Synthesis and characterization of [Cp*Fe-dicyclopenta(a,f)naphthalene-FeCp*] and [Cp*Fe-dicyclopenta(a,f)naphthalene-FeCp*] BF4

[Cp*Fe-dicyclopenta(a,f)naphthalene-FeCp*]ⁿ⁺ (Cp*=pentamethylciclopentadiene, n=0, 1), respectively named complexes V and VI, were synthesized and characterized. The X-ray structure has been solved and ¹H-, ¹³C-NMR and elemental analysis were performed for the n=0 complex. Cyclic voltammetry showed a potential difference of 360 mV within the two redox peaks. An absorption band at 850 nm was assigned to an intervalence band. The Mössbauer investigations show a uniform Fe²⁺ environment for the neutral compound and two sites, assigned to Fe²⁺ and Fe³⁺ for the monoxidized compound. The information gathered by all the previously mentioned techniques indicates that the studied binuclear compound belongs to the mixed valence class II using Robin and Day classification.     

用于设计分子导线和分子开关的双核混价配合物

分子电子器件的研制是近年来的一个热点课题，桥联混价双核配合物是分子导线和分子开关研究的理想模型化合物，本文介绍了桥配体导电性的测量评估方法和分子开关的主要类型，并着重介绍了近年来用于这一领域研究的重要配合物体系。     

Organometallic Triskelia: Novel Tris(vinylideneruthenium(II)), Tris(alkynylruthenium(II)), and Triruthenium–Triferrocenyl Complexes

Incorporation of a redox-passive bridge affords three identical redox systems in the triskelion-shaped, carbon-rich, polyvinylidenemetal complex 1 . The complex was isolated from the activation of the tripodal polyyne 1,3,5-(HC≡CC₆H₄C≡C)₃C₆H₃ with [RuCl₂({(Ph₂P)₂C₂H₄}₂] and further converted into polyynylmetal complexes and a triple ferrocenyl-substituted ruthenium complex.     

Synthesis and Structure of [NbCl3{[NPPh2(C5H4)]2Fe}]: The First Structurally Characterised Complex Containing a Chelating Di(phosphaneiminato) Ligand

Reaction of [Fe{(C₅H₄)PPh₂=NSiMe₃}₂] with niobium pentachloride affords the chelate complex [NbCl₃{[NPPh₂(C₅H₄)]₂Fe}].     

Molecular orbital calculations of binuclear systems of Fe, Co and Ni derivatives of pentalene, s-indacene and as-indacene

Extended Hückel calculations on a whole family of dinuclear complexes of pentalene, s-indacene and as-indacene allow a general rationalization of the structural and physical features of these compounds, mainly based on their electron count.     

Organoiron activation combined with electron- and proton transfer: implications in biology, organic synthesis, catalysis and nanosciences

This Account summarizes the results obtained in our research group on the intra- and intermolecular organoiron activation of substrates by combining the coordination of arenes by CpFe^+/0 and electron and/or proton transfer. The concepts involved are those of electron and proton reservoirs, activation of O₂ by single electron transfer in solution, mimic and inhibition of the reactivity of superoxide radical anion, materials synthesis (for instance fullerene anions), electronic communication between two metals connected by a hydrocarbon bridge, activation of arene ligands for multiple functionalization, giant dendrimer synthesis and electron transfer in catalysis (redox and electron-transfer-chain).     

Synthesis of two-coordinate iron aryloxides and their reactions with organic azide: Intramolecular C-H bond amination

The synthesis and reaction of homoleptic iron(II) complexes with 2,6-di-adamantyl-substituted aryloxides [OC₆H₂-2,6-Ad-4-R]⁻ ([OAr^AdR]⁻, Ad = adamantyl, R = Me, ⁱPr) are described. Monomeric two-coordinate iron aryloxides Fe(OAr^AdR)₂ (R = Me, 1; ⁱPr, 2) were synthesized by the reaction of Fe[N(SiMe₃)₂]₂ with 2 equiv of HOAr^AdR. Treatment of 1 and 2 with 1-azidoadamantane resulted in intramolecular insertion of an adamantyl nitrene into a methylene C-H bond of the aryloxide adamantyl substituent, yielding the corresponding amine-aryloxide complexes Fe(OAr^AdR)(OAr^AdR-NHAd) (R = Me, 3; ⁱPr, 4). Molecular structures of all these complexes are reported.     

