Se) central units that incorporate a first-row transition metal atom (M′). Special attention has been paid to the non-aqueous chemistry of these compounds. The structural features of these complexes are discussed in relation to their electronic structures within the framework of molecular orbital theory, spectroscopic, magnetic and electrochemical experimental data. Finally, the importance of these clusters in catalysis, nonlinear optics and in the formation of supramolecular adducts is discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The Strained η2‐NAmido−NPyridine Coordination of Aminopyridinato Ligands

Abstract: This review gives an account of the syntheses and structures of group-3 (including lanthanides), -4 and -5 metal complexes stabilised by strained η2-coordinated aminopyridinato ligands. Reactivity studies and catalytic applications of the coordination compounds are discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The Chemistry of Borylene Complexes

Abstract: Over the past seven years, complexes of various transition metals with bridged or terminal borylene ligands BR have for the first time been reported and fully characterised. Being closely related to important organometallic compounds, such as carbene, vinylidene, and carbonyl complexes, they have already attracted considerable interest both from experimental and computational points of view. Those studies have provided some detailed information about the nature of the metal−boron bond and about the nature of metal and borylene moieties required for the formation of stable complexes. Various methods for their preparation have been developed and the first studies on their reactivity have demonstrated an interesting chemistry. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2003)

Photophysical and Energy-Transfer Properties of (Salen)zinc Complexes and Supramolecular Assemblies

Abstract: Keywords: Host-guest systems / Fluorescence / Supramolecular chemistry / Salen ligands The absorption, emission, and energy-transfer properties of monomeric and supramolecular (salen)Zn complexes (square and rectangular assemblies) are reported The monomeric complexes fluoresce in solution, displaying photophysical behavior similar to typical (porphyrin)zinc complexes Rhenium coordination chemistry is used to assemble molecular rectangles and squares that largely retain the photophysical properties of the parent compounds Host-guest assemblies

Large‐Scale Synthesis of High Quality Trigonal Selenium Nanowires

Abstract: A direct and simple one-step hydrothermal reaction route has been developed for the synthesis of high quality trigonal selenium (t-Se) nanowires at 110 °C, with (NH4)2S2O3 and Na2SeO3 as starting materials in the presence of the surfactant sodium dodecyl sulfate (SDS). The diameter of the trigonal selenium nanowires can be tuned by carefully adjusting the initial feedstock concentration. The unusual chain like structure of the target material plays a key role in determining the final morphologies of the products. Several factors, such as initial concentration of the feedstock, the presence of surfactant, and the temperature which influences the quality of the t-Se nanowires, have been investigated. The optical properties of the t-Se nanowires with different diameters were examined by means of UV/Vis absorbance spectroscopy at room temperature. The investigation revealed that the absorbance peak for the t-Se nanowires with diameters of 20−40 nm shifts to the blue, relative to those for bulk t-Se nanowires (374 nm) and nanowires with diameters of 50−130 nm (306 nm). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The Use of Conductivity Measurements for the Characterization of Cationic Palladium(II) Complexes and for the Determination of Kinetic and Thermodynamic Data in Palladium‐Catalyzed Reactions

Abstract: This review illustrates how conductivity measurements are used to characterize the cationic character of aryl-, vinyl-, hydrido-, and (η3-allyl)palladium(II) complexes generated by oxidative addition of aryl and vinyl triflates, acetic/formic acid, and allylic carboxylates/carbonates, respectively, with palladium(0) complexes in DMF. These cationic palladium(II) complexes have been postulated as key intermediates in Stille, Heck, Tsuji−Trost, and Trost reactions, but most of them have never been characterized in the context of real oxidative additions, i.e., with the counteranion delivered by the reagent (triflates, carboxylates, and carbonates). The role of chloride ions has been examined and the mechanistic consequences are reported. Conductivity measurements are also used to obtain thermodynamic and kinetic data on the formation of cationic palladium(II) complexes and, consequently, to gain a deeper insight into the mechanism of palladium-catalyzed reactions. The reversibility of oxidative additions of acetic/formic acid and allylic carboxylates/carbonates with Pd0 complexes has been established and equilibrium constants have been determined. The isomerization of cyclic trans/cis cationic (η3-allyl)palladium(II) complexes is evidenced by a rate constant that depends on the Pd0 precursor: kinetic evidence for an SN2 mechanism that is responsible for the loss of stereoselectivity observed in catalytic reactions. Under conditions in which the oxidative additions are irreversible, the kinetics of the formation of cationic (η3-allyl)palladium(II) complexes has been monitored by conductivity measurements for the determination of the rate constants. By comparing the rate of disappearance of Pd0, it has been shown that oxidative additions of allylic carboxylates proceed in two steps with the detection of intermediate neutral, kinetic Pd0 complexes ligated to the allylic carboxylate unit. As an example of its application, the mechanism of a Stille reaction has been investigated by conductivity measurements of an ionic by-product in DMF. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003

