The isolation and secondary functionalisation of the mer- and fac-isomers of tris(5-hydroxymethyl-2,2 '-bipyridine) complexes of ruthenium(II)

Tris-chelate 5-hydroxymethyl-2,2 '-bipyridine complexes of ruthenium (II) and the structurally related benzo- and naphthoesters have been isolated. The mer-isomer of the alcohol functionalised complex has been isolated by selective precipitation from methylene chloride and was subsequently functionalised to the benzoester with retention of the geometrical isomerism. The fac- and merisomeric forms of the ester complexes were separated using preparative plate silica chromatography and characterised by H-1 NMR spectroscopy. X-ray structural analysis of the fac-isomer of both the ester complexes confirmed the product assignment. The photophysical properties of the three isomers were investigated, indicating very similar absorption spectra to [Ru(biPY)(3)](2+). The emission wavelength was comparable in each case, with the aromatic ester complexes giving a much longer lifetime and higher quantum yields. (c) 2004 Elsevier B.V. All rights reserved.

The comparison of fac and mer ruthenium(II) trischelate complexes in anion binding

The synthesis of three new homoleptic trischelate ruthenium( II) complexes bearing new 2,2'-bipyridine ligands, 5,5'-dibenzylamido-2,2'-bipyridine (L1) and 5-benzylamido-2,2'- bipyridine (L2) has been achieved. In the case of [Ru(L2)(3)](2+), the mer and fac isomers have been separated. H-1 NMR spectroscopic anion binding studies indicate that the two C-3-symmetric pockets provided by [ Ru(L1)(3)](2+) is conducive to receive a range of anions, although this is not readily reflected in the photophysical behaviour. The fac-isomer of [Ru(L2)(3)](2+) does appear to have an enhancement in the binding interactions over the mer form with dihydrogenphosphate salts, although the difference is much less marked with the spherical chloride ions. From X-ray crystallographic evidence, the ability to hold water in the "anion" binding cleft can inhibit the strength of the interactions with anions, giving rise to the observed selectivity for directional oxoanions such as dihydrogen phosphate.

Testate amoebae as indicators of hydroseral change: an 8,500 year record from Mer Bleue Bog, eastern Ontario, Canada.

Testate amoebae have been used widely as a proxy of hydrological change in ombrotrophic peatlands, although their response to abiotic controls in other types of mire and fenland palaeo-environments is less well understood. This paper examines the response of testate amoebae to hydroseral and other environmental changes at Mer Bleue Bog, Ontario, Canada, a large ombrotrophic peatland, which evolved from a brackish-water embayment in the early Holocene. Sediments, plant macrofossils and diatoms examined from a 5.99 m core collected from the dome of the bog record six stages of development: i) a quiet, brackish-water riverine phase (prior to ca. 8500 cal BP); ii) a shallow lake (ca. 8500–8200 cal BP); iii) fen (8200–7600 cal BP); iv) transitional mire (7600–6900 cal BP); v) pioneer raised mire (6900–4450 cal BP); and vi) ombrotrophic bog (4450 cal BP-present).

Testate amoebae, notably small (<25 µm diameter) specimens of Centropyxis aculeata type, first appear in low abundances in sediments ascribed to the lacustrine phase. Diatoms from the same horizons record a shallowing in water depth, a decline in salinity and the development of emergent macrophytic vegetation, which may have provided favourable conditions for testate amoeba colonization. The testate amoeba communities of the inferred fen phase are more diverse and include centropyxids, cyclopyxids, Arcellidae and Hyalospheniidae, although the assemblages show some differences to those recently reported in modern European fen environments. The Fen–Bog Transition (FBT) is also dominated by C. aculeata type. The change in testate amoeba communities around this key transition is apparent in the results of Detrended Correspondence Analysis (DCA), and appears to reflect a latent nutrient gradient and a secondary moisture gradient. DCA analyses of plant macrofossil remains around the FBT show a similar trend, although the sensitivity of the two proxies to the inferred environmental changes differs. Comparisons with other regional mid-Holocene peatland records confirm the important influence of reduced effective precipitation on the testate amoeba communities during the initiation and development of Sphagnum-dominated, raised bog communities.

Mer and fac isomerism in tris chelate diimine metal complexes

In this perspective, we highlight the issue of meridional (mer) and facial (fac) orientation of asymmetrical diimines in tris-chelate transition metal complexes. Diimine ligands have long been the workhorse of coordination chemistry, and whilst there are now good strategies to isolate materials where the inherent metal centered chirality is under almost complete control, and systematic methodologies to isolate heteroleptic complexes, the conceptually simple geometrical isomerism has not been widely investigated. In systems where the two donor atoms are significantly different in terms of the σ-donor and π-accepting ability, the fac isomer is likely to be the thermodynamic product. For the diimine complexes with two trigonal planar nitrogen atoms there is much more subtlety to the system, and external factors such as the solvent, lattice packing and the various steric considerations play a delicate role in determining the observed and isolable product. In this article we discuss the possibilities to control the isomeric ratio in labile systems, consider the opportunities to separate inert complexes and discuss the observed differences in their spectroscopic properties. Finally we report on the ligand orientation in supramolecular systems where facial coordination leads to simple regular structures such as helicates and tetrahedra, but the ability of the ligand system to adopt a mer orientation enables self-assembled structures of considerable beauty and complexity.