The synthesis and characterization of ( E,E )-dioxime and its transition metal complexes containing 12-membered macrocycles linked to ferrocenyl-methyl groups

13,14-bis(Hydroxyimino)-4,7-bis(ferrocenylmethyl)-2,3,4,5,6,7,8,9-octahydrobenzo[k]-4, 7-diaza-1,10-dithiacyclododecine[13,14-g]-quinoxaline (H₂L) has been prepared from (E,E)-dichloroglyoxime and 12,13-diamino-4,7-bis(ferrocenylmethyl)-2,3,4,5,6,7,8,9-octahydrobenzo[k]-4,7-diaza-1,10-dithiacyclododecine which was synthesized from 12,13-dinitro-4,7-bis(ferrocenylmethyl)-2,3,4,5,6,7,8,9-octahydrobenzo[k]4,7-diaza-1,10-dithia cyclododecine. Mononuclear nickel(II) and copper(II) complexes of H₂L have a metal-ligand ratio of 1?:?2 and the ligand coordinates through two nitrogen atoms, as do most (E,E)-dioximes. The homotrinuclear [Cu(L)₂Cu₂(dipy)₂](NO₃)₂ compound coordinates to the other two copper(II) ions through deprotonated oximate oxygens and two 2,2′-dipyridyl as an end-cap ligand to yield the trinuclear structure. The ligand and its complexes have been characterized on the basis of ¹H, ¹³C NMR, IR and MS spectroscopy and elemental analyses.     

cis- and trans-Bis(pyridine)chromium(III) complexes containing mixed-valence chrysenesemiquinonate–chrysenecatecholate ligands: Synthesis,characterization and interpretation of the electronic absorption spectra using ZINDO/S method

Two new geometrical isomers of [Cr(py)₂(chrySQ)(chryCat)] (chrySQ = chrysenesemiquinonate; chryCat = chrysenecatecholate; py = pyridine) were synthesized by two different synthetic procedures. In the first, an acetonitrile solution containing a stoichiometric mixture of Cr(CO)₆, chrysenequinone and pyridine was photolyzed with a Hg-lamp. The second procedure was based on substituting one of the chrysenesemiquinonate ligand in the tris-[Cr(chrySQ)₃] complex with two pyridine ligands. In both procedures two isomeric forms of [Cr(py)(chrySQ)(chryCat)] were isolated with the trans-isomer obtained in higher yield. The structures of the two isomers have been modeled using parameterized PM3 semiempirical method. Theoretical harmonic vibrational frequencies of the cis- and trans-isomers have been computed and compared with the experimental vibrational frequencies. Variable-temperature magnetic susceptibility has been studied for the two isomers in the 10–300 K temperature range. Theoretical modeling of the magnetic data indicated strong antiferromagnetic exchange interaction between Cr^III (S = 3/2) and chrySQ (S = 1/2) with J = −365 ± 6 and −395 ± 4 cm⁻¹ for the cis- and trans-isomers, respectively. The electrochemical behavior of cis- and trans-[Cr(py)₂(chrySQ)(chryCat)] complexes were studied by cyclic voltammetry in acetonitrile solvent. Both complexes showed two one-electron redox processes attributable to reversible reduction and oxidation of the chrySQ and chryCat ligands. Reduction of the Cr(III) to Cr(II) was observed for both complexes near−1300 mV. The electronic spectra of the two isomers were dominated by charge-transfer (LMCT, MLCT and ILCT) transitions. In addition, a low-energy intervalence charge-transfer (IVCT) transition was observed for the cis-isomer at 1085 nm. Theoretical studies of the electronic spectra by ZINDO/S-CI method were useful in interpreting the observed electronic transitions.     

Inclusion compounds: The products of the interaction of silicon,germanium and boron fluorides with crown ethers

This review deals with the problem of the interaction of Si(IV), Ge(IV) and B(III) fluorides with crown ethers and their aza analogues. The crystallographic structures have been determined of the stable products obtained by the interaction of H₂SiF₆ solution with the following crown ethers: 18-crown-6 (18C6), monoaza-18C6 (MA18C6), 1,10-diaza-18C6 (DA18C6) and 1,7-diaza-15C5 (DA 15C5). The complexes obtained are stabilized by a system of H-bonds of the O-H... O, N-H. ... O, N-H...F and O-H ... F types. For H₂GeF₆ the adducts obtained are similar to those obtained using H₂SiF₆. The crystal structures of three new boron fluoride-containing complexes with 18-membered crown ethers are also described. During macrocycle complexation the guest entities undergo chemical transformations which are stabilized by creation of the H- bond system. The results of vibrational and NMR spectra are also discussed.Presented at the Sixth International Seminar on Inclusion Compounds, Istanbul, Turkey, 27–31 August, 1995.     

