Craig J. Matthews

Synthesis of bis(ethylenedithio)tetrathiafulvalene derivatives with metal ion ligating centres

Abstract The syntheses of eight derivatives of BEDT-TTF (ET) containing pyridine, 2,2′-bipyridine or 2,4′-pyridylpyrimidine binding sites on a side chain are reported, for use in the preparation of organic/inorganic hybrid materials. The intermediate hydroxyethyl derivative of BEDT-TTF is prepared in an efficient five-step procedure.

Conformational effects in molecular tectons containing protonated benzimidazole cations

The conformational preferences of protonated 2-benzimidazole cations have been modelled. Non-alkylated benzimidazoles show no strong conformational preferences, but methylation at the N1 position leads to high rotational barriers. The crystal structures are reported for five salts of protonated cations where two or three benzimidazoles are linked by ethylene or cyclohexyl spacers and for one copper(I) complex of a bis-benzimidazole ligand. The conformations observed in the solid state agree with the models. Stacking between benzimidazoles is observed in all cases but one where a high symmetry structure involving six edge-to-face interactions is preferred. Hydrogen bonding to anions or solvent molecules is observed for all salts of protonated benzimidazoles. The packing coefficients of the structures show small but significant variations.

1,2-Bis(2-benzimidazolyl)-1,2-ethanediol, a chiral, tridentate, facially coordinating ligand

The ligand 1,2-bis(1H-benzimidazol-2-yl)-1,2-ethanediol, 1, and its methylated derivative 2 are readily synthesized from tartaric acid, and act as chiral, facially coordinating tridentate ligands, forming complexes of composition ML2 with octahedral transition metals. The copper(II) complexes show distorted 4 + 2 coordination with benzimidazoles occupying the equatorial sites and alcohol functions weakly binding in the axial sites. Nickel(II) complexes in three different states of protonation show regular octahedral geometry with the alcohols mutually cis. Deprotonation of the coordinated alcohol produces little structural change but the monodeprotonated complex forms a hydrogen bonded dimer. Magnetic measurements show the hydrogen bonded bridge to offer a pathway for weak antiferromagnetic coupling. UV-Visible spectroscopy shows the ligand to have a field intermediate between water and pyridine. The diastereoselectivity of complexation depends on the geometry: nickel(II) shows a weak preference for the homochiral complex, whereas copper(II) forms almost exclusively homochiral complexes.

A novel pentamanganese(II) cluster produced by a controlled self assembly process; an exact match between the coordination algorithm of the metals and the ligand binding site arrangement

The tetradentate ligand phaap combines a bridging alkoxide oxygen and diazine and pyridine nitrogen donors, with five critically positioned binding sites, and on reaction with Mn(ClO4)2·6H2O undergoes a controlled self assembly to produce a unique trigonal bipyramidal oxygen bridged metal cluster with an exact match between the coordination requirements of the five six-coordinate metals and the donor arrangements of the six coordinated ligands.

Synthesis and crystal structures of some bis-benzimidazoles, -benzothiazoles and -benzoxazoles by an alternative route: their complexation with copper(II) salts

A novel and convenient synthetic route towards new bis-benzimidazoles, -benzothiazoles and -benzoxazoles from readily available starting materials has been established. These compounds have thioethers at the 2 position of the heterocycle and the resultant carbon–thioether linkage is stable under the conditions of synthesis. The crystal structures of bis(benzoxazol-2-ylsulfanyl)methane, bis(benzothiazol-2-ylsulfanyl)methane and 1,8-bis(benzothiazol-2-ylsulfanyl)-3,6-dioxaoctane have been determined. Differences in the packings of the first two are attributed to the greater number of S ⋯ S interactions of the second. Two of the new series have been complexed with copper(II) salts. The bis(benzoxazole) series showed no tendency to complex copper(II). The unusual crystal structure of the copper(II) complex with 1,8-bis(benzimidazol-2-ylsulfanyl)-3,6-dioxaoctane has been determined, indicating a four-co-ordinate copper(II) atom in a distorted square-planar environment. The two bis(benzimidazole) moieties act as bidentate ligands with nitrogen donors. The thioether donors of the chain, although apparently ordered around the copper, are too distant to be regarded as donors but probably influence the spectroscopic properties of the copper site and are described as quasi-co-ordinated. Relevant spectroscopic and analytical details of the new compounds and their complexes are given.

Differential binding of a facultative tridentate ligand 4-(benzimidazol-2-yl)-3-thiabutanoic acid to CuII and NiII

The crystal structure of a new tridentate ligand 4-(benzimidazol-2-yl)-3-thiabutanoic acid (HL), which provides a benzimidazole, a thioether and a carboxyl donor group that can be regarded as mimics of His, Met and Asp/Glu side chains in proteins, has been determined, together with those of its octahedral [CuL2] (brilliant blue) and [NiL2] (bright turquoise) complexes and the ligand field spectra of the chelates, for which the ligands provide an S2N2O2 donor set, in each case, but different positional isomers for the copper (t,c,c) and the nickel (c,c,c) chelates.

13 Chromium, molybdenum, and tungsten

The following provides a selected highlight for each element of the chromium triad in 2003. Chromium: A series of remarkably stable chromium(IV) alkyl and chromium-(III) and -(IV) hydride complexes have been prepared using the triamidoamine tetradentate ligand L1H3. This ligand has also been employed to prepare the first trigonal monopyramidal chromium(II) complex. Molybdenum: Molybdenum(V) coordination complexes have been extensively studied to provide further insights into the active sites found within many molybdoenzymes. A nice example of a model complex that contains the heteroscorpionate ligand L2SH, [(L2S)MoO(bdt)2], has been reported. The complex was structurally characterised and is only the second known model compound that closely approximates the active site structure of reduced forms of sulfite oxidase. Tungsten: The field of molecular magnetism has exploited the use of the [W(CN)8]3− building block in preparing a range of 2-D and 3-D bimetallic assemblies. For example, [Cu(tn)]3[W(CN)8]2·3H2O and [Cu(pn)]3[W(CN)8]2·3H2O have a 2-D layer structure and the magnetic properties of the compounds show typical metamagnetic behaviour. The critical field at which the interlayer antiferromagnetic ground-state switches to a ferromagnetic state is approximately 1.25 T for [Cu(tn)]3[W(CN)8]2·3H2O and 0.35 T for [Cu(pn)]3[W(CN)8]2·3H2O at 1.8 K.

CCDC 975199: Experimental Crystal Structure Determination

Related Article: Craig J. Matthews, Peter N. Horton, Michael B. Hursthouse|2004|University of Southampton, Crystal Structure Report Archive||992|doi:10.5258/ecrystals/992

Synthesis, structure and magnetism of a unique dodecanuclearcopper(II) 'picture frame' held in a 4 x 4 grid-like assembly

The synthesis, structure and preliminary magnetic studies of a novel dodecanuclearcopper(II) grid-like assembly are reported.

A tetracyclic benzimidazole derivative of Kemp's triacid

Fusion of Kemps triacid with o-phenylenediamine produced a unique tetracyclic compound, identified structurally by X-ray crystallography and solution NMR spectroscopy, having one of the original carboxylic groups free, one forming a benzimidazole unit, which itself forms an amide with the remaining carboxylic group.