Tuning of Magnetic Anisotropy in Hexairon(III) Rings by Host–Guest Interactions: An Investigation by High-Field Torque Magnetometry

Full chemical control of magnetic anisotropy in hexairon(III ) rings can be achieved by varying the size of the guest alkali metal ion. Dramatically different anisotropies characterize the Li^I and Na^I complexes of [Fe₆(OMe)₁₂(L)₆] (L=1,3-propanedione derivatives; a schematic representation of the Li^I complex is shown), as revealed by high-field torque magnetometry—Iron: (g), oxygen: ○, carbon: ○, Li⁺: ⊕.     

Einfluss von H‐Brückenbindungen auf die Jahn–Teller‐Verzerrung in den Kettenstrukturen von 2,2′‐bipyMn(H2PO4)F2·H2O und 2,2′‐bipyMn(H2PO4)2F

In the system 2,2′‐bipyridine/Mn^III/HF/H₃PO₄/H₂O two compounds with chain structures could be prepared and characterised by X‐ray structure analyses. 2,2′‐bipyMn(H₂PO₄)F₂·H₂O ( 1 ): monoclinic, twinned, space group P2₁/c, Z = 4, a = 6.7883(4), b = 10.9147(5), c = 17.8102(8) Å, β = 100.142(4)°, R = 0.0328. 2,2′‐bipyMn(H₂PO₄)₂F ( 2 ): triclinic, space group P , Z = 2, a = 6.675(1), b = 10.715(1), c = 11.013(1) Å, α = 107.595(9)°, β = 90.994(9)°, γ = 95.784(8)°, R = 0.0252. Both compounds show chain structures with trans‐bridging dihydrogenphosphate ligands and bipy and two fluorine ligands for ( 1 ), or bipy, fluorine and an additional dihydrogenphosphate, respectively, for ( 2 ) in equatorial positions. Due to the pseudo‐Jahn–Teller effect, Mn^III shows elongated octahedral coordination with ferrodistortive ordering along the chain direction. The distortion is remarkably higher in ( 1 ) than in ( 2 ). This is discussed in context with additional hydrogen bonds along the chain in ( 2 ).     

A Microporous Lanthanide–Organic Framework

Stable zeolite-like microporosity , even in the absence of guest molecules, is exhibited by a lanthanide–benzenedicarboxylate (BDC) framework, which was synthesized by the copolymerization of Tb^III and 1,4-benzenedicarboxylic acid. The open Tb–BDC framework adopts an expanded PtS network structure (see diagram; Tb: open circles; C: full circles; lines connecting Tb to C represent O atoms, and those connecting C atoms are benzene rings) and is capable of reversible gas and liquid sorption.     

Structural Diversity of Metallosupramolecular Assemblies from Cu(phen)2+ (phen = 1,10‐Phenanthroline) Building Blocks and 4,4′‐Bipyridine

Attempts to crystal engineer metallosupramolecularcomplexes from Cu(phen)²⁺ building blocks and the prototypical,rod‐like, exo‐bidentate ligand 4,4′‐bipyridine (4,4′‐bipy) by layering techniques are described. Reactions of Cu(phen)²⁺ (phen = 1,10‐phenanthroline) with 4,4′‐bipy in the presence of NO₃^– counterions yielded two distinct, discrete, dinuclear, C_i symmetric, dumbbell‐typecomplexes, [{Cu(NO₃)₂(phen)}₂(4,4′‐bipy)] ( 1 ) and [{Cu(NO₃)(phen)(H₂O)}₂(4,4′‐bipy)](NO₃)₂ ( 2 ), depending upon the mixture of solvents used for crystallization. In compound 1 , a mono‐ and a bidentate nitrato group coordinate to Cu²⁺, whereas in 2 the monodentate nitrato groups are replaced by aqua ligands, which introduce additional hydrogen‐bond donor functionality to the molecule. The crystal structure of 1 was determined by single‐crystal X‐ray analysis at 296 and 110 K. Upon cooling, a disorder‐order transition occurs, with retention of the space group symmetry. The crystal structure of 2 at room temperature was reported previously [Z.‐X. Du, J.‐X. Li, Acta Cryst. 2007 , E63, m2282]. We have redetermined the crystal structure of 2 at 100 K. A phase transition is not observed for 2 , but the low temperature single‐crystal structure determination is of significantly higher precision than the room temperature study. Both 1 and 2 are obtained phase‐pure, as proven by powder X‐ray diffraction of the bulk materials. Crystals of [Cu(phen)(CF₃SO₃)₂(4,4′‐bipy) · 0.5H₂O]_n ( 3 ), a one‐dimensional coordination polymer, were obtained from [Cu(CF₃SO₃)₂(phen)(H₂O)₂] and 4,4′‐bipy. In 3 , Cu(phen)²⁺ corner units are joined by 4,4′‐bipy via the two vacant cis sites to form polymeric zig‐zag chains, which are tightly packed in the crystal. Compounds 1 – 3 were further studied by infrared spectroscopy.     