Pentacyanido(L)ferrate(III) complexes: Crystal structures, electrochemical and DFT studies (L = pyrazine, 4,4′-bipyridine, azide)

The crystal structures of two pentacyanido(L) ferrate(III) complexes, [P(C₆H₅)₄]₂[Fe(CN)₅(prz)]·4H₂O 1, [P(C₆H₅)₄]₂[Fe(CN)₅(4,4′-bipy)]·3H₂O 2, have been solved. Within the two complex anions the iron atoms are hexacoordinated by five cyanido ligands, the sixth position being occupied by the nitrogen atom arising from pyrazine and, respectively, 4,4′-bipyridine. The electrochemical properties of compounds 1, 2 and of the azido derivative, (Ph₄As)₂[Na(H₂O)₄][Fe(CN)₅(N₃)] 3, have been investigated by cyclic voltammetry. A relatively complicated redox behavior of these complexes was found, due especially to the electron transfer involving the central metallic ion that changes reversibly its oxidation state (Fe^III/Fe^II redox site) and also to the coligand (4,4′-bipyridine, pyrazine or azide) which intervenes in a distinct electron transfer. The experimental data have been rationalized through DFT calculations.     

Compromise between conjugation length and charge-transfer in nonlinear optical η-monocyclopentadienyliron(II) complexes with substituted oligo-thiophene nitrile ligands: Synthesis, electrochemical studies and first hyperpolarizabilities

A systematic series of η⁵-monocyclopentadienyliron(II) complexes with substituted oligo-thiophene nitrile ligands of general formula [FeCp(P_P)(NC{SC₄H₂}_nNO₂)][PF₆] (P_P = dppe, (+)-diop; n = 1-3) has been synthesized and characterized. The electrochemical behaviour of the new compounds was explored by cyclic voltammetry. Quadratic hyperpolarizabilities (β) of the complexes with dppe coligands have been determined by hyper-Rayleigh scattering (HRS) measurements at two fundamental wavelengths of 1.064 and 1.550 μm, to uncover the two-photon resonance effect and to estimate static β values. The obtained overall results are found to be better than for the related η⁵-monocyclopentadienyliron(II) complexes with p-benzonitrile derivatives. Although an increase of the resonant β at 1.064 μm with increasing number of thiophene units in the conjugated ligand was found (up to 910 × 10⁻³⁰ esu), the static values β₀ remain practically unchanged, as shown by the 1.550 μm measurements. Combined with the electrochemical and spectroscopic data (IR, NMR, UV-vis), this remarkable evolution of β shows that the increase of conjugation length is balanced by a decrease in charge-transfer efficiency.     

Review: Natural oxalates and their analogous synthetic complexes

Metal oxalates, commonly classified as organic minerals, are widely distributed in Nature, occurring in mineral deposits or as biominerals in plants, fungi, and lichens or in the form of deposits, of different kinds, in animal tissues. Eighteen natural species of this type have so far been reported and investigated. In the first part of this review we give an overview on the general characteristics of these minerals, including also some comments on their environmental effects. The central part of the review is devoted to the discussion of synthetic oxalates, analogous to the natural species, including the usual procedures employed for their synthesis and the thorough analysis of their crystallographic and structural peculiarities. The thermal, spectroscopic, and magnetic properties of these complexes are also discussed in detail. Some comparisons with related coordination compounds are also made along the text.     

Reaction of Selenium with Bromine in the Presence of Methyltriphenylphosphonium Bromide: Syntheses and Crystal Structures of [PMePh3]2[Se2Br6] and [PMePh3]2[SeBr6(SeBr2)2]

