Metal Complex Units Research Articles

Amplified quenching in metal-organic conjugated polymers.

The luminescence from conjugated polyelectrolytes that contain pendant metal complex units is quenched very efficiently by oppositely charged electron acceptors.

Well‐Defined Ruthenium‐Coordinated Block Copolymers of 2‐Vinylpyridine with 2‐(N‐Carbazolyl)ethyl Methacrylate and Their Optical Properties

AbstractIn order to study the energy‐transfer phenomenon in ruthenium‐coordinated polymers, novel block copolymers from carbazolylethyl methacrylate and 2‐vinylpyridine were prepared by living anionic polymerization; the copolymers possessed varying repeating units and had the desired molecular weight and a narrow‐molecular‐weight distribution. The ruthenium‐coordinated block copolymers were formed by reacting [RuII(tpy)(dmbpy)Cl] with the polymers, in which the pyridine units acted as ligands. Photoluminescence and optical absorption measurements of the coordinated block copolymers were carried out to observe the energy transfer in the complexes. The energy transfer from the carbazole blocks to the ruthenium‐coordinated blocks might take place either by an intra‐ and/or an intermolecular energy‐transfer mechanism. From the optical absorption, photoluminescence, and electroluminescence studies, it was observed that the ease of the energy transfer increased with an increasing number of metal‐complex units. Normalized electroluminescence spectra of the device (ITO/PEDOT/RuIIL2bpolym/TAZ/Alq3/Ag).magnified imageNormalized electroluminescence spectra of the device (ITO/PEDOT/RuIIL2bpolym/TAZ/Alq3/Ag).

Inclusion compounds containing a drug: structure and thermal stability of the first clathrates of nitrazepam and isothiocyanato ethanol complexes of Co(II) and Ni(II)

Syntheses, crystal structures and comparative analytical investigations on the first two inclusion compounds of an antiepileptic drug, nitrazepam (1,3-dihydro-7-nitro-5-phenyl-2 H-1,4-benzodiazepin-2-one) are reported. The biologically active molecule forms isostructural clathrates with diaquadiethanolbis(isothiocyanato) complexes of both cobalt(II) and nickel(II) in molar ratios of 1:2 [M(NCS) 2(C 2H 5OH) 2(H 2O) 2]·2C 15H 11N 3O 3 (M=Co 2+, 1, and M=Ni 2+, 2). Detailed analyses of the structures, the secondary interactions, the neutral drug conformations, the FTIR spectra and thermal stabilities of the clathrates, in comparison with those of the crystalline nitrazepam, have been carried out. In the crystal structures there are only host–guest hydrogen bonds of O⋯H, N⋯H and S⋯H type. Owing to the comparable size of the two constituents neither host–host nor guest–guest secondary interactions occur. In the first thermal decomposition step a parallel release of ethanol and water was observed by simultaneous thermogravimetric and differential thermal analysis measurements. This indicates that some bonds of the metal complex unit and the host–guest secondary interactions in 1 and 2 are weaker than interactions in the pure drug. If an easy release of ethanol and water occurs during dissolution of 1 and 2, it might result in an improved bioavailability of the drug, which is soluble only in aqueous ethanol.

Supramolecular assemblies from ditopic ligands and transition metal salts †

Tetradentate salicylaldimine ligands of the H2salen-type bearing ortho-N-morpholinomethyl substituents function as ditopic ligands, bonding to NiII or CuII with the [N2O2]2− donor set of the salen unit and a sulfate or two nitrate anions with the protonated morpholine units. The binding of the metal salt by the zwitterionic form of the ligand provides a novel approach to the transport of metal sulfates in metal recovery processes. A comparison of the solid state structures of a “free” ligand with a series of nickel(II) complexes demonstrates that the metal ion templates the ligand system, orientating the pendant morpholinium groups to form electrostatic and bifurcated hydrogen bonds in the sulfate complex to the dianion creating a neutral 1∶1∶1 [LM2+X2−] complex suitable for extraction into water immiscible solvents. Other binding modes involving bridging of metal complex units by anion binding to the pendant morpholine groups suggest that these ditopic ligands could also be used to assemble unusual three-dimensional arrays of metal complexes in the solid state.

Biimidazole complexes of ML22+ [M = Ru or Os, L = 2-(phenylazo)pyridine]. Synthesis, structure and redox properties of mono- and di-nuclear complexes ‡