A comparison of ground- and excited-state properties of [Ru(bz)2]2+ and bis(η6-benzene)ruthenium(II) p-toluenesulfonate using the density functional theory

The ground- and excited-state properties of both [Ru(bz)₂]²⁺ and crystalline bis(η⁶-benzene)ruthenium(II) p-toluenesulfonate are investigated using the density functional theory. A symmetry-based technique is employed to calculate the energies of the multiplet structure splitting of the singly excited triplet states. For the crystalline system, a Buckingham potential is introduced to describe the intermolecular interactions between the [Ru(bz)₂]²⁺ system and its first shell of neighbor molecules. The overall agreement between experimental and calculated ground- and excited-state properties is good, as far as the absolute transition energies, the Stokes shift, and the geometry of the excited states are concerned. The calculated d-d excitation energies of the isolated cluster are typically 1000–2000 cm⁻¹ too low. An energy lowering is obtained in a_1g→e_1g(³E_1g) excited state when the geometry of [Ru(bz)₂]²⁺ is bent along the e_1u Renner–Teller active coordinate. It vanishes as the crystal packing is taken into account. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1343–1353, 1999     

MnII[MnII(CN)4]—A Magnetic Interpenetrating Three-Dimensional Diamondlike Solid

Three-dimensional extended diamondlike networks containing four-coordinate metal centers can be constructed from [Mn^II(CN)₄]²⁻ building blocks. Besides the title compound, which was prepared and its magnetic properties studied in detail, other novel magnetic solids might be able to be synthesized.     

Steric Control of the Electronic Ground State in Six-Coordinate Copper(II) Complexes

Replacing the 3- and 3′′-protons of the ligand 2,6-di(pyrazol-1-yl)pyridine L by mesityl groups changes the electronic ground state of [Cu(L)₂]²⁺ complexes from {d}¹ to {d}¹. This is the best example so far for a “homoleptic” Jahn–Teller-compressed six-coordinate Cu^II complex.     

Cover Picture: “Half‐Bonds” in an Unusual Coordinated S42− Rectangle (Chem. Asian J. 2/2009)

This stone lantern is known as the “Koto‐ji”, or “harp‐tuner”, as it resembles the tuning bridge of the Japanese koto. The six windows of the lantern are said to symbolize the six essential attributes of a perfect garden, such as the one it overlooks: spaciousness, seclusion, artifice, antiquity, abundant water, and broad views. R. Hoffmann et al. report on two synthesized compounds containing the unusual S₄^2? rectangles bound to either Ir or Rh fragments, illuminated by the two lamp windows. Like the Koto‐ji lantern, this paper, which suggests the presence of S? S half‐bonds, sheds some light in the garden of beautiful compounds. For more information, see their Full Paper on page 302 ff .

     

[Mn(en)]3[Cr(CN)6]2⋅4 H2O: A Three-Dimensional Dimetallic Ferrimagnet (Tc=69 K) with a Defective Cubane Unit

The first modified analogue of the A^II₃[B^III(CN)₆]₂⋅x H₂O type of Prussian-Blue, the title compound, has a three-dimensional network structure extended by Cr^III-CN-Mn^II linkages, which is based on a defective cubane unit comprising three Cr and four Mn ions (see structure), and shows ferrimagnetic ordering below 69 K.     

A New Anion-Trapping Radical Host, [(Cu-dppe)3{hat-(CN)6}]2+

Anions PF ₆ ⁻ and CF ₃ SO ₃ ⁻ are trapped by the new radical host [(Cu-dppe)₃{hat-(CN)₆}]²⁺, which was synthesized in a one-pot reaction from a copper(I ) source, hat-(CN)₆, and dppe in acetone. The trapped salts have been characterized both in solution and in the solid state (see picture: A⁻: PF₆⁻, CF₃SO₃⁻). hat-(CN)₆=hexaazatriphenylene hexacarbonitrile; dppe=1,2-bis(diphenylphosphanyl)ethane.     