The brown crystals of [PMePh₃]₂[Se₂Br₆] ( 1 ) and red crystals of [PMePh₃]₂[SeBr₆(SeBr₂)₂] ( 2 ) were obtained when selenium and bromine reacted in the solution of acetonitrile in the presence of methyltriphenylphosphonium bromide. The crystal structures of 1 and 2 has been determined by the X‐ray methods and refined to R = 0.0373 for 2397 reflections and 0.0397 for 3417 reflections, respectively. The salt 1 crystallizes in the monoclinic space group P2₁/n with the cell dimensions a = 13.202(5) Å, b = 11.954(4) Å, c = 13.418(6) Å, β = 93.08(4)° (193(2)). The crystals of 2 are triclinic, space group with the cell dimensions a = 10.266(3) Å, b = 11.311(3) Å, c = 11.619(2) Å, α = 108.87(2)°, β = 105.72(2)°, γ = 99.40(2)° (193(2) K). In the solid state structure of 1 the dinuclear hexabromo‐diselenate(II) anion is centrosymmetric and consists of two distorted almost square planar SeBr₄ units sharing a common edge through two μ‐bridging Br atoms. The terminal Se^II–Br bonds are 2.3984(11) and 2.4273(11) Å, whereas the bridging μBr–Se^II bonds are 2.7817(11) and 2.9081(12) Å. In the solid state the trinuclear [SeBr₆(SeBr₂)₂]^2? anion of 2 is centrosymmetric too and contains a nearly regular [SeBr₆] octahedron where the four equatorial bromo ligands each have developed bonds to the Se^II atoms of the SeBr₂ molecules. The contacts between the bridging bromo and the Se^II atoms of the SeBr₂ molecules are 3.0603(15) and 3.1043(12) Å, and can be interpreted as bonds of the donor‐acceptor type with the bridging bromo ligands as donors and the SeBr₂ molecules as acceptors. The Se^IV–Br distances are in the range 2.5570(9)–2.5773(11) Å and the Se^II–Br bond lengths in coordinated SeBr₂ molecules – 2.3411(12) and 2.3421(10) Å.     

The formation of homogeneous and heterogeneous 2:1 complexes between dialkyl- and diarylammonium ions and α-cyclodextrin and cucurbit[6]uril in aqueous formic acid

Dialkyl- and diarylammonium ions are able to form complexes with α-cyclodextrin and cucurbit[6]uril. These amines are able to complex two guest molecules simultaneously resulting in the formation of homogeneous or heterogeneous 1:2 (ratio of dialkylammonium to ligand) complexes. The stability constants and reaction enthalpies for the formation of 1:1 complexes have been measured using potentiometric and calorimetric titrations. Differences between the values obtained by these methods can be attributed to solvent composition. Only for the 1:2 complex formation with cucurbit[6]uril, the ligands influenced each other. The polar carbonyl groups at each portal of the cucurbit[6]urils interacted simultaneously with the protonated amino group resulting in an electrostatic repulsion between both molecules. No further interactions between two complexed molecules of α-cyclodextrin or cucurbit[6]uril and α-cyclodextrin were observed. The absence of polar groups in the case of α-cyclodextrin led to unaffected formation of homogeneous and even heterogeneous 1:2 complexes.     

Inclusion Complexation of Loratadine with Natural and Modified Cyclodextrins: Phase Solubility and Thermodynamic Studies

The extent and mode of solubility enhancement exerted by the cyclodextrins (α-, β-, γ-, and HP-β-CDs) on loratadine (Lort) have been experimentally measured under controlled conditions in buffered aqueous solutions. Rigorous nonlinear regression analysis of the phase solubility diagrams obtained in 0.1 mol⋅L⁻¹ phosphate buffer at pH=7.0 and 25 °C revealed the following: neutral Lort (pK _a =4.6) tends to form soluble 1:1 and 1:2 Lort/CD complexes with all four of the examined CDs, where complex stability follows the decreasing order β-CD>HP-β-CD>γ-CD>α-CD. The hydrophobic character of Lort constitutes about 66% of the driving force for complex formation whereas specific interactions contribute 11.2 kJ⋅mol⁻¹ towards the stability of the complexes. Thermodynamic studies showed that Lort/CD complex formation was favored by large enthalpic contributions but was impeded by negative entropic changes. Dissolution studies indicate that the dissolution rate of Lort from the freeze-dried Lort/β-CD complex is significantly higher than that of the corresponding physical mixture. Both DSC studies and molecular mechanical modeling of Lort/β-CD interactions were carried out to explore the possible formation of inclusion complexes.     

