Actinide structural studies. 13. Three pyridine–acetylacetonate complexes of actinyl(VI) ions

Bis(1,3-diphenyl-l,3-propanedionato)oxo- (pyridine)uranium(VI) (1), (UO2(CasHllO2)2(CsHsN)), Mr= 795.6, monoclinic, P2Jn, a= 10.158 (2), b= 21.937 (8), c= 13.888 (4)A, t= 103.49 (1) ° , U = 3009 (2)/k 3, Z = 4, D x = 1.76 g cm -3, 2(Mo Ka) = 0.71069 A, /t = 51.48 cm -1, F(000) = 1536, T= 289 K, R = 0.036 for 3269 unique observed reflec- tions. Bis( 1-(tert-butoxy)- 1,3-butanedionato)dioxo- (pyridine)uranium(IV) (2), (UO2(CaHI303)2(CsHsN)), M r= 663.5, orthorhombic, Cmc2~, a = 15.939 (9), b = 19.532 (8), c= 9.777 (6) A, U= 3044 (1) A 3, Z = 4, D x = 1.45 gcm -a, 2(Mo Kct) = 0.71069/~, /t = 50.81 cm -1, F(000) = 1280, T= 289 K, R = 0.048 for 1178 unique observed reflections. Dioxobis(2,4-pen- tanedionato)(pyridine)neptunium(VI) (3), (NpO2(CsH 7- O2)2(CsHsN)), Mr=546.4, orthorhombic, Fdd2, a = 29.617 (5), b= 11.406 (2), c= 10.595 (4)A, U= 3579 (2) A 3, Z=8, D x=2.03gcm -3, 2(MoKa)= 0.71069 A, /a= 37.95 cm -~, F(000) = 2056, T= 173 K, R = 0.046 for 625 unique observed reflections. The bond angle of 177-9 (2) ° for (1) indicates a very slightly non-linear uranyl group. The neptunyl bond in complex (3) is slightly more distorted (176.5 (19)o), whilst in complex (2) the uranyl group deviates even more from linearity (175.8 (8)°). In (1), the phenyl groups are displaced out of the equatorial plane. Two rings are twisted inwards towards each other about this plane, whilst the other two are directed above and below, and are twisted away from each other, forming a cavity into which the pyridine ring nestles. The methyl groups of the tert-butoxy moiety in complex (2) and those of the 2,4-pentanedione ligand in (3) are displaced above and below the equatorial plane. The pyridine molecule of (2) is perpendicular to the equatorial plane, while those of (1) and (3) are set obliquely (dihedral angles 36.9 (2) and 49.0 (2)°). Introduction. We have previously reported the structure of dioxobis (2,4-pentanedionato)(pyridine)uranium(VI)