Magnetic Anisotropy in “Scorpionate” First‐Row Transition‐Metal Complexes: A Theoretical Investigation

In this work we have analyzed in detail the magnetic anisotropy in a series of hydrotris(pyrazolyl)borate (Tp^?) metal complexes, namely [VTpCl]⁺, [CrTpCl]⁺, [MnTpCl]⁺, [FeTpCl], [CoTpCl], and [NiTpCl], and their substituted methyl and tert‐butyl analogues with the goal of observing the effect of the ligand field on the magnetic properties. In the [VTpCl]⁺, [CrTpCl]⁺, [CoTpCl], and [NiTpCl] complexes, the magnetic anisotropy arises as a consequence of out‐of‐state spin–orbit coupling, and covalent changes induced by the substitution of hydrogen atoms on the pyrazolyl rings does not lead to drastic changes in the magnetic anisotropy. On the other hand, much larger magnetic anisotropies were predicted in complexes displaying a degenerate ground state, namely [MnTpCl]⁺ and [FeTpCl], due to in‐state spin–orbit coupling. The anisotropy in these systems was shown to be very sensitive to perturbations, for example, chemical substitution and distortions due to the Jahn–Teller effect. We found that by substituting the hydrogen atoms in [MnTpCl]⁺ and [FeTpCl] by methyl and tert‐butyl groups, certain covalent contributions to the magnetic anisotropy energy (MAE) could be controlled, thereby achieving higher values. Moreover, we showed that the selection of ion has important consequences for the symmetry of the ground spin–orbit term, opening the possibility of achieving zero magnetic tunneling even in non‐Kramers ions. We have also shown that substitution may also contribute to a quenching of the Jahn–Teller effect, which could significantly reduce the magnetic anisotropy of the complexes studied.     

Structure,Magnetic Properties and Catalase-like Activity of Asymmetric Dimanganese(III,III) Carboxylate Complexes with Salicylaldimine Ligands

The crystal structures, magnetic properties, and catalase-like activities of assymmetric dinuclear manganese(III, III) complexes, [Mn₂^{III, III}(spa)₂(μ-Me₃CCO₂)(Me₃CCO₂)(CH₃OH)] ( 1 ) and [Mn₂^{III, III}(vpa)₂(μ-Me₃CCO₂)(Me₃CCO₂)(CH₃OH)] ( 2 ), (H₂spa = 3-salicyclideneamino-1-propanol, H₂vpa = O-vanillin), were reported. The crystal structures of complexes 1 and 2 consist of the same discrete asymmetric coordination environment of dinuclear clusters, where the two manganese atoms are bridged by two alkoxo oxygens of the spa or vpa ligands and one bidentate carboxylate ion, whereas an additional oxygen atom of monodentate carboxylate coordinated to the first metal ion, and the second metal ion was coordinated by one oxygen atom of the solvent CH₃OH. Magnetic investigations (2–300 K) reveal an intramolecular antiferromagnetic spin exchange interaction with axial-field splittings: J = ?12.3 cm^?1 (D = ?0.10 cm^?1) and J = ?13.3 cm^?1 (D = ?0.15 cm^?1) for complexes 1 and 2 , respectively. The complexes should show catalase-like activity for H₂O₂ disproportionation in CH₃OH solvent at 25° with rate constants of k = 6.35 dm³moI^?1s^?1 and 6.20 dm³mol^?1s^?1 for complexes 1 and 2 , respectively.     

Probing the Origin of Magnetic Anisotropy in a Dinuclear {MnIIICuII} Single‐Molecule Magnet: The Role of Exchange Anisotropy

Using ab initio calculations all the components of the magnetic anisotropy in a dinuclear [Mn^IIICu^IICl(5‐Br‐sap)₂(MeOH)] single‐molecule magnet (SMM) have been computed. These calculations reveal that apart from the single‐ion anisotropy, the exchange anisotropy also plays a crucial role in determining the sign as well as the magnitude of the cluster anisotropy. Developed magneto‐structural correlations suggest that a large ferromagnetic exchange can in fact reduce the ground‐state anisotropy, which is an integral component in the design of SMMs.     