Polynuclear Nickel(II) Complexes: Preparation and Magnetic Properties of NiII4, NiII5, and NiII6 Species with Ligands containing O∩X∩O (X = S, Se or N) Donor Atoms

Abstract: A family of bisphenol-containing ligands with XO2 donor atoms, where X = S, Se, or N, yields [NiII]4 (1) and (2), [NiII]5 (3), and [NiII]6 (4) complexes Complex 2, 3, and 4 have been structurally characterised by X-ray diffraction The compounds were characterised spectroscopically and by variable-temperature (2−295 K), variable-field (1, 4, and 7 T) magnetic susceptibility measurements Analysis of the magnetic data shows predominant ferromagnetic interactions between the nickel centres (SNi = 1) indicating “high-spin” ground states for 1, 2, and 3, whereas complex 4 shows antiferromagnetic interactions A plot of J vs Ni−O−Ni angles for all structurally characterised Ni4O4 cubane cores, including 2, irrespective of their symmetry, shows a large variation of J values within a small range of Ni−O−Ni angles A simple two-J model was found to be adequate to describe the magnetic properties of the hexanuclear complex, 4 (© Wiley-VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2003)

Theoretical Search for Anions Possessing Large Electron Binding Energies

Abstract: The vertical electron detachment energies (VDE) of several anions were calculated at the OVGF level with 6-311++G(d) basis sets The negatively charged species studied were chosen based on the observation that the largest electron binding energies for such systems are expected to be found for the anions whose neutral parents are polynuclear superhalogens The largest vertical electron binding energy of 1263 eV was found for Ta3F16−, and this is the largest excess electron binding energy of a molecular system reported in the literature thus far Moreover, the VDEs of 1263 and 1220 eV calculated for Ta3F16− and As3F16−, respectively, exceed the upper limit for the excess electron binding energy (thought to be 12 eV) Several other anions were also found [at the OVGF/6-311++G(d) level] to possess very large VDEs (ie Al2Br7−: 708 eV, Al2Cl7−: 775 eV, Al2F7−: 1116 eV, P2F11−: 1095 eV, V2F11−: 1098 eV, As2F11−: 1143 eV, and Ta2F11−: 1184 eV) (© Wiley-VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2003)

Elucidation of the Solution Structures of Transition Metal Complex Ion Pairs by NOE NMR Experiments

Abstract: Our results from structural investigations of transition metal complex ion pairs in solution by homonuclear and heteronuclear 1D- and 2D-NOE NMR spectroscopy are reviewed. Both model (A) and catalytically active (B) complexes have been taken into account; their general formulas are: trans-[ML2(N,X)(Y)(Z)]+A− (A) {M = FeII, RuII and OsII, L = PMe3, Y = CO, Z = COMe, A− = BPh3R−, CF3SO3−, BF4−, PF6− and B[3,5-(CF3)2C6H3]4−; M = IrIII, L = PR3, Y = Z = H and A− = BPh4−, CF3SO3−, BF4−, PF6−} and [M′(N,X)(R,olefin)]+A− (B) {M′ = Pt, R = Me, olefin = ethene, propene and CH2=CHCOOMe, A− = BF4−; M′ = Pd, (R,olefin) = η1,η2-5-methoxycyclooctenyl, A− = BPh4−, CF3SO3−, BF4−, PF6−, SbF6− and B[3,5-(CF3)2C6H3]4−}, where N,X = bis(pyrazolyl)methane, bipyridine, α-diimines, α-diamines or α-oxo imines. The detection of dipolar interionic interactions in 1H-NOESY and 19F,1H-HOESY NMR spectra allowed relative anion-cation orientations to be determined, these being well defined in most cases, with one orientation predominating in solution. We often found that the anion approaches the complexes from the side of the N,X-ligands, due to an accumulation of positive charge at the junction of the moieties containing the N- and X-donor atoms. In square-planar complexes B, the apparently favoured apical positions were often protected either by electronic factors [N,X = bis(2-pyridyl)amine or bis(pyrazolyl)methane] or by a combination of electronic and steric factors (N,X = α-diimines). For M′ complexes, bearing Ar−N=C(Me)−C(Me)=N−Ar ligands, the position of the counter-anion is finely modulated by the steric hindrance of the ortho-aryl substituents. The accessibility of the metal centre, which is directly associated with the catalytic performances of the complexes, was determined by using the counteranion as a probe. Finally, average interionic distances were estimated for model complexes A, bearing unsymmetrical BPh3R− counter-anions, based on the quantification of interionic NOEs. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2003)

