Beryllium coordination chemistry

The coordination chemistry of beryllium with particular emphasis on chelates under physiological or near physiological conditions is surveyed. Hard donors such as oxygen are emphasized; equilibrium data and formation constants are reported as an indication of the strength of the complex.     

The coordination chemistry ofN-vinylimidazole

Summary The synthesis of coordination compounds of formula M(viz)_n(A)₂ is described, where viz. =N-vinylimidazole, M = Mn, Fe, Co, Ni, Cu, Zn or Cd, A = ClO ₄ ^– , BF ₄ ^– or NO ₃ ^– , and n varies from 3 to 6, depending upon the particular combination of cation and anion. The compounds are easily prepared in ethanol from the hydrated metal(II) salts and the ligand and the products were characterized using i.r., ligand-field, far-i.r. and e.p.r. spectra in conjunction with x-ray powder diagrams and magnetic techniques. Octahedral cations [M(viz)₆]²⁺ are formed in many cases, although square planar species Cu(viz)₄(A)₂ and tetrahedral species [M(viz)₄]²⁺ for M = Co and Zn are also found.Compared withN-alkylimidazole ligands, viz behaves differently in some cases, resulting in special effects in the crystal packing, and can be related to the quite rigid ligand structure. The pyridine-type N-atom of the imidazole ring appears to be coordinated; in all compounds no evidence is found for C=C double bond coordination.     

Surface-assisted coordination chemistry and self-assembly

This article discusses different approaches to build up supramolecular nanoarchitectures on surfaces, which were simultaneously investigated by scanning tunneling microscopy (STM) on the single-molecule level. Following this general road map, first, the hydrogen-bonding guided self-assembly of two different, structural-equivalent molecular building blocks, azobenzene dicarboxylic acid and stilbene dicarboxylic acid, was studied. Secondly, the coordination chemistry of the same building blocks, now acting as ligands in metal coordination reactions, towards co-sublimed Fe atoms was studied under near surface-conditions. Extended two-dimensional tetragonal network formation with unusual Fe2L(4/2)-dimers at the crossing points was observed on copper surfaces. Complementary to the first two experiments, a two-step approach based on the solution-based self-assembly of square-like tetranuclear complexes of the M4L4-type with subsequent deposition on graphite surfaces was investigated. One- and two-dimensional arrangements as well as single molecules of the M4L4-complexes could be observed. Moreover, the local electronic properties of a single M4L4-complexes could be probed with submolecular resolution by means of scanning tunnelling spectroscopy (STS).     

Metal-containing nanofibers via coordination chemistry

One-dimensional fibrous nanostructures may exhibit unique mechanical, optical, magnetic, and electronic properties as a result of their nanoscale dimensions. Various approaches have been used to prepare nanofibers (e.g., electrospinning, vapor deposition), but this review focuses on the research and development of self-assembled nanofibers formed through coordination chemistry. By employing metal–ligand interactions that extend along the backbone of the aggregates, nanofibrous, often gel-forming, materials with appealing properties have been formed. Other fibers formed through electrostatic interactions between charged coordination complexes are also discussed. The optical, electronic, and magnetic properties conferred upon the materials by the embedded coordination complexes render the nanofibers useful for applications in the fields of catalysis, sensors, and gas storage, and potentially for developing nanosized devices.     

Encapsulation of phthalocyanine supramolecular stacks into virus-like particles

We report herein the encapsulation of a water-soluble phthalocyanine (Pc) into virus-like particles (VLPs) of two different sizes, depending on the conditions. At neutral pH, the cooperative encapsulation/templated assembly of the particles induces the formation of Pc stacks instead of Pc dimers, due to an increased confinement concentration. The Pc-containing VLPs may potentially be used as photosensitizer/vehicle systems for biomedical applications such as photodynamic therapy.     

Fabrication of virus-like particles with strip-pattern surface: A two-step self-assembly approach

Spherical nanostructures with striped patterns on the surfaces resembling the essential structures of natural virus particles were constructed through a two-step self-assembly approach of polystyrene-boligo(acrylic acid)(PS-b-oligo-AA) and poly(γ-benzyI L-glutamate)-b-poly(ethylene glycol)(PBLG-bPEG) copolymer mixtures in solution.On the basis of difference in hydrophilicity and self-assembly properties of the two copolymers,the two-step self-assembly process is realized.It was found that PS-boligo-AA copolymers formed spherical aggregates by adding a certain amount of water into polymer solutions in the first step.In the second step,two polymer solutions were mixed and water was further added,inducing the self-assembly of PBLG-b-PEG on the surfaces of PS-b-oligo-AA spheres to form striped patterns.In-depth study was conducted for the indispensable defects of striped patterns which are dislocations and +1/2 disclinations.The influencing factors such as the mixing ratio of two copolymers and the added water content in the first step on the morphology and defects of the striped patterns were investigated.This work not only presents an idea to interpret mechanism of the cooperative self-assembly behavior,but also provides an effective approach to construct virus-like particles and other complex structures with controllable morphology.     

The coordination chemistry of 1,2,4,5-tetrazines

1,2,4,5-Tetrazine and its 3,6-disubstituted derivatives exhibit a particular coordination chemistry, characterized by electron and charge transfer phenomena and by the ability of these heteroatom-rich ligands to bridge metal centers in various ways. A very low-lying π* orbital localized at the four nitrogen atoms is responsible for intense low-energy charge transfer absorptions, electrical conductivity of coordination polymers, unusual stability of paramagnetic radical or mixed-valent intermediates and for often well-resolved EPR hyperfine structure in the radical complexes. Substituted 1,4-dihydro-1,2,4,5-tetrazines have also been used as bridging ligands. The structural consequences of electron transfer as well as the capability for efficient and variable metal–metal bridging render the tetrazines as valuable components of supramolecular materials.     

Synthesis and coordination chemistry of tetrabutyldithioimidodiphosphinates

Butyl substituted imidodithiophosphinates R₂P(S)NP (S)R′₂ (R=ⁿBuⁱBu^sBuR′=ⁿBuⁱBu^sBu) have been synthesised via an HBr elimination reaction between R₂P(S)NH₂ and R′₂P(S)Br The compounds were characterised spectroscopically Crystallographic and spectroscopic studies reveal ⁿBu₂P(S)NHP(S)ⁿBu₂ and ^sBu₂P(S)NHP(S)ⁱBu₂ to be hydrogen bonded transoid dimers and ⁱBu₂P(S)NHP(S)ⁱBu₂ to be a transoid hydrogen bonded chain Reactions of the imidodithiophosphinates with ZnCl₂ or MCl₂COD gave the coordination complexes M[R₂P(S)NP (S)R′₂]₂ (R=ⁿBuⁱBu^sBuR′=ⁿBuⁱBu^sBuM=ZnPd: R=ⁿBuⁱBu^sBuPt).