Analysis of the Symmetry of Crystal Packing Forces by Methyl Proton Tunneling: A Strategy for the Unambiguous Assignment of the Magnetic Jahn – Teller Effect in Molecules

Intrinsic and extrinsic forces behind the distortion in metal atom clusters can be readily distinguished provided that the clusters are embedded in a suitable ligand environment and that the tunneling of the protons in the peripheral ligands is then analyzed by inelastic neutron scattering. For the [Cr₃O(OOCCH₃)₆(H₂O)₃]Cl⋅6 H₂O model system studied, the tunneling process is very sensitive to the local environment. Thus a tool is available to allow a better assessment of the cause of structural distortions.     

Self-Assembly of Novel Polyrotaxanes: Main-Chain Pseudopolyrotaxanes with Poly(ester crown ether) Backbones

Not threading rings on chains, but chains through rings results in a new class of main-chain polyrotaxanes. The cations of bipyridinium salts thread through the crown ether units of a poly(ester crown ether) chain (shown below). The threading efficiency m/n of the polyrotaxane is controlled by stoichiometry and temperature.     

Calixarenes,Macrocycles with (Almost) Unlimited Possibilities

The condensation reaction between p-tert-butylphenol and formaldehyde leads in a single step to good yields of cyclic oligomers in which, depending on the reaction conditions, either four, six, or eight phenol units are joined by methylene bridges. The beakerlike shape of the most stable conformation of the tetramer has led to their being given the name “calixarenes” (calix = chalice). Resorcinol can undergo condensation in a similar manner with a variety of aldehydes to afford cyclic tetramers with the same basic structure (the resorcarenes). In both cases the reaction does not require the use of dilution techniques, so that large quantities of product can be readily obtained. In addition, the parent compounds can be modified in various ways, in particular at the phenolic hydroxy groups or the phenyl residues; these approaches can be used separately or in combination. Calixarenes are thus ideal starting materials for the synthesis of various types of host molecules and can also act as building blocks for the construction of larger molecular systems with defined structures and functions. Their potential applications range from use as highly specific ligands for analytical chemistry, sensor techniques and medical diagnostics to their use in the decontamination of waste water and the construction of artificial enzymes and the synthesis of new materials for non-linear optics or for ultrathin layers and sieve membranes with molecular pores.     

Struktur und magnetische Eigenschaften von Bis{3‐amino‐1,2,4‐triazolium(1+)}pentafluoromanganat(III): (3‐atriazH)2[MnF5]

Structure and Magnetic Properties of Bis{3‐amino‐1,2,4‐triazolium(1+)}pentafluoromanganate(III): (3‐atriazH)₂[MnF₅] The crystal structure of (3‐atriazH)₂[MnF₅], space group P1, Z = 4, a = 8.007(1) Å, b = 11.390(1) Å, c = 12.788(1) Å, α = 85.19(1)°, β = 71.81(1)°, γ = 73.87(1)°, R = 0.034, is built by octahedral trans‐chain anions [MnF₅]^2–_∞ separated by the mono‐protonated organic amine cations. The [MnF₆] octahedra are strongly elongated along the chain axis (<Mn–F_ax> 2.135 Å, <Mn–F_eq> 1.842 Å), mainly due to the Jahn‐Teller effect, the chains are kinked with an average bridge angle Mn–F–Mn = 139.3°. Below 66 K the compound shows 1D‐antiferromagnetism with an exchange energy of J/k = –10.8 K. 3D ordering is observed at T_N = 9.0 K. In spite of the large inter‐chain separation of 8.2 Å a remarkable inter‐chain interaction with |J′/J| = 1.3 · 10^–5 is observed, mediated probably by H‐bonds. That as well as the less favourable D/J ratio of 0.25 excludes the existence of a Haldene phase possible for Mn³⁺ (S = 2).     

Supramolecular Tilt Chirality Derived from Symmetrical Benzene Molecules: Handedness of the 21 Helical Assembly

Achiral molecules can form aggregates with chirality. This depends on the relative position of the molecules, in other words, the tilt of the molecules (so‐called supramolecular tilt chirality). In this paper, we describe supramolecular chirality appearing in a 2₁ column composed of symmetrical benzene molecules, which is formed in the host cavity of inclusion crystals of cholic acid. Moreover, we determined the handedness, that is, right or left, of the 2₁ helical column of benzene on the basis of the molecular tilt. Determination of the 2₁ helical handedness was performed on assemblies of other benzene derivatives in cholic acid crystals and benzene assemblies in other host frameworks selected from the Cambridge Structural Database. Finally, we demonstrated complementarity of the handedness between the 2₁ symmetrical host framework of cholic acid and the benzene column.