A Novel Three‐Dimensional Metal‐Organic Framework Constructed from Two‐Dimensional Interpenetrating Layers Based on Trinuclear Cobalt Clusters: [Co3(btec)(C2O4)(H2O)2]n

Abstract: A novel coordination polymer [Co3(btec)(C2O4)(H2O)2]n (1; btec = 1,2,4,5-benzenetetracarboxylate) has been hydrothermally synthesized and characterized by IR, XPS, XRPD, TG analysis and single-crystal X-ray diffraction. The structural analysis reveals that 1 exhibits a new three-dimensional metal-organic framework constructed from two-dimensional parallel interpenetrating networks based on trinuclear cobalt cluster building blocks. Such interpenetrating composite networks in 1 represent the first example in the {M-btec} (M = transition metal) system. Variable-temperature magnetic susceptibility measurements indicate an antiferromagnetic behavior in 1. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Discrete Supramolecular Assemblies of Porphyrins Mediated by Coordination Compounds

Abstract: Metal-driven self-assembly has emerged as a viable alternative to covalent synthesis in the construction of large and sophisticated multi-porphyrin architectures, whose complexity and function begin to approach the properties of naturally occurring systems. The design and preparation of robust and shape-persistent discrete assemblies, obtained by coordination of meso-pyridylporphyrins to ruthenium, palladium and zinc centers, is comprehensively discussed in this microreview, that covers research in this field carried out by the authors at the University of Trieste in the last few years. NMR spectroscopy and X-ray crystallography were used jointly for the unambiguous characterization of the new species in solution and solid state, respectively. Very often the adducts of nanoscopic dimensions, in which the number, position, relative distance and orientation of the chromophores is well defined, were obtained through hierarchical supramolecular self-assembly: multi-porphyrin components were used as building blocks for the metal-mediated assembly of more elaborate architectures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Monomeric Magnesium and Calcium Complexes Containing the Bidentate, Dianionic 1,2-Bis[(2,6-diisopropylphenyl)imino]acenaphthene Ligand

Abstract: The reduction of 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (2,6-iPr2C6H3-BIAN) with metallic magnesium or calcium in THF affords the monomeric complexes (2,6-iPr2C6H3-BIAN)Mg(THF)3 (1) and (2,6-iPr2C6H3-BIAN)Ca(THF)4·(THF)1/2 (2). The crystallisation of 1 and 2 from benzene causes the removal of one of the coordinated THF molecules, yielding (2,6-iPr2C6H3-BIAN)Mg(THF)2·(C6H6)1/2 (3a) and (2,6-iPr2C6H3-BIAN)Ca(THF)3 (4). Repeated recrystallisation of 1 from benzene gives (2,6-iPr2C6H3-BIAN)Mg(THF)2·(C6H6)2 (3b). Although the crystals of 3a and 3b differ in colour and in their crystallographic parameters, their molecular dimensions are very similar. Recrystallisation of 1 from pyridine produces (2,6-iPr2C6H3-BIAN)Mg(py)3·(py)2 (5). Complexes 1−5 have been characterised by elemental analysis, UV, IR and 1H NMR spectroscopy, as well as by single-crystal X-ray diffraction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Investigating Actinyl Oxo Cations by X-ray Absorption Spectroscopy

Abstract: Early actinide elements (from U to Am) have the ability to form linear trans-dioxo complexes with formal valence of the actinide being equal to (V) or (VI). For instance, the ubiquity of the uranyl cation in uranium aqueous chemistry is the basis for its very important industrial and environmental concerns. As a result, the physical chemistry of the actinyl moieties has been the subject of constantly growing investigations. Among all the spectroscopic probes, X-ray absorption spectroscopy is a particularly useful element and energy-selective technique. This article reviews the investigation of molecular actinyl complexes using both XANES and EXAFS tools. The absorption edge features have long been used to characterize the frontier orbitals of the absorbing atom. In the case of actinide cations, the LIII edge, located in the hard X-ray region, provides a useful fingerprint of the cation polyhedron. Tentatively, simple molecular orbital considerations together with full multiple scattering simulation codes have provided significant interpretations of the edge features. Various examples involving a distortion of the actinyl coordination sphere, starting from the aqueous species are given. Complementary structural data can be obtained in the EXAFS region of the absorption spectrum. In the literature, such molecular systems have been well documented from uranyl aqueous chemistry to neptunyl or plutonyl coordination complexes with oxygen donor ligands. Furthermore, complexation mechanisms upon absorption onto mineral surfaces have been increasingly investigated over the past few years. Overall, contribution of the XAS technique to a better understanding of the actinide bonding is demonstrated from various examples of the literature and the authors’ data. Importance of the simulation codes in order to better describe the absorption features is also strongly underlined. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)