Slow magnetic relaxation in a 3D network of cobalt(II) citrate cubanes

The synthesis, structure and magnetic properties of a 3D network based on {Co?(cit)?}?? (H?cit = citric acid) cubane units linked by octahedral Co(II) centres is reported.     

A square two‐dimensional polymer of cobalt citrate cubanes

The structure of the title complex, poly[dicaesium(I) hexaaquacobalt(II) [octaaquatetra‐μ‐citrato‐hexacobalt(II)] dodecahydrate], {Cs₂[Co(H₂O)₆][Co₆(C₆H₄O₇)₄(H₂O)₈]·12H₂O}_n, at 100 (1) K is formed by layers of a square two‐dimensional polymer composed of Co^II citrate cubanes bridged by magnetically active six‐coordinate Co^II cations. The polymer has plane symmetry p4mm in the c‐axis projection. The cubanes reside on sites of crystallographic symmetry , while the bridging Co^II centres lie on twofold axes. The basic polymeric unit has a charge of 4−, balanced by two Cs⁺ and a [Co(H₂O)₆]²⁺ (symmetry ) cation, which lie in channels between the polymeric layers. Unligated water molecules, of which there are 12 per cubane, enter into an extended intralayer and layer‐bridging hydrogen‐bond pattern, which can be described in detail even though not all of the H atoms of the water molecules were located.     

Reversible single-crystal-to-single-crystal transformation and highly selective adsorption property of three-dimensional cobalt(II) frameworks

A three-dimensional (3D) coordination polymer, [Co(3)(L)(2)(BTEC)(H(2)O)(2)]·2H(2)O [1, HL = 3,5-di(imidazol-1-yl)benzoic acid, H(4)BTEC = 1,2,4,5-benzenetetracarboxylic acid], with tfz-d topology has been hydrothermally synthesized. The framework of 1 has high thermal stability and exhibits single-crystal-to-single-crystal (SCSC) transformations upon removing and rebinding the noncoordinated and coordinated water molecules. X-ray crystallographic analyses revealed that the coordination geometry of Co(II) changes from octahedral to square pyramid upon dehydration, accompanying the appearance of one-dimensional (1D) open channels with dimensions of 2.0 × 2.8 ?. The dehydrated form [Co(3)(L)(2)(BTEC)] (2) exhibits highly selective adsorption of water molecules over N(2), CH(3)OH, and CH(3)CH(2)OH, which could be used as sensors for water molecules. Furthermore, the magnetic properties of 1 and 2 were investigated, showing the existence of ferromagnetic interaction between the Co(II) atoms within the trinuclear subunit.     

Solid-state single-crystal-to-single-crystal transformation from a 2D layer to a 3D framework mediated by lattice iodine release

We describe an exceedingly rare example of solid-state single-crystal-to-single-crystal transformation from a 2D layer to a known 3D framework via lattice iodine release, which involves the formation of a new Cu-O ligand bond and a change in the metal coordination geometry.     

2 + 2]Photocyclization in a single-crystal-to-single-crystal transformation of a TTF-amido-pyridine

The redox active ligand EDT-TTF-CONH-3-pyridine undergoes a [2 + 2] cycloaddition upon irradiation with polychromatic light, an unprecedented single-crystal-to-single-crystal transformation for a TTF derivative.     

Electron delocalization patterns in models of distorted (D2d) mixed-valence cubanes

Low-symmetry distortions are present in cubanes such as Fe(4)S(4), but their effects on electron delocalization properties are not well-understood. Mixed-valence cubanes often exhibit experimentally measurable "pair delocalization" of a delocalizable electron. An important question is, what is the role of physical interactions (vibronic, electronic, exchange) and symmetry distortions in determining the electron delocalization pattern? Semiclassical models are used to explore the electron delocalization patterns of S=1/2 tetragonally (D(2d)) distorted mixed-valence cubanes comprising four metal centers with bridging ligands, a single delocalizable "excess" electron, and either closed-shell or open-shell ion cores. Phase diagrams show that distorted S=1/2 ground state cubanes with antiferromagnetic exchange (as found in nature) have delocalization patterns qualitatively similar to those of an S=1/2 model with no Heisenberg exchange, suggesting that exchange is not necessarily a dominant factor in determining electron delocalization properties. The open-shell model reveals two types of pair delocalization for the S=1/2 ground state, with differing dimer subunit spins for compressed and elongated geometries. Previous studies emphasize the importance of exchange interactions for pair delocalization. Here, it is shown that electron exchange is not always necessary for pair delocalization and that it can be achieved with relatively small tetragonal distortions from tetrahedral (T(d)) symmetry. The results contradict those of an earlier theoretical study of distorted Fe(4)S(4) clusters, which concluded that distortions of lower symmetry than D(2d) are necessary to induce a transition to pair delocalization.     

From discrete octahedral nanocages to 1D coordination polymer: coordination-driven a single-crystal-to-single-crystal transformation via anion exchange

A discrete octahedral nano-cage has been synthesized by using a C(3)-symmetry semi-rigid pyridine-based ligand tppa. X-ray structure study reveals that the cage has a big inner cavity, flexible windows and all P=O moieties of tppa ligands are inside positions. By anion exchange the 0D nano-cages can transform to infinite chain without noticeable loss of their crystallinity.     

Reversible adsorption and complete separation of volatile chlorocarbons based on a Cd(II)-triazole MOF in a single-crystal-to-single-crystal fashion

Reversible adsorption and complete separation of volatile chlorocarbon species CH(2)Cl(2), CHCl(3) and CCl(4) on a Cd(II)-triazole MOF in a single-crystal-to-single-crystal fashion were reported.     

