Reactivity of uranyl ion with quinquedentate chelating hydrazine derivatives. Part 1. 2,6-Diacetylpyridine bis(2′-pyridylhydrazone)

Abstract

Uranyl nitrate reacts with 2,6-diacetylpyridine bis(2′-pyridylhydrazone)(H₂dapp) to give [UO₂(H₂dapp)(NO₃)]₂^–[UO₂(NO₃)₄](1) or a mixture (2) of ionic mononuclear species, in each of which H₂dapp acts as a quinquedentate chelating ligand, depending on the experimental conditions. The complexes have been characterized by a number of physicochemical measurements including the X-ray analysis of (1). Crystals of (1) are triclinic with a= 14.071(9), b= 10.801(7), c= 10.122(6)Å, α= 63.86(7), β= 75.65(9), γ= 78.86(9)°, space group P[graphic ommitted], and Z= 1. The structure has been solved by conventional techniques, and refined to a final R of 0.07. The unit cell contains two very highly distorted eight-co-ordinated cations [UO₂(H₂dapp)(NO₃)]⁺, related by a centre of symmetry and with the N₅O donor set in a symmetrically twisted ‘equatorial plane’[U–N (mean) 2.62 Å, N–U–N (mean) 59.5°, and U–O 2.48 Å for the unidentate nitrate group], and an uranyl tetranitrate counter anion [UO₂(NO₃)₄]^2–[two bidentate nitrates (U–O 2.53 Å) and two unidentate (U–O 2.45 Å)], at the centre of symmetry, in a hexagonal bipyramidal arrangement. The nature of the solvent(s), the high stabilizing effect of the 5,5,5,5 chelation mode, and reactivity tests, which allow the isolation of [UO₂(H₂dapp)(NO₃)][BPh₄](3) and [UO₂(H₂dapp)][ClO₄]₂(4), are discussed. Owing to the deprotonation of the diazapropenic sequences CN–NH–, the neutral complex [UO₂(dapp)](6), containing U–N covalent bonds, can be obtained by the action of non-hydroxylated bases on (1)–(4). Like uranyl amides, compound (6) reacts with alcohols to give alkoxy-derivatives. Polymeric [{(UO₂)₂(H₂dapp)(OCH₃)₄·xCH₃OH}_n](7) has been isolated.