New co-ordination compounds derived from barium(II) and the anionic 4-tert-butylacetyl-3-methyl-1-phenylpyrazol-5-onate ligand (Q–). Crystal and molecular structure of [Ba2Q4(H2O)4], [Ba2Q4(Him)4], [BaQ2(tetraglyme)] (tetraglyme = 2,5,8,11,14-pentaoxapentadecane) and [BaQ2(phen)2]

Abstract

By reaction of 4-tert-butylacetyl-3-methyl-1-phenylpyrazol-5-one (HQ) with metallic Ba in MeOH the dinuclear derivative [{BaQ₂(H₂O)₂}₂] 1 has been synthesized. It contains two barium atoms each eight-co-ordinated by a terminal bidentate Q ligand, two bridging double chelating Q ligands and two molecules of water. When the reaction of HQ with Ba was carried out in the presence of mono-, bi- or poly-dentate O- or N-donor ligands, derivatives of formula BaQ₂L_n(H₂O)_m have been obtained, depending on the nature of the ancillary ligand and reaction conditions employed [L = 2,5,8,11,14-pentaoxapentadecane (tetraglyme), 2,5,8,11-tetraoxadodecane (triglyme), 2,5,8-trioxanonane (diglyme), 2,2′∶6′,2″-terpyridine (terpy), 2,3-bis(2-pyridyl)pyrazine (Pypy), n = 1, m = 0 or 1; L = imidazole (Him), 1-methylimidazole (1-MeIm), 2-methylimidazole (2-MeImH), 1,10-phenanthroline (phen), 2,2′-bipyridyl (bipy), 2,9-dimethyl-1,10-phenanthroline (Cupr) and triphenylphosphine oxide (PPh₃O), n = 2, m = 0 or 1]. In the nine-co-ordinated [BaQ₂(tetraglyme)] the Ba atom is co-ordinated by all the five oxygen atoms of tetraglyme and by four oxygen atoms of two bidentate Q whereas the co-ordination number of barium in [BaQ₂(phen)₂] is eight due to four oxygen atoms of the two Q ligands and four nitrogen atoms of the two 1,10-phenanthrolines. The derivative [{BaQ₂(Him)₂}₂] is dinuclear with the Ba atoms linked by two double chelating Q ligands. The imidazoles complete the co-ordination number of Ba to 8. The compound [(BaQ₂)_n] has been obtained by heating derivative 1 in vacuo at 100 °C, whereas the 1∶1 adduct [BaQ₂(phen)] was obtained only when [(BaQ₂)_n] was treated in diethyl ether with an equimolar solution of phen. When a methanol solution of [BaQ₂(Pypy)] reacts with an equimolar methanol solution of CdCl₂ scrambling of the ligand occurs and derivatives 1 and [(CdCl₂)₂(Pypy)] are obtained. All the compounds obtained have been characterised by IR and far-IR data, conductivity and vaporimetric molecular weight measurements, ¹H NMR and in some cases also variable temperature ¹H NMR spectra. Comparison was made with structural and spectroscopic data reported for related barium(II) compounds.