A series of mono- and di-nuclear complexes of ruthenium and osmium containing the terminal ligands 2-(phenylazo)pyridine (pap), 2,2′-bipyridine (bpy) and the bridging ligand 2,2′-biimidazole(H2biim) have been prepared. The mononuclear complex [Ru(pap)2(H2biim)][ClO4]2·3CH2Cl2 was characterised by a single-crystal structure determination. The mononuclear complexes [M(pap)2(H2biim)]2+ (M = Ru or Os) act as dibasic acids and undergo deprotonation to afford [M(pap)2(Hbiim)]+ and [M(pap)2(biim)]. The completely deprotonated complexes behave as reactive building units (‘metal complex as ligand’) which react smoothly with metal complex units to produce homo- and hetero-dinuclear complexes. The structure of the dinuclear complex [Ru2(bpy)4(biim)][ClO4]2 was determined. Cyclic voltammetric studies on the above complexes were performed. The quasi-reversible half-wave potentials of the oxidation processes of the dinuclear complexes are dependent on the metal as well as on the nature of the terminal ligands. These undergo two one-electron oxidation processes centered at the metal. Partial oxidation of the dinuclear complexes led to unsymmetrical bridge cleavage to form monomeric complexes. Large numbers of ligand reduction responses were observed. In some cases the first ligand reduction occurs close to zero potential (with respect to the SCE).

Varieties of Crystalline Architecture by Using Hydrogen Bonding in Biimidazolate Metal Complex Systems. Part 3: Zigzag One-Dimensional Chains

Abstract The crystal structure of [Ni(Hbim)3](nPr4N)•MeOH (1) (Hbim− =mono- deprotonated 2,2′-biimidazolate and nPr4N+ = tetra-n-propyl-ammonium cation) has been determined. The structure was consists of Ni(II) centers hexacoordinated by three 2,2′-biimidazolate (Hbim−) ligands in an octahedral arrangement. Complex 1 possesses an intermolecular hydrogen bonding structure of zigzag one-dimensional chains in which two of the three Hbim− ligands connect the metal complex units.

Novel Carbon Compounds with “Naked” Cn Units

1,3‐Dimetallaallenes 1 or carbyne complexes 2 are the simplest examples of compounds in which different transition metal complex fragments or units of main group elements are terminally bound to Cn bridges. Polymers such as 3 with C4 bridges which link d8 ML2 building blocks are of particular interest as materials with novel properties. equation image

“Small-Upward” Approach to Nanostructures: Dendritic Polynuclear Metal Complexes For Light Harvesting

A synthetic strategy is described to obtain supramolecular dendritic structures of nanometric dimensions made of metal complex units which absorb light all over the UV and visible spectral region. Specific metal and/or ligands can be placed in designed sites of the supramolecular array by an appropriate choice of the building blocks. A made-to-order control of the patterns of electronic energy transfer can thus be achieved. Supramolecular species containing up to 22 metal atoms have been prepared and their light absorption, luminescence, and energy transfer properties have been investigated

Stereochemisty of rigid chelate–metal complexes. Part 4. Crystal structures of tetra-aquabis(1,10-phenanthroline)strontium(II) perchlorate– and tetra-aquabis(1,10-phenanthroline)barium(II) perchlorate–1,10-phenanthroline(1/2)

The crystal structures of the title complexes, [Sr(phen)2(OH2)4][ClO4]2·2phen (1) and [Ba(phen)2(OH2)4][ClO4]2·2phen (2), have been determined by X-ray diffraction from diffrectometer data and refined by least squares to R 0.120(1) and 0.13(2) for 1 423 and 2 478 observed reflections respectively. The two complexes are similar. Crystals are triclinic, space group P with Z= 1 in unit cells of dimensions: (1)a= 1 344.4(4), b= 1 268.4(4), c= 706.8(2) pm, α= 99.31 (2), β= 92.55(2), γ= 76.21 (3)°; (2)a= 1 336.9(1), b= 1 300.3(b), c= 703.2(1) pm, α= 100.01(2), β= 95.15(1), γ= 75.53(2)°. The metal ions have an eight-co-ordinate distorted cube stereo-chemistry involving four nitrogens from two phenanthroline ligands and four oxygens from water molecules.The trans-related phens pack almost parallel to ab plane containing also the metal, while the remaining phen pair, also parallel to ab but not bonded to the metal, are merely ‘sandwiched’ in the structure halfway between the metal centres, along the c axis. The point-group symmetry of the metal complex unit is approximately C2h. There appear to be no bonding forces holding the ‘floating’ phens in the structure, the shortest contact, N ⋯ H–O (to water), being 359 (1) and 378 pm (2). The bonded waters are also independent of the perchlorateanions, the closest contact being 326 and 340 pm. The perchlorate groups are disordered to the extent that the centre of symmetry in the otherwise centric complex is destroyed by a completely dissymmetric tetrahedral arrangement of oxygens.

Oxidationsprodukt von Bis-(1,2-benzochinondioximato)nickel(II), [Ni(BCD)2], mit Jod: Kristall- und Molekülstruktur

Ni(C6HsN202) 2.10.5, tetragonal, P4/mcc, a= 15553(4), c= 6.307(3) ./~, Z= 4. The structure has been determined by standard methods from single-crystal X-ray diffractometer data and refined by least-squares methods to R=0.095 for 725 independent reflexions. The metal-complex units form columnar stacks with Ni-Ni distances of 3.153(3) A. Iodine chains run parallel to the stacks.