Hervé Guillon

Synthesis, characterisation and X-ray structures of yttrium, barium and copper(II) β-ketoesterate complexes

Abstract β-Ketoesterates derivatives M(mpa)x (M=Y, Ba, Cu; mpaH=methylpivaloylacetate; x=2 or 3) were prepared by ligand exchange reactions starting from methoxides (M=Ba, Cu) or from tristrimethylsilylamide (M=Y) derivatives. Decomplexation of the oligomeric and non-volatile Ba and Y species was achieved by various Lewis bases. Adducts Y(mpa)3L [L=tmeda (N,N,N′,N′-tetramethylethane-1,2-diamine), bipy (2,2′-bipyridine)] and Ba(mpa)2L [L=diglyme, 18-crown-6 ether; pmdta=N,N,N′,N′,N″-pentamethylethylenetriamine] and [Ba(mpa)2(tmedta)2] were obtained. All compounds were synthesised in high yield and characterised by elemental analyses, 1H NMR, FT-IR and TGA. The structures of [Ba(mpa)2(tmeda)2] and [Y(mpa)3(bipy)] were established by single crystal X-ray diffraction. The metals are eight-coordinated with a slightly distorted square antiprismatic surrounding. The yttrium complexes sublime as adducts. The barium complexes, by contrast, are dissociated in the vapour phase. Better solubility properties in polar and non-polar with respect to the 2,2,6,6-tetramethylheptane-3,5-dionates analogues were observed especially for the copper species. These compounds are thus potential metal-oxide precursors for liquid injection MOCVD using solvents such as hexane or diglyme.

Proglacial sediment dynamics from daily to seasonal scales in a glaciated Alpine catchment (Bossons glacier, Mont Blanc massif, France): PROGLACIAL SEDIMENT DYNAMICS FROM DAILY TO SEASONAL SCALES

The sediment yields of Alpine catchments are commonly determined from streamload measurements made some distance downstream from glaciers. However, this approach indiscriminately integrates erosion processes occurring in both the glacial and proglacial areas. A specific method is required to ascertain the respective inputs from (i) subglacial and supraglacial sediments, (ii) proglacial hillslopes and (iii) proglacial alluvial areas or sandurs. This issue is addressed here by combining high‐resolution monitoring (2 min) of suspended sediment concentrations at different locations within a catchment with discharge gauging and precipitation data. This methodological framework is applied to two proglacial streams draining the Bossons glacier (Mont Blanc massif, France): the Bossons and Crosette streams. For the Bossons stream, discharge and suspended load data were acquired from June to October 2013 at 1.15 and 1.5 km from the glacial terminus, respectively upstream and downstream from a small valley sandur. These hydro‐sedimentary data are compared with the Crosette stream dataset acquired at the outlet of the Bossons glacier subglacial drainage system. A fourfold analysis focusing on seasonal changes in streamload and discharge, multilinear regression modelling, evaluation of the sandur flux balance and probabilistic uncertainty assessment is used to determine the catchment sediment budget and to explain the proglacial sediment dynamics. The seasonal fluctuation of the sediment signal observed is related to the gradual closing of the subglacial drainage network and to the role of the proglacial area in the sediment cascade: the proglacial hillslopes appear to be disconnected from the main channel and the valley sandur acts as a hydrodynamic sediment buffer both daily and seasonally. Our findings show that an understanding of proglacial sediment dynamics can help in evaluating paraglacial adjustment and subglacial erosion processes.