Nonisothermal deoxygenation of cobalt complexes in free form and attached to aerosil

Thermal deoxygenation under vacuum has been examined for free oxygenated cobalt complexes formed with phenanthroline, histidine, and histamine and also for those attached to aerosil; mass spectrometry has been applied to the products. The free compounds are deoxygenated in accordance with the Roginskii equation f() = (1–)^2/3 in a certain range. Deoxygenation for the grafted complexes is described by an equation for nucleation and one-dimensional growth f() = 1–. The kinetic parameters have been determined.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 3, pp. 311–317, May–June, 1987.     

Reversible hydrogenation of surface N atoms to form NH on Pt(111)

The formation and dissociation chemistry of the NH species on Pt(111) was characterized with reflection absorption infrared spectroscopy and temperature programmed desorption. Irradiation of a chemisorbed bilayer of ammonia with a 100 eV electron beam at 85 K leads to a mixture of NH, N, and H on the surface. Annealing to temperatures in the range of 200-300 K leads to reaction of N and H to form additional NH. The NH species has an intense and narrow NH stretch peak at 3320 cm(-1), while no peak due to the PtNH bend is observed above 800 cm(-1). The NH species is stable up to a temperature of approximately 400 K. The surface N atoms produced from NH dissociation are readily hydrogenated back to NH by exposure of the surface to H2. However, NH cannot be further hydrogenated to generate adsorbed NH2 or to NH3 under the conditions used here. Exposure of the NH/Pt(111) surface to D2 at 380 K produces the ND species. Comparison with the results of density functional theory calculations based on small Pt clusters indicates that NH occupies three-fold hollow sites with the molecular axis perpendicular to the surface.     

Reversible, electrochemically controlled binding of phosphine to iron and cobalt bis(dithiolene) complexes

The homoleptic bis(dithiolene) complexes [M(S(2)C(2)R(2))(2)](2) (M = Fe, Co; R = p-anisyl) undergo two successive reductions to form anions that display [M(S(2)C(2)R(2))(2)](2)(2-) <--> 2[M(S(2)C(2)R(2))(2)](1-) solution equilibria. The neutral dimers react with Ph3P to form square pyramidal [M(Ph(3)P)(S(2)C(2)R(2))(2)](0). Voltammetric measurements upon [M(Ph(3)P)(S(2)C(2)R(2))(2)](0) in CH(2)Cl(2) reveal only irreversible features at negative potentials, consistent with Ph(3)P dissociation upon reduction. Dissociation and reassociation of Ph(3)P from and to [Fe(Ph(3)P)(S(2)C(2)R(2))(2)](0) is demonstrated by spectroelectrochemical measurements. These collective observations form the basis for a cycle of reversible, electrochemically controlled binding of Ph(3)P to [M(S(2)C(2)R(2))(2)](2) (M = Fe, Co; R = p-anisyl). All members of the cycle ([M(S(2)C(2)R(2))(2)](2)(0), [M(S(2)C(2)R(2))(2)](2)(1-), [MM(S(2)C(2)R(2))(2)](2)(2-), [M(S(2)C(2)R(2))(2)](1-), [M(Ph(3)P)(S(2)C(2)R(2))(2)]) for M = Fe, Co have been characterized by crystallography. Square planar [Fe(S(2)C(2)R(2))(2)](1-) is the first such iron dithiolene species to be structurally identified and reveals Fe-S bond distances of 2.172(1) and 2.179(1) Angstrom, which are appreciably shorter than those in corresponding square planar dianions.     

From 1D to 3D single-crystal-to-single-crystal structural transformations based on linear polyanion [Mn4(H2O)18WZnMn2(H2O)2(ZnW9O34)2]4-

A 1D anionic polyoxometalate, [Mn(4)(H(2)O)(18)WZnMn(2)(H(2)O)(2)(ZnW(9)O(34))(2)](4-), undergoes 1D to 3D single-crystal-to-single-crystal structural transformations that are induced by transition-metal cations (Co(2+) and Cu(2+)) and solvent molecules. These solid materials present interesting catalytic activity for the oxidative aromatization of Hantzsch 1,4-dihydropyridines that is dependent on the inserted heterogeneous metal cations.     

Reversing the code of a template-directed solid-state synthesis: a bipyridine template that directs a single-crystal-to-single-crystal [2 + 2] photodimerisation of a dicarboxylic acid

A linear template in the form of a bipyridine has been developed and is shown to direct a single-crystal-to-single-crystal [2 + 2] photodimerisation of a dicarboxylic acid.     

Diiron amido-imido complex [(CpFe)2(mu2-NHPh)(mu2-NPh)]: synthesis and a net hydrogen atom abstraction reaction to form a bis(imido) complex

A reaction between [CpFeCl]x and LiNHPh (1 equiv to Fe) produces a new paramagnetic Fe(II)-Fe(III) mu2-amido-mu2-imido complex [(CpFe)2(mu2-NHPh)(mu2-NPh)] (1), which, upon interaction with 2,2'-azobis(2,4-dimethylvaleronitrile), undergoes a net N-H hydrogen atom abstraction reaction to give a diamagnetic Fe(III)-Fe(III) mu2-imido dimer [CpFe(mu2-NPh)]2 (2). The molecular structures of 1 and 2 have been determined by single-crystal X-ray diffraction.