Molecular recognition by β-cyclodextrin derivatives: molecular dynamics, free-energy perturbation and molecular mechanics/ Poisson–Boltzmann surface area goals and problems

 The complexation of p-tert-butylphenyl p-tert-butylbenzoate and N-(p-tert-butylphenyl)-p-tert-butylbenzamide with a β-cyclodextrin derivative formed by two cyclodextrin units linked by a disulfide bridge on one of the C6 atoms has been studied by computational methods. The better amide solubility and the better internal interactions of the ester complex explain the experimentally observed better association constant for the ester. The free-energy perturbation methodology and molecular mechanics/Poisson–Boltzmann surface area analysis have been used to explain the problem and to compare the results. Received: 14 April 2002 / Accepted: 11 August 2002 / Published online: 4 November 2002 Acknowledgements. The Kollman group at the University of California San Francisco is gratefully acknowledged for support and encouragement throughout all this study. The authors thank UAB for inland and outland fellowships to I.B.. Financial support was obtained from grant no. PPQ2000-0369 from the “Ministerio de Ciencia y Tecnologia” (Spain). Intensive computations were performed either with the computers of the Kollman group or with those of CESCA-C⁴ (Catalonia, Spain). Correspondence to: C. Jaime e-mail: carlos.jaime@uab.es     

Trigonal (-3) symmetry octahedral lanthanide(III) complexes of zwitterionic tripodal ligands: luminescence and magnetism

Sandwich coordination complexes, [Ln^III(H₃L)₂]X₃?solvents, of Tb(III), Eu(III), Dy(III), Ho(III) and Er(III) were prepared with two new zwitterionic ester-substituted tripodal amine ligands, tris((2-hydroxy-5-n-butyl benzoate)aminoethyl)-amine (H₃L¹) and tris((2-hydroxy-5-methyl benzoate)aminoethyl)-amine (H₃L²). These ligands were synthesised by condensation of the appropriately substituted salicylaldehyde with tris(2-aminoethyl)amine (tren) followed by in situ reduction of the tris-imine to tris-amine. Subsequent 2:1 reaction with lanthanide(III) ions yields [Ln^III(H₃L)₂]X₃?solvents (L = L¹, L²; X = Cl^?, NO₃^?; solvents = MeOH or H₂O). All complexes were characterised by microanalysis, infrared spectroscopy, high resolution mass spectrometry and solid-state photoluminescence measurements. The crystal structures of [Tb^III(H₃L¹)₂]Cl₃·6MeOH, [Dy(H₃L¹)₂]Cl₃·6MeOH, [Eu^III(H₃L¹)₂]Cl₃·6MeOH and [Tb^III(H₃L¹)₂](NO₃)₃ reveal high-crystallographic ?3 symmetry at the O₆-coordinated octahedral lanthanide(III) ions and that the tripodal ligands are bound in zwitterionic form: the protons from the phenolic oxygens have migrated to the amino nitrogens. Photoluminescence measurements indicate various degrees of energy transfer of the ligand chromophore to the lanthanide ions, as both ligand and lanthanide emission features are observed. Despite the high-crystallographic symmetry and the likely small transverse magnetic anisotropy of the complexes, no evidence of slow relaxation of the magnetisation, characteristic of a single-molecule magnet, was observed for [Tb^III(H₃L¹)₂]Cl₃·MeOH·3H₂O, [Dy^III(H₃L¹)₂]Cl₃·6H₂O, [Ho^III(H₃L¹)₂](NO₃)₃·2H₂O, [Er^III(H₃L¹)₂]·H₂O and [Tb^III(H₃L¹)₂](NO₃)₃ down to 2.0 K.     

Review: an overview of recent developments in coordination chemistry of polypyrazolylmethylamines. Complexes with N-scorpionate ligands created in situ from pyrazole derivatives and zerovalent metals

This paper reviews the coordination chemistry of polypyrazolylmethylamines as tripodal tetradentate (L^S = N,N,N-tris(3,5-dimethylpyrazol-1-ylmethyl)amine) and dipodal tridentate (L^D = N,N,-bis(3,5-dimethylpyrazol-1-ylmethyl)amine) ligands. References to the methods for the synthesis of both the ligands alone and their transition metal complexes are given with emphasis placed on the structural features of the latter. Special attention was paid to the one-pot synthesis, which is a new method for isolation of various metal complexes with N,N-bis- and N,N,N-trispyrazolylmethylamines and co-ligands, such as urotropine and 3,5-dimethylpyrazole. The complexes in question were created in situ from 1-hydroxymethyl-3,5-dimethylpyrazole (L⁰) and zerovalent metals.