Chemistry of 2,2,6,6,-tetramethyl-3,5-heptanedione (Hthd) modification of zirconium and hafnium propoxide precursors

The modification of different zirconium propoxide and hafnium propoxide precursors with 2,2,6,6,-tetramethyl-3,5-heptanedione (Hthd) was investigated by characterization of the isolated modified species. The complexes [Zr(OnPr)3(thd)](2), [Zr(OnPr)(OiPr)2(thd)]2, Zr(OiPr)(thd)3, [Hf(OnPr)3(thd)]2, and Hf(OiPr)(thd)3 were isolated and characterized. The structure of the n-propoxide analogue of Zr(OiPr)(thd)3 could not be refined, but its existence was clearly demonstrated by XRD and 1H NMR. The modification of the propoxide precursors involves mono- and trisubstituted intermediate compounds and does not involve a disubstituted compound; thus, the commercial product that is claimed to be "Zr(OiPr)2(thd)2" and is most commonly used for the MOCVD preparation of ZrO2 does not exist. No evidence was found for the presence of such a compound in either zirconium- or hafnium-based systems. Formation of the dimeric hydroxo-di-thd-substituted complex, [Hf(OH)(OiPr)(thd)2]2, which could be isolated only for hafnium-based systems, occurs on microhydrolysis. All heteroleptic intermediates are eventually transformed to the thermodynamically stable Zr(thd)4 or Hf(thd)4) The compounds obtained from isopropoxide precursors showed a higher stability than those with n-propoxide ligands or a combination of both types. In addition, it is important to note that residual alcohol facilitates the transformation and strongly enhances its rate. The unusually low solubility and volatility of MIV(thd)4 has been shown to be due to close packing and strong van der Waals interactions in the crystal structures of these compounds.     

Direct and β-delayed multi-proton emission from atomic nuclei with a time projection chamber: the cases of 43Cr, 45Fe, and 51Ni

The two-proton radioactivity of ⁴⁵Fe was studied experimentally with a time projection chamber. The aim of the experiment was the reconstruction of the proton tracks in three dimensions. Energy and angular correlations have been determined and the data are compared with theoretical models, in particular with a three-body model. Moreover, the decay of ⁴³Cr was studied and ??-delayed one-, two- and three-proton emission could be established. The correlations observed for ??-delayed two-proton emission favour a sequential emission. Finally, ??-delayed two-proton emission was observed for the first time for ⁵¹Ni.     

Compact Mode Converter System for the Cold Test of Assembled Gyrotrons

A microwave system is described which allows testing of the quasi-optical mode converter in a gyrotron, which is completely assembled except for the attachment of the electron gun. Test results are presented for a TE_6,2,1 gyrotron, and a similar design for a TE_28,7,1 gyrotron is shown.     

The purification of morin

Chemistry of Natural Compounds -